Conference paper
Investigation of nonlinear difference-frequency wave excitation on a semisubmersible offshore-wind platform with bichromatic-wave CFD simulations
National Renewable Energy Laboratory1
Department of Wind Energy, Technical University of Denmark2
Maritime Research Institute Netherlands3
IFP Énergies nouvelles4
Norwegian University of Science and Technology5
Dalian University of Technology6
Principle Power, Inc.7
University of Strathclyde8
University of Ulsan9
Aero- and Fluid Dynamics, Wind Turbine Design Division, Department of Wind Energy, Technical University of Denmark10
...and 0 moreThe natural surge and pitch frequencies of semisubmersible offshore wind platforms are typically designed to be below the wave frequencies to avoid direct excitation. However, surge or pitch resonance can be excited by the nonlinear low-frequency loads generated by irregular incident waves. Second-order potential-flow models with added Morison drag have been found to underpredict this low-frequency excitation and response.
As part of the OC6 project1, the authors performed computational fluid dynamics (CFD) simulations to enable a better understanding of the low-frequency loads and the limitations of lower-fidelity models. The focus of this paper is to set up a computationally cost-effective CFD simulation of a fixed semisubmersible platform to investigate nonlinear differencefrequency loads and establish the corresponding uncertainty in the results.
Because of the high computing cost, CFD simulations of irregular waves can be challenging. Instead, simulations were performed with bichromatic waves having a shorter repeat period. A preliminary comparison with quadratic transfer functions from second-order potential-flow theory shows that CFD models consistently predict higher nonlinear wave loads at the difference frequency, likely because of flow separation and viscous drag not accounted for in potential-flow theory.
Language: | English |
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Publisher: | The American Society of Mechanical Engineers (ASME) |
Year: | 2021 |
Proceedings: | ASME 2021 3rd International Offshore Wind Technical Conference |
ISBN: | 0791884767 and 9780791884768 |
Types: | Conference paper |
DOI: | 10.1115/IOWTC2021-3537 |
ORCIDs: | Sarlak, Hamid |