Hydrodynamic damping of a cylinder in still water and in a transverse current

Abstract

Laboratory measurements are presented of the hydrodynamic damping of smooth and roughened circular cylinders in still water and in the presence of a transverse current at a Stokes parameter β of 166 900 and at Keulegan Carpenter numbers in the range 0.001–0.2. The experiments were carried out by applying a known external harmonic force at constant amplitude to the elastically-mounted submerged cylinder, and observing its response. For the smooth cylinder, levels of hydrodynamic damping in still water were found to be approximately twice those predicted by Wang. Below a certain velocity, a transverse current had very little effect on the damping, but over a range of stronger currents it jumped to a new constant level of about twice the still water value. A surface roughness of k/ d=0.00079 generated an increase in damping of about 35% in still water, but only 5% in a current.