Research On Dynamic Response Of Structure Foundation Under Waves

When water waves propagate in the ocean, they generate significant dynamic pressures on the sea floor. If waves "touch bed",this pressure field induces a stress field and associated pore water pressure fluctuations within the seabed. With excess pore pressure and diminishing vertical effective stress, part of the seabed may become unstable or even liquefied.The instability of the seabed has been responsible for the damage and destruction of offshore structures.So wave-structure-foundation dynamic interaction is a vital issue in coastal engineering.In this thesis,the quasi-static models for calculation of the seabed response to wave based on Biot's consolidation equation is presented with numerical solution of FEM.Wave-induced pore water pressure response of seabed is analyzed thoroughly and systemicly.The numerical model of structure response due to seabed deformation under wave force is also set up primarily.The details of the study and conclusions are as follows:1. FEM equations for solving the transient response of seabed based on the quasi-static elastic consolidation theory and computer programs for numerical solutions are presented.Comparisions of experimental and computational results show that the poroelastic theory is valid and feasible for sandy seabed.2. The standing wave-induced soil response in the vicinity of the composite breakwater is investigated.Based on the numerical model,the pore pressure around the breakwater is examined through a parametric analysis.Comparing all graphs presented for coarse sand and fine sand,it is found that the wave-induced pore pressure is more significant affected by wave and soil parameters in coarse sand,rather than in fine sand. Further,the results indicate that the soil response is affected significantly by the permeability and shear modulus. 3. Based on 5th Stokes wave theory,the seabed response of finite thickness due to nonlinear wave is analyzed,and the stability of stratification soil is studied.Compared with liner wave theory, the amplitude of pore water pressure, displacement of soil particles and effective stress is different.In the cases of larger relative wave height and smaller relative wave depth, nonlinear influence should not be neglected.The numerical model can work for the seabed with complex boundary conditions and asymmetry stratification soil.4. Sandy seabed with worse permeability is easily liquefied under nonlinear waves.However,in the same cases, liquefaction depth in sandy seabed with better permeability is larger than it in the worse permeability sandy sand.5. The numerical model of structure response due to seabed deformation under wave force is set up.At the first step,the influence upon the stability of structure is analyzed .