An experimental and analytical study of the effects of wave grouping on the slowly varying drift oscillation of a floating rectangular barge

Abstract

An experimental study of the effects of wave grouping on the slowly varying drift oscillations of a floating moored rectangular barge has been presented. The work incorporates existing techniques to simulate wave groups with those that predict the slowly varying drift response of a moored model. The analytical model assumes that each pair of frequencies in a discrete wave spectrum will give rise to a regular wave group. Each of these regular wave groups will produce a low frequency force that is proportional to the product of the wave amplitudes in the group and varies at a frequency equal to the difference in the frequency pair. Furthermore, this low frequency force is related to the envelope of the regular wave group by a constant phase angle and the resultant force is determined by superposition of these regular slow-varying forces. Subsequently, the ensuing slowly oscillating motions are related to the envelope of the waves in a spectrum by a quadratic transfer function. A series of experimental tests were carried out on a model of a rectangular barge to evaluate the analytical model. The results demonstrate that the slowly varying drift response in linear waves can be related to the wave envelope by means of the transfer function.