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Time simulation with limited number of periods

Posted Jun 8, 2017, 8:00 a.m. EDT 5 Replies

Thibaut Meurisse
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Hi Everyone,

I am trying to simulate a simple system - a piezoelectric disc vibrating in air, with a reflecting surface. My aim is to observe the reflection of the sound waves when they are back to the disc. Problem, I want to send only 2 periods of signal (sine or square signal), but when I use the Functions in Comsol, I find no way to stop it.

Then, my question is probably basic, but I did not find it on the Internet for the while : how to implement a limited time signal in Comsol (that is, the simulation continues to run when the signal ends) ? I use Comsol 5.2 (the message editor does not allow me to put version and recommended topics...).

Thanks,
Thibaut

5 Replies Last Post Jul 6, 2017, 10:34 a.m. EDT
Edgar J. Kaiser Certified Consultant
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Posted: 7 years ago Jun 8, 2017, 10:57 a.m. EDT

One option: f(t) = sin(omega*t)*(t<t0)

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
One option: f(t) = sin(omega*t)*(t
Thibaut Meurisse
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Posted: 7 years ago Jun 8, 2017, 11:10 a.m. EDT
This was that simple !

And it seems to work, thank you very much Edgar !

Thibaut
This was that simple ! And it seems to work, thank you very much Edgar ! Thibaut
Thibaut Meurisse
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Posted: 7 years ago Jun 12, 2017, 8:01 a.m. EDT
Hi,

I have finally another problem, probably due to piezoelectric materials, but maybe to COMSOL itself.

Using Edgar's Suggestion, the voltage excitation stops after t0, but the disc keeps vibrating. I first thought this was free vibrations due to relaxation, and to the fact I initially did not put any losses. But these vibrations are still here with 100% of mechanical losses, and the same with adding dielectric or coupling losses.

Note that these free vibrations have about the same amplitude than with excitation.

Does anyone know why I obtain such a behavior ? The bottom boundary of the disc is a roller.

Thanks,
Thibaut
Hi, I have finally another problem, probably due to piezoelectric materials, but maybe to COMSOL itself. Using Edgar's Suggestion, the voltage excitation stops after t0, but the disc keeps vibrating. I first thought this was free vibrations due to relaxation, and to the fact I initially did not put any losses. But these vibrations are still here with 100% of mechanical losses, and the same with adding dielectric or coupling losses. Note that these free vibrations have about the same amplitude than with excitation. Does anyone know why I obtain such a behavior ? The bottom boundary of the disc is a roller. Thanks, Thibaut
Thibaut Meurisse
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Posted: 7 years ago Jun 13, 2017, 6:08 a.m. EDT
I may have found a solution, using a Gaussian function to smooth the start and stop of the signal.

I have some good results with a sine signal (the free vibrations are about 100 times lower in amplitude than those obtained with excitation), but this does not work with a square signal.

Does anyone know if there is a way to force the system not to move after a certain time ?

Thanks,
Thibaut
I may have found a solution, using a Gaussian function to smooth the start and stop of the signal. I have some good results with a sine signal (the free vibrations are about 100 times lower in amplitude than those obtained with excitation), but this does not work with a square signal. Does anyone know if there is a way to force the system not to move after a certain time ? Thanks, Thibaut
Thibaut Meurisse
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Posted: 7 years ago Jul 6, 2017, 10:34 a.m. EDT
It seems that using "Quasi-static", under "Structural Transient Behavior" for "Solid Mechanics" makes it ok.
It seems that using "Quasi-static", under "Structural Transient Behavior" for "Solid Mechanics" makes it ok.

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