1. Purpose

Calculate the natural vibration modes or the Euler buckling modes of a mechanical structure.

The CALC_MODESrésout operator for this a modal problem that can be either generalized (GEP) `[R5.01.01] =`_ < https://code-aster.org/V2/doc/default/fr/man_r/r5/r5.01.01.pdf>, or quadratic (QEP) < https://code-aster.org/V2/doc/default/fr/man_r/r5/r5.01.02.pdf>` [R5.01.02]] `_.

The user specifies the search criteria for the modes (for example: on a band; near given values; etc.) using the keyword OPTION. Depending on the value of this keyword, the general calculation method (simultaneous iterations or inverse powers) is then determined automatically.

Within each of these two general methods, variants exist:

• case of simultaneous iterations: subspace method (Bathe & Wilson, Lanczos or Sorensen), global QR-type method (QZ for small problems);

• case of inverse powers: direct method or accelerated by the Rayleigh quotient.

These variants can be accessed with a keyword factor SOLVEUR_MODAL.

In the case of a calculation of natural vibration modes, post-treatments can also be carried out: normalization of the modes according to a given criterion, filtering of the modes according to a given criterion, production of modal parameters, etc.

This operator produces a conceptmode_meca_* (dynamic case) or mode_flamb (Euler buckling case, only in GEP) or mode_gene depending on the value entered in the TYPE_RESU keyword and the type of the input matrices for the modal problem.

The concept mode_meca_*, or mode_flamb, contains eigenvectors and values, and modal parameters, cf. < https://code-aster.org/V2/doc/default/fr/man_r/r5/r5.01.03.pdf>` [R5.01.03] < https://code-aster.org/V2/doc/default/fr/man_r/r5/r5.01.03.pdf>``_.

In a first approach, we can simply fill in the following parameters: OPTION to define the search criteria for the modes, TYPE_RESU, the input matrices for the modal problem MATR_ *, CALC_FREQ (or CALC_CHAR_CRIT).