海洋立管错列涡激振动特性数值模拟

Numerical simulation on the vortex-induced vibration characteristics of staggered marine riser

为了掌握海洋立管系统的涡激振动规律,发展了广义α法求解圆柱振动方程,增强了解法的稳定性,在改进特征线算子分裂(Characteristic Based Split,CBS)求解流场方程的基础上,提出了流-固耦合有限元解法计算涡激振动问题,并通过基准算例验证了解法的精度和稳定性。运用该解法数值模拟了低雷诺数下多种工况条件时两错列圆柱的涡激振动过程,结果表明:当攻角较小时,上游圆柱脱落的涡直接与下游圆柱相互作用,增加了下游圆柱上、下表面的压差,导致大尺度涡激振动现象,而此时下游圆柱的振动频率由上游圆柱的涡脱落过程决定;当攻角较大时,下游圆柱将脱离上游圆柱的尾迹区,其绕流流场、受力情况及振动频率均趋近于单圆柱情况。研究结果可为海洋立管系统布置的工程应用提供参考。

In order to master the vortex-induced vibration laws of marine riser system, the generalized α method was developed to solve the cylinder vibration equation, and the stability of the solution method was enhanced. After the flow field equation was solved by the improved Characteristic Based Split(CBS), a fluid-solid coupling finite element method was developed to calculate the problem of vortex-induced vibration. In addition, the accuracy and stability of the solution method were verified using a benchmark example. Finally, this solution method was applied to numerically simulate the vortex-induced vibration process of two staggered circular cylinders under various working conditions at low Reynolds number. The results show that when the attack angle is small, the vortex shedding from the upstream cylinder interacts directly with the downstream cylinder, which increases the pressure difference between the upper and lower surfaces of the downstream cylinder, resulting in large-scale vortex-induced vibration. And at this moment, the vibrating frequency of the downstream cylinder is dominated by the shedding process of the vortex from the upstream cylinder. When the attack angle is large, the downstream cylinder will be separated from the wake region of the upstream cylinder, and its flow field, force and vibrating frequency are close to the case of single cylinder. The research results can provide some reference for the layout of marine riser system in engineering practice.