3. First time using code_aster#
Consult the document [U1.01.04] describing the graphical astk access interface.
The easiest way to perform a calculation with code_aster is to start from a similar example that is often found in the basic test cases described in the Validation Manual. The command files associated with the test cases described in the validation documentation are located in the astest directory of the version used. On the EDF R&D centralized computing server, they are located in /aster/vx/ STAx /astest where x is the operating version number.
This method of proceeding by analogy, which is generally well appreciated by the mechanical community, should not completely replace a constructive approach. Many possibilities are most often available to carry out the same work that are more or less well suited to each case.
It is therefore necessary to get in the habit of consulting this validation manual for each new need.
3.1. The main principles and key steps of a calculation#
Below is a reading path inspired by the main mandatory steps of a mechanical study with code_aster. In this approach, three documents are proposed for reading.
3.1.1. The main principles of code_aster#
Consult the document [U1.03.00] The main principles of code_aster, which summarizes the operating principles and the main rules of use.
3.1.2. Simple example of using code_aster#
Consult the document [U1.05.00] Simple example of using code_aster, the « essential » commands, on a calculation of a thin cylindrical reservoir under hydrostatic pressure, axisymmetric modeling.
3.2. The mesh#
The structure of the*Aster* mesh file is described in the document [U3.01.00] Code_aster mesh file description.
If the initial mesh comes from a mesh external to Aster such as for example GMSH, GIBI or I- DEAS, the Aster interfaces and commands that create Aster mesh objects (which are not a copy of the initial objects; their meaning may change, new objects may be created) from the objects produced by these pre-processors (which are not a copy of the initial objects; their meaning may change, new objects may be created) are described in the documents:
[U3.02.01] Interfacing the GMSH mesh file with Aster,
[U3.03.01] I-DEAS mesh file interface with Aster,
[U3.04.01] Interfacing the GIBI mesh file with Aster,
[U7.01.01] Procedure PRE_IDEAS,
[U7.01.11] Procedure PRE_GIBI,
[U7.01.31] Procedure PRE_GMSH,
The recommended mesh format when using code_aster is the MED format (Data Exchange Model). This is the format by default when reading meshes and writing results.
3.3. The orders#
The description of the Code_Aster commands are contained in the parts U4 and U7 of the User Manual. It is certainly these 2 parts of the manual that the Aster user will most often use. They are organized in the U4 manual according to a scenario that logically follows the main steps of a calculation:
U4.1- |
Allocation of disk and memory resources, |
U4.2-, U7.01.- to U7.03.- |
Acquiring mesh data, |
U4.3- and U4.4- |
Modeling (assignment of finite elements, materials, loads, etc… ), |
U4.5- |
Solving the system of equations (calculation) |
U4.6-, U4.7-, U4.8-,**U4.8-, U7.03 to U7.05.- |
Post processing and review of results |
Finally, the document [U4.01.00] How to read command documentation, explains in particular the meaning of metacharacters and typography that are encountered in command syntax documentation.
3.4. The instructions for use#
A certain number of models or types of models (such as for example static substructuring, mechanical damping, thin shells, etc.) are the subject of instructions for use. The related documents will be available on the server in part U2 of the User Manual.
3.5. Finite elements, models of phenomena#
From a numerical point of view, the choice of finite elements for a type of modeling is the responsibility of the user. The mathematical description of models supported by finite elements can be found in the Reference Manual. The description of the degrees of freedom of these elements as well as their modeling possibilities (supported loads, product fields, non-linear possibilities, etc.) can be found in the documents:
U3.1-: Mechanical modeling,
U3.2-: Thermal modeling,
U3.3-: Acoustic models.
3.6. Result user data structures#
Aster calculation operators (commands) create objects whose structure of the data they contain must be absolutely known to users.
It is imperative to read very carefully the documents devoted to Aster commands dedicated to the printing of results (on listing or files).
First, two generic documents:
[U4.91.01] Procedure IMPR_RESU (FORMAT =” RESULTAT “and” ASTER “)
Then five documents describing the commands that generate result files in the format MED, GMSH and in the formats accepted by the I- DEAS post-processor:
[U7.05.01] Procedure IMPR_RESU (FORMAT =” IDEAS “),
[U7.05.21] Procedure IMPR_RESU (FORMAT =” MED “),
[U7.05.32] Procedure IMPR_RESU (FORMAT =” GMSH “),
3.7. The errors in the command file#
Creating an Aster command file is a mandatory step for the user. Currently, the user has the choice between creating this file by hand or building it using the graphical interface EFICAS « ** »** »** »** »** »FIchier Command** Editor**** ** « , which is quite natural to use. ASter
In addition, it provides direct access to electronic documentation.
If the command file is built by hand and if*Aster* detects a syntactic, grammatical or even semantic error in this file, answer elements to remedy the errors encountered can be found in [U1.03.01] Supervisor and command language.
3.8. Telephone support#
Aster Technical Telephone Support for use is provided by an external contributor, whose contact details appear on the website, Services section (intranet access required).