考虑滑动磨损的动态脐带缆疲劳寿命分析研究

Dynamic umbilicals connect the top floating platform and the subsea production device. Fatigue failure is easily produced due to the severe ocean environment and the floating movement during operation. Therefore, the prediction of fatigue life is an important part of umbilical design. Unbounded and helical wound structures are applied in functional components and armor wires of the cross-section of umbilicals. The material wear behavior is induced by sliding frictions among components. So the fatigue analysis of this kind of structure is very difficult. The problem of fatigue life analysis with considering the effect of the wear is present in this project. Components sliding friction and wear tests are set up. The changing trend of wear parameters under different load conditions is studied. The influence of wear on the fatigue damage is investigated by umbilical alternate bending tests. And then the relationship between the reduction factor of fatigue life and wear is established. Fatigue life of a representative umbilical structure is analyzed by the numerical simulation method considering components interrelations. The analysis is verified by the prototype fatigue experiment under actual operation conditions. Through the study of the components wear mechanism and the perfection of fatigue analysis method, this project will provide solid theoretical foundation for umbilical design and actual applications.

动态脐带缆连接海上浮式平台和水下生产设备，使用中由于恶劣海洋环境及浮体运动作用容易发生疲劳失效，因此在设计中要进行疲劳寿命预测。脐带缆截面的功能单元及铠装加强均采用非粘结螺旋缠绕结构形式，单元相互滑动摩擦产生材料的磨损行为，使得这类结构的疲劳分析非常困难。本申请项目针对考虑磨损作用的脐带缆疲劳寿命分析问题，建立单元滑动摩擦磨损试验，研究不同荷载条件引起的磨损参量变化趋势；通过脐带缆纯弯曲交变加载试验，研究磨损对疲劳损伤的影响，进而建立磨损与疲劳寿命折减的关系；基于考虑单元相互接触作用的数值模拟方法，选取典型脐带缆结构进行疲劳分析，并利用模拟实际工况原型疲劳试验进行验证。本申请项目通过对单元磨损作用机理的研究，完善脐带缆疲劳寿命分析方法，为动态脐带缆结构设计及实际应用提供坚实的理论基础。

本项目针对考虑磨损作用的脐带缆疲劳寿命分析问题，设计了单元滑动摩擦磨损试验，实验结果表明，随着荷载的增加，角度的增大以及次数的递增，稳定阶段摩擦系数呈现降低趋势，载荷的大小以及摩擦次数的改变都会明显改变钢丝的磨损形貌和磨损深度，其中载荷的影响尤为突出。不同角度下磨损的形貌也会有所不同，随着载荷加大，荷载循环次数上升，磨损椭圆面积明显变大，磨损程度加剧，将加快疲劳失效的进程。基于ABAQUS有限元软件，考虑单元相互接触作用，建立了脐带缆全三维分析模型，并进行了四点弯曲疲劳试验与拉弯组合疲劳试验，通过考虑单元磨损与交变应力耦合作用对脐带缆疲劳进行了分析，考虑线性弯曲刚度进行疲劳寿命计算使，与非线性弯曲刚度相比，相差30%。考虑非线性计算的摩擦应力作为输入时，与无滑动假设计算的相差35%。忽略摩擦考虑全滑动假设的弯曲应力作为输入时，远远大于考虑摩擦时计算的疲劳寿命。在疲劳寿命分析中考虑了非线性弯曲行为的弯曲刚度和非线性摩擦应力作用，得到更为准确的疲劳寿命估计，完善了脐带缆结构疲劳寿命分析方法。