Robust Aeroelastic Control of Lifting Surfaces with Uncertainty via Multi-Objective Synthesis

A GREAT deal of research activity devoted to the aeroelastic active control and flutter suppression of flight vehicles has been accomplished so far [1]. A number of recent contributions related to the active control of an aircraft wing are discussed at length in [2-4]. Digital adaptive control of a linear aeroservoelastic model [5], the a method for robust aeroservoelastic stability analysis [6], gain scheduled controllers [7], and neural and adaptive control of a transonic wind-tunnel model [8,9] are only a few of the latest active control methods that have been developed. Linear control theory, the feedback linearizing technique, and adaptive control strategies have been derived to account for the effect of nonlinear structural stiffness [10]. A model reference variable structure adaptive control system for plunge displacement and pitch angle control has been designed using bounds on uncertain functions [11]. This approach yields a high gain feedback discontinuous control system. In [12-14], an adaptive design method for flutter suppression has been adopted while using measurements of either and both the pitching and plunging variables. To supplement the bulk of knowledge of the robust aeroelastic control of lifting surfaces present in the literature, in this paper a linear matrix inequality (LMI) approach for the multi-objective synthesis is considered. A multi-objective state-feedback control law implementing mixed control strategy with a pole placement constraint will be implemented and some of its performance characteristics will be highlighted. The design objective to be achieved is a mix of 1-1,;' performance and H2 performance satisfying constraints on the closed-loop pole locations in the presence of model uncertainties. The traditional 3-degree-offreedom aeroelastic model for the control of a thin airfoil in incompressible flow is used for such purpose.