Experimental investigation of aerodynamic effect-induced dynamic characteristics of an OC4 semi-submersible floating wind turbine

Compared to onshore wind turbines, aerodynamics-induced dynamic characteristics of a floating wind turbine are more complicated due to its coupled aero-hydro-servo-elastic behaviours. The study investigates these aerodynamics-induced dynamic characteristics using an OC4 semi-submersible floating wind turbine. In this research, a high-fidelity wind field and a 1/50th scale model were tested. The dynamic characteristics induced by the aerodynamic effects were investigated in detail via the experimental results, including aerodynamic damping effects, gyroscopic effects, dynamic responses of the Rotor-Nacelle-Assembly and dynamic responses of the mooring system. It is found that aerodynamic damping is active in reducing surge and pitch resonant responses and probably increases with the inflow wind speed and the rotating-blades-induced induction coefficient; the gyroscopic effect intensifies the yaw motion and increases with the rotational speed of a rotor; the significant responses from the Rotor-Nacelle-Assembly may occur when the natural frequencies of the tower are close to aerodynamic periodic frequencies; and the mooring system is more sensitive to wave loads rather than to aerodynamic loads. This study presents the complexity of the dynamic characteristics induced by the aerodynamic effects in a floating wind turbine, and in the design code, using time-domain analysis software, which considers the coupling effects between the wind- and wave-induced loads and responses are suggested.