3. Operands#
3.1. Operand MAILLAGE#
Name of the mesh containing the fluid domain and the fluid/structure interface. This mesh may also include the structure.
3.2. Operand GROUP_MA_FLUIDE#
♦ GROUP_MA_FLUIDE = fluid
Groups of cells (2D and 2D axisymmetric plane cells, 3D volume cells) representing the fluid domain acting on the structure under study.
3.3. Operand GROUP_MA_INTERF#
♦ GROUP_MA_INTERF = interf
Groups of cells representing the interface between the fluid and the structure (plane or wire meshes). It should be noted that this group of elements may be one of those used to model the surface of the structure, especially if it is modeled by shell elements. It is not always necessary to create a specific group of interface elements with fully-fledged meshes.
3.4. Operand MODELISATION#
Type of modeling to be assigned to the fluid domain and to the fluid/structure interface. Currently, the models” PLAN “(2D fluid domain),” 3D “(liquid volume domain) and” AXIS “(axisymmetric fluid domain) are the only ones authorized.
3.5. Keyword FLUIDE#
Key word factor in which the characteristics of fluid material are affected. If the density of the fluid varies over the fluid domain, these different densities must be specified by several occurrences of the keyword factor FLUIDE.
3.5.1. Operand RHO#
♦ RHO = rho
Value of the density of the fluid to be assigned to the topological entities defined below.
3.5.2. Operands TOUT/GROUP_MA#
Group of cells or the entire fluid domain where density RHO is affected.
3.6. Keyword DDL_IMPO#
Keyword factor by which the boundary conditions of the fluid are specified (Dirichlet type).
3.6.1. Operand GROUP_NO#
Node groups where boundary conditions are imposed on the fluid domain.
3.6.2. Operand PRES_FLUIDE#
A keyword under which to specify the value that is imposed on hydrodynamic pressure (that is, the pressure disturbance created by the vibration of the structure) on the topological entity determined above. This keyword must appear at least once because it makes it possible to calculate the unsteady pressure fields generating the added mechanical quantities.
3.6.3. Operand PRES_SORTIE#
Outlet pressure to be imposed on a permanent flow. Keyword to be used (in a different occurrence from the keyword factor DDL_IMPO where PRES_FLUIDE was used) to specify the boundary conditions on the permanent quantities to be calculated (such as the potential for permanent fluid velocities characterizing a permanent flow disturbed by vibrations). This keyword is only to be used if we want to calculate the added damping and stiffness matrices that require the calculation of a permanent flow that is assumed to be potential.
3.7. Keyword ECOULEMENT#
This keyword factor makes it possible to determine the Neumann-type boundary conditions when one wants to calculate an assumed potential permanent flow, in order to be able to calculate damping and added stiffness.
3.7.1. Operands GROUP_MA_1/GROUP_MA_2#
Names of the groups of cells at the entrance and exit respectively of the fluid domain where conditions of normal speed of entry or exit of the fluid are imposed.
3.7.2. Operands VNOR_1/VNOR_2#
Real values of the normal velocities of the fluid respectively at the inlet and at the outlet of the fluid domain.
3.7.3. Operand POTENTIEL#
Name given by the user to the potential of permanent fluid velocities if he eventually wants to post-treat it.
3.8. Operands MODE_MECA/DEPL_IMPO/MODELE_GENE#
♦/MODE_MECA = fashion
Dynamic modes calculated on the structure model. If there are several non-related structures immersed in the same fluid, for which it is desired to determine the added matrices comprising the terms of coupling by the fluid, the structure model that is defined brings together all the immersed structures. The modes used by the operator are the modes calculated for the overall structure.
/DEPL_IMPO = field
Fields at the travel nodes assigned to groups of nodes defining the fluid/structure interface. By assigning such a field of movement to the group (s) of interface nodes using the operator CREA_CHAMP, for example, it is possible to easily simulate rigid body modes of structures. This operand is to be used if one wants to estimate the terms of the added and coupling matrices for a plane geometry without first performing a modal calculation of the structure in a vacuum, and if one wants to assign these terms in discrete elements (modeling DIS_T). The INFO operand must be active to visualize the calculated terms.
Attention:
The use of this operand **excludes the use of the operand* NUME_DDL_GENE. Therefore, one cannot do a modal, transitory or harmonic calculation using the operand CHAM_NO.
In fact, to calculate water modes, it is necessary to have a generalized mass matrix and a generalized structure stiffness matrix. This presupposes having done a modal calculation on the structure in a vacuum (which is precisely what we want to avoid) .
