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# cyclic symmetry

Creator
Hello,

to save cpu time, I want to use cyclic symmetry on my model. Can someone describe how cyclic symmetry can be defined in NX Nastran Advanced Simulation (NX6)? The support told me to read the chapter "manual coupling", but I found no answers there.
5 REPLIES

# Re: cyclic symmetry

Siemens Phenom
Renk,

Support pointed you in the correct direction. NX is able to create node-node couples based upon a geometric search of the nodes in your model. For cyclic symmetry this means finding nodes on the independent side, rotating through a fixed angle about the Z axis, and finding the matching node on the dependent side. For every match a couple is created. You can also use the geometry to define the coupled DOF. The advantage there is that if the mesh updates, the couples update automatically.

This process also requires that the meshes on the independent and dependent sides match within a tolerance. That is achieved through 2D Dependent Mesh definitions.

We have a training activity that will walk you right through the process. It is in both the CAST and Learning Advantage products. In CAST, look under "Advanced Simulation" --> "Advanced FE Modeling Techniques" --> "Suggested Activities" under "Symmetry".

Regards,
Mark

Mark Lamping
CAE Technical Consultant
Siemens PLM Software
(513) 576-2073
mark.lamping@siemens.com

# Re: cyclic symmetry

Creator
czt0t0,
thanks for the information. I created a mesh with the 2D Dependent Mesh definition. How do I create the coupled nodes?
If I go to manual coupling, I can choose an independent object and a dependent object. The independent object can only be a single node, which is not what I want. You write that NX is able to create node-node couples,
but HOW?

# Re: cyclic symmetry

Siemens Phenom
Renk,

It turns out that support didn't quite get it right. They should have suggested using AUTOMATIC COUPLING. With the automatic methods, you can define many couples at once. Manual defines a single couple.

In the AUTOMATIC COUPLING dialog when you are selecting a single independent and dependent object, you are setting up the search criteria for the entire model. So traversing through the dialog, one may:

1. Select a vertex on the independent side for the independent object
2. Select the equivalent vertex on the dependend side for the dependent object
3. Define a reference coordinate system

This will be the cylindrical system used for the search for matching independent/dependent node pairs and the displacement coordinate system of paired nodes. You can define this coordinate system on the fly - it need not exist prior to entering the dialog.

4. Specify which DOF are applied in the coupled DOF

The dialog also has an optional 2nd Independent Object definition. This is used to limit the search for node pairs to just the items selected in this optional step. Otherwise all nodes will be used in the search.

Regards,
Mark

Mark Lamping
CAE Technical Consultant
Siemens PLM Software
(513) 576-2073
mark.lamping@siemens.com

# Re: cyclic symmetry

Creator
Thanks a lot! works great.

# Re: cyclic symmetry

Pioneer

Hello, Mark,

I have same problem like this,

I am studying the example "Model a cyclic symmetric structure" in NX CAST 8.5/Simulation/Advanced simulation/FE Modeling of symmetry/Modeling Symmetrical pats,

I don't understand why the DOFs are set like picture below in dialog of "Automatic coupling".

Cou.dyou explain for me ?