Abstract
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 Collaboration, 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 uncertainties 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.
Highlights
Offshore wind energy is still a largely untapped source of renewable energy
The present investigation is based on the OC6 Phase Ia model-scale validation campaign carried out at the Concept Basin of the Maritime Research Institute Netherlands (MARIN) within the framework of the MaRINET2 project [24]
Several organizations participating in the present OC6 collaborative validation study carried out computational fluid dynamics (CFD) simulations of some or all three free-decay load cases and provided numerical solutions for validation
Summary
Offshore wind energy is still a largely untapped source of renewable energy. One major barrier to the further utilization of offshore wind energy is the additional cost of the substructure supporting the wind turbine. I participants for free-decay simulations can provide reasonable estimates of the calm-water hydrodynamic damping coefficients for tuning mid-fidelity engineering models To this end, the numerical results from the OC6 participants are compared with each other and against experimental measurements for validation. The uncertainty analysis for the numerical solutions is directly based on the linear and quadratic damping coefficients and the equivalent linear damping ratios estimated from the free-decay motion of the structure This is different from prior investigations, which typically examined the uncertainty of more basic quantities, such as the maxima in the displacement of the structure.
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