FEM MeshGmshFromShape/de

Beschreibung
Für eine Finite Element Analyse muss die Geometrie in ein FEM Netz diskretisiert werden. Dieser Befehl verwendet gmsh (das auf dem System installiert sein muss) zur Berechnung des Netzes.

Gmsh is bundled with the FreeCAD installation binaries. Alternatively you can install it separately from FreeCAD and then use the menu to set the path to the gmsh.exe.

Anwendung

 * 1) Wähle die Form, die du analysieren möchtest. Bei der Volumen FEM muss es sich um einen Festkörper oder Compsolid (zusammengesetzten Festkörper) handeln. Ein Compsolid ist erforderlich, wenn dein Teil aus mehreren Materialien besteht. (Ein Compsolid kann mit dem Befehl BoolscheFragmente erstellt werden). -- Für die Schalen- und Balken FEM muss jemand die Details hier eintragen.
 * 2) Drücke den  Schaltfläche
 * 3) Bearbeite wahlweise die minimale und maximale Elementgröße . (Automatische Erkennung funktioniert gut, es sei denn, du wendest komplizierte Randbedingungen an).
 * 4) Klicke die  Schaltfläche und warte, bis die Berechnung des Netzes abgeschlossen ist
 * 5) Schließe die Aufgabe. Du solltest jetzt ein neues FEMMeshGMSH Objekt in deinem aktiven Analysebehälter sehen.

After the mesh has been crated you can change its properties using the property editor. After you changed a property, you must reopen the Gmsh dialog again and click the button. (You can leave the dialog open while changing properties.)

Properties

 * : The algorithm to create 2D meshes. The different algorithms are explained here. For Delaunay, see Delaunay triangulation.
 * : The algorithm to create 3D meshes. The different algorithms are explained here.
 * : The maximal size of the mesh elements. If set to 0.0, the size will be set automatically. This property can also be changed in the Gmsh dialog in the field Max element size.
 * : The minimal size of the mesh elements. If set to 0.0, the size will be set automatically. This property can also be changed in the Gmsh dialog in the field Min element size.
 * true (default); duplicate mesh nodes will be removed
 * false
 * : The dimension of the mesh elements. This property can also be changed in the Gmsh dialog in the field Mesh element dimension.
 * From Shape (default); the dimension will be determined from the dimension of the object that is meshed
 * 1D
 * 2D
 * 3D
 * : The mesh element order. This property can also be changed in the Gmsh dialog in the field Mesh order.
 * 1st
 * 2nd (default)
 * : The number of mesh elements per $$2\pi$$ times the radius of the curvature. To get a finer mesh at small corners or holes, this value can be increased for better results
 * : The number of mesh elements per $$2\pi$$ times the radius of the curvature. To get a finer mesh at small corners or holes, this value can be increased for better results


 * : Option if second order nodes (if set to 2nd) and/or mesh refinement points are created by linear interpolation.
 * true; linear interpolation is used
 * false (default); curvilinear interpolation is used

Nonpositive Jacobians
When you get a meshing erro about nonpositive Jacobians, you can try out the following strategies:


 * Set to true but keep  at 2nd.
 * Set to 1st.
 * Use a smaller element size by reducing the.

Mesh Growth
At edges and small geometric entities the mesh has to be smaller than in areas without edges. So the mesh element size grows away from edges. The growing strategy of Gmsh is to grow between edges with different sizes. So the growing fails when an area has the same sized edges like for example this tube:



To enable a sensible mesh growing, you must in this case add an edge to the area. In the example this would be a circle in the middle of the cylinder. The circle is added as part of a BooleanFragments compound (to form a CompSolid), see the project file of the example.