How to deal with cad-geometry next up previous contents
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How to deal with cad-geometry

A simple step-reader is integrated in cgx. It can deal with points and lines. You might start with a file containing a 2D-section, subdivide it in meshable surfaces and sweep it in the 3rd dimension to create your geometry. If features exist in the 3rd dimension only on a certain location then this feature must be included in the 2D-section. Then sweep the 2D-section to the location were the feature starts, then right to the end and at last to the end of the geometry. Then delete the bodies before and after the feature. You might also project the sweped sections to target surfaces if the feature is shaped in the 3rd dimension. This is the approach which I often use even to generate complex 3D-models. For complicated models you should also consider to use a tet-mesher like NETGEN [4] which can read step and generates quite nice tet-meshes. You can read this meshes with cgx and combine it with cgx-geometry and meshes. Then create your boundary conditions etc. You might read the native-netgen format (.vol) instead of abaqus-format because this stores also the 2D meshing regions as separate sets which can be used to apply boundary conditions (``cgx -ng file.vol'').

But you can also create a so called stl-file based on your cgx-geometry and feed it to external meshers. The following section explains how to do that:

In general hexahedra-elements perform better than tets but if the mesh should be derived from a cad-geometry it is often more convenient to create a tetrahedra mesh as to modify or rebuild the geometry to make it meshable with hexahedra-elements. In this case the user can mesh the surfaces with unstructured triangles and export them in the stl-format (see ''send'') as a basis for an auto-mesher [4]. The following steps have to be done:

Figure 12: CAD-file meshed with tet-elements using NETGEN
\begin{figure}\epsfig{file=halter.eps,width=9cm}\end{figure}


next up previous contents
Next: How to check an Up: Tips and Hints Previous: How to run cgx   Contents
root 2012-10-04