Specifies the number of modes to expand and write for a modal or buckling analysis.

Compatible Products: DesSpc | Pro | Premium | Enterprise | Ent PP | Ent Solver | –


Number 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.


Beginning, 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.


Ending, or upper end, of frequency range of interest.


Element calculation key:



Do not calculate element results, reaction forces, and energies (default).



Calculate element results, reaction forces, energies, and the nodal degree of freedom solution.


Expand 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.


Element result superposition key:



Do not write element results to the mode file Jobname.MODE.



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 Elcalc = YES and the mode shapes are normalized to the mass matrix).


Methods for mode selection (not supported for complex eigensolvers):



No mode selection is performed (default).



The mode selection is based on the modal effective masses.



The mode selection is based on the mode coefficients.



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).

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.


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.

Menu Paths

Main Menu>Preprocessor>Loads>Analysis Type>Analysis Options
Main Menu>Preprocessor>Loads>Load Step Opts>ExpansionPass>Single Expand>Expand Modes
Main Menu>Solution>Analysis Type>Analysis Options
Main Menu>Solution>Load Step Opts>ExpansionPass>Single Expand>Expand Modes

Release 18.2 - © ANSYS, Inc. All rights reserved.