PhD Theses
Rodrigues, S. S.
Aero-Thermal Analysis and Design of Turbomachinery Blades using Multi-Stage Adjoint Methods PhD Thesis
Instituto Superior Técnico, Universidade de Lisboa, 2019.
@phdthesis{Rodrigues:2019:PhD,
title = {Aero-Thermal Analysis and Design of Turbomachinery Blades using Multi-Stage Adjoint Methods},
author = {S. S. Rodrigues},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_PhDthesis_Rodrigues_2019.pdf, PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=630939, WWW},
year = {2019},
date = {2019-04-01},
urldate = {2019-04-01},
pages = {156},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The use of high-fidelity computational fluid dynamics (CFD) tools in turbomachinery design has seen a continuous increase as a result of computational power growth and the improvement of numerical methods. These tools are often used in optimization environments, where gradient-based optimization algorithms are the most common due to their efficiency. In cases where the optimization contains a large number of design variables, as is often the case in turbomachinery design problems, the adjoint approach for calculating the gradients is beneficial, as it provides a way of obtaining exact function sensitivities with a computational cost that is nearly independent of the number of design variables. Taking the coupling between adjacent blade rows of a turbomachine in its analysis if of the utmost importance, as the interaction between the various rows both in the direction of the flow and in the opposite direction can cause complex phenomena that considering a single row will not capture. The most commonly used method to address these effects (i.e. coupling in the simulation of multiple rows) is the mixing-plane treatment, which has become a standard industrial tool in the design environment. This thesis presents the formulation and implementation of the adjoint counterpart of the mixing-plane interface in a legacy adjoint solver for sensitivity analysis of turbomachinery applications to handle multi-row problems. The solver is developed using the discrete ADjoint approach, where the partial derivatives required for the assembly of the adjoint system of equations are obtained using automatic differentiation tools. The differentiation is not performed in one go, but, instead, the individual routines that perform the various steps of the mixing-plane algorithm are differentiated and the final differentiated routine, corresponding to the differentiated mixing-plane is assembled by hand. The implementation is verified with finite-difference approximations and the sensitivity of several performance metrics relative to neighbor blade/hub row geometry and boundary conditions are shown to highlight the physical coupling in multi-row turbomachines.
Keywords: Turbomachinery, Mixing-plane, Computational fluid dynamics, Sensitivity analysis, Discrete adjoint, Automatic differentiation, Shape optimization, Aerospace engineering},
howpublished = {https://scholar.tecnico.ulisboa.pt/records/L5eZ7tqRao3G6qiCaeX3RomiNHbjctDqBGOc},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
The use of high-fidelity computational fluid dynamics (CFD) tools in turbomachinery design has seen a continuous increase as a result of computational power growth and the improvement of numerical methods. These tools are often used in optimization environments, where gradient-based optimization algorithms are the most common due to their efficiency. In cases where the optimization contains a large number of design variables, as is often the case in turbomachinery design problems, the adjoint approach for calculating the gradients is beneficial, as it provides a way of obtaining exact function sensitivities with a computational cost that is nearly independent of the number of design variables. Taking the coupling between adjacent blade rows of a turbomachine in its analysis if of the utmost importance, as the interaction between the various rows both in the direction of the flow and in the opposite direction can cause complex phenomena that considering a single row will not capture. The most commonly used method to address these effects (i.e. coupling in the simulation of multiple rows) is the mixing-plane treatment, which has become a standard industrial tool in the design environment. This thesis presents the formulation and implementation of the adjoint counterpart of the mixing-plane interface in a legacy adjoint solver for sensitivity analysis of turbomachinery applications to handle multi-row problems. The solver is developed using the discrete ADjoint approach, where the partial derivatives required for the assembly of the adjoint system of equations are obtained using automatic differentiation tools. The differentiation is not performed in one go, but, instead, the individual routines that perform the various steps of the mixing-plane algorithm are differentiated and the final differentiated routine, corresponding to the differentiated mixing-plane is assembled by hand. The implementation is verified with finite-difference approximations and the sensitivity of several performance metrics relative to neighbor blade/hub row geometry and boundary conditions are shown to highlight the physical coupling in multi-row turbomachines.
Keywords: Turbomachinery, Mixing-plane, Computational fluid dynamics, Sensitivity analysis, Discrete adjoint, Automatic differentiation, Shape optimization, Aerospace engineering
Keywords: Turbomachinery, Mixing-plane, Computational fluid dynamics, Sensitivity analysis, Discrete adjoint, Automatic differentiation, Shape optimization, Aerospace engineering
Marta, A. C.
Rapid Development of Discrete Adjoint Solvers with Applications to Magnetohydrodynamic Flow Control PhD Thesis
Stanford University, 2007, ISBN: 978-0-549-06309-4.
@phdthesis{Marta:2007:PhD,
title = {Rapid Development of Discrete Adjoint Solvers with Applications to Magnetohydrodynamic Flow Control},
author = {A. C. Marta},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_PhDthesis_Marta_2007.pdf, PDF
https://www.worldcat.org/title/959162049, WWW},
isbn = {978-0-549-06309-4},
year = {2007},
date = {2007-06-01},
pages = {210},
address = {Stanford, USA},
school = {Stanford University},
abstract = {The motivation for this work arose from initial efforts in magnetohydrodynamics (MHD) flow control when plasma generated at high Mach numbers allows for electromagnetic actuators to change the characteristics of the flow. In the context of gradient-based optimization, this dissertation focuses on the problem of efficiently estimating the sensitivity of a given function of interest with respect to a large number of variables, in environments modeled by complex equations. The discrete adjoint approach emerges as the best suitable option to deal with such complex equations and, in addition, allows for the use of automatic differentiation (AD) tools in the derivation of the adjoint solver. The selective application of AD is the central idea behind the Automatic Differentiation adjoint (ADjoint) approach. This approach has the advantages that it is applicable to arbitrary sets of governing equations and cost functions, and it is exactly consistent with the gradients that would be computed by exact numerical differentiation of the original solver. Furthermore, the approach is largely automatic, thus avoiding the lengthy development times usually required to develop discrete adjoint solvers for partial differential equations. It takes days, not years, to construct the ADjoint solver. Sensitivities of aerodynamic coefficients with respect to several types of parameters, totaling over a half million variables, are computed and successfully validated against finite-difference approximations. The overall performance and accuracy of the method is shown to be better than conventional continuous adjoint approaches. The increased memory requirements can be eliminated at the expense of larger computational times for the ADjoint, that would bring the computational performance roughly on par with that of the best continuous adjoint solvers.
Keywords: Computational fluid dynamics, Sensitivity analysis, Adjoint solvers, Automatic differentiation, Flow control, Gradient-based optimization, Mechanical engineering, Aerospace engineering},
howpublished = {https://www.proquest.com/docview/304809805},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
The motivation for this work arose from initial efforts in magnetohydrodynamics (MHD) flow control when plasma generated at high Mach numbers allows for electromagnetic actuators to change the characteristics of the flow. In the context of gradient-based optimization, this dissertation focuses on the problem of efficiently estimating the sensitivity of a given function of interest with respect to a large number of variables, in environments modeled by complex equations. The discrete adjoint approach emerges as the best suitable option to deal with such complex equations and, in addition, allows for the use of automatic differentiation (AD) tools in the derivation of the adjoint solver. The selective application of AD is the central idea behind the Automatic Differentiation adjoint (ADjoint) approach. This approach has the advantages that it is applicable to arbitrary sets of governing equations and cost functions, and it is exactly consistent with the gradients that would be computed by exact numerical differentiation of the original solver. Furthermore, the approach is largely automatic, thus avoiding the lengthy development times usually required to develop discrete adjoint solvers for partial differential equations. It takes days, not years, to construct the ADjoint solver. Sensitivities of aerodynamic coefficients with respect to several types of parameters, totaling over a half million variables, are computed and successfully validated against finite-difference approximations. The overall performance and accuracy of the method is shown to be better than conventional continuous adjoint approaches. The increased memory requirements can be eliminated at the expense of larger computational times for the ADjoint, that would bring the computational performance roughly on par with that of the best continuous adjoint solvers.
Keywords: Computational fluid dynamics, Sensitivity analysis, Adjoint solvers, Automatic differentiation, Flow control, Gradient-based optimization, Mechanical engineering, Aerospace engineering
Keywords: Computational fluid dynamics, Sensitivity analysis, Adjoint solvers, Automatic differentiation, Flow control, Gradient-based optimization, Mechanical engineering, Aerospace engineering
Masters Theses
Cardoso, P.
Aerostructural design of a medium-altitude medium-endurance UAV wing Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2024.
@mastersthesis{Cardoso:2024:MSc,
title = {Aerostructural design of a medium-altitude medium-endurance UAV wing},
author = {P. Cardoso},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Cardoso_2024.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Cardoso_2024_ExtendedAbstract.pdf, Extended abstract PDF},
year = {2024},
date = {2024-12-01},
pages = {85},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {In a competitive market, manufacturers strive to enhance UAV performance through advanced design technologies. This study focuses on maximizing UAV range by optimaly designing the wing with the aerostructural, gradient-based framework, MACH, integrating high-fidelity computational models. The process optimizes aerodynamic and structural variables like chord, airfoil, span, panel thickness and composite fiber orientation, using the discrete adjoint method for efficient derivative computation. Single-discipline optima were studied to establish a baseline for the aerostructural problem. The impact of higher-fidelity geometry wing models was examined through aerostructural analysis of a simplified wing, a detailed wing, and a wing-fuselage group, revealing aspects missed in single-discipline analyses, including the impact of structural twist in the aerodynamic response. Manufacturing constraints in multilayer composites, including neighboring ply angle adjacency and orthogonality, had minimal impact. However, the tip displacement constraint affected significantly the aerodynamic airfoil variable and final designs. Exploring the response at dive speed for a more flexible wing showed promising results. Comparing aerostructural and single-discipline optimizations, highlighted the computational intensity of the former but superior design outcomes, including extended range achieved by root-heavy and tip-light thickness, and lift distribution. Addressing both aerodynamic and structural disciplines concurrently offers valuable insights into trade-offs among design variables. Compered to baseline wing design final optimal showed from 4.2% increase in range with a 10.4% gain in aerodynamic efficiency and 43.9% reduction in mass, up to 9.9% increase in range if span was a variable, with a 32% improvement in aerodynamic efficiency, despite a 114% increase in wing weight.
Keywords: Multidisciplinary optimization, Fluid-structure interaction, Wing design, Adjoint method, Free-form deformation, Composite materials},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
In a competitive market, manufacturers strive to enhance UAV performance through advanced design technologies. This study focuses on maximizing UAV range by optimaly designing the wing with the aerostructural, gradient-based framework, MACH, integrating high-fidelity computational models. The process optimizes aerodynamic and structural variables like chord, airfoil, span, panel thickness and composite fiber orientation, using the discrete adjoint method for efficient derivative computation. Single-discipline optima were studied to establish a baseline for the aerostructural problem. The impact of higher-fidelity geometry wing models was examined through aerostructural analysis of a simplified wing, a detailed wing, and a wing-fuselage group, revealing aspects missed in single-discipline analyses, including the impact of structural twist in the aerodynamic response. Manufacturing constraints in multilayer composites, including neighboring ply angle adjacency and orthogonality, had minimal impact. However, the tip displacement constraint affected significantly the aerodynamic airfoil variable and final designs. Exploring the response at dive speed for a more flexible wing showed promising results. Comparing aerostructural and single-discipline optimizations, highlighted the computational intensity of the former but superior design outcomes, including extended range achieved by root-heavy and tip-light thickness, and lift distribution. Addressing both aerodynamic and structural disciplines concurrently offers valuable insights into trade-offs among design variables. Compered to baseline wing design final optimal showed from 4.2% increase in range with a 10.4% gain in aerodynamic efficiency and 43.9% reduction in mass, up to 9.9% increase in range if span was a variable, with a 32% improvement in aerodynamic efficiency, despite a 114% increase in wing weight.
Keywords: Multidisciplinary optimization, Fluid-structure interaction, Wing design, Adjoint method, Free-form deformation, Composite materials
Keywords: Multidisciplinary optimization, Fluid-structure interaction, Wing design, Adjoint method, Free-form deformation, Composite materials
Palaio, A.
Sounding rocket multidisciplinary preliminary design and trajectory optimisation Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2024.
@mastersthesis{Palaio:2024:MSc,
title = {Sounding rocket multidisciplinary preliminary design and trajectory optimisation},
author = {A. Palaio},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Palaio_2024.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Palaio_2024_ExtendedAbstract.pdf, Extended abstract PDF},
year = {2024},
date = {2024-12-01},
pages = {100},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The design of rockets is known to be a complex task, not only due to the harsh operating conditions but also the strong coupling among disciplines. A multidisciplinary optimisation (MDO) framework was developed, aimed at providing preliminary designs of a single-stage solid propellant rocket. The choice of the optimiser algorithm, MDO architecture and discipline models, namely, mass and sizing, flight dynamics, aerodynamics, propulsion, structural and atmospheric, were such that the developed numerical tool has a very low computational cost while being able to meet a set of pre-established mission requirements. The resulting design framework solved a co-design optimisation problem, due to the coupling between the trajectory and rocket sizing optimization processes. The capabilities of the design framework were tested for different sets of design variables and multiple missions, with increasing complexity, for an optimisation problem aimed at minimizing the total mass of the rocket while imposing a minimum altitude constraint, with a prescribed payload capacity. First, studies with up to 10 geometric design variables showed that the latter were capable of achieving the best results, as expected. Then, sensitivity studies of the payload and the minimum altitude confirmed that the rocket sizing is greatly impacted by both. Lastly, comparisons with real rockets, namely, the REXUS 2 and REXUS 10, showed very good agreement, achieving a total mass reduction of 14.5% and 14.9%, respectively. Given the great modularity of the framework, a straightforward extension to other types of rockets, such as multi-stage or liquid-propellant, is expected upon additional development.
Keywords: MDO, Trajectory optimization, Co-design, Sounding rocket, Modularity},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The design of rockets is known to be a complex task, not only due to the harsh operating conditions but also the strong coupling among disciplines. A multidisciplinary optimisation (MDO) framework was developed, aimed at providing preliminary designs of a single-stage solid propellant rocket. The choice of the optimiser algorithm, MDO architecture and discipline models, namely, mass and sizing, flight dynamics, aerodynamics, propulsion, structural and atmospheric, were such that the developed numerical tool has a very low computational cost while being able to meet a set of pre-established mission requirements. The resulting design framework solved a co-design optimisation problem, due to the coupling between the trajectory and rocket sizing optimization processes. The capabilities of the design framework were tested for different sets of design variables and multiple missions, with increasing complexity, for an optimisation problem aimed at minimizing the total mass of the rocket while imposing a minimum altitude constraint, with a prescribed payload capacity. First, studies with up to 10 geometric design variables showed that the latter were capable of achieving the best results, as expected. Then, sensitivity studies of the payload and the minimum altitude confirmed that the rocket sizing is greatly impacted by both. Lastly, comparisons with real rockets, namely, the REXUS 2 and REXUS 10, showed very good agreement, achieving a total mass reduction of 14.5% and 14.9%, respectively. Given the great modularity of the framework, a straightforward extension to other types of rockets, such as multi-stage or liquid-propellant, is expected upon additional development.
Keywords: MDO, Trajectory optimization, Co-design, Sounding rocket, Modularity
Keywords: MDO, Trajectory optimization, Co-design, Sounding rocket, Modularity
Pedro, B.
Development of a sense and avoid system for small fixed-wing UAV Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2024.
@mastersthesis{Pedro:2024:MSc,
title = {Development of a sense and avoid system for small fixed-wing UAV},
author = {B. Pedro},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Pedro_2024.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Pedro_2024_ExtendedAbstract.pdf, Extended abstract PDF},
year = {2024},
date = {2024-12-01},
pages = {98},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Given the rising number of applications of Unmanned Aerial Vehicles (UAVs) and consequent expansion of that market, enhanced flight safety systems need to be developed. The main objective of this work is to develop a Sense and Avoid (S&A) system for small fixed-wing UAVs. To achieve this, firstly, a literature review of the sensors and systems used to detect obstacles, cooperatively and non-cooperatively, was made, followed by a review of the main local and global path planning methods for collision avoidance. Then, a hardware implementation was proposed, consisting of two ultrasonic sensors, two laser rangefinders, and one LiDAR, integrated with a flight controller, a companion computer, and other components essential to the UAV operation. A complete software implementation was also proposed, ranging from the study and adaptation of the flight control software (PX4), with emphasis on the handle and communication of sensor data, to the development of a software prototype, based on the Vector Field Histogram (VFH) method, to be executed in the companion computer, to receive sensor data, obtain obstacle positions, and return setpoints of a collision avoidance trajectory. The validation tests have shown that the system is capable of, based on sensor data, compute obstacle positions, transform them to polar histogram format, and generate trajectory setpoints representing avoidance maneuvers of small deviations, with an update rate of 10Hz, thus real-time capable.
Keywords: Obstacle detection, Collision avoidance, Vector field histogram, Flight controller, Companion computer, Ultrasonic sensor, Laser rangefinder, LiDAR},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Given the rising number of applications of Unmanned Aerial Vehicles (UAVs) and consequent expansion of that market, enhanced flight safety systems need to be developed. The main objective of this work is to develop a Sense and Avoid (S&A) system for small fixed-wing UAVs. To achieve this, firstly, a literature review of the sensors and systems used to detect obstacles, cooperatively and non-cooperatively, was made, followed by a review of the main local and global path planning methods for collision avoidance. Then, a hardware implementation was proposed, consisting of two ultrasonic sensors, two laser rangefinders, and one LiDAR, integrated with a flight controller, a companion computer, and other components essential to the UAV operation. A complete software implementation was also proposed, ranging from the study and adaptation of the flight control software (PX4), with emphasis on the handle and communication of sensor data, to the development of a software prototype, based on the Vector Field Histogram (VFH) method, to be executed in the companion computer, to receive sensor data, obtain obstacle positions, and return setpoints of a collision avoidance trajectory. The validation tests have shown that the system is capable of, based on sensor data, compute obstacle positions, transform them to polar histogram format, and generate trajectory setpoints representing avoidance maneuvers of small deviations, with an update rate of 10Hz, thus real-time capable.
Keywords: Obstacle detection, Collision avoidance, Vector field histogram, Flight controller, Companion computer, Ultrasonic sensor, Laser rangefinder, LiDAR
Keywords: Obstacle detection, Collision avoidance, Vector field histogram, Flight controller, Companion computer, Ultrasonic sensor, Laser rangefinder, LiDAR
Silva, V.
Structural design of a MAME UAV wing using high-fidelity numerical tools Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2023.
@mastersthesis{Silva:2023:MSc,
title = {Structural design of a MAME UAV wing using high-fidelity numerical tools},
author = {V. Silva},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Silva_2023.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Silva_2023_ExtendedAbstract.pdf, Extended abstract PDF},
year = {2023},
date = {2023-12-01},
pages = {98},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {With the rapid growth of the UAV market, more efficient solutions obtained from high-fidelity analyses and optimisation techniques during aircraft design, promotes a huge competitive advantage. This work addresses the desire of a leading UAV manufacturer to improve its fleet to remain competitive in the surveillance UAV market. For this, a structural analysis tool using the finite element method was demonstrated, which was then used as part of a structural optimisation framework. For this demonstration, static analyses of the wingbox of an existing UAV model, with a CFRP material with different lay-ups were carried out for two flight conditions. Results of deformation and failure helped to evaluate the wingbox structural behaviour. Validation of the numerical design framework using available experimental data presented slight differences due to model simplifications and lack of accurate material properties. Several new optimal wingbox solutions were found with variable ply thicknesses and fibre orientations. The first was optimised only with failure constraints; a maximum allowed displacement was added to the following two but had different starting points; manufacturing constraints such as ply angle continuity, orthogonality of plies and monotonically decreasing thickness were added to the next three, respectively; and finally, for the fully constrained solution, a maximum allowed wing tip torsion was added. Mass reduction between about 44% and 56%, while respecting a safety factor of 1.5, was found possible.
Keywords: Optimisation, Design framework, Adjoint method, Finite element method, Composite materials, Fibre orientation},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
With the rapid growth of the UAV market, more efficient solutions obtained from high-fidelity analyses and optimisation techniques during aircraft design, promotes a huge competitive advantage. This work addresses the desire of a leading UAV manufacturer to improve its fleet to remain competitive in the surveillance UAV market. For this, a structural analysis tool using the finite element method was demonstrated, which was then used as part of a structural optimisation framework. For this demonstration, static analyses of the wingbox of an existing UAV model, with a CFRP material with different lay-ups were carried out for two flight conditions. Results of deformation and failure helped to evaluate the wingbox structural behaviour. Validation of the numerical design framework using available experimental data presented slight differences due to model simplifications and lack of accurate material properties. Several new optimal wingbox solutions were found with variable ply thicknesses and fibre orientations. The first was optimised only with failure constraints; a maximum allowed displacement was added to the following two but had different starting points; manufacturing constraints such as ply angle continuity, orthogonality of plies and monotonically decreasing thickness were added to the next three, respectively; and finally, for the fully constrained solution, a maximum allowed wing tip torsion was added. Mass reduction between about 44% and 56%, while respecting a safety factor of 1.5, was found possible.
Keywords: Optimisation, Design framework, Adjoint method, Finite element method, Composite materials, Fibre orientation
Keywords: Optimisation, Design framework, Adjoint method, Finite element method, Composite materials, Fibre orientation
Vizeu, G.
Aerodynamic characterization of UAV propellers using numerical analysis and experimental testing Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2023.
@mastersthesis{Vizeu:2023:MSc,
title = {Aerodynamic characterization of UAV propellers using numerical analysis and experimental testing},
author = {G. Vizeu},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Vizeu_2023.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Vizeu_2023_ExtendedAbstract.pdf, Extended abstract PDF},
year = {2023},
date = {2023-12-01},
pages = {76},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Over the last decades, there have been major developments in Unmanned Aerial Vehicles (UAVs) and, nowadays, they are used for a wide range of commercial applications such as traffic and weather monitoring, deliveries and forest fire detection. This study presents and compares different low-fidelity and high-fidelity aerodynamic numerical models that predict the performance of a UAV propeller for a wide range of flight conditions, such as hovering and vertical climbing. First, the thrust and torque of two commercial propellers are obtained recurring to JavaProp, a software based on the Blade Element Theory. Then, computational fluid dynamics analysis is carried out in the commercial software ANSYS Fluent, which includes the construction of the CAD model of the propellers and the flow domain modeling. Furthermore, turbulence model and mesh studies were conducted and the propeller thrust and torque were determined for different flight configurations and flow conditions. Finally, experimental testing to evaluate the aerodynamic performance of one propeller was conducted and the results were validated with computational simulations. The findings of this study suggest that high-fidelity computational models provide results more consistent with experimental testing, whereas the accuracy of results derived from the low-fidelity Blade Element Theory decreases with increasing the propeller angular velocity. Nevertheless, both methods are shown to be suitable for forecasting propeller performance in various flow and flight scenarios.
Keywords: Propeller design, CFD, Blade element theory, Thrust, Torque, Validation},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Over the last decades, there have been major developments in Unmanned Aerial Vehicles (UAVs) and, nowadays, they are used for a wide range of commercial applications such as traffic and weather monitoring, deliveries and forest fire detection. This study presents and compares different low-fidelity and high-fidelity aerodynamic numerical models that predict the performance of a UAV propeller for a wide range of flight conditions, such as hovering and vertical climbing. First, the thrust and torque of two commercial propellers are obtained recurring to JavaProp, a software based on the Blade Element Theory. Then, computational fluid dynamics analysis is carried out in the commercial software ANSYS Fluent, which includes the construction of the CAD model of the propellers and the flow domain modeling. Furthermore, turbulence model and mesh studies were conducted and the propeller thrust and torque were determined for different flight configurations and flow conditions. Finally, experimental testing to evaluate the aerodynamic performance of one propeller was conducted and the results were validated with computational simulations. The findings of this study suggest that high-fidelity computational models provide results more consistent with experimental testing, whereas the accuracy of results derived from the low-fidelity Blade Element Theory decreases with increasing the propeller angular velocity. Nevertheless, both methods are shown to be suitable for forecasting propeller performance in various flow and flight scenarios.
Keywords: Propeller design, CFD, Blade element theory, Thrust, Torque, Validation
Keywords: Propeller design, CFD, Blade element theory, Thrust, Torque, Validation
Portugal, M.
Optimal multi-sensor collision avoidance system for small fixed-wing UAV Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2023.
@mastersthesis{Portugal:2023:MSc,
title = {Optimal multi-sensor collision avoidance system for small fixed-wing UAV},
author = {M. Portugal},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Portugal_2023.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Portugal_2023_ExtendedAbstract.pdf, Extended abstract PDF},
year = {2023},
date = {2023-11-01},
pages = {88},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {This work provides a solution for the safety enhancement of small fixed-wing UAVs regarding obstacle detection during flight. The main goal is to implement an optimal multi-sensor system configuration. Therefore, select sensors were modeled for collision detection and avoidance simulations using the potential fields method. An optimization study using a genetic algorithm was conducted to find the sets of sensors and respective orientation that result in the best collision avoidance performance. To do so, a set of collision scenarios with both stationary and moving obstacles were randomly generated. This study resulted in relatively simple detection configurations that provided high collision avoidance success rate. The ultrasonic sensor revealed to be inappropriate given its short range, while the laser rangefinder benefited from long range but had very limited field-of-view. In contrast, both the LIDAR and the RADAR are the most promising, as they exhibit a significant range and a broad field-of-view. The best multi-sensor configuration was a front-facing LIDAR complimented by a pair of laser rangefinders pointing sideways at 10 degrees. The assembly of the final system, including sensors and a PixHawk flight controller, was then designed and executed. The software (PX4, QGroundControl) was also built and adapted to the current work. To validate the proposed system, all sensors were first individually tested. The bench tests attested the accuracy of the sensor specifications and previous simulations. Ground tests on a rover using a simple obstacle avoidance algorithm displayed satisfactory results.
