Wave-current induced scour around complex offshore structures: Towards a refined analysis of local scour at jacket piles

Jacket-type foundation structures are increasingly being used in offshore wind development. Such structures are geometrically more complex than monopiles. This makes it necessary to develop methods that more accurately predict the equilibrium scour depth as well as the temporal scour development. The complex interplay between hydrodynamic boundary conditions and the geometry and the structural elements lead to appreciable scour differences between piles. This study examines the applicability of monopile scour prediction methods on a jacket-type foundation structure for combined wave and current loading coming at a 90° angle, taking into account the location of the pile within the structure. It proposes new equations for the estimation of end scour depth based on the relative wave-current velocity (U_cw) and the Keulegan-Carpenter number (KC) for the front and the rear pile. Additionally, a single equation based on the effective work flow (W^∗) for both the front and the rear pile is proposed, eliminating the need to use separate equations for each pile. In regards to the temporal scour development, this paper proposes equations for the determination of the dimensionless time scale for the front and rear pile.