OC6 Phase Ib : validation of the CFD predictions of difference-frequency wave excitation on a FOWT semisubmersible

Wang, Lu and Robertson, Amy and Jonkman, Jason and Yu, Yi-Hisang and Kroop, Arjen and Nadal, Adrià Borràs and Li, Haoran and Bachynski-Polić, Erin and Pinguet, Romain and Shi, Wei and Zeng, Xinmeng and Zhou, Yang and Xiao, Qing and Kumar, Rupesh and Sarlak, Hamid and Ransley, Edward and Brown, Scott and Hann, Martyn and Netzband, Stefan and Wermbter, Malwin and Méndez López, Beatriz (2021) OC6 Phase Ib : validation of the CFD predictions of difference-frequency wave excitation on a FOWT semisubmersible. Ocean Engineering, 241. 110026. ISSN 0029-8018 (https://doi.org/10.1016/j.oceaneng.2021.110026)

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Abstract

During the previous OC511 project, state-of-the-art mid-fidelity engineering tools for floating wind systems were found to consistently underpredict the nonlinear, low-frequency responses of semisubmersible offshore wind platforms, leading to substantial errors in the structural loads because of low-frequency surge and pitch resonance. To examine this underprediction, a coordinated investigation with computational fluid dynamics (CFD) simulations and model-basin experiments was carried out. Both investigations involved a fixed and simplified OC5-DeepCwind semisubmersible in bichromatic waves. The wave excitations—especially the nonlinear, difference-frequency excitation—on the structure from the CFD simulations were compared to the experimental measurements for validation, with uncertainty analyses for both the experimental and the CFD results. Further, the wave excitations on each column of the semisubmersible were measured separately in the experiment, allowing the validation of the CFD results to be done on a per-column basis. Overall, the CFD predictions of the difference-frequency excitations agree with the experimental measurements, suggesting the CFD solutions can be used as a reference for tuning and improving the engineering-level tools and can provide a means to better understand the underprediction at low frequencies.

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