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steady state for a standing ultrasonic wave

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Old   March 2, 2014, 03:13
Default steady state for a standing ultrasonic wave
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I intend to simulate an ultrasonic standing wave by using an pressure inlet with a reflector. The pressure inlet is supposed to oscillate sinusoidal to generate the wave. Now the question: Is it possible to generate the steady state by using a .ttab profile while the time step size is much larger than the profile step sizes?
Do I need to calculate in the same time step size as the profile step size is?
What could be the alternative to simualte this if Iīm only interested in the steady state and therefore donīt want to calculate in the transient mode?

Thanks a lot!
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Old   November 25, 2015, 11:58
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Hello flueth,
have you been able to generate te ultrasonic wave? am actually facing similar problem : i want to simulate the ultrasonic field generated by 2 transducers mounted on a pipe with streaming water.
please see attached.. i would be thankful for help
WP_20151125_16_48_48_Pro.jpg





Last edited by houss; November 25, 2015 at 12:00. Reason: bad url
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Old   November 27, 2015, 09:14
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I don't know if this can be simulated in steady state: from my point of view, no, because in a standing wave, waves continuously interact..If you look at the transducer it will never reach a steady state, as it continues to oscillate.
I simulated in the past simple ultasonic waves in water, in 2d and 3d, with the approach of a udf, compiled with the DEFINE_GRID_MOTION macro: this means you must know the displacement that your transducer produces.
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Old   November 27, 2015, 09:48
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Quote:
Originally Posted by ghost82 View Post
I don't know if this can be simulated in steady state: from my point of view, no, because in the ultrasonic wave the high pressure zones are replaced by low pressure, and then by high pressure again, and so on, so the steady state can't exist..
What is called "steady state" is reached after few periods, so this is not computationally expensive.
I simulated in the past simple ultasonic waves in water, in 2d and 3d, with the approach of a udf, compiled with the DEFINE_GRID_MOTION macro: this means you must know the displacement that your transducer produces.
Thanks for your reply ghost82
what is udf?
i am actually intending to set up the simulation for openfoam. All i know about the transducer is that the emitted wave frequency is about 1MHz and some other information related to emitted longitudinal and transversal waves.
Do you mean with Displacement the wave height on a free surface of water?

Best regards
Houssam.
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Old   November 27, 2015, 10:05
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I mean the dispacement of the tip of the transducer or of the plate.
I was inspired by this article (from page 5 of the pdf):
http://www2.arnes.si/~mdula/Numerica...ic%20field.pdf

Maybe it can help.
Udf is a user define function, to expand the capabilities of fluent.
Maybe you can look at the openfoam section of this forum.
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Old   November 27, 2015, 11:10
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ah ok. My plan was to define a sinusoidal pressure BC at the tranducer location. You are right it seems to make more sense to rather define a periodic displacement somehow.. the journal's paper seems to be interesting. I have also to take the generated acoustic cavitation into account because it will affect the fluid proporties (density, viscosity) and hence the wave propagation velocity ..
have you used a dynamic mesh for your simulations?
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Old   November 27, 2015, 11:15
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Yes, the DEFINE_GRID_MOTION" defines o moving/deforming mesh.
I also included liquid compressiblity, by including an udf for density and speed of sound.
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Old   November 27, 2015, 11:26
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sounds good.
Surely i have also to define appropriate functions in OpenFoam. Unfortunately there are here no threads discussing the issue for openfoam. I would be very thankful if i could have a look into your udf ghost82
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