FEFLOW: A Finite Element Code For Simulating Groundwater Flow, Heat Transfer And Solute Transport

Abstract

The FEFLOW code is a finite element program package developed at VTT Energy to model flow, solute transport and heat transfer in coupled and non-coupled, steady-state and transient situations, as well as in deterministic and stochastic modes. The code offers a novel finite element technique to model groundwater phenomena in fractured crystalline rock. Linear and bi-quadratic one-, twoand threedimensional finite elements can be used for describing engineered and natural bedrock structures. One of the solute transport models implemented in the package is capable of taking into account matrix diffusion as well. Highly convective cases are handled with different kinds of upwind schemes. The system of linear algebraic equations emerging from the standard Galerkin approximation can be solved with a direct frontal solver, as well as with an array of iterative solvers partly from the NSPCG package. The nonlinear algebraic equations resulting from coupled cases are solved with the Picard iterative approach with options for relaxation. The discretization of time is based on a simple finite difference scheme. For each result quantity to be determined, the code offers a wide selection of nodal boundary conditions including prescribed values, sources, sinks and/or fluxes. These may be constant or a function of time. Hydraulic properties of the bedrock features may also be constant or vary with depth. Besides the finite element analysis code the FEFLOW package comprises several programs to compute derived quantities (like flow paths and flow rates) and to facilitate generic modelling tasks. The code has been tested in a series of test cases, and verified in the international HYDROCOIN project. Main application areas of the FEFLOW package have been site investigations and safety analyses undertaken by the Finnish power company Teollisuuden Voima/Posiva Oy operating two nuclear power plants. It has also been employed to simulate various hydraulic disturbances and solute transport phenomena in the Aspo Hard Rock Laboratory, Sweden. Transactions on Ecology and the Environment vol 10, © 1996 WIT Press, www.witpress.com, ISSN 1743-3541