OC6 Phase Ia: CFD Simulations of the Free-Decay Motion of the DeepCwind Semisubmersible

Lu Wang, Amy Robertson, Jason Jonkman, Jang Kim, Zhi-Rong Shen, Arjen Koop, Adria Borras Nadal, Wei Shi, Xinmeng Zeng, Edward Ransley, Scott Brown, Martyn Hann, Pranav Chandramouli, Axelle Vire, Likhitha Ramesh Reddy, Xiang Li, Qing Xiao, Beatriz Mendez Lopez, Guillen Campana Alonso, Sho OhHamid Sarlak, Stefan Netzband, Hyunchul Jang, Kai Yu

Research output: Contribution to journalArticlepeer-review

23 Scopus Citations


Currently, the design of floating offshore wind systems is primarily based on mid‐fidelity models with empirical drag forces. The tuning of the model coefficients requires data from either experiments or high‐fidelity simulations. As part of the OC6 (Offshore Code Comparison Collabo-ration, Continued, with Correlation, and unCertainty (OC6) is a project under the International Energy Agency Wind Task 30 framework) project, the present investigation explores the latter option. A verification and validation study of computational fluid dynamics (CFD) models of the DeepCwind semisubmersible undergoing free‐decay motion is performed. Several institutions provided CFD results for validation against the OC6 experimental campaign. The objective is to evaluate whether the CFD setups of the participants can provide valid estimates of the hydrodynamic damping coefficients needed by mid‐fidelity models. The linear and quadratic damping coefficients and the equivalent damping ratio are chosen as metrics for validation. Large numerical uncertain-ties are estimated for the linear and quadratic damping coefficients; however, the equivalent damping ratios are more consistently predicted with lower uncertainty. Some difference is observed between the experimental and CFD surge‐decay motion, which is caused by mechanical damping not considered in the simulations that likely originated from the mooring setup, including a Coulomb-friction‐type force. Overall, the simulations and the experiment show reasonable agreement, thus demonstrating the feasibility of using CFD simulations to tune mid‐fidelity models.

Original languageAmerican English
Article number389
Number of pages38
Issue number1
StatePublished - 2022

Bibliographical note

Publisher Copyright:
© 2022 by the authors. Licensee MDPI, Basel, Switzerland.

NREL Publication Number

  • NREL/JA-5000-81448


  • CFD
  • Free decay
  • IEA
  • OC6
  • Offshore wind
  • Semisubmersible
  • Uncertainty
  • Validation


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