In this study, a three-dimensional (3D) model is adopted to investigate the problem of fluid-seabed-structure interactions (FSSI) around offshore detached breakwaters. The Volume-Averaged Reynolds-Averaged Navier-Stokes (VARANS) equations are used to simulate the 3D fluid motion in the vicinity of breakwaters, including reflected, diffracted waves and non-linear turbulence. The partially dynamic Biot’s equations (i.e., the $u-p$ approximations) and poro-elastoplastic constitutive model are adopted to describe fluid-seabed interactions in a porous seabed. A one-way coupling algorithm is established to integrate the fluid motion and seabed response. By using the present model, this study addresses the long term cyclic loading induced seabed response and liquefaction potential of a loosely packed foundation. In addition, the effects of the perpendicular longshore currents on the hydrodynamic properties and liquefaction potential are also taken into account. The numerical results reveal that the loose sandy seabed around the offshore detached breakwaters experienced a gradual decrease of stiffness until liquefaction occurs under successive loading cycles. Longshore currents tend to exacerbate the wave field and increase the risk of liquefaction of seabed foundation, especially in the shallow soil layer near the seabed surface.

在这项研究中，采用三维（3D）模型来研究离岸离岸防波堤周围的流体-海床-结构相互作用（FSSI）问题。体积平均雷诺平均Navier-Stokes（VARANS）方程用于模拟防波堤附近的3D流体运动，包括反射波，衍射波和非线性湍流。部分动态的毕奥方程（即$ü-p$近似）和孔隙弹塑性本构模型被用来描述多孔海底中的流体-海底相互作用。建立了一种单向耦合算法来整合流体运动和海床响应。通过使用本模型，本研究解决了长期循环荷载引起的松散地基的海床响应和液化潜力。此外，还考虑了垂直的近岸海流对水动力特性和液化潜力的影响。数值结果表明，离岸分离式防波堤周围的松散沙质海床刚度逐渐降低，直到在连续的载荷循环下发生液化为止。沿岸潮流往往会加剧波场并增加海床基础液化的风险，