Damping identification of a FOWT by means of a CFD-based simulation tool

The focus of this thesis is to obtain the damping response for the structure of an offshore wind turbine subjected to different frequencies, consistent with the most probable sea conditions. The simulations replicate a hypothetical testing facility, where a floating body is in controlled motion and the dynamic response of the system is analyzed, treating the water-body system as a mass-spring-damper. The simulations are performed using the CFD software "Star CCM+", based on the RANS model. The results will be compared to a linear BEM model obtained from the software NEMOH, with corrections introduced to achieve higher-fidelity data, while maintaining the simplicity and low computational cost of the linear BEM simulations. All post-processing is carried out in Matlab, where the F(z) report is transformed from the time domain to the frequency domain using FFT, allowing the damping coefficient to be expressed as a function of frequency. To test this approach, the first test case chosen is a simple sphere with a 1-meter radius. Once the procedure is validated, it's applied to a more realistic scenario, simulating a reference floating substructure, the UMaine VolturnUS-S. Offshore wind energy production is a complex sector in steady growth, and a valid model that produces accurate results with a low computational cost is crucial in the initial stages of design. Given the high computational cost of each simulation, testing every specific geometry would be impractical. The future goal, with sufficient data, is to propose a generic correction model for the BEM, at least for similar geometries. Another important step would be validating the results of the numerical simulations with real experiments to ensure that the modeling accurately represents the phenomenon.