Defining a Problem
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:
Unsaturated/Variable Saturated Media
Flow and Mass/Heat Transport
Steady flow, steady transport
Steady flow, transient transport
Transient flow, transient transport
Generating a Finite Element Mesh
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.
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 pre-determined by importing ESRI Shape files.
Element types available in the 2D FEFLOW module include the linear 4-nodal & 8-nodal quadrilateral elements and the linear 3-nodal & 6 nodal triangular elements. Element types available
in the 3D FEFLOW module include include 8-nodal & 20-nodal quadrilateral prisms and the 6 nodal & 15 nodal triangular prisms.
Create Multiple Layers/Slices
The 3D-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 throughout the model domain and the geometric relationships shared between layers.
Z-elevations can also be manually assigned to every slice or imported from a database for greater representation of the variable layer thickness.(e. g., top or bottom of stratigraphy).
Import Variable Surfaces
FEFLOW can import & 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),
ESRI Shape File (*.shp),
FEFLOW also allows the user to choose which interpolation technique best suites their data set.
The popular Kriging technique, Akima, Inverse
Distance Weighting or 1D 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 3-D.
Assigning Model Properties
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
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 (3) major categories that define the various characteristics and conditions of both the flow and the transport model.
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 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)
The Parameter Association 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 pipelines from the FEFLOW parameter list to a database is just a matter of clicking the links.
The model properties can be imported and regionalized to the entire model region, to local zones within the model, or along a digitized line of nodes or elements.