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mirror 3D for three times, I think.

mirror 3D for three times, I think.

nah, tried that. it gave me the wrong geometry...

What is cyclic symmetry?

It can’t be done with Mirror 3D as you noticed. You need a “Rotate 3D” option where you set a rotation angle of 45 degrees. As far as I know, there is no such feature for Data Sets.

Nagi Elabbasi
Veryst Engineering

Ah hah... Okay thanks.

Hi

For a 1/8 symmetric model in 2D I have no problems to mirror 3x and get out a full 3D plot (v4.2a)

but this is not "cyclic" or ?

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Good luck
Ivar

Here is a figure (from the internet) that shows what I think Chong means by cyclic symmetry. I find this type of symmetry more typically called rotational symmetry. There is a different analysis procedure, mainly in solid mechanics, called cyclic symmetry for solving a rotationally symmetric structure under general (non-rotationally symmetric) loads.

Nagi Elabbasi
Veryst Engineering

Hi

indeed the mirror implies local symmetry, while the rotation allows to repeat non symmetric shapes

ut I would be interested to understand more what you mean by structural and rotational symmetry geometry with, non rotational symmetry loads. Do you have any other references, or web pointers to propose ?

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Good luck
Ivar

Hi Ivar,

If a structure (including boundary conditions) has X sectors of rotational symmetry you can transform the full model into X/2 decoupled sub-models (via this cyclic symmetry transformation). If each sector has N degrees of freedom then solving the full system at once involves a solution of N.X equations. With the cyclic transformation, you solve instead N complex equations X/2 times. You can do this for linear stationary, transient and even eigenvalue problems. There is no loss of accuracy in this method.

I could not find a good reference online. The best one I saw so far is an Ansys document www.ansys.spb.ru/pdf/present/cyclic_symmetry_analysis.pdf. The following reference is better however: W. Zhong and C. Qiu, "Analysis of Symmetric or Partially Symmetric Structures," Computer Methods in Applied Mechanics and Engineering, 38, 1-18 (1983). The complex constraints involved in this cyclic symmetry analysis (between two edges/faces of the cyclic part) can be implemented relatively easily in COMSOL.

Nagi Elabbasi
Veryst Engineering

Hi Nagi

Thanks will have a look, havent used ANSYS for more than a decade now. As I have many symmetric geometry, non-symmetric load cases it might be something to push up to COMOSL developpers too, if really useful ;)

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Good luck
Ivar

Hi,
this thread contains two questions:
1) For a sector-symmetric model, how do I map the solution of a 3D sector to a full 3D plot for visualization?
2) How can I do cyclic symmetry in structural mechanics? Cyclic symmetry for dynamic structural models can have different excitation modes in different sectors.

Attached is an example from the model library that answers both questions. The cyclic symmetry structural problem can be solved with Floquet boundary conditions on the cyclic symmetry boundaries. This model is a slightly involved in its implementation, but the good news is we will release a ready made physics interface for cyclic symmetry in the next major release, spring 2012.

Another improvement that is in the pipe are datasets that can be revolved, so you will not need to to use extrusion coupling operators to make the full 3D plot (see attached example for details).

Note: to get this model available in the model library, you need to be licensed the Structural Mechanics module, and perform a Model Library update.

kind regards
Niklas

Hei Niklas

Thanks for the input, it's clear that you begin to have so many models in the library, and I do not know what to propose to easier find "the" one for a given issue ;)

Search is nice but one need to identify also the correct keyword(s). I have the same problem to find back one of my own many test models ;)

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Having fun Comsoling
Ivar

argh, where do I find this option? :( using v4.4
thx