MESH

General information

The MESH class is dedicated to the handling of unstructured meshes. Two classes derive from it : MESHING supplies functions for creating meshes from scratch (c.f. MESHING), while GRID gives specific constructors for creating structured meshes.

Content of the connectivity array

Underlying the unstructured meshes is the notion of connectivity. This section only covers meshes made out of standard elements, the MED_POLYGON and MED_POLYHEDRA case being detailed in section Polyhedra and polygons .

connectivity_arrays_small.png

Nodal connectivity storage scheme

In MEDMEM, an unstructured mesh nodal connectivity is defined with these arrays (if the mesh has no MED_POLYGON and MED_POLYHEDRA element) :

The cell types are ordered by their number of nodes.

As an example, let us consider a mesh made out of a linear triangle, two linear quadrangles and a quadratic triangle (c.f. figure fig_connectivity_example ).

connectivity_example_small.png

Example for mesh connectivity

The number of types is : 3

The type array writes : MED_TRIA3, MED_QUAD4, MED_TRIA6

The global numbering index is : 1,2,4,5 }. Its dimension is $ n_{types}+1 $ so that elements of type $ type[i] $ are stored between element $ index[i] $ and $ index[i+1] $ ( $ index[i] \leq j < index[i+1] $).

The connectivity array writes : 1, 2, 3, 2, 4, 5, 3, 5, 6, 7, 8, 4, 6, 5, 10, 11, 9

The connectivity index array writes : 1, 4, 8, 12, 18

Its dimension is $n_{cell}+1$, in order to be able to write that nodes of element $i$ are located in the connectivity array between $index[i]$ and $index[i+1]$ ( $index[i] \leq j < index[i+1]$).\

Warning:
As MEDMEM respects MED numbering which starts Fortran-style at 1, reading these information to set C structures requires careful handling of index offsets.

Outline

The description of MESH methods is given by the following sections :

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