This is an answer to this post.
https://forum.freecadweb.org/posting.ph ... 2#pr170043
But I think it should be written here.
bernd wrote:Solve this on either shell or solid mesh is possible, but on mixed meshes we really are in trouble ...
This is also a problem for pure 2D-meshes, when we want using more options from calculix. Those meshes are useful in several cases, where only a 2D-section needs to be analyzed, in order to get insight into the stresses of a 3D-objekt:
For a part with rotational symmetry you can use a section and analyze the section with axisymmetric elements. Example for Ansys:
http://mae.uta.edu/~lawrence/ansys/thic ... linder.htm
For a flat part, you can use Plane-Stress-elements to calculate stresses in plane. See here for an explanation of Plane-stress-elements:
http://www.digitaleng.news/de/simplifyi ... ne-strain/
Other cases are shells or membranes. All of them can base on a pure 2D-geometry.
Depending on the type of element used, the constraints and other things are different in the input file, even if the geometry of the mesh is just a flat face. I already went through this, where I used a section of a part with rotational symmetry. I could make the mesh and node sets and element sets in FreeCAD, but had to edit the file and needed to apply the constraints with cgx.
So we need a user input, what sort of element should be used for the geometry, the user wants to analyze. This information needs to be accessible for the definition of the other parts of the analysis: mesh element type, writing of the geometry definition into the input file, constraints definitions and others. In order to give this a clean structure, an object defining 3D-geometry independent from material is helpful.
When the user selects the part to be analyzed at time of adding of the analysis-object, a geometry object could be made automatically.
Ulrich