Keywords: Safety, Obstacle detection, Collision avoidance, Sensor fusion, Laser rangefinder, LIDAR},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
This work provides a solution for the safety enhancement of small fixed-wing UAVs regarding obstacle detection during flight. The main goal is to implement an optimal multi-sensor system configuration. Therefore, select sensors were modeled for collision detection and avoidance simulations using the potential fields method. An optimization study using a genetic algorithm was conducted to find the sets of sensors and respective orientation that result in the best collision avoidance performance. To do so, a set of collision scenarios with both stationary and moving obstacles were randomly generated. This study resulted in relatively simple detection configurations that provided high collision avoidance success rate. The ultrasonic sensor revealed to be inappropriate given its short range, while the laser rangefinder benefited from long range but had very limited field-of-view. In contrast, both the LIDAR and the RADAR are the most promising, as they exhibit a significant range and a broad field-of-view. The best multi-sensor configuration was a front-facing LIDAR complimented by a pair of laser rangefinders pointing sideways at 10 degrees. The assembly of the final system, including sensors and a PixHawk flight controller, was then designed and executed. The software (PX4, QGroundControl) was also built and adapted to the current work. To validate the proposed system, all sensors were first individually tested. The bench tests attested the accuracy of the sensor specifications and previous simulations. Ground tests on a rover using a simple obstacle avoidance algorithm displayed satisfactory results.
Keywords: Safety, Obstacle detection, Collision avoidance, Sensor fusion, Laser rangefinder, LIDAR
Keywords: Safety, Obstacle detection, Collision avoidance, Sensor fusion, Laser rangefinder, LIDAR
Gameiro, R.
Aerodynamic design of a MAME UAV wing using high-fidelity numerical tools Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2023.
@mastersthesis{Gameiro:2023:MSc,
title = {Aerodynamic design of a MAME UAV wing using high-fidelity numerical tools},
author = {R. Gameiro},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Gameiro_2023.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Gameiro_2023_ExtendedAbstract.pdf, Extended abstract PDF},
year = {2023},
date = {2023-11-01},
urldate = {2023-11-01},
pages = {100},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The UAV market is currently very competitive, with the frequent release of new products and a wide range of solutions already available, forcing manufacturers to explore the design space faster and more efficiently than ever. A cost effective approach is to develop growth versions, improving an existing product with new technologies and design tools. Some of these tools include RANS based high fidelity computational fluid dynamics methods and discrete adjoint gradient-based optimization, which are used in this work on a numerical design framework to explore the aerodynamic shape optimization of a wing, as part of the development of a growth version of a UAV of a leading Portuguese manufacturer. A comprehensive aerodynamic analysis of its current wing, including fuselage interference, is performed, followed by an optimization procedure to minimize drag subject to a prescribed lift coefficient constraint. To that end, three different starting geometries are considered and parameterized with common design variables, including twist and chord distributions, sweep, dihedral and airfoil shape. The use of two simple wings as starting geometries allowed the framework and set-up verification, with all optimizations considering different sets of design variables approaching an elliptical lift distribution, although not exactly considering the trade-offs needed between viscous and pressure drag. Challenges associated with the use of a complex wing geometry as a starting point are then addressed and optimizations considering the current UAV wing as a starting point are performed. Notably, a drag reduction of 4.5% is achieved considering all design variables.
Keywords: Aerodynamic optimization, Gradient-based optimization, Discrete adjoint method, Wing design, Computational fluid dynamics, Free-form deformation},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The UAV market is currently very competitive, with the frequent release of new products and a wide range of solutions already available, forcing manufacturers to explore the design space faster and more efficiently than ever. A cost effective approach is to develop growth versions, improving an existing product with new technologies and design tools. Some of these tools include RANS based high fidelity computational fluid dynamics methods and discrete adjoint gradient-based optimization, which are used in this work on a numerical design framework to explore the aerodynamic shape optimization of a wing, as part of the development of a growth version of a UAV of a leading Portuguese manufacturer. A comprehensive aerodynamic analysis of its current wing, including fuselage interference, is performed, followed by an optimization procedure to minimize drag subject to a prescribed lift coefficient constraint. To that end, three different starting geometries are considered and parameterized with common design variables, including twist and chord distributions, sweep, dihedral and airfoil shape. The use of two simple wings as starting geometries allowed the framework and set-up verification, with all optimizations considering different sets of design variables approaching an elliptical lift distribution, although not exactly considering the trade-offs needed between viscous and pressure drag. Challenges associated with the use of a complex wing geometry as a starting point are then addressed and optimizations considering the current UAV wing as a starting point are performed. Notably, a drag reduction of 4.5% is achieved considering all design variables.
Keywords: Aerodynamic optimization, Gradient-based optimization, Discrete adjoint method, Wing design, Computational fluid dynamics, Free-form deformation
Keywords: Aerodynamic optimization, Gradient-based optimization, Discrete adjoint method, Wing design, Computational fluid dynamics, Free-form deformation
Afonso, L.
Aerodynamic design and wind tunnel testing of the rear end of a Formula Student vehicle Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2022.
@mastersthesis{Afonso:2022:MSc,
title = {Aerodynamic design and wind tunnel testing of the rear end of a Formula Student vehicle},
author = {L. Afonso},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Afonso_2022.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Afonso_2022_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=1697035, Catalog IST},
year = {2022},
date = {2022-12-01},
urldate = {2022-12-01},
pages = {85},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The aerodynamics design among Formula Student teams has been seeing increasing complexity. Particularly for the FST Lisbon team, the design phase of new prototypes is currently revolving solely around CFD simulations. This work focus on improving the performance of the car and validating it through wind tunnel testing, to boost confidence in the obtained results and to pave the way for it to become a more broadly resorted procedure. By updating a lap simulator tool provided to predict the aerodynamic influence of the scores more accurately, the target was set to increase the downforce generated. An aerodynamic performance assessment was performed by analyzing the simulation data from the baseline design. The most critical regions identified were both lateral and back diffusers, and the rear wing. The lateral diffuser was the first to be redesigned and simulated. The large separation region previously identified was successfully mitigated while granting that no downforce was lost. The rear region was also modified by extending the monocoque and varying the diffuser profile yielding a 4.3% increase in downforce. This last design was scaled and 3D printed to be tested in the wind tunnel. Regarding the force measurements for slip angles of 0 and 4 degrees, the results stood very close to the predicted CFD simulations while the moments were substantially underestimated. However, the results for β = 10 degrees were considered unsatisfactory and the flow visualization via wool tufts, while capturing some important phenomena, has to be further improved. The redesign was validated in the wind tunnel.
Keywords: Computational Fluid Dynamics, Aerodynamic Performance, Car Diffuser, Vehicle Dynamics, Validation, Flow Visualization},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The aerodynamics design among Formula Student teams has been seeing increasing complexity. Particularly for the FST Lisbon team, the design phase of new prototypes is currently revolving solely around CFD simulations. This work focus on improving the performance of the car and validating it through wind tunnel testing, to boost confidence in the obtained results and to pave the way for it to become a more broadly resorted procedure. By updating a lap simulator tool provided to predict the aerodynamic influence of the scores more accurately, the target was set to increase the downforce generated. An aerodynamic performance assessment was performed by analyzing the simulation data from the baseline design. The most critical regions identified were both lateral and back diffusers, and the rear wing. The lateral diffuser was the first to be redesigned and simulated. The large separation region previously identified was successfully mitigated while granting that no downforce was lost. The rear region was also modified by extending the monocoque and varying the diffuser profile yielding a 4.3% increase in downforce. This last design was scaled and 3D printed to be tested in the wind tunnel. Regarding the force measurements for slip angles of 0 and 4 degrees, the results stood very close to the predicted CFD simulations while the moments were substantially underestimated. However, the results for β = 10 degrees were considered unsatisfactory and the flow visualization via wool tufts, while capturing some important phenomena, has to be further improved. The redesign was validated in the wind tunnel.
Keywords: Computational Fluid Dynamics, Aerodynamic Performance, Car Diffuser, Vehicle Dynamics, Validation, Flow Visualization
Keywords: Computational Fluid Dynamics, Aerodynamic Performance, Car Diffuser, Vehicle Dynamics, Validation, Flow Visualization
Cavaco, N.
Design and assembly of a ground control station for long range and long endurance UAVs Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2022.
@mastersthesis{Cavaco:2022:MSc,
title = {Design and assembly of a ground control station for long range and long endurance UAVs},
author = {N. Cavaco},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Cavaco_2022.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Cavaco_2022_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=1704036, Catalog IST},
year = {2022},
date = {2022-11-01},
urldate = {2022-11-01},
pages = {82},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The increasing number of applications for unmanned aerial vehicles demands reliable systems that can meet the requirements of a wide range of missions. Having a fully operational ground control station that provides reliability, easy setup, safety, adaptability, easy decision making, among others, is a key point for the success of any unmanned aerial system mission. Therefore, the design and assembly of a ground control station for long range and long endurance unmanned aerial vehicles is presented. The mission requirements are derived from civilian surveillance applications, such as forest, coast or border patrol. The main steps of the design and assembly are covered as well as the description of each system and component and how they operate together to comprise a ground station. The feasibility of a low cost mobile ground control station for missions up to 8h and 100km range is demonstrated.
Keywords: Ground control station, Unmanned aerial vehicle, Unmanned aerial system, Long endurance, Long range},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The increasing number of applications for unmanned aerial vehicles demands reliable systems that can meet the requirements of a wide range of missions. Having a fully operational ground control station that provides reliability, easy setup, safety, adaptability, easy decision making, among others, is a key point for the success of any unmanned aerial system mission. Therefore, the design and assembly of a ground control station for long range and long endurance unmanned aerial vehicles is presented. The mission requirements are derived from civilian surveillance applications, such as forest, coast or border patrol. The main steps of the design and assembly are covered as well as the description of each system and component and how they operate together to comprise a ground station. The feasibility of a low cost mobile ground control station for missions up to 8h and 100km range is demonstrated.
Keywords: Ground control station, Unmanned aerial vehicle, Unmanned aerial system, Long endurance, Long range
Keywords: Ground control station, Unmanned aerial vehicle, Unmanned aerial system, Long endurance, Long range
Seixas, C.
Estimation of aerodynamic and control derivatives of small fixed-wing aircraft using numerical simulations and wind tunnel experiments Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2022.
@mastersthesis{Seixas:2022:MSc,
title = {Estimation of aerodynamic and control derivatives of small fixed-wing aircraft using numerical simulations and wind tunnel experiments},
author = {C. Seixas},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Seixas_2022.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Seixas_2022_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=1712621, Catalog IST},
year = {2022},
date = {2022-11-01},
urldate = {2022-11-01},
pages = {100},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {In recent years, the use of small UAVs (Unmanned Aerial Vehicles) in recreational and commercial activities has experienced significant growth. The benefits of UAVs mainly come from their high autonomy using automatic guidance and control systems. The performance of such systems depends a lot on the quality of the identified aircraft model, which becomes extremely important for the general process. The objective of this Thesis is to establish the necessary steps for the conception of a UAV, building a new model in XFLR5 ”Test Aircraft” and completely recreating the model physically elaborated for analysis in the Wind Tunnel, so it is possible to compare the results for validation of the themselves, making it possible to analyze any model, so that it is possible to build the identification of the model, incorporating analytical estimates and respective numerical simulations. It will be followed by wind tunnel tests. In the first instance, the aerodynamic and control derivatives will be determined to be used in simplified equations of longitudinal and lateral motion using analytical approximations. found in the base literature for the present activity. Later, using available numerical tools, such as XFLR5 or Start-CCM+, best estimates are calculated based on a more detailed geometric definition of the UAV selected for the case study. Finally, a preliminary UAV model is identified, which can be validated in a wind tunnel.
Keywords: UAV, Aerodynamics, Aerodynamic and control derivatives, Flight dynamics, Flight stability, Flight control},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
In recent years, the use of small UAVs (Unmanned Aerial Vehicles) in recreational and commercial activities has experienced significant growth. The benefits of UAVs mainly come from their high autonomy using automatic guidance and control systems. The performance of such systems depends a lot on the quality of the identified aircraft model, which becomes extremely important for the general process. The objective of this Thesis is to establish the necessary steps for the conception of a UAV, building a new model in XFLR5 ”Test Aircraft” and completely recreating the model physically elaborated for analysis in the Wind Tunnel, so it is possible to compare the results for validation of the themselves, making it possible to analyze any model, so that it is possible to build the identification of the model, incorporating analytical estimates and respective numerical simulations. It will be followed by wind tunnel tests. In the first instance, the aerodynamic and control derivatives will be determined to be used in simplified equations of longitudinal and lateral motion using analytical approximations. found in the base literature for the present activity. Later, using available numerical tools, such as XFLR5 or Start-CCM+, best estimates are calculated based on a more detailed geometric definition of the UAV selected for the case study. Finally, a preliminary UAV model is identified, which can be validated in a wind tunnel.
Keywords: UAV, Aerodynamics, Aerodynamic and control derivatives, Flight dynamics, Flight stability, Flight control
Keywords: UAV, Aerodynamics, Aerodynamic and control derivatives, Flight dynamics, Flight stability, Flight control
Pacheco, J.
Wind tunnel testing of a complete Formula Student vehicle Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2022.
@mastersthesis{Pacheco:2022:MSc,
title = {Wind tunnel testing of a complete Formula Student vehicle},
author = {J. Pacheco},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Pacheco_2022.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Pacheco_2022_ExtendedAbstract.pdf, Extended abstract PDF
https://scholar.tecnico.ulisboa.pt/records/AmPDMePjmkSYIZLoc7OqSRFPNCBj5y6MRZuR, Scholar IST},
year = {2022},
date = {2022-06-01},
pages = {99},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Formula Student teams are putting a great effort into aerodynamics as it is an important feature to enhance car performance. They focus on designing the best aerodynamic concept through numerical simulations. Before being manufactured, the final concept should pass an experimental test phase which is usually overlooked but essential to build trust in the numerical results. This work presents a first evaluation of the numerical methods adopted by the Formula Student Técnico team. The objective is to verify the quality of CFD results by using verification (quantification of numerical errors) and validation (quantification of modeling errors). First, the numerical errors were estimated through a mesh convergence analysis. Then, to validate the numerical models, a 1/3 scale model of the latest prototype FST10e was built and tested. The wind tunnel tests were performed not only to obtain measurements of quantities of interest (lift, drag and pitching moment) but also to evaluate the physics of the CFD simulations by using flow visualization techniques. First, the wind tunnel facility was characterized by taking speed measurements inside its test section. The data was then used to perform an initial evaluation of the numerical simulations. Finally, the model was tested in six different configurations, in which aerodynamic forces were recorded. In general, the qualitative evaluation of the results revealed that the numerical simulations captured the experimental trends and the sensitivity of each coefficient studied. Also, wool tufts were used as a flow visualization technique, which enhanced the agreement between the numerical simulations and the wind tunnel testing. Despite capturing the wind tunnel results trends and physics, the CFD simulations still need time investment and more testing to provide accurate data. However, they proved to be useful in assessing how the geometry changes affect the aerodynamic performance of the car.
Keywords: Validation, Wind tunnel, Experimental tests, Numerical simulation, Formula Student, Aerodynamic performance},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Formula Student teams are putting a great effort into aerodynamics as it is an important feature to enhance car performance. They focus on designing the best aerodynamic concept through numerical simulations. Before being manufactured, the final concept should pass an experimental test phase which is usually overlooked but essential to build trust in the numerical results. This work presents a first evaluation of the numerical methods adopted by the Formula Student Técnico team. The objective is to verify the quality of CFD results by using verification (quantification of numerical errors) and validation (quantification of modeling errors). First, the numerical errors were estimated through a mesh convergence analysis. Then, to validate the numerical models, a 1/3 scale model of the latest prototype FST10e was built and tested. The wind tunnel tests were performed not only to obtain measurements of quantities of interest (lift, drag and pitching moment) but also to evaluate the physics of the CFD simulations by using flow visualization techniques. First, the wind tunnel facility was characterized by taking speed measurements inside its test section. The data was then used to perform an initial evaluation of the numerical simulations. Finally, the model was tested in six different configurations, in which aerodynamic forces were recorded. In general, the qualitative evaluation of the results revealed that the numerical simulations captured the experimental trends and the sensitivity of each coefficient studied. Also, wool tufts were used as a flow visualization technique, which enhanced the agreement between the numerical simulations and the wind tunnel testing. Despite capturing the wind tunnel results trends and physics, the CFD simulations still need time investment and more testing to provide accurate data. However, they proved to be useful in assessing how the geometry changes affect the aerodynamic performance of the car.
Keywords: Validation, Wind tunnel, Experimental tests, Numerical simulation, Formula Student, Aerodynamic performance
Keywords: Validation, Wind tunnel, Experimental tests, Numerical simulation, Formula Student, Aerodynamic performance
Serrano, P.
Optimization of obstacle detection for small UAVs Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2022.
@mastersthesis{Serrano:2022:MSc,
title = {Optimization of obstacle detection for small UAVs},
author = {P. Serrano},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Serrano_2022.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Serrano_2022_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=1695189, Catalog IST},
year = {2022},
date = {2022-06-01},
urldate = {2022-06-01},
pages = {64},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The UAV market grows every year and in order to keep this, it is required a large investment in Sense and Avoid systems. With this in mind, the thesis is centered on this type of systems with special focus on the detection phase in small fixed-wing UAVs. Firstly, a presentation of the various types of available sensors and avoidance algorithms is made culminating with a list of the most suitable sensors for this type of work and a background explanation on the Potential fields method that will be used as the avoidance algorithm. Next, parameters are defined to characterize the sensing systems and then tested in simulated obstacle avoidance missions. At the end of these simulations, several conclusions were drawn on the influence of the parameters in the overall performance of the system. The work continues with a presentation of the hardware and software required to implement a Sense and Avoid system. After the sensors and controller have been chosen, a schematic is drawn up with all the necessary devices and the connections between them. Furthermore, the flight controller firmware and the ground control station software are chosen taking into account their specifications. Next, the work proceeds to the elaboration of experiments with the sensors, obtaining real information about their capabilities such as maximum range, average error of the measurements, etc. Finally, a simple sense and avoid system is implemented in a small rover in order to perform experiences that can evaluate the capabilities of the sense and avoid system.
Keywords: UAVs, Sense and avoid, Potential fields, Parameters, Experiments, Rover},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The UAV market grows every year and in order to keep this, it is required a large investment in Sense and Avoid systems. With this in mind, the thesis is centered on this type of systems with special focus on the detection phase in small fixed-wing UAVs. Firstly, a presentation of the various types of available sensors and avoidance algorithms is made culminating with a list of the most suitable sensors for this type of work and a background explanation on the Potential fields method that will be used as the avoidance algorithm. Next, parameters are defined to characterize the sensing systems and then tested in simulated obstacle avoidance missions. At the end of these simulations, several conclusions were drawn on the influence of the parameters in the overall performance of the system. The work continues with a presentation of the hardware and software required to implement a Sense and Avoid system. After the sensors and controller have been chosen, a schematic is drawn up with all the necessary devices and the connections between them. Furthermore, the flight controller firmware and the ground control station software are chosen taking into account their specifications. Next, the work proceeds to the elaboration of experiments with the sensors, obtaining real information about their capabilities such as maximum range, average error of the measurements, etc. Finally, a simple sense and avoid system is implemented in a small rover in order to perform experiences that can evaluate the capabilities of the sense and avoid system.
Keywords: UAVs, Sense and avoid, Potential fields, Parameters, Experiments, Rover
Keywords: UAVs, Sense and avoid, Potential fields, Parameters, Experiments, Rover
Carreira, M.
Aerodynamic mapping of a Formula Student prototype using numerical simulations and on-track validation Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2022.
@mastersthesis{Carreira:2022:MSc,
title = {Aerodynamic mapping of a Formula Student prototype using numerical simulations and on-track validation},
author = {M. Carreira},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Carreira_2022.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Carreira_2022_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=1694749, Catalog IST},
year = {2022},
date = {2022-06-01},
urldate = {2022-06-01},
pages = {98},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Aerodynamic forces on a race car depend on its attitude, which changes along the track given the accelerations they are subjected to. The main objective of this work is to understand how these attitude changes affect the FST10e aerodynamics, the latest prototype made by FST Lisboa team. The car’s attitude was broken down into five parameters of interest: front and rear ride heights, roll, steering and yaw angles, with the vehicle behaviour being estimated by CFD simulations. The primary focus of CFD was cornering condition simulation, with the corresponding numerical error estimated by performing a mesh convergence. The influence of each of these parameters was evaluated individually, revealing some unexpected results, with the most impactful sensitivity being the yaw angle with a 16% change in downforce across the interval. Roll angle revealed to have a monotonic and rather independent behaviour resulting in 9% change in downforce and a shift of 12% in pressure centre. Ride height presented a significant change with a 10% change in CD.A and 20% in −CL.A between peak values in symmetric conditions. An aerodynamic map was then created based on over 100 data points, which provided a thorough understanding across the whole working envelope. The results can be promptly obtained by using a surrogate model, which overcomes the slow CFD analyses. Lastly, an aerodynamic validation component was also addressed to estimate downforce and drag coefficients with on-track testing. The main challenge encountered was to estimate air speed during validation testing, which revealed to be a great source of uncertainty to correlate CFD with track results.
Keywords: CFD, Formula Student, Aerodynamic mapping, On-track validation, Ride height, Vehicle attitude},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Aerodynamic forces on a race car depend on its attitude, which changes along the track given the accelerations they are subjected to. The main objective of this work is to understand how these attitude changes affect the FST10e aerodynamics, the latest prototype made by FST Lisboa team. The car’s attitude was broken down into five parameters of interest: front and rear ride heights, roll, steering and yaw angles, with the vehicle behaviour being estimated by CFD simulations. The primary focus of CFD was cornering condition simulation, with the corresponding numerical error estimated by performing a mesh convergence. The influence of each of these parameters was evaluated individually, revealing some unexpected results, with the most impactful sensitivity being the yaw angle with a 16% change in downforce across the interval. Roll angle revealed to have a monotonic and rather independent behaviour resulting in 9% change in downforce and a shift of 12% in pressure centre. Ride height presented a significant change with a 10% change in CD.A and 20% in −CL.A between peak values in symmetric conditions. An aerodynamic map was then created based on over 100 data points, which provided a thorough understanding across the whole working envelope. The results can be promptly obtained by using a surrogate model, which overcomes the slow CFD analyses. Lastly, an aerodynamic validation component was also addressed to estimate downforce and drag coefficients with on-track testing. The main challenge encountered was to estimate air speed during validation testing, which revealed to be a great source of uncertainty to correlate CFD with track results.
Keywords: CFD, Formula Student, Aerodynamic mapping, On-track validation, Ride height, Vehicle attitude
Keywords: CFD, Formula Student, Aerodynamic mapping, On-track validation, Ride height, Vehicle attitude
Sá, P. J.
Structural detailed design of a UAV with a fuel cell energy system Masters Thesis
Portuguese Air Force Academy, Sintra, Portugal, 2021.
@mastersthesis{Sa:2021:MSc,
title = {Structural detailed design of a UAV with a fuel cell energy system},
author = {P. J. Sá},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Sa_2021.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Sa_2021_ExtendedAbstract.pdf, Extended abstract PDF},
year = {2021},
date = {2021-12-01},
pages = {82},
address = {Sintra, Portugal},
school = {Portuguese Air Force Academy},
abstract = {Recently, hydrogen has gained relevance in the national context, as a source of storage of renewable energy. According to the “Strategic Vision for Portugal’s Economic Recovery Plan 2020-2030”, hydrogen is essential to achieve the political objective of carbon neutrality and sustainability. In this sense, the Portuguese Air Force (FAP) created a project for an Unmanned Aerial Vehicle (UAV), with hydrogen as a source of energy storage, in detriment to lithium batteries. Energy transformation is carried out by an hydrogen fuel cell. This dissertation aims at the structural design of the UAV. Firstly, the conceptual design was made, in which the aircraft geometry and its flight envelope were defined to determine the design load factor. Additionally, a market study was carried out to assess the expected structural weight percentage for a UAV of this type. In the preliminary design, the composite materials and their mechanical properties were defined, from which the necessary laminates for a preliminary spar were calculated. Subsequently, the distribution of components throughout the aircraft was evaluated, calculating the total weight of the UAV and its center of gravity. Finally, the detailed design was carried out through modeling in Computer Aided Design (CAD), from which a Finite Element Analysis (FEA) was produced to confirm whether the laminates assigned to the structure met the requirements stipulated. It was found that the selected configuration supports the critical load condition, with the structural weight being within the expected values.
Keywords: FAP, UAV, CAD, FEA, Composite materials},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Recently, hydrogen has gained relevance in the national context, as a source of storage of renewable energy. According to the “Strategic Vision for Portugal’s Economic Recovery Plan 2020-2030”, hydrogen is essential to achieve the political objective of carbon neutrality and sustainability. In this sense, the Portuguese Air Force (FAP) created a project for an Unmanned Aerial Vehicle (UAV), with hydrogen as a source of energy storage, in detriment to lithium batteries. Energy transformation is carried out by an hydrogen fuel cell. This dissertation aims at the structural design of the UAV. Firstly, the conceptual design was made, in which the aircraft geometry and its flight envelope were defined to determine the design load factor. Additionally, a market study was carried out to assess the expected structural weight percentage for a UAV of this type. In the preliminary design, the composite materials and their mechanical properties were defined, from which the necessary laminates for a preliminary spar were calculated. Subsequently, the distribution of components throughout the aircraft was evaluated, calculating the total weight of the UAV and its center of gravity. Finally, the detailed design was carried out through modeling in Computer Aided Design (CAD), from which a Finite Element Analysis (FEA) was produced to confirm whether the laminates assigned to the structure met the requirements stipulated. It was found that the selected configuration supports the critical load condition, with the structural weight being within the expected values.
