Suppression of limit cycle oscillations in an aeroelastic system using robust and adaptive control
In this thesis control systems are designed for the flutter control of nonlinear aeroelastic system. The aeroelastic model describes the plunge and pitch motion of a wing. The model includes plunge and pitch nonlinearities, and has both leading and trailing edge control surfaces for the purpose of control. First the existence of limit cycle oscillations and domain of stability (attraction) of prototypical aeroelastic wing sections with pitch structural nonlinearity using the describing function method is determined. The model includes unsteady aerodynamics based on Theodorsen's theory. The dual-input describing functions of the nonlinearity are used for the limit cycle analysis. Interestingly it is found that flutter can exist not only when the origin in the state space is unstable but also when it is asymptotically stable if the initial conditions are not small. For such cases, an estimate of the domain of stability surrounding the origin in the state space is computed in which flutter cannot exist. The Nyquist criterion is used to establish the stability of the limit cycle and it is shown that unstable as well as the stable limit cycles exist when the origin is exponentially stable; Secondly, an adaptive and a neural controller is designed with structural nonlinearity using leading- and trailing-edge control surfaces. (Abstract shortened by UMI.).
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