## 4 Wind Pressure Characteristics with Different Vortex Isolation Plates  
To gain a better understanding of the vortex behavior around the sections and the vortex isolation plate's impact on VIVs, the wind pressure characteristics around the sections were studied. Combined with those in Section 3, the findings here suggest that sections without a vortex isolation plate exhibit an obvious heave at a \(-3^{\circ}\) AOA and obvious torsional vibrations at a \(+3^{\circ}\) AOA. To further study the differences between the control zones under the two vibration modes, the peak points of heaving and torsional vibrations were recorded. The influence of vortex isolation plates with different opening ratios on the VIVs was also studied. The key points of the VIV response are clearly shown in Figure 6.  
Figure 7 showcases the pressure characteristics of the original section at different AOAs. The graph clearly shows the heave at \(-3^{\circ}\) AOA and the torsional vibrations at \(+3^{\circ}\) AOA. It appears that the average pressure coefficient of the heave exhibits significant dispersion across various zones in the upstream section. Specifically, there is a clear decreasing trend in the average pressure coefficient in zones U-1 to U-4, while in zone U-5, there is an increasing trend in the average pressure coefficient. In the downstream section, a decreasing trend in the average pressure coefficient is displayed across zones D-1 to D-3. Conversely, zones U-4 to U-5 exhibit an increasing trend in the average pressure coefficient. It appears that there is significant variability in the average pressure coefficient for torsional vibrations in the D-3 to D-4 region. In the upstream section, the average pressure coefficient steadily increases from U-1 to U-4 and then decreases, before rising again in the U-5 region. The average pressure coefficient in the downstream section gradually decreases and then increases from D-1 to D-2, followed by a sudden spike and subsequent drop in D-3. In Figure 7b, the fluctuating pressure coefficient of the heave has a small dispersion, while in the D-2 and D-3 zones, there is a noticeable jump. As for the fluctuating pressure coefficient of torsional vibrations, two platforms are connected by the jump phenomenon between the D-2 and D-3 zones. Based on Figure 7c, the frequency of each pressure tap is close to the natural frequency. However, for heaving, some pressure taps are near the frequency multiplication of the heaving frequency. Additionally, according to Figure 7d, there is a small change in the frequency amplitude of each zone in the heave. It is worth noting that two different changes in the frequency amplitude occur in both the upstream and downstream sections. Specifically, the D-1 zone in the upstream section typically exhibits a rise in frequency, while  
Figure 6: The key points in the lock-in region. H1, H2, H3, and H4 denote the start point, peak point, descend point, and end point in the heaving lock-in region, respectively; T1, T2, T3, T4, and T5 denote the start point, rising point, peak point, descend point, and end point in the torsional lock-in region. in the D-2 zone, the frequency tends to fluctuate sharply. Additionally, in both the D-3 and D-4 zones, the frequency exhibits a sudden increase and then a decrease. Meanwhile, in the oblique web, which is located far from the center, a rising trend is observed in both sections. When torsional vibrations occur at a +3\({}^{\circ}\) AOA, the average pressure coefficient, fluctuating pressure coefficient, and frequency amplitude of the lower surface of the downstream section and the middle slot at each pressure tap exhibit clear discontinuities. Additionally, the oblique web on the windward side exhibits a rising trend. When heave occurs at a \(-\)3\({}^{\circ}\) AOA, the average pressure coefficient both at the downstream upper surface and in the upstream section exhibits notable dispersions. In addition, the fluctuating pressure coefficient shows clear discontinuities near the central slot in the downstream section.