Code Aster Procedure

The fem_data_file can be generated by Code Aster, using the macro provided in the cms.py file, which is located in directory contrib/CodeAster/cms/ of the distribution, and is installed in directory $PREFIX/share/py/.

Preparing the input for Code Aster essentially requires to prepare the bulk of the mesh either manually or using some meshing tools (e.g. gmsh), as illustrated in the related documentation and tutorials, and then writing a simple script in python (http://www.python.org/) that defines the execution procedure.

To produce the data for MBDyn's modal element, a specific macro needs to be invoked during the execution of Aster. The macro instructs Aster about how the solution procedure needs to be tailored to produce the desired results, and then generates the .fem file with all the requested data.

The steps of the procedure are as follows:

1. prepare a Code Aster input model (the .mail file), containing the nodes, the connections and at least a few groups of nodes, as indicated in the following;

2. prepare a Code Aster command file (the .comm file), following, for example, one of the given templates;

3. as soon as the model, the materials, the element properties and any optional boundary constrains are defined, call the CMS macro with the appropriate parameters. The syntax of the macro is:

       CMS(
           MAILLAGE = <mesh concept> ,
           [ INTERFACE = <interface node set name> , ]
           EXPOSED = _F( { GROUP_NO = <exposed node set name> | TOUT = 'OUI' } ),
           MODELE = <model concept> ,
           CARA_ELEM = <element properties concept> ,
           CHAM_MATER = <material properties concept> ,
           [ CHAR_MECA = <boundary conditions concept> ,
           [ OPTIONS = _F(
               [ NMAX_FREQ = <maximum number of frequencies> ]
           ), ]
           OUT = _F(
               TYPE = { 'MBDYN' },
                   [ PRECISION = <number of digits> , ]
                   [ DIAG_MASS = { 'OUI' | 'NON' } , ]
                   [ RIGB_MASS = { 'OUI' | 'NON' } , ]
                   FICHIER = <output file name> 
           )
       );
   

   where:
   • MAILLAGE is the name of a python object returned by LIRE_MAILLAGE;
   • INTERFACE is a string containing the name of the group of nodes, defined in the mesh file, that will be used as interface to add Craig-Bampton shapes to the base (if omitted, only normal modes are used);
   • EXPOSED allows two formats:
     • GROUP_NO is a string containing the name of the group of nodes, defined in the mesh file, that will be exposed, i.e. that will appear in the .fem file generated by this macro;
     • TOUT is a string that must be set to 'OUI', indicating that all nodes will be exposed (technically speaking, all nodes involved in at least one connection);
   • MODELE is the name of a python object returned by AFFE_MODELE;
   • CARA_ELEM is the name of a python object returned by AFFE_CARA_ELEM;
   • CHAM_MATER is the name of a python object returned by AFFE_MATERIAU;
   • CHAR_MECA is the name of a python object returned by AFFE_CHAR_MECA (optional);
   • OPTIONS allows a set of generic options to be passed:
     • NMAX_FREQ is the number of frequencies expected from the eigenanalysis, and thus the number of normal modes that will be added to the modal base; the smallest frequencies are used;
   • OUT describes the parameters related to the type of output the macro generates; right now, only output in the format specified in this section is available:
     • TYPE indicates the type of output the macro is requested to generate; it must be 'MBDYN';
     • FICHIER (``file'' in French) is the name of the file where the generated data must be written; it must be a fully qualified path, otherwise it is not clear where the file is actually generated;
     • PRECISION contains the number of digits to be used when writing the data (for example, PRECISION = 8 results in using the format specifier %16.8e);
     • DIAG_MASS requests the output of the diagonal of the mass matrix (block 11); this option really makes sense only if all nodes are output (namely, if the nodes set passed to EXPOSED consists in all nodes);
     • DIAG_MASS requests the output of the rigid-body inertia properties (block 12);
   the macro returns a python object consisting in the generalized model it used to generate the file, as returned by MACR_ELEM_DYNA.

4. prepare a .export file, either following the examples or using astk;

5. run Aster.

Annotated examples are provided in directory contrib/CodeAster/cms/.