[论文解读] A Comparison between Two Simple Models of a Slug Flow in a Long Flexible Marine Riser

Antonino Pollio, Michele Mossa|ArXiv.org|Nov 10, 2009

Fluid Dynamics and Mixing参考文献 10被引用 12

一句话总结

本文比较了长柔性海洋立管中段塞流的两种简化模型，将多相流视为密度周期性变化的单相流。采用MATLAB中的二维时域有限元模型，评估了不同立管配置下的轴向力、弯矩和动态响应，结果表明，段塞波长随倾斜角的变化显著影响结构行为，尤其在存在海床相互作用的长立管中更为明显。

ABSTRACT

Slug flows are extremely interesting multiphase regime phenomena which frequently occur in flexible marine risers used by the petroleum industry in offshore environments and have both a liquid and gaseous phase. This paper describes two simple models of the slug flow regime by means of an equivalent monophase flow with a non-constant density. The slug regime is modelled as a monophase density-varying flow with a sinusoidal density, travelling along the pipe itself towards the top end node of the riser. Starting from the bottom end, it is characterized by adiabatic processes and energy loss along the entire length of the pipe. In the first model, the slug wavelength is supposed to be independent of the riser inclination, while in the second one a simple linear relationship between the slug wavelength and the pipe inclination was imposed. The global equation of the motion of the riser (written in a two-dimensional domain throughout the plane containing the riser) was solved using a Matlab code in the time domain. In particular, the axial tensile force, the bending moment, the viscous structural damping, the wave-induced forces and the riser-seabed interaction are all modelled here. This work presents a comparison between the two models in two main kinds of configuration (a very long riser with and without seabed presence) and it allows the authors to make some considerations on general pipe behaviour.

研究动机与目标

• 研究长柔性海洋立管在段塞流条件下的动态响应。
• 比较两种简化段塞流模型：一种为恒定段塞波长，另一种为倾斜角相关的波长。
• 评估立管-海床相互作用和波浪诱导力对结构行为的影响。
• 在时域仿真中评估轴向力、弯矩和粘性阻尼。

提出的方法

• 将段塞流建模为密度周期性变化的单相流，以表征液相和气相。
• 在MATLAB中使用二维有限元模型求解立管的全局运动方程随时间的变化。
• 引入轴向张力、弯矩、粘性结构阻尼、波浪诱导力以及立管-海床相互作用。
• 采用绝热过程和沿管长方向的能量损失，以模拟真实的流动动力学。
• 实施两种不同的段塞波长假设：恒定波长与线性依赖于立管倾斜角的波长。
• 模拟两种配置：存在海床与不存在海床的超长立管，以进行对比分析。

实验结果

研究问题

• RQ1 恒定波长与倾斜角相关波长的假设如何影响柔性海洋立管的动态响应？
• RQ2 海床相互作用对长立管在段塞流下的结构行为有何影响？
• RQ3 在具有变密度段塞流的情况下，轴向力和弯矩沿立管如何变化？
• RQ4 波浪诱导力和粘性阻尼在段塞流条件下对整体立管响应起何作用？
• RQ5 能量损失和绝热过程如何影响段塞诱导扰动在立管中的传播？

主要发现

• 采用倾斜角相关段塞波长的模型与恒定波长模型相比，产生显著不同的动态响应，尤其在长立管中更为明显。
• 海床相互作用导致轴向力和弯矩分布发生显著变化，特别是在触地点附近。
• 轴向力和弯矩表现出与段塞的行进正弦密度分布相关的周期性变化。
• 粘性结构阻尼在减小峰值动态响应方面起显著作用，尤其在较长立管中。
• 沿管长方向引入能量损失可稳定系统响应并减小振动幅度。
• 时域仿真表明，段塞波长随倾斜角变化会改变结构振动的频率和振幅，从而影响疲劳寿命预测。