# Discussion Forum

## Rigid Wall / Basement Mechanical Constraint

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Hello,

it´s probably a ridiculous question, but I need a mechanical constraint just like an ideal rigid wall or basement which the DUT is unable to penetrate but is able to lift off it. A roller constraint where a displacement in z is possible and -z=0 would be perfect. Imagine a flat metal sheet which experiences a force just in the middle and is able to deform like a bowl. I know such a constraint from other CAD (FEM) programs like SolidWorks as "rigid wall" but did'nt found a handy solution in COMSOL. I hope it´s possible without writing own eq´s. Currently I a built a 3d model.

Thanks for your help,

BR Sven

5 Replies Last Post Mar 27, 2020, 2:00 PM EDT

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Posted: 2 weeks ago

Sven,

sounds like this might be a contact pair.

Cheers Edgar

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com

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Posted: 2 weeks ago

Hi Edgar,

thanks for the reply. Maybe, but wouldn´t it necessary to have a second geometry to create a contact pair? This geometry would have to be meshed as wel, right? I wanna avoid an additional geometry and thought there is a simple solution as described like a roller constraint with a free +z direction. If not than something like that should be implemented in COMSOL because one need it very often.

Thanks,

BR Sven

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Posted: 2 weeks ago

Hi Sven,

Adding that extra geometry and meshing it is a quick operation.

1. Add a Workplane (maybe reorient it, but Z-normal is the default)
2. Add a Square in that workplane, and set its size to be large enough
3. Under Mesh, add a Mapped node, and select the newly generated square.

Now you can use the square as the Source in a contact pair.

-------------------
Henrik Sönnerlind
COMSOL

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Posted: 2 weeks ago

Hi Henrik,

that sounds as if it could work=). Thank you very much, I will try it like that.

BR Sven

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Posted: 2 weeks ago

Hi Henrik,

I tried your suggestions. The plane and the square are fine and the meshing too. Do I have to create the plane in a certain distance to the object or directly on the objects lower surface? Additionaly, if I wanna apply a fixed constraint to the square it´s not selectable (the square). Is this necessary at all? Or is this already implemented? If the study doesn´t converge, what are the typical problems?

Thanks so far,

BR Sven

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