HYDRODYNAMIC DAMPING OF A CYLINDER IN STILL WATER AND IN A TRANSVERSECURRENT

Laboratory measurements are presented of the hydrodynamic damping of s mooth and roughened circular cylinders in still water and in the prese nce of a transverse current at a Stokes parameter beta 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 consta nt amplitude to the elastically-mounted submerged cylinder, and observ ing its response. For the smooth cylinder, levels of hydrodynamic damp ing in still water were found to be approximately twice those predicte d by Wang. Below a certain velocity, a transverse current had very lit tle effect on the damping, but over a range of stronger currents it ju mped to a new constant level about 70% greater than the still water va lue. A surface roughness of k/d = 0.00079 generated an increase in dam ping of about 35% in still water, but only 5% in a current. (C) 1998 E lsevier Science Ltd. All rights reserved.