## 3 Results and Analysis
### Analysis of Aeroelastic Response  
Figure 6 shows the maximum tip displacements of three blades in the direction of the flap at yaw angles of 0, 30, 60, 90, 120, 150 and 180 degrees under typhoon. The height of blade 1 is the highest, which means that the wind speed was higher, so the total vibration of blade 1 is significantly more intense than that of the other blades. Since the yaw angle is defined as the left side of the inflow axis is positive (Figure 3), there is a positive superposition between aerodynamic and inertial load of blade 3. On the contrary, the aerodynamic and inertial loads on the blade 2 are partially offset to each other, resulting in a weakened load on the blade, and the overall vibration is slightly lower than that of blade 3. It should be noticed that, influenced by extreme fluctuating wind speed of typhoon and the combined force of lift and drag, the blade displacement reaches a maximum at this angle of attack, and the maximum displacement of the blade tip reaches 15.79 m at yaw angle of 30 degrees. As a result, it may lead to serious safety hazards of blade yaw angle of 30 degrees caused by large ultimate loads. In order to illustrate the relationship between the ultimate design loads and the response loads under typhoon, we calculate the ultimate design loads of the blade and tower of the 6 MW wind turbine according to GL2010 standards. In addition, the dynamic loads in 10 min under different inflow conditions in the direction of the flap are also studied, and the maximum/minimum values are compared with the ultimate design loads. Figure 7 shows the comparison of the flap bending moments at the root of three blades, in which the negative value represents the direction, the red and blue curves are the maximum and minimum, respectively, and the dashed line is the ultimate design load. From  
Figure 5: Fluctuating wind speed at hub height. Figure 6: Comparison of the maximum tip displacement. the series of curves, the maximum bending moment appears at yaw angle of the 30 degrees of blade 1, and the maximum value is \(2.24\times 10^{7}\) Nm, which reached 71.5% of the ultimate design value according to GL2010 standards, and the minimum value is \(-1.17\times 10^{7}\) Nm (the negative sign indicates that the direction of flapwise moment is negative), occurring at blade 3 at the inflow angle of the 30 degrees. The results show that the loads on the blades of wind turbines did not exceed the ultimate value, but the average wind speed of the typhoon simulated in this paper is only 40 m/s, far less than the ultimate wind speed of 70 m/s in the specification, and the maximum load is very close to the ultimate value. The dynamic response of the tower under the typhoon is also analyzed. Figures 8 and 9 show the results of the load on the top of the tower and the ultimate design values under different inflow conditions. When the inflow yaw angle is 120 degrees, the minimum load in the \(y\)-direction exceeds the design extreme value of the model. When the inflow angle is 30 degrees, it is very close to the design ultimate value. Figure 10 shows the load variations in the \(y\)-direction within ten minutes under six yaw inflow angles. When the inflow angle is 30 degrees and 120 degrees, respectively, the amplitude of vibration load is higher than other conditions, which means that more vibration energy is included in these cases. The above results show that, if the typhoon enters the flow at these two yaw angles, and if the yaw system does not adjust in time, the tower could be damaged. Figure 7: Flap bending moment of blade root. (**a**) Blade 1; (**b**) Blade 2; (**c**) Blade 3. Figure 8: \(\mathrm{Fx}\) of tower. Figure 10: \(\mathit{Cont}\). Figure 9: \(\mathrm{Fy}\) of tower. The above results reveal that the inflow yaw angle has a significant effect on the blades and tower of the wind turbine. In order to study whether such effect is universal, a 2 MW wind turbine which is widely used at present is also modeled and calculated.