剪切流下发生涡激振动的柔性立管阻力特性研究

利用缩尺模型试验的方法研究了线性剪切流下涡激振动发生时柔性立管的阻力特性.文中基于光纤光栅应变传感器测得的模型应变信息,采用梁复杂弯曲理论计算了立管的平均阻力,继而分析了阻力系数沿管长方向和雷诺数的分布特性以及涡激振动对阻力系数的放大效应,并提出了用于估算柔性立管发生涡激振动时阻力系数的经验公式.结果表明:涡激振动对阻力系数有放大效应,使得立管局部阻力系数高达3.2;平均阻力系数在1.0×104到1.2×105的雷诺数区间内的值为1.3~2.0,并随雷诺数的增大而减小.本文提出的经验公式可准确估算高雷诺数下涡激振动发生时柔性立管的阻力系数,此经验公式考虑了流速、涡激振动主导模态以及主导频率对阻力系数的影响. 

INVESTIGATION OF DRAG FORCES FOR FLEXIBLE RISERSUNDERGOING VORTEX-INDUCED VIBRATION IN SHEARED FLOW

The drag forces of a flexible riser undergoing vortex-induced vibration(VIV) in sheared flow were investigated using a scale model test.The mean drag forces were determined based on beam theory using the strains measured by the fiber bragg grating strain sensors of the riser.The distributions of the drag coefficients along the riser and Reynolds numbers(Re), and the VIV amplification of the drag coefficient, were studied, and a new empirical model to estimate the drag coefficient on a flexible riser undergoing VIV was proposed.The results show that VIV can amplify the drag coefficient, resulting in the local drag coefficient of the riser up to 3.2.For Re values from 1.0×10⁴~1.2×10⁵, the mean drag coefficient value was between 1.3 and 2.0, and decreased as Re increased.Furthermore, the proposed empirical prediction model, which accounts for the effects of current, the VIV dominant modal number and the frequency in the cross-flow direction, can predict riser drag coefficients under VIV accurately at high Re values.