Active Control of a Reduced Scale Riser Undergoing Vortex-Induced Vibrations

This article concerns the use of an active control applied to a reduced scale riser undergoing vortex-induced vibrations (VIV). The control system relies upon the fact that a flexible structure undergoing VIV oscillates at frequencies corresponding to the structure resonant modes. These experiments were carried out in a recirculating water channel at IFP. For control design, the structure dynamic behavior is approximated by the dynamic behavior of its most excited mode. This is achieved through modal analysis and leads to a simple linear second order system. Its input is a displacement at the structure top end; its output is the structure displacement of a point away from the top end. The input is computed to attenuate the vibrations associated the most excited mode. This control strategy has been tested on a reduced scale experiment. These results are shown to agree with numerical results obtained on a phenomenological model. Both suggest a VIV reduction about 30%.