This thesis presents a comprehensive study on Floating Offshore Wind Turbine’s (FOWT’s) modeling and simulation, focusing on the IEA 15MW wind turbine coupled to the VolturnUS-S semi-submersible platform. The primary goal was to develop the building blocks of a high-fidelity Computational Fluid Dynamics (CFD) coupled model using OpenFOAM to simulate large-scale FOWT behavior, verify, and compare each component individually against the mid-fidelity tool OpenFAST. The project builds on the frameworks of previous studies by Pere Frontera Pericàs [81] and Scarlatti [98], expanding them to accommodate the complexities of a larger turbine and more intricate environmental conditions.

The model was implemented using OpenFOAM’s waves2Foam and Moody libraries for wave and mooring modeling, respectively, while aerodynamic simulations employed the turbinesFoam package with an actuator line approach. A spatial convergence study optimized mesh parameters for computational efficiency and accuracy, ensuring reliable and stable simulation results for motions up to 24 meters in surge. Comparisons between OpenFOAM and OpenFAST using a P-Q analysis highlighted significant differences, particularly in modeling damping. OpenFAST was shown to underestimate both linear and quadratic hydrodynamic damping due to its simplified representation of fluid dynamics. Discrepancies in the equilibrium positions were found between the decay tests using CFD; their origin still needs more investigation.

In aerodynamic simulations, steady-state and prescribed motion tests revealed critical differences in thrust and power predictions between OpenFOAM and OpenFAST. OpenFAST overpredicted the reduction in axial wind speed, leading to a reduced power output for steady turbine simulations. The CFD model provided a more accurate representation of rotor wake effects and dynamic responses, particularly in high-frequency surge conditions, where OpenFAST overestimated power fluctuations. These findings underscore the importance of using high-fidelity models like OpenFOAM to improve the accuracy of performance predictions in floating wind turbines.

The study concludes by offering recommendations for future research, including model validation using experimental data and the implementation of overset mesh techniques to improve simulation stability for large motions. The work establishes a reliable CFD framework for simulating this large FOWT, offering insights into enhancing mid-fidelity models and guiding future developments in floating wind turbine design and analysis. It also builds a fully coupled CFD model in OpenFOAM to investigate its behavior.