Comparison of SDRE and SMC control approaches for flutter suppression in a nonlinear wing section

The effect of flutter phenomenon on dynamic stability of aeroelastic systems is a main interest of recent studies. Among many approaches for suppression of flutter, in this paper two control strategies are introduced and their results are compared. State-Dependent Riccati Equation (SDRE) approach and Sliding Mode Control (SMC) approach are used for stabilization of an Aeroservoelastic system with structural nonlinearities at subsonic flight speed regime. These two control techniques suppress flutter as well as reduce the vibration level in sub-critical and post-flutter speeds. The developed aeroservoelastic model describes the pitch and plunge motion of a wing section associated with a single control surface. For state-space representation of the model, the measured pitch angle, plunge displacement and their derivatives are allocated as state vector, and control surface deflection as input command. For a given initial state conditions, two modes of open loop and closed loop control system are simulated. It is shown that, with a nonlinear structure in subsonic regime, the open loop system is unstable and Limit Cycle Oscillations (LCOs) are generated. However, the closed loop system is asymptotically stable and converges to the origin. Therefore, the proposed approaches have a good performance on suppressing flutter and LCOs. However, comparing between the two approaches shows that SMC method requires larger control input, as well as a shorter time response with respect to SDRE method.