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Defining a Problem in Feflow
The specifications of all model attributes on a given finite element mesh are completed in the Feflow Problem Classifier Menu. It allows you to define model physics, specify problem classes, control data and time characteristics, and manipulate mesh
data.
The following model classifications are available:
Model Type:
- Saturated Media
- Unsaturated/Variable Saturated Media
Problem Class:
- Flow Only
- Steady Flow
- Transient Flow
Flow and Mass/Heat Transport
- Steady flow, steady transport
- Steady flow, transient transport
- Transient flow, transient transport
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 Generating a Finite Element Mesh in Feflow
The most common procedure to defining a Feflow model area is through the use of
overlain maps. Feflow can import various map files to act as templates for generating the super-element mesh. Once the outer boundary of the mesh is defined, Feflow
automatically generates a finite element mesh based on a user-defined number of elements.
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 Refining a Finite Element Mesh
Once the super-element mesh has been generated, mesh refinement is conducted
through the MESH Editor. Unlike finite difference models such as MODFLOW, Feflow's finite element approach allows the user to perform local mesh refinements only in the areas of interest and avoids creating excessive elements.
Mesh refinement can be conducted on a single element, a group of selected elements, or on a global basis. Alternatively, mesh refinements can be predetermined
by importing ESRI Shape files.
Element types available in the 2-D Feflow module include the linear 4-nodal and
8-nodal quadrilateral elements and the linear 3-nodal and 6-nodal triangular elements. Element types available in the 3-D Feflow module include 8-nodal and 20-nodal quadrilateral prisms and the 6-nodal and
15-nodal triangular prisms.
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 Create Multiple Layers/Slices
The 3-D Layer Configurator allows the user to add or delete slices at any given
Z-elevation in the model. In addition, the user can define the extent of the layers and the geometric relationships between layers. Z-elevations can also be manually
assigned to every slice or imported from a database for greater representation of the variable layer thicknesses ( top or bottom of stratigraphy).
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 Import Variable Surfaces
Feflow can import and interpolate raw data to create variable surfaces for accurate
representation of variable layer thicknesses found in the field. Data formats include: ASCII Triplets (XYF) (*.trp), ASCII Database (XYF) (*.dat), dBASE IV (XYF) (*.dbf), and ESRI Shape File (*.shp).
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 Feflow also allows the user to choose which interpolation technique best suits their
data set. The popular Kriging technique, Akima, Inverse Distance Weighting or 1-D interpolation (only for boundary conditions), can be used for calculating the variable
surfaces. Once completed, the model layers including the variable surfaces can be seen in three dimensions.
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Assigning Model Properties in Feflow
Feflow has a comprehensive selection of graphical tools for assigning and modifying all model properties (e.g., flow, mass transport and heat transport
properties). The graphical tools allow you to assign properties using:
- A global-uniform value for the entire model
- Element-specific values for selected elements
- Node-specific values for selected nodes
- Uniform values to an area defined by a box
- Stored values from an external database (x, y, value) or ARC/INFO GIS file
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Imported model properties can be regionalized to a local model region or extrapolated to the entire model domain.
Feflow model properties are divided into three major categories that define the various characteristics and conditions of both the flow and the transport model.
Flow Attributes
- Flow Initials - initial hydraulic head, saturation, moisture content or pressure
- Flow Materials - conductivity (Kx, Ky, Kz), storativity, storage compressibility, and density ratio
- Flow Boundaries - head (first type), flux (second type), transfer (third type), well (fourth type)
Transport Attributes
- Transport Initials - initial mass concentration (or temperature), density and viscosity effects
- Transport Materials - porosity, sorption, molecular diffusion, longitudinal dispersivity, transverse dispersivity, decay rates, source/sinks and transfer
rates
- Transport Boundaries - mass (1st type, Dirichlet), flux (2nd type, Neumann), transfer (3rd type, Cauchy), well (4th type)
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 Parameter Association
This Menu links spatial data in the form of polygons or lines (ASCII or Shape files)
with attribute data from databases (ASCII, Shape file or dBASE). Defining the pipe lines from the Feflow parameter list to a database is just a matter of clicking the
links. Model properties can be imported and regionalized to the entire model region, local zones within the model or along a digitized line of nodes or elements.
