Cyclic symmetry

The newest version (1.2.0) introduced support for axisymmetric models. So the only type of symmetry that’s missing is cyclic symmetry. It can be very useful for shafts, impellers and so on. In CalculiX it’s defined based on tie constraint - additional parameter (cyclic symmetry) has to be added to it and then a new *Cyclic symmetry model keyword follows. Since the Keyword Editor can’t modify existing keywords (which is understandable because that could break the model but maybe it would be possible to prevent these potential issues somehow), such tie constraint for cyclic symmetry has to be created manually based on the predefined surfaces:

It would be really nice to have support for this functionality in GUI.

As a side note, boundary conditions and constraints (such as rigid body constraint) can’t be applied to the nodes of the slave surface of cyclic symmetry since that would cause overconstraint. So in cases like the one above it’s necessary to remove nodes belonging to the edge on the side of slave surface from BC/RB definition.

Another important thing is that if there are multiple tie constraints in the model then it might be necessary to reference the one serving for cyclic symmetry by name using tie parameter of the *Cyclic symmetry model keyword.


I did not test the cyclic symmetry by myself. I was put off by many exceptions in the CalculiX documentation where, for some keywords, special care must be taken when using the cyclic symmetry model. Is that not a problem in general?

Indeed, there are some special considerations when using cyclic symmetry. Apart from the ones mentioned in my first post (which are rather harmless if one remembers about them), the biggest differences are in the case of *Frequency analyses. There is a separate keyword *Select cyclic symmetry modes that can be used to specify which cyclic symmetry modes should be used in eigenfrequency analysis. The same keyword is used in Abaqus.

I couldn’t find any other important issues with cyclic symmetry models (some apply to very specific types of analyses such as HCF added to CalculiX 2.19 and thus are not relevant for now). Generally speaking, cyclic symmetry works very well in CalculiX, at least from what I’ve noticed so far.

Ok, that was only my feeling then. I will look into it in the future and add it to the to-do list.


Hi @Matej ,

I have the same opinion like @FEAnalyst: it would be great to have such a tool in the GUI.

I already simulate a fan and used cyclic symmetry. In comparison with Ansys the results are identical.

I am very surprised about PrePoMax. It is such a great GUI. For me it is the best Open source FEA Gui I ever Seen before!! You did a great Job!

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I was asked to share the file from my first post so here it is:

Cyclic symm.pmx (1.3 MB)

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Is the output from cyclic symmetrical analyses managed in PMX ok (ststic snd vibes) and additional entities like MAXS for STRESSDOMAIN?

Currently, there’s no support for cyclic symmetry but you can open the results with this kind of output:

FYI In a previous role with Alstom Power, I wrote automated python code for steam turbine blade analysis looping over 3000 different designs in service. Model creation was in CGX including geometry, full hex meshing static analysis followed by modal analysis and forced response. Blade shroud has cyclic symmetry and contact. Solves in CCX and back to back with abaqus is excellent and also with tests (frequencies}. Post procesing in CGX again automated. This software is looking good. I’ll give it a closer look.
MIDAS was the application we created

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