双向剪切流作用下柔性立管平均阻力特性研究

Mean Drag Force of Flexible Riser Under Bidirectionally Sheared Flow

中国南海存在由内孤立波诱发形成的特殊双向剪切流场.开展了双向剪切流场下的涡激振动状态柔性立管的阻力特性实验研究,基于模态分析法以及张力梁弯曲理论处理实验测量应变时历得到了立管模型的平均阻力,分析了双向剪切流下的柔性立管初始位移、平均阻力以及平均阻力系数特性,确证了双向剪切流具有与线性剪切流相当的阻力系数放大效果.同时发现了双向剪切流下柔性立管独特的中部剪力极值特性,提出剪力系数并拟合得到了双向剪切流下柔性立管中部剪力极值经验公式,该公式将为南海立管设计提供强度校核外载荷输入.

There exists a special bidirectionally sheared flow field due to solitons in the South China Sea.An experimental study of the mean drag force of a flexible riser undergoing vortex-induced vibration under bidirectionally sheared flow is conducted.Modal analysis and the beam theory are applied to processing the strain signal measured in the experiment to obtain the mean drag force.The initial displacement,mean drag force,and mean drag coefficient are investigated,and the amplification of the mean drag coefficient is confirmed under bidirectionally sheared flow with comparable amplification to linear shear flow.Meanwhile,a unique phenomenon that the shear force reaches an extreme value in the center of the riser under bidirectionally sheared flow is found in the experiment.The shear force coefficient is proposed and fitted to obtain an empirical formula for the extreme value of the central shear force of the flexible riser under bidirectionally sheared flow,which will provide external load input for the design of the riser in the South China Sea.