In this paper, the vortex-induced force characteristics of a flexible riser with buoyancy modules and strakes were experimentally investigated. The strain information caused by vortex-induced vibration (VIV) at different cross-sections on the flexible cylinder was measured in the model test. Combined with the modal superposition method and inverse analysis method for vortex-induced force, the vortex-induced forces on the flexible cylinder were inverted, including the excitation force in phase with velocity and added mass force in phase with acceleration. Then, the excitation coefficients and added mass coefficients at each time step were identified via a least-squares method. The results show that the added mass coefficient and excitation coefficient of the flexible riser covering buoyancy modules present a “sawtooth” distribution along the length of the pipe, while the total mass (sum of structural mass and added mass) is consistent along the pipe. The strake has little effect on the added mass coefficient of the buoyancy module and the bare pipe section, but when it covers the bare pipe section, the excitation coefficient of the bare pipe section decreases to a negative value, showing a damping effect. In addition, when the bare pipe section of the flexible riser is completely covered with helical strakes, only the vortex-shedding frequency component of the buoyancy modules remains in the VIV response of the pipe. The reason for this phenomenon is that helical strakes completely suppress the vortex shedding of the bare pipe section, resulting in the reduction in the VIV excitation energy of the original bare pipe section to 0.

中文翻译：

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带浮力模块和条板的柔性立管涡致受力特性试验研究

本文对带有浮力模块和列板的柔性立管的涡激受力特性进行了实验研究。在模型试验中测量了柔性圆柱体不同截面的涡激振动（VIV）引起的应变信息。结合模态叠加法和涡激力反演分析方法，对柔性圆柱体上的涡激力进行反演，包括与速度同相的激振力和与加速度同相的附加质量力。然后，通过最小二乘法确定每个时间步的激励系数和附加质量系数。结果表明，柔性立管覆盖浮力模块的附加质量系数和激励系数沿管道长度呈“锯齿”分布，而总质量（结构质量和附加质量之和）沿管道是一致的。列板对浮力模块和裸管段的附加质量系数影响不大，但当覆盖裸管段时，裸管段的激振系数减小到负值，表现出阻尼作用。此外，当柔性立管的裸管段被螺旋板完全覆盖时，只有浮力模块的涡旋脱落频率分量保留在管道的VIV响应中。