Keywords: FAP, UAV, CAD, FEA, Composite materials
Keywords: FAP, UAV, CAD, FEA, Composite materials
Alves, B. M.
Multidisciplinary optimisation of an unmanned aerial vehicle with a fuel cell powered energy system Masters Thesis
Portuguese Air Force Academy, Sintra, Portugal, 2021.
@mastersthesis{Alves:2021:MSc,
title = {Multidisciplinary optimisation of an unmanned aerial vehicle with a fuel cell powered energy system},
author = {B. M. Alves},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Alves_2021.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Alves_2021_ExtendedAbstract.pdf, Extended abstract PDF},
year = {2021},
date = {2021-12-01},
pages = {84},
address = {Sintra, Portugal},
school = {Portuguese Air Force Academy},
abstract = {To explore the use of hydrogen fuel cells as a feasible alternative to pollutant fuels on Unmanned Aerial Vehicles (UAVs), a class I concept was designed at the Portuguese Air Force Research Centre. This work focuses on the trade-off studies performed during its design and on the optimisation that followed. First, a multi-objective optimisation approach was used with the aid of the Algorithm NSGAII to balance between two conflicting objectives: low weight and high endurance. It was found that it is possible to fly for more than 3 hours with a Maximum Take-off Weight of 21.6 kg, an 800 W fuel cell and 148 g of hydrogen. A heavier configuration with more power and fuel was discarded due to a wingspan constraint. Later, after the concept satisfied the project requirements, Multi-Disciplinary Design Optimisation (MDO) was performed to achieve the maximum endurance possible. The software used was OpenAeroStruct, low fidelity Finite Element Analysis (FEA) and Vortex Lattice Method (VLM) to model lifting surfaces. Initially, a cruise and a load flight point were used with wing geometric twist only as design variable. After, more complexity was added by introducing taper, wing chord and span. Finally, a third flight point was introduced to ensure the stall requirements were satisfied. The use of MDO allowed a 21% increase in endurance with a smaller wing area. Other improvements could not be achieved without violation of the constraints. This work marks an important milestone in the development of a future prototype at the Research Centre.
Keywords: MDO, UAV, Green aircraft, Multi-objective optimisation, eVTOL, Conceptual design},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
To explore the use of hydrogen fuel cells as a feasible alternative to pollutant fuels on Unmanned Aerial Vehicles (UAVs), a class I concept was designed at the Portuguese Air Force Research Centre. This work focuses on the trade-off studies performed during its design and on the optimisation that followed. First, a multi-objective optimisation approach was used with the aid of the Algorithm NSGAII to balance between two conflicting objectives: low weight and high endurance. It was found that it is possible to fly for more than 3 hours with a Maximum Take-off Weight of 21.6 kg, an 800 W fuel cell and 148 g of hydrogen. A heavier configuration with more power and fuel was discarded due to a wingspan constraint. Later, after the concept satisfied the project requirements, Multi-Disciplinary Design Optimisation (MDO) was performed to achieve the maximum endurance possible. The software used was OpenAeroStruct, low fidelity Finite Element Analysis (FEA) and Vortex Lattice Method (VLM) to model lifting surfaces. Initially, a cruise and a load flight point were used with wing geometric twist only as design variable. After, more complexity was added by introducing taper, wing chord and span. Finally, a third flight point was introduced to ensure the stall requirements were satisfied. The use of MDO allowed a 21% increase in endurance with a smaller wing area. Other improvements could not be achieved without violation of the constraints. This work marks an important milestone in the development of a future prototype at the Research Centre.
Keywords: MDO, UAV, Green aircraft, Multi-objective optimisation, eVTOL, Conceptual design
Keywords: MDO, UAV, Green aircraft, Multi-objective optimisation, eVTOL, Conceptual design
Matos, N. M. B.
Concurrent trajectory optimization and aircraft design for the Air Cargo Challenge 2022 competition Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2021.
@mastersthesis{Matos:2021:MSc,
title = {Concurrent trajectory optimization and aircraft design for the Air Cargo Challenge 2022 competition},
author = {N. M. B. Matos},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Matos_2021.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Matos_2021_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=1674025, Catalog IST},
year = {2021},
date = {2021-12-01},
urldate = {2021-12-01},
pages = {90},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {In this work, a coupled aerostructural aircraft design and trajectory optimization framework is developed for the Air Cargo Challenge 2022 competition to ultimately achieve the optimal conceptual design decisions. It is based on the OpenAeroStruct framework, a low-fidelity aero-structural optimizer that uses the vortex-lattice method for the aerodynamic solver and a 1D truss, beam and torsional finite element for the structural solver. Additional capabilities were developed, namely a trajectory optimization module using a collocation method, with the option of using b-spline interpolation methods to increase optimizer efficiency. Two different propulsive models were also added to accurately determine the aircraft propulsive response to control input. The framework controls both aircraft geometry (wing planform and tail sizing) as well as the trajectory control (throttle and stabilizer incidence) and state variables, while successfully preventing structural failure. Using gradient-based algorithms, the Air Cargo Challenge competition was studied using two methods: single score optimization and global score optimization. Optimal conceptual tendencies were observed and analysed. Single optimization revealed individual parts (climb, distance and payload) optimal results. Global optimization showed that cargo carried is of the utmost importance along with the trajectory choice and the trimmed conditions of the aircraft in each flight segment. Furthermore, wing and tail surface area relation was deduced along with optimal wing planform surface area. Trajectory optimization b-spline interpolation efficiency method revealed promising with a decrease in computational time of 43% and a better optimizer response overall. The propulsive models showed the importance of accurately representing a system’s behaviour.
Keywords: Trajectory optimization, Aerostructural design, Multidisciplinary design optimization, Optimization efficiency, Air Cargo Challenge},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
In this work, a coupled aerostructural aircraft design and trajectory optimization framework is developed for the Air Cargo Challenge 2022 competition to ultimately achieve the optimal conceptual design decisions. It is based on the OpenAeroStruct framework, a low-fidelity aero-structural optimizer that uses the vortex-lattice method for the aerodynamic solver and a 1D truss, beam and torsional finite element for the structural solver. Additional capabilities were developed, namely a trajectory optimization module using a collocation method, with the option of using b-spline interpolation methods to increase optimizer efficiency. Two different propulsive models were also added to accurately determine the aircraft propulsive response to control input. The framework controls both aircraft geometry (wing planform and tail sizing) as well as the trajectory control (throttle and stabilizer incidence) and state variables, while successfully preventing structural failure. Using gradient-based algorithms, the Air Cargo Challenge competition was studied using two methods: single score optimization and global score optimization. Optimal conceptual tendencies were observed and analysed. Single optimization revealed individual parts (climb, distance and payload) optimal results. Global optimization showed that cargo carried is of the utmost importance along with the trajectory choice and the trimmed conditions of the aircraft in each flight segment. Furthermore, wing and tail surface area relation was deduced along with optimal wing planform surface area. Trajectory optimization b-spline interpolation efficiency method revealed promising with a decrease in computational time of 43% and a better optimizer response overall. The propulsive models showed the importance of accurately representing a system’s behaviour.
Keywords: Trajectory optimization, Aerostructural design, Multidisciplinary design optimization, Optimization efficiency, Air Cargo Challenge
Keywords: Trajectory optimization, Aerostructural design, Multidisciplinary design optimization, Optimization efficiency, Air Cargo Challenge
Oliveira, G.
Coupled aircraft design and trajectory optimization of an electric UAV Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2021.
@mastersthesis{Oliveira:2021:MSc,
title = {Coupled aircraft design and trajectory optimization of an electric UAV},
author = {G. Oliveira},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Oliveira_2021.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Oliveira_2021_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=1651661, Catalog IST},
year = {2021},
date = {2021-06-01},
urldate = {2021-06-01},
pages = {84},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {In this work, coupled aircraft design and trajectory optimization is performed with the objective of producing a tailored UAV configuration and path that fulfill a mission at peak performance. The aerostructural component is handled by the OpenAeroStruct framework. This is a low-fidelity tool that uses a vortex-lattice method and a 1D finite-element analysis to model lifting surfaces. An upgrade of the framework is developed to accommodate propulsion and its performance metrics, as well as trajectory dependent computations. An electric propulsive system is considered where the propeller is modelled using a relation derived from Blade Element and Momentum Theory. A direct collocation method is used for the trajectory component. Gradient-based optimization is performed for different objectives, such as minimum energy consumed during climb, minimum time to climb to an arbitratry altitude, and maximum final distance starting from a cruise flight stage. The energy minimization problem is also optimized solely through trajectory or aircraft design, isolated, to better quantify the benefits of the coupled optimization. We verify that the coupled optimization is able to further minimize energy in 33% and 10.8%, relative to the isolated trajectory and aircraft design optimizations. We also see that flight time and energy are strongly linked, with the objectives of both solutions varying less than 0.2%. We observe that the coupled optimization is computationally more expensive and that the cost does not increase linearly with problem size.
Keywords: Trajectory optimization, Aerostructural design, Multidisciplinary design optimization, Gradient-based optimization},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
In this work, coupled aircraft design and trajectory optimization is performed with the objective of producing a tailored UAV configuration and path that fulfill a mission at peak performance. The aerostructural component is handled by the OpenAeroStruct framework. This is a low-fidelity tool that uses a vortex-lattice method and a 1D finite-element analysis to model lifting surfaces. An upgrade of the framework is developed to accommodate propulsion and its performance metrics, as well as trajectory dependent computations. An electric propulsive system is considered where the propeller is modelled using a relation derived from Blade Element and Momentum Theory. A direct collocation method is used for the trajectory component. Gradient-based optimization is performed for different objectives, such as minimum energy consumed during climb, minimum time to climb to an arbitratry altitude, and maximum final distance starting from a cruise flight stage. The energy minimization problem is also optimized solely through trajectory or aircraft design, isolated, to better quantify the benefits of the coupled optimization. We verify that the coupled optimization is able to further minimize energy in 33% and 10.8%, relative to the isolated trajectory and aircraft design optimizations. We also see that flight time and energy are strongly linked, with the objectives of both solutions varying less than 0.2%. We observe that the coupled optimization is computationally more expensive and that the cost does not increase linearly with problem size.
Keywords: Trajectory optimization, Aerostructural design, Multidisciplinary design optimization, Gradient-based optimization
Keywords: Trajectory optimization, Aerostructural design, Multidisciplinary design optimization, Gradient-based optimization
Alturas, N.
Modeling and optimization of an obstacle detection system for small UAVs Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2021.
@mastersthesis{Alturas:2021:MSc,
title = {Modeling and optimization of an obstacle detection system for small UAVs},
author = {N. Alturas},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Alturas_2021.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Alturas_2021_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=1644757, Catalog IST},
year = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
pages = {86},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {In the last years, the unmanned aerial vehicles (UAV) market has expanded and diversified substantially. This work presents a solution for the enhancement of safety during the flight of small fixed-wing UAVs, regarding the detection of obstacles during flight. This task was achieved by making a market study on available sensors to find the most suitable to equip a UAV and by modeling them, so that these models could be integrated into collision detection and avoidance simulations. A study was also made on different tracking filters and sensor fusion techniques, where the Converted Measurement Kalman Filter and the Weighted Filter technique were found to be the best options to implement. In the performed simulations, the used avoidance method was the Potential Fields for being computationally inexpensive and for providing feasible solutions in real time. Several parametric studies were conducted to test the performance of the studied sensors and to see how different sensor parameters affect the success of the obstacle avoidance. In these tests, the characteristics of the sensors were deemed adequate for avoiding obstacles when integrated into small UAVs. An optimization study was also conducted, using a genetic algorithm, to find the orientation of sensors, for different sets of sensors, that results in the best performance in a collection of random generated scenarios. It is shown that, overall, the developed system provided a satisfactory solution.
Keywords: Potential fields, Genetic algorithm, Kalman filter, Unbiased conversion, Sensor
fusion, Parametric study},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
In the last years, the unmanned aerial vehicles (UAV) market has expanded and diversified substantially. This work presents a solution for the enhancement of safety during the flight of small fixed-wing UAVs, regarding the detection of obstacles during flight. This task was achieved by making a market study on available sensors to find the most suitable to equip a UAV and by modeling them, so that these models could be integrated into collision detection and avoidance simulations. A study was also made on different tracking filters and sensor fusion techniques, where the Converted Measurement Kalman Filter and the Weighted Filter technique were found to be the best options to implement. In the performed simulations, the used avoidance method was the Potential Fields for being computationally inexpensive and for providing feasible solutions in real time. Several parametric studies were conducted to test the performance of the studied sensors and to see how different sensor parameters affect the success of the obstacle avoidance. In these tests, the characteristics of the sensors were deemed adequate for avoiding obstacles when integrated into small UAVs. An optimization study was also conducted, using a genetic algorithm, to find the orientation of sensors, for different sets of sensors, that results in the best performance in a collection of random generated scenarios. It is shown that, overall, the developed system provided a satisfactory solution.
Keywords: Potential fields, Genetic algorithm, Kalman filter, Unbiased conversion, Sensor
fusion, Parametric study
Keywords: Potential fields, Genetic algorithm, Kalman filter, Unbiased conversion, Sensor
fusion, Parametric study
Pereira, M.
Multi-fidelity methods for improved efficiency in multi-disciplinary optimization problems Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2021.
@mastersthesis{Pereira:2021:MSc,
title = {Multi-fidelity methods for improved efficiency in multi-disciplinary optimization problems},
author = {M. Pereira},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Pereira_2021.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Pereira_2021_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=1646320, Catalog IST},
year = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
pages = {92},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {In the pursuit of designing complex systems accurately and with affordable computational cost, multifidelity Super Efficient Global Optimization (SEGO) is one of the most recent approaches. Furthermore, various systems involve multiple disciplines interaction that must be considered during the optimization. These disciplines directly influence each other, hence information between them needs to be exchanged during the optimization through transfer schemes. Since the transfer schemes are a significant part of the computational cost in the optimization process, new configurations can be used to try to reduce this time. Therefore, this work considers the extension of a multi-disciplinary optimization problem to multi-fidelity using SEGO. An aircraft wing is desired to be optimized with the aim of consuming the minimum fuel during the flight mission. The problem is defined using a low fidelity multi-disciplinary tool, OpenAeroStruct (OAS), that considers models for the aerodynamics and structures. In this work, we verify that the transfer schemes implemented in OAS do not fulfill the conservation requirement. Then, an extension of the transfer schemes is developed to enable different disciplines discretization. Multi-fidelity SEGO with fidelity levels varied from one to three and two types of design of experiments is performed. We verify that the best approach is the one that uses two fidelity levels with only nested samples in the initial dataset. Then, the transfer schemes extension is employed in the best approach of multi-fidelity SEGO for the same problem. We verify that very similar results are obtained with a computational cost reduction.
Keywords: Surrogate modeling, Bayesian optimization, Efficient global Optimization, Aerostructural design},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
In the pursuit of designing complex systems accurately and with affordable computational cost, multifidelity Super Efficient Global Optimization (SEGO) is one of the most recent approaches. Furthermore, various systems involve multiple disciplines interaction that must be considered during the optimization. These disciplines directly influence each other, hence information between them needs to be exchanged during the optimization through transfer schemes. Since the transfer schemes are a significant part of the computational cost in the optimization process, new configurations can be used to try to reduce this time. Therefore, this work considers the extension of a multi-disciplinary optimization problem to multi-fidelity using SEGO. An aircraft wing is desired to be optimized with the aim of consuming the minimum fuel during the flight mission. The problem is defined using a low fidelity multi-disciplinary tool, OpenAeroStruct (OAS), that considers models for the aerodynamics and structures. In this work, we verify that the transfer schemes implemented in OAS do not fulfill the conservation requirement. Then, an extension of the transfer schemes is developed to enable different disciplines discretization. Multi-fidelity SEGO with fidelity levels varied from one to three and two types of design of experiments is performed. We verify that the best approach is the one that uses two fidelity levels with only nested samples in the initial dataset. Then, the transfer schemes extension is employed in the best approach of multi-fidelity SEGO for the same problem. We verify that very similar results are obtained with a computational cost reduction.
Keywords: Surrogate modeling, Bayesian optimization, Efficient global Optimization, Aerostructural design
Keywords: Surrogate modeling, Bayesian optimization, Efficient global Optimization, Aerostructural design
Oliveira, A.
Design, construction, calibration and testing of a wind tunnel force balance Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2020.
@mastersthesis{Oliveira:2020:MSc,
title = {Design, construction, calibration and testing of a wind tunnel force balance},
author = {A. Oliveira},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Oliveira_2020.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Oliveira_2020_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=1630172, Catalog IST},
year = {2020},
date = {2020-09-01},
urldate = {2020-09-01},
pages = {98},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Experimental activities are essential in the aerospace industry, with wind tunnels being the most used devices in the validation of concepts and design. Therefore, this work aims to endow the Aerospace Engineering Laboratory at Instituto Superior Técnico with an aerodynamic balance capable of measuring forces and moments. The balance follows an existing Stewart platform configuration design, here readjusted to the current requirements. The design and validation of mechanical performance were initially done computationally using SolidWorks, then some experimental tests were performed for verification. In addition to the construction, the instrumentation of the balance was necessary to compute forces and moments, as well as additional quantities for the tests, such as speed, temperature and attitude. To this end, strain gauges and several sensors were studied and implemented. The balance user interface was done in LabVIEW. To make the balance as accurate as possible, a static calibration was performed to relate the application of well-known loads on the balance with the response of the strain gauges. This way, it was possible to obtain a matrix with calibration coefficients for all aerodynamic components using the collected data and the least squares method with a second-order polynomial. Finally, an experimental test was performed with a model of the rear wing of a racing car to confirm the optimisation in CL/CD when using endplates with a curved profile instead of a flat profile. The influence of velocity in the rear wing performance was also analysed and a comparison with CFD was carried out.
Keywords: Wind tunnel, Aerodynamic force balance, Mechanical design, Sensors and instrumentation, Calibration, Experimental tests},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Experimental activities are essential in the aerospace industry, with wind tunnels being the most used devices in the validation of concepts and design. Therefore, this work aims to endow the Aerospace Engineering Laboratory at Instituto Superior Técnico with an aerodynamic balance capable of measuring forces and moments. The balance follows an existing Stewart platform configuration design, here readjusted to the current requirements. The design and validation of mechanical performance were initially done computationally using SolidWorks, then some experimental tests were performed for verification. In addition to the construction, the instrumentation of the balance was necessary to compute forces and moments, as well as additional quantities for the tests, such as speed, temperature and attitude. To this end, strain gauges and several sensors were studied and implemented. The balance user interface was done in LabVIEW. To make the balance as accurate as possible, a static calibration was performed to relate the application of well-known loads on the balance with the response of the strain gauges. This way, it was possible to obtain a matrix with calibration coefficients for all aerodynamic components using the collected data and the least squares method with a second-order polynomial. Finally, an experimental test was performed with a model of the rear wing of a racing car to confirm the optimisation in CL/CD when using endplates with a curved profile instead of a flat profile. The influence of velocity in the rear wing performance was also analysed and a comparison with CFD was carried out.
Keywords: Wind tunnel, Aerodynamic force balance, Mechanical design, Sensors and instrumentation, Calibration, Experimental tests
Keywords: Wind tunnel, Aerodynamic force balance, Mechanical design, Sensors and instrumentation, Calibration, Experimental tests
L'ucio, L.
Multidisciplinary aircraft design and trajectory control optimization Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2019.
@mastersthesis{Lucio:2019:MSc,
title = {Multidisciplinary aircraft design and trajectory control optimization},
author = {L. L'ucio},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Lucio_2019.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Lucio_2019_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=641447, Catalog IST},
year = {2019},
date = {2019-12-01},
urldate = {2019-12-01},
pages = {80},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {In the pursuit of increasing aircraft performance, one approach which can yield better results than a conventional design process is a multidisciplinary optimization process. In this paradigm, a design architecture is established so that the analyses for the several disciplines pertinent to the problem are handled simultaneously, rather than sequentially. In this work, a numerical tool was developed in order to perform low-fidelity multidisciplinary optimization upon a commercial airliner - the B777-300 - considering models for aerodynamics, propulsion, structures and trajectory. For the aerodynamic analysis, a vortex-lattice method (VLM) is employed. The lifting surface structures were modeled by finite elements with the shape of hollow tubular spars. For the propulsion system, a model based on empirical data collected from the target engines was utilized. Finally, the system was optimized for cruise conditions, and then control optimization was performed on the resulting configuration for additional mission phases. The performance metric optimized in this work was be the amount of fuel burnt by the aircraft in order to complete its mission. The described optimization processes were successfully carried out, the former outputting the cruise optimized wing and tail configurations, and the latter providing the optimized control parameter values for descent flight conditions. These values were validated by means of comparison with those of the original B777-300, including that of the performance metric - which improved as more disciplines were considered.
Keywords: Multidisciplinary optimization, Trajectory control optimization, Aerostructural optimization, Vortex lattice method, Finite element method},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
In the pursuit of increasing aircraft performance, one approach which can yield better results than a conventional design process is a multidisciplinary optimization process. In this paradigm, a design architecture is established so that the analyses for the several disciplines pertinent to the problem are handled simultaneously, rather than sequentially. In this work, a numerical tool was developed in order to perform low-fidelity multidisciplinary optimization upon a commercial airliner - the B777-300 - considering models for aerodynamics, propulsion, structures and trajectory. For the aerodynamic analysis, a vortex-lattice method (VLM) is employed. The lifting surface structures were modeled by finite elements with the shape of hollow tubular spars. For the propulsion system, a model based on empirical data collected from the target engines was utilized. Finally, the system was optimized for cruise conditions, and then control optimization was performed on the resulting configuration for additional mission phases. The performance metric optimized in this work was be the amount of fuel burnt by the aircraft in order to complete its mission. The described optimization processes were successfully carried out, the former outputting the cruise optimized wing and tail configurations, and the latter providing the optimized control parameter values for descent flight conditions. These values were validated by means of comparison with those of the original B777-300, including that of the performance metric - which improved as more disciplines were considered.
Keywords: Multidisciplinary optimization, Trajectory control optimization, Aerostructural optimization, Vortex lattice method, Finite element method
Keywords: Multidisciplinary optimization, Trajectory control optimization, Aerostructural optimization, Vortex lattice method, Finite element method
Alexandre, D.
Closed dynamic soaring trajectories for surveillance missions of aerial vehicles Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa / Roma Sapienza, Lisboa, Portugal / Roma, Italy, 2019.
@mastersthesis{Alexandre:2019:MSc,
title = {Closed dynamic soaring trajectories for surveillance missions of aerial vehicles},
author = {D. Alexandre},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Alexandre_2019.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Alexandre_2019_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=641442, Catalog IST},
year = {2019},
date = {2019-12-01},
urldate = {2019-12-01},
pages = {82},
address = {Lisboa, Portugal / Roma, Italy},
school = {Instituto Superior Técnico, Universidade de Lisboa / Roma Sapienza},
abstract = {Dynamic soaring is a flight technique used by albatrosses to cover large distances without the expenditure of energy, which is extracted from the available wind conditions. Closed dynamic soaring trajectories use spatial variations of wind speed to hover, in principle, indefinitely over a prescribed area. Applying the concept of closed dynamic soaring trajectories to aerial vehicles, in particular, UAVs may provide a solution to improve the endurance of these vehicles in certain particular missions. The main limitation of dynamic soaring is its dependence on the wind. The present thesis studies the feasibility of closed, single-loop, energy-neutral trajectories for a broad set of conditions. Through the use of trajectory optimization methods, it was possible to see how the wind profile, initial flight conditions and vehicle constraints influence the required wind strength to perform dynamic soaring and consequently the trajectories’ viability. It was possible to conclude from the study that there are optimal values for the initial airspeed and initial height of the vehicle, that minimise the required wind strength to perform the trajectories. In addition, it was seen that the structural and aerodynamic constraints of the vehicle affect dynamic soaring trajectories at high and low airspeeds respectively. The thesis ends by proposing some new trajectories that can be performed in conditions of excess wind to maximize the time spent on the air and the trajectory length while maintaining the concept of single-loop, energy-neutral trajectories, making them especially useful for aerial vehicles surveillance applications.
Keywords: Trajectory optimization, Non-linear flight dynamics, Energy harvesting, Endurance, Feasibility conditions},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Dynamic soaring is a flight technique used by albatrosses to cover large distances without the expenditure of energy, which is extracted from the available wind conditions. Closed dynamic soaring trajectories use spatial variations of wind speed to hover, in principle, indefinitely over a prescribed area. Applying the concept of closed dynamic soaring trajectories to aerial vehicles, in particular, UAVs may provide a solution to improve the endurance of these vehicles in certain particular missions. The main limitation of dynamic soaring is its dependence on the wind. The present thesis studies the feasibility of closed, single-loop, energy-neutral trajectories for a broad set of conditions. Through the use of trajectory optimization methods, it was possible to see how the wind profile, initial flight conditions and vehicle constraints influence the required wind strength to perform dynamic soaring and consequently the trajectories’ viability. It was possible to conclude from the study that there are optimal values for the initial airspeed and initial height of the vehicle, that minimise the required wind strength to perform the trajectories. In addition, it was seen that the structural and aerodynamic constraints of the vehicle affect dynamic soaring trajectories at high and low airspeeds respectively. The thesis ends by proposing some new trajectories that can be performed in conditions of excess wind to maximize the time spent on the air and the trajectory length while maintaining the concept of single-loop, energy-neutral trajectories, making them especially useful for aerial vehicles surveillance applications.
Keywords: Trajectory optimization, Non-linear flight dynamics, Energy harvesting, Endurance, Feasibility conditions
Keywords: Trajectory optimization, Non-linear flight dynamics, Energy harvesting, Endurance, Feasibility conditions
Rocha, I. M. D.
Experimental and numerical aeroelastic study of wings Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2019.
