Research on Dynamic Characteristics of Monopile Offshore Wind Turbine Tower Under Different Wind Speed Conditions

Based on the ANSYS finite element software, the NREL 5 MW monopile offshore wind turbine tower system was modeled in 3D. The influence of different wind speeds on the dynamic characteristics of the tower structure was simulated and analyzed under the full consideration of the soil structure coupling effect and the impeller rotation. The six average wind speeds and the corresponding impeller speeds in the interval between the cut-in wind speed of 3 m/s and the cut-out wind speed of 25 m/s were selected as simulation conditions. The analysis results show that, with the increase of wind speed and impeller speed, the modal frequency of the tower structure gradually increases, and the first two modal frequencies change most obviously. Moreover, the peak value of the tower displacement increases as the wind speed and impeller speed increases, but the amplitude decreases. The displacement shows a non-linear growth trend. The equivalent stress value of the tower increases as the wind speed and impeller speed increases, but the change trend is different from the displacement, which is roughly linear. The fatigue life of the tower decreases sharply, but they are far more than the actual working hours, the fatigue damage and safety factor hazard values are mainly distributed at the bottom of the tower and at the single pile, consistent with the maximum equivalent stress distribution position.