Numerical Analysis on the Pitch Motion Response of a Semi-Submersible Floating Wind Platform

The pitch motion of floating wind turbine (FWT) platforms can significantly affect aerodynamic performance, and ultimately power output and control efficiency of FWT. Accurately modelling the pitch behaviour of the platform is essential for evaluating the dynamic response and the control system performance of FWTs. In this paper, a numerical model accounting for viscous damping and second-order potential wave loads was employed to predict pitch motion response. More specifically, quadratic transfer functions (QTFs) for second order difference-frequency wave loads were integrated into a time-domain simulation. Morison elements were incorporated to account for viscous damping effects. Simulation results show good agreement with measured pitch responses across most sea states, both at the spectral level and in terms of key statistics. Large deviations are observed between measurements and simulations for long-period swell conditions, which necessitates further investigation. As QTF calculation depends on first-order vertical motion, the impact of viscous contribution in linear heave motion on QTF contour plots and low-frequency pitch motion response has also been examined. It was found that applying a viscous correction to linear heave motion slightly improves the prediction of pitch motion spectrum.