@mastersthesis{Rocha:2019:MSc,
title = {Experimental and numerical aeroelastic study of wings},
author = {I. M. D. Rocha},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Rocha_2019.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Rocha_2019_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=637261, Catalog IST},
year = {2019},
date = {2019-07-01},
urldate = {2019-07-01},
pages = {84},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Since the early days of aviation, aeroelastic problems have shown to be some of the most challenging to solve. With the development of numerical methods, the study of aircraft structures and their interaction with the surrounding air flow at different flight conditions has become easily accessible and, thus, is now mandatory in the design phase of an aircraft. This work focuses on the development of a numerical tool for aircraft wing fluid-structure interaction (FSI) analyses, in which the external airflow and the internal structure interact, as well as the wind tunnel testing of two half wing prototypes to help validate the accuracy of the numerical tool developed. A panel method was implemented for the aerodynamic analysis and a finite-element model using equivalent beam elements was implemented for the structural analysis, both coded in MATLAB language. The wing shape was parametrized using area, airfoil cross-section shape, aspect ratio, taper ratio, sweep angle and dihedral angle. Each analysis models were successfully individually verified against other bibliographic sources and then the two disciplines were coupled into the FSI numerical tool. A parametric study was also conducted to study the influence of the wing aspect ratio on flutter speed. The validated FSI tool was then used in an optimization framework to obtain three separate optimized wing shapes with the objectives of maximizing the lift-to-drag ratio, minimizing wing mass and maximizing wing flutter velocity respectively, whilst guaranteeing that the new wing performance is not worse than that of the baseline wing.
Keywords: Aircraft design, Flutter, Divergence speed, Fluid-structure interaction, Wind tunnel, Optimization},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Since the early days of aviation, aeroelastic problems have shown to be some of the most challenging to solve. With the development of numerical methods, the study of aircraft structures and their interaction with the surrounding air flow at different flight conditions has become easily accessible and, thus, is now mandatory in the design phase of an aircraft. This work focuses on the development of a numerical tool for aircraft wing fluid-structure interaction (FSI) analyses, in which the external airflow and the internal structure interact, as well as the wind tunnel testing of two half wing prototypes to help validate the accuracy of the numerical tool developed. A panel method was implemented for the aerodynamic analysis and a finite-element model using equivalent beam elements was implemented for the structural analysis, both coded in MATLAB language. The wing shape was parametrized using area, airfoil cross-section shape, aspect ratio, taper ratio, sweep angle and dihedral angle. Each analysis models were successfully individually verified against other bibliographic sources and then the two disciplines were coupled into the FSI numerical tool. A parametric study was also conducted to study the influence of the wing aspect ratio on flutter speed. The validated FSI tool was then used in an optimization framework to obtain three separate optimized wing shapes with the objectives of maximizing the lift-to-drag ratio, minimizing wing mass and maximizing wing flutter velocity respectively, whilst guaranteeing that the new wing performance is not worse than that of the baseline wing.
Keywords: Aircraft design, Flutter, Divergence speed, Fluid-structure interaction, Wind tunnel, Optimization
Keywords: Aircraft design, Flutter, Divergence speed, Fluid-structure interaction, Wind tunnel, Optimization
Morgado, F.
Coupled preliminary design and trajectory optimization of rockets using a multidisciplinary approach Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2019.
@mastersthesis{Morgado:2019:MSc,
title = {Coupled preliminary design and trajectory optimization of rockets using a multidisciplinary approach},
author = {F. Morgado},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Morgado_2019.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Morgado_2019_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=636982, Catalog IST},
year = {2019},
date = {2019-06-01},
urldate = {2019-06-01},
pages = {94},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {A tool was developed to perform a rocket preliminary design by finding the optimal design and trajectory parameters for a specific mission. A multidisciplinary coupled approach was used to optimize both trajectory and design. The design optimization is performed using a continuous genetic algorithm, able to perform parallel computation, also developed and benchmarked in this work. The mass and sizing models required to estimate the rocket structure are created using historical data regression or taken from literature. The trajectory optimization is done using the Pontryagin’s minimum principle. The optimality equations are deduced and the optimal values are found using a particle swarm optimization. The Earth’s curvature and the contribution due to Earth’s rotation is taken into account to simulate the trajectory. The drag model is created using data from Missile DATCOM software to test the nose geometry influence with Mach number. The models are validated using real rockets and the influence of the coast phase in trajectory optimization is analyzed using the Vega rocket. The genetic algorithm is subjected to a simplified parameter tuning. Finally, the tool is tested by optimizing the design of a small launch vehicle and comparing it to the state-of-the-art rocket. The tool shows promising results in both trajectory and design optimization. It handles the imposed constraints and is able to successfully perform a launch vehicle conceptual design and trajectory calculation in a reasonable time.
Keywords: Coupled approach, Launch vehicle, Trajectory optimization, Genetic algorithm, Particle swarm optimization},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
A tool was developed to perform a rocket preliminary design by finding the optimal design and trajectory parameters for a specific mission. A multidisciplinary coupled approach was used to optimize both trajectory and design. The design optimization is performed using a continuous genetic algorithm, able to perform parallel computation, also developed and benchmarked in this work. The mass and sizing models required to estimate the rocket structure are created using historical data regression or taken from literature. The trajectory optimization is done using the Pontryagin’s minimum principle. The optimality equations are deduced and the optimal values are found using a particle swarm optimization. The Earth’s curvature and the contribution due to Earth’s rotation is taken into account to simulate the trajectory. The drag model is created using data from Missile DATCOM software to test the nose geometry influence with Mach number. The models are validated using real rockets and the influence of the coast phase in trajectory optimization is analyzed using the Vega rocket. The genetic algorithm is subjected to a simplified parameter tuning. Finally, the tool is tested by optimizing the design of a small launch vehicle and comparing it to the state-of-the-art rocket. The tool shows promising results in both trajectory and design optimization. It handles the imposed constraints and is able to successfully perform a launch vehicle conceptual design and trajectory calculation in a reasonable time.
Keywords: Coupled approach, Launch vehicle, Trajectory optimization, Genetic algorithm, Particle swarm optimization
Keywords: Coupled approach, Launch vehicle, Trajectory optimization, Genetic algorithm, Particle swarm optimization
Pereira, J. L.
Preliminary design and analysis of a chassis side beam for stiffness and crashworthiness of an electric vehicle Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2018.
@mastersthesis{Pereira:2018:MSc,
title = {Preliminary design and analysis of a chassis side beam for stiffness and crashworthiness of an electric vehicle},
author = {J. L. Pereira},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Pereira_2018.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Pereira_2018_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=635403, Catalog IST},
year = {2018},
date = {2018-11-01},
urldate = {2018-11-01},
pages = {96},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Environmental concerns about internal combustion engine cars are pulling constructors to build them electric. The majority of the electric car power cells are lithium-ion batteries. In the event of battery leakage, lithium can cause serious injuries on the passengers’ body. Regarding side collisions, that represent 15% to 40% from all injury accidents, if only serious and fatal injuries are considered these values are increased by 50%. To protect passengers and batteries and also develop a component capable of integrating a chassis, this work focuses in the preliminary design and analysis of a chassis side beam for stiffness and crashworthiness. Taking into account the beam’s function, a judicious choice of the aluminum alloy that will integrate it, was carried out. Two robust Finite Element Analysis (FEA) models are constructed, one that test the crash performance and another that certifies that the beam has the strength and stiffness enough to integrate the chassis. These models are inserted in a multi-objective optimization program based on a genetic algorithm. This program searches for the best pole crash performance and the lightest beam, subjected to non-linear constraints. This tool will allow to obtain the optimized beam without losing engineering time in the iterative process of design and calculate. In this program, adaptive to new structures and purposes, several beams with different strategies were tested. Finally, a multi-thickness beam with a quadricular misaligned cross-sectional shape was chosen. This solution overcomes several project requirements and has the best commitment between pole crash performance and weight.
Keywords: Multi-objective optimization, Genetic algorithm, Pole crash performance, Stiffness},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Environmental concerns about internal combustion engine cars are pulling constructors to build them electric. The majority of the electric car power cells are lithium-ion batteries. In the event of battery leakage, lithium can cause serious injuries on the passengers’ body. Regarding side collisions, that represent 15% to 40% from all injury accidents, if only serious and fatal injuries are considered these values are increased by 50%. To protect passengers and batteries and also develop a component capable of integrating a chassis, this work focuses in the preliminary design and analysis of a chassis side beam for stiffness and crashworthiness. Taking into account the beam’s function, a judicious choice of the aluminum alloy that will integrate it, was carried out. Two robust Finite Element Analysis (FEA) models are constructed, one that test the crash performance and another that certifies that the beam has the strength and stiffness enough to integrate the chassis. These models are inserted in a multi-objective optimization program based on a genetic algorithm. This program searches for the best pole crash performance and the lightest beam, subjected to non-linear constraints. This tool will allow to obtain the optimized beam without losing engineering time in the iterative process of design and calculate. In this program, adaptive to new structures and purposes, several beams with different strategies were tested. Finally, a multi-thickness beam with a quadricular misaligned cross-sectional shape was chosen. This solution overcomes several project requirements and has the best commitment between pole crash performance and weight.
Keywords: Multi-objective optimization, Genetic algorithm, Pole crash performance, Stiffness
Keywords: Multi-objective optimization, Genetic algorithm, Pole crash performance, Stiffness
Cardoso, S. A.
Front secondary crash management system Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2018.
@mastersthesis{Cardoso:2018:MSc,
title = {Front secondary crash management system},
author = {S. A. Cardoso},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Cardoso_2018.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Cardoso_2018_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=635374, Catalog IST},
year = {2018},
date = {2018-11-01},
urldate = {2018-11-01},
pages = {84},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Over the past 20 years, more than 800,000 people have died on the roads of the European Union. Thanks to the joint effort of some organizations and governments, these numbers have been decreasing due to the creation of regulations to include passive and active protection systems in vehicles. This way, this work was developed to create a structure or several structures that protect the occupants in case of frontal collision in order to be applied in a modular platform that will carry several types of vehicles. Thus, for each case, the structures were developed to protect the occupants regarding the Euro NCAP frontal full width test protocol. The structural development process was based on some geometric parametrization and a multi-objective genetic optimization was used to find the best solutions from the finite element analyses. Four types of vehicles were considered. For the lighter case, a primary structure was developed to absorb the corresponding energy during the impact. The heavier vehicles have a secondary structure to absorb the energy corresponding to the added weight. The final geometries have proven to fulfil the assumptions, obtaining a good relation between the mass increase in these structures and the energy absorption during the impact. On the other hand, the insertion of the secondary structure proved to have satisfactory effects on the overall behaviour during the crash events.
Keywords: Frontal collision, Multi-objective optimization, Euro NCAP, Genetic algorithm, Secondary system, Energy absorption},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Over the past 20 years, more than 800,000 people have died on the roads of the European Union. Thanks to the joint effort of some organizations and governments, these numbers have been decreasing due to the creation of regulations to include passive and active protection systems in vehicles. This way, this work was developed to create a structure or several structures that protect the occupants in case of frontal collision in order to be applied in a modular platform that will carry several types of vehicles. Thus, for each case, the structures were developed to protect the occupants regarding the Euro NCAP frontal full width test protocol. The structural development process was based on some geometric parametrization and a multi-objective genetic optimization was used to find the best solutions from the finite element analyses. Four types of vehicles were considered. For the lighter case, a primary structure was developed to absorb the corresponding energy during the impact. The heavier vehicles have a secondary structure to absorb the energy corresponding to the added weight. The final geometries have proven to fulfil the assumptions, obtaining a good relation between the mass increase in these structures and the energy absorption during the impact. On the other hand, the insertion of the secondary structure proved to have satisfactory effects on the overall behaviour during the crash events.
Keywords: Frontal collision, Multi-objective optimization, Euro NCAP, Genetic algorithm, Secondary system, Energy absorption
Keywords: Frontal collision, Multi-objective optimization, Euro NCAP, Genetic algorithm, Secondary system, Energy absorption
Fernandes, J.
Design of a wind tunnel force balance Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2018.
@mastersthesis{Fernandes:2018:MSc,
title = {Design of a wind tunnel force balance},
author = {J. Fernandes},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Fernandes_2018.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Fernandes_2018_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=630536, Catalog IST},
year = {2018},
date = {2018-06-01},
urldate = {2018-06-01},
pages = {98},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Wind tunnels are used to simulate the behaviour of models in the presence of an airflow thus allowing to obtain the components that better define this interaction, forces and moments. In order to take full advantage of the Aerospace Engineering Laboratory’s wind tunnel at Instituto Superior Técnico, it has proved necessary to design a balance to measure forces and moments. Firstly, the force balance dimensioning was based in the possibility of testing both aircraft and halfwing models that fit the wind tunnel test section, using a simulation software (XFLR5) to obtain the maximum load range the force balance has to be able to support in each of the situations. The Analytic Hierarchy Process and a set of comparison criteria allowed the selection of the most adequate force balance architecture from the most widely used, the external platform balance. Once the “skeleton” of the force balance was defined, it was necessary to carefully define each of its mechanical components and guarantee that its integrity was fulfilled using the software SolidWorks. This is followed by the selection of all the electronic components like strain gauges and data acquisition system that will assess the deformation of the balance for a certain loading condition. Several considerations on the mechanical assembly were made and a cost analysis was presented. Finally, it is suggested a calibration procedure to make the force balance fully functional.
Keywords: Six components aerodynamic balance, Experimental testing, Mechanical design, Sensors and instrumentation, Calibration procedure},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Wind tunnels are used to simulate the behaviour of models in the presence of an airflow thus allowing to obtain the components that better define this interaction, forces and moments. In order to take full advantage of the Aerospace Engineering Laboratory’s wind tunnel at Instituto Superior Técnico, it has proved necessary to design a balance to measure forces and moments. Firstly, the force balance dimensioning was based in the possibility of testing both aircraft and halfwing models that fit the wind tunnel test section, using a simulation software (XFLR5) to obtain the maximum load range the force balance has to be able to support in each of the situations. The Analytic Hierarchy Process and a set of comparison criteria allowed the selection of the most adequate force balance architecture from the most widely used, the external platform balance. Once the “skeleton” of the force balance was defined, it was necessary to carefully define each of its mechanical components and guarantee that its integrity was fulfilled using the software SolidWorks. This is followed by the selection of all the electronic components like strain gauges and data acquisition system that will assess the deformation of the balance for a certain loading condition. Several considerations on the mechanical assembly were made and a cost analysis was presented. Finally, it is suggested a calibration procedure to make the force balance fully functional.
Keywords: Six components aerodynamic balance, Experimental testing, Mechanical design, Sensors and instrumentation, Calibration procedure
Keywords: Six components aerodynamic balance, Experimental testing, Mechanical design, Sensors and instrumentation, Calibration procedure
Rodrigues, P.
Efficient aerodynamic optimization of aircraft wings Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2018.
@mastersthesis{Rodrigues:2018:MSc,
title = {Efficient aerodynamic optimization of aircraft wings},
author = {P. Rodrigues},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Rodrigues_2018.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Rodrigues_2018_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=628683, Catalog IST},
year = {2018},
date = {2018-04-01},
urldate = {2018-04-01},
pages = {94},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {One of the most important keys to the successful design of complex systems is disciplinary integration. Multidisciplinary Design and Optimization is now a promising methodology for the efficient design of such systems, since it combines multidisciplinary analysis with gradient-based optimization techniques. Therefore, this methodology requires the derivatives evaluation of the functions of interest with respect to the design variables, which is the most demanding computational task in the optimization process. Traditionally, those derivatives are calculated inefficiently and inaccurately using approximate methods. Therefore, the objective of this work is to develop an efficient optimization framework to solve aerodynamic design problems using exact gradient information. Firstly, a survey on sensitivity analysis methods is conducted to identify which tools are available and understand their respective merits. Secondly, an aerodynamic model based on the panel method is reformulated into five smaller modules, in which the respective sensitivity analysis blocks are constructed using exact gradient estimation methods: automatic differentiation, symbolic differentiation and the adjoint method. Both the aerodynamic tool and respective sensitivity analysis are validated using a wing design tool and the finite-differences method, respectively. Subsequently, a parametric study is also presented for a baseline wing configuration to survey the impacts of changing the wing’s design variables on the aerodynamic coefficients and therefore, to understand the wing’s aerodynamic behavior. Finally, aerodynamic optimization problems are solved using the new tool with remarkable success since, when compared to the finite-differences method, the optimization time can be reduced by 90%.
Keywords: Gradient-based optimization, Aerodynamic design, Sensitivity analysis, Panel method, Automatic differentiation, Adjoint method},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
One of the most important keys to the successful design of complex systems is disciplinary integration. Multidisciplinary Design and Optimization is now a promising methodology for the efficient design of such systems, since it combines multidisciplinary analysis with gradient-based optimization techniques. Therefore, this methodology requires the derivatives evaluation of the functions of interest with respect to the design variables, which is the most demanding computational task in the optimization process. Traditionally, those derivatives are calculated inefficiently and inaccurately using approximate methods. Therefore, the objective of this work is to develop an efficient optimization framework to solve aerodynamic design problems using exact gradient information. Firstly, a survey on sensitivity analysis methods is conducted to identify which tools are available and understand their respective merits. Secondly, an aerodynamic model based on the panel method is reformulated into five smaller modules, in which the respective sensitivity analysis blocks are constructed using exact gradient estimation methods: automatic differentiation, symbolic differentiation and the adjoint method. Both the aerodynamic tool and respective sensitivity analysis are validated using a wing design tool and the finite-differences method, respectively. Subsequently, a parametric study is also presented for a baseline wing configuration to survey the impacts of changing the wing’s design variables on the aerodynamic coefficients and therefore, to understand the wing’s aerodynamic behavior. Finally, aerodynamic optimization problems are solved using the new tool with remarkable success since, when compared to the finite-differences method, the optimization time can be reduced by 90%.
Keywords: Gradient-based optimization, Aerodynamic design, Sensitivity analysis, Panel method, Automatic differentiation, Adjoint method
Keywords: Gradient-based optimization, Aerodynamic design, Sensitivity analysis, Panel method, Automatic differentiation, Adjoint method
Moita, N.
Optimization of propeller-driven propulsion system for small UAV Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2018.
@mastersthesis{Moita:2018:MSc,
title = {Optimization of propeller-driven propulsion system for small UAV},
author = {N. Moita},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Moita_2018.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Moita_2018_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=628682, Catalog IST},
year = {2018},
date = {2018-04-01},
urldate = {2018-04-01},
pages = {98},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Since the end of the 2nd World War, there has been a growth of the development of UAVs and, nowadays, there are UAVs aimed to a variety of functionalities and missions. Integrated in the LEEUAV project, an UAV developed by IDMEC, together with AeroG and INEGI, the objective of this dissertation is to optimize the propeller-driven propulsion system designed and built previously. After some literature review and research about the different existing softwares for propulsion systems analysis, the chosen software was the QPROP. After software selection, a propeller parametrization was made, including the parameters that characterize the planform shape of the propeller, such as the diameter and the chord and the pitch angle distributions of each blade and the characteristics of the airfoil used in each blade, namely the derivative of the lift coefficient with the angle of attack, the lift coefficient at zero angle of attack, the maximum and the minimum lift coefficient, the profile drag coefficient and its corresponding lift coefficient, the Reynolds number used as a reference and the exponent used to adjust the polar curve to different Reynolds numbers. After running QPROP, some functions were used to evaluate the performance of the propeller, such as the thrust, the power and thrust coefficient and the propeller efficiency. To perform the experimental tests, three different propellers were chosen to study how the performance varies for different diameters, pitches and motors and to validate the software. Since it was not known accurately which airfoil was used in each propeller, two different airfoils, whose data was obtained using the software XFOIL, were considered. The geometric parameters of the propeller were measured manually. Following the experimental tests and the validation of the software QPROP, a progressive optimization using the software MATLAB, for cruise and climb, was performed. Initially, only the motor rotation speed was considered in the optimization and only later the geometry optimization was performed. At the end of this optimization, a system motor+propeller with an higher efficiency for both flight conditions was obtained, as desired.
Keywords: Propeller, Optimization, Efficiency, Thrust, Electrical power},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Since the end of the 2nd World War, there has been a growth of the development of UAVs and, nowadays, there are UAVs aimed to a variety of functionalities and missions. Integrated in the LEEUAV project, an UAV developed by IDMEC, together with AeroG and INEGI, the objective of this dissertation is to optimize the propeller-driven propulsion system designed and built previously. After some literature review and research about the different existing softwares for propulsion systems analysis, the chosen software was the QPROP. After software selection, a propeller parametrization was made, including the parameters that characterize the planform shape of the propeller, such as the diameter and the chord and the pitch angle distributions of each blade and the characteristics of the airfoil used in each blade, namely the derivative of the lift coefficient with the angle of attack, the lift coefficient at zero angle of attack, the maximum and the minimum lift coefficient, the profile drag coefficient and its corresponding lift coefficient, the Reynolds number used as a reference and the exponent used to adjust the polar curve to different Reynolds numbers. After running QPROP, some functions were used to evaluate the performance of the propeller, such as the thrust, the power and thrust coefficient and the propeller efficiency. To perform the experimental tests, three different propellers were chosen to study how the performance varies for different diameters, pitches and motors and to validate the software. Since it was not known accurately which airfoil was used in each propeller, two different airfoils, whose data was obtained using the software XFOIL, were considered. The geometric parameters of the propeller were measured manually. Following the experimental tests and the validation of the software QPROP, a progressive optimization using the software MATLAB, for cruise and climb, was performed. Initially, only the motor rotation speed was considered in the optimization and only later the geometry optimization was performed. At the end of this optimization, a system motor+propeller with an higher efficiency for both flight conditions was obtained, as desired.
Keywords: Propeller, Optimization, Efficiency, Thrust, Electrical power
Keywords: Propeller, Optimization, Efficiency, Thrust, Electrical power
Nunes, T.
Multi-objective design optimization of a frontal crash energy absorption system for a road-safe vehicle Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2017.
@mastersthesis{Nunes:20217MSc,
title = {Multi-objective design optimization of a frontal crash energy absorption system for a road-safe vehicle},
author = {T. Nunes},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Nunes_2017.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Nunes_2017_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=625526, Catalog IST},
year = {2017},
date = {2017-11-01},
urldate = {2017-11-01},
pages = {98},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Since 2013, more than 1.25 million people die each year in road accidents, making road safety a global concern. With regard to protection in frontal and rear collisions, a common solution is to use a structure designed to deform in a controlled manner in the event of collision, avoiding deformation of the cabin and excessive accelerations in the passengers, which can lead to serious injuries or even fatalities. This work focus on the development of an aluminum structure of this type, aiming for an optimized design, within the design parameters available for the vehicle project in which it is included. A Finite Element Analysis (FEA) model of the frontal energy absorption structure for frontal impact is developed and validated with a quasi-static compression experimental procedure. A multi-objective optimization process, that can be adaptable to the future needs of the project, is developed. Several changes in the geometry are tested, focusing on specific deficits in the performance of the structure. Through this process, a robust and adaptable FEA model is achieved and a compilation of the influence of several parameters on the impact performance is obtained. The optimized structure shows a significant performance improvement in the event of a frontal collision and, according to the established limits, it is expected to satisfy the legal values of safety in the tests carried out by the responsible entities.
Keywords: Thin-walled beams, Front collision, Energy absorption, Crash performance, Multiobjective optimization},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Since 2013, more than 1.25 million people die each year in road accidents, making road safety a global concern. With regard to protection in frontal and rear collisions, a common solution is to use a structure designed to deform in a controlled manner in the event of collision, avoiding deformation of the cabin and excessive accelerations in the passengers, which can lead to serious injuries or even fatalities. This work focus on the development of an aluminum structure of this type, aiming for an optimized design, within the design parameters available for the vehicle project in which it is included. A Finite Element Analysis (FEA) model of the frontal energy absorption structure for frontal impact is developed and validated with a quasi-static compression experimental procedure. A multi-objective optimization process, that can be adaptable to the future needs of the project, is developed. Several changes in the geometry are tested, focusing on specific deficits in the performance of the structure. Through this process, a robust and adaptable FEA model is achieved and a compilation of the influence of several parameters on the impact performance is obtained. The optimized structure shows a significant performance improvement in the event of a frontal collision and, according to the established limits, it is expected to satisfy the legal values of safety in the tests carried out by the responsible entities.
Keywords: Thin-walled beams, Front collision, Energy absorption, Crash performance, Multiobjective optimization
Keywords: Thin-walled beams, Front collision, Energy absorption, Crash performance, Multiobjective optimization
Baptista, F.
A 0-D off-design performance prediction model of the CFM56-5B turbofan engine Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2017.
@mastersthesis{Baptista:2017:MSc,
title = {A 0-D off-design performance prediction model of the CFM56-5B turbofan engine},
author = {F. Baptista},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Baptista_2017.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Baptista_2017_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=624837, Catalog IST},
year = {2017},
date = {2017-10-01},
urldate = {2017-10-01},
pages = {92},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Gas turbines performance loss can be identified at the engine module level, in terms of reduction in the component mass flow and efficiency. The identification of the faults will facilitate and allow to focus the financial and human resources in an effective engine maintenance work scope. In this thesis, a performance model for the CFM56-5B engines was developed using the gas turbine computer simulator GasTurb, in order to study the impact that the high pressure compressor performance has on the overall performance of the engine. The modelling phase begins by selecting an appropriate cycle reference point, followed by the off-design, where the model is matched to the performance of an existing engine. GasTurb tools allow the assessment of the condition of an engine and its components, by inputting parameters of the tested engine in the software. A database using Excel VBA macros was created to ease the data processing and store the performance of different engines. This allows to identify which components of the engine that are at fault. The thesis focus primarily in the performance of the HPC, and the difference in performance when using repaired or new blades. It was demonstrated that the HPC is more efficient when the percentage of new blades installed is greater. The developed study emphasizes the importance the first stages of the HPC have on its performance With the work developed in this thesis, TAP M&E has been offered a decision making tool that can be used to evaluate the condition of the CFM56-5B engine components, and help the maintenance engineers to optimize the resources in time and cost to meet the desired engine performance of their customers.
