58 / 2019-09-16 01:42:58

Multi-modal vortex induced vibrations of stay cables of long-span bridges

VIV,Stay cable,Sheared airflow,Multi-modal behaviours

Vortex-induced vibration of an inclined cable under sheared wind flow is investigated through computational fluid dynamics numerical simulation$^1$ and wind tunnel tests$^2$. The results indicated that the cable vibration exhibits two types of behavior—single-mode vibration (uniform wind or the wind with small velocity changes) and multimode vibration (the wind with large velocity changes)—according to the velocity profile over the inclined cable. The single-mode vibration of the cable exhibited a standing wave response (a chessboard pattern), whereas the multimode vibration exhibited a traveling wave motion (a parallel line pattern). The lift coefficients exhibited similar features as the cable vibration under wind with varying velocity profiles. Dominant frequencies of the lift coefficients could be observed over the upper segments of the cable under wind with small velocity changes (or the entire cable length under uniform wind), but a broader frequency band appeared in the lift coefficients over the low segments of the cable under wind with large velocity changes. The wake patterns and vortex shedding lock-in regions depended on the vibration type (or the wind velocity profiles). The single-mode vibration had large lock-in regions (the entire cable length or the upper segments of the cable), and over these regions, the vortex shedding was in phase or synchronous. However, for a multimode vibration (wind with large velocity changes), the vortex shedding is irregular and complicated along the cable axis.