8. Definition of depreciation

8.1. Keyword factor AMORTISSEMENT

◊ AMORTISSEMENT = _F (…)

Keyword factor that allows the introduction of different types of depreciation.

8.1.1. TYPE_AMOR = “RAYLEIGH”

♦ TYPE_AMOR = “RAYLEIGH”,

This option allows you to calculate the Rayleigh damping matrix based on the parameters (AMOR_ALPHA, AMOR_BETA) of the materials affected in CHAM_MATER (see § 4.2) and of the discretes of type (A_T*) defined in CARA_ELEM (see § 4.3). Also, this option makes it possible to calculate the contribution of fluid absorbent boundaries, if they are present in the model.

If we are in the presence of a harmonic calculation (TYPE_CALCUL = “HARMO”), we activate other options to manage the contribution of fluid absorbent borders.

8.1.2. Operands VNOR and MATR_IMPE_PHI

These operands are activated exclusively in the case where TYPE_CALCUL = “HARMO” and TYPE_AMOR = “RAYLEIGH”.

◊ 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”).

◊ MATR_IMPE_PHI =

If we use the fluid formulation \(u-p-\phi\) in a harmonic calculation, we have the possibility of taking into account the contribution of 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). If you want to use this third-order matrix instead of the first-order term (calculated via AMOR_MECA), you must impose MATR_IMPE_PHI = “OUI” (by default MATR_IMPE_PHI = “OUI”).

8.1.3. TYPE_AMOR = “HYST”

♦ TYPE_AMOR = “HYST”,

This option is used in the case of a harmonic calculation (TYPE_CALCUL == “HARM”). It makes it possible to calculate the imaginary part of the stiffness matrix in the case of:

of a material with hysterical damping specified by the parameter (AMOR_HYST) assigned in CHAM_MATER (see § :ref:`4.2 <RefHeading___Toc 10804_2130749778>`) and type discretes (A_T) defined in CARA_ELEM (see § 4.3).

of a viscoelastic material of type ELAS_VISCO_ affected in CHAM_MATER (see § 4.2)

8.1.4. TYPE_AMOR = “MODAL”

♦ TYPE_AMOR = “MODAL”,

In the case of a generalized calculation, it is sometimes simpler and more relevant to define modal depreciation. In this case, you must specify in AMOR_REDUIT the reduced amortizations (percentages of critical damping) corresponding to each mode of the system in the form of a list of reals.

♦ AMOR_REDUIT = l_love, [l_R]

If the number of reduced depreciations given is less than the number of base vectors used in the modal base, the dampenings of the additional vectors are taken equal to the last damping in the list l_amor.