FEM Mesh/fr

Créer un FEM Mesh
L'analyse par éléments finis (FEA) est effectuée sur un maillage composé de multiples éléments triangulaires et quadrilatéraux qui subdivisent le corps d'origine. Plus le maillage est raffiné, plus les résultats numériques seront précis, mais le temps de calcul sera également plus long. Un équilibre entre la taille du maillage, le temps de calcul et la précision des résultats est une caractéristique importante d'une analyse par éléments finis bien définie.


 * L'outil graphique Fem MeshFromShape Netgen avec interface graphique ou par programmation Python
 * L'outil graphique Fem MeshFromShape GMSH avec interface graphique ou par programmation Python
 * Directement en Python pour faire FEM Mesh manuellement
 * Importer un FEM Mesh

There are different possibilities to set up a mesh in the FEM Workbench:
 * The Gmsh tool from the graphical user interface.
 * The Netgen tool from the graphical user interface.
 * Importing a mesh from another program. In particular, Gmsh and Netgen can be used by themselves outside of FreeCAD to mesh solid bodies like Step files.
 * Manually creating the mesh through Python scripting.

Les objets créés avec PartDesign et Part sont supportés, ainsi que des copies simples de ces objets. Il y a deux possibilités pour l'utilisateur: Netgen et GMSH. Netgen est inclus dans FreeCAD. Pour GMSH, un binaire externe doit être installé. Faire référence à FEM Install.





The Gmsh and Netgen tools are convenience tools to quickly mesh a body, and thus don't expose the full capabilities of these programs; they normally create triangular meshes, which may not be ideal for some types of analysis. If you'd like to have more control of the created mesh (use only quadrilaterals, precise element number and size, variable resolution of the mesh, etc.), you should use these programs externally, produce a mesh file in a supported format, and import this file into FreeCAD.

Previously, Netgen was included with FreeCAD and could be used immediately. Now, both Netgen and Gmsh should be installed before they can be used by the FEM Workbench. Refer to FEM Install for instructions.

implémenté

 * Gmsh
 * http://gmsh.info/
 * https://gitlab.onelab.info/gmsh/gmsh
 * Netgen
 * https://ngsolve.org/
 * https://github.com/NGSolve/netgen

Meshing software operates on solid bodies that can be in different formats, like Step and Brep. These programs can be used independently of FreeCAD, and typically have many options to control the meshing algorithms, element size, and boundary conditions.

The FEM Workbench has developed simple communication interfaces to use Gmsh and Netgen directly inside FreeCAD. Other programs don't have an interface, but this could change in the future if there is interest from the community, and if those applications are easy to integrate. The meshing software can be compiled and distributed together with FreeCAD only if its license is compatible with the GPL2 or LGPL2 licenses; otherwise, the program has to be used as an external binary, like Gmsh is used.

Interface implemented in FreeCAD

 * Gmsh: main website, code repository
 * Netgen: main website, code repository

d'intérêt

 * ENigMA
 * https://forum.freecadweb.org/viewtopic.php?f=18&t=33048
 * https://github.com/bjaraujo/ENigMA
 * libMesh
 * https://forum.freecadweb.org/viewtopic.php?f=18&t=33621
 * http://libmesh.github.io/
 * https://github.com/libMesh/libmesh
 * Trés intéressant. En C++ seulement.
 * PythonOCC
 * http://www.pythonocc.org/
 * SnappyHexMesh
 * https://openfoamwiki.net/index.php/SnappyHexMesh
 * Tetgen
 * http://wias-berlin.de/software/tetgen/


 * ENigMA, forum thread, code repository
 * libMesh, main website, code repository, forum thread; it's a very active project, and it's C++ only
 * PythonOCC, main website
 * SnappyHexMesh, main website
 * Tetgen, main website

Éléments FEM Mesh dans FreeCAD
FreeCAD supporte différents types d'éléments. Il existe un blog externe qui en explique les différences et comment les utiliser: https://www.comsol.com/blogs/meshing-your-geometry-various-element-types/


 * "ni" signifie que le type d'élément n'est pas implémenté dans FreeCAD, mais le format est supporté.
 * "-" signifie que la spécification de format n'est pas supporté, donc ne sera pas accepté par FreeCAD.
 * "?" on ne sait pas si ce type d'élément est supporté.

Généralités
Plus d'informations sur les types d'éléments FEM et la structure des données incluses dans FreeCAD peuvent être trouvées dans FEM Types d'éléments.

More information on the elements, and their data structure inside FreeCAD can be found in FEM Element Types.

Création d'un objet mesh avec 10 Éléments
FreeCAD Scripting Basics.

The Python API allows the user to define a finite element mesh by directly adding individual nodes, and defining edges, faces, and volumes.

The mesh itself is of type, which needs to be attached to a proper document object of type.

Creating a mesh with one Tet-10 element
Create an empty FemMesh, populate it with nodes, create the volume, and finally call to create the document object with the corresponding mesh.

Vous pouvez utiliser les éléments prédéfini et nombre de noeuds:

To create an actual document object, instead of you can also use the document  method; then attach the created mesh to this object's  attribute.

Manipulations visuelles
sélectionnez des noeuds dans la vue 3D:

Once a FemMesh object has been created with, some of its visual properties can be changed by modifying the different attributes of its. This can be useful to postprocess the mesh after a finite element solution has been obtained.

Highlight some nodes in the mesh

Post-traitement des Couleurs et déplacement: Sélectionnez des noeuds dans la vue 3D:

Set volume 1 to red

Set nodes 1, 2 and 3 to a certain color; the faces between the nodes acquire an interpolated color

Displace the nodes 1 and 2 by the magnitude and direction defined by a vector

Double the factor of the displacement shown

Shell, 3 node triangle, tria3 (linear)
Add a face with the element number.

Shell, 6 node triangle, tria6 (quadratic)
Add a face with the element number.

Shell, 4 node quadrangle, quad4 (linear)
Add a face with the element number.

Shell, 8 node quadrangle, quad8 (quadratic)
Add a face with the element number.

Volume, 4 node tetrahedron, tetra4 (linear)
Add a volume with the element number.

Volume, 10 node tetrahedron, tetra10 (quadratic)
Add a volume with the element number.

Volume, 8 node hexahedron, hexa8 (linear)
Add a volume with the element number.

Volume, 20 node hexahedron, hexa20 (quadratic)
Add a volume with the element number.

Volume, 6 node pentahedron, penta6 (linear)
Add a volume with the element number.

Volume, 15 node pentahedron, penta15 (quadratic)
Add a volume with the element number.

Volume, 5 node pyramid, pyra5 (linear)
Add a volume with the element number.

Volume, 13 node pyramid, pyra13 (quadratic)
Add a volume with the element number.