The Simulation Control Parameters Dialog defines the following groups of input parameters that control the numerical mesh design, simulation time step, flow and transport equation solution accuracies (Picard iteration and iterative matrix solver tolerances), and other simulation control parameters:
Parallel Processing: Adaptive Groundwater allows the user to set the number of parallel processing threads that the program will use during the simulation and post-processing (i.e., output viewing).
Hydraulic conductivity (K) may be assigned either as homogeneous K zones or a correlated, lognormally-distributed random K [ln(K)] field.
Flow: In this menu you can specify “flow and transport” or “flow-only” solutions. You can also have the program compute an approximate steady-state solution of the flow field to be used as the initial hydraulic head distribution before the first time step (“Compute Initial Heads” checkbox; if not checked a uniform starting head is used). The user can also specify the hydraulic head convergence tolerance for the Picard iterations used in the flow solution.
Transport: Specify the solute concentration convergence tolerance for the Picard iterations used to solve the transport equation. Also, set the degree of the interpolation polynomial used for the advection equation solution (interpolation of concentrations at the feet of the characteristic lines).
Adaptive Mesh Refinement: This group of input parameters controls the overall mesh refinement (i.e., cell size distribution) based on the number of telescoping levels (NLEVEL) of progressively finer subgrids and the degree of cell refinement (IREFINE) from one AMR level to another. You also control grid refinement by specifying head and concentration tolerances (dH_mesh and dC_mesh) which the program uses to decide where to add higher levels of grid refinement [e.g., in areas where dH_mesh (m) and/or dC_mesh (mg/L) are exceeded between coarse cell centers — due to large gradients in head or concentration, or both — these coarse cells are flagged for refinement]. The overall mesh resolution is controlled by limiting the maximum total number of cells in the mesh (NCELL_max), which forces the program to adjust (i.e., increase) dH_mesh and dC_mesh in order to optimize the grid resolution so that NCELL_max is not exceeded.
Time Stepping: Adaptive Groundwater automatically adjusts the time step size during a simulation based on transient or spatial variations in the velocity field, local cell sizes as they relate to the plume location [i.e., Courant number (Cu) criteria], and the Picard iteration tolerances. Due to the Eulerian-Lagrangian transport solution the program can generally use much larger time steps (i.e., Cu >> 1) than traditional codes. The program automatically adjusts the time step, based on user-specified Courant number criteria, as a plume advects through different resolution regions of the global mesh and areas of higher pore velocity (e.g., near pumping wells).
Iterative Matrix Solver: The user can adjust the maximum number of iterations and convergence criteria for the iterative matrix solver [hydraulic head and solute concentration (solution of the dispersion part of the transport equation)].
Saved Simulation Results: This input parameter group specifies the times at which simulation results (hydraulic head, solute concentration, pore velocities, etc.) will be written to an output file for subsequent viewing.