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Modal Cyclic Symmetry Analysis
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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.
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
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.
Input File for the Analysis
! Modal Cyclic Symmetry Analysis Example
! Ring-Strut-Ring Configuration
! STEP #1
! Start an ANSYS 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"
set,2,5
! STEP #16
! Plot the tangential displacement contour
plns,u,y
Analysis Steps
The following table describes the input listing and the steps involved in the example modal cyclic symmetry analysis in more detail.
Step
Description
ANSYS Command
1.
Start an ANSYS interactive session.
---
2.
Read the input file: cyc_symm.inp
/INPUT,CYC_SYMM.INP
3.
Specify a cyclic symmetry analysis and configure the database accordingly.
CYCLIC
4.
Mesh the areas.
AMESH,ALL
5.
Activate cyclic symmetry graphical expansion.
/CYCEXPAND,,ON
6.
Plot the elements.
EPLOT
7.
List the cyclic status.
CYCLIC,STATUS
8.
List the cyclic solution option settings.
CYCOPT,STATUS
9.
Solve the modal cyclic symmetry analysis.
/SOLU
SOLVE
10.
Specify the global cylindrical coordinate system.
/POST1
RSYS,1
11.
Read results for “load step 1 - substep 4 - harmonic index 0.”
SET,2,6
12.
Plot the tangential displacement contour.
Executing this step causes the struts of the assembly to bend “in phase.”
PLNSOL,U,Y
13.
Read results for “load step 13 - substep 1 - harmonic index 12.”
SET,13,1
14.
Plot the tangential displacement contour.
Executing this step causes the struts of the assembly to bend “out of phase.”
PLNSOL,U,Y
15.
Read results for “load step 2 - substep 5 - harmonic index 1.”
SET,2,5
16.
Plot the tangential displacement contour.
----
This step completes the example modal cyclic symmetry analysis. Your results should match those shown in Figure 5.19.
PLNSOL,U,Y
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