Short-term extreme value prediction for the structural responses of the IEA 15 MW offshore wind turbine under extreme environmental conditions

As offshore wind turbines enter deep seas, large-scale models ranging from 15 MW to 20 MW are becoming the mainstream choice for the future market. The dynamic responses of 15 MW wind turbines under extreme environmental conditions should be considered in the design process. With increasing structure sizes, the mooring systems and tower base structures play essential roles in maintaining position and supporting wind turbines under harsh environmental conditions. Accurate estimation of the extreme mooring loads and dynamic responses at the tower base is crucial, particularly for the ultimate limit state (ULS) analysis. The dynamic responses of the offshore wind turbine are calculated by Open Fast and validated with other numerical tools. For the safety of deep-sea structures, it is necessary to consider the extreme environmental conditions with a 100year return period, which is beyond the current standards. An environmental contour-based approach is proposed to select the short-term extreme conditions, enabling approximate prediction of the extreme values of the dynamic responses during the preliminary design stage. The Gumbel method and the ACER method are used to predict the short-term extreme dynamic responses. Comparative evaluations against the relevant standards for floating wind turbines are conducted to assess structural safety.