Interaction Of The Wave With Submerged Porous Breakwater And Dynamical Response Analysis For Sandy Seabed

It is of importance to analyze the dynamic stability of seabed or structure foundation under wave action in the design and construction of offshore and coastal structures. When wave propagates over ocean surface, a sequence of wave pressure is induced on the seafloor, which causes the fluctuations of pore water pressure or effective stress, displacement of soil particles, and deformation of soil skeleton within seabed simultaneously. Because of unsuitable treatment in engineering, part of seabed may even lead to soil shear fracture or sandy liquefaction under certain conditions, which is responsible to the damage or destruction of offshore structures. In spite of the technologic difficulties widely existing in offshore engineering, it has important significance in theory and application to study the interaction between wave and breakwater, the corresponding dynamic pore water pressure etc. responses within sandy seabed and riprap porous media of breakwater.This paper researches those questions, the interaction between wave and breakwater with riprap porous media, the corresponding elastic dynamic response within its sandy seabed or riprap porous media and the natural sandy seabed without breakwater as well as following.(1) A series of lab tests in wave tank were performed for the models of breakwater with riprap media, sandy seabed with or without breakwater, to study the interaction between wave and breakwater and the dynamic responses within seabed or riprap media. By means of different lab group situation, such as different seabed media,water depth, approaching wave height or wave period, under the action of linear wave or shallow water cnoidal wave,the laws of the pore water pressure within sandy seabed or riprap media and the wave height before or after breakwater were obtained and analyzed as well.(2) Based on the theoretical analysis of wave field and porous fluid field within riprap media, the optimum numerical model was built, which applied turbulent Navier—Stokes Equation and introduced k-?model to close Renault Equation, can describe more objectively the nonlinear effect caused by fluid—solid boundary action and the turbulent fluctuation effect by viscous fluid action in wave field domain. As for porous fluid field, turbulent Forchheimer Equation was used to reveal the relationship between Non—ancy porous flow velocity and pressure gradient. On the basis of the analysis model above, this paper developed a large-scale practical finite difference method program so called VOFFDM, in which, VOF method was employed to trace water free surface and the problem of the fluid-solid coupling on the interface between wave field and porous media was solved by making sure that the velocities or pressures of the two field flows on the interface keep to be equal all the time, so that the program VOFFDM can calculate the wave field and porous media simultaneously with any type of breakwater and complicated boundary.(3) The comparison between VOFFDM numerical results and test results showed good agreement and demonstrated that the numerical model can successfully simulated the interaction between wave and breakwater with riprap porous media. With different wave parameter, water depth, riprap porosity, the dimension of breakwater section, and under the action of linear wave or shallow water cnoidal wave, the details of wave height before or after breakwater and pore water pressure or flow velocity within riprap media were discussed. The analysis results above were the important basis on further studying not only the responses of the seabed below breakwater but also the stability of riprap single or the structure itself.(4) Based on the inherent anisotropy characteristics of natural saturation seabed, the natural seabed was assumed to be transversely isotropic saturated porous media. According to Biot dynamic penetration- consolidation theory of transversely isotropic saturated porous media, this paper built the dynamic equation of transversely isotropic saturated seabed for the first time and developed the dynamic consolidation finite element program so called BCFEM. Furthermore, its correctness was verified by model tests.(5) By applying the dynamic consolidation finite element program BCFEM, an amount of system parameter analysis on the dynamic responses of homogeneous and isotropic saturated seabed and the responses of heterogeneous anisotropic saturated seabed was carried out,and the laws of pore water pressure etc. within seabed under the action of linear wave or shallow water cnoidal wave were obtained with different conditions such as the sandy seabed with or without breakwater, different wave parameter group, water depth etc.. From the results above, it was concluded that the wave dynamic responses are decided by both wave parameters and the characteristics of seabed media, wave parameters such as wave height or wave period are mainly controlling elements, seabed inherent heterogeneity and anisotropy have significant effect on the distribution of pore water pressure or effective stress within it.