Numerical simulation of interactions between water waves and inclined-moored submerged floating breakwaters

Abstract

This paper studies the interactions of water waves with submerged floating breakwaters moored by inclined tension legs, using a numerical wave tank model proposed by Lee and Mizutani (2009) and based on the Navier–Stokes solver. This model combines a direct-forcing immersed boundary (IB) method, volume of fluid (VOF) method, and the mechanics model of the floating breakwater. The floating breakwaters are free on three degrees of freedoms, namely, surge, heave and pitch. Two floating breakwater shapes, rectangular and circular, are used in the experimental and numerical investigations to validate that the model is capable of treating solid boundaries with complex shapes. The non-breaking and breaking waves are carefully chosen to study the nonlinear interactions between water waves and the submerged floating breakwaters. Comparisons of the computed and measured results reveal a favorable agreement in terms of the free water surface, tension force acting on the mooring line, and dynamics of the floating body. A slight phase discrepancy is found between the offshore and onshore mooring forces in the case of a circular floating breakwater, whereas this phenomenon is not observed in the rectangular case. In addition, fully nonlinear phenomena and viscous process in the flow field such as wave breaking, the boundary layer separation on the interface, vortex formation, and motion can be reproduced and captured accurately using the numerical model.