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the CYCPHASE,STAT command to determine the value of ϕ at which maximum equivalent stress occurred. You can shift the mode shape to that angle via the /CYCEXPAND,,PHASEANG command and plot the expanded mode shape via the PLNSOL,S,EQV command.

Note

The CYCPHASE command uses full model graphics (/GRAPHICS,FULL) to compute peak values. Because of this, there may be slight differences between max/min values obtained with CYCPHASE, and those obtained via /CYCEXPAND (/GRAPHICS,POWER).

7.4.3. Static, Buckling, and Full Harmonic Solutions

If cyclic expansion via the /CYCEXPAND command is active, the PLNSOL and PRNSOL commands have summation of all required harmonic index solutions by default. (You can override the default behavior if necessary.)

In a static or harmonic cyclic symmetry analysis with non-cyclic loading, all applicable harmonic index solutions are computed and saved in the results file as load step results.

A SET,LIST command lists the range of load step numbers in the group containing each solution. Each load step post data header contains the first, last, and count of load steps from the given SOLVE command, as shown:

*****INDEX OF DATA SETS ON RESULTS FILE *****

The SET command establishes which SOLVE load step group should display. Summation via /CYCEXPAND is automatic (although you can override the default behavior). Plots and printed output show the summation status.

With /CYCEXPAND turned on, the results are expanded at each load step and then combined to plot the full solution as a complete sum. For example, in a four sector model where harmonic index results

0 through 2 are available in the results file, the plot command PLNSOL will display the results as STEP=1 THRU=3 COMPLETE SUM.

Accumulation occurs at the first applicable PLNSOL or PRNSOL command. After accumulation, the last load step number of the current group becomes the new current load step number.

7.4.4. Mode-Superposition Harmonic Solution

The postprocessing is described in Review the Results (p. 190) in the Solving a Mode-Superposition Harmonic Cyclic Symmetry Analysis (p. 186) section.

7.5. Example Modal Cyclic Symmetry Analysis

This example modal cyclic symmetry analysis presents a simplified ring-strut-ring structure used in many rotating-machinery applications.

7.5.1. Problem Description

7.5.2.Problem Specifications

7.5.3.Input File for the Analysis

7.5.4.Analysis Steps

7.5.1. Problem Description

The component is a simplified fan inlet case for a military aircraft engine. As part of the design process for the assembly, you must determine the vibration characteristics (natural frequencies and mode shapes) of the inlet case.

7.5.2. Problem Specifications

The geometric properties for this analysis are as follows:

The material properties for this analysis are as follows:

Young's modulus (E) = 10e6

Poisson's ratio (υ) = 0.3

Density = 1e-4

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All applicable degrees of freedom are used for the cyclic symmetry edge-component pairs. The first six mode shapes for all applicable harmonic indices are requested.

7.5.3. Input File for the Analysis

Use this input file (named cyc_symm.inp) to perform the example modal cyclic symmetry analysis. The file contains the complete geometry, material properties and solution options for the finite element model.

!Modal Cyclic Symmetry Analysis Example

!Ring-Strut-Ring Configuration

!STEP #1

!Start an interactive session

!STEP #2

!Read in this input file: cyc_symm.inp

finish /clear

r1=5

r2=10

d1=2

nsect=24 alpha_deg=360/nsect alpha_rad=2*acos(-1)/nsect

/view,1,1,1,2

/plopts,minm,0

/plopts,date,0

/pnum,real,1

/number,1

/prep7

csys,1

k,1,0,0,0

k,2,0,0,d1

k,3,r1,0,0

k,4,r1,0,d1

l,3,4 arotat,1,,,,,,1,2,alpha_deg/2 k,7,r2,0,0

k,8,r2,0,d1

l,7,8 arotat,5,,,,,,1,2,alpha_deg/2 arotat,2,,,,,,1,2,alpha_deg/2 arotat,6,,,,,,1,2,alpha_deg/2 a,5,6,10,9

mshkey,1

et,1,181

r,1,0.20

r,2,0.1

mp,ex,1,10e6

mp,prxy,1,0.3 mp,dens,1,1e-4 esize,0.5 asel,,,,1,4 aatt,,1 asel,,,,5 aatt,,2

allsel finish

/solution

antype,modal

modopt,lanb,6

mxpand,6,,,yes

dk,5,uz,0

finish

aplot /prep7

/eof

!STEP #3

!Configure the database for a cyclic symmetry analysis

cyclic

!STEP #4

!Mesh the areas

amesh,all

!STEP #5

!Turn on cyclic symmetry graphical expansion

/cycexpand,,on

!STEP #6

!Plot the elements

eplot

!STEP #7

!List the cyclic status

cyclic,status

!STEP #8

!List the cyclic solution option settings

cycopt,status

!STEP #9

!Solve the modal cyclic symmetry analysis

/solution solve

!STEP #10

!Specify global cylindrical as the results coordinate system

/post1

rsys,1

!STEP #11

!Read results for "load step 1 - substep 4 - harmonic index 0"

set,2,6

!STEP #12

!Plot the tangential displacement contour

plns,u,y

!STEP #13

!Read results for "load step 13 - substep 1 - harmonic index 12"

set,13,1

!STEP #14

!Plot the tangential displacement contour

plns,u,y

!STEP #15

!Read results for "load step 2 - substep 5 - harmonic index 1"