HydroGeoSphere/3-D Mesh Generation

Once you have a 2-D slice, you have the option of exiting the grid definition procedure, which will cause grok to automatically generate a unit thickness 3-D grid. It does this by duplicating the 2-D slice and constructing the appropriate 6-node prism or 8-node hexahedral element incidences and assigning a unit element length perpendicular to the slice. The element zone numbers for the slice are used to assign default zone numbers for each element. Such a grid could be used to simulate 2-D cross-sectional problems.

More often, you will want to generate a 3-D layered grid, perhaps with topography defined by a DEM (Digital Elevation Model) and/or uneven layer contacts based on the observed hydrostratigraphy.

To do so you should start by issuing the following instruction:

Generate layers interactive...End

Causes grok to begin reading a group of 3-D grid generation instructions until it encounters an End instruction.

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The basic procedure is to build up the 3-D mesh by defining the base, then adding layers one at a time from the base to ground surface.

By default, the domain will contain a single layer, one element high with a base elevation of zero and a top elevation of 1, and the element zone numbering scheme from the 2-D slice will be used to assign the 3-D mesh element zone numbers. Instructions that change the default behaviour are described below:

These commands are optional but should not be used more than once:

Zone by layer

Causes grok to assign the 3-D mesh layer number to the element zone number.

By default, the element zone numbering scheme from the 2-D slice is used to assign the 3-D mesh element zone number.

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Base elevation...End

Causes grok to begin reading a group of base elevation instructions until it encounters an End instruction. Available instructions are described in Section 5.3.5.4.

By default, the base elevation of the domain will be set to zero.

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