动态边界条件下柔性立管涡激振动试验研究

Experimental study on vortex-induced vibration of flexible riser under dynamic boundary conditions

为探究柔性立管顶部运动与涡激振动(VIV)响应之间的关系,对伴随顶部运动激励的柔性立管VIV进行了试验研究.立管垂直安装,其直径为2 cm,长度为5 m,在均匀流条件下,详细分析了立管在不同顺流向顶部激励幅值和激励频率下的横流向振动幅值、频率、模态、行波传递等特性.研究结果表明:伴随顶部运动激励的柔性立管VIV与传统VIV相比有显著不同;在低流速下,立管顶部的运动使得立管横流向振幅减小;顶部激励幅值和激励频率的增加可以使得横流向振动频率增加,并发生模态转换,表现为多模态响应特性;频率能量呈现周期性变化,其变化频率近似等于顶部激励频率,这些特性有别于常规的均匀流下柔性立管VIV;在高流速下,立管顶部的运动对立管横流向振幅的影响不显著,其频率能量变化规律与低流速时相同.上述结论可为考虑浮体效应的柔性立管VIV研究提供基本的参考.

To investigate the relation between in-line top-motion and vortex-induced vibration(VIV) response of flexible risers,the VIV of flexible riser with top-motion excitation was studied.The riser was mounted vertically,with the diameter of 2 cm and the length of 5 m.The responses of amplitude,frequency,mode and travelling wave transmission were analyzed in detail under conditions of different excitation amplitude and frequency in uniform flow.Research results show that the VIV phenomena under top-end excitation are significantly different from those of typical VIV.At low flow velocity,the top-motion of the riser can reduce the vibration amplitude of cross-flow direction.With the increase of the top-motion excitation amplitude and frequency,the vibration amplitude of cross-flow direction increases,and the mode conversion occurs,which shows multimodal response characteristics.The frequency energy presents periodic change,and its frequency is approximately equal to the top-motion excitation frequency,which is different from the conventional VIV of the flexible riser under uniform flow.At high flow velocity,the top-motion of the riser has no obvious effect on the vibration amplitude of cross-flow direction,and the frequency energy change is the same as that at low flow velocity.The above conclusions can provide a basic reference for the study on VIV of flexible risers considering floating body effect.