This operand is ultimately only used to **evaluate the matrix of added mass, stiffness, and damping, and use them to couple beam-like structures by discrete mass elements, for example.*
/MODELE_GENE = modgen
Generalized model built by operator DEFI_MODELE_GENE [U4.65.02]. This keyword is to be used when doing a calculation by dynamic substructuring, and when one wants to calculate the added mass matrix coupling all the substructures. In this case, the substructures may be in different mesh files, and these files may themselves be distinct from the fluid mesh file. Substructures that are repeatable within the fluid need only be meshed once, but care will be taken at the level of the fluid mesh to mesh all the fluid/structure interfaces. In addition, care must be taken to ensure that the fluid interface nodes best coincide with the structure interface nodes, in order to be able to copy, on the basis of a geometric proximity criterion, the values of the structure displacement fields onto the fluid interface nodes (see operand DIST_REFE).
3.9. Operands MATR_MASS_AJOU/MATR_AMOR_AJOU/MATR_RIGI_AJOU#
These keywords specify the user name for the mass, stiffness or added damping matrices that you want to calculate. At least one of these keywords is required to perform the calculation. The 3 keywords can be used simultaneously, but in the case of using MATR_AMOR_AJOU or MATR_RIGI_AJOU, you must enter the keywords ECOULEMENT and DDL_IMPO with PRES_SORTIE.
3.10. Operand DIST_REFE#
Reference distance to be entered when calculating added mass on a generalized model. This distance is an absolute geometric proximity criterion intended to copy values of structural displacements in a fluid domain, in order to solve the Laplace equation of the unsteady pressure field. By default, it is 10—2.
3.11. Operand NOEUD_DOUBLE#
◊ NOEUD_DOUBLE = 'OUI'
This operand is to be used when calculating added mass from a generalized model that includes a substructure meshed by a wire or surface mesh (i.e. without thickness such as a beam or shell) and surrounded by two fluids. In this case, at the level of the mesh, it is necessary to split the nodes of the fluid interfaces from those of the structure, in order to be able to calculate the hydrodynamic pressure jump on both sides of the structure (cf. figure below).
3.12. Operand AVEC_MODE_STAT#
◊ AVEC_MODE_STAT = 'NON'
This operand makes it possible to unplug the calculation of the terms of mass added to the static modes contained in the modal base of the substructures in the case of a calculation with a generalized model (cf. [§3.8]).
3.13. Operand NUME_DDL_GENE#
◊ NUME_DDL_GENE = number
Generalized numbering based on the mechanical modes of the overall structure. The presence of this operand makes it possible to calculate an added mass matrix of the Matr_asse_Gene_R type. It must necessarily be present if one subsequently wants to perform modal, harmonic or transitory calculations.
3.14. Description of the seismic drive movement#
3.14.1. Operand MONO_APPUI#
♦/MONO_APPUI = 'OUI'
The structure is excited uniformly at all supports (solid body training movement).
3.14.2. Multi-support excitation: operand MODE_STAT#
In this case, the accelerations undergone by all the anchor points of the structure under study are not necessarily identical and in phase.
/♦ MODE_STAT = fashion
Static modes of the structure: mode_meca concept produced by the operator MODE_STATIQUE [U4.52.14] with the option DDL_IMPO. They correspond to the 3 or 6 * nb_supports static modes where nb_supports is the number of different accelerograms undergone by the structure.
Note:
If the structure is only requested by translations, then there are 3 nb_supports static modes.
3.15. Added forces due to the seismic drive movement: keyword FORC_AJOU#
3.15.1. Operand GROUP_NO#
♦ GROUP_NO = g_bow
Groups of nodes (g_noeu) of the structure subjected to seismic excitation: these nodes support the ddls of the supports of the structure to which the imposed movements are applied.
3.15.2. Operand DIRECTION#
♦ DIRECTION = (d1, D2, D3, D3, R1, R2, R3)
Components of a vector giving the direction of the training earthquake in the global coordinate system. It is a list of three reals if the accelerograms imposed are only translations. If we also impose rotational accelerations, we expect a list of six real numbers (valid for models with discrete elements).
3.15.3. Operand VECTEUR#
♦ VECTEUR = vector [vect_asse_gene]
Name of the added force vector created by launching the CALC_FORC_AJOU [:ref:`U4.66.03 <U4.66.03>`] operator. There were as many vectors created as there were occurrences of the FORC_AJOU keyword.
3.16. Keyword SOLVEUR#
Keyword factor specifying the technique for solving a linear system appearing here in the calculation of unsteady pressure fields. See [U4.50.01].
3.17. Operand INFO#
◊ INFO =
Indicates the level of printing of operator results,
1: |
no impression, |
2: |
impression of the upper triangular part of the matrices with added mass, added damping or stiffness. |
Column layout.