3. Operands#

3.1. Operand SPEC_TURB#

♦ SPEC_TURB = l_spec

List of spectrum-type concepts produced by operator DEFI_SPEC_TURB [U4.44.31] defining several turbulent excitation spectra.

Notes:

  1. The operand SPEC_TURB allows several turbulent excitation spectra to be taken into account. The generalized excitation interspectra are calculated for each of the physical spectra provided and then added up.

  2. Turbulence spectra of the « correlation length » type only apply to steam generator tubes. It is possible to project several turbulence spectra of the « correlation length » type simultaneously, but the excitation zones of each spectrum must be strictly disjunct from one another. The areas to which these excitations apply are defined for each spectrum, with the command DEFI_SPEC_TURB [U4.44.31].

  3. Turbulence spectra of the « correlation length » type cannot be combined with spectra of another type.

  4. In the case of a spectrum SPEC_CORR_CONV_3 , double projection is very resource intensive, because it is necessary to loop over the directions, the meshes, their gauss points and the modes (double loop), and each time evaluate the analytical function that defined the spectrum. It is recommended to use this type of spectrum on reduced meshes (less than 1000 degrees of freedom), starting with a small number of frequency discretization points to evaluate the calculation time.

3.2. Operand BASE_ELAS_FLUI#

The operand BASE_ELAS_FLUI is used when it is desired to project a spectrum defined by one of the key factors SPEC_LONG_COR_n, SPEC_FONC_FORME or SPEC_EXCI_POINT of the DEFI_SPEC_TURB [U4.44.31] operator. In this case, the speed of the vital fluid must be entered.

♦/BASE_ELAS_FLUI = baseball

Melasflu-like concept produced by the operator CALC_FLUI_STRU [U4.66.02], which defines one or a set of modal bases onto which or (which) the spectra are projected, as well as speed discretization.

The operator calculates a matrix of generalized excitation interspectra \({S}_{\mathrm{fifj}}^{k}(\omega )\) corresponding to the speed of the vital fluid that must be entered.

The melasflu concept also provides the name of the type_flui_stru concept produced at the start of the study by the DEFI_FLUI_STRU [U4.25.01] command. The type_flui_stru concept contains all the information characteristic of the configuration studied: among other things, it contains the data necessary for the dimensionalization of the projected excitation.

3.3. Keyword VITE_FLUI#

The VITE_FLUI operand must be entered if a melasflu base is used.

♦ VITE_FLUI = vitefl

Fluid flow speed for response calculation.

3.4. Keyword PRECISION#

◊ PRECISION = prec

Precision on the flow speed of the fluid (by default 1.E-3).

3.5. Operands MODE_MECA or CHAM_NO#

The operands MODE_MECA or CHAM_NO are used when it is desired to project a pressure spectrum defined by one of the key factors SPEC_CORR_CONV_n of the operator DEFI_SPEC_TURB [U4.44.31].

/MODE_MECA = basemeca

A mode_meca-like concept produced by the operator CALC_MODES [U4.52.02], which defines the modal basis on which spectra are projected. This modal base was possibly calculated taking into account a fluid added mass effect, using the CALC_MATR_AJOU [U4.66.01] or MACRO_MATR_AJOU [U4.66.11] operator.

/CHAM_NO = l_cham

List of concepts such as cham_no_depl_r, which define the deformations of the modal base on which the spectra are projected.

This way of defining the modal base makes it possible to impose a particular type of movement on the structure; a similar approach is adopted in the operator CALC_MATR_AJOU [U4.66.01], where the operand CHAM_NO also appears.

Note:

The operator determines the mutual acceptance matrix linking the pressure spectrum to the interspectral matrix of generalized excitations acting on the structure: \({S}_{\mathit{fifj}}(\omega )={S}_{p}(\omega )\times {J}_{\mathit{Aij}}(\omega )\) where *:math:`{S}_{p}(omega )`*is the pressure power spectral density, * *:math:`{J}_{mathit{Aij}}(omega )`*is the mutual acceptance matrix, * *:math:`{S}_{mathit{fifj}}(omega )`*is the matrix of generalized excitation interspectra. *

Note:

  • In the case where the modal base is defined by a list of fields at the nodes (keyword CHAM_NO ), it is imperative to fill in the mechanical model associated with the elements on which the spectrum projection must be applied (by the keyword * MODELE_INTERFACE ) .

  • If a modal base of type mode_meca is given and if the structure is modelled in thin shells of type DKT * , it is not mandatory to fill in the keyword * MODELE_INTERFACE * .

Theoretical details are given in internal report HP-51/97/027/B.

3.6. Operand MODELE_INTERFACE#

The operand MODELE_INTERFACE is used when it is desired to project a pressure spectrum defined by one of the key factors SPEC_CORR_CONV_n of the operator DEFI_SPEC_TURB [U4.44.31].

