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No solution near boundary

Posted 19 oct. 2010, 11:17 UTC−4 11 Replies

Dan Peters
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I'm using the PDE coefficient form equation to model a diffusion equation. COMSOL will not give a solution up to and including the boundary. I'm using a Dirichlet Boundary Condition with the concentration set to 0 to simulate a perfect absorbing boundary. Any ideas on what I'm doing wrong?

Attached is a screen shot. I would attach my model but it's 80MB for some strange reason.

Thanks!
Dan

Attachments:

11 Replies Last Post 22 oct. 2010, 15:49 UTC−4
Özen Özdemir
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Posted: 1 decade ago 19 oct. 2010, 12:03 UTC−4
First of all, your file is 80 MB because it includes the solution. You can upload your model file without running the analysis (just the model setup). So that it will be small and you can upload here.

About your question, it looks like a postprocessing error.

It would be better to see the model file.

Regards,

Özen
First of all, your file is 80 MB because it includes the solution. You can upload your model file without running the analysis (just the model setup). So that it will be small and you can upload here. About your question, it looks like a postprocessing error. It would be better to see the model file. Regards, Özen
Dan Peters
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Posted: 1 decade ago 19 oct. 2010, 16:43 UTC−4
I deleted the solution and all the plots and got down to the 80MB. I don't see any option of just saving the model geometry and equations.
I deleted the solution and all the plots and got down to the 80MB. I don't see any option of just saving the model geometry and equations.
Danial Tz
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Posted: 1 decade ago 19 oct. 2010, 17:30 UTC−4

I deleted the solution and all the plots and got down to the 80MB. I don't see any option of just saving the model geometry and equations.


You probably still have some solutions in study1 or study2. Right click on each solver sequence and clear the solution. If you have some very fine mesh it also holds space. You model should come around 10mb or so.


--
Comsol 4.0a
Ubuntu 10.04.1
[QUOTE] I deleted the solution and all the plots and got down to the 80MB. I don't see any option of just saving the model geometry and equations. [/QUOTE] You probably still have some solutions in study1 or study2. Right click on each solver sequence and clear the solution. If you have some very fine mesh it also holds space. You model should come around 10mb or so. -- Comsol 4.0a Ubuntu 10.04.1
Dan Peters
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Posted: 1 decade ago 19 oct. 2010, 18:02 UTC−4
I deleted the Solver and it did decrease the size of the file. I thought all the solution results would be stored under "Solution" and not "Solver".

Thanks and attached is the file.
I deleted the Solver and it did decrease the size of the file. I thought all the solution results would be stored under "Solution" and not "Solver". Thanks and attached is the file.

Attachments:

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 20 oct. 2010, 02:03 UTC−4
Hi

in the newer versions you also have the :
"File - Reset history",
"File - Clear Meshes" and
"File - Clear Ssolutions"

to reset nicely the model and to make the file size manageable / exchangeable

--
Good luck
Ivar
Hi in the newer versions you also have the : "File - Reset history", "File - Clear Meshes" and "File - Clear Ssolutions" to reset nicely the model and to make the file size manageable / exchangeable -- Good luck Ivar
Özen Özdemir
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Posted: 1 decade ago 20 oct. 2010, 03:55 UTC−4
Hi Dan,

do you use COMSOL 4.0 ?
Hi Dan, do you use COMSOL 4.0 ?
Magnus Ringh COMSOL Employee

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Posted: 1 decade ago 20 oct. 2010, 05:08 UTC−4
Hi,

There is no valid value to plot near the boundary because you are plotting log(u) where u is equal or close to zero, and log(0) is undefined. Try plotting log(u+eps), for example, where eps is a small number representing the machine precision. In COMSOL Multiphysics the plot is empty where the data is undefined or "not-a-number."

Best regards,
Magnus Ringh, COMSOL
Hi, There is no valid value to plot near the boundary because you are plotting log(u) where u is equal or close to zero, and log(0) is undefined. Try plotting log(u+eps), for example, where eps is a small number representing the machine precision. In COMSOL Multiphysics the plot is empty where the data is undefined or "not-a-number." Best regards, Magnus Ringh, COMSOL
Dan Peters
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Posted: 1 decade ago 21 oct. 2010, 13:03 UTC−4
Thanks for the reply. In the surface plot I plotted log(u), but I was trying to integrate the flux across the boundary and it's zero which it shouldn't be.

I am using 4.0a.

Dan
Thanks for the reply. In the surface plot I plotted log(u), but I was trying to integrate the flux across the boundary and it's zero which it shouldn't be. I am using 4.0a. Dan
Dan Peters
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Posted: 1 decade ago 21 oct. 2010, 13:48 UTC−4
Just realized that I should probably integrate the concentration slightly inside the boundary since I made it a perfect absorber.

Just realized that I should probably integrate the concentration slightly inside the boundary since I made it a perfect absorber.
Dan Peters
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Posted: 1 decade ago 22 oct. 2010, 13:32 UTC−4
My 4.0a doesn't have "clear solutions" nor "clear meshes" does have reset history.

My 4.0a doesn't have "clear solutions" nor "clear meshes" does have reset history.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 22 oct. 2010, 15:49 UTC−4
Hi

correct its in 4.1, but you can clear (not delete) the solution individually per solver node, and you can clear the mesh by selectng the first "size" and do a "build to here" in V4.0a this reduces nicely the file size

--
Good luck
Ivar
Hi correct its in 4.1, but you can clear (not delete) the solution individually per solver node, and you can clear the mesh by selectng the first "size" and do a "build to here" in V4.0a this reduces nicely the file size -- Good luck Ivar

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