Wave-drift damping in slow surge–sway–yaw coupling motions of a cylinder array

Abstract

Both experimental and theoretical investigations were made on wave-drift damping of a moored array of circular cylinders which undergo slow oscillations in horizontal modes, i.e., surge, sway, and yaw, due to the nonlinear excitation of ocean waves. Detail descriptions of the experimental arrangement and methods of processing the measured data are given. The model is restrained from the linear responses to wave excitations. An assumption of a quasisteady state for each position of rotation is made in data processing for the yaw mode of slow motion. To calculate wave-drift damping, the slow oscillations are approximated by the corresponding steady motions. The velocity potential is expanded into perturbation series based on two small parameters that measure wave slope and the velocity of steady flow, respectively. Wave-drift forces (moment) are calculated by the far-field method. Some new treatments to deal with the integral over the free surface are presented to improve the convergence and accuracy. The results of calculations and experiments are compared and satisfactory agreement is observed, which verifies the theory.