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# Example of usage mesh 3D algorithms and hypothesis

## Example of usage mesh 3D algorithms and hypothesis

This sample is known to work on the latest SALOME release.
The compatibility with previous versions of SALOME is not guaranteed, though the sample can work on old versions also.

### Objective

This exercise illustrates the use of SMESH SALOME 3D algorithms and hypothesis and functionalities for meshing of the prism shape.

### Geometry

The sequence of actions is as follows:
• Launch SALOME.
• Create a new study.
• Launch GEOM module.
• Create group of faces Group_1: (menu New Entity/Group/Create Group)
Check 3rd radio button of "Shape Type" - "Face”
Select Main shape Prism_1
Select 4 side Faces holding down the Shift key
Apply and Close.

### Construction and modification of the mesh

Launch SMESH module.
• Creation of Mesh_1: (menu Mesh/Create Mesh)
Geometry: Prism_1
3D algorithm: Netgen 1D-2D-3D
3D hypothesis: Netgen 3D parameters
Max Size = 15
Fineness - Moderate
Uncheck “Second order”, “Optimize” check-boxes
OK, Apply and Close
• Compute Mesh_1
• Controls/Volume Controls/Volumes
Netgen 1D-2D-3D algorithm does not require 2D and 1D algorithms and hypothesis. It creates tetrahedrons. Computed Mesh may to differ from the picture depending of algorithm Netgen.

• Hide item in 3D Viewer from popup menu - Display entity/Faces
• Select in 3D Viewer from popup menu - Clipping
New -> Relative
Orientation - ||X-Y
Distance - 0.5
Rotation around X (Y to Z) - 0
Rotation around Y (X to Z) - 0
Apply and Close
Clipping shows only part of mesh and permits to analyse mesh inside.

• Edit Mesh_1: (menu Mesh/Edit Mesh/Sub-mesh)
3D algorithm: Tetrahedron(Netgen)
3D hypothesis: Max Element Volume = 100
2D algorithm: Triangle Mefisto
2D hypothesis: Max Element Area = 100
1D algorithm: Wire Discretization
1D hypothesis: Local length =20
Apply and Close

• Compute Mesh_1
Tetrahedron(Netgen) creates only tetrahedrons in this case.

• Creation of SubMesh_1: (menu Mesh/Create Sub-mesh)
Geometry: Group_1 (side faces)
Apply and Close

• Compute Mesh_1
Tetrahedron(Netgen) together with Quadrangle mapping creates pyramids (external layer) and tetrahedrons.

• Edit Mesh_1: (menu Mesh/Edit Mesh/Sub-mesh)
3D algorithm: 3D extrusion
Apply and Close
• Compute Mesh_1
3D extrusion creates only prisms in this case.

• Edit Mesh_1: (menu Mesh/Edit Mesh/Sub-mesh)
3D algorithm: Hexahedron(I,j,k)
1D algorithm: Wire Discretization
1D hypothesis: Local length = 20
Apply and Close

• Compute Mesh_1
Existing 2D and 1D algorithms and hypothesis are used (do not create new). Hexahedron(I,j,k) creates hexahedrons and prisms in this case.