MXPAND, NMODE, FREQB, FREQE, Elcalc, SIGNIF, MSUPkey, ModeSelMethod
Specifies the number of modes to expand and write for
a modal or buckling analysis.
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 FREQB and FREQE are 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 SIGNIF threshold (only applicable when ModeSelMethod is defined).
If ModeSelMethod = MODC, the significance level of a mode
is defined as the mode coefficient of the mode, divided by the maximum
mode coefficient of all modes.
If ModeSelMethod = MODM, 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 SIGNIF is considered insignificant and is not expanded.
The higher the SIGNIF threshold, the fewer
the number of modes expanded. SIGNIF defaults
to 0.001, except for the case of DDAM mode selection method where
it defaults to 0.01. If SIGNIF is 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,
transient, or harmonic analysis (default if |
ModeSelMethodMethods for mode selection (not supported for complex eigensolvers):
blank | — | No mode selection is performed (default). |
MODM | — | 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 Procedure in the Mechanical APDL Structural Analysis Guide for more information). |
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.
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 PSD
analyses. This significantly reduces computation time for the combination
or expansion passes. For limitations, see Option: Number of Modes to Expand (MXPAND) in the Mechanical APDL Structural Analysis Guide.
If a mode selection method (ModeSelMethod) is defined, only the selected modes will be expanded. See Using Mode Selection in the Mechanical APDL 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 MSUP or PSD analysis can only reuse the nonlinear information
contained in the Jobname.MODE file that is generated
in the linear perturbation.
In a Distributed ANSYS analysis, you must issue MXPAND to specify the number of modes to expand when computing the modes and mode shapes. In a Distributed ANSYS run, MXPAND cannot be issued in an expansion pass (EXPASS).
This command is also valid in PREP7.