The reflection of normal incident waves by absorbing-type breakwaters is investigated in this paper. The breakwaters consist of a perforated wall, a porous caisson and an impermeable back wall. The flow field is divided into four regions: a porous caisson region and three pure water regions. Under the assumptions of linear wave theory, the Darcy's law in the perforated wall, and the pore velocity potential theory of Sollitt and Cross (1972) in the porous caisson region, a 2-D BEM model is created to calculate the reflection coefficients of water waves by several properties of the breakwaters. The numerical model is calibrated by previous numerical studies of the limiting cases of a partially perforated-wall caisson breakwater and a vertical porous breakwater with an impermeable back wall. Generally speaking, the evaluation of the wave dissipation in absorbing-type breakwaters is bigger than a partially perforated-wall caisson breakwater. The reflection coefficient value implies the performance of wave absorbers in this study. Therefore, we examine the major factors that affect the reflection coefficient.


Breakwaters that are widely used along shorelines, channel entrances, beaches, harbors, or marinas may vary in type according to their use. A traditional and the simplest form of breakwater, a rubble mound breakwaters, is quite suitable but very expensive for increasing water depths. Recently, many new types of breakwaters have been proposed and extensively studied for controlling ocean waves efficiently. In recent decades, perforated breakwaters have become popular as they can allow water waves to transmit through it, reduce the wave reflection and wave run-up in front of the structures. Thick permeable structures were considered by several researchers. Sollitt and Cross (1972) used Lorentz's principle of equivalent work to analyze the problem about ocean wave reflection and transmission at a permeable breakwater.

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