深水钢悬链立管的双向涡致疲劳损伤时域模型

Research on a time domain model for vortex induced fatigue damage in two-degree-of-freedom of deepwater steel catenary riser

针对深水钢悬链立管(SCR)的双向涡激振动的疲劳损伤问题,采用点涡强度计算流体对结构的横向和顺流向脉动水作用力,进而推导出一种新的尾流振子模型来预报立管结构的双向涡激振动响应.使用该模型对深水钢悬链立管的双自由度涡激振动问题进行数值计算.结果表明,在均匀流作用下,立管横向和流向振动呈现稳定的驻波振动形态;在剪切流作用下,立管各节点的运动轨迹可能不会得到稳定的"8"字形,沿管方向的驻波振动形态被打破,形成贯穿结构整体、同时各处振幅趋于均匀的行波振动状态.相比仅考虑横向疲劳而言,双向涡致疲劳分析更能全面评估结构的疲劳损伤情况,尤其在深水钢悬链立管的结构分析中,顺流向疲劳问题应给予充分的关注.

The research study examines the vortex-induced fatigue damage of the deepwater steel catenary riser （SCR） in two-degree-of-freedom. For the hydrodynamic loads acting on the structure, the strength of point vortex is used to calculate the fluctuating in-line （IL） and cross-flow （CF） fluid forces. Consequently, a new wake-oscil- lator model has been deduced to aid in the predicting of the response of the two-degree-of-freedom vortex induced vibration （VIV）. The VIV response of deepwater SCR has been calculated numerically by current research models. The results point out that the IL and CF dynamic response behavior of uniform flow provide standing waves ; but un- der sheared flow, the figure-of-eight trajectory of every node on structure is unstable ~ allowing for structure vibration changes from standing waves along the direction of SCR to traveling waves that run through the whole structure and whose amplitudes tend to be uniform everywhere. When the data analysis was compared with that considering only CF, the vortex-induced fatigue analysis in two-degree-of-freedom reflects the damage of the structure more comprehensively. This was especially true in the case for the structural analysis of deepwater SCR, thus, confirming the IL fatigue problem should be studied in more detail.