全局响应和涡激振动耦合作用下悬链线立管触地区域疲劳特性研究

The touchdown point (TDP) of steel catenary riser (SCR) is one of the key positions prone to fatigue failure, thus should be elaborated on the fatigue assessment. Existing method often carry out the analyses of global response and vortex induced vibration (VIV) separately without considering the coupling effect of global response and VIV. Therefore, based on the fundamental experiment and existing hydrodynamic force database, this project firstly investigates the effect of the oscillatory flow on the response characteristics and hydrodynamic force of VIV, and takes this effect into account in the VIV prediction by using the modification factor of the hydrodynamic force obtained based on equivalent energy. The global response would induce the oscillation of each riser element leading to the formation of the oscillatory flow between riser element and fluid, which would affect the riser VIV, in turn, the riser VIV can affect the global response by amplifying the wave and current forces. According to these aspects, this project would establish an approach for the coupling analysis of global response and VIV, and then discuss the coupling response characteristics. The interaction model between SCR and seabed would be improved to consider the initial seabed trench, and then applied to the coupling analysis of global response and VIV. Based on the coupling analysis, the fatigue damage near TDP is then in detail studied, which would be helpful for the accurate fatigue design of SCR.

触地区域是悬链线立管发生疲劳破坏的关键部位，因此需要进行准确的疲劳评估。目前的方法通常独立预报全局响应和涡激振动引起的疲劳损伤，无法反映两者耦合效应的影响。为此，本项目首先将从基础性实验出发，结合已有的流体力数据库，研究振荡流对涡激振动响应特征和流体力的影响，并基于能量等效对已有的流体力数据库进行修正，形成计及振荡流效应的立管涡激振动分析方法。在此基础上，将全局响应引起的立管与流体之间的相对流看作振荡流，并将其计入立管涡激振动，同时考虑涡激振动对全局响应波流载荷的影响，建立全局响应和涡激振动的耦合分析方法，揭示全局响应和涡激振动的耦合特性。改进管土作用模型，使其考虑初始沟槽的影响，并应用于悬链线立管全局响应和涡激振动的耦合动力响应分析，总结触地区域的疲劳损伤规律，为提高悬链线立管的疲劳设计精度提供指导。

触地区域是悬链线立管发生疲劳破坏的关键部位，因此需要进行准确的疲劳评估。目前的方法通常独立预报全局响应和涡激振动引起的疲劳损伤，无法反映两者耦合效应的影响。为此，本项目从试验、理论研究和数值分析出发，开展了以下工作：.(1) 开展了圆柱体振荡流试验，结合已有的流体力数据库，研究了振荡流对涡激振动响应特征和流体力的影响，并基于能量等效对已有的流体力数据库进行修正，形成计及振荡流效应的立管涡激振动分析方法；.(2) 将全局响应引起的立管与流体之间的相对流看作振荡流，并将其计入立管涡激振动，同时考虑涡激振动对全局响应波流载荷的影响，建立了全局响应和涡激振动的耦合分析方法；.(3) 改进管土作用模型，使其考虑初始沟槽的影响，并应用于悬链线立管全局响应和涡激振动的耦合动力响应分析，总结触地区域的疲劳损伤规律。. 通过以上研究，得到如下结论：.(1) 振荡流KC数对圆柱体的涡激振动具有重要的影响，KC数越大，涡激振动的多模态特性越明显；.(2) 在临界雷诺数区间内，圆柱体的双自由度涡激振动对雷诺数的敏感性不明显；.(3) 横流和顺流的相位差、幅值和频率对尾涡模态和流体力具有重要影响；.(4) 海床沟槽的发展可以缓解触地区域的疲劳损伤；.(5) 当顶端运动与海流共面时，顶端运动在一定程度上可以抑制涡激振动。. 本项目的研究进展和结论可以为如何考虑深海悬链线立管设计中多种外载荷的耦合影响提供指导，有助于提高立管的设计精度。