Keywords: Compressor blades, Performance loss, Turbofan Engine, Performance Model, Maintenance repair, Decision making tool},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Gas turbines performance loss can be identified at the engine module level, in terms of reduction in the component mass flow and efficiency. The identification of the faults will facilitate and allow to focus the financial and human resources in an effective engine maintenance work scope. In this thesis, a performance model for the CFM56-5B engines was developed using the gas turbine computer simulator GasTurb, in order to study the impact that the high pressure compressor performance has on the overall performance of the engine. The modelling phase begins by selecting an appropriate cycle reference point, followed by the off-design, where the model is matched to the performance of an existing engine. GasTurb tools allow the assessment of the condition of an engine and its components, by inputting parameters of the tested engine in the software. A database using Excel VBA macros was created to ease the data processing and store the performance of different engines. This allows to identify which components of the engine that are at fault. The thesis focus primarily in the performance of the HPC, and the difference in performance when using repaired or new blades. It was demonstrated that the HPC is more efficient when the percentage of new blades installed is greater. The developed study emphasizes the importance the first stages of the HPC have on its performance With the work developed in this thesis, TAP M&E has been offered a decision making tool that can be used to evaluate the condition of the CFM56-5B engine components, and help the maintenance engineers to optimize the resources in time and cost to meet the desired engine performance of their customers.
Keywords: Compressor blades, Performance loss, Turbofan Engine, Performance Model, Maintenance repair, Decision making tool
Keywords: Compressor blades, Performance loss, Turbofan Engine, Performance Model, Maintenance repair, Decision making tool
Baião, T.
Energy monitoring system for low-cost UAVs Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2017.
@mastersthesis{Baiao:2017:MSc,
title = {Energy monitoring system for low-cost UAVs},
author = {T. Baião},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Baiao_2017.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Baiao_2017_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=622539, Catalog IST},
year = {2017},
date = {2017-07-01},
urldate = {2017-07-01},
pages = {94},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {In the present, unmanned aerial vehicles, particularly low-cost models, lack intrinsic safety systems despite increasing interest by the civilian public for these platforms, posing a threat to other aircraft, people and property. Integrated in a larger project that addresses safety issues for this type of aircraft, this work aims to contribute to the enhancement of their safety features by proposing an energy monitoring system capable of providing updated estimates of the final state of energy of the onboard sources, enabling the operator to understand if the planned mission can be completed safely, given its energetic requirements and taking into account environmental conditions such as wind and solar radiation. The remaining energy estimate enables better energy awareness during mission planning and the online updates allow to account for unexpected disturbances and obstacle avoidance. The proposed energy monitoring system is qualitatively validated and three methods not previously considered in the literature are proposed to estimate the required energy to complete a given planned mission, and their performance is evaluated using simulation software. It is concluded that the methods discussed are very sensitive to the quality of the data and simulation tools used and those available would be inadequate for simulating a real scenario. Nonetheless, solid foundations for future work are established.
Keywords: UAV safety, Mission feasibility, Mission energy requirements, Energy estimation models, Energy sources, System integration},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
In the present, unmanned aerial vehicles, particularly low-cost models, lack intrinsic safety systems despite increasing interest by the civilian public for these platforms, posing a threat to other aircraft, people and property. Integrated in a larger project that addresses safety issues for this type of aircraft, this work aims to contribute to the enhancement of their safety features by proposing an energy monitoring system capable of providing updated estimates of the final state of energy of the onboard sources, enabling the operator to understand if the planned mission can be completed safely, given its energetic requirements and taking into account environmental conditions such as wind and solar radiation. The remaining energy estimate enables better energy awareness during mission planning and the online updates allow to account for unexpected disturbances and obstacle avoidance. The proposed energy monitoring system is qualitatively validated and three methods not previously considered in the literature are proposed to estimate the required energy to complete a given planned mission, and their performance is evaluated using simulation software. It is concluded that the methods discussed are very sensitive to the quality of the data and simulation tools used and those available would be inadequate for simulating a real scenario. Nonetheless, solid foundations for future work are established.
Keywords: UAV safety, Mission feasibility, Mission energy requirements, Energy estimation models, Energy sources, System integration
Keywords: UAV safety, Mission feasibility, Mission energy requirements, Energy estimation models, Energy sources, System integration
Alves, J.
Path planning and collision avoidance algorithms for small RPAS Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2017.
@mastersthesis{Alves:2017:MSc,
title = {Path planning and collision avoidance algorithms for small RPAS},
author = {J. Alves},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Alves_2017.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Alves_2017_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=622202, Catalog IST},
year = {2017},
date = {2017-06-01},
urldate = {2017-06-01},
pages = {80},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The development of Remotely Piloted Aerial Systems (RPAS) for civil applications has been rapidly growing over the past years. One of the main drawbacks in their integration into the National Airspace System (NAS) is the lack of a reliable collision avoidance systems. While sophisticated large RPAS, often military, have sensing technology and avionics on-par or even more advanced than manned aircraft, on the other end of the spectrum of RPAS, the low-cost light-weight off-the-shelf drones, are deprived of almost any safety system. Given the exponential rise in the number of the latter platform types, typically operated by uncertified operators, there is an urgent need to develop low-cost collision avoidance systems that can be easily embedded in such platforms. Among the vast topic of Sense and Avoid (S&A), this thesis addresses the problem of generating optimal paths for RPAS subject to maneuverability and collision avoidance constraints, and replanning them when in risk of collision. To achieve this task, a two-steps approach is proposed. In the first stage, classical path planning techniques are implemented to generate flyable paths in a known static environment. Grid based search algorithms, particularly the A* algorithm and Ant Colony Optimization (ACO), are used to find an optimal sequence of waypoints in a discrete environment. To ensure that the path is flyable and complies with curvature and safety constraints, an optimization of Rational Bezier curves is implemented. While the first stage is performed before the mission execution, the second planning module, responsible for avoiding dynamic and static obstacles that were not previously known, is developed with the limitations of real-time implementation in mind. Potential Fields methods are used to adapt the initial path to avoid unexpected obstacles in real-time. It is assumed that the vehicle is equipped with an autopilot and a trajectory control unit. Examples of path planning between a set of waypoints in a bidimensional and tridimensional environment with static obstacles, using the algorithms developed in the first stage, are presented. Several cases of path replanning, using the potential fields method, when encountering moving obstacles are also tested. For the first path planning stage, the best results were obtained using a combination of the A* algorithm and ACO to optimize waypoint sequence. The Potential Fields method is fast and computationally inexpensive, being a feasible solution for real-time implementation. It is shown that the algorithms perform reasonably well in several scenarios.
Keywords: Remotely piloted aerial systems, Obstacle avoidance, Trajectory planning, Heuristic search, Ant colony optimization, Potential fields, Bezier curves},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The development of Remotely Piloted Aerial Systems (RPAS) for civil applications has been rapidly growing over the past years. One of the main drawbacks in their integration into the National Airspace System (NAS) is the lack of a reliable collision avoidance systems. While sophisticated large RPAS, often military, have sensing technology and avionics on-par or even more advanced than manned aircraft, on the other end of the spectrum of RPAS, the low-cost light-weight off-the-shelf drones, are deprived of almost any safety system. Given the exponential rise in the number of the latter platform types, typically operated by uncertified operators, there is an urgent need to develop low-cost collision avoidance systems that can be easily embedded in such platforms. Among the vast topic of Sense and Avoid (S&A), this thesis addresses the problem of generating optimal paths for RPAS subject to maneuverability and collision avoidance constraints, and replanning them when in risk of collision. To achieve this task, a two-steps approach is proposed. In the first stage, classical path planning techniques are implemented to generate flyable paths in a known static environment. Grid based search algorithms, particularly the A* algorithm and Ant Colony Optimization (ACO), are used to find an optimal sequence of waypoints in a discrete environment. To ensure that the path is flyable and complies with curvature and safety constraints, an optimization of Rational Bezier curves is implemented. While the first stage is performed before the mission execution, the second planning module, responsible for avoiding dynamic and static obstacles that were not previously known, is developed with the limitations of real-time implementation in mind. Potential Fields methods are used to adapt the initial path to avoid unexpected obstacles in real-time. It is assumed that the vehicle is equipped with an autopilot and a trajectory control unit. Examples of path planning between a set of waypoints in a bidimensional and tridimensional environment with static obstacles, using the algorithms developed in the first stage, are presented. Several cases of path replanning, using the potential fields method, when encountering moving obstacles are also tested. For the first path planning stage, the best results were obtained using a combination of the A* algorithm and ACO to optimize waypoint sequence. The Potential Fields method is fast and computationally inexpensive, being a feasible solution for real-time implementation. It is shown that the algorithms perform reasonably well in several scenarios.
Keywords: Remotely piloted aerial systems, Obstacle avoidance, Trajectory planning, Heuristic search, Ant colony optimization, Potential fields, Bezier curves
Keywords: Remotely piloted aerial systems, Obstacle avoidance, Trajectory planning, Heuristic search, Ant colony optimization, Potential fields, Bezier curves
Freire, T.
Efficient structural optimization of aircraft wings Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2017.
@mastersthesis{Freire:2017:MSc,
title = {Efficient structural optimization of aircraft wings},
author = {T. Freire},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Freire_2017.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Freire_2017_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=620131, Catalog IST},
year = {2017},
date = {2017-02-01},
urldate = {2017-02-01},
pages = {94},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Nowadays, gradient-based methods are one of the most widely used tools in aircraft Multidisciplinary Design Optimization. However, these methods require the computation of the sensitivities of the interest functions with respect to the design variables, representing one of the most computationally expensive steps in the optimization process, since these are frequently obtained by approximation methods that are highly dependent on the number of design variables. Therefore, the main objective of this work is to develop an efficient optimization tool for wing preliminary design, using exact gradient information. Firstly, a survey on the existent sensitivity analysis methods is conducted, with the application to a beam design problem modeled with finite elements, providing valuable insight in the implementation process and advantages of each method. Subsequently, a tool to represent a 3D wing structure is adapted into three blocks and the correspondent modules for sensitivity computation are developed, with the application of the automatic differentiation, the symbolic derivative and the adjoint methods. A parametric study is presented for a reference wing case and the total sensitivities are computed with the developed framework and verified with the finite difference method. Lastly, structural optimization tests, using the reference case as the initial design point, are performed. The objective of minimizing the wing mass is achieved with a remarkable increase in computational efficiency in the optimization process, translated in a reduction of the computational time to, roughly, half and one third when compared to the forward difference and central difference methods, respectively.
Keywords: Structural optimization, Gradient-based methods, Sensitivity analysis, Adjoint method, Automatic differentiation, Finite element method},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Nowadays, gradient-based methods are one of the most widely used tools in aircraft Multidisciplinary Design Optimization. However, these methods require the computation of the sensitivities of the interest functions with respect to the design variables, representing one of the most computationally expensive steps in the optimization process, since these are frequently obtained by approximation methods that are highly dependent on the number of design variables. Therefore, the main objective of this work is to develop an efficient optimization tool for wing preliminary design, using exact gradient information. Firstly, a survey on the existent sensitivity analysis methods is conducted, with the application to a beam design problem modeled with finite elements, providing valuable insight in the implementation process and advantages of each method. Subsequently, a tool to represent a 3D wing structure is adapted into three blocks and the correspondent modules for sensitivity computation are developed, with the application of the automatic differentiation, the symbolic derivative and the adjoint methods. A parametric study is presented for a reference wing case and the total sensitivities are computed with the developed framework and verified with the finite difference method. Lastly, structural optimization tests, using the reference case as the initial design point, are performed. The objective of minimizing the wing mass is achieved with a remarkable increase in computational efficiency in the optimization process, translated in a reduction of the computational time to, roughly, half and one third when compared to the forward difference and central difference methods, respectively.
Keywords: Structural optimization, Gradient-based methods, Sensitivity analysis, Adjoint method, Automatic differentiation, Finite element method
Keywords: Structural optimization, Gradient-based methods, Sensitivity analysis, Adjoint method, Automatic differentiation, Finite element method
Parada, L.
Conceptual and preliminary design of a long endurance electric UAV Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2016.
@mastersthesis{Parada:2016:MSc,
title = {Conceptual and preliminary design of a long endurance electric UAV},
author = {L. Parada},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Parada_2016.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Parada_2016_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=619033, Catalog IST},
year = {2016},
date = {2016-11-01},
urldate = {2016-11-01},
pages = {101},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The present thesis documents the conceptual and preliminary design of a solar long endurance Unmanned Aerial Vehicle (UAV). Having in mind surveillance goals, the mission profile requires an initial climb, at a rate that allows to ascend 1000 m above runway in 10 minutes, followed by cruise with an endurance of 8 hours and a range 200 km during the equinox. In the conceptual stage, several aircraft configurations were evaluated considering the mission requirements. Resorting to the Analytic Hierarchy Process methodology, the rear pusher V-tail airplane concept was chosen through pairwise comparisons between 10 mission criteria (Aerodynamics, Structures an Weight, Solar Panels Integration, Propulsion, Manufacturing and Maintenance, Stability and Control, Payload Volume, Remote-Person View Integration, Take-off and Landing and Portable Capabilities) and 8 prospective candidate configurations. A UAV market investigation provided an initial estimate of the empty weight fraction and airframe dimensions. Through bibliographic research, the communications system was defined beforehand and the propulsion system also received an initial estimate. In the preliminary design phase, the airframe was resized by performing a set of fixed point iterations, whose resulting design point ensured it is physically possible to fulfill flight requirements. Allying multiple aerodynamic analyses, performed on a low Reynolds number computational tool, with the ascertained efficiency of the propulsion system, power consumption at each mission stage was determined under ideal weather conditions. The solar energy received by the photo-voltaic arrays installed was determined in a single location applying a theoretical irradiation model in different seasons of the year. It was verified that in the March equinox endurance reached 7.5 hours, while in September its maximum increased to almost 10 hours. An aircraft CAD assembly was modeled without internal airframe detail. The developed parts include a three-piece 5 meter span wing, a fuselage composed by two connectable pieces, totaling 1.9 meter length, and two individual V-tail halves. On-board propulsion and avionics components were also modeled in a simplified way, as solids of uniform density. A flight stability analysis was performed, resulting in a static margin of 5.6% with null Cm in cruise conditions. Looking at a future detailed design, the cruise flight envelope was created and the wing pressure distribution was obtained.
Keywords: Solar UAV, Analytic hierarchy process, Design point, Low Reynolds number, Endurance, Flight envelope},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The present thesis documents the conceptual and preliminary design of a solar long endurance Unmanned Aerial Vehicle (UAV). Having in mind surveillance goals, the mission profile requires an initial climb, at a rate that allows to ascend 1000 m above runway in 10 minutes, followed by cruise with an endurance of 8 hours and a range 200 km during the equinox. In the conceptual stage, several aircraft configurations were evaluated considering the mission requirements. Resorting to the Analytic Hierarchy Process methodology, the rear pusher V-tail airplane concept was chosen through pairwise comparisons between 10 mission criteria (Aerodynamics, Structures an Weight, Solar Panels Integration, Propulsion, Manufacturing and Maintenance, Stability and Control, Payload Volume, Remote-Person View Integration, Take-off and Landing and Portable Capabilities) and 8 prospective candidate configurations. A UAV market investigation provided an initial estimate of the empty weight fraction and airframe dimensions. Through bibliographic research, the communications system was defined beforehand and the propulsion system also received an initial estimate. In the preliminary design phase, the airframe was resized by performing a set of fixed point iterations, whose resulting design point ensured it is physically possible to fulfill flight requirements. Allying multiple aerodynamic analyses, performed on a low Reynolds number computational tool, with the ascertained efficiency of the propulsion system, power consumption at each mission stage was determined under ideal weather conditions. The solar energy received by the photo-voltaic arrays installed was determined in a single location applying a theoretical irradiation model in different seasons of the year. It was verified that in the March equinox endurance reached 7.5 hours, while in September its maximum increased to almost 10 hours. An aircraft CAD assembly was modeled without internal airframe detail. The developed parts include a three-piece 5 meter span wing, a fuselage composed by two connectable pieces, totaling 1.9 meter length, and two individual V-tail halves. On-board propulsion and avionics components were also modeled in a simplified way, as solids of uniform density. A flight stability analysis was performed, resulting in a static margin of 5.6% with null Cm in cruise conditions. Looking at a future detailed design, the cruise flight envelope was created and the wing pressure distribution was obtained.
Keywords: Solar UAV, Analytic hierarchy process, Design point, Low Reynolds number, Endurance, Flight envelope
Keywords: Solar UAV, Analytic hierarchy process, Design point, Low Reynolds number, Endurance, Flight envelope
Margarido, P.
Flight dynamics and simulation of a generic aircraft for aeroservoelastic design Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2016.
@mastersthesis{Margarido:2016:MSc,
title = {Flight dynamics and simulation of a generic aircraft for aeroservoelastic design},
author = {P. Margarido},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Margarido_2016.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Margarido_2016_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=619522, Catalog IST},
year = {2016},
date = {2016-11-01},
urldate = {2016-11-01},
pages = {90},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The emerging market of the aviation sector begins to request the need for tools to study the aeroservoelastic behaviour of an aircraft. There are mathematical models for this kind of study, but its interpretation is not easy and many use the frequency domain. In this thesis the aeroservoelastic equations of motion of a general aircraft for equilibrium conditions in time domain were developed. A program was also developed, produced in C++, which integrates these same equations, and that in the future may be included in other projects as an interconnection tool between different fields of aeronautics, such as aerodynamics, structural dynamics and flight control. To develop this tool, various integration methods were inspected and consequently the utility of each one was found. Aeroelasticity consequences were also discussed and used to introduce the optimal control. It was also carried out a flight simulator in MATLAB using optimal control. The optimal control behaviour, more specifically the linear quadratic regulator, in the flight dynamics was also studied. This flight simulator allows the simulation of the motion for a general aircraft, adopting a set of aerodynamics derivatives of general aircraft from the literature, on turbulent air flows and in engine failure cases in aircraft up to five engines. The simulation study in this thesis had more in mind to ensure that the aircraft maintains its equilibrium and course in critical situations, as referred above.
Keywords: Flight dynamics, Optimal control, Aeroservoelasticity, Flight simulation, Integration},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The emerging market of the aviation sector begins to request the need for tools to study the aeroservoelastic behaviour of an aircraft. There are mathematical models for this kind of study, but its interpretation is not easy and many use the frequency domain. In this thesis the aeroservoelastic equations of motion of a general aircraft for equilibrium conditions in time domain were developed. A program was also developed, produced in C++, which integrates these same equations, and that in the future may be included in other projects as an interconnection tool between different fields of aeronautics, such as aerodynamics, structural dynamics and flight control. To develop this tool, various integration methods were inspected and consequently the utility of each one was found. Aeroelasticity consequences were also discussed and used to introduce the optimal control. It was also carried out a flight simulator in MATLAB using optimal control. The optimal control behaviour, more specifically the linear quadratic regulator, in the flight dynamics was also studied. This flight simulator allows the simulation of the motion for a general aircraft, adopting a set of aerodynamics derivatives of general aircraft from the literature, on turbulent air flows and in engine failure cases in aircraft up to five engines. The simulation study in this thesis had more in mind to ensure that the aircraft maintains its equilibrium and course in critical situations, as referred above.
Keywords: Flight dynamics, Optimal control, Aeroservoelasticity, Flight simulation, Integration
Keywords: Flight dynamics, Optimal control, Aeroservoelasticity, Flight simulation, Integration
Rebelo, P.
Design study of a side intrusion beam for automotive safety Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2016.
@mastersthesis{Rebelo:2016:MSc,
title = {Design study of a side intrusion beam for automotive safety},
author = {P. Rebelo},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Rebelo_2016.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Rebelo_2016_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=621154, Catalog IST},
year = {2016},
date = {2016-11-01},
urldate = {2016-11-01},
pages = {90},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Road safety is one of the major global concerns regarding the protection of human lives. Every year, 1.2 million people die in road related accidents, and 20-50 million suffer from non-fatal injuries. After frontal crash, side impact is the leading cause of road fatalities. Designing safety systems for preventing the accident, or controlling the damages it inflicts on the passengers once it occurs, is a global research subject in which the work developed in thesis is inserted. The side intrusion beam is a protective component installed in the vehicle door, designed to enhance passengers safety in the event of a side collision. This structure’s role is to absorb the maximum amount of impact energy through an elasto-plastic deformation process. Thin-walled beams are frequently applied due to their high energy absorption capacity. Metals are commonly selected for the beam design, since they combine a high strength with an also high ductility, both crucial to energy absorption. The present work focuses on studying the impact of the cross-section geometry and material of a thin-walled beam in its bending performance. With a higher bending performance of the side intrusion beam, a better overall performance in a crash event is expected. After significant improvements in bending performance are achieved, the beam solutions are installed in a complete vehicle and tested in different crash configurations. The side intrusion beam is proven to improve the crash performance under specific conditions, for example, during a side pole impact, where the intrusion levels are reduced by the installation of this component.
Keywords: Thin-walled beams, Energy absorption, Bending performance, Crash performance, Elasto-plastic deformation},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Road safety is one of the major global concerns regarding the protection of human lives. Every year, 1.2 million people die in road related accidents, and 20-50 million suffer from non-fatal injuries. After frontal crash, side impact is the leading cause of road fatalities. Designing safety systems for preventing the accident, or controlling the damages it inflicts on the passengers once it occurs, is a global research subject in which the work developed in thesis is inserted. The side intrusion beam is a protective component installed in the vehicle door, designed to enhance passengers safety in the event of a side collision. This structure’s role is to absorb the maximum amount of impact energy through an elasto-plastic deformation process. Thin-walled beams are frequently applied due to their high energy absorption capacity. Metals are commonly selected for the beam design, since they combine a high strength with an also high ductility, both crucial to energy absorption. The present work focuses on studying the impact of the cross-section geometry and material of a thin-walled beam in its bending performance. With a higher bending performance of the side intrusion beam, a better overall performance in a crash event is expected. After significant improvements in bending performance are achieved, the beam solutions are installed in a complete vehicle and tested in different crash configurations. The side intrusion beam is proven to improve the crash performance under specific conditions, for example, during a side pole impact, where the intrusion levels are reduced by the installation of this component.
Keywords: Thin-walled beams, Energy absorption, Bending performance, Crash performance, Elasto-plastic deformation
Keywords: Thin-walled beams, Energy absorption, Bending performance, Crash performance, Elasto-plastic deformation
Ferreira, M.
Multidisciplinary design analysis and optimisation of rear wings for sports cars Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2016.
@mastersthesis{Ferreira:2016:MSc,
title = {Multidisciplinary design analysis and optimisation of rear wings for sports cars},
author = {M. Ferreira},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Ferreira_2016.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Ferreira_2016_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=619685, Catalog IST},
year = {2016},
date = {2016-06-01},
urldate = {2016-06-01},
pages = {100},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {This thesis covers aero-structural optimisation of rear wing designs to minimise aerodynamic drag and structural mass. These structures highly influence the performance of vehicles, and in order to achieve effective and safe optimal designs, the multiphysics involved was considered by means of fluid-structure interaction (FSI). The objective was to fold the implementation of a process for optimal automotive aerodynamic devices design. To solve the aero-structural optimisation problem, a multidisciplinary design analysis and optimisation (MDAO) framework was applied. Two study cases were considered: a traditional rear wing design strategy used in automotive and motorsport applications; and a proposed design, where the surface connection between the endplates and vertical supports is used to create additional downforce. Concerning the multidisciplinary synergy to obtain feasible solutions, a Computer Aided Engineering (CAE) software was used (ANSYS Workbench 14.5). The project was divided into three parts: the numerical models settings, the aerodynamic and structural parametric studies (focused on the effects of the design variables), and aerodynamic and structural optimisation problems (focused on the most impacting variables) to obtain optimal designs. From the studies performed in this thesis, a MDAO process for optimal preliminary design was developed for rear wings, but it can also be applied to any other automotive aerodynamic devices. Mesh and turbulence modelling strategy proved to be very important regarding the accuracy of the numerical solutions and for problems with small deformations, a one-way FSI coupling technique has significant computational advantages.
Keywords: Aero-structural problem, Fluid-structure interaction, Computer-aided engineering, Aerodynamic devices, Composite materials},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
This thesis covers aero-structural optimisation of rear wing designs to minimise aerodynamic drag and structural mass. These structures highly influence the performance of vehicles, and in order to achieve effective and safe optimal designs, the multiphysics involved was considered by means of fluid-structure interaction (FSI). The objective was to fold the implementation of a process for optimal automotive aerodynamic devices design. To solve the aero-structural optimisation problem, a multidisciplinary design analysis and optimisation (MDAO) framework was applied. Two study cases were considered: a traditional rear wing design strategy used in automotive and motorsport applications; and a proposed design, where the surface connection between the endplates and vertical supports is used to create additional downforce. Concerning the multidisciplinary synergy to obtain feasible solutions, a Computer Aided Engineering (CAE) software was used (ANSYS Workbench 14.5). The project was divided into three parts: the numerical models settings, the aerodynamic and structural parametric studies (focused on the effects of the design variables), and aerodynamic and structural optimisation problems (focused on the most impacting variables) to obtain optimal designs. From the studies performed in this thesis, a MDAO process for optimal preliminary design was developed for rear wings, but it can also be applied to any other automotive aerodynamic devices. Mesh and turbulence modelling strategy proved to be very important regarding the accuracy of the numerical solutions and for problems with small deformations, a one-way FSI coupling technique has significant computational advantages.
Keywords: Aero-structural problem, Fluid-structure interaction, Computer-aided engineering, Aerodynamic devices, Composite materials
Keywords: Aero-structural problem, Fluid-structure interaction, Computer-aided engineering, Aerodynamic devices, Composite materials
Valente, G.
