Design optimization of offshore wind jacket piles by assessing support structure orientation relative to metocean conditions

Abstract. The orientation of a 3-legged offshore wind jacket structure in 60 meter water depth, supporting the IEA 15MW reference turbine, has been assessed for optimizing the jacket pile design. A reference site off the coast of Massachusetts was considered, including site specific metocean conditions and realistically plausible geotechnical conditions. Soil-structure interaction was modelled using three dimensional FE ground-structure simulations to obtain equivalent mudline springs which were subsequently used in nonlinear elastic simulations, considering aerodynamic and hydrodynamic loading of extreme sea states in the time domain. Jacket pile loads were found to be sensitive to the maximum 50 year wave direction, as opposed to the wind direction, indicating that the jacket orientation should be considered relative to the dominant wave direction. The results further demonstrated that the jacket orientation has a substantial impact on the overall jacket pile mass and maximum pile embedment depth, and therefore represents an important opportunity for project cost and risk reductions. Finally, this research highlights the importance of detailed knowledge of the full global model behavior (both turbine and foundation) for capturing this optimization potential, particularly due to the influence of wind-wave misalignment on pile loads. Close collaboration between the turbine supplier and foundation designer, at the appropriate design stages, is essential.