Numerical Study Of Seabed Dynamic Response And Liquefaction Around A Jacket Support Offshore Wind Turbine Foundation Under Combined Wave And Current Loading

Driven by the "carbon peaking and carbon neutrality" policy,the development of the offshore wind and power has attracted by the local government.Selecting the appropriate form of the offshore wind turbine foundation plays an important role in offshore wind and power development.Among many forms of the offshore wind turbine foundation,the jacket foundation is widely applied in the field of offshore wind power by virtue of its mature technology and high foundation stiffness,and has also become the object in this paper.The jacket foundation is subjected to complex marine environment loading inevitably,like random wave and current.The cyclic loads affect the distribution of pore water pressure and effective stress in the seabed soil around the jacket foundation and cause seabed liquefaction,which will further threaten the safety of marine structures.Therefore,it is of great scientific significance and practical engineering value to calculate the dynamic seabed response around the jacket foundation under the action of random wave and current.In this paper,a wave/current--jacket foundation--seabed interaction model is established by using the numerical method.The variation characteristics of flow field,pore water pressure response and transient liquefaction in the seabed soil around jacket foundation under regular wave and random wave loading are studied successively.The research contents of this study are detailed as follows:(1)In the flow model,by solving the Reynolds averaged Navier-Stokes(RANS)equation with the k-? turbulence model,the fluid dynamics around the jacket foundation can be controlled.And the RANS equation is solved by using the PORO--FSSI--FOAM solver,which is based on ola Flow solver.The quasi--static Biot equation is used to govern the wave-driven dynamic behaviour of porous elastic seabed.The present model is built by integrating the hydrodynamic model and seabed model,which are based on the open source software Open FOAM.The grid convergence test was carried out for sub-models to ensure the computation results are convergent and accurate in a short time.(2)To prove the computational accuracy and solving efficiency of the new 3D model,the numerical results of the new 3D model are compared with those of the existing flume experiments.Firstly,the feasibility of the hydrodynamic model is verified by flume experiments and three-dimensional physical model experiments.Results show that the hydrodynamic model can effectively simulate the flow field characteristics around the jacket foundation.Then,the feasibility of the seabed model is verified by onedimensional cylinder experiment and flume experiments.Results indicate that the seabed model can effectively simulate the pore water pressure response in the seabed around the jacket foundation.It is proved that the integrated model can accurately solve the seabed response and transient liquefaction around jacket foundation under the action of random wave and current.(3)Based on the new three-dimensional model describing the random wave/current--jacket foundation--seabed interaction,the dynamic response and transient liquefaction of the seabed around jacket foundation under regular wave and current are studied systematically.The distribution characteristics of field around jacket foundation under the action of regular wave is revealed.The pore pressure and effective stress response of seabed around the jacket foundation are analyzed.According to the transient liquefaction criterion,the distribution of transient liquefaction around jacket foundation is obtained,and the parameters of influencing factors of seabed liquefaction are analyzed.(4)Based on the new three-dimensional model describing the random wave/current--jacket foundation--seabed interaction,the dynamic response and transient liquefaction of the seabed around jacket foundation under random wave and current are studied.The dynamic changes of flow field around jacket foundation under the influence of random wave flow are analyzed.The dynamic changes of flow field around jacket foundation under the influence of random wave flow are analyzed.The distribution of the maximal seabed liquefaction depth around jacket foundation is obtained,the wave surface elevation and pore pressure response around jacket foundation under random wave and regular wave are compared.The parameters affecting the transient seabed liquefaction depth,including the geometric characteristics about jacket and current parameters,are discussed.