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Flow123d
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Flow123d is a simulator of underground water flow and transport processes. It is aimed in particular for large scale simulations and includes models for water flow in fully saturated porous medium, transport of several chemical substances, sorption of chemical substances into the rock matrix, and chemical reactions.
Complex domains The main feature that distinguish it from other similar software is its capability to represent tiny dislocations in large scale domains as 2D and 1D objects and allows interaction of solution on domains of various dimensions.
Mixed-hybrid discretization of Darcy flow. The water flow is driven by Darcy flow, this is basically steady state elliptic problem, but optionally one can consider compressibility of the water and surrounding rock. In the later case we solve a time dependent parabolic problem. For discretization of the elliptic or parabolic problem we use mixed-hybrid scheme of zero order using lowest order Raviart-Thomas base functions for discretization of the velocity field and piecewise constant base functions for the pressure and its traces on the interior mesh edges. Main advantage of the MH scheme is good approximation of the velocity field which is later used in the transport model. For the parabolic case we have implemented a lumping technique in order to prevent possible oscillations due to violation of the discrete maximum principle.
Advection is modeled only by convection (diffusion/dispersion is in developement). We use simple Finite volume scheme with upwind and backward Euler for time discretization. Unfortunately for highly heterogeneous velocity field which is natural for preferential fracture flow, we have to satisfy CFL condition which bounds the time step to very small values. Advection module can also compute sorption and dual porosity model (substance exchange between mobile and immobile pores.
Reactions. There are two modules for simulation of chemical reactions. SEMCHEM module can solve nonlinear differential equations rising form general multicompoent reactiong systems. On the other side this is very costly and is suitable only for small meshes. The second chemical module is fast but can cope only with linear reactions, i.e. decays.
Paralellism. Both the water flow solver and transport solver can run in parallel on distributed memory systems. We use essentially PETSc and MPI libraries.
Input module defines possible formats and structures of input files and their readers.
Mesh Mesh module contains discretization of a multidimensional computational domain and geometrical coincidence of mesh elements.
Darcy flow module with mixed-hybrid solver of linear flow equation.
Transport module with model of chemical substances transport.
Reactions module.
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1.8.17