非饱和土壤水动力弥散系数研究

Study of hydrodynamic dispersion coefficient in unsaturated soil

在非饱和土壤中,分子扩散、机械弥散作用对不同质地土壤溶质扩散影响各不相同。本文以粉壤土为研究对象,采用三种形式水动力弥散系数计算公式(分子扩散作用、机械弥散作用、分子扩散与机械弥散共同作用)对溶质浓度进行数值模拟。以土壤含水率和Br^-浓度实测值与计算值均方差最小为优化目标,建立溶质运移参数识别模型,采用遗传算法对模型求解,将所得参数代入对溶质运移方程,计算1 345min时刻的Br^-离子浓度值。结果表明:分子扩散与机械弥散共同作用下的Br^-浓度计算值与实测值相关性最高、分子扩散次之、机械弥散最小,相关系数分别为0.949、0.916、0.793。在非饱和溶质运移的试验中,分子扩散和机械弥散共同影响着数值模拟的精度。

Molecular diffusion and mechanical dispersion have a different impact on soil solute transport in unsaturated soil for the different soil textures. In this paper, we take the loam soil as research goal, with the solute concentration simulated using three calculating formulae of hydro- dynamic dispersion coefficient （molecular diffusion, mechanical dispersion and both the effect of them）. An optimization mathematical model for the parameter identification of the solute trans- port parameter is established to minimize the mean square error both of soil water content and Br- concentration between measured and calculated values. The optimization mathematical model is solved by a genetic algorithm. Those parameters are taken to the optimized solute transport e- quation, with Br- concentration at 1 345 min minutes obtained. The results show that the joint action of diffusion and dispersion has the greatest influence on the correlation coefficient between calculation values and the measured values of Br- concentration, diffusion effect less, and the least dispersion action. The correlation coefficients of which are 0. 949, 0. 916 and 0. 793. Both the molecular diffusion and the mechanical dispersion action have an influence on the numerical simulation modulated precision for solute transport in unsaturated soils.