1. Introduction#

For Code_Aster, an elementary calculation option corresponds to a calculation leading to the production of one or more fields « by elements »

Examples of calculation options (option):

  • RIGI_MECA: stiffness calculation (elastic behavior)

  • FLUX_ELGA: heat flow calculation knowing the temperature at the nodes

  • CHAR_MECA_PESA_R: calculation of the second limb associated with a loading of gravity.

The 3 previous examples show that elementary calculations can be used almost everywhere in Code_Aster: in calculation commands (matrices and second members), as in post-processing commands (calculation of heat fluxes, mechanical energies,…)

An elementary calculation option has a name (K16) and is described in a catalog stored in the catalog/cataelem/options directory

Doing an elementary calculation is equivalent to requesting the calculation of an option on a list of finite elements (ligrel). This calculation is carried out by calling the « hat » routine for all elementary calculations: calcul.F90

The calculation is said to be « elementary » because it is the finite elements of Ligrel that do the calculation. For a calculation to be « elementary », it must be « local », that is to say that a finite element can calculate its participation by only having knowledge of local data (fields local to itself).

Knowing only local quantities, he logically calculates a « local » result (the participation of the finite element).

The collection of the results calculated by the various elements constitutes a (global) field « by elements ». It is a field that is inherently discontinuous between the elements.

Note: Calculating a basic calculation option can produce multiple fields. For example, this is the case with option RAPH_MECA used in the STAT_NON_LINE operator: a constraint field, an internal variables field and a « residue » field are calculated at the same time.

The global field produced by an elementary calculation can be a cham_elem or a resuelem. The difference between the two types of data structure is small: the resuelem is an elementary field containing matrices or elementary vectors intended to be assembled to form a global matrix or a second member.

When an elementary calculation produces a cham_elem, this one can be ELNO, ELGA, or ELEM. A ELNO field contains values on element nodes. A ELEM field is a constant field per mesh. A ELGA field is a field containing values on the integration (or Gauss) points of the elements.

In the next paragraph, we will detail the syntax that the catalog of an option should have.

Writing the catalog of a new option is not an end in itself. This is only a preliminary step for finite elements to be able to calculate this option. This is explained in the document [D5.02.05] « Introducing a new elementary calculation ».