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Need help with Meshing

Posted 21 feb 2012, 07:11 GMT-5 MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Mesh, Structural Mechanics Version 4.2 7 Replies

Sanjay Mukuntha Madhava
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Hi Everyone,
I need to simulate the deflection of a Membrane with Internal Stress in it. I have attached the file here and the problem is it take too long to execute and i believe the problem is with meshing. Can someone please check it and let me know if there is a better way to mesh the model.

Thanks in Advance
Sanjay

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7 Replies Last Post 21 feb 2012, 11:06 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 21 feb 2012, 08:05 GMT-5
Hi

Indeed your aspect ratio is extreme. I would suggest that you mesh the top in "triangles", then use a sweep mesh with 3 or more elements in the tickness.

Now your short beams will take all the stress at their sharp corners, ideally you should have at least 3 elements acros the width of the beams. One way is to split them with a layer, or tu set up the "Size custom" Resolution of narow regions = 3.5 or so, and check that the min, max sizeas are coherent

--
Good luck
Ivar
Hi Indeed your aspect ratio is extreme. I would suggest that you mesh the top in "triangles", then use a sweep mesh with 3 or more elements in the tickness. Now your short beams will take all the stress at their sharp corners, ideally you should have at least 3 elements acros the width of the beams. One way is to split them with a layer, or tu set up the "Size custom" Resolution of narow regions = 3.5 or so, and check that the min, max sizeas are coherent -- Good luck Ivar
Sanjay Mukuntha Madhava
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Posted: 1 decade ago 21 feb 2012, 08:18 GMT-5
Thanks for your reply but Can you please elaborate your solution further?
I get this error when i try to follow your instructions.

Regards
Sanjay
Thanks for your reply but Can you please elaborate your solution further? I get this error when i try to follow your instructions. Regards Sanjay

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Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 21 feb 2012, 08:30 GMT-5
Hi

are you sure you got all the top surfaces, also the small ones of the beams ?

--
Good luck
Ivar
Hi are you sure you got all the top surfaces, also the small ones of the beams ? -- Good luck Ivar
Sanjay Mukuntha Madhava
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Posted: 1 decade ago 21 feb 2012, 08:31 GMT-5
Yes i guess and also am new to this (was using the Quad for the entire geometry till now) and its not helping either .
Also can i run upto 4 Parametric sweeps at the sametime (width, length, stress and number of beams in this case)

Thanks and Regards
Sanjay
Yes i guess and also am new to this (was using the Quad for the entire geometry till now) and its not helping either . Also can i run upto 4 Parametric sweeps at the sametime (width, length, stress and number of beams in this case) Thanks and Regards Sanjay
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 21 feb 2012, 09:39 GMT-5
Hi
Another point I did not catch was your initial stress value, how are you sure about the stress tensor ?

Have you though about modelling only a section using symmetry ?

Anyhow, snall beams like that have high stress concetration at the sharp corners => needs small mesh => require time to solve, so spending a little time to reduce the model complexity can globally gain a lot of time ;)

--
Good luck
Ivar
Hi Another point I did not catch was your initial stress value, how are you sure about the stress tensor ? Have you though about modelling only a section using symmetry ? Anyhow, snall beams like that have high stress concetration at the sharp corners => needs small mesh => require time to solve, so spending a little time to reduce the model complexity can globally gain a lot of time ;) -- Good luck Ivar
Sanjay Mukuntha Madhava
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Posted: 1 decade ago 21 feb 2012, 09:44 GMT-5
The stress is between -100 MPa to + 100 MPa, later i'd have to expand it to 1 GPa .
I wasnt aware that only a section can be modelled. And are there any tutorials for the same.
And finally are there any study material for Meshing that you would recommend :)

Thanks and Regards
Sanjay
The stress is between -100 MPa to + 100 MPa, later i'd have to expand it to 1 GPa . I wasnt aware that only a section can be modelled. And are there any tutorials for the same. And finally are there any study material for Meshing that you would recommend :) Thanks and Regards Sanjay
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 21 feb 2012, 11:06 GMT-5
Hi

I'm not aware of anything special apart testing out the model library examples and learn from there. Otherwise COMSOL organises regularly some excellent courses, also on advanced meshing

But check out your initial stress description, and test out if there is not a more relaistic way to introduce your stress than "just" play with a few diagonal tensor elements, specially since Si is normally crystal rahter anisotropic !

--
Good luck
Ivar
Hi I'm not aware of anything special apart testing out the model library examples and learn from there. Otherwise COMSOL organises regularly some excellent courses, also on advanced meshing But check out your initial stress description, and test out if there is not a more relaistic way to introduce your stress than "just" play with a few diagonal tensor elements, specially since Si is normally crystal rahter anisotropic ! -- Good luck Ivar

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