# Discussion Forum

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## Symmetry

Dear all,

sorry the continuous questions today! I am going to use symmetry for the geometry as in the picture I attached. The simplified geometry is a multilayer (only the green part) composed of layers of different materials and thickness, and four strips A (=C) and B (=D) jointed on top and at the bottom of it.
For time calculation reducing (I have to deal with a more complex structure), I would use symmetry, as A=C and B=D, with a plane of symmetry in the middle of the multilayer. Therefore, I would consider only A and B in the calculation, for example.
But I can't use Symmetry, as it is required a face in the middle plane of the multilayer, but the multilayer is not Symmetric! I should need something like a plane recognized by the function Symmetry, and not a physical surface.

Any suggestions?
Thank you in advance

4 Replies Last Post Oct 31, 2013, 7:04 AM EDT
Posted: 5 years ago
Hi

to apply symmetry you need that all items are "symmetric" so if you thickness of the central multilayer are not symmetric, you will get some discrepancies if you apply a symmetry plane at mid "middle Layer" indeed

Now you might be able to apply "symmetry" for half the length, it's already something

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Good luck
Ivar

Posted: 5 years ago
Hi Ivar,

thank you for your reply (always satisfactory!). In conclusion, I can't use symmetry in my case. What other solutions are available to reduce the time calculation, in the particular case of my model?

Furthermore, is it worth suggesting to COMSOL support to modify the symmetry function for the next releases, in order to take into account parts not in contact with the middle plane? Thus, something already present in the function Mirror (Geometry), where you can define the plane of reflection...

Thank you
Kind regards

Posted: 5 years ago
Hi

but I believe that is rather tricky, you can do it now but you need to write out the equations, and I'm not sure your demand can be made generic, and COMSOL so far has only proposed generic BC's that apply (almost) for any situation)

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Good luck
Ivar

Posted: 4 years ago
Hi Ivar,
I have been using the symmetry boundary condition for structural mechanics. Now that I see the results, I realize that the symmetry condition in Structural Mechanics only forces the normal displacements to the symmetry surface to be zero (n·u = 0), but not the rotations. The result is that the deformed geometry has no continuity in symmetry plane.
Would you know how to force rotations to be zero as well? Is it normal that the symmetry condition does not acocunt for that already?

Regards,

Andrés

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