The Analysis Of Dynamic Response On A Porous Seabed Under Wave And Current Loadings

In recent years,the failure of offshore structures(such as submarine pipeline,breakwater and offshore platform foundation)have occurred continuously,therefore more and more coastal and geotechnical scholars engage in the stability analysis of seabed and marine structures under oceanic enviroumental loadings.In some research it is found that the phenomenon of the instability of offshore structures is caused by the deformation or liquefaction of seabed around offshore structures.The wave and current loadings in oceanic enviroumental loadings are the main factors which caused seabed deform and liquefy.Therefore the study on the dynamic response of free seabed under combined wave and current loadings is an important theoretical basis for the further analysis of the dynamic interaction between seabed and offshore structures,and the stability of a porous seabed under wave and current loadings is particularly important for engineers to design marine structures such as submarine pipelines,breakwaters and offshore platform foundations.In this paper,taking the seabed surrounded offshore structures as the object of the research,the dynamic response of seabed in different ocean situations under wave loading is analyzed firstly.On this basis of the new computation model,the transient and accumulative response of seabed under wave and current loadings is examined by using the numerical method.Further,the stability of seabed is evaluated through the liquefaction analysis of seabed.The specific research work is as follows: 1.The dynamic response of seabed in different ocean situations under wave loadingBased on the different wave theories,the dynamic response of seabed in different ocean situations under wave loading is studied.The dynamic response of seabed near the vertical breakwater under the standing wave loadings is examined based on the linear wave theory.Using the nonlinear cnoidal wave theory which is suitable to the offshore shallow water area,the dynamic response of seabed in offshore area is analyzed.Base on the Stokes wave theory,the effect of the nonlinearity of wave loading on the dynamic response of seabed is discussed in detail.2.The transient dynamic response of seabed under wave and current loadingsAccording to the two solutions of wave and current interaction,the influences of the current characteristic on the wave features and pressure fields in the sea field are studied by numerical analysis method.On the basis of the study on seabed response under wave loading and combined the extended model of u-p,the influence of current velocity,seabed features and wave characteristics on the transient dynamic response such as effective stresses and excess pore pressures in the seabed are discussed in detail.Further,the stability of seabed is evaluated through the transient liquefaction analysis.3.The accumulative dynamic response of seabed under wave and current loadingsOn the basis of the seabed transient dynamic response under wave and current loadings,combining excess pore pressure calculation model which considered the effect of transient pore pressure on accumulative pore pressure,the transient and accumulative response of excess pore pressure in the seabed under the combined wave and current loadings are calculated by the numerical method.The effects of the cumulative time,current velocity,the wave characteristics and seabed features on excess pore pressure are discussed in detail.Further,the stability of seabed is evaluated through the accumulative liquefaction analysis.