Fully coupled aero-hydrodynamic analysis of a floating VAWT with enhanced spar platforms

Vertical axis wind turbines (VAWTs) are attracting attention in floating offshore wind because of their low center of gravity, compact structure, and insensitivity to wind direction. Despite these advantages, floating VAWTs are nascent: dedicated platforms are scarce and coupled aero-hydrodynamic mechanisms under wind–wave conditions remain poorly understood. To fill these gaps, the study establishes a fully coupled aero-hydro-mooring numerical model by integrating computational fluid dynamics (CFD) with the Dynamic Fluid-Body Interaction (DFBI) method. The dynamic responses of a Spar-type floating VAWT are systematically evaluated under both operation and shutdown conditions, and five modified Spar-type platforms with specific design objectives are subsequently proposed. Results indicate that compared to a fixed-bottom turbine, the floating system achieves a higher average power coefficient but exhibits more severe fluctuations, primarily due to the platform's pitch motion. Under operational conditions, the rotor experiences increased thrust loads relative to the parked state, leading to significantly larger surge displacements and pitch equilibrium angles, as well as markedly enhanced yaw responses. Analysis of the five modified platforms shows that adding heave plates or transverse/longitudinal damping plates can effectively increase radiation damping in their respective directions, thereby suppressing motion responses. However, the effect of a single damping plate is limited in scope. The S-HTL platform, which incorporates multi-directional damping devices, demonstrates the most stable performance by effectively dissipating energy from external loads and improving mooring tension distribution, thus comprehensively enhancing platform stability.