3. Operands#

3.1. Operand OPTION#

♦ OPTION =

The following table lists the matrices calculated by an option and the type of element to which the option applies.

This type of element is given either by the name of the phenomenon that made it possible to define the model, or by the name of the operator that produced the charge concept.

Option	Phenomenon or operator	Matrix
“AMOR_MECA”	MEcanique	Damping of elements calculated by linear combination of stiffness and mass [U2.06.03] or by direct assignment for discrete elements. Damping of the absorbent boundary elements belonging to the specific “3D_ ABSO “or “D_ PLAN_ABSO” models of the moet model calculated from the mechanical characteristics \(E\), \(\mathrm{\nu }\) and \(\mathrm{\rho }\) of the affected material. Damping of the fluid absorbent boundary elements belonging to the specific models “3D_ FLUI_ABSO “, “2D_ FLUI_ABSO” or “AXIS_FLUI_ABSO” of the model moet calculated from the mechanical characteristics \(c\), \(\mathrm{\rho }\) and \(\mathrm{\alpha }\) of the mechanical characteristics, and of the affected material.
“MECA_GYRO”	MECANIQUE	Gyroscopic damping [R5.05.07]
“RIGI_GYRO”	MECANIQUE	Gyroscopic stiffness [R5.05.07]
“IMPE_MECA”	MECANIQUE	Acoustic impedance of surface or line elements belonging to the “3D_ FLUI_ABSO “or “2D_ FLUI_ABSO” or “AXIS_FLUI_ABSO” models of the mo model [U4.53.11] exclusively for modeling \(u-p-\phi\). In particular, we evaluate the third-order matrix that can be used for harmonic calculation.
“MASS_FLUI_STRU “*	MEcanique	Mass of the elements of the mo model taking into account the fluids external and internal to the structure and the confinement coefficient.
“MASS_MECA”	MEcanique	Mass of the elements in the mo model. Damping of the fluid absorbent boundary elements belonging to the specific models “3D_ FLUI_ABSO “, “2D_ FLUI_ABSO” or “AXIS_FLUI_ABSO” for the formulation \(u-p-\phi\) of the moet model calculated from the mechanical characteristics \(R\), \(\mathrm{\rho }\) and \(\mathrm{\alpha }\) from the mechanical characteristics, and of the affected material. This amortization is added as a mass contribution.
“MASS_MECA_DIAG”	MEcanique	Mass (diagonal) of the elements in the mo model.
“ONDE_FLUI”	MECANIQUE	Acoustic impedance of the surface elements of the model mo belonging to the “3D_ FLUIDE “and “2D_ FLUIDE” models. This impedance corresponds to the influence of an incident harmonic pressure wave [U4.53.11].
“RIGI_FLUI_STRU “*	MEcanique	Stiffness of the elements of the mo model taking into account the fluids external and internal to the structure and the confinement coefficient.
“RIGI_GEOM”	MEcanique	Geometric stiffness of mo model elements.
“RIGI_MECA”	MEcanique	Real part of the stiffness of the elements in the mo model. Damping of the fluid absorbent boundary elements belonging to the specific models “3D_ FLUI_ABSO “, “2D_ FLUI_ABSO” or “AXIS_FLUI_ABSO” for formulations \(u-p\) and \(u-\psi\) of the moet model calculated from the mechanical characteristics \(R\), \(\mathrm{\rho }\) and \(\mathrm{\alpha }\) of the affected material calculated from the mechanical characteristics, and of the affected material. This damping is added as a stiffness contribution.
	AFFE_CHAR_MECA	Matrix associated with the Lagrange multipliers of lchar.
“RIGI_MECA_HYST”	MEcanique	Complex stiffness of model elements.Calculated by multiplying the real stiffness by a complex number [U2.06.03] or by assembling the real and imaginary parts of the stiffness of a viscoelastic material together.
	AFFE_CHAR_MECA	Matrix associated with the Lagrange multipliers of lchar.
“RIGI_ROTA”	MECANIQUE	Rotational stiffness of model elements mo

