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Problem trying to pulse heat source

Posted Jan 31, 2011, 5:08 a.m. EST Heat Transfer & Phase Change, Materials Version 3.5a, Version 4.0a 5 Replies

Adam Collins
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Hi,

I am trying to model laser heating of a block.
As a rough model I have a 3D block with a cylinder embedded in it.
I am then applying a heat flux to one of the circular faces of the cylinder to repersent the laser spot.

I wish to pulse the laser spot and so I have defined a pulse train expression using the heaviside function:
(flc2hs(mod(t,0.01)-1,1)-flc2hs(mod(t,0.01)-3,1)

I then multiply this step function by a large heat flux on the appropriate boundary.

However when I solve the boundary stays at the same temperature.

Any help would be greatly appreciated.
5 Replies Last Post Aug 2, 2011, 5:53 p.m. EDT
Kai Herbrig
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Posted: 1 decade ago Jan 31, 2011, 8:28 a.m. EST
Hi,

have you tried to analyse the "laser heatflux" in postprocessing mode? What about the solver options: do the time stepping options fit to the pulse frequency?

At least, you pulse function looks like a sharp saw - only one side is smooth. Not recommendable for numerical analysis ...
Hi, have you tried to analyse the "laser heatflux" in postprocessing mode? What about the solver options: do the time stepping options fit to the pulse frequency? At least, you pulse function looks like a sharp saw - only one side is smooth. Not recommendable for numerical analysis ...
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 31, 2011, 8:31 a.m. EST
Hi

have you tried to plot that function ?

first there is a closing bracket ")" missing at the end, second it's a sawtooth when I try to plot it, the function is with a lot of discontinuities !!

The solver gets crazy on such functions. the Heaviside functions are there to "smoothen". So why not try a 0.5*(1-cos(2*pi*f*t)) then ?

And do not forget to set the solver stepping to intermediate, or strict, and to define sufficient points per period to resolve the sinus or your general periodicity

So I see I'm not alone here, I believe you have missed something in the periodicity of your function, it requires a little more tweaking
--
Good luck
Ivar
Hi have you tried to plot that function ? first there is a closing bracket ")" missing at the end, second it's a sawtooth when I try to plot it, the function is with a lot of discontinuities !! The solver gets crazy on such functions. the Heaviside functions are there to "smoothen". So why not try a 0.5*(1-cos(2*pi*f*t)) then ? And do not forget to set the solver stepping to intermediate, or strict, and to define sufficient points per period to resolve the sinus or your general periodicity So I see I'm not alone here, I believe you have missed something in the periodicity of your function, it requires a little more tweaking -- Good luck Ivar
Adam Collins
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Posted: 1 decade ago Jan 31, 2011, 10:21 a.m. EST
Thank you for your prompt replies the function is now working correctly.
It seems the error was in the discontinuities of my earlier function.

I would be lost without your help!
Thanks again.
Thank you for your prompt replies the function is now working correctly. It seems the error was in the discontinuities of my earlier function. I would be lost without your help! Thanks again.
Xiangping Li
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Posted: 1 decade ago May 2, 2011, 10:28 p.m. EDT
I know this maybe an old topic for you. As I am new to Comsol, I have problems to simulate the temperature rising of the plasmonic structure during the laser illumination. Assuming the Electromagnetic wave plus the heat transfer will do the job. According to the suggestion from the Comsol support, one heat source was added using the total power loss of the electromagnetic wave. However, it doesn't work.
Apprecieate any of your suggestions.
I know this maybe an old topic for you. As I am new to Comsol, I have problems to simulate the temperature rising of the plasmonic structure during the laser illumination. Assuming the Electromagnetic wave plus the heat transfer will do the job. According to the suggestion from the Comsol support, one heat source was added using the total power loss of the electromagnetic wave. However, it doesn't work. Apprecieate any of your suggestions.
Sajjadi Amir
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Posted: 1 decade ago Aug 2, 2011, 5:53 p.m. EDT
I am trying to model the pulse laser train. I am using flc2hs((mode(t.0.2)-0),1)-flch2hs((mod(t,0.2)-2e-12),1).
I multiply this by intensity to get the pulse train.
For some reason the COMSOL hangs when I am trying to run the program.

Can you help me to figure out the problem?

Thanks,
Amir
I am trying to model the pulse laser train. I am using flc2hs((mode(t.0.2)-0),1)-flch2hs((mod(t,0.2)-2e-12),1). I multiply this by intensity to get the pulse train. For some reason the COMSOL hangs when I am trying to run the program. Can you help me to figure out the problem? Thanks, Amir

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