19. Keyword MASS_AJOU

19.1. Syntax

MASS_AJOU = _F (

♦ GROUP_MA = gma, [group_ma]

♦ GROUP_MA_POI1 = gma, [group_ma]

♦ FONC_GROUP = fg, [function]

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19.2. Affordable characteristics

The objective of this keyword is to simply take into account the added mass of fluid in dam problems without having to model the fluid as in MACRO_MATR_AJOU and to keep only the structure for nonlinear dynamic studies.

The idea is therefore, in a new option of AFFE_CARA_ELEM, to distribute point mass characteristics to the nodes of the fluid-structure interface of the upstream facing without adding degrees of freedom outside the structure.

We are thus inspired by the distribution of overall stiffness or damping characteristics by option RIGI_PARASOL of AFFE_CARA_ELEM.

In this new option MASS_AJOU, elementary values of directional mass obtained by integrating the normal pressure to each element from distribution functions of this normal pressure dependent on coordinates - in particular on the altitude - are distributed to the nodes of the fluid-structure interface with characteristics” M_T_N “in order to express Westergaard relationships, for example, or more simply the expression of hydrostatic pressure.

The assignment of these terms (modeling to be declared in AFFE_MODELE: “DIS_T” for a fluid-surface structure interface in 3D and “2D_DIS_T” for a fluid-linear structure interface in 2D) is then done to the point cells POI1des nodes of the fluid-structure interface using the keyword GROUP_MA_POI1 of the key word factor MASS_AJOU.

It is necessary to distinguish these point cells from groups of surface or linear cells for the fluid-structure interface, to be declared behind the keyword GROUP_MA.

Note

Dans le cas où le résultat de la commande AFFE_CARA_ELEM avec le mot-clé MASS_AJOU est utilisé pour effectuer un calcul avec des résultats provenant d’un modèle analogue sans MASS_AJOU, par exemple dans le cadre d’un calcul avec un état initial provenant d’un modèle sans masse ajoutée, il est nécessaire de prolonger le résultat sur l’ensemble du nouveau modèle au préalable. Ceci afin de correctement initialiser les champs.

This can be done via command PROJ_CHAMP with PROL_VALE = 0.0.

19.3. Description of operands

♦ GROUP_MA

Group of surface (in 3D) or linear (in 2D) cells of the fluid-structure interface.

♦ GROUP_MA_POI1

Point mesh group of fluid-structure interface nodes.

♦ FONC_GROUP

Normal pressure distribution function depending on the coordinates of the group of elements composing the fluid-structure interface (defined under the keywords GROUP_MA or GROUP_MA_POI1). The function must be homogeneous at a mass surface density.