Dynamic and structural performances of offshore floating wind turbines in turbulent wind flow

A realistic turbulent wind field differs from a steady uniform one, in terms of the wind shear, the turbulence intensity and the coherence structure. Although it has been clear that an offshore floating wind turbine will behave differently in the turbulent wind, the individual effect of the above three items are not investigated sufficiently until now. The primary objective of the present research is to investigate in details how the wind shear, the turbulence intensity and the coherence influence the dynamic and structural responses of offshore floating wind turbines. Aero-hydro-servo-elastic coupled simulation of a semi-submersible floating wind turbine is run in time-domain. The wind shear has a limited effect on the global responses of the floating wind turbine although its influence on each individual blade is considerable. Comparatively, the floating wind turbine is quite sensitive to the turbulence intensity. In a wind field with high turbulence intensity, the platform motions become more violent and the structural loads are increased substantially. The proper orthogonal decomposition method is used to investigate the coherence quantitatively. A partial coherence structure helps to reduce the flow variation seen by the rotor and thereby beneficial to the safety of the floating wind turbine.