Wave motions over and under the submerged porous or solid plates is studied by the multi-domain boundary element method and by the direct numerical simulation (DNS) for the fully nonlinear wave interactions with structures. The mechanism of the blockage effects by a submerged solid plate or the wave energy dissipation effects by porous plates has been investigated and discussed. It is found that the both effects are incompatible against each other. A series of multi-plates were studied parametrically, and a dual system has been chosen for the optimum performance as a new breakwater that is plausible and favorable in the costal engineering practice. The system design parameters are properly tuned against the incident waves so that the incompatible effects become to be complementary to each other, having outstanding performances over the wide range of frequencies.


Application of the submerged horizontal solid or porous plate as breakwaters has been studied by numerous researchers for last several decades as a promising alternative means against conventional breakwaters for the aesthetics and environments of the coastal region, especially of the steeply sloping shorelines with a less tidal range. Since it insures open scenic views, free water circulations in the sheltered region to prevent stagnations and pollutions, and sediment transports to keep in general partitioning the natural seabed. Stoker (1957) triggered the study of hydrodynamic performance (reflection and transmission) of long waves passing over a horizontal single surface solid plate fixed at the free surface. Siew and Hurley (1977) obtained an analytic expression for the reflection and transmission coefficient for long waves propagating past a submerged plate in shallow water. Patarapanish (1978) has examined the average energy flux passing around the submerged plate and found that the reflection coefficients varied with plate length. Takaki (1988) also investigated the fluid phenomena around a horizontal submerged-plate and investigated the characteristics of hydrodynamic forces on submerged plates.

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