Rotational Symmetry

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Hi everyone,

I'm currently trying to reduce the size of my model by applying symmetry. While I’ve had some success with basic symmetry cases, I’m still struggling to correctly define rotational symmetry for my cross-section.

I’m performing a linear buckling analysis, and my geometry has a three-fold (120°) rotational symmetry. Despite experimenting with simpler models, I haven't been able to set it up properly in COMSOL.

Could someone please guide me on how to define and implement this type of symmetry in my model? I’ve attached a simple sketch of both the full and reduced models for reference.

Thank you very much in advance for your help!

Best regards, https://drive.google.com/file/d/1-ygSbmOydDTfKx1leXw_7t2vOn5RRqnV/view?usp=drive_link

sketch


4 Replies Last Post Apr 14, 2025, 8:13 a.m. EDT
Henrik Sönnerlind COMSOL Employee

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Posted: 6 days ago Apr 9, 2025, 9:58 a.m. EDT

It is unsafe to use symmetry for buckling problems, since the buckling modes may be nonsymmetric, even though geometry and loading are symmetric.

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Henrik Sönnerlind
COMSOL
It is unsafe to use symmetry for buckling problems, since the buckling modes may be nonsymmetric, even though geometry and loading are symmetric.

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Posted: 6 days ago Apr 9, 2025, 2:40 p.m. EDT

It is unsafe to use symmetry for buckling problems, since the buckling modes may be nonsymmetric, even though geometry and loading are symmetric.

Dear Henrik Sönnerlind,

Thank you for your quick and helpful response.

I was wondering—is there a way to reduce the model size in a buckling analysis?

Best regards, Mirhan

>It is unsafe to use symmetry for buckling problems, since the buckling modes may be nonsymmetric, even though geometry and loading are symmetric. Dear Henrik Sönnerlind, Thank you for your quick and helpful response. I was wondering—is there a way to reduce the model size in a buckling analysis? Best regards, Mirhan

Henrik Sönnerlind COMSOL Employee

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Posted: 5 days ago Apr 10, 2025, 7:29 a.m. EDT
Updated: 5 days ago Apr 10, 2025, 10:47 a.m. EDT

For structures with a single symmetry plane, you can analyze half of the structure using symmetry boundary conditions as one case, and antisymmetry boundary conditions as the other. This will give you all modes and corresponding buckling loads.

With two orthogonal symmetry planes, you would need four sets of boundary conditions on a quarter of the structure.

For rotational symmetry it is more complicated. Buckling modes can have different types of cyclic behavior. Such problems can be treated using Floquet Theory, but that is not a built-in functionality. It is, however, possible to set up such boundary conditions by editing Periodic Condition constraints in Equation View.

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Henrik Sönnerlind
COMSOL
For structures with a single symmetry plane, you can analyze half of the structure using symmetry boundary conditions as one case, and antisymmetry boundary conditions as the other. This will give you all modes and corresponding buckling loads. With two orthogonal symmetry planes, you would need four sets of boundary conditions on a quarter of the structure. For rotational symmetry it is more complicated. Buckling modes can have different types of cyclic behavior. Such problems can be treated using Floquet Theory, but that is not a built-in functionality. It is, however, possible to set up such boundary conditions by editing *Periodic Condition* constraints in *Equation View*.

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Posted: 20 hours ago Apr 14, 2025, 8:13 a.m. EDT

Dear Henrik Sönnerlind,

Thank you very much for your response! I’ll look into the suggested solutions and do my best to implement them as advised.

Best regards, Mirhan

Dear Henrik Sönnerlind, Thank you very much for your response! I’ll look into the suggested solutions and do my best to implement them as advised. Best regards, Mirhan

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