Mitigating vortex-induced vibration by acceleration feedback control

Abstract

Vortex-induced vibration is a common phenomenon observed in many engineering applications and it is detrimental to the performances and health of the system. It is, therefore, imperative for engineers to make suitable design modifications or arrange for some type of control device to mitigate such oscillations. In this paper, the performance of the acceleration feedback control is compared with that of the simple passive vibration absorber. The effect of time-delay in the feedback loop is also investigated. The acceleration of the primary system is measured and passed through a second-order compensator. The active absorber is designed by setting the filter frequency same as the natural frequency of vibration and the optimum filter damping is numerically obtained. Nonlinear analysis is performed using the Describing Function method and the results are validated using direct numerical simulation performed in MATLAB Simulink. In the present paper, vortex shedding frequencies are selected from two different regions, one with vortex shedding frequency less than the natural frequency of the system and other having vortex shedding frequency higher than the natural frequency of the system. It is observed that the acceleration feedback control can effectively reduce the amplitude of vibration to a great extent. It is also observed that the amplitude of the system changes marginally (up to a certain value of time-delay) in the pre-locking and locking region. However, the effect of time-delay in post-locking zone is detrimental. Beyond a certain value of the time-delay, the amplitude becomes large and even the system may become unstable.