CYCFREQ
CYCFREQ, Option, Value1, Value2, Value3, Value4, Value5
Specifies solution options for a cyclic symmetry mode-superposition
harmonic analysis.
-
Option One of the following options:
AERO
—
Specify the array containing the aerodynamic damping coefficients.
Value1—
The name of the array containing the aerodynamic stiffness damping coefficients.
BLADE
—
Blade information required for a mistuning or aerodamping analysis.
Value1—
The name of the nodal component containing the blade boundary nodes at the blade-to-disk interface. Also include boundary nodes at any shroud interfaces.
Value2—
The name of the element component containing the blade elements.
Value3—
The number of blade modes to include in the CMS reduction.
Value4—
The lower bound of the frequency range of interest. This value is optional.
Value5—
The upper bound of the frequency range of interest. This value is optional.
DEFAULT
—
Set the default cyclic harmonic solution settings.
EO
—
Excitation engine order.
Value1—
An integer value indicating the the excitation order. The loadings on the other sectors will be related to the loading on the base sector based on the engine order phase shift.
Value2—
The name of the Mechanical APDL array containing the modal forces corresponding to the modes kept in the mode-superpostion analysis.
MIST
—
Mistuning parameters.
Value1—
The type of mistuning:
K
—
Stiffness (frequency) mistuning
Value2—
The name of the array containing the stiffness mistuning parameters.
MODAL
—
Specifies if a damped modal analysis should be performed on the reduced system.
Value1—
On/Off key.
0 (OFF or NO)
—
No modal solution. Perform the harmonic solution.
1 (ON or YES)
—
Perform a damped modal analysis of the reduced system in order to obtain the complex frequencies. The harmonic solution is not performed.
Value2—
Number of modes for the damped modal analysis.
Value3—
The beginning, or lower end, of the frequency range of interest (in Hz).
Value4—
The ending, or upper end, of the frequency range of interest (in Hz).
RESTART
—
Defines the point at which to restart the harmonic analysis.
Value1—
The restart point:
OFF
—
No restart (default)
SWEEP
—
Restart for a new frequency sweep range (HARFRQ)
MIST
—
Restart for new mistuning parameters (new mistuning arrays)
USER
—
Causes the program to call for a user-defined solution.
Value1-5—
Values passed down to the user-defined solution.
STATUS
—
List the harmonic solution option settings active for the cyclic model.
Command Default
No defaults are available for the CYCFREQ command. You must specify an Option label
when issuing this command. Other values which may be necessary depend
upon which Option label you specify.
Notes
The program solves a cyclically symmetric model (set up via the CYCLIC command during preprocessing) at the harmonic indices specified via the CYCOPT command.
When Option = AERO, the
aerodynamic coefficients are specified in a 5×(N×r) array (*DIM),
where N is the number of blades and r can be any positive integer. Each column has the
structure:
where:
 = the ith interblade phase angle (IBPA) |
 = the mth vibrating blade mode |
 = the nth blade mode generating the pressure oscillations |
 and  = the real and imaginary coefficients. |
One aerodynamic damping coefficient must be specified for each IBPA (equal to the number of blades) while keeping m and n constant.
The following table shows how the IBPA index () relates to other quantities for a system with 22 blades:
| IBPA Index () | Nodal Diameter | IBPA (degrees) |
|---|---|---|
| 0 | 0 | 0 |
| 1 | 1 | 16.36 |
|
|
|
| 20 | -2 | -32.73 |
| 21 | -1 | -16.36 |
The CYCFREQ,AERO command is only valid if CYCFREQ,BLADE is also specified. The blade mode numbers, m and n, are relative to the values kept in the CYCFREQ,BLADE command.
For constant (frequency-independent) mistuning, the stiffness parameters are specified in an N×1 array (*DIM) where N is the number of blades.
For stiffness mistuning, each row entry
represents the deviation of Young’s modulus from nominal, 
(or equivalently, the ratio of the frequency deviation
squared). Each frequency can also be independently mistuned, in which
case the array is N×M, where M is the number of blade frequencies
(Value3 of CYCFREQ,BLADE).
The entries in each row therefore correspond to the ratio of the mistuned
frequency to the tuned frequency squared minus one:
The USER option activates the solution macro CYCMSUPUSERSOLVE.MAC. The normal solution is skipped. You may implement your own mistuning solution using APDL and APDL Math operations, or call your own program for the solution.
The CYCFREQ command is valid in the preprocessing and solution stages of an analysis.
The CYCFREQ,MODAL,ON command writes modal frequencies to the output file. No other postprocessing is available for this modal solve.
When using CYCFREQ,RESTART, only mistuning parameters or frequency range may be changed. All other changes in parameters are ignored. This type of restart can only be performed by exiting the current mistuning solution using FINISH and re-entering the solution phase using /SOLU and then calling the desired CYCFREQ,RESTART command.
To learn more about analyzing a cyclically symmetric structure, see the Cyclic Symmetry Analysis Guide.
Example Usage
For an example demonstrating how to apply modal loads directly in the cyclic harmonic analysis step of a mode-superposition harmonic cyclic symmetry analysis, see Apply Modal Loads Directly Using an Ordered Array in the Cyclic Symmetry Analysis Guide.