Advanced multi-physics modeling of floating offshore wind turbines for aerodynamic design and load management

Floating offshore wind turbines (FOWTs) offer distinct advantages for improving the competitiveness of offshore wind energy. However, their operation involves complex dynamics characterized by multiple sources of loading, considerable temporal variability, and high nonlinearity. Understanding the multi-physics coupling mechanisms and subsystem interactions governing the behavior of FOWTs is essential for enhancing operational safety, increasing power output, and promoting commercial deployment. To address these challenges, this study develops a high-fidelity, fully coupled aero-elastic-hydro-mooring framework by integrating computational fluid dynamics (CFD) and the finite element method (FEM). The NREL 5 MW horizontal-axis wind turbine (HAWT) mounted on a semi-submersible platform is used as an exemplar to investigate its nonlinear dynamic responses under combined wind and wave loading. The results show that the platform's six-degree-of-freedom motion leads to continuous changes in the rotor inflow conditions, resulting in a 6.84 % reduction in the average power coefficient compared with its bottom-fixed counterpart, and producing a noticeable increase in power fluctuations. Nevertheless, the wake behind the FOWT exhibits higher turbulence intensity and a faster rate of dissipation. The two-way fluid–structure interaction analysis indicates that the blades undergo flapwise elastic deformation, particularly from the mid-span to the tip, which alters the angle of attack and induces continuous vortex shedding along the trailing edges. The structural stress distribution highlights significant stress concentration at the tower base, the bottom of the main column, and the connections between the braces and the platform. Although blade stress remains relatively low overall, higher stresses are observed near the blade root transition and at the shear web connections. In addition, the contact opening analysis between the mooring lines and the seabed shows that the windward mooring line periodically separates from and recontacts the seabed due to the surge motion of the platform, resulting in varying contact pressure distributions and large fluctuations in the mooring tension.