Improved tropical cyclone boundary layer model and its application in floating offshore wind turbine structural response analysis

The accurate simulation of tropical cyclone (TC) wind fields is essential for analyzing structural responses, given the potential severe damage to infrastructure caused by TCs. An improved TC boundary layer mean wind field model is proposed, building upon the Kepert model, by introducing a two-dimensional pressure field that varies with height and radius, a surface turbulent diffusivity influenced by wind speed at the lower boundary, and a surface roughness length affected by waves and spray. The accuracy of the improved model is validated through comparisons with TC observational data. Comparative analysis indicates that the Kepert model overestimates the tangential wind speed component. The two-dimensional pressure field employed in the improved model more accurately simulates the central pressure difference within the TC boundary layer. Furthermore, the incorporation of a surface turbulent diffusivity and sea surface roughness length that better reflects physical phenomena further enhances the accuracy of the improved wind field model. The structural responses of a floating offshore wind turbine (FOWT) situated in the TC eyewall region under emergency shutdown conditions are computed using both wind field models separately. The results indicate that blade tip displacement, tower top displacement, platform translation, and rotation responses (pitch and yaw) are overestimated by the Kepert model. In conclusion, the improved model accurately represents the TC structure, offering precise wind field data for assessing FOWT structural responses in TC conditions.