Flow-induced vibration marine current energy harvesting using a centrally-pivoted cylinder

The phenomenon of vortex-induced vibration (VIV) for elastically restrained cylindrical structures in cross-flows is relatively well investigated. The utility of this mechanism in harvesting energy from marine current and tidal flows is however arguably still in its infancy. With relatively few moving components, a flow-induced vibration based energy conversion device augers low complexity compared to the commonly employed turbine design. Despite the interest in this concept, a practical device has yet to emerge. It is desirable for optimal system performance to design for a very low mass or mass moment of inertia ratio. The device operating range in particular is maximised below the vortex-induced vibration critical point where an infinite resonant response region is realised. An unfortunate consequence of this requirement is large buoyancy forces that need to be mitigated by gravity-based, suctioncaisson or anchor mooring systems. The focus of this paper is the testing of a novel VIV marine current energy-harvesting configuration that utilises a centrally-pivoted horizontal cylinder. The results of experimental investigations, utilising the University of Wollongong fluid mechanics laboratory towing tank, are analysed and presented. A reduced velocity test range of 0 to 27 was covered. Power take-off (PTO) damping ratios spanning from 0.041 to 0.392 were examined in order to determine the optimal conditions and hence the maximum device energy conversion efficiency