Aeroservoelastic Control of a Highly Coupled Dynamic System with Nonlinear Additions
- Autores: Álvaro Muñoz Medina
- Directores de la Tesis: Pablo García-Fogeda Núñez (dir. tes.)
- Lectura: En la Universidad Politécnica de Madrid ( España ) en 2025
- Idioma: inglés
- Tribunal Calificador de la Tesis: José Manuel Perales Perales (presid.), Rubén Moreno Ramos (secret.), David Quero Martín (voc.), Rauno Cavallaro (voc.), Jesús Gonzalo de Grado (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería Aeroespacial por la Universidad Politécnica de Madrid
- Calificación: Sobresaliente Cum Laude
- Materias:
- Enlaces
- Tesis en acceso abierto en: Archivo Digital UPM
- Resumen
The increasing use of high-aspect-ratio wings in UAVs has opened new opportunities in long-endurance and high-altitude operations, but has also introduced significant aeroelastic challenges. The structural flexibility inherent to these aircraft makes them particularly vulnerable to aeroelastic instabilities. To address these issues, the application of active flutter suppression (AFS) techniques has gained growing interest, offering the potential to extend flight envelopes and improve safety margins in flexible aircraft.
This thesis presents the modelling, simulation, and control design of an AFS system based on an H-infinity controller applied to a high-aspect-ratio aircraft. The research focuses on developing a complete time-domain aeroservoelastic simulator and using it to synthesise and test a robust stabilisation strategy. The aircraft model used as a case study was designed to exhibit representative flexible behaviour while remaining within the linear deformation range.
The time simulator is constructed from first principles and integrates structural, aerodynamic and actuator models. The structural dynamics are modelled using a finite element stick approach, and an original algorithm is developed to explicitly preserve rigid-body modes while expressing the entire system in modal coordinates. Aerodynamic loads are derived in the Laplace domain for subsonic, transonic, sonic, and supersonic regimes using two-dimensional aerodynamic theories. These loads are projected onto the modal basis and converted to the time domain through Rogers rational function approximation (RFA). A reduced basis is introduced to mitigate the numerical stiffness caused by the large number of augmented aerodynamic states. Additional contributions include the modelling of actuator lags and simplified thrust dynamics.
A nonlinear state-space model is formulated and integrated using stiff numerical solvers. Trimmed flight conditions are computed, and the system is linearized around the equilibrium point to enable controller design. The aeroelastic poles evolution reveals that the flutter mechanism involves a coupling between the antisymmetric torsional mode and the roll mode.
In order to stablish the feedback loop, first the optimal sensor placement problem is solved using modified observability Gramians for unstable systems, and a Luenberger observer is developed to estimate modal states from sensor data. Then, a strongly stabilising H-infinity controller is synthesised, designed to independently address the symmetric and antisymmetric subsystems.
The resulting controller is implemented in the nonlinear time-domain simulator and is shown to suppress flutter effectively. The system maintains attitude controllability, testing its response through a parallel autopilot at speeds beyond the original flutter boundary, demonstrating the feasibility of active stabilisation without sacrificing control authority.
In conclusion, this thesis proposes a comprehensive framework for the analysis and control of flexible aircraft, highlighting the importance of realistic physical modelling, sensor optimisation and robust controller synthesis. The formulation of the aerodynamic loads directly in the Laplace domain and the implementation of strong stabilisation methods represent key contributions to the state of the art in aeroservoelastic control.
