海流引起海底管道悬空的数值模拟

Numerical Study of the Occurrence of Pipeline Spanning under the Influence of Steady Current

海底管道悬跨将影响管道的安全运营。在海底管道稳定性设计中，需要合理分析具有初始嵌入深度的海底管道产生悬空的物理机制。本文对海流作用下铺设于砂质海床上的海底管道悬空进行了数值模拟。求解不可压缩流体N-S方程，分析了海流作用下管道周围的流场特性，研究了管道两侧的压力分布特性和海床表面剪应力的分布特点。在管道绕流流场分析的基础上，通过对土体渗流方程的求解，得到了管道周围砂质海床内的渗流场以及渗流水力梯度场的分布情况。与海床表面剪应力计算结果进行比较分析发现，管道下方渗流出口处土体的流土渗透破坏将诱导管道发生悬空。

The pipeline spanning is a potential threat to the pipeline safety, so it is essential to analyze the mechanism of the spanning of pipeline with some initial embedment when designing submarine pipelines. In this paper, the occurrence of the spanning of submarine pipeline under the current action is investigated numerically. The property of the flow around the pipe is analyzed by solving the N-S equations for incompressible fluid. The pressure distribution around the pipeline and shear stress along seabed are thereby analyzed. Furthermore, the distribution of the seepage force and the seepage gradient in the sandy seabed closeto the pipeline is obtained by solving the seepage flow equation numerically. The comparison between the properties of seepage gradient in sandy seabed and those of shear stress along seabed shows that, the seepage failure of soil beneath pipeline is the main cause for the spanning of the pipeline laid upon sandy seabed.