Control of Unsteady Aeroelastic System via State-Dependent Riccati Equation Method

Abstract

A nonlinear control system for the flutter control of an aeroelastic system with unsteady aerodynamics is designed. The model describes the plunge and pitch motion of a wing. In this model both plunge and pitch structural nonlinearities are included. A single control surface is utilized for the flutter control. For the purpose of design, it is assumed that there exists a specified hard magnitude constraint on the control input. For the synthesis of the controller, only the plunge displacement, pitch angle, and control-surface deflection are measured. The control system design is based on the state-dependent Riccati equation method. A slack variable is introduced to transform the constrained control problem into an unconstrained problem and then a suboptimal nonlinear control law is designed. An observer is constructed to estimate the unavailable state variables of the system for the synthesis of the control system. In the closed-loop system, including the observer and nonlinear controller, the zero state is (locally) asymptotically stable, and the state vector asymptotically converges to the origin. Simulation results for various flow velocities and elastic axis locations are presented, which show that the designed control system is effective in flutter suppression.