中文摘要：

涡激振动是诱发海洋立管、浮式平台系泊缆和海底悬跨管道等柔性圆柱结构疲劳损伤的重要因素.目前，海洋工程中用于柔性圆柱涡激振动预报的流体力系数主要来源刚性圆柱横流向受迫振动的实验数据，存在一定缺陷和误差.本文综合考虑横流向与顺流向振动耦合作用，建立了柔性圆柱涡激振动流体力模型，运用有限元法和最小二乘法确定升力系数、脉动阻力系数和附加质量系数.为了准确识别柔性圆柱涡激振动流体力系数，设计并开展了拖曳水池模型实验，实验用柔性圆柱模型的质量比为1.82，长径比为195.5.通过与刚性圆柱流体力系数对比，深入分析了柔性圆柱流体力系数的特性.结果表明：柔性圆柱在一阶模态控制区，流体力系数随约化速度变化趋势与刚性圆柱大致相似；二阶模态控制区，升力系数和脉动阻力系数显著增大；附加质量系数在响应频率较低时与振动位移的相关性增强；当响应频率较低时，振动位移较大区域为能量耗散区，当响应频率较高时，振动位移较大区域为能量输入区.

英文摘要：

Vortex-induced vibrations(VIV)may cause serious fatigue damage on flexible cylinder structures,such as marine risers,mooring lines of floating platform and free spanning pipelines.Nowadays,in ocean engineering application,the hydrodynamic coe_cients,used to predict the VIV of flexible cylinders,are mainly acquired from the forced oscillations of rigid cylinders in cross-flow,which may account for the unexpected errors.Taking the coupling between cross-flow(CF)and in-line(IL)vibrations into account,a fluid force model is proposed in this paper.Lift,impulse drag and added mass coe_cients are obtained by the finite element method and least square method.A series of experimental tests of a flexible cylinder with a mass ratio of1.82and an aspect ratio of195.5are conducted in a towing tank to investigate the hydrodynamic coe_cients on the flexible cylinder undergoing VIV.Comparing to the hydrodynamic characteristics of rigid cylinders,those of a flexible cylinder are further studied.Under the first-order mode,the hydrodynamic coe_cients of a flexible cylinder share the same variation with those of rigid cylinders.A remarkable growth on lift and impulse drag coe_cients is observed under the second-order mode.The added mass coe_cients are strongly related to the displacement as the frequency is low.The large displacement region is the energy dissipation region with low frequency.While,the large displacement region may turn into the energy input region with high frequency.