## 4 Results and Discussion
### Influence of Initial Conditions on Wind Parameter
#### 4.1.4 Oncoming Wind Direction  
Considering the terrain and climate features of the valley, the oncoming wind direction at the bridge site may be related to the valley extension direction and the dominant wind directions [1,2,17], so three directions along the extension of the valley and two dominant wind directions were designed: 102\({}^{\circ}\), 211\({}^{\circ}\), 326\({}^{\circ}\), 90\({}^{\circ}\), and 270\({}^{\circ}\), as shown in Figure 1a. The surface roughness was set as 0.12 m, and the class C wind speed profile was set at the entrance. The wind speed at the monitoring point was divided by the wind speed at gradient height, and the result is shown in Figure 9.  
Figure 8: Influence of wind speed profile on wind parameters: (**a**) Nondimensional wind speed profile; (**b**) Nondimensional wind speed factor; (**c**) Wind attack angle profile; (**d**) Wind attack angle factor; (**e**) Wind azimuth angle; (**f**) Wind azimuth angle factor.  
Then taking the condition with the oncoming wind direction of 90\({}^{\circ}\) as the reference condition, and according to Equations (7)-(9), the nondimensional factors were shown in Figure 5b,d,f.  
It can be seen from Figure 9 that, compared with the main wind direction of 90\({}^{\circ}\) (north wind), the oncoming wind direction had the most obvious influence on the wind parameters. The wind speed factor, wind attack angle factor, and wind azimuth angle factor were much larger than the other initial conditions. Specifically, when the oncoming wind direction was along the valley, the shape of the wind speed profiles was similar: 102\({}^{\circ}\), 211\({}^{\circ}\), and 326\({}^{\circ}\). In addition, due to the limited influence of mountain blocking in this direction, the difference between the main wind direction of 90\({}^{\circ}\) and the wind profile of 102\({}^{\circ}\) was also not obvious. The most obvious distortion of the wind speed profile occurred in the 270\({}^{\circ}\) oncoming wind direction, and the wind speed factor was about 0.4-1.3. When a height of 2500 m was reached, the wind speed profiles tended to be the same. When analyzing  
Figure 9: Influence of wind direction on wind parameters: (**a**) Nondimensional wind speed profile; (**b**) Nondimensional wind speed factor; (**c**) Wind attack angle profile; (**d**) Wind attack angle factor; (**e**) Wind azimuth angle; (**f**) Wind azimuth angle factor.  
the wind speed of a bridge in a valley, it is recommended that more attention is paid to the oncoming wind direction along the valley. The impact of the oncoming wind direction on the wind attack angle and wind azimuth angle is very severe, especially when the oncoming flow is blocked by mountains. According to Figure 9a,c,e and Figure 10b, in the range below 1900 m such as 270\({}^{\circ}\), the oncoming flow was severely blocked by mountains. There was a large wake area, causing the wind speed value at the monitoring point to be significantly lower than the surroundings, the wind direction was distorted, and the wind attack angle and wind azimuth angle fluctuated drastically; the ranges were \(-\)10-20\({}^{\circ}\) and \(-\)90-90\({}^{\circ}\).  
The influence of the oncoming wind direction on wind parameters could also be seen from the wind profile and velocity contour shown in Figure 10. It could be found that the oncoming wind direction had an obvious influence on the wind characteristics, especially when the oncoming wind direction was 270\({}^{\circ}\), that is, blocked by the mountains, as shown in Figures 1a and 10b. Therefore, the wind speed, wind attack angle, and wind azimuth angle fluctuated strongly in the low height region such as the height was lower than 2200 m.