Hydrodynamic damping of a large scale surface piercing circular cylinder in planar oscillatory motion

Measurements of the hydrodynamic damping acting on a vertical, 0.5 m diamet er cylinder in planar oscillatory motion at Stokes parameter, beta, up to 1 .4 x 10(5) are presented. The results are also shown as a variation of drag coefficient, C-d, with Keulegan-Carpenter number, KC, where the range of K C numbers studied is from 1 x 10(-3) to 1. The experiments were carried out in the Delta Flume at Delft Hydraulics Laboratories in Holland and the cyl inder was mounted from a pendulum suspension system. The hydrodynamic dampi ng is the sum of radiation damping, due to gravity waves generated by the c ylinder piercing the water surface, and viscous damping. A frequency-domain solution from Dalrymple & Dean (1972) is used to predict the radiation dam ping. An estimate of the viscous damping is then obtained by subtracting th e predicted radiation damping from the measured hydrodynamic damping. Resul ts for the viscous damping derived in this way are found to be close to tho se expected from experimental studies carried out by Bearman & Russell (199 6) and Chaplin & Subbiah (1996) to measure viscous damping on a submerged c ylinder. (C) 2001 Academic Press.