Study On VIV Characteristics Of Double Column Cable Tower

As the span of the bridge increases,the height of the bridge tower continues to increase,and the bridge tower changes from a concrete structure to a steel-concrete composite structure and a steel structure,which makes the bridge tower extremely prone to vortex-induced vibration.Study the VIV mechanism of the bridge tower to provide favorable support for the vibration suppression of the bridge tower.In this paper,the double column cable tower is taken as the research object,and the VIV performance of the bridge tower under different wind conditions is studied by using wind tunnel test and numerical simulation method.The main research contents include:(1)The wind tunnel test research on the wind-induced vibration of the bridge tower under seven winds in the uniform flow and turbulent flow field shows that: Bending VIV on the outside of the bridge tower surface and torsional VIV will occur in both 90° and 75° wind directions of the bridge tower;the torsional VIV and the bending VIV on the outside of the bridge tower surface appear sequentially in the wind direction of 90°;the torsional VIV and the bending VIV on the outside of the bridge tower surface appear simultaneously in the wind direction of 75°.(2)The numerical calculation of the four key height sections of the bridge tower found that: 90° wind direction,with the increase of wind speed,the excellent frequency of the lift coefficient of the upper half of the tower is successively close to the frequency of the torsional VIV and the frequency of the bending VIV on the outer side of the bridge tower face;with a wind direction of 75°,the lift coefficient of the upper half of the tower has two excellent frequencies,which are respectively close to the frequencies of the bending VIV on the outer side of the bridge tower surface and torsional VIV.At 90° wind direction,the cross-section wake vortex is in a "swing state" when the torsional VIV occurs,and the cross-section wake vortex is "separated state" when the bending VIV on the bridge tower surface occurs;the wake vortex of the two tower columns with a wind direction of 75° is an asymmetric structure.(3)The POD analysis of the cross-sectional vorticity field when vortex vibration occurs shows that: the 1st-order modal energy of the 90° wind direction fluctuating flow field accounts for more than 60%;the 75° wind direction fluctuating flow field 1st and 2nd order modal energy together account for more than 80%.When the wind direction is 90°,the torsional VIV and the bending VIV on the outside of the bridge tower surface correspond to the third and fourth mode wake vortices in different shapes;when the wind direction is 75°,the wake vortices of the two pillars are asymmetrical.(4)The three-dimensional numerical calculation of the bridge tower shows that: in the wind direction range from 0° to 45°,the beam causes the hairpin vortex in the wake,but the range of the flow field affected by the hairpin vortex caused by the beam in the tower height direction is relatively small;in the wind direction range from 60° to 90°,no hairpin vortex was found in the wake of the beam,and the three-dimensional effect caused by the beam is not significant,so the three-dimensional calculation can be simplified by two-dimensional numerical calculation.(5)Numerical calculations and POD analysis found: The flow field characteristics of the section at the top,2/3 tower height and 1/2 tower height are similar,but different from the flow field at the bottom of the tower.It shows that the superstructure of the bridge tower contributes more to the VIV of the bridge tower,and the suppression of the VIV of the bridge tower can be achieved by increasing the stiffness of the superstructure of the bridge tower along the bridge direction.