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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Time dependent boundary

Posted 2013年6月24日 GMT-4 10:36 Fluid & Heat, Computational Fluid Dynamics (CFD), Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.3, Version 4.3a, Version 4.3b 10 Replies

Jonathan Erbelding
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Hi all,
I have flow through a cylinder, and want the inlet velocity to be periodic [ u(r,t) ]. Im new to comsol and havent been able to find an answer to this.

Thanks in advance for any help!.
10 Replies Last Post 2013年7月2日 GMT-4 03:31
Barend
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Posted: 1 decade ago 2013年6月24日 GMT-4 11:07
Hi Jonathan,

I use the analytic function under definitions for that.
I needed a pulse and solve it with a rectangle (rect1) under definitions and an analytic function:

Analytic function name: an1
Expression: mod1.rect1(mod(t,period1))
argument: t
and fill in at your inlet velocity: "value" *an1(t[1/s])
I hope this will help you.

Good luck,

--
Barend
Hi Jonathan, I use the analytic function under definitions for that. I needed a pulse and solve it with a rectangle (rect1) under definitions and an analytic function: Analytic function name: an1 Expression: mod1.rect1(mod(t,period1)) argument: t and fill in at your inlet velocity: "value" *an1(t[1/s]) I hope this will help you. Good luck, -- Barend
Jonathan Erbelding
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Posted: 1 decade ago 2013年6月24日 GMT-4 11:18
Thanks for your response.

One question, where do you define the "period1" variable?
Thanks for your response. One question, where do you define the "period1" variable?
Barend
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Posted: 1 decade ago 2013年6月24日 GMT-4 11:24
you are welcome,
I define it in the parameters under Global definitions, but you can also fill in the value of your period instead of periond1.

--
Barend
you are welcome, I define it in the parameters under Global definitions, but you can also fill in the value of your period instead of periond1. -- Barend
Jonathan Erbelding
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Posted: 1 decade ago 2013年6月24日 GMT-4 11:36

Ok, so I defined the parameters, Amp and period1 in the parameters menu. When I try to plot the an1, it gives me an error "unknown function or operator" mod1.rect1.

I attached a picture of the error if you want to take a look.

Thanks again for helping!

Ok, so I defined the parameters, Amp and period1 in the parameters menu. When I try to plot the an1, it gives me an error "unknown function or operator" mod1.rect1. I attached a picture of the error if you want to take a look. Thanks again for helping!

Attachments:

Barend
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Posted: 1 decade ago 2013年6月24日 GMT-4 12:08
Sorry, that is because I had an rectangle function that was named rect1 in my model 1 (mod1), if you dont have a rectangle function you can loose that term.
Hope that it will work now.

--
Barend
Sorry, that is because I had an rectangle function that was named rect1 in my model 1 (mod1), if you dont have a rectangle function you can loose that term. Hope that it will work now. -- Barend
Barend
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Posted: 1 decade ago 2013年6月24日 GMT-4 12:26
What kind of function do you want for your velocity input?
That you velocity have a particular value of t=1 till t=3 in a period and for the rest the inlet velocity is 0.
Or do you want a wavelike kind of inlet velocity?
That will make it perhaps easier to help you.

--
Barend
What kind of function do you want for your velocity input? That you velocity have a particular value of t=1 till t=3 in a period and for the rest the inlet velocity is 0. Or do you want a wavelike kind of inlet velocity? That will make it perhaps easier to help you. -- Barend
Jonathan Erbelding
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Posted: 1 decade ago 2013年6月24日 GMT-4 12:32
Wavelike would be exactly what im trying to do. Essentially imagine a membrane covering one end of the channel, and it oscillates. That's what im trying to model

Wavelike would be exactly what im trying to do. Essentially imagine a membrane covering one end of the channel, and it oscillates. That's what im trying to model
Barend
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Posted: 1 decade ago 2013年6月24日 GMT-4 12:44
Try the Waveform as a function under Definitions. I think that will do the trick

--
Barend
Try the Waveform as a function under Definitions. I think that will do the trick -- Barend
Jonathan Erbelding
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Posted: 1 decade ago 2013年6月24日 GMT-4 13:16
I'll try the waveform function. Thanks so much for your help!

-Jon
I'll try the waveform function. Thanks so much for your help! -Jon
Nur Sharif
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Posted: 1 decade ago 2013年7月2日 GMT-4 03:31
hi, just want to know how to add this kind of inlet
hi, just want to know how to add this kind of inlet

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