Applicability of Multiple Submerged Narrow-Crested Breakwaters for Reduction of Mean Water Level in Rear Side and Flow Control

Abstract

In this study, to confirm the applicability of multiple submerged narrow-crested breakwaters (SNCBs), a 3-D numerical simulation was conducted. The numerical simulation used the numerical model developed for analyzing the 3-D flow structure around the submerged breakwaters. In addition, to verify the validity and effectiveness of the numerical model, the wave height distribution and mean water level distribution around impermeable submerged breakwater (ISB) and permeable submerged breakwater (PSB) were compared with the results of the numerical model experiment. As a result, the simulated results accurately realized the experimental values. The numerical simulation was conducted by applying the multiple SNCBs and common PSB for comparative analysis of the effectiveness on flow control and increased mean water level in the rear side, respectively. When the SNCBs are installed by more than two rows, the flow control was better than that achieved by installing PBS. However, the wave reflection was high, and the water level difference between onshore and offshore increased, owing to increased water level in the rear side. Based on this, an opening was installed on the multiple SNCBs, for the reduction of water level in the rear side. As a result, an outgoing flow toward the open sea was generated, which reduced the mean water level in the rear side. When W/L-r >= 0.2, the mean water level difference between onshore and offshore decreased, compared to the case of the PSB. Therefore, when appropriately installing the multiple SNCBs, whose applicability has been confirmed in this study, this can become one of the methods that can replace existing PBSs, which are bulky in size and expensive to construct.