Laboratory Observations of Nearshore Flow Patterns Behind a Single Shore-Parallel Submerged Breakwater

摘要

In order to understand the efficacy of submerged breakwater constructed for the beach protection,laboratory experiments were carried out by observing the characteristics of flow around a single shore-parallel submerged breakwater.The velocity field near the shoreline was measured by utilizing the LSPIV (Large-Scale Particle Image Velocimetry) technique,and mean surface and wave height distributions were observed around the submerged breakwater,according to various combinations of incident waves and submerged breakwaters.In this experiment,it was found that the mean flow pattern behind the submerged breakwater was determined by the balance among the gradients of mean water surface and excess wave-momentum flux (i.e.,radiation stress tensors) which interact with the wave-induced current developed by the gradients on the rear and the side of the submerged breakwater.The divergent and convergent flow patterns behind the submerged breakwater (i.e.,accretion and erosion response) of the numerical study of Ranasinghe et al.(2010) were observed in the measured velocity distributions,and their empirical formula mostly agreed with the experimental results.However,for some cases in this experiment,it was difficult to say that the flow pattern was one of them and was agreed with the empirical formula.