Probabilistic Anchor Design for Floating Offshore Wind Turbines using Whole-Life Geotechnical Modelling

Abstract. Floating offshore wind turbines require anchoring systems capable of sustaining variable cyclic loads over their operational lifetime, which may induce changes in seabed strength and anchor capacity. Conventional anchor design approaches are based on the conservative assumption that the largest applied load over the design lifetime occurs when the seabed soil is at its weakest state. To address this conservatism, this paper presents a probabilistic design framework for floating and deepwater offshore wind anchors utilising whole-life geotechnical modelling. This approach accounts for both the reduction in seabed strength due to cyclic loading and the potential increases in strength resulting from consolidation. The proposed framework involves generating time series of metocean conditions, simulating whole-life anchor loading via a probabilistic surrogate model, calculating soil damage accumulation and consolidation, and estimating the risk of failure over multiple lifetimes. The methodology is demonstrated using a case study of a 15 MW floating offshore wind turbine located in the Scottish North Sea. The results show that seabed strength initially decreases rapidly under cyclic loading and subsequently recovers through consolidation, with relatively little variation (less than 3.5 %) in the strength evolution between different metocean realisations. Accounting for whole-life seabed hardening reduces the required anchor area by 6–8 % for the baseline load distribution. However, sensitivity analysis shows that substantially larger reductions, of up to 27 %, are possible when the distribution of extreme loads has greater separation from frequently occurring loads. The results therefore indicate that the benefit of whole-life geotechnical design is governed not only by the magnitude and rate of seabed strength recovery, but also by the relationship between frequent operational loading and rare extreme loading.