On Some Problems In Active Flutter Suppression

In recent years, the active flutter suppression by changing the deflection of airfoil's control surfaces is expected to be used in engineering. With the progress of studies on active flutter suppression of various airfoils systems, the problems of system saturation, non-linear feedback and the uncertainty of system parameters brought new challenges to the traditional control theory. The thesis presents theoretical and numerical studies on the control of a typical two-dimensional wing section with the actuator saturation, the adaptive feedback control of a nonlinear aeroelastic wing section with leading- and trailing-edge control surfaces, and the sub-optimal/μcontrol of a high-aspect-ratio (HAR) straight wing with two actuators. The main progresses and contributions of the thesis are as follows.Chapter 2 focuses on the control law design of an airfoil model with system saturation. First the aeroelastic system is changed into canonical modal and then is decoupled into a planar unstable subsystem and a multi-dimensional stable subsystem. Then, the largest domain of attraction of the unstable subsystem is constructed though a time-reversed system. Next, the saturation control law designed by combined unstable subsystem's domain of attraction and original canonical system's.Last, control performance is demonstrated by numerical simulations.Chapter 3 presents the adaptive control method of a nonlinear aeroelastic airfoil with leading-and trailing-edge control surfaces. The dynamics equation is established by considering the uncertainty of aerodynamic loads. Feedback linearization and adaptive control method based on the Lyapunov stability are used to get a controller. Numerical simulations verify the good performance of the flutter suppression method.Chapter 4 deals with the active flutter suppression of a high aspect ratio (HAR) straight wing through the use of two non-continuous control surfaces. The chapter presents the dynamic equation of the wing section and control surface subject to Theodorsen's aerodynamic load, and the aerodynamic equation of the whole system based on the strip theory. The flutter critical speed and deflection amplitude of the wing are analyzed, and a sub-optimal control law is designed. The numerical simulations show that the sub-optimal control law works well for suppressing the flutter of the wing and increased the flutter critical speed by 12.3%.Chapter 5 presents the robust flutter suppression of the HAR straight wing bases on the aeroelastic dynamics equation established in chapter 4. Theμcontroller is designed when the damping and stiffness uncertainties in pitch directions, as well as the modeling error of the actuator are taken into consideration. The numerical simulations show that theμcontroller is able to suppress the flutter of the HAR straight wing effectively and increased the flutter critical speed by 9.9 %.