Flow Induced Vibration and Energy Extraction of an Equilateral Triangle Prism at Different System Damping Ratios

The flow induced vibration and energy extraction of an equilateral triangle prism elastically mounted in a water channel are investigated experimentally at different system damping ratios ζ total with the constant oscillating mass M osc and system stiffness K . A power take-off system with a variable damping function is developed. The translation-rotation equation of the vibration system deduced in the study indicates that the total oscillating mass includes the material mass, and the equivalent mass due to the rotation of the gears and rotor. Besides, increasing load resistance can result in a decrease in ζ total when K and M osc remain unchanged. The prism experiences, in turn, soft galloping, hard galloping 1 and hard galloping 2 with increasing ζ total . As ζ total increases up to 0.335, only the vortex-induced vibration is observed because the extremely high ζ total prevents the prism from galloping. The response amplitude decreases with the increasing ζ total . In addition, higher ζ total promotes the galloping to start at a higher reduced velocity. The galloping characteristics of the prism, including large amplitude responses in an extremely large range of flow velocities, excellent vibration stationarity, and steady vibration frequencies, are beneficial for improving energy conversion. The prism can extract hydraulic energy for the flow velocity U > 0.610 m/s. The harnessed power P out and the energy conversion efficiency η out increase with increasing ζ total in the galloping zone. The maximum P out and η out reach 53.56 W and 40.44%, respectively. The optimal system damping ratio for extracting energy is the maximum system damping ratio that the prism can overcome to experience stable galloping.