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Electrostatic force on cantilever beam

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Hi,

I'm modelling a CNT cantilever beam with above a silicon substrate. I've used the assemble mode to use the contact pair. The problem is that when I define some potencial over the beam It does distribute the electric charge but when I apply the structural mechanics module to compute the electrostatic force the beam does not deform.
I've tried with a pure mechanical load and the model works perfectly. I don't know if the BC or the pairs might be affecting this.

I'll attach the model.

Hope somebody can help me.

Thank you


2 Replies Last Post 23 feb 2011, 22:01 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 23 feb 2011, 02:20 GMT-5
Hi

I have a few other comments:
- Check your materials, I do not believe the beam should be of "air" (domain 4) or is the beam only domain "5" ?
- Check your structural physics: if you use ALE you should not define the air as a "solid", and the bottom electrode is probably also to be fixed
- Check your ES physics, by default in union mode you have continuity so you do not need the pairs and continuity

Your overall air domain is very large and not symmetric, your electric field will be influenced by these close boundaries, while you loose a lot of mesh volume. I use mostly round circle/sphere air domains to minimise the edges and to not disturb the fields by square shapes, then I add a thin "infinite element layer

in your example when you come to a contact you will change the topology, the ALE mash must locally wanish which is not acceptable, so you must use an offset >0 to leave some volume for the ALE mesh

Anyhow you will also face the difficulty of the bifurcation of the pull in voltage, but leave that to later when your model solves at least up to a given voltage

--
Good luck
Ivar
Hi I have a few other comments: - Check your materials, I do not believe the beam should be of "air" (domain 4) or is the beam only domain "5" ? - Check your structural physics: if you use ALE you should not define the air as a "solid", and the bottom electrode is probably also to be fixed - Check your ES physics, by default in union mode you have continuity so you do not need the pairs and continuity Your overall air domain is very large and not symmetric, your electric field will be influenced by these close boundaries, while you loose a lot of mesh volume. I use mostly round circle/sphere air domains to minimise the edges and to not disturb the fields by square shapes, then I add a thin "infinite element layer in your example when you come to a contact you will change the topology, the ALE mash must locally wanish which is not acceptable, so you must use an offset >0 to leave some volume for the ALE mesh Anyhow you will also face the difficulty of the bifurcation of the pull in voltage, but leave that to later when your model solves at least up to a given voltage -- Good luck Ivar

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Posted: 1 decade ago 23 feb 2011, 22:01 GMT-5
Hello,

thanks for your advice Ivan,

I've followed your advice, but there's a thing I can't get done yet.
My model is in assembly mode but I just used the union operation in the air boundaries. The beam is only the boundary 5. Now I get a inverted mesh warning and my model does not find any solution. I'm still thinking that there must be some kind of problem with the BC.

Thanks for your help.

I'm attanching a modified model
Hello, thanks for your advice Ivan, I've followed your advice, but there's a thing I can't get done yet. My model is in assembly mode but I just used the union operation in the air boundaries. The beam is only the boundary 5. Now I get a inverted mesh warning and my model does not find any solution. I'm still thinking that there must be some kind of problem with the BC. Thanks for your help. I'm attanching a modified model

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