Comparative Investigation of Coupled Dynamic Mechanisms of Floating Vertical-Axis Wind Turbines Supported by Different Platform Configurations

Dedicated platforms for floating vertical-axis wind turbines (VAWTs) require an in-depth understanding of their strongly unsteady coupled dynamics, yet the effects of platform configuration on motion stability, aerodynamic loading, and wake recovery remain insufficiently clarified. This study develops a high-fidelity aero-hydro-mooring coupled framework base on computational fluid dynamics (CFD) to compare Φ-type floating VAWTs supported by semi-submersible and spar platforms under identical wind–wave excitation. The results show that the semi-submersible configuration, owing to its larger structural scale near the free surface, experiences stronger wave interaction and more pronounced wave-frequency heave, surge, and pitch responses. The spar configuration reduces wave-frequency hydrodynamic excitation because of its deep-draft slender structure, but it is more prone to mean pitch offset and sway–roll–yaw coupling. Mooring responses are governed by mean surge drift, mean pitch inclination, and wave-frequency motions, with the semi-submersible system exhibiting stronger tension fluctuations and the spar system showing a more uneven load distribution among the mooring lines. Under the examined wind–wave condition, the spar configuration exhibits larger fluctuations in instantaneous power, thrust and single-blade torque than the semi-submersible configuration. Wake analysis indicates that the semi-submersible system maintains stronger wake coherence, while the spar system enhances vortex breakdown, turbulent mixing, and velocity-deficit recovery. These findings support platform selection, load control, and array layout optimization for floating VAWTs.