A vortex-induced vibration(VIV)experiment on three side-by-side risers subjected to a uniform flow was carried out in a combined wave-current flume.The dynamic features of interference effect on three side-by-side ris...A vortex-induced vibration(VIV)experiment on three side-by-side risers subjected to a uniform flow was carried out in a combined wave-current flume.The dynamic features of interference effect on three side-by-side risers were investigated by varying fluid velocity and inter-riser spacing.The distributions of dimensionless displacement,dominant frequency,and displacement trajectory of the model risers were measured using mode decomposition and wavelet transform techniques.The coupled interference of inter-riser fluid to adjacent risers at different spacings was disclosed by introducing the"interference ratio"concept.The results show that at spacings smaller than 6.0 D,the three model risers display appreciable deviations in their displacement responses in cross-flow or in-line direction,attributable to the strong proximity disturbance and wake interference between the risers.When the spacing is increased to 8.0 D,wake interference still makes great difference to the dynamic response of the risers in both directions.As reduced velocity increases,the three risers show higher agreement with an isolated riser in overall dominant vibration frequency in CF direction than that in IL direction at all spacings and the side risers,although symmetrically placed,do not vibrate symmetrically,as a result of the steady deflection of clearance flow within the riser group.Interference effect results in a remarkable unsteady mode competition within the risers;quantitation of the interference levels for the three risers at different spacings with interference ratio revealed that under low flow velocities and large spacing ratios,clearance flow constitutes a non-neglectable interferer for three side-by-side risers.展开更多
Taking the three-riser group arranged in tandem as the research subject,an experimental study was carried out on the risers arranged in tandem.The purpose is to explore the sensitivity of the dynamic response of each ...Taking the three-riser group arranged in tandem as the research subject,an experimental study was carried out on the risers arranged in tandem.The purpose is to explore the sensitivity of the dynamic response of each riser to spacing ratio and reveal the physical mechanism of riser groups under the interference effect.The spacing ratios of the adj acent risers are 4.0,5.0,6.0,and 8.0.At the spacing between the risers of 4.0D,the strong feedback effect increases the cross-flow(CF) displacement amplitude of the upstream riser.The shielding effect is the key factor affecting the interference effect on the midstream and downstream risers.At low reduced velocities,the shielding area initially appears,the displacement amplitude of the midstream and downstream risers varies greatly,the vibration of the two risers is still dominated by the first-order mode,and the transition between adjacent vibration modes is restrained.The multi-frequency superposition phenomenon is very significant at high reduced velocities.The most sensitive interference spacing under the test conditions is obtained.Due to the separation of the incoming flow and the double shielding effect of the upstream and midstream risers,the regular vortex-induced vibration in the wake area of the downstream riser is broken,and the vibration in the two directions is weakened.In general,the interference effect is more significant for the CF vibration of the three-riser groups than the in-line(IL) vibration.展开更多
A large amount of experimental work has been carried out in the past tounderstand mean and fluctuating forces on a single circular cylinder in cross flows. In comparisonsubstantially less work can be found on the inte...A large amount of experimental work has been carried out in the past tounderstand mean and fluctuating forces on a single circular cylinder in cross flows. In comparisonsubstantially less work can be found on the interference between multiple cylinders and the numberof publications a-vailable becomes drastically smaller as the number of cylinders involvedincreases. The current experimental work systematically examines the wake shielding effects of threecylinders in a towing tank. Though staggered, the three cylinders are arranged mainly along theflow direction with the downstream cylinders situating in the wakes of the upstream cylinders. Thetests are mainly carried out in the sub-critical Reynolds number regime with the upper end close tothe critical Reynolds number regime. Significant drag reduction on downstream cylinders isidentified.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.51709161)Shandong Province Young and Middle-Aged Scientists Research Awards Fund(Grant No.BS2015HZ017)+1 种基金Colleges and Universities of Shandong Province Science and Technology Plan Projects(Grant No.J16LH04)Key R&D Projects in Shandong Province(Grant No.2018GHY115045)。
文摘A vortex-induced vibration(VIV)experiment on three side-by-side risers subjected to a uniform flow was carried out in a combined wave-current flume.The dynamic features of interference effect on three side-by-side risers were investigated by varying fluid velocity and inter-riser spacing.The distributions of dimensionless displacement,dominant frequency,and displacement trajectory of the model risers were measured using mode decomposition and wavelet transform techniques.The coupled interference of inter-riser fluid to adjacent risers at different spacings was disclosed by introducing the"interference ratio"concept.The results show that at spacings smaller than 6.0 D,the three model risers display appreciable deviations in their displacement responses in cross-flow or in-line direction,attributable to the strong proximity disturbance and wake interference between the risers.When the spacing is increased to 8.0 D,wake interference still makes great difference to the dynamic response of the risers in both directions.As reduced velocity increases,the three risers show higher agreement with an isolated riser in overall dominant vibration frequency in CF direction than that in IL direction at all spacings and the side risers,although symmetrically placed,do not vibrate symmetrically,as a result of the steady deflection of clearance flow within the riser group.Interference effect results in a remarkable unsteady mode competition within the risers;quantitation of the interference levels for the three risers at different spacings with interference ratio revealed that under low flow velocities and large spacing ratios,clearance flow constitutes a non-neglectable interferer for three side-by-side risers.
基金financially supported by the National Natural Science Foundation of China (Grant No. 42177167)the Natural Science Foundation of Shandong Province (Grant No. ZR2019QEE008)。
文摘Taking the three-riser group arranged in tandem as the research subject,an experimental study was carried out on the risers arranged in tandem.The purpose is to explore the sensitivity of the dynamic response of each riser to spacing ratio and reveal the physical mechanism of riser groups under the interference effect.The spacing ratios of the adj acent risers are 4.0,5.0,6.0,and 8.0.At the spacing between the risers of 4.0D,the strong feedback effect increases the cross-flow(CF) displacement amplitude of the upstream riser.The shielding effect is the key factor affecting the interference effect on the midstream and downstream risers.At low reduced velocities,the shielding area initially appears,the displacement amplitude of the midstream and downstream risers varies greatly,the vibration of the two risers is still dominated by the first-order mode,and the transition between adjacent vibration modes is restrained.The multi-frequency superposition phenomenon is very significant at high reduced velocities.The most sensitive interference spacing under the test conditions is obtained.Due to the separation of the incoming flow and the double shielding effect of the upstream and midstream risers,the regular vortex-induced vibration in the wake area of the downstream riser is broken,and the vibration in the two directions is weakened.In general,the interference effect is more significant for the CF vibration of the three-riser groups than the in-line(IL) vibration.
文摘A large amount of experimental work has been carried out in the past tounderstand mean and fluctuating forces on a single circular cylinder in cross flows. In comparisonsubstantially less work can be found on the interference between multiple cylinders and the numberof publications a-vailable becomes drastically smaller as the number of cylinders involvedincreases. The current experimental work systematically examines the wake shielding effects of threecylinders in a towing tank. Though staggered, the three cylinders are arranged mainly along theflow direction with the downstream cylinders situating in the wakes of the upstream cylinders. Thetests are mainly carried out in the sub-critical Reynolds number regime with the upper end close tothe critical Reynolds number regime. Significant drag reduction on downstream cylinders isidentified.
