Unified Momentum Model-based macrodynamic rotor modeling for floating offshore wind turbines in the Mediterranean Sea

Substantial growth in wind energy capacity is essential to meeting global mid-century net-zero carbon emissions targets. As wind turbines scale up and expand into offshore environments, they encounter operating conditions where traditional aerodynamic models often fail: high-thrust regions and yaw-misaligned winds. By leveraging a first-principles approach, the recently developed Unified Momentum Model (UMM) circumvents the limitations associated with the empirical corrections applied to the classical momentum theory-based models to predict rotor dynamics under these operating conditions. Replacing classical momentum theory, the UMM can be coupled with a traditional blade element model to obtain a Blade Element Momentum (BEM) that works across all operating regimes without empirical corrections. With the primary aim of verifying the UMM for the analysis of Floating Offshore Wind Turbines (FOWTs), this thesis develops a comparative analysis for a numerical case study based on the floating NREL 5-MW reference wind turbine in the spar configuration. For a preliminary analysis, the bottom fixed case is first considered. The power coefficient versus Tip Speed Ratio (TSR) curve is evaluated for different blade pitch angles in both fully aligned and yaw misaligned wind conditions leveraging three different thrust-induction momentum closures (classical momentum, classical momentum with high-thrust correction, and UMM) to the BEM. Findings indicate that traditional one-dimensional momentum theory without high-thrust modifications fails to converge when thrust coefficients exceed unity, limiting the determination of optimal control settings. In contrast, the other two momentum closures achieve convergence across all operating scenarios. However, only the UMM-based model yields an optimal control strategy predicting an increase in thrust levels under yaw misalignment in agreement with recent literature. With the aim to further verify the UMM for estimating the productivity of FOWTs, the analysis was extended to the floating case, considering metocean conditions related to the Pantelleria installation site in Italy, integrating the UMM within the Matlab for Offshore floating wind turbines Simulation Tool (MOST) framework. Results show that across all wind directions and for both BEM models, fixed configurations generally outperform floating ones in terms of productivity due to the dynamic response of floating platforms to ocean currents and waves. While the UMM-integrated version of MOST generally shows improved productivity compared to the traditional BEM implementation, the trend is reversed for yaw angles exceeding 40°, suggesting the need for further analysis under varying yaw conditions. The higher computational cost of the UMM-integrated version of MOST is justified by its increased fidelity and ability to model wakes.