1. General principles#

CodeAster makes it possible to perform structural calculations for thermal, mechanical, thermo-mechanical, or coupled thermo-hydro-mechanical phenomena, with linear or non-linear behavior, and internal acoustics calculations.

Nonlinearities relate to the behaviors of materials (plasticity, viscoplasticity, damage, metallurgical effects, hydration and drying of concrete,…), large deformations or large rotations and contact with friction. Refer to the Code_Aster presentation brochure for the presentation of the various functionalities.

Common industrial studies require the implementation of mesh and graphical visualization tools, which are not part of the code. However, several tools can be used for these operations through interface procedures integrated into the code.

To carry out a study, the user must, in general, prepare two data files:

the**mesh file: *

This file defines the geometric and topological description of the mesh without choosing, at this stage, the type of formulation of the finite elements used or the physical phenomenon to be modelled. Some studies may lead to the use of several mesh files.

This mesh file is, in general, produced by commands integrated into Code_Aster from a file from a mesh software used as a pre-processor (SALOME, GIBI, GMSH, IDEAS…).

The information that this file should contain is specific to*Code_Aster*. They define classical entities of the finite element method:

  • nodes: points defined by a name and by their Cartesian coordinates in 2D or 3D space,

  • mesh: topological figures named plane or solid (point, segment, triangle, quadrangle, tetrahedron,…) on which various types of finite elements, boundary conditions or loads can be applied.

To improve the safety of use and the comfort of modeling and analysis of results operations, it is possible to define, in the mesh file, higher levels of entities, possessing in common any property and which can be used directly by name and which can be used directly by name:

  • node groups: named lists of node names,

  • mesh groups: named lists of mesh names.

As of now, it should be noted that all the geometric entities manipulated (nodes, meshes, groups of nodes, groups of cells) are named by the user and can be used at any time by their name (8 characters maximum). The user can use this possibility to explicitly identify certain parts of the structure studied and thus facilitate the analysis of the results. Entity numbering is never explained: it is only used internally to point to the values of the various associated variables.

the**command file*: to define the command text that allows:

  • to read and possibly enrich the data from the mesh file (or other sources of external results),

  • to assign the modeling data to the entities in the mesh,

  • to combine different processing operations: calculations, specific post-treatments,

  • to edit the results on various files.

The command text refers to the names of geometric entities defined in the mesh file. It also allows you to define new groups at any time.

From a computer perspective, these two files are ASCII files in free format. The main characteristics are given here:

Mesh file syntax:

  • line length limited to 80 characters,

  • allowed characters are:

the 26 uppercase letters**A-Z**and the 26 lowercase**a-z* automatically converted to uppercase letters, except in the texts (provided between quotes),

the ten digits**0-9**and the signs representing numbers (**+ - .*),

the**_ white underlined character* usable in keywords or names,

  • a word must always start with a letter,

the**white* character is always a separator,

the character**%**indicates the beginning, until the end of the line, of a**comment*.

  • The other reading rules are specified in the paper [U3.01.00]

Command file syntax:

  • syntax linked to the Python language, allowing to include instructions from this language

the character**#**indicates the beginning, until the end of the line, of a**comment*.

  • Commands must start in column 1, unless they are part of an indented block (loop, test)

The other reading rules are specified in the paper [U1.03.01].