EFFECTS OF CONTROLLER DYNAMICS ON AERODYNAMIC DAMPING OF A SEMI-SUBMERSIBLE FLOATING WIND TURBINE

Aerodynamic damping is essential in suppressing resonant responses of a floating wind turbine (FWT) under operation conditions. However, aerodynamic damping has not been investigated thoroughly due to its nonlinearity, interaction with floater motions, and effects on controller dynamics. The effects of controller dynamics have been explored in the present study to understand aerodynamic damping better using fully coupled time- domain simulations. The aerodynamic damping in surge and pitch motions are obtained through the comparisons of decay tests with and without wind actions in still water with verification against results from the model tests. Results show that under over-rated wind speed conditions, the blade-pitch controller can affect the aerodynamic damping. In addition, the aerodynamic damping in surge motion is not sensitive to the natural frequencies of the blade-pitch controller. However, the aerodynamic damping in pitch motion has a strong dependence on the controller's natural frequency. Through reasonably tuning the controller gains, the negative aerodynamic damping effect can be well mitigated. The outcomes of the present study can provide insight into aerodynamic damping and the controller design of FWTs.