Menu

Discussion Forum

New Discussion
Filtra

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 The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Time dependent boundary

Posted 24 giu 2013, 10:36 GMT-4 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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

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 2 lug 2013, 03:31 GMT-4
Barend
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 24 giu 2013, 11:07 GMT-4
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 24 giu 2013, 11:18 GMT-4
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 24 giu 2013, 11:24 GMT-4
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 24 giu 2013, 11:36 GMT-4

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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 24 giu 2013, 12:08 GMT-4
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 24 giu 2013, 12:26 GMT-4
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 24 giu 2013, 12:32 GMT-4
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 24 giu 2013, 12:44 GMT-4
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 24 giu 2013, 13:16 GMT-4
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 2 lug 2013, 03:31 GMT-4
hi, just want to know how to add this kind of inlet
hi, just want to know how to add this kind of inlet

Attachments:

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content