Uncertainty Assessment of CFD Investigation of the Nonlinear Difference-Frequency Wave Loads on a Semisubmersible FOWT Platform
National Renewable Energy Laboratory (NREL), Golden, CO 80401, USA
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Sustainability 2021, 13(1), 64; https://doi.org/10.3390/su13010064
Received: 27 October 2020 / Revised: 8 December 2020 / Accepted: 19 December 2020 / Published: 23 December 2020
(This article belongs to the Special Issue Development and Application of Computational Fluid Dynamics in Offshore Renewable Energy)
Current mid-fidelity modeling approaches for floating offshore wind turbines (FOWTs) have been found to underpredict the nonlinear, low-frequency wave excitation and the response of semisubmersible FOWTs. To examine the cause of this underprediction, the OC6 project is using computational fluid dynamics (CFD) tools to investigate the wave loads on the OC5-DeepCwind semisubmersible, with a focus on the nonlinear difference-frequency excitation. This paper focuses on assessing the uncertainty of the CFD predictions from simulations of the semisubmersible in a fixed condition under bichromatic wave loading and on establishing confidence in the results for use in improving mid-fidelity models. The uncertainty for the nonlinear wave excitation is found to be acceptable but larger than that for the wave-frequency excitation, with the spatial discretization error being the dominant contributor. Further, unwanted free waves at the difference frequency have been identified in the CFD solution. A wave-splitting and wave load-correction procedure are presented to remove the contamination from the free waves in the results. A preliminary comparison to second-order potential-flow theory shows that the CFD model predicted significantly higher difference-frequency wave excitations, especially in surge, suggesting that the CFD results can be used to better calibrate the mid-fidelity tools.
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Keywords:
FOWT; offshore wind; semisubmersible; bichromatic waves; QTF; second order; CFD; nonlinear wave load; IEA Wind; OC6
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MDPI and ACS Style
Wang, L.; Robertson, A.; Jonkman, J.; Yu, Y.-H. Uncertainty Assessment of CFD Investigation of the Nonlinear Difference-Frequency Wave Loads on a Semisubmersible FOWT Platform. Sustainability 2021, 13, 64. https://doi.org/10.3390/su13010064
AMA Style
Wang L, Robertson A, Jonkman J, Yu Y-H. Uncertainty Assessment of CFD Investigation of the Nonlinear Difference-Frequency Wave Loads on a Semisubmersible FOWT Platform. Sustainability. 2021; 13(1):64. https://doi.org/10.3390/su13010064
Chicago/Turabian StyleWang, Lu, Amy Robertson, Jason Jonkman, and Yi-Hsiang Yu. 2021. "Uncertainty Assessment of CFD Investigation of the Nonlinear Difference-Frequency Wave Loads on a Semisubmersible FOWT Platform" Sustainability 13, no. 1: 64. https://doi.org/10.3390/su13010064
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