“RIGI_THER”	THERMIQUE	Stiffness of model elements mo.
	AFFE_CHAR_THER	Stiffness from lchar exchange conditions.
	AFFE_CHAR_THER	Matrix associated with the Lagrange multipliers of lchar.
“MASS_THER”	THERMIQUE	Mass of the elements in the mo model.
“AMOR_ACOU”	ACOUSTIQUE	Damping model elements mo.
“MASS_ACOU”	ACOUSTIQUE	Mass of the elements in the mo model.
“RIGI_ACOU”	ACOUSTIQUE	Stiffness of model elements mo.
	AFFE_CHAR_ACOU	Matrix associated with the Lagrange multipliers of lchar.

The options marked * relate to the resorption of the software FLUSTRU:

These two options: “RIGI_FLUI_STRU” and “MASS_FLUI_STRU” make it possible to calculate mass and stiffness matrices (and therefore a modal basis) for a beam structure (SEG2) bathed by an external fluid. The material behavior relationship should be ELAS_FLU.

3.2. Operands MODELE/CHAM_MATER/CARA_ELEM#

♦ MODELE = mo

This operand is used to indicate the elements for which the elementary calculations must be carried out: remember that the finite elements are for the most part defined in the model.

There are two exceptions:

The elements of dualization of the conditions of DIRICHLET, that is to say the elements that make it possible to impose conditions on the degrees of freedom of movement in mechanics, the degrees of freedom of temperature in thermal and the degrees of freedom of pressure in acoustics.
Nodal loading elements.

These elements are defined in concepts such as char_meca, char_ther, or char_acou.

We must therefore provide the l_char argument for the calculation of elementary stiffness matrices: RIGI_MECA, RIGI_THER, RIGI_ACOU, RIGI_MECA_HYST.

◊ CHAM_MATER = chmat

Name of the material field where the material characteristics of the elements are defined.

This argument is almost always needed.

In practice, we can do without:

for discrete elements whose elementary matrices are defined in the cara_elem concept. See AFFE_CARA_ELEM [U4.42.01],
for the calculation of rigidities due to the dualization of boundary conditions.

◊ INST = GST

The tps argument is used when hardware characteristics or loads depend on time. A fairly frequent case is that of a mechanical material dependent on temperature which itself depends on time.

◊ CARA_ELEM = character

The elementary characteristics carac are necessary if there are elements of beams, shells or discrete elements in the model or if an anisotropy coordinate system has been defined on massive elements (keyword MASSIF of the AFFE_CARA_ELEM command).

3.3. Operand CHARGE#

◊ CHARGE = tank

This operand has several distinct functions:

Allow the calculation of elementary stiffness matrices corresponding to the dualization of certain conditions at the Dirichlet limits,
For option “ONDE_FLUI”: give the value of the pressure of the incident wave,
For the “RIGI_ROTA” option: give the value of the rotation imposed on the model.

3.4. Operand MODE_FOURIER#

◊ MODE_FOURIER =/nh

/0 [DEFAUT]

Positive or zero integer indicating the Fourier harmonic on which the elementary matrices are calculated.

3.5. Operand CALC_ELEM_MODELE#

◊ CALC_ELEM_MODELE =/'OUI' [DEFAUT]

/”NON”

This operand makes it possible to calculate the elementary stiffness matrix associated only with the macroelements of the model (“NON”). By default, the matrix is calculated over the entire model (“OUI”).

3.6. Operand GROUP_MA#

◊ GROUP_MA = lgma,

This operand makes it possible to calculate the elementary matrices only on the cells of the lgma groups. The operand is allowed for the gyroscopy options, RIGI_MECA, RIGI_MECA_HYST,,,, AMOR_MECA, MASS_MECA, IMPE_MECA, MASS_MECA_DIAG, and MASS_FLUI_STRU.

