Cyclic response and load transfer mechanism of suction bucket jackets supporting offshore wind turbines in soft clay

The increasing water depth and capacity expansion have necessitated the foundation of offshore wind turbines (OWTs) to evolve from the early design of monopiles to recent suction bucket jackets, particularly in offshore regions with presence of soft clay and typhoons. In conventional analysis, a pull-push mechanism is routinely assumed for each bucket (only considering vertical load V), ignoring the horizontal load (H) and moment (M) which co-exist in each bucket. It remains unclear (1) how would these load components (V, H and M) transfer between each other when clay around the buckets cyclically degrades, (2) how would the H and M facilitate the cumulative rotation of the jacket. For these purposes, this study reports a series of 3D numerical analyses, where the jacket dimensions, clay parameters, and environmental loadings are defined with respect to an OWT foundation case in South China Sea. An advanced cyclic plasticity clay model (developed by the authors) was implemented numerically in ABAQUS to realistically capture the cyclic degradation of clay in each analysis. The analyses reveal that when the clayey seabed cyclically degrades, V of each bucket reduces, and contributes less to resist the overturning moment of the jacket. A load transfer thus occurs to increase H and M taken by each bucket, compensating the moment resistance of the jacket. Ignoring H and M would underestimate cumulative rotation of the jacket by 31%, suggesting the assumed pull-push mechanism may be treated with caution. © 2024 Elsevier Ltd