3. Risk of producing a non-compliant mesh#

A number of the functionalities of the CREA_MAILLAGE command can lead to the production of a non-conforming mesh. For this reason, the user should be particularly careful when using CREA_MAILLAGE to transform meshes.

A mesh is non-compliant when the shape functions of 2 adjacent elements do not have the same trace on their common border.

For example:

  • 2 pentahedra assembled to form a hexahedron and placed on another hexahedron (1 quadrangle facing each other 2 triangles).

  • 1 QUAD8 sharing an edge with 1 QUAD4 or 1 TRIA3

  • 1 TRIA6 sharing an edge with 2 TRIA3

Non-compliant meshes generally lead to false results (at least locally).

Among the possibilities of CREA_MAILLAGE, several situations are potentially dangerous:

  • Use of one of the keywords QUAD_TRIA3 [§ 4.4.1], LINE_QUAD [§ 4.5], [§], QUAD_LINE [§ 4.11], HEXA20_27 [§ 4.7], PENTA15_18 [§ 4.6] with the keyword. GROUP_MA

For example, if you partially transform a linear mesh into a quadratic mesh, the mesh will be non-compliant on the border between the linear elements and the quadratic elements.

When using the keyword GROUP_MA, care must be taken to provide all the meshes involved in the transformation, in particular skin elements otherwise, a HEXA27pourrait for example be bordered by skin elements QUAD8.

  • Use of the keyword HEXA20_27 [§ 4.7] (or PENTA15_18 [§ 4.6] (or [§]) if there are solid elements with quadrangular faces in the mesh that are of a type different from the elements that are being modified. For example, if pentahedra or pyramids exist when hexahedra are modified.

The risk is that, for example, a quadrangular face of HEXA27 (9 knots) is attached to a quadrangular face with 8 knots of an adjacent PENTA15.

  • Use the QUAD_TRIA3 keyword if it exists in the mesh of TRIA6 elements. In this case, quadrangles transformed into TRIA3 will be incompatible with TRIA6.