Cyclic symmetry analysis

[cocodrillo1]

Dear users,

I am a new user of FEMAP and I have a problem, how to define the cyclic symmetry constraints. In Ansys, where I work every day, it is very easy (CYCLIC or CPCYC command and ready). Here I cannot cope....

Please help me, thank you,

 

[rob768]

set model to a basic circular coordinate system and add symmetry boundary conditions on the planes of your model.

 

[cocodrillo1]

Thank you.
I compared the results of a modal analysis of circular sector using ANSYS (CYCLIC) and FEMAP (your hint), and they differ (skipping certain frequencies).
What can I do wrong?

 

[BlasMolero]

Dear Cocodrilo,
Cyclic Symmetry is a native feature of NX NASTRAN, yes, but is not supported in the FEMAP graphic user interface.
Many structures, including pressure vessels, rotating machines and antennas for space communications, are made up of virtually identical segments that are symmetrically arranged with respect to an axis.
When performing analyses on symmetrical structures, you can exploit that symmetry to reduce greatly reduce the time needed to create and solve an FE model. One advantage is that you will be required to provide an analytical model for only the “fundamental regional” of a structure, and this fundamental region is generally substantially smaller than the analytical model required by more traditional analysis techniques.

Investigating in the "NX Nastran User's Guide > Cyclic Symmetry" we can read the following:

• In a cyclic symmetry analysis, your total model consists of N identical segments which are numbered consecutively from 1 to N. In your input file, you use the CYSYM bulk data entry to specify the type of cyclic symmetry (rotational, dihedral, or axisymmetric) and the number of segments in the model.
• You then generate the model for one segment, using regular elements and standard modeling techniques. You can use any element in the NX Nastran Element Library, except axisymmetric elements.
• NX Nastran automatically rotates all other segments and their coordinate systems to equally spaced positions about the polar axis. The segment boundaries must be conformable; i.e., when the segments are put together, the grid points and the displacement coordinate systems of adjacent segments must coincide. This is easiest to ensure if you use a cylindrical or spherical coordinate system.

Typical Case Control Section Example

TITLE=CYCLIC SYMMETRY-STATICS
SUBTITLE=FIVE DEGREE SEGMENT OF CYLINDER
LABEL=AXISYMMETRIC LOADING
SPC=1
SET 1=0
SET 2=1
HARMONICS=1
NOUTPUT=2
DISP=ALL
STRESS=ALL
FORCE=ALL
SUBCASE 1
  LABEL=BAND LOADING
  LOAD=1
SUBCASE 2
  LABEL=CENTRIFUGAL LOADING
  LOAD=2
BEGIN BULK

In summary, if you plan to run a linear static (SOL101) or a normal modes eigenvalue (SOL103) analysis that feature cyclic symmetry the only way is to study the full model, in FEMAP do not exist yet an easy way to take advanced of the simplification of cyclic symmetry.

But if we us users request this feature to be implemented in FEMAP, this will be done for sure, FEMAP developers hear what the users need and request to be implemented in FEMAP, and the way is to go to GTAC (

http://support.industrysoftware.automation.siemens.com/gtac.shtml)

and file an Enhancement Request, the most users requesting this feature more chance to be implemented!!.

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[cocodrillo1]

All clear, thank you