PLCAMP, Option, SLOPE, UNIT, FREQB, Cname, STABVAL, KeyAllFreq, KeyNegFreq
Plots Campbell diagram data for applications involving rotating structure dynamics.

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Flag to activate or deactivate sorting of forward or backward whirl frequencies:

0 (OFF or NO)


No sorting.

1 (ON or YES)


Sort. This value is the default.


The slope of the line to be printed. This value must be positive.



The line represents the number of excitations per revolution of the rotor. For example, SLOPE = 1 represents one excitation per revolution, usually resulting from unbalance.



The line represents the stability threshold for stability values or logarithmic decrements printout (STABVAL = 1, 2, or 3)


Specifies the unit of measurement for rotational angular velocities:



Rotational angular velocities in radians per second (rad/s). This value is the default.



Rotational angular velocities in revolutions per minute (RPMs).


The beginning, or lower end, of the frequency range of interest. The default is zero.


The rotating component name.


Flag to plot the stability values:

0 (OFF or NO)


Plot the frequencies (the imaginary parts of the eigenvalues in Hz). This value is the default.

1 (ON or YES)


Plot the stability values (the real parts of the eigenvalues in Hz).



Plot the inverse of the logarithmic decrements. A negative logarithmic decrement indicates stable motion.



Plot the logarithmic decrements. A positive logarithmic decrement indicates stable motion and is consistent with API (American Petroleum Institute) standards.

For more information about complex eigenmodes and corresponding logarithmic decrements, see Complex Eigensolutions in the Mechanical APDL Theory Reference.


Key to specify if all frequencies above FREQB are plotted:

0 (OFF or NO)


A maximum of 10 frequencies are plotted. This value is the default.

1 (ON or YES)


All frequencies are plotted.


Key to specify if the negative frequencies are plotted. It only applies to solutions obtained with the damped eigensolver (Method = DAMP on the MODOPT command):

0 (OFF or NO)


Only positive frequencies are plotted. This value is the default.

1 (ON or YES)


Negative and positive frequencies are plotted.


The following items are required when generating a Campbell diagram:

  • Take the gyroscopic effect into account by issuing the CORIOLIS command in the SOLUTION module.

  • Run a modal analysis using the QR damped (MODOPT,QRDAMP) or damped (MODOPT,DAMP) method. Complex eigenmodes are necessary (MODOPT,QRDAMP,,,,Cpxmod = ON), and you must specify the number of modes to expand (MXPAND).

  • Define two or more load step results with an ascending order of rotational velocity (OMEGA or CMOMEGA).

In some cases where modes are not in the same order from one load step to the other, sorting the frequencies (Option = 1) can help to obtain a correct plot. Sorting is based on the comparison between complex mode shapes calculated at two successive load steps.

At each load step, the application compares the mode shape to the loads at other load steps to determine whirl direction at the load step. If applicable, a label appears (in the plot legend) representing each whirl mode (BW for backward whirl and FW for forward whirl).

At each load step, the program checks for instability (based on the sign of the real part of the eigenvalue). The labels “stable” or “unstable” appear in the plot legend for each frequency curve.

The rotational velocities of a named component (Cname) are displayed on the X-axis.

For information on plotting a Campbell diagram for a prestressed structure, see Solving for a Subsequent Campbell Analysis of a Prestressed Structure Using the Linear Perturbation Procedure in the Rotordynamic Analysis Guide.

In general, plotting a Campbell diagram is recommended only when your analysis is performed in a stationary reference frame (CORIOLIS,,,,RefFrame = ON).

For a usage example of the PLCAMP command, see Campbell Diagram in the Rotordynamic Analysis Guide.

Distributed ANSYS Restriction This command is not supported in Distributed ANSYS.

Menu Paths

Main Menu>General Postproc>Rotor Dynamics>Plot Campbell

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