MODELING MULTICOMPONENT REACTIVE CHEMICAL-TRANSPORT IN NONISOTHERMAL UNSATURATED SATURATED SOILS .2. NUMERICAL SIMULATIONS

The set of partial differential equations developed for the simultaneo us transfer of moisture, hear, and reactive chemicals under saturated/ unsaturated soil conditions (Wu and Chieng, 1995) has been solved by t he Galerkin finite element method. The nonlinear algebraic equations o f the chemical reactions are solved by the iterative Newton-Raphson me thod. The chemical transport equations are formulated in terms of the total analytical concentration of each component species, and can be s olved sequentially. Three methods of solving the resulting systems of linear equations are implemented-the banded matrix method for one-dime nsional and small two-dimensional problems, the iterative method and t he sparse matrix method for large two-dimensional and three-dimensiona l problems. Two efficient and reliable iterative methods are provided- the conjugate gradient method for symmetric matrix equations and the b iconjugate gradient squared method for general nonsymmetric matrix equ ations. A typical subsurface drainage problem was solved using the dev eloped computer program. Two simulations were run to investigate the b ehavior of the program. Both simulations produced reasonable and satis factory results.