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How add a weak constraint to limit the displacement

Posted 26 sept. 2022, 23:55 UTC−4 MEMS & Piezoelectric Devices, Structural Mechanics Version 6.0 4 Replies

Tzu-huan Peng
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Hi I have a model that simulates an upward(+z) large pressure on the diaphragm. And want to set a limit on the amount of displacement "w" , such as 5[um], to imitate the diaphragm being confined by a housing. I'm thinking this should be possible using weak constraint.

Firstly, I try it only on the center point of the diaphragm. I use a "Point Probe" to acquire displacement "w" of the the center point with vaiable name "BP_center_w" . Then, add a point "Weak Inequality Constraint" and enter "comp1.BP_center_w - 5[um]" in the Constraint expression, 1e6 for spring contant of Penalty Method. This setting can work!

Next, I try to set the whole upper boundary of the diaphragm. So, with settings like: Use a "Boundary Probe" to acquire the max. displacement "w" of the whole upper boundary with vaiable name "BP_w" . Then, add a boundary "Weak Inequality Constraint" and enter "comp1.BP_w - 5[um]" in the Constraint expression, 1e6 for spring contant of Penalty Method. However, this setting doesn't work.

I don't understand why this happens. Do anyone can tell me how can I set it up to achieve my desired conditions?

Thanks.

4 Replies Last Post 27 sept. 2022, 21:43 UTC−4
Henrik Sönnerlind COMSOL Employee

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Posted: 2 years ago 27 sept. 2022, 02:28 UTC−4

Why not use the built-in contact functionality?

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Henrik Sönnerlind
COMSOL
Why not use the built-in contact functionality?
Tzu-huan Peng
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Posted: 2 years ago 27 sept. 2022, 05:12 UTC−4
Updated: 2 years ago 27 sept. 2022, 06:55 UTC−4

Henrik Sönnerlind, thanks for your reply. I have considered your suggestion. But, actually, I'm going to be simulating some acoustic properties later, I don't want to put any obstacleto to affect the passage of sound waves. Or, is it possible to set the acoustic properties of obstacles so that sound waves can easily pass through ?

Henrik Sönnerlind, thanks for your reply. I have considered your suggestion. But, actually, I'm going to be simulating some acoustic properties later, I don't want to put any obstacleto to affect the passage of sound waves. Or, is it possible to set the acoustic properties of obstacles so that sound waves can easily pass through ?
Henrik Sönnerlind COMSOL Employee

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Posted: 2 years ago 27 sept. 2022, 15:02 UTC−4

The obstacle can be a pure geometrical surface, where you can use acoustics domains on both sides.

However, if you want to pursue the weak inequality constraint path (which should also be possible), you need a weak inequality constraint over the boundary, which depends on the local difference between displacecement and stop location.

-------------------
Henrik Sönnerlind
COMSOL
The obstacle can be a pure geometrical surface, where you can use acoustics domains on both sides. However, if you want to pursue the weak inequality constraint path (which should also be possible), you need a weak inequality constraint over the boundary, which depends on the local difference between displacecement and stop location.
Tzu-huan Peng
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Posted: 2 years ago 27 sept. 2022, 21:43 UTC−4

Thanks for the suggestion, I will try the way with tjhe obstacle first.

Thanks for the suggestion, I will try the way with tjhe obstacle first.

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