Analytical Study On The Shelter Function Of A Submerged Bar On A Partially Reflecting Vertical Breakwater

The breakwater plays an important role in defensing the offshore wave, guaranteeing the steady of the harbor fluid and suppressing sediment deposition. The perforated vertical breakwaters, with the nature of partial reflection, has the advantage of low reflection, low wave overtopping and low wave force, which have been widely used in the practical engineering. For the aim of improving the security performance and the working performance of a perforated vertical breakwater, a rubble mound submerged bar can be constructed in front of the breakwater without influencing the water exchange and the coastal landscape, and leading to a better engineering effect. This study examines wave interaction with a partially reflecting vertical breakwater protected by a submerged porous bar through theoretical analysis. The present research results may be used to determine the optimum parameters of structures at a preliminary engineering design stage.Based on the linear potential theory, this study uses matched eigenfunction expansions to develop a series of analytical solutions. The analytical solutions are confirmed by the multi-domain boundary element method (BEM) solution and some other scholars’ research results. After validating the correctness of the analytical solutions, we use a series of calculation examples to show the influence of a submerged porous bar on the partially reflecting vertical breakwater, and give some engineering design suggestions of key influencing parameters. According to the analysis, some major conclusions are given as follows. The increases of the bar thickness, width and the porosity can increase the dissipation of the incident wave energy and then provide better shelter for the rear vertical wall. The vertical breakwater with a large reflection coefficient may lead to a resonance effect between the incident and the reflected wave. But the resonance effect disappears gradually with the decreasing reflection coefficient of the rear vertical breakwater. For obliquely incident waves with a small incident angle, the influence of different porous bar factors on the hydrodynamic characteristics are similar to that of normally incident waves. However, the influences of porous bar on the partially reflecting vertical breakwater become very complicated when the incident wave angle are rather large,. When the dominant wave direction is determined in practical engineering, the horizontal space between the vertical wall and the submerged porous bar is a key factor for engineering design. The present analytical solution can be used to find the optimum horizontal space, which can both guarantee good shelter function of submerged porous bar and save the construction cost.