Vasculature optimization of actively-cooled materials Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2016.
@mastersthesis{Valente:2016:MSc,
title = {Vasculature optimization of actively-cooled materials},
author = {G. Valente},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Valente_2016.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Valente_2016_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=620101, Catalog IST},
year = {2016},
date = {2016-06-01},
urldate = {2016-06-01},
pages = {84},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Associated with an eagerness to explore every possibility from humankind imagination came the field of engineering. In engineering applications where heat transfer processes are present arise vascular actively-cooled materials, which provide motivation for this thesis. The goal of this work is to implement the tools required to model and optimize conjugated heat transfer problems (heat disperses through the domain not only via. heat conduction but also convection). In order to obtain an implementation that is independent of the configuration of the cooling channels (important for the optimization process), an innovative solution for the discretization method is in order, which can be found in the Interface-enriched Finite Element Method. The equations that define heat transfer in the two phases of vascular materials are different. In the convection dominated regions, the standard finite element formulations are ineffective and it is necessary to find a different solution, being the Streamline Upwind/Petrov-Galerkin techique the chosen one. Being developed in a work group at TU Delft, all implementation aspects are integrated in hybrida, a computational tool developed by said group. Following this procedure made it possible to match results with verification tests for the discussed methods and also to optimize vascular geometries by minimizing their maximum domain temperature. Using the approach and results described above, it has been possible conclude that the developed work resulted in the correct implementation of each method and also that their combination is effective and efficient modeling and optimizing conjugated heat transfer problems defined by vascular actively cooled domains.
Keywords: Interface-enriched finite element method, Streamline upwind/Petrov-Galerkin, Heat convection, Optimization},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Associated with an eagerness to explore every possibility from humankind imagination came the field of engineering. In engineering applications where heat transfer processes are present arise vascular actively-cooled materials, which provide motivation for this thesis. The goal of this work is to implement the tools required to model and optimize conjugated heat transfer problems (heat disperses through the domain not only via. heat conduction but also convection). In order to obtain an implementation that is independent of the configuration of the cooling channels (important for the optimization process), an innovative solution for the discretization method is in order, which can be found in the Interface-enriched Finite Element Method. The equations that define heat transfer in the two phases of vascular materials are different. In the convection dominated regions, the standard finite element formulations are ineffective and it is necessary to find a different solution, being the Streamline Upwind/Petrov-Galerkin techique the chosen one. Being developed in a work group at TU Delft, all implementation aspects are integrated in hybrida, a computational tool developed by said group. Following this procedure made it possible to match results with verification tests for the discussed methods and also to optimize vascular geometries by minimizing their maximum domain temperature. Using the approach and results described above, it has been possible conclude that the developed work resulted in the correct implementation of each method and also that their combination is effective and efficient modeling and optimizing conjugated heat transfer problems defined by vascular actively cooled domains.
Keywords: Interface-enriched finite element method, Streamline upwind/Petrov-Galerkin, Heat convection, Optimization
Keywords: Interface-enriched finite element method, Streamline upwind/Petrov-Galerkin, Heat convection, Optimization
Brogueira, H.
Design of a test bench for micro combustion engines Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2016.
@mastersthesis{Brogueira:2016:MSc,
title = {Design of a test bench for micro combustion engines},
author = {H. Brogueira},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Brogueira_2016.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Brogueira_2016_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=619724, Catalog IST},
year = {2016},
date = {2016-06-01},
urldate = {2016-06-01},
pages = {102},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {This study is about the design, construction and instrumentation of a test bench for testing micro combustion engines used in model vehicles. Several sensors and actuators were used to obtain its performance specifications. There is no standard test bench for micro engines, so this equipment intends to present drivers with viable information, something that is missing. Several technical requirements were considered for the test bench to be safe, effective and practical to use. Some of the components were manufactured while others were off-the-shelf and, at a final stage of the construction, the test bench was assembled with all the required model parts. One of the objectives is to characterise a 3.5 cc micro engine. For that, the test bench was designed to obtain the power and torque diagrams and the fuel consumption rate. These results are displayed on a PC through a data acquisition board able to conduct all the necessary readings and processing for characterisation. First a conceptual design was made to assess the idea behind the project. After a thorough research on test benches and micro engines, the concept gave way to the actual design of an inertia dynamometer. A program in LabView was developed for the data acquisition system including the actual control of the actuators. Components were produced in Instituto Superior Técnico and, finally, the test bench was assembled with the required flywheel and all the necessary electronic components. Tests were made for an electric motor driving a gyroscope to validate the instrumentation and then the 3.5 cc glow plug engine was tested, whose results of the power curves validated the whole design of the test bench. The inertia dynamometer is viable and flexible, able to test any kind of micro engine from 2.0 to 20.0 cc. The program running the acceleration tests is fully automatic, allowing the test bench to have good repeatability which is essential to get realistic data.
Keywords: Power curves, Inertia dynamometer, Micro engines, Performance, Data acquisition},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
This study is about the design, construction and instrumentation of a test bench for testing micro combustion engines used in model vehicles. Several sensors and actuators were used to obtain its performance specifications. There is no standard test bench for micro engines, so this equipment intends to present drivers with viable information, something that is missing. Several technical requirements were considered for the test bench to be safe, effective and practical to use. Some of the components were manufactured while others were off-the-shelf and, at a final stage of the construction, the test bench was assembled with all the required model parts. One of the objectives is to characterise a 3.5 cc micro engine. For that, the test bench was designed to obtain the power and torque diagrams and the fuel consumption rate. These results are displayed on a PC through a data acquisition board able to conduct all the necessary readings and processing for characterisation. First a conceptual design was made to assess the idea behind the project. After a thorough research on test benches and micro engines, the concept gave way to the actual design of an inertia dynamometer. A program in LabView was developed for the data acquisition system including the actual control of the actuators. Components were produced in Instituto Superior Técnico and, finally, the test bench was assembled with the required flywheel and all the necessary electronic components. Tests were made for an electric motor driving a gyroscope to validate the instrumentation and then the 3.5 cc glow plug engine was tested, whose results of the power curves validated the whole design of the test bench. The inertia dynamometer is viable and flexible, able to test any kind of micro engine from 2.0 to 20.0 cc. The program running the acceleration tests is fully automatic, allowing the test bench to have good repeatability which is essential to get realistic data.
Keywords: Power curves, Inertia dynamometer, Micro engines, Performance, Data acquisition
Keywords: Power curves, Inertia dynamometer, Micro engines, Performance, Data acquisition
Diogo, R.
Design optimization of a high aspect ratio wing using ant colony optimization algorithm Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2016.
@mastersthesis{Diogo:2016:MSc,
title = {Design optimization of a high aspect ratio wing using ant colony optimization algorithm},
author = {R. Diogo},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Diogo_2016.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Diogo_2016_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=615980, Catalog IST},
year = {2016},
date = {2016-04-01},
urldate = {2016-04-01},
pages = {84},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Every aircraft currently crossing the sky are using fossil fuels in order to generate the propulsion required to fly, which leads to the production of greenhouse gases that warm the environment. Having this in mind, the main drive for the next generation of aircraft is fuel efficiency. One of the solutions that is being tested to increase the fuel efficiency is the introduction of high aspect ratio (AR) wings. A high aspect ratio wing leads to many structural problems, and to solve them one needs to have a considerably stiff wing box. The given solution increases the weight of the wing and reduces the advantages brought by the introduction of a high AR wing, thus making the design of the wing box a fundamental aspect. In order to have the stiffest possible structure having the minimum possible weight, one can do a topology optimization to find the optimal design for the given constraints. The main goal of this thesis is to find the optimal design of the wing box by performing a topology optimization using Ant Colony Optimization (ACO) algorithm. ACO is a meta-heuristic biologically. Its application to solve topology optimization has been introduced recently. Conclusions on the close to optimal topology of a wing box from a high aspect ratio wing are presented. In this thesis, a MATLAB code integrated with ANSYS for the structural analysis, is developed, in order to do a topology optimization. One will start by solving a literature case. Afterwards, the wing box of the NOVEMOR project of the EU 7th framework wing was optimized.
Keywords: Heuristic method, Topology optimization, High aspect ratio wings},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Every aircraft currently crossing the sky are using fossil fuels in order to generate the propulsion required to fly, which leads to the production of greenhouse gases that warm the environment. Having this in mind, the main drive for the next generation of aircraft is fuel efficiency. One of the solutions that is being tested to increase the fuel efficiency is the introduction of high aspect ratio (AR) wings. A high aspect ratio wing leads to many structural problems, and to solve them one needs to have a considerably stiff wing box. The given solution increases the weight of the wing and reduces the advantages brought by the introduction of a high AR wing, thus making the design of the wing box a fundamental aspect. In order to have the stiffest possible structure having the minimum possible weight, one can do a topology optimization to find the optimal design for the given constraints. The main goal of this thesis is to find the optimal design of the wing box by performing a topology optimization using Ant Colony Optimization (ACO) algorithm. ACO is a meta-heuristic biologically. Its application to solve topology optimization has been introduced recently. Conclusions on the close to optimal topology of a wing box from a high aspect ratio wing are presented. In this thesis, a MATLAB code integrated with ANSYS for the structural analysis, is developed, in order to do a topology optimization. One will start by solving a literature case. Afterwards, the wing box of the NOVEMOR project of the EU 7th framework wing was optimized.
Keywords: Heuristic method, Topology optimization, High aspect ratio wings
Keywords: Heuristic method, Topology optimization, High aspect ratio wings
Martins, D.
Off-design performance prediction of the CFM56-3 aircraft engine Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2015.
@mastersthesis{Martins:2015:MSc,
title = {Off-design performance prediction of the CFM56-3 aircraft engine},
author = {D. Martins},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Martins_2015.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Martins_2015_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=619498, Catalog IST},
year = {2015},
date = {2015-11-01},
urldate = {2015-11-01},
pages = {88},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Ever since the appearance of aircraft at the beginning of the past century, they have been transforming the world. Their capability of travelling at speeds much greater than that of trains or ships helped the world by facilitating economic trades and helped people to learn about other cultures. The overall performance of a gas turbine can be estimated by knowing the main design parameters, however, this is quite challenging due to the limited data that the engine manufacturer releases to the general public. Although a turbine manufacturer usually provides data about the turbine interface, the data required to estimate the thermodynamic cycle of a particular gas turbine remains hidden. A model of that engine capable of estimating that data must then be created. In this thesis, a performance model of the CFM56-3 engine has been developed using the modelling software GasTurb. The chosen engine was the CFM56-3 due to the facts that it is one of the world’s most used aircraft engines and that TAP M&E Engine Shop is certified to maintain it. The model is first created for its design point, where its geometry is defined. The off-design performance of the engine is then modelled using data from TAP M&E test bed. The model is useful to predict the data that the engine manufacturers do not reveal. The best application of this work is the analysis of the condition of CFM56-3 engines. With some test bed data from a particular engine, the model might diagnose the problems of that same engine. The thesis places major emphasis on the development and validation of the engine model, as well as its use in TAP M&E Engine Shop. The developed model allows TAP M&E to analyse the performance of the gas turbine as well as to compare the performance of any CFM56-3 engine to the performance of the model in order to estimate components degradation. The main benefit to TAP M&E by using the performance model is the possibility of performing selective repairs, allowing to save work hours and reducing repair costs.
Keywords: Gas turbine, Thermodynamics, Performance model, GasTurb, Degradation effects, Repair costs, Tip clearance},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Ever since the appearance of aircraft at the beginning of the past century, they have been transforming the world. Their capability of travelling at speeds much greater than that of trains or ships helped the world by facilitating economic trades and helped people to learn about other cultures. The overall performance of a gas turbine can be estimated by knowing the main design parameters, however, this is quite challenging due to the limited data that the engine manufacturer releases to the general public. Although a turbine manufacturer usually provides data about the turbine interface, the data required to estimate the thermodynamic cycle of a particular gas turbine remains hidden. A model of that engine capable of estimating that data must then be created. In this thesis, a performance model of the CFM56-3 engine has been developed using the modelling software GasTurb. The chosen engine was the CFM56-3 due to the facts that it is one of the world’s most used aircraft engines and that TAP M&E Engine Shop is certified to maintain it. The model is first created for its design point, where its geometry is defined. The off-design performance of the engine is then modelled using data from TAP M&E test bed. The model is useful to predict the data that the engine manufacturers do not reveal. The best application of this work is the analysis of the condition of CFM56-3 engines. With some test bed data from a particular engine, the model might diagnose the problems of that same engine. The thesis places major emphasis on the development and validation of the engine model, as well as its use in TAP M&E Engine Shop. The developed model allows TAP M&E to analyse the performance of the gas turbine as well as to compare the performance of any CFM56-3 engine to the performance of the model in order to estimate components degradation. The main benefit to TAP M&E by using the performance model is the possibility of performing selective repairs, allowing to save work hours and reducing repair costs.
Keywords: Gas turbine, Thermodynamics, Performance model, GasTurb, Degradation effects, Repair costs, Tip clearance
Keywords: Gas turbine, Thermodynamics, Performance model, GasTurb, Degradation effects, Repair costs, Tip clearance
Paulo, A.
Enhanced methods development for high-end low-fidelity numerical wing weight and flutter prediction Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2015.
@mastersthesis{Paulo:2015:MSc,
title = {Enhanced methods development for high-end low-fidelity numerical wing weight and flutter prediction},
author = {A. Paulo},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Paulo_2015.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Paulo_2015_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=622373, Catalog IST},
year = {2015},
date = {2015-11-01},
urldate = {2015-11-01},
pages = {90},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The work developed was based on an aeroelasticity tool created by Bauhaus Luftfahrt, named dAEDalus, and its objective was to improve the wing mass estimation. Therefore, two new modules were introduced: the first to include the high lift devices contribution into the wing box dimensioning; the second to predict the wing flutter speed. To estimate the mass of the devices were used several methods of different references, together with the ones here developed. The comparison between the devices’ mass found with the different methods and the reference value of each aircraft, allowed to verify the estimates found. The implemented approach improved the initial wing mass estimate, fulfilling the proposed objective. The flutter speed was studied using an existing method, but corrected in such a way that allowed an improvement in its results. Verification was achieved by comparing the results with the Goland’s wing. With this approach it was improved the speed estimate (more important parameter) in detriment of the frequency. Afterwards the method was implemented into dAEDalus to predict the flutter speed of some contemporary commercial aircraft wings. When the flutter speed was inside the minimum fail-safe clearance envelope, an optimization of the wing box was made to ensure the safety of the aircraft. The method allowed an estimation of the flutter speed of different aircraft, and the optimization loop made the wing flutter free inside the envelope. As the previous, this implementation also fulfilled the purposed objective.
Keywords: Aeroelasticity, dAEDalus, Flutter, Goland wing, High lift devices},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The work developed was based on an aeroelasticity tool created by Bauhaus Luftfahrt, named dAEDalus, and its objective was to improve the wing mass estimation. Therefore, two new modules were introduced: the first to include the high lift devices contribution into the wing box dimensioning; the second to predict the wing flutter speed. To estimate the mass of the devices were used several methods of different references, together with the ones here developed. The comparison between the devices’ mass found with the different methods and the reference value of each aircraft, allowed to verify the estimates found. The implemented approach improved the initial wing mass estimate, fulfilling the proposed objective. The flutter speed was studied using an existing method, but corrected in such a way that allowed an improvement in its results. Verification was achieved by comparing the results with the Goland’s wing. With this approach it was improved the speed estimate (more important parameter) in detriment of the frequency. Afterwards the method was implemented into dAEDalus to predict the flutter speed of some contemporary commercial aircraft wings. When the flutter speed was inside the minimum fail-safe clearance envelope, an optimization of the wing box was made to ensure the safety of the aircraft. The method allowed an estimation of the flutter speed of different aircraft, and the optimization loop made the wing flutter free inside the envelope. As the previous, this implementation also fulfilled the purposed objective.
Keywords: Aeroelasticity, dAEDalus, Flutter, Goland wing, High lift devices
Keywords: Aeroelasticity, dAEDalus, Flutter, Goland wing, High lift devices
Almeida, J.
Structural dynamics for aeroelastic analysis Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2015.
@mastersthesis{Almeida:2015:MSc,
title = {Structural dynamics for aeroelastic analysis},
author = {J. Almeida},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Almeida_2015.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Almeida_2015_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=617981, Catalog IST},
year = {2015},
date = {2015-11-01},
urldate = {2015-11-01},
pages = {94},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Aeroelasticity is a physical phenomenon resulting from the interaction of aerodynamic, elastic and inertial forces. It is very important to study aeroelasticity in aircraft structures, due to their lightweight and flexible design. The present work aims to study the aeroelastic behavior of a 3D aircraft wing. For that, a beam representation of the wing structure is developed using the finite-element method. The one-dimensional beam coincides with the wing elastic axis with the whole rigidity of the wing concentrated along it. Therefore, a new computational aeroelasticity framework was created using the structural model developed and integrating an available fluid solver, which uses a panel method to solve the fluid flow. Both the fluid and structural solvers are validated with published results. The coupling of the two domains is made using an adequate time discretization scheme, which is chosen after performing several analyses using different temporal schemes. The framework is validated with available trim results from a wing model. The results are then presented for a wing denoted as reference case. A parametric study is conducted and its results compared with the reference values. It is concluded that the results show very good agreement with the theoretical expectations. Moreover, an aero-structural optimization of a wing is tackled aiming to minimize its total mass while fixing the lift coefficient. Despite the many simplifications implemented in both the fluid and structural solvers, this framework proves to be useful to predict the aeroelastic performance of a wing in the early stages of aircraft design.
Keywords: Aeroelasticity, Panel method, Finite element method, Fluid-structure interaction, Coupling schemes, Flutter},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Aeroelasticity is a physical phenomenon resulting from the interaction of aerodynamic, elastic and inertial forces. It is very important to study aeroelasticity in aircraft structures, due to their lightweight and flexible design. The present work aims to study the aeroelastic behavior of a 3D aircraft wing. For that, a beam representation of the wing structure is developed using the finite-element method. The one-dimensional beam coincides with the wing elastic axis with the whole rigidity of the wing concentrated along it. Therefore, a new computational aeroelasticity framework was created using the structural model developed and integrating an available fluid solver, which uses a panel method to solve the fluid flow. Both the fluid and structural solvers are validated with published results. The coupling of the two domains is made using an adequate time discretization scheme, which is chosen after performing several analyses using different temporal schemes. The framework is validated with available trim results from a wing model. The results are then presented for a wing denoted as reference case. A parametric study is conducted and its results compared with the reference values. It is concluded that the results show very good agreement with the theoretical expectations. Moreover, an aero-structural optimization of a wing is tackled aiming to minimize its total mass while fixing the lift coefficient. Despite the many simplifications implemented in both the fluid and structural solvers, this framework proves to be useful to predict the aeroelastic performance of a wing in the early stages of aircraft design.
Keywords: Aeroelasticity, Panel method, Finite element method, Fluid-structure interaction, Coupling schemes, Flutter
Keywords: Aeroelasticity, Panel method, Finite element method, Fluid-structure interaction, Coupling schemes, Flutter
Ramos, M.
Construction and analysis of a lightweight UAV wing prototype Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2015.
@mastersthesis{Ramos:2015:MSc,
title = {Construction and analysis of a lightweight UAV wing prototype},
author = {M. Ramos},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Ramos_2015.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Ramos_2015_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=619573, Catalog IST},
year = {2015},
date = {2015-11-01},
urldate = {2015-11-01},
pages = {94},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {An increase in the usage of Unmanned Aerial Vehicles (UAV) in the last couple of years has led to a more competitive market where more attention is being given to the efficiency and safety with which those aircraft accomplish their mission goals. Bearing that in mind, a greater focus is put on their preliminary structural design, where the development of computational Finite Element Analysis (FEA) methods allow for a better prediction of the behavior of the final structure. In this thesis, a prototype based on a new, suggested wing structure for a particular fixed wing UAV is built, and the results obtained by the experimental tests carried out on it compared to those yielded by a numerical model developed in CATIA. To do so, a CAD model of both the suggested wing structure and its prototype is created, based on identified design parameters. The materials selected for the prototype are tested, their elastic properties determined and a validation of those tests made in CATIA’s Generative Structural Analysis workbench. The building process of the prototype is described, and considerations regarding the influence of each material and part in its final weight are made. The tests performed on the prototype are presented, and a comparison between their results and those of the FEA is made, followed by a discussion of the differences between them. Conclusions on the accuracy of the numerical model are drawn, and suggestions of ways to minimize those discrepancies by means of a more controlled building process are presented. This effort is aimed to pave the way for future higher-fidelity computational structural designs of UAVs using the tuned FEA tools.
Keywords: Finite element method, Material properties, Materials testing, Validation, Prototype, Structural analysis},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
An increase in the usage of Unmanned Aerial Vehicles (UAV) in the last couple of years has led to a more competitive market where more attention is being given to the efficiency and safety with which those aircraft accomplish their mission goals. Bearing that in mind, a greater focus is put on their preliminary structural design, where the development of computational Finite Element Analysis (FEA) methods allow for a better prediction of the behavior of the final structure. In this thesis, a prototype based on a new, suggested wing structure for a particular fixed wing UAV is built, and the results obtained by the experimental tests carried out on it compared to those yielded by a numerical model developed in CATIA. To do so, a CAD model of both the suggested wing structure and its prototype is created, based on identified design parameters. The materials selected for the prototype are tested, their elastic properties determined and a validation of those tests made in CATIA’s Generative Structural Analysis workbench. The building process of the prototype is described, and considerations regarding the influence of each material and part in its final weight are made. The tests performed on the prototype are presented, and a comparison between their results and those of the FEA is made, followed by a discussion of the differences between them. Conclusions on the accuracy of the numerical model are drawn, and suggestions of ways to minimize those discrepancies by means of a more controlled building process are presented. This effort is aimed to pave the way for future higher-fidelity computational structural designs of UAVs using the tuned FEA tools.
Keywords: Finite element method, Material properties, Materials testing, Validation, Prototype, Structural analysis
Keywords: Finite element method, Material properties, Materials testing, Validation, Prototype, Structural analysis
Borges, M.
Design of an apparatus for wind tunnel tests of electric UAV propulsion systems Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2015.
@mastersthesis{Borges:2015:MSc,
title = {Design of an apparatus for wind tunnel tests of electric UAV propulsion systems},
author = {M. Borges},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Borges_2015.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Borges_2015_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=618793, Catalog IST},
year = {2015},
date = {2015-06-01},
urldate = {2015-06-01},
pages = {114},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The demand for alternative energy sources has grown in recent years. The shift to electricity can already be seen in the automotive industry, and the aviation industry is slowly follow the same path. This thesis focuses on the design, construction and validation of a system to test electrical propulsive systems capable of being used in unmanned aerial aircraft. The system developed was a test rig capable of testing electric motors with propellers with a maximum diameter of 27 inches. The measuring system installed on the test rig flexible enough to be able to perform measurements of different ranges generated by different propulsive systems. The experimental apparatus was installed in the aero-acoustic wind tunnel IST that allows out tests in a dynamic and static environment. All the mechanical design take into account the measurement limits previously studied according to data provided the propeller manufacturers. Through this test bench it is possible to generate the data for the propulsion system in a simple and flexible way. For this, it was created an interface so that the user can have access to all the generated data by the propulsion system in real time, but at the same time can also store that data for further post processing.
Keywords: UAV, Electric propulsion, Test rig, Wind tunnel, Propeller performance, Data acquisition},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The demand for alternative energy sources has grown in recent years. The shift to electricity can already be seen in the automotive industry, and the aviation industry is slowly follow the same path. This thesis focuses on the design, construction and validation of a system to test electrical propulsive systems capable of being used in unmanned aerial aircraft. The system developed was a test rig capable of testing electric motors with propellers with a maximum diameter of 27 inches. The measuring system installed on the test rig flexible enough to be able to perform measurements of different ranges generated by different propulsive systems. The experimental apparatus was installed in the aero-acoustic wind tunnel IST that allows out tests in a dynamic and static environment. All the mechanical design take into account the measurement limits previously studied according to data provided the propeller manufacturers. Through this test bench it is possible to generate the data for the propulsion system in a simple and flexible way. For this, it was created an interface so that the user can have access to all the generated data by the propulsion system in real time, but at the same time can also store that data for further post processing.
Keywords: UAV, Electric propulsion, Test rig, Wind tunnel, Propeller performance, Data acquisition
Keywords: UAV, Electric propulsion, Test rig, Wind tunnel, Propeller performance, Data acquisition
Branco, J.
Aeroacoustic optimization of a low speed fan Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2015.
@mastersthesis{Branco:2015:MSc,
title = {Aeroacoustic optimization of a low speed fan},
author = {J. Branco},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Branco_2015.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Branco_2015_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=621845, Catalog IST},
year = {2015},
date = {2015-06-01},
urldate = {2015-06-01},
pages = {92},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The use of air conditioning systems has increased in the recent decades due to the growth of the purchasing power in the developed world and the confort they provide, whereas the awareness regarding the negative health impacts of these systems has also increased. Many studies were conducted to predict and minimize the noise of the fans present in most of these systems. In this work, a noise prediction framework based on the Blade Element Momentum method for aerodynamic prediction was coupled to the empirical aeroacoustic models based on the works of Carolus et al (2007) and Brooks et al (1989) and to XFOIL for boundary layer parameter calculations. This framework was validated against experimental data of a known axial impeller and an existing air conditioning fan model was analyzed and its baseline noise values were characterized. A blade parameterization method was developed where the chord and twist distributions and airfoil sections were described by Bézier curves. A parametric study to determine the impact of fan diameter and blade number on the produced noise was conducted. The aeroacoustic code was coupled to the optimization framework pyOpt, and by using the NSGA-II genetic algorithm, a set of single and multi-objective optimizations, with chord, twist and curvature as design variables were performed on the baseline fan and on the minimum noise fan resultant from the parametric study. The optimal solutions indicated a maximum reduction of 4.1% in noise and a maximum increase of 5.3% in efficiency. Introducing diameter and blade number changes, a significant noise reduction is possible but with a moderate aerodynamic penalty.
