3D Numerical Study of Wave–Current-Induced Hydrodynamic and Seabed Dynamic Responses Around a Twin-Pile Group with Various Flow Skew Angles

This paper systematically investigates the hydrodynamic and seabed dynamic responses around twin-pile groups under various wave–current combinations (current velocity Uc=±1.0,±0.8,±0.6,±0.4,±0.2, 0 m/s) and flow skew angles (θ=0°,30°,60°,90°) using a 3D coupled model developed in OpenFOAM. Hydrodynamic results indicate that water surface profiles and gap vortex shedding are heavily modulated by wave–current superposition and pile arrangements. Specifically, strong following currents elongate separated shear layers and amplify gap vorticity, whereas increasing the flow skew angle (θ≥60°) effectively mitigates upstream wake interference. Furthermore, pore water pressure escalates sharply from strong opposing to strong following currents, exhibiting significant attenuation with depth. Strong opposing currents drastically intensify lateral liquefaction risks around the upstream pile, while strong following currents induce irregular liquefaction distribution. Especially, the maximum pore water pressure and maximum liquefaction depths are induced under strong currents (Uc=±1.0 m/s) at a 60° staggered arrangement. These findings highlight the vulnerability of the lateral seabed regions, indicating that targeted asymmetric reinforcement strategies offer an effective approach for mitigating liquefaction risks in offshore twin-pile foundation designs.