An experimental investigation on vortex induced vibration of a flexible inclined cable under a shear flow

In the present study, an experimental investigation was performed to characterize the vortex induced vibration (VIV) of a flexible cable in an oncoming shear flow. The VIV tests were conducted in a wind tunnel with a flexible cable model. It was found that, under different oncoming velocity profiles, the cable model behaved in single-mode and multi-mode VIVs. The displacement amplitudes of the single mode VIVs were found to be larger than those of multi-mode VIVs, and the cross-flow (CF) response was larger than that of in-line (IL) direction for either the single mode or multi-mode VIVs. For a single mode vibration, the largest CF response occurs in the 1st mode VIV, and the motion trajectory of the 1st mode VIV was found to be an inclined figure of eight shape, while other single mode VIVs behaved in ellipse or straight line trajectories. For multi-mode VIVs, no stable vibration trajectories were found to exist since the vibration frequency bands covered two or more vibration modes. The vortex-shedding frequencies in the wake behind the inclined cable were also characterized in the present study. The shedding frequencies of the wake vortices were found to coincide well with the vibration modes: for a single mode VIV, they were close to the dominant vibration mode; for a multi-mode VIV, they could also cover the appearing vibration modes. In recent years, more and more long-span bridges, such as suspension or cable-stayed bridges have been widely constructed worldwide due to their superior structural performance and elegant appearance. As we all know that, a uniform flow induces a single vortex shedding frequency, in contrast, non-uniform flows can potentially trigger responses with multiple narrow-band components since the vortex shedding frequency depends on the oncoming flow velocity and more than one modal frequency will be excited. All these long-span bridges are built in the atmospheric boundary layer where the velocity increases with the height. The key components of these long-span bridges, stayed cables, easily behave in multi-mode VIVs while in this non-uniform flow, performed full-scale measurement investigations on the Fred Hartman Bridge in Houston (Texas, USA) and observed VIVs of cables with sixth and seventh modes or with fifth and sixth modes, respectively. Chen et al. (2011) observed the occurrence of higher multi-mode (nearly 20th) VIVs of the inclined cables in a cable-stayed bridge in China. Under a large velocity profile, when the velocity differences between the upper and lower …