Keywords: Aeroacoustic design, Noise reduction, Air conditioning, Multi-objective optimiza-
tion, Genetic algorithms},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The use of air conditioning systems has increased in the recent decades due to the growth of the purchasing power in the developed world and the confort they provide, whereas the awareness regarding the negative health impacts of these systems has also increased. Many studies were conducted to predict and minimize the noise of the fans present in most of these systems. In this work, a noise prediction framework based on the Blade Element Momentum method for aerodynamic prediction was coupled to the empirical aeroacoustic models based on the works of Carolus et al (2007) and Brooks et al (1989) and to XFOIL for boundary layer parameter calculations. This framework was validated against experimental data of a known axial impeller and an existing air conditioning fan model was analyzed and its baseline noise values were characterized. A blade parameterization method was developed where the chord and twist distributions and airfoil sections were described by Bézier curves. A parametric study to determine the impact of fan diameter and blade number on the produced noise was conducted. The aeroacoustic code was coupled to the optimization framework pyOpt, and by using the NSGA-II genetic algorithm, a set of single and multi-objective optimizations, with chord, twist and curvature as design variables were performed on the baseline fan and on the minimum noise fan resultant from the parametric study. The optimal solutions indicated a maximum reduction of 4.1% in noise and a maximum increase of 5.3% in efficiency. Introducing diameter and blade number changes, a significant noise reduction is possible but with a moderate aerodynamic penalty.
Keywords: Aeroacoustic design, Noise reduction, Air conditioning, Multi-objective optimiza-
tion, Genetic algorithms
Keywords: Aeroacoustic design, Noise reduction, Air conditioning, Multi-objective optimiza-
tion, Genetic algorithms
Miller, P.
Design of a remote person view system for a long range UAV Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2015.
@mastersthesis{Miller:2015:MSc,
title = {Design of a remote person view system for a long range UAV},
author = {P. Miller},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Miller_2015.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Miller_2015_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=621495, Catalog IST},
year = {2015},
date = {2015-06-01},
urldate = {2015-06-01},
pages = {100},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Unmanned Air Vehicles (UAV) made their way through the military sector. They have evolved exponentially in the last decade due to the fact that they are seen as a low cost and expendable way for highly dangerous, secret or politically sensitive missions. They are, in fact, getting a bad reputation but a large number of civil applications are taking advantage of these technological advancements for a greater good. Sensor technology, data processing hardware and software algorithms have made the Unmanned Aircraft System (UAS) a highly feasible approach in fire detection, rescue operations, precision agriculture, maintenance or journalism. A solution for RPV using commercial off-the-shelf (COTS) equipment is presented and analyzed. An Unmanned Air Vehicle (UAV) design was proposed and evaluated through, not only, in a controlled environment but also flight testing. The performance of this UAV was, then, used to evaluate the choices made and purpose a definite and better solution for Long Range Unmanned Air Systems. The platform in question is a glider and is composed by three main systems: the radio control, the video feed and the telemetry radio that together connect the UAV to the ground station. The parameter received signal strength indicator (RSSI) was used for control evaluation. While propagation, polarization and obstruction losses were used for evaluation of the video system. Although the long range system encountered difficulties in reaching a maximum flight range, it proved to be useful for long range applications.
Keywords: RPV, UAV, Long range, Video, Radio control},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Unmanned Air Vehicles (UAV) made their way through the military sector. They have evolved exponentially in the last decade due to the fact that they are seen as a low cost and expendable way for highly dangerous, secret or politically sensitive missions. They are, in fact, getting a bad reputation but a large number of civil applications are taking advantage of these technological advancements for a greater good. Sensor technology, data processing hardware and software algorithms have made the Unmanned Aircraft System (UAS) a highly feasible approach in fire detection, rescue operations, precision agriculture, maintenance or journalism. A solution for RPV using commercial off-the-shelf (COTS) equipment is presented and analyzed. An Unmanned Air Vehicle (UAV) design was proposed and evaluated through, not only, in a controlled environment but also flight testing. The performance of this UAV was, then, used to evaluate the choices made and purpose a definite and better solution for Long Range Unmanned Air Systems. The platform in question is a glider and is composed by three main systems: the radio control, the video feed and the telemetry radio that together connect the UAV to the ground station. The parameter received signal strength indicator (RSSI) was used for control evaluation. While propagation, polarization and obstruction losses were used for evaluation of the video system. Although the long range system encountered difficulties in reaching a maximum flight range, it proved to be useful for long range applications.
Keywords: RPV, UAV, Long range, Video, Radio control
Keywords: RPV, UAV, Long range, Video, Radio control
Carrolo, E.
Passive control of aerodynamic load in wind turbine blades Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2015.
@mastersthesis{Carrolo:2015:MSc,
title = {Passive control of aerodynamic load in wind turbine blades},
author = {E. Carrolo},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Carrolo_2015.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Carrolo_2015_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=620075, Catalog IST},
year = {2015},
date = {2015-06-01},
urldate = {2015-06-01},
pages = {94},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Large wind turbine blades have many advantages in terms of power efficiency, despite representing an hazard concerning the high loads applied on the structure. Traditionally, there are active control systems that allow blades to adapt according to wind conditions, and so maintain power efficiency and aerodynamic load within acceptable levels. Since the end of the last century, some researchers have been discussing about passive control techniques. The implementation of this kind of aeroelastic response does not bring additional maintenance or weight, unlike active control, because there are no additional devices or complementary structures, and is very useful either to reduce fatigue loads or optimize energy output. The main purpose was to achieve an effective reduction in aerodynamic loading in a wind turbine blade. In the scope of this work, computational models were developed that simulated the fluid-structure interaction on a enhanced blade model. Coupled analysis considering first only the aerodynamic load and then combining it with inertial were performed. The results demonstrated that this design could reduce 2.1% aerodynamic load in high wind speeds at the cut-out wind speed, thus proving to be a realistic passive control technique. A preliminary static validation of the enhanced blade model was successfully done, taking into account maximum reference values.
Keywords: Aeroelastic tailoring, Bend-twist coupling, Passive control, Aerodynamic load, Fluid-structure interaction},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Large wind turbine blades have many advantages in terms of power efficiency, despite representing an hazard concerning the high loads applied on the structure. Traditionally, there are active control systems that allow blades to adapt according to wind conditions, and so maintain power efficiency and aerodynamic load within acceptable levels. Since the end of the last century, some researchers have been discussing about passive control techniques. The implementation of this kind of aeroelastic response does not bring additional maintenance or weight, unlike active control, because there are no additional devices or complementary structures, and is very useful either to reduce fatigue loads or optimize energy output. The main purpose was to achieve an effective reduction in aerodynamic loading in a wind turbine blade. In the scope of this work, computational models were developed that simulated the fluid-structure interaction on a enhanced blade model. Coupled analysis considering first only the aerodynamic load and then combining it with inertial were performed. The results demonstrated that this design could reduce 2.1% aerodynamic load in high wind speeds at the cut-out wind speed, thus proving to be a realistic passive control technique. A preliminary static validation of the enhanced blade model was successfully done, taking into account maximum reference values.
Keywords: Aeroelastic tailoring, Bend-twist coupling, Passive control, Aerodynamic load, Fluid-structure interaction
Keywords: Aeroelastic tailoring, Bend-twist coupling, Passive control, Aerodynamic load, Fluid-structure interaction
Cardeira, A.
Aeroelastic analysis of aircraft wings Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2014.
@mastersthesis{Cardeira:2014:MSc,
title = {Aeroelastic analysis of aircraft wings},
author = {A. Cardeira},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Cardeira_2014.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Cardeira_2014_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=620645, Catalog IST},
year = {2014},
date = {2014-12-01},
urldate = {2014-12-01},
pages = {85},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Aeroelasticity phenomena involve the study of the interaction between aerodynamic and elastic forces (static aeroelasticity), and aerodynamic, inertial, and elastic forces (dynamic aeroelasticity). Modern aircraft structures, making more and more use of lightweight composite structures, may be very flexible making the aeroelastic study an important aspect of the aircraft design. Flutter is a dynamic aeroelastic instability characterized by sustained oscillation of structure arising from interaction between those three forces acting on the body. The present work aims to study the flutter behavior on three-dimensional subsonic aircraft wings, using a computationally efficient method. For that, a new computational aeroelasticity design framework was created using a panel method to solve the fluid flow approximated as potential flow and a commercial software for the structural analysis. A validation of the fluid solver is made using wind tunnel data, while the structure solver is verified using the available tests. The coupling of the two domains is made with a main script using an adequate time discretization scheme. The results are presented for a wing example which is denoted as reference case. Later, a study of the influence of pertinent parameters is performed, concluding with the comparison between the many values tested. It is concluded that the framework shows very good agreement to the theoretical influences of the parameters studied. Despite the simplification of the fluid flow, which was assumed to be potential, this method proves to be a very useful tool in aircraft preliminary design.
Keywords: Aeroelasticity, Panel method, Fluid-structure interaction, Finite element method, Flutter, Divergence velocity},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Aeroelasticity phenomena involve the study of the interaction between aerodynamic and elastic forces (static aeroelasticity), and aerodynamic, inertial, and elastic forces (dynamic aeroelasticity). Modern aircraft structures, making more and more use of lightweight composite structures, may be very flexible making the aeroelastic study an important aspect of the aircraft design. Flutter is a dynamic aeroelastic instability characterized by sustained oscillation of structure arising from interaction between those three forces acting on the body. The present work aims to study the flutter behavior on three-dimensional subsonic aircraft wings, using a computationally efficient method. For that, a new computational aeroelasticity design framework was created using a panel method to solve the fluid flow approximated as potential flow and a commercial software for the structural analysis. A validation of the fluid solver is made using wind tunnel data, while the structure solver is verified using the available tests. The coupling of the two domains is made with a main script using an adequate time discretization scheme. The results are presented for a wing example which is denoted as reference case. Later, a study of the influence of pertinent parameters is performed, concluding with the comparison between the many values tested. It is concluded that the framework shows very good agreement to the theoretical influences of the parameters studied. Despite the simplification of the fluid flow, which was assumed to be potential, this method proves to be a very useful tool in aircraft preliminary design.
Keywords: Aeroelasticity, Panel method, Fluid-structure interaction, Finite element method, Flutter, Divergence velocity
Keywords: Aeroelasticity, Panel method, Fluid-structure interaction, Finite element method, Flutter, Divergence velocity
Figueiredo, D.
Autopilot and ground control station for UAV Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2014.
@mastersthesis{Figueiredo:2014:MSc,
title = {Autopilot and ground control station for UAV},
author = {D. Figueiredo},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Figueiredo_2014.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Figueiredo_2014_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=624601, Catalog IST},
year = {2014},
date = {2014-11-01},
urldate = {2014-11-01},
pages = {70},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The Unmanned Air Vehicle sector has become the most dynamic growth sector in the aerospace industry. There are more and more civilian applications that greatly benefit from the use of these aircraft. The objective of this work is to test and implement an autopilot and a ground control station for an UAV that is being sponsored by LAETA (Laboratório Associado de Energia, Transportes e Aeronáutica). It is also expected to implement a Remote Person View system along with the autopilot. The autopilot that was chosen to be implemented is the Ardupilot APM 2.6, which is an open source, low cost autopilot. This will help reduce the total cost of the project, while also offering similar performances to commercial autopilots. This autopilot can be used in different types of vehicles. For the ground control station it is used the Mission Planner. In order to safely test the autopilot without the risk of damaging any component it was first installed and tested on a rover. In this test, the autopilot and the RPV system worked correctly. Next, the system was installed on the UAV. Several flight tests were conducted and it was verified that the autopilot was working properly even with the default parameter settings. This work allowed the implementation of a low cost autopilot that has good quality performances. This autopilot proved its flexibility when being implemented in different platforms. This autopilot is ready to be used in the UAV that is being developed.
Keywords: Autonomous flight, Remotely piloted vehicle, Artificial cockpit, Flight control, Telemetry, Rover},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The Unmanned Air Vehicle sector has become the most dynamic growth sector in the aerospace industry. There are more and more civilian applications that greatly benefit from the use of these aircraft. The objective of this work is to test and implement an autopilot and a ground control station for an UAV that is being sponsored by LAETA (Laboratório Associado de Energia, Transportes e Aeronáutica). It is also expected to implement a Remote Person View system along with the autopilot. The autopilot that was chosen to be implemented is the Ardupilot APM 2.6, which is an open source, low cost autopilot. This will help reduce the total cost of the project, while also offering similar performances to commercial autopilots. This autopilot can be used in different types of vehicles. For the ground control station it is used the Mission Planner. In order to safely test the autopilot without the risk of damaging any component it was first installed and tested on a rover. In this test, the autopilot and the RPV system worked correctly. Next, the system was installed on the UAV. Several flight tests were conducted and it was verified that the autopilot was working properly even with the default parameter settings. This work allowed the implementation of a low cost autopilot that has good quality performances. This autopilot proved its flexibility when being implemented in different platforms. This autopilot is ready to be used in the UAV that is being developed.
Keywords: Autonomous flight, Remotely piloted vehicle, Artificial cockpit, Flight control, Telemetry, Rover
Keywords: Autonomous flight, Remotely piloted vehicle, Artificial cockpit, Flight control, Telemetry, Rover
Ferreira, T.
Hybrid propulsion system of a long endurance electric UAV Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2014.
@mastersthesis{Ferreira:2014:MSc,
title = {Hybrid propulsion system of a long endurance electric UAV},
author = {T. Ferreira},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Ferreira_2014.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Ferreira_2014_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=615934, Catalog IST},
year = {2014},
date = {2014-11-01},
urldate = {2014-11-01},
pages = {96},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The demand for alternative and clean power sources has been growing in the past years. The change to electric power can already be seen in the automotive industry, and the aeronautical industry is slowly following. The use of solar panels is a good alternative power source to use with electrical drives, since it is clean and readily and abundantly available. This thesis focuses on a system combining solar power generation and an electrical drive to power a 4.5 m span unmanned aerial vehicle for aerial surveillance over long periods of time. A solar-battery hybrid is a good solution for long endurance aerial vehicles, since there is a large area available on the wings to mount a solar array capable of supplying enough energy to maintain the aircraft airborne. The hybrid propulsion system was tested and verified for energy and power availability versus mission requirements, since this is the main drawback of a solar system. Since these cells are to be mounted on a heat shrink film covered wing, and these cell tend to heat up, the behaviour of the film was studied to verify the viability of the system assembly. The tests proved that the hybrid propulsion system is a feasible system, since the maximum output was 106 W , more than twice the energy required during the cruise phase. The film should be further tested on a test wing, since the 39.76% force decrease could induce serious changes to the geometry of the wing.
Keywords: Solar power, UAV, Hybrid propulsion, Electric flight, Long endurance},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The demand for alternative and clean power sources has been growing in the past years. The change to electric power can already be seen in the automotive industry, and the aeronautical industry is slowly following. The use of solar panels is a good alternative power source to use with electrical drives, since it is clean and readily and abundantly available. This thesis focuses on a system combining solar power generation and an electrical drive to power a 4.5 m span unmanned aerial vehicle for aerial surveillance over long periods of time. A solar-battery hybrid is a good solution for long endurance aerial vehicles, since there is a large area available on the wings to mount a solar array capable of supplying enough energy to maintain the aircraft airborne. The hybrid propulsion system was tested and verified for energy and power availability versus mission requirements, since this is the main drawback of a solar system. Since these cells are to be mounted on a heat shrink film covered wing, and these cell tend to heat up, the behaviour of the film was studied to verify the viability of the system assembly. The tests proved that the hybrid propulsion system is a feasible system, since the maximum output was 106 W , more than twice the energy required during the cruise phase. The film should be further tested on a test wing, since the 39.76% force decrease could induce serious changes to the geometry of the wing.
Keywords: Solar power, UAV, Hybrid propulsion, Electric flight, Long endurance
Keywords: Solar power, UAV, Hybrid propulsion, Electric flight, Long endurance
Simões, C.
Optimal design of a UAV co-axial propulsion system and its airframe Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2014.
@mastersthesis{Simoes:2014:MSc,
title = {Optimal design of a UAV co-axial propulsion system and its airframe},
author = {C. Simões},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Simoes_2014.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Simoes_2014_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=616858, Catalog IST},
year = {2014},
date = {2014-07-01},
urldate = {2014-07-01},
pages = {90},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {This dissertation discusses the optimization of coaxial propulsion systems in UAVs (Unmanned Aerial Vehicles) and the structural analysis of a quadcopter (UAV with four arms equally spaced around the center body) equipped with the optimized coaxial system. This propulsion system is usually used because it presents a good thrust to volume ratio since the two engines are near and the total output thrust is higher than in a single engine. The Glauert’s theory was used to predict the behavior of coaxial propulsion systems. Finally, several experimentations were realized to test coaxial systems and conclude the influence of certain parameters on the efficiency of the propulsion system. The optimized coaxial system was compared to a propulsion system composed of a single engine and a 14x4.7 propeller (base system). A structural analysis was performed on a quadcopter equipped with the optimized coaxial system obtained from the previous experimental tests. A static and a modal analysis were realized using Ansys, a finite elements software. Then, a dynamic analysis was realized by attaching an accelerometer to the propulsion system, which was operated at different power consumptions. We concluded from the present dissertation that the main parameters that influence the efficiency of a coaxial propulsion system were the diameter and the pitch of the propellers. Any variation of the pitch of the upper propellers resulted in a decrease of the efficiency of the propulsion system. Regarding the lower propeller’s pitch, when this parameter is increased the efficiency of the propulsion system increases but when this parameter is decreased the efficiency decreases. We also concluded that the variation of the upper propeller’s diameter had no influence on the efficiency of the coaxial propulsion system. However, the same results were not observed upon the study of the variation of the lower propeller’s diameter. Increasing the lower propeller’s diameter resulted in an increase of the efficiency of the propulsion system and, contrarily, decreasing the lower propeller’s diameter resulted in a decrease of the efficiency of the coaxial propulsion system. Lastly, we observed that the response time of the two propellers of the propulsion system was directly related to the diameter of the propellers. Increasing the diameter of the propellers resulted in an increase of the response time while decreasing the diameter resulted in a decrease of the response time.
Keywords: Coaxial propulsion system, Glauert theory, UAV, Quadcopter, Structural analysis},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
This dissertation discusses the optimization of coaxial propulsion systems in UAVs (Unmanned Aerial Vehicles) and the structural analysis of a quadcopter (UAV with four arms equally spaced around the center body) equipped with the optimized coaxial system. This propulsion system is usually used because it presents a good thrust to volume ratio since the two engines are near and the total output thrust is higher than in a single engine. The Glauert’s theory was used to predict the behavior of coaxial propulsion systems. Finally, several experimentations were realized to test coaxial systems and conclude the influence of certain parameters on the efficiency of the propulsion system. The optimized coaxial system was compared to a propulsion system composed of a single engine and a 14x4.7 propeller (base system). A structural analysis was performed on a quadcopter equipped with the optimized coaxial system obtained from the previous experimental tests. A static and a modal analysis were realized using Ansys, a finite elements software. Then, a dynamic analysis was realized by attaching an accelerometer to the propulsion system, which was operated at different power consumptions. We concluded from the present dissertation that the main parameters that influence the efficiency of a coaxial propulsion system were the diameter and the pitch of the propellers. Any variation of the pitch of the upper propellers resulted in a decrease of the efficiency of the propulsion system. Regarding the lower propeller’s pitch, when this parameter is increased the efficiency of the propulsion system increases but when this parameter is decreased the efficiency decreases. We also concluded that the variation of the upper propeller’s diameter had no influence on the efficiency of the coaxial propulsion system. However, the same results were not observed upon the study of the variation of the lower propeller’s diameter. Increasing the lower propeller’s diameter resulted in an increase of the efficiency of the propulsion system and, contrarily, decreasing the lower propeller’s diameter resulted in a decrease of the efficiency of the coaxial propulsion system. Lastly, we observed that the response time of the two propellers of the propulsion system was directly related to the diameter of the propellers. Increasing the diameter of the propellers resulted in an increase of the response time while decreasing the diameter resulted in a decrease of the response time.
Keywords: Coaxial propulsion system, Glauert theory, UAV, Quadcopter, Structural analysis
Keywords: Coaxial propulsion system, Glauert theory, UAV, Quadcopter, Structural analysis
Silva, N.
Parametric design, aerodynamic analysis and optimization of a solar UAV Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2014.
@mastersthesis{Silva:2014:MSc,
title = {Parametric design, aerodynamic analysis and optimization of a solar UAV},
author = {N. Silva},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Silva_2014.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Silva_2014_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=618477, Catalog IST},
year = {2014},
date = {2014-06-01},
urldate = {2014-06-01},
pages = {90},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The aim of this thesis was to develop and implement a computational process to enable the swift design of different UAV configurations and their aerodynamic analysis. To this end, a CAD tool using scripts was adopted to define the UAV external shape which was later imported into a CFD tool to generate suitable meshes. The test case consisted of a Long Endurance Electric UAV (LEEUAV), that was aerodynamically analyzed and parametrically optimized. While performing the aerodynamic analyses, turbulence models Spalart-Allmaras and k − ω SST, the later being employed in tandem with the γ − Re θ transition model, were employed and their predictions compared with experimental data. Only the k − ω SST turbulence model and the γ − Re θ transition model were employed in the detailed aerodynamic simulations. During cruise, the baseline LEEUAV presents a lift-to-drag ratio of 14.01, stall speed of 6.21 m/s and maximum cruise speed of 29.3 m/s. To enhance the baseline cruise performance, a series of parametric optimization and sensitivity studies were performed where its nose, wing and fuselage shapes were modified. With the nose shape modification proposal, the adverse pressure gradients that previously existed in that surface were reduced. With rounded wingtips, the wing long laminar separation bubbles were predicted to decrease. With the proposed wing root fairing, a region of separated flow that formed beginning at 2 degrees disappeared thus reducing the aircraft drag. With the proposed wing washout, aileron control effectiveness was extended to angles of attack up to 10 degrees.
Keywords: Solar UAV, UAV airframe, Long endurance, Hybrid propulsion, Computational fluid dynamics, Computer-aided design, Parametric modeling, Sensitivity analysis},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The aim of this thesis was to develop and implement a computational process to enable the swift design of different UAV configurations and their aerodynamic analysis. To this end, a CAD tool using scripts was adopted to define the UAV external shape which was later imported into a CFD tool to generate suitable meshes. The test case consisted of a Long Endurance Electric UAV (LEEUAV), that was aerodynamically analyzed and parametrically optimized. While performing the aerodynamic analyses, turbulence models Spalart-Allmaras and k − ω SST, the later being employed in tandem with the γ − Re θ transition model, were employed and their predictions compared with experimental data. Only the k − ω SST turbulence model and the γ − Re θ transition model were employed in the detailed aerodynamic simulations. During cruise, the baseline LEEUAV presents a lift-to-drag ratio of 14.01, stall speed of 6.21 m/s and maximum cruise speed of 29.3 m/s. To enhance the baseline cruise performance, a series of parametric optimization and sensitivity studies were performed where its nose, wing and fuselage shapes were modified. With the nose shape modification proposal, the adverse pressure gradients that previously existed in that surface were reduced. With rounded wingtips, the wing long laminar separation bubbles were predicted to decrease. With the proposed wing root fairing, a region of separated flow that formed beginning at 2 degrees disappeared thus reducing the aircraft drag. With the proposed wing washout, aileron control effectiveness was extended to angles of attack up to 10 degrees.
Keywords: Solar UAV, UAV airframe, Long endurance, Hybrid propulsion, Computational fluid dynamics, Computer-aided design, Parametric modeling, Sensitivity analysis
Keywords: Solar UAV, UAV airframe, Long endurance, Hybrid propulsion, Computational fluid dynamics, Computer-aided design, Parametric modeling, Sensitivity analysis
Amândio, L. F.
Stochastic optimization in aircraft design Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2013.
@mastersthesis{Amandio:2013:MSc,
title = {Stochastic optimization in aircraft design},
author = {L. F. Amândio},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Amandio_2013.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Amandio_2013_ExtendedAbstract.pdf, Extended abstract
PDF https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=588051, Catalog IST},
year = {2013},
date = {2013-11-01},
urldate = {2013-11-01},
pages = {84},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {This thesis focuses on analysing the advantages and disadvantages of using stochastic optimization, especially in aircraft design problems. First, a literature review served as a starting point to choosing some of the most common and promising methods of robust design optimization, reliability based design optimization and robust and reliability based design optimization. The chosen methods were Monte-Carlo, method of moments, Sigma point, reliability index approach, performance measure approach, sequential optimization and reliability assessment, and reliable design space. After implementing these methods, they were tested for two analytic functions and their performances compared. Four of these methods were then chosen based on their performances to be implemented in a multidisciplinary optimization tool specially tailored to solve aircraft optimization problems. To evaluate the chosen methods in a more realistic environment, two new reliability based test cases related to aircraft design were developed. In these test cases, surrogate models were employed instead of the more computationally expensive disciplinary analysis, with the main objective being the study of how the efficiency of each method changed with the number of uncertainty parameters. The obtained results revealed that the efficiency of each method is closely related to the type of problem solved. While in the analytic cases, for high levels of uncertainty, the robust optimization method showed some difficulties in achieving the target reliability, in the aircraft design cases, it proved to be the best method in terms of the relation between accuracy and computational cost.
