Scour formation and hydrodynamic loading on cables in offshore wind turbines

We conduct high-fidelity, two-way coupled simulations to investigate sediment transport and flow interactions around a periodic array of seabed-mounted monopiles under oscillatory forcing. The unsteady, turbulent flow is modeled by solving the incompressible Navier-Stokes equations, while the evolving sediment bed is governed by the Exner equation, assuming bedload transport as the sole sediment transport mechanism. Empirical correlations, calibrated from experimental and particle-scale simulations, are used to estimate the bedload flux. The simulations span a range of idealized tidal conditions, including both symmetric and asymmetric oscillatory flows and various Shields stress values. We find that scour development is strongly influenced by initial bed topography, flow characteristics, and the spatial layout of the computational domain. Even under symmetric forcing, the sediment bed exhibits persistent asymmetries and localized deposition near the equatorial regions of the monopiles. To improve sediment entrainment prediction, we implement a modified erosion rate model based on a dimensionless shear parameter. The resulting erosion field exhibits a circular high-entrainment zone around the monopile, consistent with patterns reported in experimental and numerical studies. This supports the physical fidelity of the model and its ability to capture vortex-driven sediment mobilization. To complement the sediment analysis, we develop a post-processing strategy to evaluate hydrodynamic forces on subsea cables. By sampling velocity and pressure fields along hypothetical cable paths, this method enables efficient estimation of force magnitudes and directions across multiple orientations without re-running the primary simulations.