# Wind Speed Spectrum of a Moving Vehicle under Turbulent Crosswinds
## 4 Wind Speed Spectrum of a Moving Vehicle
### Discussion of Wind Speed Spectrum Peak  
Figure 8 shows the change regulation of the wind speed spectrum peak at different wind yaw angles and different \(V_{\rm ratio}\) values, in which the amplification coefficient \(\varepsilon\) represents the ratio of the peak between the moving point and the static point. Generally, the wind speed spectrum peak changes with the wind yaw angles into the sinusoidal curve. Figure 6: Wind speed spectra of a moving vehicle. When the \(V_{\rm ratio}\) value is 0.1 or 0.3, the wind speed spectrum peak of the moving point roughly coincides with the peak of the static point at different wind yaw angles. That is, when the vehicle's moving speed is small, the influence of movement can be neglected. When the \(V_{\rm ratio}\) is 0.5 and \(\varphi\) is \(120^{\circ}\), the wind speed spectrum peak is at its maximum and reaches its minimum at \(15^{\circ}\) and \(175^{\circ}\). The influence of the vehicle's moving speed should be considered, and the maximum increase rate of the wind speed spectrum peak could be 0.6%. Figure 8: Wind speed spectrum peak coefficients. Figure 7: Wind speed spectra of a moving vehicle at different wind yaw angles. When the \(V_{\rm ratio}\) is 0.75 and \(\varphi\) is 135\({}^{\circ}\), the wind speed spectrum peak is at its maximum and reaches its minimum at 15\({}^{\circ}\) and 175\({}^{\circ}\). The maximum increase rate of the wind speed spectrum peak could be 2.7%. When the \(V_{\rm ratio}\) is 1 and \(\varphi\) is 175\({}^{\circ}\), the wind speed spectrum peak is at its maximum. The maximum increase rate of the wind speed spectrum peak is 7.6%. While this would not happen in the condition where \(\varphi\) is 175\({}^{\circ}\). That is, when the wind is coming from behind the vehicle. There is no sense for this condition. The wind speed spectrum peak is at its minimum at 15\({}^{\circ}\). When the \(V_{\rm ratio}\) is 2, the wind speed spectrum peak is at its minimum at a wind yaw angle of 15\({}^{\circ}\) and is at its maximum at 120\({}^{\circ}\). The maximum increase rate of the wind speed spectrum peak could be 7.6%. When the \(V_{\rm ratio}\) increases to 5 from 3, the wind speed spectrum peak is also at its minimum at 15\({}^{\circ}\) and reaches its maximum at 105\({}^{\circ}\). The maximum increase rate of the wind speed spectrum peak could be 7.5%. That is, when the \(V_{\rm ratio}\) value is small, the influence of the vehicle's moving speed is low, and the wind speed spectrum is close to that of the static point. In a natural wind environment, the influence of the vehicle's movement must be considered, and the wind speed spectrum peak increased by only about 8.0% at a wind yaw angle of 105\({}^{\circ}\). That is, the wind speed spectrum peaks are roughly the same at different wind yaw angles and \(V_{\rm ratio}\) values. When the \(V_{\rm ratio}\) is larger than 1, the maximum wind speed spectrum peaks are all increased by 8.0%. The wind speed spectrum peak of a moving point is larger than that of a static point. The change law is shown in Figure 9a. As the \(V_{\rm ratio}\) value increases, the wind yaw angle corresponding to the maximum wind speed spectrum peak was firstly increased and then decreased. When the \(V_{\rm ratio}\) value is smaller than 1, the frequencies corresponding to the wind speed spectrum peak are increased with the increasing \(V_{\rm ratio}\) values. When the \(V_{\rm ratio}\) value is larger than 1, the frequencies corresponding to the wind speed spectrum peak were decreased and then remained unchanged for \(V_{\rm ratio}\) values larger than 3. As the \(V_{\rm ratio}\) value increased, the wind yaw angle corresponding to the maximum value of \(\varepsilon\) was firstly increased and then decreased. In Figure 9b, the maximum wind speed spectrum peak increase rate is shown. Under the condition that the \(V_{\rm ratio}\) value is larger than 1, the wind speed spectrum peaks increase by 8% and exhibit little change.