## 4 Results and Discussion
### Fluctuating Wind Characteristics
#### 4.2.2 Fluctuating Wind Power Spectra  
The fluctuating wind power spectrum is used to describe the distribution of energy at different frequencies, clearly reflecting the dynamic wind characteristics, and is an important parameter in bridge buffeting. The peak of the power spectrum refers to the maximum value of the power spectral density, which can reflect the degree of fluctuation in wind turbulence [27; 28]. The high-frequency decay of the power spectrum refers to  
Figure 28: Turbulence intensity of the main beam under uniform inflow with different wind speeds and directions. Figure 27: Turbulence intensity of the northeast tower under ABL inflow with different wind speeds and directions. Figure 29: Turbulence intensity of the main beam under ABL inflow with different wind speeds and directions. the rate at which the power spectrum decreases in the high-frequency region. A faster decay indicates less high-frequency energy in the turbulence [29, 30]. The peak value and high-frequency decay of the longitudinal fluctuating wind power spectrum at various locations on the bridge are focused on in this section. The longitudinal fluctuating wind power spectrum of the southwest bridge tower is shown in Figures 30 and 31. When the oncoming wind is uniform, the power spectrum peak with the increase in height is increased under the \(0^{\circ}\) wind direction, as shown in Figure 30a. The power spectrum for the \(30^{\circ}\) and \(180^{\circ}\) wind directions shows a smaller degree of variation with height. Additionally, the peak of the power spectrum significantly decreases with the increase in wind speed. This indicates that the wind fluctuations are smaller, which is consistent with the conclusion in Section 4.2.1 that the higher the wind speed, the smaller the turbulence intensity under uniform inflow. With the increase in oncoming wind speed, the high-frequency part of the power spectrum decays more slowly. This result suggests that there is more high-frequency energy in the turbulent vortices, and there may be more small-scale vortices in the flow field. When the oncoming wind is ABL inflow, compared to uniform inflow, the peak frequency of the power spectrum decreases, and the high-frequency part decays significantly faster. The power spectrum hardly changes with the variation in oncoming wind speed. Therefore, in Section 4.2.1, the turbulence intensity remains largely unchanged with the change in oncoming wind speed under ABL inflow. The longitudinal fluctuating wind power spectrum of the northeast bridge tower is presented in Figures 32 and 33. When the oncoming wind is uniform, the variation in the power spectrum with wind speed follows the same pattern as observed on the southwest bridge tower; that is, the higher the wind speed, the smaller the power spectrum peak and the slower the high-frequency decay rate, and there is an increase in peak frequency. This pattern is most evident in Figure 32c. However, unlike the southwest bridge tower, the power spectrum of the northeast bridge tower is essentially unchanged with the increase in height. When the oncoming wind is ABL inflow, the power spectrum shows no significant variation with the oncoming wind speed, and the power spectrum curves under different wind speeds are largely coincident. Figure 30: Longitudinal fluctuating wind power spectra of the southwest tower under uniform inflow with different wind speeds and directions. Figure 31: Longitudinal fluctuating wind power spectra of the southwest tower under ABL inflow with different wind speeds and directions. Figure 32: Longitudinal fluctuating wind power spectra of the northeast tower under uniform inflow with different wind speeds and directions. The longitudinal fluctuating wind power spectrum of the main beam is shown in Figures 34 and 35. The variation in the power spectrum with oncoming wind speed on the main beam is consistent with the patterns observed on the two towers.