## 4 Response Analysis of the Wind Turbine Coupling Structure  
### Finite Element Modeling and Dynamic Characteristics  
The tower-blade integrated finite element coupling model was constructed by the large universal finite element analysis software ANSYS. The tower body and blade were simulated by Shell63 unit, whereas the nacelle and internal structure were simulated as a whole by using Beam 189 units. The round raft basis unit was Solid65. The interaction between the foundation and the basis was simulated by a Combin14 unit. After finite element models of different wind turbine parts were constructed, a coupling connection may cause the relative slippage of models under loads, which was attributed to the different unit types of different parts. Therefore, the multipoint restriction unit coupling command was used to connect different parts and construct the tower-blade integrated simulation model. According to the principle of efficiency and the accuracy balance, the model was divided into 4122 units.  
The natural frequency of vibration and the mode of vibration of the wind turbine were solved by a block Lanczos algorithm after modeling [47; 48]. The finite element model of the wind turbine, the first 100 orders of the frequency distribution, and the mode of vibration at typical orders are shown in Figures 18 and 19. The tower-blade integrated model had a low natural frequency of vibration. The fundamental frequency was 0.137 Hz, and the first 10 orders of frequency were lower than 1 Hz. At the same time, the natural frequency of the vibration of the structure was low and distributed densely. The structural frequency achieved approximately linear growth with the number of vibration orders, but the growth rate decreased after 90 orders. In addition, three blades in the tower-blade integrated model made front-to-back movement at the first, fifth, and 10 th order. The blades made complicated front-to-back and left-to-right swings at the 30 th order and 50 th order, which were accompanied by the bending deformation of the tower body. According to the multi-order mode of vibration, the low-order mode of vibration in the tower-blade integrated model was mainly manifested by the front-to-back and left-to-right swing of the blades. Under the high order of vibration, the tower body and blades developed deformations and buckling failure.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{\(\mathbf{C_{L}}\)/\(\mathbf{C_{D}}\)} & \multicolumn{8}{c}{**Height of the Tower Body**} \\ \cline{2-10}  & **12.4 m** & **24.8 m** & **37.2 m** & **49.6 m** & **62 m** & **74.4 m** & **86.8 m** & **99.2 m** & **111.6 m** \\ \hline Normal wind & \(-0.040\) & \(-0.071\) & \(-0.072\) & \(-0.055\) & \(-0.011\) & \(-0.074\) & \(-0.107\) & \(-0.064\) & \(-0.179\) \\ Typhoon loads & \(0.024\) & \(-0.019\) & \(0.001\) & \(0.001\) & \(0.042\) & \(-0.010\) & \(-0.028\) & \(-0.002\) & \(-0.078\) \\ \hline \hline \end{tabular}
\end{table}
Table 6: Lift-drag coefficient ratio of the tower body under normal wind and typhoon loads.  
Figure 18: Finite element model of wind turbine and the first 100 orders of inherent frequency. (**a**) Finite element model; (**b**) First 100 orders of inherent frequency.