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How to define a surface charge that depends on electrostatic potential (stationary solver)

Posted 21 oct. 2011, 15:08 UTC−4 Low-Frequency Electromagnetics, Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions, Studies & Solvers Version 4.2 2 Replies

George123
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Hi There,

I am using COMSOL 4.2 and I have a 1D electrostatic model. At one boundary, I have a simple fixed potential boundary condition, which is no problem to implement. At the other boundary, I would like to define a surface charge density that depends on the potential at that same boundary. For example, it would be similar to the following equation: Q[C/m^2] = Q_0*exp(-phi/E_A). I would then like the solver to calculate the appropriate value of phi (electric potential) at the boundary and elsewhere in the model, based on the constraint between phi and the surface charge defined at the boundary (which depends on phi).

Does anyone know how I can do this? It seems there should be an easy, straightforward way to define a self-referencing boundary condition.

Thanks in advance,

George
2 Replies Last Post 10 mai 2012, 05:01 UTC−4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 22 oct. 2011, 06:12 UTC−4
Hi

in the doc of 3.5 somewhere there was an example (or was it the Model library?) of a thermal case (rectangle) where one boundary was driven by an an equation based ont he integration of another boundary.

The way to mix new variables Global with weak constrains, integration coupling operators is very nice in COMSOL, but you need to train it a litle when you start ;). Try to sketch out on a peac of paper hwat you want to do, the variables linkled, the one missing, and I'm sure you'll find it out

--
Good luck
Ivar
Hi in the doc of 3.5 somewhere there was an example (or was it the Model library?) of a thermal case (rectangle) where one boundary was driven by an an equation based ont he integration of another boundary. The way to mix new variables Global with weak constrains, integration coupling operators is very nice in COMSOL, but you need to train it a litle when you start ;). Try to sketch out on a peac of paper hwat you want to do, the variables linkled, the one missing, and I'm sure you'll find it out -- Good luck Ivar
Peng Wang
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Posted: 1 decade ago 10 mai 2012, 05:01 UTC−4
How about your case, George?
Now I'm aslo facing some questions similar to yours.
Maybe we could help each other for the topic defining a changeable surface charge density vs. some parameters.
How about your case, George? Now I'm aslo facing some questions similar to yours. Maybe we could help each other for the topic defining a changeable surface charge density vs. some parameters.

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