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11.2.3. Superelement Expansion in Transformed Locations

When creating a new CMS superelement from an existing superelement (via the SESYMM or SETRAN command) during the use pass, you can specify an offset value to the node or element IDs in the FE geometry record saved in the .rst results file. The command to do so is RSTOFF.

With appropriate offsets, you can write additional results files with unique node or element IDs and thus display the entire model, even if the original superelements have overlapping node or element sets. Results files containing the offset node or element IDs are incompatible with the .db database files saved at the generation pass.

After performing the use pass and expansion pass for all CMS superelements, the mode shape display of the entire assembled structure shows the offset superelements in their transformed locations.

For more information, see Example: Superelement Expansion in a Transformed Location (p. 305).

11.2.4. Plotting or Printing Mode Shapes

Plotting or printing the mode shapes of the assembled structure occurs during postprocessing. The postprocessor (/POST1) uses the results files generated by the CMS superelements to display shape results. Issue the CMSFILE command to import the CMS superelement results files into the postprocessor where you can view the assembled structure. (You can issue the command as often as needed to include all or some of the component results files.)

If you created new CMS superelements from existing superelements (via SESYMM or SETRAN commands) during the use pass, you can issue the SEEXP command to expand the results with the offset superelements appearing in their transformed locations.

Set the desired mode shape of the assembled structure via the SET command, then plot (PLNSOL) or print (PRNSOL) the mode shapes.

11.3. Example Component Mode Synthesis Analysis

This section introduces you to the program's component mode synthesis (CMS) analysis capabilities by way of example. The example CMS presents a modal analysis of a 2-D tuning fork.

11.3.1. Problem Description

The model is an unconstrained stainless steel tuning fork. After dividing the fork into three CMS superelements, you must determine the vibration characteristics (natural frequencies and mode shapes) of the entire model.

11.3.2. Problem Specifications

The geometric properties for this analysis follow.

 

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Example Component Mode Synthesis Analysis

 

 

 

0.1 m

5 mm

0.025 m

0.035 m

The fork is divided into three CMS superelements:

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Part 2

 

 

Part 3

 

 

 

 

 

 

Part 1

The three interfaces are as follows:

In e f ce

In e f ce

 

In e f ce

 

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Example Component Mode Synthesis Analysis

The material properties for this analysis are as follows:

Young's modulus (E) = 190e9 Poisson's ratio (υ) = 0.3 Density = 7.7e3

The first 10 eigenfrequencies are extracted, and the fourth mode shape (the first nonrigid body mode) is expanded.

11.3.3. Input for the Analysis: Fixed-Interface Method

Use this input file (named cms_sample.inp) to perform the example CMS analysis via the fixed-inter- face method. The file contains the complete geometry, material properties, and components (nodes

and elements).

/batch,list

/title, 2D Tuning Fork

!Component Mode Synthesis - 2-D example

!The Structure is divided into 3 CMS Superelements

!STEP #1

!Start an interactive session

!STEP #2

!Read in this input file: cms_sample.inp

finish /clear

/filnam,full

/units,si

blen=0.035

radi=0.025

tlen=0.1

tthk=0.005

/plopts,minm,0

/plopts,date,0

/pnum,real,1

/number,1

/prep7 k,1,-tthk/2 k,2,tthk/2 k,3,-tthk/2,blen k,4,tthk/2,blen

local,11,1,,blen+tthk+radi k,5,radi+tthk,-180 k,6,radi,-180 kgen,2,3,4,1,-tthk k,9,radi

k,10,radi+tthk

a,5,6,7,3

a,3,7,8,4

a,4,8,9,10

csys,0

a,1,2,4,3 k,11,-radi-tthk,blen+tthk+radi+tlen k,12,-radi,blen+tthk+radi+tlen k,13,radi,blen+tthk+radi+tlen k,14,radi+tthk,blen+tthk+radi+tlen a,5,6,12,11

a,9,10,14,13

eshape,2

esize,tthk/3.5

et,1,plane182,,,3

r,1,tthk

amesh,all

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mp,ex,1,190e9

mp,dens,1,7.7e3

mp,nuxy,1,0.3

nsel,s,,,38

nsel,a,,,174,176

nsel,a,,,170

cm,interface1,node

nsel,s,,,175

nsel,a,,,168

nsel,a,,,180,182

nsel,a,,,38,176,138

cm,interface2,node

nsel,s,,,175

nsel,a,,,168

nsel,a,,,180,182

nsel,a,,,170,174,4

cm,interface3,node

esel,s,,,273,372

cm,part1,elem

esel,s,,,373,652

esel,a,,,1,129

esel,a,,,130

esel,a,,,133,134

esel,a,,,137,138

esel,a,,,141,142

cm,part2,elem

cmsel,s,part1

cmsel,a,part2

esel,inve

cm,part3,elem

allsel,all save finish

!STEP #3 (a. through j.)

!Generation pass

!Generation pass 1

!a.

!Change the active jobname which will become the superelement name

/filnam,part1

!b.

!Specify the analysis type as substructuring

/solu

antype,substr

!c.

!Specifies the name to be assigned to superelement matrix file

!Strongly suggested to be the same as the active jobname

seopt,part1,2

!d.

!Specifies CMS options

cmsopt,fix,10

!e.

!Selects element component named "part1"

cmsel,s,part1

!f.

!Selects node component named "interface1"

cmsel,s,interface1

! g.

 

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Example Component Mode Synthesis Analysis

!All the active DOFs (that is, on the nodes which belong to "interface1")

!are set as masters

m,all,all

!h.

!Selects all the nodes attached to the selected elements

!(that is, elements which belong to "part1")

nsle

!i.

!solve the first CMS generation pass

solve finish

!j.

!Save the generation pass 1 database

save

!Repeat the generation pass for "part2"

!Generation pass 2

/filnam,part2

/solu

antype,substr

seopt,part2,2

cmsopt,fix,10

cmsel,s,part2

cmsel,s,interface2

m,all,all nsle solve finish save

!Repeat the generation pass for "part3"

!Generation pass 3

/filnam,part3

/solu

antype,substr

seopt,part3,2

cmsopt,fix,10

cmsel,s,part3

cmsel,s,interface3

m,all,all nsle solve finish save

!STEP #4 (a. through i.)

!Use pass

!a.

!Clears the database

/clear,nostart

!b.

!Change the active jobname which will become the use pass name

/filnam,use

! c.

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! A superelement element type is created

/prep7

et,1,matrix50

!d.

!Element type attribute pointer set to 1

type,1

!e.

!Brings in the three superelements created above

se,part1

se,part2

se,part3 finish

!f.

!A modal analysis is performed

/solu

antype,modal

!g.

!Specifies modal analysis options

modopt,lanb,10

!h.

!Expands 10 modes

mxpand,10

!i.

!Solve the modal analysis

solve finish

!STEP #5 (a. through g.)

!Expansion pass

!Expansion pass 1

!a.

!Clears the database

/clear,nostart

!b.

!Changes the jobname to superelement 1 name

/filnam,part1

!c.

!resume the database

resume

!d.

!Specifies the expansion pass

/solu

expass,on

!e.

!Specifies superelement name and use pass name

seexp,part1,use

! f.

 

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