This example is very similar to Example Modal Cyclic Symmetry Analysis, except that a damped modal analysis is performed. The component is a simplified fan inlet case for a military aircraft engine.

The problem specifications follow those of Example Modal Cyclic Symmetry Analysis, with the addition of alpha (mass proportional) and structural damping coefficients equal to 0.1.

! Damped Modal Cyclic Symmetry Analysis Example
! Ring-Strut-Ring Configuration

! Define constants
r1=5
r2=10
d1=2
nsect=24
alpha_deg=360/nsect
alpha_rad=2*acos(-1)/nsect

! Plot settings
/view,1,1,1,2
/plopts,minm,0
/plopts,date,0
/plopts,logo,on
/pnum,real,1
/number,1

! Create a cyclic symmetry ring-strut-ring model
/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
cyclic
amesh,all
finish

! Perform a damped modal solve
/solution
antype,modal
modopt,damp,6   ! Select damped eigensolver (unity norm by default)
mxpand,6,,,yes
alphad,0.1      ! Apply global alpha damping
dmpstr,0.1      ! Apply structural damping
dk,5,uz,0
solve
finish

/post1
set,list
set,list,,, ,,, ,order
/cycexpand
rsys,1

! Read results for "load step 1 - substep 3 - harmonic index 0"
! Plot the real and imaginary tangential displacement contour
set,1,3,,real
plns,u,y

set,1,3,,imag
plns,u,y

! Read results for "load step 13 - substep 1 - harmonic index 12"
! Plot the real tangential displacement contour
set,13,1,,real
plns,u,y

! Read results for "load step 3 - substep 5 - harmonic index 1"
! Plot the real and imaginary tangential displacement contour
set,3,5,,real
plns,u,y

set,3,5,,imag
plns,u,y

The following table describes the input listing and the steps involved in this example damped modal cyclic symmetry analysis in more detail.

The results of your analysis should match those shown below.

Figure 5.22: Damped Modal Cyclic Symmetry Analysis Results - Real

Figure 5.23: Damped Modal Cyclic Symmetry Analysis Results - Imaginary