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Running the Feflow Model Simulation
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Advanced Numerical Methods
Feflow uses a Galerkin finite element numerical
approach with a selection of numerical solvers and state-of-the-art tools for controlling and optimizing the solution process including:
- Fast and direct solvers such as the PCG and Restarted ORTHOMIN Methods with preconditioning.
- Variable types of solution up-winding techniques to minimize numerical dispersion.
- Picard and Newton iterative techniques for nonlinear flow problems and adaptive time-stepping.
- Contaminant transport processes include advection, hydrodynamic dispersion, linear and nonlinear sorption isotherms, and first order chemical
non-equilibrium.
- Automated adaptive mesh refinement scheme to optimize the numerical solution in regions where steep gradients exist.
- Real-time graphs of transient heads and concentrations at a number of points throughout the model domain are plotted during the solution process.
- Simulation progress can be paused at any time to view intermediate results in three dimensions.
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Visualization of Results in Feflow
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Feflow comes with state-of-the-art visualization capabilities for creating high impact, three-dimensional graphics for displaying model results:
- Isolines and fringes;
- Velocity vector fields;
- Particle tracking (forward/reverse);
- Cross sections and fence diagrams;
- 3-D projections; and
- 3-D Cutaways.
All graphical editing is completed through FEPLOT, the Microsoft Windows-based graphical design tool included with Feflow. Captured plots can be georeferenced
to ensure exact overlay of the map objects. File formats include FEPLOT *.plx files, ESRI shape files or ARC/INFO compatible ASCII (Generated) files.
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 Fence Diagrams
Feflow creates cross sections and true fence diagrams to display mass
concentrations, temperature distributions, computed hydraulic heads, streamline velocities, moisture and saturation distributions, and pressure distributions. Line
segments can be arbitrarily selected using the graphical interface and can be exported for presentation purposes.
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 3-D Projections
3-D Projections are helpful when describing mass concentrations, temperature
distributions, computed hydraulic heads, streamline velocities, moisture and saturation distributions, and pressure distributions. The 3-D projections options
displays these data overlaying the georeferenced map objects for a better understanding of the simulation.
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 3-D Cutaways
The Cutaway-Viewer gives the user the ability to define a block portion of the model's
body to be cutaway. It is a helpful tool to view parameter distributions in the inner part of the model. You can define the cutaway by inserting screen related position
coordinates in the menu or by moving the 3-D handlers on the model's body via the mouse.
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 Budget Analyzer
The 'Budget' analyzer computes quantities of fluid masses and contaminant masses
entering or exiting the simulated region, subregions or boundary sections. The balance computation takes into account only mesh nodes occupied by values for
areal recharge or boundary conditions as listed below. The computed quantities for the fluid and contaminant mass are:
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- Fluxes along outer or inner boundaries, i.e., borders occupied with Dirichlet, Neumann or Cauchy boundary conditions (1st, 2nd and 3rd kind)
- Injections and withdrawals through single wells (4th kind)
- Areal fluxes due to infiltration, recharge, leakage etc.
- Imbalance: Gain (+)/Loss(-)
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 FEPLOT
FEPLOT has been developed as a design and plotting tool for Feflow generated vector
data. FEPLOT allows the user to easily georeference plots as overlays, add text for reports, and print the simulation graphics. Plots can also be saved as templates for
future use when preparing reports. Acceptable georeferenced file formats include: *.plx files, ESRI Shape files and ARC/INFO compatible ASCII files.
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Feflow Documentation
Feflow includes a User's manual, (2) Reference Manuals, one Dongle, and an installation CD-ROM. Technical support and upgrades are available for a duration of 6
months free of charge. An annual maintenance fee will be charged beyond the free six-month period (optional but recommended). Contact us for more information regarding the annual maintenance fee.
Feflow Hardware Requirements (PC)
- Pentium PC 133 or higher
- Exactly 256 color video mode with a resolution of 1280X1024 or higher
- 32 MB RAM (64 or higher recommended for 3-D models)
- 130 MB free disk space
- Windows 95 or NT installed
- TCP/IP protocol installed
- XVision X Windows server (supplied w/ Feflow)
Feflow Hardware Requirements (UNIX)
- High resolution color graphics UNIX workstation providing 8-bit planes (25 simultaneous colors) and full 32-bit or 64-bit virtual memory architecture
- 32 MB main memory
- 130 MB free disk space recommended: RISC workstations with 1280 X1024 pixel UNIX System V or equivalent and optional NFS for networking
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