The fundamentals of actively controlling vortex-induced vibration of flexible cylinders using the theory of robust controls are presented. A variable structure robust controller is devised to reject the persistent disturbances produced by the periodic shedding of vortices. In addition, the controller is capable of accommodating changes in the structural parameters of the cylinders and the non-linearities resulting from fluid-structure interactions.;Finite element-based model of the vortex-induced vibrations of flexible cylinders is presented using the wake-oscillator approach. The model is coupled with the time dependent flow-induced forcing function and integrated with the variable structure-sliding mode control strategy. The mathematical model developed is validated experimentally by testing various prototypes of flexible cylinders in a low-speed wind tunnel under various flow conditions. The effect of varying the design parameters of the controller and the cylinders on the attenuation of the vortex-induced vibrations is monitored. Emphasis is placed in this research effort on demonstrating the effectiveness of the variable structure-sliding mode controller in suppressing vortex-induced vibration of flexible cylinders.
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