Reductions in current and wave-driven flows in jacket structures: A numerical investigation

This study investigates the interaction between large waves, in-line currents, and offshore jacket structures using computational fluid dynamics simulations. The objective is to improve understanding of wave-current blockage, where local current speeds are reduced due to the presence of the jacket acting as an obstacle array. The simulations reproduced the laboratory experiments of Archer et al. (2025), with the jackets represented as porous blocks characterised by uniformly-distributed hydrodynamic area for Morison drag and volume for inertia forces. The porous representation was validated by accurately reproducing measured force time histories across a wide range of wave-current conditions. Reduced average current speeds within the jackets were estimated independently by both inferring currents from force time histories, using analytical amplitude-scaling arguments derived from Archer et al. (2025) , and by averaging simulated flow kinematics. The two methods produced consistent results, showing that average current speeds within the jackets under combined wave-current loading were reduced to as low as 33 % of the undisturbed current, substantially lower than for current-only cases. Analysis of the simulated kinematics further revealed significant local reductions of wave-driven horizontal motions within jackets, representing a novel insight that challenges the common assumption that wave kinematics remain unaffected. These findings highlight the potential for improved force prediction and hence cost reductions in offshore wind jacket foundations.