Transverse vortex-induced vibrations of a near-wall cylinder under oblique flows

Abstract

Transverse vortex-induced vibrations (VIVs) of a near-wall cylinder under oblique flows are studied experimentally in a water flume for both increasing and decreasing velocities. The VIV responses and the wake flow patterns around the cylinder are measured with a synchronous measurement system and a PIV. The validity of the Independence Principle (IP) for a cylinder in proximity to a wall is examined in terms of the vibration amplitude, frequency and critical normal reduced velocity. The results show that the combinations of the gap ratio and oblique angle have significant effect on the VIV response of a circular cylinder. The IP is found to be valid in predicting the VIV response for small oblique angles (θ ≤ 30º) and large gap ratios (e/D ≥ 0.8) whereas for large oblique angles (θ > 30º) or small gap ratios (e/D < 0.8), the deviations from the IP are pronounced. The upper and lower critical normal reduced velocities for the onset of VIV are obtained for both increasing and decreasing velocities. Empirical relationships between the correction factor of the critical normal reduced velocity and gap ratio and the oblique angles (θ ≤ 45º) are established. Based on the analyses of the wake flow patterns obtained by PIV, it is found that the difference in the onset of VIV for increasing and decreasing velocities corresponds to different vortex shedding modes at the initial branch: the 2S vortex shedding mode for increasing velocity and the C(2S) mode for decreasing velocity.

Experimental investigation on vortex-induced vibration and solid-structure impact of a near-bottom horizontal flexible pipeline in oblique shear flow

“…Therefore, the first-mode lower branch does not wholly belong to the impact branch. This observation is different from that reported in Daneshvar and Morton (2020) and Zang and Zhou (2017) for elastically mounted rigid cylinders, due to the flexibility of the long horizontal pipe in the present study. In the following, the two solid-pipe impact types corresponding to the first-and second-mode dominant responses are discussed in further detail.…”

“…Additionally, cross-flow amplitudes in the first-mode lower branch and the second-mode initial branch exhibit a negligible variation due to the spatial constraint. This region was named as the impact branch by Daneshvar and Morton (2020) or bounce back branch by Zang and Zhou (2017).…”

Flow-induced vibration and impact of a cylinder between two close sidewalls

“…Elastically mounted cylinders placed near a plane boundary are also of interest because of their engineering significance, such as in submarine pipelines near the seafloor (Yang et al 2009;Li et al 2016;Zang & Zhou 2017). Tham et al (2015) conducted numerical simulations of the dynamics of a two-dimensional cylinder near a stationary wall parallel to a free stream at a low Reynolds number of Re = 100.…”