Based on linear potential theory, this study gives an analytical solution for wave interaction with a submerged double-layer horizontal porous plate breakwater by using the matched eigenfunction expansions. The analytical solution is confirmed by the multi-domain boundary element method solution and experimental data. The reflection and transmission coefficients of the breakwater are calculated and their main effect factors are analyzed. Some useful results are presented for practical engineering.
Submerged horizontal porous plates have been proposed as offshore breakwaters for protecting shoreline and coastal structures (Yu, 2002). Compared to other type breakwaters, the horizontal plate may have minimum effect on the nearshore current and sediment transport. This should be the major merit of the submerged horizontal plate breakwater. On the other hand, perforating the horizontal plate is to reduce the uplift force acting on the plate. In practice, the sea water level may acutely change due to tide. To meet the change of sea water level, a submerged double-layer horizontal porous plate breakwater may be more feasible. Some researchers have examined the hydrodynamic performance of multiple-layer horizontal plates. Usha and Gayathri (2005) used the matched eigenfunction expansion method to examine the reflection and transmission coefficients of double-layer horizontal solid plates fixed on the free surface. Wang et al. (2006) proposed an effective surface-piercing multiple-layer horizontal solid plate breakwater. Liu et al. (2008) examined the performance of a submerged breakwater with an upper horizontal porous plate and a lower horizontal solid plate, and indicated that the wave-absorbing performance of the breakwater may be further enhanced by perforating the lower solid plate. Kee (2009) presented an optimized plate breakwater with an upper horizontal porous plate and a lower slightly inclined solid plate. Recently, Guo et al. (2011) experimentally examined the hydrodynamic performance of double-layer horizontal solid plates.