In this paper, a well-validated numerical model, based on the Reynolds Averaged Navier-Stokes (RANS) equations, was developed to simulate the interaction between a solitary wave and impermeable submerged double breakwaters. Fairly good agreements between simulation results and experiment data were obtained. Based on this model, the pressure drag on front submerged breakwater and the wave transformation were studied. The numerical results showed that the negative peak value of front obstacle is larger than that of single submerged breakwater and the optimal distance, judged as minimum transmission coefficient, between two submerged breakwaters is approximately 3 times the water depth.
Marine structures are commonly adopted for the protection of the coastal environment. For decades submerged breakwaters have been employed as cost-effective structures in nearshore regions to dissipate and reflect destructive waves. Because of the lower crown, submerged breakwaters have advantages in better water circulation, clearer ocean views and lower construction costs. Moreover, submerged breakwaters have minimal impact on ship navigation (Ting and Kim, 1994), which is important for coastal engineers and planners. The main characteristics as water waves propagating over a submerged obstacle are the process of the reflection, dissipation and transmission. Especially, coastal engineers care about the transmitted wave and the protection for coastline. For these reasons, an understanding of the interaction between water waves and submerged breakwaters is very important.
Solitary waves have been frequently employed to determine the characteristics of nonlinear long waves, such as tsunamis and strong surges (Hsiao and Lin, 2010; Synolakis and Bernard, 2006). Laboratory experiments using Laser Doppler Velocimetry (LDV) and PIV have been commonly used to investigate the velocity around structures. As the wave front approaches the obstacle, the vortex is generated around bar edges (Rey et al. 1992) and the solid front side of the obstacle forces an upward motion of fluid in front of it. As a result, part of wave energy is reflected back. If the obstacle is long enough, the transmitted wave splits into a series of individual solitons. This was demonstrated experimentally and numerically (Seabra-santntos et al. 1987). If the obstacle is high enough, the transmitted wave breaks and experiences another reflection when it re-enter the water. If breaking appears after the beginning of the fission process, waves maintain their fission process. Losada et al. (1989) also identified an oscillatory tail in the rear side of soliton.