As a 3D finite element mesh is constructed in GMS, a list of materials is defined and each element in the 3D mesh has a material type associated with it. The list of materials is initially created using the Materials Editor dialog accessed through the Edit menu. This dialog is used to specify a name and a display color for each material. The Material Properties dialog accessed through the FEMWATER menu is used to enter the properties associated with each type which are needed by FEMWATER. The items in the dialog are as follows:
The materials are listed in a box on the left side of the dialog. One of the materials is highlighted at all times. The parameters associated with the highlighted material are displayed in the dialog and can be edited.
The flow parmeters are specified in the Femwater Flow tab of the Materials Editor dialog.
The hydraulic conductivity tensor is entered in the upper right corner of the dialog. Since the tensor is symmetric, only the upper right half of the matrix must be specified.
A set of head series curves for the unsaturated zone must be defined for each material. The curves can be defined using either the XY Series Editor or the Curve Generator.
A set of curves entered by selecting one of the windows labeled Moisture content, Rel conductivity, or Water capacity. This brings up the XY Series Editor. Guidelines for selecting the appropriate series to use for a particular material can be found in the FEMWATER Reference Manual.
In most cases, the simplest way to generate a set of pressure head curves for the unsaturated zone is to use the Curve Generator. The Generate Curves button brings up the Van Genuchten Curve Generator dialog. The Curve Generator dialog is used to automatically generate a set of unsaturated zone curves using the van Genuchten equations described in the FEMWATER Reference Manual. The items in the top of the dialog are used to select the desired units (this should be consistent with the rest of the model) and enter the max height of capillary rise above the water table. Two methods are available for entering the Van Genuchten parameters: 1) you can select the Manual parameter input option and enter the values directly, or 2) you can select the Preset parameter values option and choose from a list of pre-defined soil types.
Once the parameters are defined the Compute curves button can be used to generate a set of curves. The curves are displayed in the bottom of the dialog. New values can be entered and the process can be repeated until a satisfactory result is obtained. When the OK button is selected, the active curves are assigned to the current material.
Each of the unsaturated zone curves is a piece-wise linear curve defined by a sequence of points. The number of points in each curve is defined by the Max percent value. A new point is added to the curve each time the parameter changes by the Max percent value.
Note that the effective porosity for each material is defined from the pressure head vs. moisture content curve. The value at p = 0 is taken from the curve and is written to the model file as part of the MP2 card.
If the current FEMWATER simulation includes transport then the transport parameters can be edited in the FEMWATER Transport tab of the materials editor.
Related Links:
FEMWATER Interface
Model Input