◊ MODELE_INTERFACE = model

Model type concept produced by the operator AFFE_MODELE [U4.41.01], defining:

  1. Let’s say the (thermal) interface model between the structure and the fluid used previously for the calculation of the matrices added by CALC_MATR_AJOU [U4.66.01] or MACRO_MATR_AJOU [U4.66.11].

  2. Consider the mechanical model of the structure if it is modeled by thin shell elements (DKT).

Note:

In the case where a thermal interface model is defined, the calculation of the acceptance coefficients is carried out using this model, which characterizes the wet surface of the structure, assuming homogeneous turbulence over the entire fluid-structure interface.

In the case where the given model is mechanical, the acceptance coefficients can be calculated on the structure, provided that it is modeled in thin shells of type DKT.

If the keyword MODELE_INTERFACE is not entered, the mechanical model used is the one associated with the stiffness matrix, referenced in the modal projection base.

Note:

In the case where the spectrum has been defined analytically with the option SPEC_CORR_CONV_3, the interface model must be filled in, because the projection is done using the shape functions carried by the elements of the model.

3.7. Operand GROUP_MA/TOUT#

The operand GROUP_MA is used when it is desired to project a pressure spectrum defined by one of the key factors SPEC_CORR_CONV_n of the operator DEFI_SPEC_TURB [U4.44.31].

♦ GROUP_MA/TOUT

List of groups of cells or the whole mesh, on which the projection will be carried out. The groups of cells must be part of the mesh associated with the model (thermal or mechanical) used to calculate the acceptance coefficients.

3.8. Operand VECT_X#

The operand VECT_X is used when it is desired to project a pressure spectrum defined by one of the key factors SPEC_CORR_CONV_n of the operator DEFI_SPEC_TURB [U4.44.31], in the case where the correlations of CORCOS or AU_YANG are used.

◊ VECT_X = l_cmpx

List of three components of a unit vector \(x\) defining:

  • the direction of flow on the surface of the plane structure, in the case of a correlation of CORCOS,

  • the direction of the axis of revolution of the cylindrical structure with a circular cross section, in the case of a correlation of AU_YANG.

(see diagrams below)

3.9. Operand VECT_Y#

The operand VECT_Y is used when it is desired to project a pressure spectrum defined by one of the key factors SPEC_CORR_CONV_n of the operator DEFI_SPEC_TURB [U4.44.31], in the case where the correlation of CORCOS is used.

◊ VECT_Y = l_cmpy

List of the three components of a unit vector \(y\) defining the direction orthogonal to the direction of flow on the surface of the plane structure (see diagrams below).

3.10. Operand ORIG_AXE#

The operand ORIG_AXE is used when it is desired to project a pressure spectrum defined by one of the key factors SPEC_CORR_CONV_n of the operator DEFI_SPEC_TURB [U4.44.31], in the case where the correlation of AU_YANG is used.

◊ ORIG_AXE = l_coor

List of the three coordinates defining the position of an origin \(O\) on the axis of revolution of the circular cylindrical structure (see diagrams below).

_images/10001F2A0000211300002113E6A204DFA2CDF5AA.svg

3.11. Operands FREQ_INIT, FREQ_FIN, and NB_POIN#

♦ FREQ_FIN = ff ♦ NB_POIN = no

These operands define the frequency band and the number of frequency discretization points of the interspectra to be calculated. The number of discretization points must be equal to a power of 2, in order to allow post-treatments of the FFT type (Fast Fourier Transform). It is recommended that these three items be calculated using the following method.

If \(({f}_{1}^{k},\mathrm{...},{f}_{N}^{k})\) designate the frequencies of the modes of the \(k\) th base of the structure then:

\(\text{FREQ\_INIT}=\underset{k}{\mathrm{min}}(\frac{{f}_{1}^{k}}{2})\) \(\text{FREQ\_FIN}\mathrm{=}\underset{k}{\mathit{max}}({f}_{N}^{k}+\frac{{f}_{1}^{k}}{2})\)

The number of discretization points can then be deduced from the minimum frequency step defined by:

\(\mathit{df}\mathrm{=}\underset{i,k}{\mathit{min}}(2\mathrm{\times }\pi \mathrm{\times }{\mu }_{i}^{k}\mathrm{\times }{f}_{i}^{k})\)

where \({\mu }_{i}^{k}\) refers to the reduced damping of the \(i\) th mode of the \(k\) th modal base.

3.12. Operand TOUT_CMP#

◊ TOUT_CMP = 'OUI' or 'NON'

Indicator of the components of the modal deformations that are adopted to calculate the excitation interspectra on a modal basis:

  • “OUI”

we use the three components in translation,

  • “NON”

we only use the translational component that was previously defined using the DEFI_FLUI_STRU operator.

3.13. Operand OPTION#

◊ OPTION = 'TOUT' or 'DIAG'

Indicator of the choice of calculation to be carried out:

  • “TOUT”

if you want to calculate all the generalized excitation interspectra (option by default),

  • “DIAG”

if you only want to calculate generalized excitation autospectra.

3.14. Operand TITRE#

◊ TITRE = title

Text argument defining the title attached to the output interspectrum concept.