Micro-Fem Related Programs
To allow the largest possible models to be run on a microcomputer, making full use of the computer's memory, the modeling procedure has been split into several well-defined parts and related programs.
FemGrid FemGrid is a mesh-generating program within Micro-Fem. It generates a triangular irregular network with variable spacing based on a subdivision of the area into irregular polygons with uniform internal node spacing. FemGrid is suitable for irregular geometries which are often encountered in regional studies (e.g., meandering rivers).
FemMesh FemMesh is an alternative mesh-generating program within Micro-Fem. Like FemGrid, it also generates triangular irregular networks with variable spacing. FemMesh is based on a subdivision into triangular and quadrangular areas with gradually-changing node spacing. FemMesh is useful for problems which require high contrasts in spacing (for example, sheet piling or excavations).
FeModel The core of Micro-Fem consists of FeModel, a fully-interactive graphics input/output program with a built-in calculation module. As a preprocessor, it offers the possibility to add, move and remove nodes at any time and allows the graphical, interactive input of model parameters. The postprocessing capabilities include all kinds of contour maps, flow vectors, flowlines and water budgets.
FemInvs FemInvs was developed to automatically calibrate steady-state models (inverse modeling). The program adjusts the selected model input data to reduce the differences between observed and computed heads. The model may consist of 16 aquifers, and the EM version can handle up to 12,500 nodes. Anisotropy in all layers is allowed.
FemCat and FemCurve FemCat handles transient calculations. An FeModel file with the initial conditions and files with the storativities for each aquifer must be prepared. One or more time periods and the number of time steps can be specified.
FemCurv visualizes the time-head files written by FemCat. Time-head or drawdown curves and time-distance profiles with various drawing options are among the possibilities. It also writes HPGL files that can be plotted or imported into word processors.
FemPath and FemProf FemPath is a three-dimensional particle tracking program which interprets an FeModel file using additional aquifer and aquitard thickness data. Flowlines run forward or backward, starting at any node, in any aquifer and at any depth. The number of flowlines is unlimited.
FemPath can be activated from FemCat to create coupled steady-state and transient pathlines. FemProf draws isohypses and flowlines in a vertical cross section.
FemPlot FemPlot plots map views generated by FeModel and FemPath and writes HPGL and DXF files.
Inner Workings of the Modeling Procedures
To allow the largest possible models to run on a microcomputer, making full use of the computer's memory, the modeling procedure has been split into several well-defined parts and related programs. The core of Micro-Fem consists of FeModel, a fully interactive graphics input/output program with a built-in calculation module.
Micro-Fem Modeling Procedure
- Finite-Element Grid Generation
- Preprocessing
- Steady-State Modeling
- Postprocessing
- Transient Modeling
- Plotting and Interfacing
- Automated Calibration
Finite-Element Grid Generation in Micro-Fem FemGrid and FemMesh are the mesh-generating programs of Micro-Fem. Both make triangular irregular networks with variable spacing.
FemGrid generates a mesh based on a subdivision of the area into irregular polygons with uniform internal node spacing. FemGrid is suitable for irregular geometries which are often encountered in regional studies (for example, meandering rivers).
FemMesh is based on a subdivision into triangular and quadrangular areas with gradually-changing node spacing. FemMesh is useful for problems which require high contrasts in spacing (e.g., sheet piling or excavations).
Preprocessing with Micro-Fem FeModel is both the pre and the postprocessor of Micro-Fem. As a preprocessor, it offers the possibility to add, move and remove nodes at any time, and it allows the graphical, interactive input of model parameters. You "walk" from node to node with the arrow keys and enter or change model parameters on the fly. You can also define an area by "walking and marking" along its boundary. It is possible to enter labels and parameters for a node, a group of nodes, an area or the whole model at once. FeModel is able to assign values to the model parameters by evaluating functions and expressions; a wide variety of variables and standard functions is incorporated. Interesting possibilities arise by making values a function of distance or position. To check the entered data, FeModel draws colored maps of the model parameters and shows the minimum and maximum values on the screen.
Steady-State Modeling in Micro-Fem Both FeModel and the stand-alone finite-element program FemCalc can calculate the steady-state heads and prepare results for postprocessing by FeModel or FemPath. Generally calculation times are short: a steady-state model of moderate size (e.g., three aquifers and 4,000 nodes) takes less than one minute on a 66 MHz 486-type PC.
Micro-Fem Postprocessing FeModel's postprocessing capabilities include fast and easy construction of maps of flow vectors, heads, drawdowns and the vertical flow components for every aquifer. Flowlines can be drawn up and downstream indicating travel times. Water balances can be computed for any selected node or area of the model. The FeModel options will be adequate for those occasions where only the distribution of heads and water balances are the objective of the modeling study.
Transient Modeling in Micro-Fem Transient calculations are handled by FemCat. An FeModel file with the initial conditions and files with the storativities for each aquifer must be prepared. One or more time periods and the number of time steps for each period can be specified. At each timestep, FemCat allows changes in pumping, boundary heads and all other parameters. The number of time periods is unlimited. For selected nodes, heads can be saved in a special file for each time step. FemCat also offers the user other features: in phreatic aquifers, seepage to surface water can be modeled, and after each time step, transmissivities can be adjusted to the calculated height of the water table. Anisotropic transmissivities can be incorporated for each node and each aquifer. FemCurv is the program that visualizes the time-head and flux data written by FemCat. Time-head or drawdown curves and time-distance profiles with various drawing options are among the possibilities. It also writes HPGL files that can be plotted or imported into word processors.
Micro-Fem Plotting and Interfacing Graphical output from all Micro-Fem programs can be plotted on an HP-compatible plotter or translated to HPGL or DXF graphics files by FemPlot. FeModel and FemPath save different types of ASCII-files with model data for easy interfacing with geographic information systems (GIS) and database programs. FemCat files can also be loaded into a spreadsheet program.
Automated Calibration in Micro-Fem FemInvs was developed to automatically calibrate steady-state models (inverse modeling). The program adjusts the selected model input data to reduce the differences between observed and computed heads. The model may consist of 16 aquifers and can handle up to 12,500 nodes. Anisotropy in all layers is allowed. Since hydraulic properties usually vary from node to node and since the number of parameters to be optimized is limited to 40, it is not the hydraulic properties themselves that are calculated, but rather the corrections to these properties.
For each parameter a subarea has to be selected for which the correction will be computed. When referring to a transmissivity, a hydraulic resistance or a discharge, the correction is a multiplication factor that is applied to all values in the selected area; when fixed heads are optimized, the correction is added to the original model heads.
Micro-Fem Input and Output
- Single model file in ASCII format
- Plots of grids, contours, flowlines and time series
- True-scale screen dump program for dot matrix and laser printers
- SURFER and spreadsheet-compatible XYZ-data files
- HP plotter interactive use
- HPGL- and DXF-file output and DXF-file input
Micro-Fem Requirements: PC with 640K and a math coprocessor. Extended memory supported. |