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Non-Isothermal Flow, initial values and bias: am I doing something wrong?
Posted 2 feb 2012, 03:56 GMT-5 Heat Transfer & Phase Change, Computational Fluid Dynamics (CFD), Studies & Solvers Version 4.2 1 Reply
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Good morning!
I'm simulating a water-cooling device for a heated cylinder and I'm testing different geometries.
The standard geometry would be a heated cylinder cooled on the sides by a water film (-> I'm using the physics "Non-Isothermal Flow").
I'm now trying to test cylinders of different thicknesses; however, the computation will not converge if I don't impose proper Initial Values.
I've then tried to start from a simple (thick enough) geometry (that converges quite easily) and slowly decrease the thickness of my cylinder. I have created two different studies and I feed one study with the Solution of the other (in order to have the Initial Values reasonably close to the final solution), once I've slightly changed my geometry.
It seems to be working (almost) well. But my question now is: am I doing the right thing? Will COMSOL give me the right solution or by doing this "loop" (Study 1 - Study 2 - Study 1) I'm introducing some "bias" (i.e. I'm forcing a solution in one direction)?
Thanks a lot for your help!!!
Best wishes,
/Andrea
I'm simulating a water-cooling device for a heated cylinder and I'm testing different geometries.
The standard geometry would be a heated cylinder cooled on the sides by a water film (-> I'm using the physics "Non-Isothermal Flow").
I'm now trying to test cylinders of different thicknesses; however, the computation will not converge if I don't impose proper Initial Values.
I've then tried to start from a simple (thick enough) geometry (that converges quite easily) and slowly decrease the thickness of my cylinder. I have created two different studies and I feed one study with the Solution of the other (in order to have the Initial Values reasonably close to the final solution), once I've slightly changed my geometry.
It seems to be working (almost) well. But my question now is: am I doing the right thing? Will COMSOL give me the right solution or by doing this "loop" (Study 1 - Study 2 - Study 1) I'm introducing some "bias" (i.e. I'm forcing a solution in one direction)?
Thanks a lot for your help!!!
Best wishes,
/Andrea
1 Reply Last Post 2 feb 2012, 04:06 GMT-5
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Posted:
1 decade ago
Hi
I believe there are different means to address your model, you have the DG to change geoemetry shape/scale for optimisation, that normally would allow you to stay within 1 study (I believe from what you tell)
One thing you need to really check in time domain is that your mesh and time stepping is correct, 90% of the COMSOL users I see here on the FORUM forget to look carefully a their material properties, and in particular the heat diffusivity versusus time steps. This is a subject described in "old books" on HT, I have notived it's often overlooked in the newer ones, and it becomes increasingly important for small scale devices as there the volume to surface ratio changes drastically, and our habits from larger HT problems, makes us fully fail for MEMS devices, if we do not adapt ;)
--
Good luck
Ivar
I believe there are different means to address your model, you have the DG to change geoemetry shape/scale for optimisation, that normally would allow you to stay within 1 study (I believe from what you tell)
One thing you need to really check in time domain is that your mesh and time stepping is correct, 90% of the COMSOL users I see here on the FORUM forget to look carefully a their material properties, and in particular the heat diffusivity versusus time steps. This is a subject described in "old books" on HT, I have notived it's often overlooked in the newer ones, and it becomes increasingly important for small scale devices as there the volume to surface ratio changes drastically, and our habits from larger HT problems, makes us fully fail for MEMS devices, if we do not adapt ;)
--
Good luck
Ivar