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periodic inlet condition

Posted Dec 12, 2011, 12:55 a.m. EST Version 4.2 3 Replies

Kumar
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Hi,

I am using the Transport of Diluted Species module (2D) and I want to apply a periodic square wave input for concentration.

My geometry is a simple rectangle and the left side of the rectangle is the inlet.

How do I use the 'rectangle' input for the inlet?

Is there any other way to specify a square wave as the inlet condition for species concentration?




3 Replies Last Post Dec 13, 2011, 1:23 a.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 12, 2011, 1:48 a.m. EST
Hi

have you tried the "waveform" functions in V4 ? these should do. They do also include a smoothing region to remain continuous, but they do not include any "offset", so you must combine them then with a other analytical function

--
Good luck
Ivar
Hi have you tried the "waveform" functions in V4 ? these should do. They do also include a smoothing region to remain continuous, but they do not include any "offset", so you must combine them then with a other analytical function -- Good luck Ivar
Kumar
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Posted: 1 decade ago Dec 12, 2011, 3:46 p.m. EST
Hi Ivar,

Thanks for your reply.

I tried using the waveform function. It appears to be what I am looking for.

But how do I apply such a waveform to the inlet as a periodic condition for concentration of species?

I also did not understand what you meant by combining the waveform with another analytic function
Hi Ivar, Thanks for your reply. I tried using the waveform function. It appears to be what I am looking for. But how do I apply such a waveform to the inlet as a periodic condition for concentration of species? I also did not understand what you meant by combining the waveform with another analytic function
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 13, 2011, 1:23 a.m. EST
Hi

the waveform is defined symmetric around "0" if you need to offset it, you might by calling it from another analytical function.

To use that in a BC definition you "simply" call the function depending on your time variable "t" i.e. wv1(t[1/s]) where the [1/s] is to make "t" without units and expressed in seconds (you might want to use "min" or "h" or "d" or "a" or "y" for minutes, hours, days or years/années instead of "s" for seconds"

This supposes that you use a time dependent solver.

Note: if for any reason you use a stationary solver to get the initial conditions, then the "t" will NOT be defined by default so your BC relying on "t" will be flagged ERROR. Try then to define a Parameter t = 0[s] this will solve the issue for the stationary solver, and the variable will be overwritten by the time dependent solver correctly

--
Good luck
Ivar
Hi the waveform is defined symmetric around "0" if you need to offset it, you might by calling it from another analytical function. To use that in a BC definition you "simply" call the function depending on your time variable "t" i.e. wv1(t[1/s]) where the [1/s] is to make "t" without units and expressed in seconds (you might want to use "min" or "h" or "d" or "a" or "y" for minutes, hours, days or years/années instead of "s" for seconds" This supposes that you use a time dependent solver. Note: if for any reason you use a stationary solver to get the initial conditions, then the "t" will NOT be defined by default so your BC relying on "t" will be flagged ERROR. Try then to define a Parameter t = 0[s] this will solve the issue for the stationary solver, and the variable will be overwritten by the time dependent solver correctly -- Good luck Ivar

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