Seepage Modeling with SEEP/W - GeoStudio 2007 version 7.22

Chapter 3: Geometry and Meshing
SEEP/W
This meshing simplicity however has some numerical and interpretation consequences as discussed in
more detail in the Structured versus Unstructured Section below.
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Figure 3-18 Unstructured triangular mesh
Triangular grid regions
GeoStudio has a special structured pattern for triangular regions called a triangular grid of
quads/triangles. The next figure (Figure 3-19) shows a typical triangular region with the resulting
structured mesh. The elements are a mixture of squares, rectangles, trapezoids and triangles. The use of
this pattern is fairly general, but it does have some limitations and restrictions.
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Figure 3-19 Triangular grid region
It is useful to think of the region as having three sides: a short side, an intermediate length side and a long
side. The algorithm attempts to sort the edges so that the sides go from the shortest to the longest in a
counter-clockwise direction. In this example, the shortest side is 3-1, the intermediate 1-2 and the longest
2-3.
The meshing algorithm works best when the number of divisions is controlled on the shortest and
intermediate sides. To retain the even pattern shown in Figure 3-19, the number of divisions should be
defined on the shortest side first and then on the intermediate side. The number of divisions on the
intermediate side can be an even multiple of the number on the shortest side. In the above example, the
shortest side has 5 divisions and the intermediate side can have 10, or 2 times that of the shortest side.
The algorithm works best and gives the best structured mesh if the numbers of divisions on the longest
side are left undefined allowing the algorithm to compute the appropriate number of divisions.
If a triangular region is mixed in with other more general regions, GeoStudio will attempt to ensure mesh
compatibility. Sometimes however it may not be possible to adhere to the requirements for generating a
structured mesh in a triangular region and then GeoStudio will substitute an unstructured mesh.
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