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A time domain approach for response statistics in non-Gaussian seas.

During recent years, thorough experimental and numerical investigation has led to an improved understanding of dynamic phenomena affecting fatigue life and survivability of offshore structures, e.g. ringing and springing and extreme wave impacts [1, 2]. However, most of these efforts have focused either on modelling selected extreme events or sequences of highly nonlinear waves impacting offshore structures, possibly overestimating the actual load to be experienced by the structure. Overall, not much has been done regarding short-term statistics. Although clear non-Gaussian statistics and therefore higher probabilities of extreme waves have been observed in random seas due to wave-wave interaction phenomena [3, 4], which can impact short-term statistics for the structural load, they have not been studied properly regarding the assessment of dynamic behaviour of offshore structures. Computational Fluid Dynamics (CFD) models have shown their viability for studying wave-structure interaction phenomena. Still, nonetheless the continuously increasing computational resources, these models remain too computationally demanding for application to the large spatial domains and long periods of time necessary in studying short-term statistics of non-Gaussian seas. Higher-order spectral (HOS) models, on the other hand, have proven to be efficient as well as adequate in studying non-Gaussian seas [3, 5]. We therefore propose a one-way domain decomposition strategy, which takes full advantage of the recent advances in CFD as well as of the computational benefits of the higher-order spectral model. As a benchmark, a non-Gaussian sea obtained by this coupled HOS-CFD model shows good agreement with the target wave field generated by the HOS numerical wave tank. In addition, the structural response obtained for a simplified monopile model, excited by a similarly generated non-Gaussian sea, seems to be captured well.

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