Meshing Efficiently

by Nate Hekman on November 19, 2008

GeoStudio 2007 tries to let you focus on the definition of the geometry, boundary conditions and material properties, without being distracted by the mesh. If you want, you can define your model, solve it, and view the results without once looking at the mesh.

But the reality is if you’re doing a finite-element analysis, the mesh can’t be ignored forever.

Start Simple

We always encourage you to start your model simply, and add complexity.  The same can be said for meshing.  Start with the default mesh, look at your results, and then decide if you need to use a finer mesh in certain areas (or everywhere).

Set the Global Element Size

If you want a finer mesh, the place to start is to use Draw Mesh Properties to change the “Approx. Global Element Size”.  This will change the entire mesh.

You’re setting the preferred length of each element edge.  So a smaller number will make for a finer mesh, and a larger number gives a coarser mesh.

Remember this size is “approximate”.  The mesher will do the best it can to stay close to the size you specified, but it won’t be exact.

Constrain the Mesh

Often you’ll find there are certain areas of your geometry that have more “activity”.  These areas may benefit by having a finer mesh.  You’ll get more exacting results at the expense of a longer solve time.

To get a finer (or coarser) mesh in specific areas, you select a region, line or point in that area, and change the Element Edge Length for the object you selected.  (You can also multi-select to adjust several objects simultaneously.) 

This is called “constraining the mesh”, because you’re giving the mesher specific instructions about this part of the mesh.

When adding a constraint, you are again specifying the preferred (or approximate) length of every element edge in this area.  But there are several ways to specify it:

  1. Using a ratio of the global length.
  2. Specifying the approximate length.
  3. Specifying the exact number of divisions (this option is only avialable on lines).

Normally #1 is the better approach, just defining it as a ratio, like “0.5” to make the mesh in this area half the size as the rest of the mesh.  That way you can later adjust the Global Element Size to make the entire mesh finer, and this area becomes finer yet.

Here’s an Example

Draw a simple geometry.  Choose Draw Mesh Properties to look at the mesh.

Make a finer mesh everywhere by adjusting the global element size.

Make the left side finer still, using a ratio.

Make the entire mesh finer by adjusting the global element size again.  Notice that elements along the left side are still half the size of the rest of the mesh.

Conclusions

Meshing is half science and half black art.  Making a finer mesh does NOT always give you a better result.  Discussing the ins and outs of how to mesh properly is beyond the scope of this article.  Read the engineering books that came with your software for a better treatment of this subject.

But adjusting and fine-tuning the mesh in GeoStudio 2007–or ignoring it completely–is easier than it has been in any previous version.

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