Modular adaptive control of a nonlinear aeroelastic system

The paper treats the question of adaptive control of prototypical aeroelastic wing sections with structural nonlinearity. The chosen dynamic model describes the nonlinear plunge and pitch motion of a wing. The model has both the plunge and pitch structural nonlinearities, and a single control surface is used for the purpose of control. It is assumed that only the sign of the coefficient of the control input and the lower bound on its absolute value are known, and the remaining parameters of the model are completely unknown. Modular adaptive control systems based on estimation-based design are derived for the control of the pitch angle and the plunge displacement. Unlike the direct adaptive controllers available in the literature, an input-to-state stabilizing control law is used herein. This control law accomplishes input-to-state stability with respect to parameter estimation error treated as a disturbance input. The control system includes a passive identifier (an observer and an adaptation law) for the parameter estimation. In the closed-loop system asymptotic stabilization of the plunge and pitch motion is accomplished. Simulation results are presented to show that the modular adaptive control systems accomplish flutter suppression in spite of the large uncertainties in the system. Simulation results also show that the closed-loop system without parameter adaptation fails to suppress flutter, but the input-to-state-stabilizing controller is effective in keeping the pitch and plunge responses bounded.