Control Law Synthesis for Active Flutter Suppression Using Optimal Control Theory

Abstract

This paper describes a study investigating the use of optimal control theory for the synthesis of an active flutter-suppression control law. For an example design application, a high-aspect-ratio cantilever wind-tunnel wing model is considered. The structural dynamics are represented by analytically computed natural frequencies and mode shapes. The three-dimensional unsteady aerodynamic forces for oscillatory motion are computed employing the doublet-lattice technique. With the aid of finite-order approximating functions for representing the aerodynamic forces in the time domain, the equations are written in the standard state vector form. Linear optimal control theory is then applied to find particular sets of gain values which minimize a quadratic cost function of the states and controls. These control laws are shown to increase the flutter dynamic pressure by at least 50% at Mach numbers 0.7 and 0.9. The closed-loop system's control surface activity in a gust environment is also examined.