OC6 Phase Ib: Validation of the CFD predictions of difference-frequency wave excitation on a FOWT semisubmersible. (1st December 2021)

• Record Type: Journal Article
• Authors: Wang, Lu; Robertson, Amy; Jonkman, Jason; Yu, Yi-Hsiang; Koop, Arjen; Borràs Nadal, Adrià; Li, Haoran; Bachynski-Polić, Erin; Pinguet, Romain; Shi, Wei; Zeng, Xinmeng; Zhou, Yang; Xiao, Qing; Kumar, Rupesh; Sarlak, Hamid; Ransley, Edward; Brown, Scott; Hann, Martyn; Netzband, Stefan; Wermbter, Malwin; Méndez López, Beatriz
• Is Part Of: Ocean engineering. Volume 241(2021)
• Publication Date: 2021-12-01
• Subjects: Offshore wind -- Bichromatic wave -- CFD -- Nonlinear excitation -- Validation -- OC6; Ocean engineering -- Periodicals; Ocean engineering; Periodicals; 620.4162
• DOI: 10.1016/j.oceaneng.2021.110026
• Languages: English
• ISSNs: 0029-8018

Abstract

Abstract: During the previous OC5 1 1 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. Highlights: The wave loads on a fixed FOWT semisubmersible in bichromatic waves were studied. A coordinated CFD investigation and wave-basin experiments were performed. The difference-frequency loads were predicted using CFD and validated experimentally. Uncertainty estimation was carried out for both numerical and experimental results. 2nd-order potential-flow theory underpredicts the difference-frequency loads.