Stability assessment and mooring diameter optimization of tension leg platform floating offshore wind turbine using a fully-coupled numerical model

With rapid upscaling of floating offshore wind turbines (FOWT) and large-scale development of deep-sea offshore wind farms, extreme wind-wave-current conditions pose significant challenges for platform stability. To enhance the platform stability and propose an optimal mooring line diameter applicable to mean water depths of the East China Sea, this study presents a fully coupled aero-hydro-servo-elastic numerical model of tension leg platform (TLP) wind turbine using combined ANSYS-AQWA and OpenFAST. The proposed model has higher fidelity and can more accurately capture the nonlinear platform motion characteristics under irregular wind-wave loads. The model has been verified via comparisons to frequency-domain calculations as well as the NREL published data. Furthermore, the TLP stability assessment with different mooring diameters under complicate external environment such as varying significant wave heights, wind-wave misalignments, and average seawater depths is conducted systematically both in time-frequency domains, according to both the American Bureau of Shipping (ABS) guidelines and IEC 61400-3 offshore wind turbine design standard. A mooring diameter optimization approach employing the Gaussian mixture model (GMM) and expectation maximization (EM) algorithms is proposed. Consequently, a mooring line diameter of 0.134 m is recommended for seawater depths ranging from 300 m to 370 m. The research is of scientific significance for enhancing platform resistance to wind-waves load, improving mooring system fatigue life and facilitating large-scale deployment of TLP FOWT.