3.7. Operand SIEF_ELGA (option “RIGI_GEOM”)#

♦ SIEF_ELGA = sig

The constraint field sig given for the calculation of the option “RIGI_GEOM” must in principle have been calculated with the option “SIEF_ELGA” (constraint field at the Gauss points of the elements) (cf. command CALC_CHAMP [U4.81.04]) (cf. command []). The theory of linear buckling in fact assumes a theory of small elastic movements.

3.8. Operands RIGI_MECA and MASS_MECA (options” AMOR_MECA “and” RIGI_MECA_HYST “)#

♦ RIGI_MECA =

Real part of the elementary stiffness matrices (“RIGI_MECA”) required to calculate the matrices:

amortization (“AMOR_MECA”)
of hysteretic stiffness by global hysteretic damping (“RIGI_MECA_HYST”) see « Instructions for use of damping and hysteretic stiffness » [U2.06.03].
of complex stiffness for viscoelastic materials, the “RIGI_MECA_HYST” option calculates the imaginary part of the elementary stiffness matrix and combines it with the real part passed as an argument of the option.

◊ MASS_MECA =

Elementary mass matrices (“MASS_MECA” or “MASS_MECA_DIAG”) required to calculate damping matrices (“AMOR_MECA”).

Note:

For the option “ RIGI_MECA_HYST “, the result of the calculation will contain, in addition to the hysteretic stiffness of the elements of the model, the matrix associated with the Lagrange multipliers induced by the dualization of the loads supplied.

Note:

For a model containing only massless Finite Elements (for example “3D_ ABSO “or “D_ PLAN_ABSO”) , the user can build a damping matrix without having to build a mass matrix using the operator ASSEMBLAGE.

3.9. Operands AMOR_FLUI and VNOR#

◊ AMOR_FLUI =

This option allows us to deactivate the contribution of absorbent fluid boundaries (”3D_ FLUI_ABSO “, “2D_ FLUI_ABSO” and “AXIS_FLUI_ABSO”). In particular, if the fluid formulation \(u-p-\phi\) is used in a harmonic calculation, it is possible to take into account the contribution of the absorbent fluid boundaries via the calculation of a third-order matrix (with option IMPE_MECA). This third-order matrix can only be used in a harmonic calculation (operand MATR_IMPE_PHI in DYNA_VIBRA) and allows us to symmetrize the matrix (in contrast to calculating this contribution via AMOR_MECA). The option AMOR_FLUI = “NON” saves us from calculating this contribution twice. By default, AMOR_FLUI = “OUI”. This operand is available exclusively for option AMOR_MECA.

◊ VNOR =

This option allows us to take into account the case of an emissive border. The most common case is the radiative one (or partially radiative if we define a reflection coefficient \(\alpha \ne 0\)). In the case of a radiative border VNOR = 1. (option activated by default). In the case of an emissive border VNOR = -1. This coefficient is multiplied by the value of the impedance of the absorbing fluid boundaries (”3D_ FLUI_ABSO “, “2D_ FLUI_ABSO” and “AXIS_FLUI_ABSO”). This operand is available exclusively for options AMOR_MECA, IMPE_MECA, and AMOR_ACOU.

3.10. Operand TYPE_AMOR#

◊ TYPE_AMOR =

This option allows us to calculate all the damping sources present in the model or only the source linked to the absorbent boundary elements (fluid or not). The option by default (TYPE_AMOR = “TOUT”) takes into account possible Rayleigh damping, damping coming from discrete elements and damping coming from absorbent boundary elements. In this case it is necessary to provide either the mass and stiffness matrices for Rayleigh damping (and the material field), or the characteristics of the discrete elements. If there is only damping coming from the absorbent boundary elements, it is necessary to specify TYPE_AMOR = “ABSO” and provide only the material field as input.