Numerical simulations on cables attached with different shapes of lights and its mitigations by using perforated shrouds

Abstract

To reduce the cable vibration caused by rectangular lights, the light shape is modified to be ellipsoidal and circular sections, together with the use of a perforated shroud. Numerical simulations on six types of cable-light models were conducted using computational fluid dynamics. The mean drag coefficient CD, mean and mean lift coefficient CL, mean of the ellipsoidal lights, circle lights, and perforated shroud cable are reduced compared to the rectangular light. CD, mean can be reduced by a maximum of 50%; CL, mean can be reduced by a maximum of 43%. The maximum fluctuating drag and lift coefficient are also significantly reduced. This indicates that the perforated shrouds might be useful to mitigate the vortex-induced vibration. The ellipsoidal and circular lights are significantly better than rectangular lights in terms of galloping critical wind speed. Furthermore, the perforated shroud is very beneficial for suppressing galloping vibration. The variation of Strouhal number St with the wind attack angle for the shroud rectangular light cable model is relatively smooth, all around 0.1. The wake vortices of rectangular light, ellipsoidal light, and circular light are shed alternately in a typical 2S pattern. However, the alternately shedding vortex of the shroud cable was interrupted by the flow of air through the holes. When the wind attack angle exceeds the most dangerous wind attack angle, the incoming stream cannot be reattached after separation, and the force on the cable is greatly reduced, resulting in a sudden drop in the average lift coefficient. Wind pressure in the gap between the shroud and the cable is negative. The fluctuating wind pressure coefficients on the shrouded cables are significantly lower than those of rectangular lights because of the interference effect of the outer perforated shrouds. In total, the perforated shroud is the best to reduce the galloping caused by the rectangular light.