A Dynamic Submerged Breakwater

Abstract

An analytical solution is developed to investigate the behavior of a submerged or surface-piercing, long tethered breakwater of rectangular cross section. The equations of motion are solved to provide the surge, heave, and pitch responses of the structure. The wave reflection and transmission coefficients are calculated. Numerical results are presented for a range of wave and geometric parameters that illustrate the suitability of this type of structure as a barrier to wave action. Small-scale physical model tests were carried out to verify the theory. Reasonable agreement is found between theoretical and experimental values of the reflection and transmission coefficients. It was observed both in the numerical results and model tests that low wave transmission coefficients occur when the diffracted and radiated waves in the lee of the structure are of similar magnitude, but 180° out of phase. The lowest transmission coefficients occurred near the surge natural frequency of the floating breakwater, where significant energy dissipation was present. Under these circumstances, destructive wave interference and energy dissipation combine to give transmission coefficients on the order of 0.5.