CFD Simulations for Hydrodynamics of Floating Offshore Wind Turbine

To support the commercialization of offshore semi-submersible platforms, such as a Floating Offshore Wind Turbine (FOWT), Computational Fluid Dynamics (CFD) simulations have matured to a stage that their results can be used with confidence in the design stage of these systems.

Applying the best practices and guidelines derived by joint research consortia, such as the Reproducible CFD JIP and OC6, the CFD code ReFRESCO is utilized by MARIN and blueOASIS to investigate the hydrodynamics of the VolturnUS FOWT semi-submersible platform.

Free decay CFD simulations are carried out in multiple degrees of freedom, and the motion response is obtained in regular and irregular waves. The two CFD practitioners performed the calculations separately from each other using their own set-up for the calculations. Their calculated results agree very well with each other and with the results from the model tests.

It should be noted that for the irregular wave simulations a dedicated wave matching procedure is developed to provide an input wave signal that is as close as possible to the measured wave time trace. This is necessary to minimize differences in calculated motion response due to a deviation in input wave signal. Although a good match in spectrum is obtained between measurement and CFD results, we recommend to further improve this procedure to improve the agreement for the highest wave crests.

Based on the results and comparisons presented in this paper we conclude that with CFD the estimations for hydrodynamic damping and global motion response in regular and irregular waves can be accurately obtained. As a result, CFD can be utilized in the design stage of floating offshore platforms by providing accurate reference time signals, which can then be used to calibrate mid-fidelity time domain simulations.

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