Model Reference Adaptive Control Laws: Application to Nonlinear Aeroelastic Systems

Nonlinear Aeroelastic Control has been a research topic of great interest for the past few decades. Dierent approaches has been attempted aiming to obtain better accuracy in the model dynamics description and better control performance. As far as the aeroelastic mathematical model is concerned, the scientic world converged in the use of a bi-dimension, two degree of freedom, plunging and pitching, wing section model, of which the bigger advantages are to be reproducible experimentally with an appropriate wind tunnel apparatus and to allow LCO (Limit Cycle Oscillation) exhibition at low values of wind speed, facilitating parametric studies of the nonlinear aeroelastic system and its control architecture. A parametric analysis of the linearized system, typical of aircraft ight dynamic studies, is employed to verify and validate the model dynamic properties dependency, focusing in particular to the eect of stiness reduction as means of failure simulation. In fact, despite of the recent years ourishing literature on aeroelastic adaptive controls, there is a noted lack of robustness and sensitivity analysis with respect to structural proprieties degradation which might be associated with a structural failure. Structural mode frequencies and aeroelastic response, including Limit Cycle Oscillations (LCOs) characteristics, are signicantly aected by changes in stiness. This leads to a great interest in evaluating and comparing the adaptation capabilities of dierent control architectures subjected to large plant uncertainties and unmodeled dynamics. Motivated by the constantly increasing diusion of the new L adaptive control theory, developed for the control of uncertain non-autonomous nonlinear systems, and by the fact that its application to aeroelasticity is in its infancy, a deep investigation of this control scheme properties and performance drew our attention. The new control theory is conceptually similar to the Model Reference Adaptive Control (MRAC) theory to which has often been compared indeed for performance evaluation purpose. In this dissertation, a comprehensive analysis of the new control theory is obtained by performance evaluation and comparison of four dierent control schemes, two MRAC and two L 1 , focusing the attention on the states and control input time response, adaptive law parameters' convergence, transient evolution and fastness, and robustness in terms of tolerance of uncertainties in o-design conditions. The objective is pursued by re- writing the aeroelastic model nonlinear equations of motion in an amenable form to the development of the four dierent control laws. The control laws are then derived for the appropriate class of plant which the system belongs to, and design parameter obtained, when necessary, following the mathematical formulation of the control theories developers. A simulation model is employed to carry out the numerical analysis and to outline pros and cons of each architecture, to obtain as nal result the architecture that better ts the nonlinear aeroelastic problem proposed. This methodology is used to guarantee a certain robustness in controlling a novel actuation architecture, developed for utter suppression of slender/highly exible wing, based on a coordinated multiple spoiler stripe, located at fteen percent of the mean aerodynamic chord. The control actuation system design, manufacturing and experimental wind tunnel test is part of the dissertation. Two dierent experimental setup are developed for two dierent purpose. First, a six-axis force balance test is carried out to validate the numerical aerodynamic results obtained during the validation process, and to collect the aerodynamic coecient date base useful for the development of the simulation model of the novel architecture. The second experimental apparatus, is a two degree of freedom, plunging/pitching, system on which the prototyped wing section is mounted to obtain LCO aeroelastic response during wind tunnel experiment. The nonlinear aeroelastic mathematical formulation is modied to take into account of the novel actuation architecture and, coupled with the more robust MRAC control laws derived for the previous model, serves as benchmark for properties assessment of the overall architecture, for utter suppression. The novel control actuation architecture proposed, is successfully tested in wind tunnel experimentation conrming the validity of the proposed solution. This dissertation provides a step forward to the denition of certain MRAC control schemes properties, and together provides a novel actuation solution for utter suppression which demonstrates to be a viable alternative to classical leading and/or trailing-edge ap architecture or to be used as redundancy to them.