3. Operands#

The classical post-processing of a seismic analysis in transient dynamics consists in carrying out the following calculations:

  • The floor spectrum obtained from the absolute accelerations, for direction \(Z\), calculated at a specified node of the mesh (for example in the case of a « skewer » model);

Three*Code_Aster operators can produce result concepts corresponding to transient dynamic calculations:

  • DYNA_TRAN_MODAL [U4.53.21] produces a resu_gene concept, including acceleration and relative displacement fields. In this case, ground accelerations must be added to obtain the absolute accelerations, necessary for calculating the floor spectrum.

  • CALC_MISS [U7.03.12] produces a dyna_trans concept, including acceleration and absolute displacement fields. In this case, the accelerations are directly used to calculate the floor spectrum; conversely, the deduction of ground displacements is mandatory (to be read with the command LIRE_FONCTION [U4.32.02] from a specific file given by its logical unit) to obtain the relative displacements.

  • DYNA_NON_LINE [U4.53.01]. The treatment is then the same as for the previous point.

Here is a basic diagram of the algorithm for calculating this macro command:

Loop #1sur the floors

  • Retrieving the properties of the support and equipment

Loop #2 on the floor knots

• Retrieving acceleration functions relating to nodes: RECU_FONCTION

• If relative calculation

Combination or not with the ground acceleration function: * CALC_FONCTION/COMB

• Calculating the transfer function

• Calculation of the response spectrum, with specified values of frequencies and * of damping with CALC_FONCTION/SPEC_OSCI

• Printing the acceleration spectrum for each node : IMPR_FONCTION

End of loop #2

End of loop #1

The floor-mass interaction is taken into account by transforming the acceleration measured at the N node by a transfer function. This transfer function converts the response from model A to model B, as shown in the figure below. The R4.07.05 documentation provides more complete explanations of the method and assumptions.

_images/10000200000002F300000118B3E887521B497B0D.png

3.1. Keyword MAILLAGE#

This keyword corresponds to the mesh read by the operator LIRE_MAILLAGE [U4.21.01].

This keyword is optional. Knowledge of the mesh is necessary only in the case where the user uses the simple keyword GROUP_NO of the factor keyword PLANCHER. In fact, as described in the previous algorithm, the processing is carried out on the nodes and if the user directly gives the name of the nodes present in the table, the mesh is not necessary.

3.2. Keyword PLANCHER#

This keyword is mandatory to define the names of the floors, where the spectra will be calculated. These names will be used to select or filter display parameters in the table structure produced by the table_sdaster macro command.

3.2.1. Operand NOM#

This mandatory operand allows you to name the floor in question.

3.2.2. Operands NOEUD/GROUP_NO#

These operands make it possible to define the nodes (individually or by groups) composing the floor where the spectra will be calculated. It is possible to enter GROUP_NOsi the mesh has been filled in.

3.2.3. Keyword RAP_MASS#

This is the ratio of the masses of the equipment to the mass of the floor \(\mathrm{\lambda }=\frac{{m}_{2}}{{m}_{1}}\). It is between 0 and 1.

3.2.4. Keyword RAP_MASS_COEFF#

This is the list of the ratios of the individual masses \({\alpha }_{i}\) of each piece of equipment to the total mass of the \({m}_{i}\mathrm{=}{\alpha }_{i}{m}_{2}\) equipment. The sum of the coefficients must be equal to 1.

3.2.5. Keyword FREQ_SUPP#

This keyword defines the frequency of support \({f}_{1}\) of model A.

3.2.6. Keyword FREQ_EQUI#

This keyword defines the list of equipment frequencies. \({f}_{i}\).

3.2.7. Keyword AMOR_SUPP#

This keyword defines the amortization of support \({\xi }_{1}\).

3.2.8. Keyword AMOR_EQUI#

This keyword defines the list of depreciation of equipment \({\xi }_{i}\).

3.3. Keyword CALCUL#

This mandatory keyword allows you to define the nature of the dynamic transient calculation used for post-processing: in the absolute coordinate system (“ABSOLU”) or the relative coordinate system (“RELATIF”).

3.4. Operand AMOR_SPEC#

This mandatory operand makes it possible to define the values of the reduced damping coefficient used in calculating the spectral response. See also CALC_FONCTION [U4.32.04], keyword SPEC_OSCI.

3.5. Operand LIST_INST#

This optional operand allows you to specify the list, produced by DEFI_LIST_REEL [U4.34.01], defining all the time steps for calculating transient dynamics.

3.6. Operand FREQ/LIST_FREQ#

/◊ FREQ = L_FR

/◊ LIST_FREQ = LFREQ

List of frequencies previously defined by a listr8 concept.

This optional operand allows you to define frequency values, see also CALC_FONCTION [U4.32.04], keyword SPEC_OSCI.

3.7. Operand NORME#

♦ NORME = r

The response spectrum will be normalized by the value \(r\) (pseudo-acceleration value). The calculations are done in most cases in International System Units (USI) and the acceleration histories are often given in \(m\mathrm{/}{s}^{2}\) units. Response spectra are generally given with \(g\mathrm{=}\mathrm{9.81m}\mathrm{/}{s}^{2}\).

Thus, this mandatory operand NORME can be used as a unit conversion factor between the calculated accelerations and the response spectrum, see also CALC_FONCTION [U4.32.04], keyword SPEC_OSCI.

3.8. Keyword RESU#

This mandatory keyword allows you to specify the input data where the nodal accelerations are extracted.

♦/”TABLE” = TAB [TABLE_SDASTER]

/”FONCTION” = FCT [FONCTION_SDASTER]

The post-processing is carried out from a table or a function containing the results to be read. Typically, a table or an observation function deduced from a transient dynamics calculation.

The table provided has two possible formats:

  • Or it has (at least) columns INST, NOEUD,, NOM_CHAM, NOM_CMP and VALE. In this case, only rows that have both the value ACCE in column NOM_CHAM and the DZ value in the column NOM_CMP are taken into account. The calculation stops if there are no such rows in the table.

  • Or it has (at least) columns INST, NOEUD, NOM_CHAM and DZ. In this case, only rows with the value ACCE in column NOM_CHAM are taken into account. The calculation stops if there are no such rows in the table.

3.8.1. Keyword ACCE_Z#

♦ ACCE_Z =/AC_Z [FONCTION]

In this case CALCUL =” RELATIF “, the user must provide the ground acceleration function, defined on the same list of times, in each direction of space, in order to combine them with the relative accelerations to calculate the absolute accelerations.

3.9. Operand TOLE_INIT#

◊ TOLE_INIT = 1e-3

This optional operand allows you to specify a limit criterion for the initial value of the initial accelerations of the signals. It is verified that the ratio between the initial value of the signal and the maximum of the signal is less than the defined tolerance.

3.10. Operand CORR_INIT#

◊ CORR_INIT =/”NON” [DEFAUT]

/”OUI”

This optional operand makes it possible to correct the initial value of the signal if it is greater than the given tolerance.