Flow blockage and drag reduction for jacket structures under misaligned wave and current conditions

This study uses computational fluid dynamics simulations to investigate misaligned wave and current interaction with jacket structures. The objective is to extend understanding of the flow reductions within jackets that significantly lower predicted drag forces, by considering more realistic loading conditions in which long-crested waves and currents approach from different directions. A robust numerical framework for simulating combined waves and skew currents is developed through a novel application of existing techniques, demonstrating physically realistic behaviour. By varying both the relative wave–current angle and the jacket orientation, it is shown that the component of current perpendicular to the waves has only a small influence on these flow reductions and therefore a modest (up to 6%) effect on peak drag loads (neglecting the straightforward modification to Morison drag via its contribution to the velocity magnitude). From an engineering perspective, present offshore design practice accurately captures reductions associated with this transverse component, yet overestimates in-line drag due to its inability to account for the large reductions in the flow in-line with waves driven by the additional wave loading. To reduce the complexity of estimating these in-line flow reductions, the study shows that these can be approximated by considering only the component of current projected onto the wave direction.