MXPAND
MXPAND,
NMODE, FREQB,
FREQE, Elcalc,
SIGNIF, MSUPkey,
ModeSelMethod,
EngCalc
Specifies modal or buckling analysis expansion
options.
NMODENumber of modes or array name (enclosed in percent signs) to expand and write. If blank or ALL, expand and write all modes within the frequency range specified. If -1, do not expand and do not write modes to the results file during the analysis. If an array name is input, the array must contain 1 for the expanded modes and zero otherwise, where the array index corresponds to the mode number. To specify an array containing the individual modes to expand, enclose the array name in percent (%) signs (for example, MXPAND,%arrname%). Use the *DIM command to define the array.
FREQBBeginning, or lower end, of frequency range of interest. If
FREQBandFREQEare both blank, expand and write the number of modes specified without regard to the frequency range. Defaults to the entire range.FREQEEnding, or upper end, of frequency range of interest.
ElcalcElement calculation key:
NO
—
Do not calculate element results, reaction forces, and energies (default).
YES
—
Calculate element results, reaction forces, energies, and the nodal degree of freedom solution.
SIGNIFExpand only those modes whose significance level exceeds the
SIGNIFthreshold (only applicable whenModeSelMethodis defined).If
ModeSelMethod= MODC, the significance level of a mode is defined as the mode coefficient divided by the maximum mode coefficient of all modes.If
ModeSelMethod= EFFM, the significance level of a mode is defined as the modal effective mass, divided by the total mass.If
ModeSelMethod= DDAM, the significance level of a mode is defined as the modal effective weight, divided by the total weight.Any mode whose significance level is less than
SIGNIFis considered insignificant and is not expanded. The higher theSIGNIFthreshold, the fewer the number of modes expanded.SIGNIFdefaults to 0.001, except for the case of DDAM mode selection method where it defaults to 0.01. IfSIGNIFis specified as 0.0, it is taken as 0.0.MSUPkeyElement result superposition key:
NO
—
Do not write element results to the mode file Jobname.mode.
YES
—
Write element result to the mode file for use in the expansion pass of a subsequent mode-superposition PSD, spectrum, transient, or harmonic analysis. This value is the default if all of the following conditions exist:
Elcalc= YES.The mode shapes are normalized to the mass matrix.
FREQBandFREQEare blank or 0.0.No superelement is defined.
ModeSelMethodMethods for mode selection (not supported for complex eigensolvers):
blank
—
No mode selection is performed (default).
EFFM
—
The mode selection is based on the modal effective masses.
MODC
—
The mode selection is based on the mode coefficients.
DDAM
—
The mode selection is based on DDAM procedure (see Mode Selection Based on the DDAM Method in the Structural Analysis Guide for more information).
EngCalcAdditional element energies calculation key:
NO
—
Do not calculate additional energies (default).
YES
—
Calculate average, amplitude, and peak values for the following: stiffness and kinetic energies, and damping energy.
Command Default
Mode shapes (displacements) are expanded and output to the results file (so that if you need to inspect the mode shapes, it is not necessary to run the analysis again). Element stresses are not expanded.
Notes
Specifies the number of modes to expand and write over a frequency range for a modal (ANTYPE,MODAL) or buckling (ANTYPE,BUCKLE) analysis. If used in SOLUTION, this command is valid only within the first load step.
There is no limit on the number of expanded modes (NMODE). However, there is a limit on the maximum number of modes used via the *GET,,MODE command, mode combinations, and the MDAMP command.
With MSUPkey = YES, the computed element results
(Elcalc = YES) are written to
Jobname.mode for use in subsequent downstream
mode-superposition analyses, including harmonic, transient, and all spectrum analyses. This significantly
reduces computation time for the combination or expansion passes. For
limitations and available elemental results, see Option: Number of Modes to Expand (MXPAND) in the Structural Analysis Guide.
The calculation of additional energies (EngCalc = YES)
is valid only for Method = DAMP on the
MODOPT command and Method = QRDAMP
with Cpxmod = CPLX on the MODOPT
command. The average, amplitude, and peak potential energies for complex results
(see Potential Energy (or Stiffness Energy) for Complex Results) calculated for a linear
perturbation full harmonic analysis with a nonlinear base analysis are approximate
solutions and may not be accurate.
If a mode selection method (ModeSelMethod) is defined, only the selected modes will be expanded. See Using Mode Selection in the Structural Analysis Guide for more details about the procedure.
For array input (NMODE), the array
must be dimensioned to be the size of the number of modes extracted
(NMODE on the MODOPT command). A value of 1 in the array indicates the mode is to be
expanded, and a value of 0 indicates not to expand the mode. For the
DAMP modal solution, the modes are in pairs, so be sure to verify
that both modes of a pair have the same value. (For example, if modes
#3 and #4 are a pair, indices 3 and 4 in the array should have the
same value, 0 or 1.)
For linear perturbation modal
analyses, you must set both Elcalc and
MSUPkey to YES so that the downstream stress
expansion pass can produce a solution consistent with the linear or nonlinear base
(static or full transient) analysis. The prestressed nonlinear element history
(saved variables) is accessible only in the first and second phases of the linear
perturbation. The downstream mode superposition
analysis (such as MSUP or PSD) can only reuse the nonlinear
information contained in the Jobname.mode file that is
generated in the linear perturbation.
In a distributed-memory parallel (DMP) analysis, you must issue MXPAND to specify the number of modes to expand when computing the modes and mode shapes. In a DMP run, MXPAND cannot be issued in an expansion pass (EXPASS).
This command is also valid in PREP7.