The offshore wind industry is following a fast increase in Europe, leadingdevelopers to consider sites with higher water depths, for which GravityBased Foundations (GBF) could be a better option than monopiles. GBFare reported as potentially subject to “ringing” issues, and very highloads have been observed during basin tests on a generic foundation. Theobjective of this study is to propose a numerical methodology to estimatethe probability of occurrence of such very high loads on a GBF. Thehydrodynamic load model used here relies partially on potential flowtheory and partially on strip theory, with Morison, Rainey and FNVterms applied on the smallest section of the foundation. In order tocapture the wave asymmetry observed in high sea states, the free surfaceelevation is computed under irregular and nonlinear assumption, usingthe HOS method to solve the Zakharov’s equation. Results demonstratethe interest of using nonlinear free surface model as compared to firstorder model. The distribution of the overturning moment for three levelsof Hs is also provided, making possible the evaluation of ringingoccurrence.
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