The component is a simplified fan inlet case for a military aircraft engine. As part of the design process for the assembly, the harmonic response characteristics of the inlet case may be investigated, as shown in this example.

The geometric and material properties used for the harmonic cyclic analysis are the same as used in Example Modal Cyclic Symmetry Analysis.

All applicable degrees of freedom are used for the cyclic symmetry edge-component pairs. The harmonic response to a pressure load applied on the assembly is computed.

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

! Harmonic Cyclic Symmetry Analysis Example ! Ring-Strut-Ring Configuration

! STEP #1
! Start an interactive session 

! STEP #2
! Read in this input file: harm_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

dk,5,all,0

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
fini

! STEP #9
! Solve the harmonic cyclic symmetry analysis

/solution
! Specify harmonic analysis option and frequency sweep values 
antype,harmic 
hropt,full
harfrq,860,878
nsub,9

! Apply pressure load on the outer surface area
asel,s,area,,2
asel,a,area,,4
! Loading to be applied on sector number 3
cycopt,ldsect,3
sfa,all,,pres,-124
asel,all

solve
fini

! STEP #10
! Go to database results post processor

/post1
set,list

! STEP #11
! Read results for "substep 3  - excitation freq. of 866 HZ"

set,,3
plns,u,sum,1
fini

! STEP #12
! Go to time/freq. history postprocessor

/post26

! STEP #13
! Store X and Y disp. of node #34 on sector #3"

nsol,2,34,U,x,UX_34,3
nsol,3,34,U,y,UY_34,3

! STEP #14
! Plot UX and UY disp. of node #34 as a function of freq.

plvar,2,3

The following table describes the input listing and the steps involved in the example harmonic cyclic symmetry analysis in detail.

The results of your analysis should match those shown below:

Figure 5.5: Element Plot Showing Pressure Load on Sector 3

Figure 5.6: Contour Plot of Displacement Sum at Frequency of 866 HZ

Figure 5.7: Displacement Plot as a Function of Excitation Frequency