FEM MeshGmshFromShape/it

Descrizione
Per un'analisi degli elementi finiti, la geometria deve essere discretizzata in Mesh FEM. Questo comando utilizza gmsh (che deve essere installato sul sistema) per il calcolo della mesh.

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.

Utilizzo

 * 1) Selezionare la forma da analizzare. Il volume FEM deve essere un solido o un solido composto. Se la parte è composta da più materiali è necessario un solido composto. (Un solido composto può essere creato con il comando Frammenti booleani.) -- Per travi e solette FEM qualcuno dovrebbe aggiungere qui delle spiegazioni dettagliate.
 * 2) Premere il pulsante
 * 3) Modificare facoltativamente la dimensione dell'elemento minimo e massimo. (Il rilevamento automatico funziona correttamente a meno che non si applichino complicate condizioni.)
 * 4) Cliccare sul pulsante  e attendere il completamento del calcolo della mesh
 * 5) Chiudere l'attività. Ora nel contenitore delle analisi attivo si dovrebbe vedere un nuovo oggetto FEMMeshGMSH.

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.