Wave-induced Seabed Dynamic Response Around Composite Offshore Wind Turbine Foundation

Wave is one of important factors that can affect the stability of offshore structures. With the cyclic wave actions, pore water pressure in the seabed changes circularly. The stress distributions in the seabed change with the pore-water pressure increasing and shear strength is weakened to threat the stability of seabed and structures. Therefore, an integrated model coupling the open source code OpenFOAM to the ABAQUS was setup, and the dynamic response of seabed around the composite bucket foundation under wave loading was studied. Main research contents and conclusions were as follows:(1) A 3D wave-induced seabed dynamic response model is established, whose results are compared with experimental data and analytical results of progressing wave and standing wave. It can be concluded that the numerical model is reasonable to simulate the dynamic response of seabed under waves.(2) An integrated model is established by OpenFOAM and finite element software ABAQUS. The results of wave-induced seabed dynamic response around composite bucket foundation by the integrated model indicate that attenuation velocity of pore pressure is faster in the back-side than that in front of the structure. Pore pressure inside the bucket due to seepage below barrel skirt is much smaller than the pressure outside the bucket.(3) Effects of parameters of seabed on the dynamic response of seabed around the composite bucket foundation have been investigated. The more obviously anisotropic of soils is, the slower the attenuation of pore water pressure will be. Exponential distribution of soil permeability and shear modulus has no significant influence on the attenuation of pore pressure, while linear distribution may take an effect on the attenuation of pore water pressure in the vertical direction.(4) The 3D numerical model is established to simulate wave-induced seabed dynamic response around composite bucket foundations considering the sinking processes due to negative pressures. Value of negative pressure has more obvious influence on pore-pressure of seabed closely to the foundation than other parts. Sinking velocity of the foundation does not have evident influence on wave-induced pore water pressure of seabed. Incompletely sinking foundation condition decrease negative pressure around composite bucket foundation. What's more, liquefied area around suction wind turbine foundation is decreased by negative pressure.(5) The seabed response and liquefaction in two different conditions are simulated. It can be see that the stratified soils have an influence on wave-induced seabed response. In these conditions, liquefactions of the seabed around the composite bucket foundation do not occur.