3. Examples#

3.1. Geometry and meshing GMSH#

We create a very simple geometry: a square with side \(1\). Here, we create the points, the lines, the surface; we could also have done it by translation/extrusion…

NOTE:

We create a « physical » that contains the square area of number 107.

L=1;

d=0.45;


Point (1) = {0, 0, 0, d};

Dot (2) = {L, 0, 0, d};

Dot (3) = {L, L, 0, d};

Dot (4) = {0, L, 0, d};

Line (1) = {1, 2};

Line (2) = {2, 3};

Line (3) = {3, 4};

Line (4) = {4, 1};

Line Loop (106) = {2, 3, 4, 1};

Plane Surface (6) = {106};

Physical Surface (107) = {6};

The mesh created with the 2D anisotropic algorithm is:

_images/100000000000018C0000015931B0074ACD8FA6B0.png

The GMSH mesh file contains the description of the nodes and meshes:

$ NOD

9

1 0 0 0

2 1 0 0

3 1 1 0

4 0 1 0

5 0.4999999999999931 0 0

6 1 0.4999999999999931 0

7 0.500000000000007 1 0

8 0 0.500000000000007 0

13 0.5000000000000001 0.5 0

$ ENDNOD

$ ELM

8

1 2 107 6 3 13 1 5

2 2 107 6 3 8 1 13

3 2 107 6 3 5 2 13

4 2 107 6 3 13 2 6

5 2 107 6 3 6 3 13

6 2 107 6 3 3 13 3 7

7 2 107 6 3 7 4 13

8 2 107 6 3 13 4 8

$ ENDELM

The syntax for this file is described in the « File Formats/GMSH mesh file format « section of the GMSH manual.

3.2. Aster mesh file produced by operator PRE_GMSH#

TITRE

AUTEUR = INTERFACE_GMSH DATE =17/07/2003

FINSF

%

COOR_3D NBOBJ =9

% FORMAT =( 1*NOM_DE_NOEUD ,3* COORD)

N1 0.00000000000000E+00 0.00000000000000E+00 0.00000000000000E+00

N2 1.00000000000000E+00 0.00000000000000E+00 0.00000000000000E+00

N3 1.00000000000000E+00 1.00000000000000E+00 0.00000000000000E+00

N4 0.00000000000000E+00 1.00000000000000E+00 0.00000000000000E+00

N5 4.99999999999993E-01 0.00000000000000E+00 0.00000000000000E+00

N6 1.00000000000000E+00 4.99999999999993E-01 0.00000000000000E+00

N7 5.00000000000007E-01 1.00000000000000E+00 0.00000000000000E+00

N8 0.00000000000000E+00 5.00000000000007E-01 0.00000000000000E+00

N13 5.00000000000000E-01 5.00000000000000E-01 0.00000000000000E+00 E+00

FINSF

%

TRIA3 NOM = INDEFINI NBOBJ =8

M1 N13 N1 N5

M2 N8 N1 N13

M3 N5 N2 N13

M4 N13 N2 N6

M5 N6 N3 N13

M6 N13 N3 N7

M7 N7 N4 N13

M8 N13 N4 N8

FINSF

%

GROUP_MA NOM = GM107

M1 M2 M3 M4 M5 M5 M6 M7 M8

FINSF

%

FIN

The eight triangles that make up the mesh square are then accessible in Aster in mesh group GM107.