Floating offshore wind platforms may be subjected to severe sea states, which include both steep and long waves. The hydrodynamic models used in the offshore industry are typically based on potential-flow theory and/or Morison’s equation. These methods are computationally efficient and can be applied in global dynamic analysis considering wind loads and mooring system dynamics. However, they may not capture important nonlinearities in extreme situations. The present work compares a fully nonlinear numerical wave tank (NWT), based on the viscous Navier–Stokes equations, and a second-order potential-flow model for such situations. A comparison of the NWT performance with the experimental data is first completed for a moored vertical floating cylinder. The OC5-semisubmersible floating platform is then modeled numerically both in this nonlinear NWT and using a second-order potential-flow based solver. To test both models, they are subjected to nonsteep waves and the response in heave and pitch is compared with the experimental data. More extreme conditions are examined with both models. Their comparison shows that if the structure is excited at its heave natural frequency, the dependence of the response in heave on the wave height and the viscous effects cannot be captured by the adjusted potential-flow based model. However, closer to the inertia dominated region, the two models yield similar responses in pitch and heave.
Modeling of a Semisubmersible Floating Offshore Wind Platform in Severe Waves
Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the Journal of Offshore Mechanics and Arctic Engineering. Manuscript received December 3, 2018; final manuscript received May 22, 2019; published online June 26, 2019. Assoc. Editor: Amy Robertson.
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Rivera-Arreba, I., Bruinsma, N., Bachynski, E. E., Viré, A., Paulsen, B. T., and Jacobsen, N. G. (June 26, 2019). "Modeling of a Semisubmersible Floating Offshore Wind Platform in Severe Waves." ASME. J. Offshore Mech. Arct. Eng. December 2019; 141(6): 061905. doi: https://doi.org/10.1115/1.4043942
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