近饱和条件下非饱和多孔介质渗流过程的数值分析

Numerical analysis of seepage processes in unsaturated porous media under nearly saturated conditions

在非饱和多孔介质渗流分析中,近饱和条件下物理模型与数值模型之间的差异会导致数值不稳定问题。为解决这一问题,并保证模拟结果的可靠性,提出了3种方法,并在有限元分析程序U-DYSAC2中分别进行了程序代码的实施。通过数值试验与试验数据的比较,证实了在近饱和条件下土-水特征曲线和水力传导函数的高非线性可引起数值收敛性、稳定性和精度问题,而且在不同条件下含水率和基质吸力的预测结果差异明显。在3种方法中,修正的Van Genuchten模型(MVGM)方法对含水率的预测较为准确,而Line方法对基质吸力的预测较为合理。因此,解决在分析近饱和条件下非饱和多孔介质渗流问题时,为获得接近真实的模拟结果,采用合适的数值方法进行预测是非常关键的。

In analyzing the seepage processes in unsaturated porous media, numerical instability may occur due to the difference between the adopted physical and numerical models under nearly saturated conditions. To resolve the issue and improve the numerical results, three methods are proposed and then implemented into the finite element code U-DYSAC2. Numerical simulations are compared with the experimental data available in the literature, showing that the problems related to numerical stability, convergence and accuracy can be induced by the high nonlinearity of soil water characteristics and hydraulic conductivity functions under nearly saturated conditions; and significant numerical discrepancies can appear in predicting the water content and matric suction of the porous media. Among the three proposed methods, modified Van Genuchten model （MVGM） method yields the best results in calculating the moisture content; while the Line method achieves best prediction for matric suction. Consequently, in analyzing the seepage processes in unsaturated porous media, it is crucial to introduce a proper analysis procedure such that reliable numerical results can be achieved.