基于Richards方程切换的土壤水流及溶质运移数值模拟

根据每个节点的土壤水分状态来选择合适的Richards方程形式,并用隐式迭代算法求解,得到一种用于模拟土壤水盐运移过程的通用方程切换方法。该方法能自由切换任意节点的控制方程,从而充分利用水头型和含水量型Richards方程的优势,适用于所有主流的迭代求解算法。成功将该方法应用于非均质土壤饱和-非饱和的溶质运移过程模拟。通过室内及数值试验,证明其在干燥砂土淋盐及干湿交替上边界的土壤积盐等普遍难题中,相比传统数值算法能大幅度提高计算效率和精度。本文方法对大区域饱和-非饱和水流运动及溶质运移数值模拟具有显著优势及应用前景。

Numerical modeling of soil water flow and solute transport based on Richards' Equation switching

The high non-linearity in the hydraulic retention curve introduces potential numerical instability and mass balance error in the traditional unsaturated-saturated flow models, which subsequently increases the difficulty for solute transport simulation. This paper proposed a generalized equation switching scheme, which implicitly solves different governing equations at adjacent vertices. The proposed method is applicable to all kinds of iterative solvers and fully considers the priorities in different forms of Richards'' Equation. We successfully implemented the method into a one-dimensional unsaturated-saturated flow and solute trans-port model. A series of soil column experiments as well as numerical tests are conducted to validate the proposed model. Regarding the difficulties in simulating (1) the salt leaching process within a dry-sandy soil column,and (2) the salt accumulation in layered soils under rapidly drying-wetting atmospheric bound-ary, the proposed model shows significant improvement in numerical accuracy and computational cost com-pared with the conventional HYDRUS-1D model. The developed method is promising for the application to large-scale simulation of flow and solute transport.