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Example Buckling Cyclic Symmetry Analysis

7.6.4. Analysis Steps

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

Step

Description

Command

1.

Start an interactive session.

---

2.

Read in the input file: buck_cyc_sym.inp

/IN-

 

 

PUT,buck_cyc_sym.inp

3.

Specify a cyclic symmetry analysis and configure the database

CYCLIC

 

accordingly.

 

4.

Activate cyclic symmetry graphical expansion.

/CYCEXPAND,,ON

5.

Plot the elements.

EPLOT

6.

List the cyclic status.

CYCLIC,STATUS

7.

List the cyclic solution option settings.

CYCOPT,STATUS

8.

Specify a static analysis type with prestress effects.

/SOLU

 

 

AN-

 

 

TYPE,STAT-

 

 

IC

 

 

PSTRES,

 

 

ON

9.

Solve the prestress static analysis.

SOLVE

10.

Specify a buckling analysis type.

FINISH

 

 

/SOLU

 

 

AN-

 

 

TYPE,BUCKLE

11.

Specify buckling analysis options

BUCOPT, LANB, 3

12.

Specify mode expansion options.

MXPAND, 3, , , YES

13.

Solve the buckling analysis.

SOLVE

14.

Read the results from the smallest load factor. (This should corres-

FINISH

 

pond to the smallest frequency.)

/POST1

 

 

SET, FIRST ,

 

 

, , , , , , OR-

 

 

DER

15.

Plot the buckled mode shape.

PLNSOL, U, SUM

 

----

 

This step completes the example buckling cyclic symmetry analysis. Your results should match those shown in Figure 7.22: Ex- ample Buckling Cyclic Symmetry Analysis Results (p. 208).

The results of your analysis should match those shown here:

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Figure 7.22: Example Buckling Cyclic Symmetry Analysis Results

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

You can automatically solve for the critical strut temperature by iterating on the variable loads until the eigenvalue becomes 1.0 (or nearly 1.0 within some tolerance). The iterations ensure that the eigen-

value solution does not factor the stress stiffness matrix from the constant loads. The following flowchart illustrates the process:

Figure 7.23: Buckling Cyclic Symmetry Results: Load Factor Iterations

Use the /PREP7 portion of the previous input file (buck_cyc_sym.inp) to construct your model. After defining the model parameters--but before activating cyclic symmetry--define the arrays and the programming operations, as follows:

*dim,Tstrut,array,10

*dim,Tfact,array,10

*do,I,1,10

/prep7

 

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Example Buckling Cyclic Symmetry Analysis

*if,I,eq,1,then

Tstrut(I)=100

*else Tstrut(I)=Tstrut(I-1)*Tfact(I-1) cyclic,undouble

*endif

asel,,real,,2

bfa,all,temp,Tstrut(I) allsel

After you have defined the iterative parameters, proceed with the cyclic symmetry portion of the analysis:

cyclic /cycexpand,,on eplot cyclic,status cycopt,status /solution antype,static pstres,on solve

finish /solution antype,buckle bucopt,lanb,3 mxpand,3,,,yes solve

finish /post1

set,first,,,,,,,order

plnsol,u,sum

*get,loadmult,active,,set,freq

Tfact(I)=loadmult

*enddo

The program then plots the data to determine the critical strut temperature:

*dim,data,table,10,2

data(0,1)=1

data(0,2)=2

*do,I,1,10

data(I,0)=I

data(I,1)=Tstrut(I)

data(I,2)=Tfact(I)

*enddo

/AXLAB,X,Strut Temperature /AXLAB,Y,Load Factor /GROPT,DIVX,5 /GROPT,DIVY,5 /XRANGE,100,200 /YRANGE,0.9,1.4 /GTHK,CURVE,1

/GMARKER,1,3

*VPLOT,data(1,1),data(1,2)

The eigenvalues (frequencies) calculated for the buckling analysis represent the buckling load factors. The eigenvalues represent load factors for all applied loads.

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of ANSYS, Inc. and its subsidiaries and affiliates.

209