The Research Of Wave Transformation Through Two-arrayed Trapezoidal Permeable Submerged Breakwaters

Recently, as people pay more attention to the ecological environment and life quality, submerged breakwater is widely applied in port and coastal engineering. Submerged breakwater is built below the water. It can prevent the waves, and also won’t cause sight block. At the same time, it is advantageous to water exchange. Besides, it plays an important role on beach protection and siltation promotion. The materials of actual engineering are using dimension stones and artificial blocks, these materials are permeable, and permeability will cause energy loss, so it is necessary to take permeability into account. But the capacity of wave absorbing to one-arrayed permeable submerged breakwater is limited; scholars start to focus on serious submerged breakwater. When meeting certain conditions, water will resonate and it will lead to larger reflection, this has great influence on wave height behind the breakwater and channel out of breakwater. The research achievements of this paper can provide a reference to coastal protection engineering using submerged breakwaters in our country.In this paper, the condition of wave Bragg reflection through two-arrayed permeable submerged breakwater and its influencing factors are investigated, and the transmission coefficient and the energy loss caused by permeating are also discussed. Physical model experiments and numerical simulation are combined in the researching. Since fitting well, the numerical simulation is applied extending to two-arrayed groove submerged breakwaters to discuss the reflection, transmission coefficient and energy loss.It shows that, when wave passing through the two-arrayed submerged breakwaters, two resonant frequency regions are observed. Primary resonance peak is about2S/L≈0.92, that is to say, the specific value of wave length and central distance is about2.17. Second-harmonic resonant peak is about2S/L≈1.78. The relative depth, central distance, gradient and width have different influence on reflection coefficient, transmission coefficient and energy loss; but relative wave height does not much affect them, it is not the main factor.Two-arrayed groovy submerged breakwaters have a series of advantages, such as the smaller reflection coefficient, the transmission coefficient and the energy loss are almost the same. What is more, groovy structures use less material, and save cost. Groovy permeable submerged breakwater can be an ideal style for submerged jetty protection engineering, if there are restrictions on both reflected wave height in front of dike and transmission wave height behind the jetty.