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HELP: Which model should I take?

Posted 9 juin 2014, 08:56 UTC−4 MEMS & Nanotechnology, MEMS & Piezoelectric Devices Version 4.3b 8 Replies

Jianguo Feng
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Hi everyone,

I have been trying to simulate a system where an elastic membrane undergo different deformation with the change of pressure in the cavity.

There is a cylindrical cavity and the outlet is sealed by an elastic membrane. I use a vacuum pump to pump out the air at the inlet. Then the membrane will have a deformation. I want to simulate the deformation of the membrane. So which model should I take? And how do I set up?

Thanks for any suggestions!

Jianguo
8 Replies Last Post 10 juin 2014, 21:56 UTC−4
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago 9 juin 2014, 23:30 UTC−4
Dear Jianguo,

The Structural Mechanics “Module” as it has the FSI interface and also Membrane and Shell elements. The basic package has laminar CFD but if you want more advanced fluid flow capabilities you may also need the CFD Module.

Nagi Elabbasi
Veryst Engineering
Dear Jianguo, The Structural Mechanics “Module” as it has the FSI interface and also Membrane and Shell elements. The basic package has laminar CFD but if you want more advanced fluid flow capabilities you may also need the CFD Module. Nagi Elabbasi Veryst Engineering
Pieter Westerik
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Posted: 1 decade ago 10 juin 2014, 05:49 UTC−4
If the pressure change is slow relative to the lowest eigenfrequency of the membrane than you can do a steady state analysis and leave out the modelling of the cavity. Just take a 2d membrane and apply the desired pressure.
If the pressure change is slow relative to the lowest eigenfrequency of the membrane than you can do a steady state analysis and leave out the modelling of the cavity. Just take a 2d membrane and apply the desired pressure.
Jianguo Feng
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Posted: 1 decade ago 10 juin 2014, 08:13 UTC−4
Thank you, Nagi Elabbasi,

I will have a try.
Thank you, Nagi Elabbasi, I will have a try.
Jianguo Feng
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Posted: 1 decade ago 10 juin 2014, 09:00 UTC−4
Thank you ,Pieter Westerik,

I have already tried this model. However, there are some problems.
In reality, you know, the direction of pressure is always along the normal direction of membrane surface (normal force) with the deformation of the membrane.
However, if you apply pressure in the model, the pressure is just perpendicular to the initial position. That is to say, the direction of pressure is not change when the membrane undergo deformation. The result is the same to the situation that you apply fixed force. It is obviously wrong.

What do you think of this phenomenon?

Thank you ,Pieter Westerik, I have already tried this model. However, there are some problems. In reality, you know, the direction of pressure is always along the normal direction of membrane surface (normal force) with the deformation of the membrane. However, if you apply pressure in the model, the pressure is just perpendicular to the initial position. That is to say, the direction of pressure is not change when the membrane undergo deformation. The result is the same to the situation that you apply fixed force. It is obviously wrong. What do you think of this phenomenon?
Pieter Westerik
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Posted: 1 decade ago 10 juin 2014, 09:07 UTC−4
I believe you can also specify a pressure instead of a force distribution. But if the deflections are very small compared to the membrane diameter this will not make a big difference. If the deflections are larger you have to be carefull anyway because you will get many other non-linear effects as well.
I believe you can also specify a pressure instead of a force distribution. But if the deflections are very small compared to the membrane diameter this will not make a big difference. If the deflections are larger you have to be carefull anyway because you will get many other non-linear effects as well.
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago 10 juin 2014, 09:17 UTC−4
If you enable nonlinear geometry the pressure should stay normal to the deformed membrane surface. It will also change magnitude (and not just direction) if the membrane is significantly stretched. So basically that should not be a factor in deciding whether you solve an FSI problem or a structural problem only with a prescribed pressure.

Nagi Elabbasi
Veryst Engineering
If you enable nonlinear geometry the pressure should stay normal to the deformed membrane surface. It will also change magnitude (and not just direction) if the membrane is significantly stretched. So basically that should not be a factor in deciding whether you solve an FSI problem or a structural problem only with a prescribed pressure. Nagi Elabbasi Veryst Engineering
Jianguo Feng
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Posted: 1 decade ago 10 juin 2014, 20:24 UTC−4
Hi, Pieter Westerik,

You are right. As you said, the deflections are large, and the differences are not neglectful. The material of membrane is also non-linear. This is my further work. So only applying pressure may not be a appropriate method.

Hi, Pieter Westerik, You are right. As you said, the deflections are large, and the differences are not neglectful. The material of membrane is also non-linear. This is my further work. So only applying pressure may not be a appropriate method.
jianguo feng
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Posted: 1 decade ago 10 juin 2014, 21:56 UTC−4
Hi, Nagi Elabbasi,

I have tried FSI model. But there is a problem bothering me.
I apply the "Inlet". If the pressure is very small (just 0.009 psi), it will have a result. But if the pressure is a little bit large (0.01 psi), it will have an error. I also try the "Vacuum Pump", but it has the same problem.

Segregated group 2
Attempt to evaluate real square root of negative number.
-Function: sqrt
Failed to evaluate expression

Jianguo
Hi, Nagi Elabbasi, I have tried FSI model. But there is a problem bothering me. I apply the "Inlet". If the pressure is very small (just 0.009 psi), it will have a result. But if the pressure is a little bit large (0.01 psi), it will have an error. I also try the "Vacuum Pump", but it has the same problem. Segregated group 2 Attempt to evaluate real square root of negative number. -Function: sqrt Failed to evaluate expression Jianguo

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