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Example Buckling Cyclic Symmetry Analysis

Figure 7.21: Example Modal Cyclic Symmetry Analysis Results

Note

Mode shape values may vary slightly depending on your computer system.

To view a traveling wave animation of your model, issue the ANCYC,24,,0.1 command. For more information, see Applying a Traveling Wave Animation to the Cyclic Model (p. 196).

7.6. Example Buckling Cyclic Symmetry Analysis

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

7.6.1.Problem Description

7.6.2.Problem Specifications

7.6.3.Input File for the Analysis

7.6.4.Analysis Steps

7.6.5.Solve For Critical Strut Temperature at Load Factor = 1.0

7.6.1. Problem Description

The object is a simplified structure that experiences a thermal load emanating outward from the center. The inner ring is kept at a constant 600° F temperature and the outer ring is kept at a constant 0° F. A linear eigenvalue buckling analysis determines when the struts will buckle as the temperature in the struts increases from 100° F to 500° F.

7.6.2. Problem Specifications

The geometric properties for this analysis are as follows:

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The material properties for this analysis are as follows:

Poisson's ratio (υ) = 0.3 Density = 1e-4

Coefficient of thermal expansion (α) = 5e-5 Young's modulus (E) = 10e6 (at 0° F) Young's modulus (E) = 4e6 (at 600° F)

The Young's modulus value varies linearly between 0 and 600° F. All applicable degrees of freedom

(DOFs) are used for the cyclic symmetry edge-component pairs. The first six mode shapes for all applicable harmonic indices are requested.

7.6.3. Input File for the Analysis

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

 

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Example Buckling Cyclic Symmetry Analysis

!Cyclic Symmetry Buckling Example

!Ring-Strut-Ring Configuration

!STEP #1

!Start an interactive session

!STEP #2

!Read in the input file: buck_cyc_sym.inp

r1=5

r2=15

d1=4

nsect=6 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

mptemp,1,0

mptemp,2,600

mpdata,ex,1,1,10e6

mpdata,ex,1,2,4e6

mp,prxy,1,0.3,0.0 mp,dens,1,1e-4 mp,alpx,1,5e-5 tref,0

esize,1.0

asel,,loc,x,r1

bfa,all,temp,600

asel,a,loc,x,r2

aatt,,1

asel,inve

bfa,all,temp,100

aatt,,2 allsel amesh,all

lsel,,loc,z,d1/2 lsel,r,loc,y,alpha_deg/2 ksll

nslk nrotate,all dk,all,uz,0 dk,all,uy,0 allsel finish aplot /prep7

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/eof

!STEP #3

!Configure the database for a cyclic symmetry analysis

cyclic

!STEP #4

!Turn on cyclic symmetry graphical expansion

/cycexpand,,on

!STEP #5

!Plot the elements

eplot

!STEP #6

!List the cyclic status

cyclic,status

!STEP #7

!List the cyclic solution option settings

cycopt,status

!STEP #8

!Specify static analysis type with prestress effects

/solution

antype,static

pstres,on

!STEP #9

!Solve the prestress static analysis

solve

!STEP #10

!Specify buckling analysis type

finish /solution antype,buckle

!STEP #11

!Specify buckling analysis options

bucopt,lanb,3

!STEP #12

!Specify mode expansion options

mxpand,3,,,yes

!STEP #13

!Solve the buckling analysis

solve

!STEP #14

!Read results for the smallest load factor

finish /post1

set,first,,,,,,,order

!STEP #15

!Plot the buckled mode shape

plnsol,u,sum

 

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