Hoballah Jalloul, M., Satari, R., Welzel, M., Schendel, A., Kerpen, N. B., Wynants, M., Neuweiler, I., & Schlurmann, T. (2025). Wave-current induced scour around complex offshore structures: Towards a refined analysis of local scour at jacket piles. Ocean Engineering, 338, 121983. https://doi.org/10.1016/j.oceaneng.2025.121983
The paper “Wave‑current induced scour around complex offshore structures”, published in Ocean Engineering (2025), offers timely and highly relevant insights for the coastal and ocean engineering community, particularly those involved with Germany’s offshore infrastructure and educational institutions. This study addresses a pressing issue in the context of Germany's accelerating offshore wind energy expansion—namely, the underestimated scour risks associated with jacket-type foundations, which are commonly deployed in the North and Baltic Seas.
Unlike monopile structures, which have been extensively researched and for which robust design guidelines exist, jacket foundations present a far more complex interaction with hydrodynamic forces. Their multi-leg configuration and intersecting bracing elements generate intricate flow fields, which in turn lead to highly localized sediment transport and scour phenomena. This complexity has, until now, limited the accuracy of predictive models used in German and broader European engineering practice.
The authors approach this problem through carefully controlled physical model experiments. Scaled jacket structures were subjected to realistic combinations of current and wave conditions replicating those found in the German Bight. By isolating the effects of steady currents and superimposing regular waves, the study quantified scour development over time, monitored through precise velocity and depth sensors around the foundation legs. A key finding is that the presence of both waves and currents leads to significantly deeper scour pits—nearly doubling the maximum scour depth observed under current-only conditions. This effect is not merely additive but strongly synergistic, indicating that existing empirical approaches may severely underestimate scour in combined flow regimes.
Further observations reveal that scour patterns are far from symmetric. Local wake interactions, particularly around bracing elements, create high-turbulence zones that shift the maximum erosion points away from the structurally intuitive locations. The onset of such complex patterns was found to depend critically on current velocity. Once a threshold—identified at approximately 0.6 m/s—was exceeded, the sediment response entered a nonlinear regime, with rapid and asymmetrical scour development even under moderate wave forcing. This is a crucial insight for German offshore engineers, as it highlights the potential for rapid seabed destabilization at flow speeds previously considered benign.
A practical contribution of the study is the development of a new empirical formula that captures the observed scour behavior with higher fidelity than current models. This formula integrates both wave and current parameters via an adapted Shields parameter, providing a straightforward yet more accurate tool for practitioners. This represents a valuable finding to be integrated into design workflows and monitoring protocols.
The study offers an experimental dataset that can serve both as a reference and as a basis for numerical model validation or parametric studies. It encourages the incorporation of combined flow conditions into thesis work and engineering curricula—moving beyond the simplified current-only cases still often used in coursework. Moreover, the results support a broader pedagogical shift toward multi-physics problem solving, reflecting the realities faced in the coastal zone and offshore wind sectors.
