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.

Use the input file (input_cyclicExample07.dat, download: input_cyclicExample07.zip) given below to perform this example damped modal cyclic symmetry analysis. The file contains the complete geometry, material properties, and solution options for the finite element model.

! Damped modal cyclic symmetry analysis for a ring-strut-ring configuration.

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

/prep7

! Define geometry, mesh, and boundary conditions or read the CDB file.
generateGeom = 0                    ! Set value to 1 to generate model.
*if,generateGeom,eq,1,then
    ! Define geometry parameters.
    r1 = 5
    r2 = 10
    d1 = 2
    nsect = 24
    alpha_deg = 360 / nsect
    alpha_rad = 2*acos(-1) / nsect

    ! Set coordinate system to cylindrical.
    csys,1

    ! Create keypoints, lines, and areas.
    ! Define keypoints and lines.
    k,1,0,0,0
    k,2,0,0,d1
    k,3,r1,0,0
    k,4,r1,0,d1
    l,3,4

    ! Rotate line to create area.
    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

    ! Mesh with shell-181 elements.
    mshkey,1
    et,1,181
    r,1,0.20     ! Thickness of the inner and outer rings.
    r,2,0.1      ! Thickness of the strut.
    mp,ex,1,10e6
    mp,prxy,1,0.3
    mp,dens,1,1e-4
    esize,0.25

    ! Select areas and assign attributes.
    asel,,,,1,4
    aatt,,1
    asel,,,,5
    aatt,,2
    allsel
    amesh,all

    ! Apply boundary conditions.
    dk,5,uz,0

    ! Save the database.
    cdwrite,comb,cyclicExample07,cdb
*else
    cdread,comb,cyclicExample07,cdb,,,
*endif

! Configure cyclic symmetry.
cyclic

! Plot elements.
eplot

! List cyclic status.
cyclic,status
! List cyclic solution option settings.
cycopt,status

finish

! Perform a damped modal solve.
/solution
csys,1
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.
solve
finish
/post1
! Print eigenvalues.
set, list,,, ,,, ,order
! Set cyclic expansion
/cycexpand,,on

rsys,1

! Read results for load step 1, substep 3
! Plot the real and imaginary tangential displacement contours.
set,1,3,,real
plns,u,y

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

! Read results for load step 13, substep 1
! Plot the real tangential displacement contour.
set,13,1,,real
plns,u,y

! Read results for load step 3, substep 5
! Plot the real and imaginary tangential displacement contours.
set,3,5,,real
plns,u,y

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

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