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Unknown 'lm' variables with Diode Example using COMSOL 4.2

Posted Jul 18, 2011, 4:48 p.m. EDT Version 4.3b 6 Replies

Mohammad Amin Baghban
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I am attempting to replicate the Semiconductor Diode 4.1 Model file found at this address:

www.comsol.com/showroom/documentation/model/114/

by starting from a new COMSOL file and essentially applying the Physics, Geometry, Definitions, etc. from the example to my new COMSOL file. All I have to work with is this model file and whatever I can garner from the 3.5 tutorial. I have successfully duplicated nearly all of the components of this model with a few crucial exceptions:

The mesh I have generated does not look like the one in the example and does not seem to be affected by the contact points of the diode.
COMSOL is not recognizing my Lagrange Multiplier variables 'cn_lm' and 'cp_ln' in my file while it recognizes them in the model file even though the expression declarations are identical. I suspect this issue has a lot to do with why I'm not getting a proper mesh.
I'm wondering whether my issues have to do with the fact that I found no way to ensure that 'Lagrange - Quadratic' is selected from what the 3.5 tutorial labels the Element list and that I could not deduce how to ensure that I was using Conservative equations with Weak Constraints On.

Earlier, I successfully followed the COMSOL 3.5 step-by-step guide to create the model in the older version of the software, but being able to learn how to generate similar models in COMSOL 4.0 could prove more valuable to our research group.

Any help is appreciated in understanding why this isn't working.
6 Replies Last Post Sep 27, 2013, 2:02 a.m. EDT
Mohammad Amin Baghban
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Posted: 1 decade ago Jul 21, 2011, 11:28 a.m. EDT
It seems that I need to be checking the "Weak Constraints" checkbox under the Convection and Diffusion Node, but I can't seem to find this checkbox! Can anyone give specific directions to this box on 4.2?
It seems that I need to be checking the "Weak Constraints" checkbox under the Convection and Diffusion Node, but I can't seem to find this checkbox! Can anyone give specific directions to this box on 4.2?
Daniel Prestin
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Posted: 1 decade ago Jul 22, 2011, 3:01 a.m. EDT
You find the checkbox "Weak Constraints" if you rightclick on Convection-Diffusion-Equation and go to "More". ;-)
Hope this will solve your problem!
You find the checkbox "Weak Constraints" if you rightclick on Convection-Diffusion-Equation and go to "More". ;-) Hope this will solve your problem!
Mohamad Hamady
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Posted: 1 decade ago Oct 6, 2011, 7:44 p.m. EDT
knowing that the file of the diode of the version 4.1 can be opened by the new version 4.2,
were you able to re-built this diode using the new version 4.2 if you follow the same procedures?
Explain please more where I can find the checkbox "Weak Constraints"
thx

knowing that the file of the diode of the version 4.1 can be opened by the new version 4.2, were you able to re-built this diode using the new version 4.2 if you follow the same procedures? Explain please more where I can find the checkbox "Weak Constraints" thx
Daniel Prestin
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Posted: 1 decade ago Oct 7, 2011, 2:42 a.m. EDT
I had not the time to rebuild the model, I just know how to find the checkbox. First you have to add the correct physics. Go to Mathematics -> Classical PDEs -> Convection-Diffusion Equation (cdeq).
Then rightclick on Convection-Diffusion-Equation and go to "More". Here you find the "Weak Constraints".
I had not the time to rebuild the model, I just know how to find the checkbox. First you have to add the correct physics. Go to Mathematics -> Classical PDEs -> Convection-Diffusion Equation (cdeq). Then rightclick on Convection-Diffusion-Equation and go to "More". Here you find the "Weak Constraints".
Xiaotie Wu
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Posted: 1 decade ago Dec 7, 2012, 10:41 p.m. EST
I am having exactly the same issue. The Convection-Diffusion Equation used in the diode model is not from Mathematics -> Classical PDEs. It is from Chemical Species Transport -> Transport of Diluted Species (chds). There is no "More" menu for the latter.

Hi Mohammad,
Do you finally figure out how to solve this?
I am having exactly the same issue. The Convection-Diffusion Equation used in the diode model is not from Mathematics -> Classical PDEs. It is from Chemical Species Transport -> Transport of Diluted Species (chds). There is no "More" menu for the latter. Hi Mohammad, Do you finally figure out how to solve this?
Mohammad Ali Mohammadzadeh Kashan
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Posted: 1 decade ago Sep 27, 2013, 2:02 a.m. EDT
Hi Xiaotie Wu
Im trying to regenerate the diode simulation using comsol 4.3b. But im facing problems to plot the IV characteristics plot. I appreciate if you help me to obtain it.

Cheers
Hi Xiaotie Wu Im trying to regenerate the diode simulation using comsol 4.3b. But im facing problems to plot the IV characteristics plot. I appreciate if you help me to obtain it. Cheers

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