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Frequency Domain Analysis of a Heat Transfer System

Posted Sep 19, 2011, 4:16 a.m. EDT Heat Transfer & Phase Change Version 4.2 3 Replies

Jochen Zöllin
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Hello,
I am trying to determine the frequency response of a 2D heat transfer system to a harmonic heat source, but I can't seem to get the frequency domain study working with heat transfer physics.

My model so far is attached below. I have the geometry, materials, and physics set up and I have included the heat source to be varied harmonically. However, when I run the solver, only the initial conditions get returned and the solver reports solving for 0 degrees of freedom.

I am thinking this might be because the source term in the heat transfer equation is static, and does not vary harmonically. If this is the case, does anyone know how I can force this term to vary harmonically?

Otherwise, does anyone know how I should proceed?

Thanks for your time.

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3 Replies Last Post Sep 19, 2011, 9:32 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Sep 19, 2011, 5:45 a.m. EDT
Hi

but the thermal eqautions are not really that often developped as harmonic functions, so there could well be that the equations have not been written out in "harmonic form" (I do not have direct access t COMSOL just now, so I cannot check).

You can either use the time solver to see the time evolution, or if you are interested in the amplitudes, then you give a rms power level and you will get the stead sate rms values out. It all depends on the time constant of your model w.r.t your frequency.

Anyhow you do not get "waves" from the diffusion equations, as for the Maxwell equations

--
Good luck
Ivar
Hi but the thermal eqautions are not really that often developped as harmonic functions, so there could well be that the equations have not been written out in "harmonic form" (I do not have direct access t COMSOL just now, so I cannot check). You can either use the time solver to see the time evolution, or if you are interested in the amplitudes, then you give a rms power level and you will get the stead sate rms values out. It all depends on the time constant of your model w.r.t your frequency. Anyhow you do not get "waves" from the diffusion equations, as for the Maxwell equations -- Good luck Ivar
Jochen Zöllin
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Posted: 1 decade ago Sep 19, 2011, 7:58 a.m. EDT
Thanks for your reply,

I am using the heat transfer model as an analogy for squeeze-film damping in micro-structures (pressure = temperature, plate normal velocity = heat source). I would like to extract the damping pressure and squeeze-stiffness pressure, (real temperature and imaginary temperature in the heat transfer analogy), at various frequencies.

I can do this using a time response analysis, but it requires much more solver time than I would like, as it takes a while for the transients to die out. As for using a power-based approach, I don't think I will be able to separate the real and imaginary responses.

A harmonic analysis, therefore, would be ideal. Is there no way that I can make it work?

Cheers,
Jochen
Thanks for your reply, I am using the heat transfer model as an analogy for squeeze-film damping in micro-structures (pressure = temperature, plate normal velocity = heat source). I would like to extract the damping pressure and squeeze-stiffness pressure, (real temperature and imaginary temperature in the heat transfer analogy), at various frequencies. I can do this using a time response analysis, but it requires much more solver time than I would like, as it takes a while for the transients to die out. As for using a power-based approach, I don't think I will be able to separate the real and imaginary responses. A harmonic analysis, therefore, would be ideal. Is there no way that I can make it work? Cheers, Jochen
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Sep 19, 2011, 9:32 a.m. EDT
Hi

you would need to rewrite the equations I believe using the math PDE and creating a harmonic development of the math diffusion equations,
Not sure where to start as I have become lazy with the latest COMSOL versions and manange to use the predefined physics for all my problems ;)

--
Good luck
Ivar
Hi you would need to rewrite the equations I believe using the math PDE and creating a harmonic development of the math diffusion equations, Not sure where to start as I have become lazy with the latest COMSOL versions and manange to use the predefined physics for all my problems ;) -- Good luck Ivar

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