The wave scattering of normal incident waves by absorbing-type breakwaters is investigated in this paper. The absorbing-type breakwaters consist of a submerged permeable structure, a solid back wall and a submerged horizontal or slightly inclined porous plate. The whole fluid domain is divided into four regions: a permeable structure region and three pure water regions. Under the assumptions of linear wave theory, the Darcy's law in the porous plate, and the pore velocity potential theory of Sollitt and Cross (1972) in the permeable structure region, a multi-domain BEM model is created to calculate the reflection coefficients and the wave forces 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 submerged impermeable structure and a horizontal porous plate with a solid back wall. From the numerical results, the wave dissipation effect of permeable structure was found as expected better than that of impermeable structure. In the cases of horizontal porous plate, the smaller submergence depth of the plate makes the smaller reflection coefficient. However, the reflection coefficient increased as inclined angle increased in the cases of inclined porous plate.
Breakwaters that are widely used along shorelines, beaches, harbors, or marinas may vary in type according to their use. The general trend of breakwater development is from gentle slope breakwaters to vertical ones, from rubble-mound breakwaters to composite breakwaters. It is customary to use rock or concrete blocks mound at the front of the upright section of a vertical breakwater. This type of breakwater is considered as a defense structure not only reduces the incident wave energy but also uses as the toe protection. Recently, many new types of breakwaters have been proposed and extensively studied for controlling ocean waves efficiently.
