3 \page about_meshes_page About meshes
5 \n \b MESH represents a discrete approximation of a subset of the
6 three-dimensional space by \ref mesh_entities "elementary geometrical
9 A SALOME study can contain multiple meshes, but they do not
10 implicitly compose one super-mesh, and finally each of them
11 can be used (e.g. exported) only individually.
13 Mesh module provides several ways to create the mesh:
15 <li>The main way is to \subpage constructing_meshes_page "construct the mesh"
16 on the basis of the geometrical shape produced in the Geometry
17 module. This way implies selection of
18 - a geometrical object (<em>main shape</em>) and
19 - <em>meshing parameters</em> (\ref
20 basic_meshing_algos_page "meshing algorithms" and
21 characteristics (e.g. element size) of a
22 required mesh encapsulated in \ref about_hypo_page "hypothesis"
25 Construction of \subpage constructing_submeshes_page "sub-meshes"
26 allows to discretize some sub-shapes of the main shape, for example a face,
27 using the meshing parameters that differ from those used for other sub-shapes.<br>
28 Meshing parameters of meshes and sub-meshes can be
29 \subpage editing_meshes_page "edited". (Upon edition only mesh entities
30 generated using changed meshing parameters are removed and will be
32 \note Algorithms and hypotheses used at mesh level are referred to as
33 \a global ones and those used at sub-mesh level are referred to as \a
36 <li>Bottom-up way, using \ref modifying_meshes_page "mesh modification"
37 operations, especially \ref extrusion_page "extrusion" and \ref
38 revolution_page "revolution". To create an empty mesh not based on a
39 geometry, use the same dialog as to \ref constructing_meshes_page
40 "construct the mesh on geometry" but do not specify a geometry
41 or a meshing algorithm.
43 <li>The mesh can be \subpage importing_exporting_meshes_page "imported" from
44 (and exported to) the file in MED, UNV, STL, CGNS, DAT, GMF and
47 <li>The 3D mesh can be generated from the 2D mesh, which was \ref
48 importing_exporting_meshes_page "imported" or manually created. To
49 setup the meshing parameters of a mesh not based on a geometry, just
50 invoke \ref editing_meshes_page "Edit mesh / sub-mesh" command on
53 <li>Several meshes can be \subpage building_compounds_page "combined"
56 <li>The whole mesh or its part (sub-mesh or group) can be
57 \subpage copy_mesh_page "copied" into a new mesh.
59 <li>A new mesh can be created from a transformed, e.g. \ref
60 translation_page "translated", part of the mesh.</li>
63 Meshes can be edited using the MESH functions destined for
64 \ref modifying_meshes_page "modification" of meshes.
66 Attractive meshing capabilities include:
67 - 3D and 2D \ref viscous_layers_anchor "Viscous Layers" (boundary
68 layers of highly stretched elements beneficial for high quality
69 viscous computations);
70 - automatic conformal transition between tetrahedral and hexahedral
73 The \b structure of a SALOME mesh is described by nodes and elements based on
74 these nodes. The geometry of an element is defined by the sequence of
75 nodes constituting it and
76 the <a href="http://www.code-aster.org/outils/med/html/connectivites.html">
77 connectivity convention </a> (adopted from MED library). Definition of
78 the element basing on the elements of a lower dimension is NOT supported.
81 The mesh can include the following entities:
83 <li>\b Node — a mesh entity defining a position in 3D
84 space with coordinates (x, y, z).</li>
85 <li>\b Edge (or segment) — 1D mesh element linking two nodes.</li>
86 <li>\b Face — 2D mesh element representing a part of
87 surface bound by links between face nodes. A face can be a
88 triangle, quadrangle or polygon.</li>
89 <li>\b Volume — 3D mesh element representing a part of 3D
90 space bound by volume facets. Nodes of a volume describing each
92 the <a href="http://www.code-aster.org/outils/med/html/connectivites.html">
93 MED connectivity convention.</a> A volume can be a tetrahedron, hexahedron,
94 pentahedron, pyramid, hexagonal prism or polyhedron.</li>
95 <li>\b 0D element — mesh element defined by one node.</li>
96 <li>\b Ball element — discrete mesh element defined by a
97 node and a diameter.</li>
100 Every mesh entity has an attribute associating it to a sub-shape it is
101 generated on (if any). The node generated on the geometrical edge or
102 surface in addition stores its position in parametric space of the
103 associated geometrical entity.
105 Mesh entities are identified by integer IDs starting from 1.
106 Nodes and elements are counted separately, i.e. there can be a node
107 and element with the same ID.
109 SALOME supports elements of second order, without a central node
110 (quadratic triangle, quadrangle, polygon, tetrahedron, hexahedron,
111 pentahedron and pyramid) and with central nodes (bi-quadratic triangle
112 and quadrangle and tri-quadratic hexahedron).<br>
113 Quadratic mesh can be obtained in three ways:
114 - Using a global \ref quadratic_mesh_anchor "Quadratic Mesh"
115 hypothesis. (Elements with the central node are not generated in this way).
116 - Using \ref convert_to_from_quadratic_mesh_page operation.
117 - Using an appropriate option of some meshing algorithms, which
118 generate elements of several dimensions starting from mesh segments.