Abstract:

When fracture extension occurs in CO₂ pipelines, the influence of the decompression behavior of the medium inside the pipe on the process must be considered. Due to the high computational cost and convergence difficulty of the fluid-solid coupling method, this paper proposes a decoupling calculation method with partitioned load application, which can greatly simplify the complexity of the calculation of pipeline boundary conditions and reduce the computational time. This paper uses the shock tube model, decompression wave model and pipeline flap decompression empirical formula as the CO₂ decompression model, and applies pressure loads of different decompression forms to the crack tip and its front and back, respectively, to simulate the decompression behavior of CO₂ during the fracture process. At the same time, the model considers the influence of backfill and pipe deadweight on the fracture process, and adopts the structured grid transition technology to divide the grid, which greatly improves the calculation efficiency under the premise of ensuring the calculation accuracy. The calculated results of the model are compared with those of the burst test and the previous fluid-structure coupling model. The model can predict the initiation velocity better, and the peak velocity obtained is closer to the experimental value. The average fracture speed measured by the test is 108.21 m/s, and the average fracture speed calculated by the model is 114.18 m/s, with a relative error of 5.52%. The calculation results of this model reflect higher accuracy while considering conservatism.

Key words: safety, carbon dioxide, numerical simulation, fracture propagation, decompression model

摘要：

CO₂管道出现断裂扩展时，必须考虑管内介质减压行为对该过程的影响。由于流固耦合方法存在计算成本高、收敛困难等问题，本文提出分区施加载荷的解耦计算方法，该方法可以大大简化管道边界条件计算的复杂性，并缩短运算时间。借助激波管模型、减压波模型以及管道襟翼减压经验公式作为CO₂减压模型，分别对裂尖及其前后施加不同减压形式的压力载荷，以此来模拟断裂发生过程中CO₂的减压行为。同时，所建立的有限元模型考虑了回填土及管道自重对断裂过程的影响，采用结构化网格过渡技术进行网格划分，在保证计算精度的前提下大大提高了计算效率。经对比，试验测得的平均断裂速度为108.21 m/s，相应的模型计算值为114.18 m/s，相对误差为5.52%，模型更好地预测了启裂速度，并且得到的峰值速度也与试验值更为接近。本模型计算结果在考虑保守性的同时体现出了更高的精度。

关键词: 安全, 二氧化碳, 数值模拟, 断裂扩展, 减压模型