Numerical study of vortex-induced vibration of pivoted cylinders

Abstract

This study was motivated by an idea of harvesting abundant renewable energy in the ocean currents. In order to capture the energy in the ocean currents, vortex-induced vibration (VIV) is exploited and a new configuration of a cylinder is considered. In particular, we investigate numerically the effect of the cross-sectional shape of a cylinder on VIV, when the cylinder is pivoted at a point in the wake. Three different cross-sectional shapes are tested in this study; their ratios of the minor axis to the major axis are 0.6, 0.8 and 1. We compare numerically hydrodynamic drag and lift forces on the stationary elliptic cylinders. The VIV simulations of these three cylinders show that two ellipses with smaller ratios have two times larger displacements than the circular cylinder with ratio I. Such a superior performance of the elliptic cylinders is observed over a wide range of reduced velocities. A simplified model of a pivoted cylinder is analyzed to confirm that drag forces contribute positively to excitation torques and consequently VIVs. In order to take advantage of the drag forces which work favorably on VIVs, the pivot should be placed in the wake. (C) 2014 Elsevier Ltd. All rights reserved.