Abstract The features of hydrodynamic coefficients including drag and added mass coefficients on a flexible pipe fitted with helical strakes in an oscillatory flow are studied experimentally. The experiment of a flexible straked pipe was conducted in an oscillatory flow with the Keulegan-Carpenter (KC) number varying from 9 to 165 and the maximum reduced velocities ranging from 4 to 8. Strain response in both in-line and cross-flow directions are measured by fiber bragg grating sensors. Using displacement reconstruction and inverse analysis methods, displacement response and hydrodynamic force of the straked pipe are identified. Then, through the least squares method, corresponding drag and added mass coefficients are extracted. The asymmetric features at the acceleration and deceleration stages of hydrodynamic force on a flexible pipe in the in-line direction under oscillatory flow are first observed. Compared with a bare pipe, helical strakes can effectively reduce the higher frequency fluctuating force and enhance the wake effects. The hydrodynamic coefficients on the straked pipe are significantly magnified in the case of a relatively small KC number. The maximum mean drag coefficients can reach approximately 10. The presented work suggests that the risk of helical strakes application should be fully evaluated through flexible pipe experiments in both steady flow and unsteady flow.

中文翻译：

---

振荡流中装有螺旋列板的挠性管上的水动力系数放大

摘要 通过实验研究了带螺旋列板的挠性管在振荡流中的水动力系数特性，包括阻力系数和附加质量系数。在 Keulegan-Carpenter (KC) 数从 9 到 165 不等、最大降低速度从 4 到 8 不等的振荡流中进行了柔性板管的实验。 在线和横向流动方向的应变响应由光纤布拉格光栅传感器测量。利用位移重建和逆分析方法，确定了排管的位移响应和水动力。然后，通过最小二乘法，提取相应的阻力和附加质量系数。首次观察了振荡流作用下柔性管在轴向上的流体动力在加速和减速阶段的不对称特征。与裸管相比，螺旋列板能有效降低高频脉动力，增强尾流效应。在 KC 值相对较小的情况下，列管上的水动力系数显着放大。最大平均阻力系数可以达到大约 10。目前的工作表明，螺旋列板应用的风险应该通过稳定流和非稳定流中的柔性管实验来充分评估。在 KC 值相对较小的情况下，列管上的水动力系数显着放大。最大平均阻力系数可以达到大约 10。目前的工作表明，螺旋列板应用的风险应该通过稳定流和非稳定流中的柔性管实验来充分评估。在 KC 值相对较小的情况下，列管上的水动力系数显着放大。最大平均阻力系数可以达到大约 10。目前的工作表明，螺旋列板应用的风险应该通过稳定流和非稳定流中的柔性管实验来充分评估。