| Recent years have witnessed considerable attention paid to the semi-active control for structural vibration, especially the semi-active control based on MR (Magneto-Rheological) dampers. Such a kind of technique features simple mechanism, low energy requirement, high robustness and flexible control algorism. It is quite natural, hence, to develop the proper semi-active control based on MR dampers to suppress the flutter of aeroelastic systems in aerospace engineering. The primary objective of this study is to develop the semi-active flutter control for airfoil systems. The study starts with the new concept of stepped MR damper, of which the restoring torque can be adjusted by changing the area of magnetic field or the number of powered coil sets inside, in Chapter 2. Then, the chapter outlines the design procedure of a novel rotational MR damper of shear mode for the semi-active flutter control of the airfoil with aileron. Chapter 3 presents the simplified mathematical model for the stepped MR damper and the theoretical analysis based on the theory of rheology so as to establish the relation between the number of powered coils and the restoring torque for the design of the MR damper. To provide a more accurate model for the control simulation, the dissertation gives the relation between the restoring torque and the relative angular velocity of the MR damper through the use of experimental modeling based on a BP neural network. Chapter 4 focuses on the semi-active flutter control for an aeroelastic system of three degrees of freedom, including a two-dimensional airfoil section with a control surface and a stepped MR damper installed on the aileron rotation axis. The numerical simulations based on the Theodoson's aerodynamic load showed that the MR damper was able to increase not only the structure damping, but also the critical flutter speed by at most 53.85% when one of the four semi-active control strategies proposed was put into use. Chapter 5 deals with the semi-active flutter control of a high-aspect-ratio (HAR) wing-aileron system through the use of multiple MR dampers mounted on the hinge axis along span-wise. The chapter presents how to establish the dynamic equation of the wing-aileron section of unit span subject to Theodorsen's aerodynamic load, and how to reach the aerodynamic equation of the whole system through the use of the strip theory. The numerical simulations showed that the semi-active control strategies based on multiple MR dampers worked well for suppressing the flutter of an entire HAR wing with aileron and increased the flutter critical speed by 17.24%. Chapter 6 presents a wind tunnel test of the aeroelastic system under semi-active flutter control to testify the theoretical and numerical results. In the study, the test rig includes the airfoil section with an aileron and a stepped MR damper installed, the measurement system, the signal processing system and the semi-active controller with amplification circuit for the stepped MR damper. The control system increased the flutter critical speed by at most 26% using various control straties under different air flow speed. The experimental results got an agreement with the simulation results, demonstrating a profound increase in the critical flutter speed of the whole aeroelastic system in the wind tunnel test.
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