Sediment Erosion around Seabed Structures and Flow-Induced Forces on Subsea Cables

We perform high-fidelity, two-way coupled simulations to examine sediment transport and flow interactions around a periodic array of seabed-mounted monopiles subjected to oscillatory forcing. The unsteady turbulent flow is resolved by solving the incompressible Navier–Stokes equations, while the evolving sediment bed is modeled using the Exner equation, considering bedload transport as the sole sediment transport mechanism. Bedload fluxes are estimated through empirical correlations calibrated against laboratory experiments and particle-scale simulations. The simulations encompass a range of idealized tidal conditions, including symmetric and asymmetric oscillatory flows and various Shields stress values. Results show that scour evolution is strongly affected by the initial bed topography, flow characteristics, and spatial configuration of the computational domain. Even under symmetric forcing, the sediment bed develops persistent asymmetries and localized deposition near the monopile’s equatorial regions. To enhance predictions of sediment entrainment, we implement a modified erosion-rate model based on a dimensionless shear parameter. The resulting erosion patterns reveal a circular high-entrainment zone around each monopile, consistent with observations from experimental and numerical studies, thereby confirming the model’s physical fidelity and its capability to capture vortex-induced sediment mobilization. In addition, we introduce a post-processing framework to assess hydrodynamic forces on subsea cables. By sampling velocity and pressure fields along hypothetical cable trajectories, this approach enables efficient estimation of force magnitudes and directions for multiple orientations without requiring additional flow simulations.