Keywords: Uncertainty propagation, Robust design optimization, Reliability-based design optimization, Multidisciplinary optimization, Benchmarking},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
This thesis focuses on analysing the advantages and disadvantages of using stochastic optimization, especially in aircraft design problems. First, a literature review served as a starting point to choosing some of the most common and promising methods of robust design optimization, reliability based design optimization and robust and reliability based design optimization. The chosen methods were Monte-Carlo, method of moments, Sigma point, reliability index approach, performance measure approach, sequential optimization and reliability assessment, and reliable design space. After implementing these methods, they were tested for two analytic functions and their performances compared. Four of these methods were then chosen based on their performances to be implemented in a multidisciplinary optimization tool specially tailored to solve aircraft optimization problems. To evaluate the chosen methods in a more realistic environment, two new reliability based test cases related to aircraft design were developed. In these test cases, surrogate models were employed instead of the more computationally expensive disciplinary analysis, with the main objective being the study of how the efficiency of each method changed with the number of uncertainty parameters. The obtained results revealed that the efficiency of each method is closely related to the type of problem solved. While in the analytic cases, for high levels of uncertainty, the robust optimization method showed some difficulties in achieving the target reliability, in the aircraft design cases, it proved to be the best method in terms of the relation between accuracy and computational cost.
Keywords: Uncertainty propagation, Robust design optimization, Reliability-based design optimization, Multidisciplinary optimization, Benchmarking
Keywords: Uncertainty propagation, Robust design optimization, Reliability-based design optimization, Multidisciplinary optimization, Benchmarking
González, H.
Design, construction and test of the propulsion system of a solar UAV Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2013.
@mastersthesis{Gonzalez:2013:MSc,
title = {Design, construction and test of the propulsion system of a solar UAV},
author = {H. González},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Gonzalez_2013.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Gonzalez_2013_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=592762, Catalog IST},
year = {2013},
date = {2013-03-01},
urldate = {2013-03-01},
pages = {100},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Pollution problems and the need to achieve a lower oil dependency have given solar and electric technologies, an important role in propulsion systems, from automotive to, more recently, aviation industry. This thesis contains the conceptual design of a hybrid propulsion system of an unmanned aerial vehicle (UAV). The solar-powered plant aimed at a small UAV with a wingspan of 4.5 m and an approximate weight of 5 kg, with a specific civil surveillance mission. Its architecture is completely different from the conventional methods of propulsion. From all the different efficiencies of the components that influence the use of energy, the most important factor is the solar irradiance and the ability that the solar panels have to harvest that energy, that is, their efficiency. The design and sizing of the different components of the propulsion system depends on the available energy stored in the battery or the generate power in the solar panels. As solar radiation is different throughout the year, different combinations of batteries, solar panels or hybrid systems are studied. The propulsion system is designed according to the requirements of energy available and energy required, and after appropriate design, the different components of the propulsion system are selected following design criteria. In the end, a road-map to achieve the necessary tests and check the proper functioning of the designed system will be established.
Keywords: Green aviation, Electric flight, Solar panels, Solar irradiance, Hybrid propulsion},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Pollution problems and the need to achieve a lower oil dependency have given solar and electric technologies, an important role in propulsion systems, from automotive to, more recently, aviation industry. This thesis contains the conceptual design of a hybrid propulsion system of an unmanned aerial vehicle (UAV). The solar-powered plant aimed at a small UAV with a wingspan of 4.5 m and an approximate weight of 5 kg, with a specific civil surveillance mission. Its architecture is completely different from the conventional methods of propulsion. From all the different efficiencies of the components that influence the use of energy, the most important factor is the solar irradiance and the ability that the solar panels have to harvest that energy, that is, their efficiency. The design and sizing of the different components of the propulsion system depends on the available energy stored in the battery or the generate power in the solar panels. As solar radiation is different throughout the year, different combinations of batteries, solar panels or hybrid systems are studied. The propulsion system is designed according to the requirements of energy available and energy required, and after appropriate design, the different components of the propulsion system are selected following design criteria. In the end, a road-map to achieve the necessary tests and check the proper functioning of the designed system will be established.
Keywords: Green aviation, Electric flight, Solar panels, Solar irradiance, Hybrid propulsion
Keywords: Green aviation, Electric flight, Solar panels, Solar irradiance, Hybrid propulsion
Liquito, J.
Design of structural elements of aircraft wings with uncertainty in loads and materials Masters Thesis
Portuguese Air Force Academy, Sintra, Portugal, 2012.
@mastersthesis{Liquito:2012:MSc,
title = {Design of structural elements of aircraft wings with uncertainty in loads and materials},
author = {J. Liquito},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Liquito_2012.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Liquito_2012_ExtendedAbstract.pdf, Extended abstract PDF},
year = {2012},
date = {2012-12-01},
pages = {88},
address = {Sintra, Portugal},
school = {Portuguese Air Force Academy},
abstract = {Uncertainty quantification in the structural design of wing elements is the main objective of this thesis. Uncertainties could be from materials, loads and sizing. A literature review was done related to different studies in this field, as well as the existing methods of quantification. For the study, three different methods were used: Monte Carlo simulation method, Latin hypercube sampling method and perturbation method. First, the methods were implemented and validated using a simple truss as test case. Then, they were applied to a simple case of a wing spar. For this case, the methods implemented were used in an analytic analysis and later in a finite elements method analysis, thus validating the application of the numerical analysis. Finally, an analysis was made of a structure of a wing with several variables with uncertainty. The results reveal the importance of this approach, since there are significant differences between the deterministic calculus and the results with uncertainty quantification.
Keywords: Uncertainty quantification, Monte-Carlo simulation, Latin hypercube sampling, Perturbation method, Finite elements, Robust design},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Uncertainty quantification in the structural design of wing elements is the main objective of this thesis. Uncertainties could be from materials, loads and sizing. A literature review was done related to different studies in this field, as well as the existing methods of quantification. For the study, three different methods were used: Monte Carlo simulation method, Latin hypercube sampling method and perturbation method. First, the methods were implemented and validated using a simple truss as test case. Then, they were applied to a simple case of a wing spar. For this case, the methods implemented were used in an analytic analysis and later in a finite elements method analysis, thus validating the application of the numerical analysis. Finally, an analysis was made of a structure of a wing with several variables with uncertainty. The results reveal the importance of this approach, since there are significant differences between the deterministic calculus and the results with uncertainty quantification.
Keywords: Uncertainty quantification, Monte-Carlo simulation, Latin hypercube sampling, Perturbation method, Finite elements, Robust design
Keywords: Uncertainty quantification, Monte-Carlo simulation, Latin hypercube sampling, Perturbation method, Finite elements, Robust design
Rodrigues, S. S.
Aero-acoustic optimization of wind turbine blades Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2012.
@mastersthesis{Rodrigues:2012:MSc,
title = {Aero-acoustic optimization of wind turbine blades},
author = {S. S. Rodrigues},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Rodrigues_2012.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Rodrigues_2012_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=581753, Catalog IST},
year = {2012},
date = {2012-11-01},
urldate = {2012-11-01},
pages = {100},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {Power production from wind energy has been increasing for the past few decades, with more areas being used as wind farms and larger wind turbines being built. With this development, awareness of the impact of wind energy on the environment and on human health as also increased. Much research has been done to predict and reduce the noise generated by wind turbines. In this work, a blade element momentum theory model is used to predict the aerodynamic performance of a wind turbine, coupled to an empirical aeroacoustic noise model based on the works of Brooks et al (1989) and Amiet (1975), and using the XFOIL panel code for the boundary layer computations. The aeroacoustic prediction code developed was validated against measurement data of the NREL Phase II and AOC 15/50 wind turbines and used in the optimization framework pyOpt, using the genetic algorithm NSGA-II. The geometry of the blade was parameterized using NURBS curves for the cross sectional airfoil shapes and Bézier curves for the twist and chord distributions. Various optimizations were performed in blades of the two previous turbines, both single- and multi-objective, totaling up to 62 design variables. The optimal solutions are indicated in the obtained Pareto fronts and their geometries are discussed in detail. These solutions ranged from an increase in annual energy production of 139.9% to a reduction in noise levels of 10.7%. It was demonstrated that significant noise reduction could be obtained at an expense of a minor aerodynamic penalty.
Keywords: Genetic algorithms, NURBS, Multi-disciplinary design optimization, Multi-objective optimization},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
Power production from wind energy has been increasing for the past few decades, with more areas being used as wind farms and larger wind turbines being built. With this development, awareness of the impact of wind energy on the environment and on human health as also increased. Much research has been done to predict and reduce the noise generated by wind turbines. In this work, a blade element momentum theory model is used to predict the aerodynamic performance of a wind turbine, coupled to an empirical aeroacoustic noise model based on the works of Brooks et al (1989) and Amiet (1975), and using the XFOIL panel code for the boundary layer computations. The aeroacoustic prediction code developed was validated against measurement data of the NREL Phase II and AOC 15/50 wind turbines and used in the optimization framework pyOpt, using the genetic algorithm NSGA-II. The geometry of the blade was parameterized using NURBS curves for the cross sectional airfoil shapes and Bézier curves for the twist and chord distributions. Various optimizations were performed in blades of the two previous turbines, both single- and multi-objective, totaling up to 62 design variables. The optimal solutions are indicated in the obtained Pareto fronts and their geometries are discussed in detail. These solutions ranged from an increase in annual energy production of 139.9% to a reduction in noise levels of 10.7%. It was demonstrated that significant noise reduction could be obtained at an expense of a minor aerodynamic penalty.
Keywords: Genetic algorithms, NURBS, Multi-disciplinary design optimization, Multi-objective optimization
Keywords: Genetic algorithms, NURBS, Multi-disciplinary design optimization, Multi-objective optimization
Tojo, B. M.
Aero-structural blade design of a high-power wind turbine Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2012.
@mastersthesis{Tojo:2012:MSc,
title = {Aero-structural blade design of a high-power wind turbine},
author = {B. M. Tojo},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Tojo_2012.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Tojo_2012_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=561833, Catalog IST},
year = {2012},
date = {2012-07-01},
urldate = {2012-07-01},
pages = {97},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The present work focused on the development of an aero-structural design framework for a high-power horizontal axis wind turbine. To achieve this, it was necessary to carefully characterize the blade, to develop a suitable fluid-structure interaction solver and, finally, to combine both with post-processing tools. The blade parameterization was inspired in the disc actuator concept, which was then improved through computational fluid dynamics simulations and, the structure was modeled as main spar that has the shape of the blade. It was developed a fluid-structure interaction solver for OpenFOAM, dedicated to simulate wind turbine rotors. The fluid-structure coupling was achieved through a loose coupling strategy, which means that there are separated solvers for the flow and structure analysis, which are combined through the update of boundary conditions. To simulate the blades rotation movement, it was used an approach based on the single rotating frame method, meaning that the whole domain rotated with the turbine rotor with a constant angular velocity. For the structural domain, a linear elastic solver was used, able to model the small deformations due to the distributed aerodynamic forces. The simulations of the rotor produced valid and interesting results namely, correct flow fields and pressure distributions. Considering that it is expected horizontal axis wind turbine rotors to continue growing to even larger sizes than the one modeled, it was shown that blade displacements due to flow induced forces are definitely a problem that needs to be taken into account when designing new wind turbine blades. Although it was not possible to analyze the consequences of these effects in the turbine output power, a post-processing method to make this evaluation was presented. To obtain relevant results on this subject, it would be important to further develop the structural solver and model, giving them the correct proprieties to model wind turbine blades.
Keywords: Wind turbine, Fluid-structure interaction, CFD development, High-fidelity analysis, Single rotating frame, OpenFOAM, ICEMCFD},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The present work focused on the development of an aero-structural design framework for a high-power horizontal axis wind turbine. To achieve this, it was necessary to carefully characterize the blade, to develop a suitable fluid-structure interaction solver and, finally, to combine both with post-processing tools. The blade parameterization was inspired in the disc actuator concept, which was then improved through computational fluid dynamics simulations and, the structure was modeled as main spar that has the shape of the blade. It was developed a fluid-structure interaction solver for OpenFOAM, dedicated to simulate wind turbine rotors. The fluid-structure coupling was achieved through a loose coupling strategy, which means that there are separated solvers for the flow and structure analysis, which are combined through the update of boundary conditions. To simulate the blades rotation movement, it was used an approach based on the single rotating frame method, meaning that the whole domain rotated with the turbine rotor with a constant angular velocity. For the structural domain, a linear elastic solver was used, able to model the small deformations due to the distributed aerodynamic forces. The simulations of the rotor produced valid and interesting results namely, correct flow fields and pressure distributions. Considering that it is expected horizontal axis wind turbine rotors to continue growing to even larger sizes than the one modeled, it was shown that blade displacements due to flow induced forces are definitely a problem that needs to be taken into account when designing new wind turbine blades. Although it was not possible to analyze the consequences of these effects in the turbine output power, a post-processing method to make this evaluation was presented. To obtain relevant results on this subject, it would be important to further develop the structural solver and model, giving them the correct proprieties to model wind turbine blades.
Keywords: Wind turbine, Fluid-structure interaction, CFD development, High-fidelity analysis, Single rotating frame, OpenFOAM, ICEMCFD
Keywords: Wind turbine, Fluid-structure interaction, CFD development, High-fidelity analysis, Single rotating frame, OpenFOAM, ICEMCFD
Coimbra, J. F. G.
Aero-acoustic optimization of airfoils for wing turbines Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2012.
@mastersthesis{Coimbra:2012:MSc,
title = {Aero-acoustic optimization of airfoils for wing turbines},
author = {J. F. G. Coimbra},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Coimbra_2012.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Coimbra_2012_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=619988, Catalog IST},
year = {2012},
date = {2012-06-01},
urldate = {2012-06-01},
pages = {99},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The subject of airfoil design, in the context of wind turbines, is approached with the objective of optimizing the geometry for the best aerodynamic and aero-acoustic trade-off. The work developed is made up of four stages: the aerodynamic analysis module, which consists of two parts, one responsible for airfoil design and parameterization and another dedicated to flow analysis; an aero-acoustic module, based in the semi-empirical model from Brooks, Pope and Marcolini and the turbulent inflow prediction scheme from Moriarty, Guidati and Migliore; the integration of both modules in one single computational tool; and the development of a multi-objective optimization framework. The mathematical description of the airfoil geometry build tool is based on Bézier curves and, the wind turbine dedicated computational tool Rfoil has been used for boundary-layer modeling and inclusion of rotational effects. The code developed integrated both developed modules in a single interactive shell in Python. The Python module pyOpt was selected as the interactive development environment in which the optimization took place. A genetic algorithm was selected to handle multiple local minima and multi-objective problems. Several airfoil families, commonly used in the wind turbine technology, were analyzed from the aerodynamic and aero-acoustic perspectives with the developed tools, and used as reference for general comparison. Optimized airfoil geometries, that either minimize noise emission or favour aerodynamic performance were obtained and classes of aero-acoustically optimized airfoils were identified in the resulting Pareto fronts. Results show that very good aerodynamic performance can be achieved with negligible increase in noise levels.
Keywords: Airfoil design, Wind turbines, Aero-acoustics, Multi-objective optimization, Multidisciplinary optimization},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The subject of airfoil design, in the context of wind turbines, is approached with the objective of optimizing the geometry for the best aerodynamic and aero-acoustic trade-off. The work developed is made up of four stages: the aerodynamic analysis module, which consists of two parts, one responsible for airfoil design and parameterization and another dedicated to flow analysis; an aero-acoustic module, based in the semi-empirical model from Brooks, Pope and Marcolini and the turbulent inflow prediction scheme from Moriarty, Guidati and Migliore; the integration of both modules in one single computational tool; and the development of a multi-objective optimization framework. The mathematical description of the airfoil geometry build tool is based on Bézier curves and, the wind turbine dedicated computational tool Rfoil has been used for boundary-layer modeling and inclusion of rotational effects. The code developed integrated both developed modules in a single interactive shell in Python. The Python module pyOpt was selected as the interactive development environment in which the optimization took place. A genetic algorithm was selected to handle multiple local minima and multi-objective problems. Several airfoil families, commonly used in the wind turbine technology, were analyzed from the aerodynamic and aero-acoustic perspectives with the developed tools, and used as reference for general comparison. Optimized airfoil geometries, that either minimize noise emission or favour aerodynamic performance were obtained and classes of aero-acoustically optimized airfoils were identified in the resulting Pareto fronts. Results show that very good aerodynamic performance can be achieved with negligible increase in noise levels.
Keywords: Airfoil design, Wind turbines, Aero-acoustics, Multi-objective optimization, Multidisciplinary optimization
Keywords: Airfoil design, Wind turbines, Aero-acoustics, Multi-objective optimization, Multidisciplinary optimization
Martins, P.
Aircraft maintenance scheduling optimization for the Fokker 100 fleet Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2012.
@mastersthesis{Martins:2012:MSc,
title = {Aircraft maintenance scheduling optimization for the Fokker 100 fleet},
author = {P. Martins},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Martins_2012.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Martins_2012_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=557443, Catalog IST},
year = {2012},
date = {2012-02-01},
urldate = {2012-02-01},
pages = {57},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {The strategies pursued by airline companies are based on strong plans for drastic cost containment. The aviation industry has become increasingly challenging, being the maintenance costs and reliability control two main points that contribute strongly to the success of an airline company. The concept of optimization is present in all sectors in this industry and closely related to the systematization concept of the Aircraft Maintenance Plan (AMP). This thesis report aims at studying the effects of the inclusion of inspections provided with an interval of 4000 Flight Hours in the Block A Check and afterwards, proceeding with the equalization of this new Aircraft Maintenance Plan with applicability to the Fokker 100 aircraft. With this purpose, this work was integrated in Portugália Airlines company. This work has started with an organization of the database regarding the Fokker 100’s AMP which consisted of including missing information concerning the aircraft tools and materials needed to perform maintenance tasks. Subsequently, after the analysis of the several variables, an application based on Visual Basic for Applications programming language was developed. The methodology used was based on the assumption of combining the largest number of tasks with similar intervals and, when possible, collect them based on shared common access panels. From a temporal point of view, the results were reasonable reflecting a benefit simultaneously on the implementation of the two inspection types presented above, with a 2.5% time gain, as well as the optimization of time generated regarding the ground time of the aircraft through the equalization of the AMP.
Keywords: Maintenance plan optimization, Fokker 100, Equalization, Portugália Airlines},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
The strategies pursued by airline companies are based on strong plans for drastic cost containment. The aviation industry has become increasingly challenging, being the maintenance costs and reliability control two main points that contribute strongly to the success of an airline company. The concept of optimization is present in all sectors in this industry and closely related to the systematization concept of the Aircraft Maintenance Plan (AMP). This thesis report aims at studying the effects of the inclusion of inspections provided with an interval of 4000 Flight Hours in the Block A Check and afterwards, proceeding with the equalization of this new Aircraft Maintenance Plan with applicability to the Fokker 100 aircraft. With this purpose, this work was integrated in Portugália Airlines company. This work has started with an organization of the database regarding the Fokker 100’s AMP which consisted of including missing information concerning the aircraft tools and materials needed to perform maintenance tasks. Subsequently, after the analysis of the several variables, an application based on Visual Basic for Applications programming language was developed. The methodology used was based on the assumption of combining the largest number of tasks with similar intervals and, when possible, collect them based on shared common access panels. From a temporal point of view, the results were reasonable reflecting a benefit simultaneously on the implementation of the two inspection types presented above, with a 2.5% time gain, as well as the optimization of time generated regarding the ground time of the aircraft through the equalization of the AMP.
Keywords: Maintenance plan optimization, Fokker 100, Equalization, Portugália Airlines
Keywords: Maintenance plan optimization, Fokker 100, Equalization, Portugália Airlines
Cadete, B.
Aero-structural optimization of sailplane wings Masters Thesis
Portuguese Air Force Academy, Sintra, Portugal, 2011.
@mastersthesis{Cadete:2011:MSc,
title = {Aero-structural optimization of sailplane wings},
author = {B. Cadete},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Cadete_2011.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Cadete_2011_ExtendedAbstract.pdf, Extended abstract PDF},
year = {2011},
date = {2011-12-01},
pages = {106},
address = {Sintra, Portugal},
school = {Portuguese Air Force Academy},
abstract = {This thesis presents a framework for the multi-disciplinary design analysis and optimization of sailplane wings. Its objective was to run an aero-structural optimization on sailplane wings. A literature review on the studies from various authors is presented and used as base for the establishment of the multi-disciplinary optimization (MDO) framework. The approach used employs a multi-disciplinary feasible architecture. The geometric parametrization method employed follows a free-form deformation method. To solve the aero-structural analysis problem, a panel method coupled with a finite-element solver is implemented in the framework, tested and used for the MDO of sailplane wings. The coupled non-linear system is solved using an approximate Newton-Krylov approach. The optimization algorithm uses sequential quadratic programming. Two study cases on sailplane wings are exploited within the MDO framework: a semi-tapered wing and a real sailplane wing, based on the L-23 Super Blanik from the Portuguese Air Force. Single disciplinary analysis assess the capabilities of the disciplinary modules of the framework. Results are presented for a drag minimization problem using aerodynamic and multi-disciplinary optimizations. They reveal important trade-offs between disciplinary optimum and multi-disciplinary optimum at the preliminary design stage.
Keywords: Aero-structural problem, Multi-disciplinary optimization, Free-form deformation method, Panel method, Finite-element method, Sailplane wings},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
This thesis presents a framework for the multi-disciplinary design analysis and optimization of sailplane wings. Its objective was to run an aero-structural optimization on sailplane wings. A literature review on the studies from various authors is presented and used as base for the establishment of the multi-disciplinary optimization (MDO) framework. The approach used employs a multi-disciplinary feasible architecture. The geometric parametrization method employed follows a free-form deformation method. To solve the aero-structural analysis problem, a panel method coupled with a finite-element solver is implemented in the framework, tested and used for the MDO of sailplane wings. The coupled non-linear system is solved using an approximate Newton-Krylov approach. The optimization algorithm uses sequential quadratic programming. Two study cases on sailplane wings are exploited within the MDO framework: a semi-tapered wing and a real sailplane wing, based on the L-23 Super Blanik from the Portuguese Air Force. Single disciplinary analysis assess the capabilities of the disciplinary modules of the framework. Results are presented for a drag minimization problem using aerodynamic and multi-disciplinary optimizations. They reveal important trade-offs between disciplinary optimum and multi-disciplinary optimum at the preliminary design stage.
Keywords: Aero-structural problem, Multi-disciplinary optimization, Free-form deformation method, Panel method, Finite-element method, Sailplane wings
Keywords: Aero-structural problem, Multi-disciplinary optimization, Free-form deformation method, Panel method, Finite-element method, Sailplane wings
Carli, S.
Closed loop development tests of an evaporating experiment for the International Space Station Fluid Science Laboratory Masters Thesis
Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal, 2011.
@mastersthesis{Carli:2011:MSc,
title = {Closed loop development tests of an evaporating experiment for the International Space Station Fluid Science Laboratory},
author = {S. Carli},
url = {https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Carli_2011.pdf, Thesis PDF
https://mdo.tecnico.ulisboa.pt/wp-content/uploads/publications_MScThesis_Carli_2011_ExtendedAbstract.pdf, Extended abstract PDF
https://catalogo-ist.biblioteca.ulisboa.pt/cgi-bin/koha/opac-detail.pl?biblionumber=549276, Catalog IST},
year = {2011},
date = {2011-09-01},
urldate = {2011-09-01},
pages = {99},
address = {Lisboa, Portugal},
school = {Instituto Superior Técnico, Universidade de Lisboa},
abstract = {CIMEX-1 (Convection and Interfacial Mass Exchange) is a microgravity research project foreseen to be carried out onboard the Columbus Module of the International Space Station. The project is sponsored by the European Space Agency and EADS Astrium is the prime contractor for developing the experiment. The main scientific purpose of the mission is studying mass transfer processes through interfaces and their coupling with the surface tension driven instabilities that affect mass and energy transfer. The experiment takes place in a cell, in which the liquid interface allows evaporation to take place through a flow of inert gas. The system is equipped with a liquid and gas closed loop in order to avoid the limitations caused by the use of consumables. The assignments which were carried out were building, testing and analyzing a breadboard setup which is meant to verify the closed loop and the components operability, as it has the same functional characteristics of the flight model. Due to the decision of changing the evaporating fluid from Ethanol to HFE-7100, the system behavior and operability had to be tested. A test campaign took place in June 2011 to collect experimental data and to verify the operability of the CIMEX-1 foreseen parameters range with the new fluid. Moreover, the test campaign aimed to assess the properties of new essential components like the liquid pump and the anti-wetting micro groove. This work was carried out in the TO-52 department of Astrium Space Transportation in Friedrichshafen, Germany.
Keywords: CIMEX, Anti-Wetting, Closed loop, Columbus, Condenser, Evaporator, Flow meter, Gas concentration sensor, Pressure controller},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
CIMEX-1 (Convection and Interfacial Mass Exchange) is a microgravity research project foreseen to be carried out onboard the Columbus Module of the International Space Station. The project is sponsored by the European Space Agency and EADS Astrium is the prime contractor for developing the experiment. The main scientific purpose of the mission is studying mass transfer processes through interfaces and their coupling with the surface tension driven instabilities that affect mass and energy transfer. The experiment takes place in a cell, in which the liquid interface allows evaporation to take place through a flow of inert gas. The system is equipped with a liquid and gas closed loop in order to avoid the limitations caused by the use of consumables. The assignments which were carried out were building, testing and analyzing a breadboard setup which is meant to verify the closed loop and the components operability, as it has the same functional characteristics of the flight model. Due to the decision of changing the evaporating fluid from Ethanol to HFE-7100, the system behavior and operability had to be tested. A test campaign took place in June 2011 to collect experimental data and to verify the operability of the CIMEX-1 foreseen parameters range with the new fluid. Moreover, the test campaign aimed to assess the properties of new essential components like the liquid pump and the anti-wetting micro groove. This work was carried out in the TO-52 department of Astrium Space Transportation in Friedrichshafen, Germany.
Keywords: CIMEX, Anti-Wetting, Closed loop, Columbus, Condenser, Evaporator, Flow meter, Gas concentration sensor, Pressure controller
Keywords: CIMEX, Anti-Wetting, Closed loop, Columbus, Condenser, Evaporator, Flow meter, Gas concentration sensor, Pressure controller