EFFECTS OF ROTOR-NACELLE ASSEMBLY MODELS ON THE STRUCTURAL NATURAL FREQUENCIES AND SEISMIC RESPONSE OF OFFSHORE WIND TURBINE

For the Rotor-nacelle assembly (RNA), which is also known as the head of wind turbine (WT), the frequently used simplified models mainly include point mass (RNA_M), point mass with eccentricity (RNA_ME), point mass with eccentricity and rotational inertia (RNA_MEJ) and rigid nacelle with rigid blades (RNA_RB). Based on the prototype of the NREL 5MW offshore wind turbine (OWT) with monopile foundation, Abaqus is adopted to establish WT models with these four simplified RNA models. Taking the elaborated RNA_FB WT model as the baseline, this paper analyzes the influences of these different simplified RNA models on the natural frequency and seismic response of the WT structure. The results show that for the problems involving only the 1st order mode of the supporting structure, the calculated frequency values of the four simplified RNA models are all accurate and reliable; The RNA_MEJ, RNA_RB or RNA_FB model should be used when the 2nd order mode or/and torsion mode of the supporting structure is involved; The RNA_FB model should be used when higher-order modes of the supporting structure are involved. For the seismic response analysis of WT structure, the structural responses calculated by the RNA_MEJ and RNA_RB models are more accurate, but the maximum relative deviation (RD) of the majority of their structural response peaks still exceeds 10%. Therefore, the simplified RNA models should be used cautiously in engineering application.