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How to define a equation between the derivative of two variables

Posted 8 ago 2016, 20:58 GMT-4 Parameters, Variables, & Functions 3 Replies

Sunny Wang
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Hello, I am a new user of COMSOL 5.1, and I'm using the mathematics module to define my physical model.
I defined two dependent virables: c (concentration) and phi (potential); I also defined two PDEs to describe them respectively.
I hope to have a boundary condition that links the 1st order derivative of two variables.
That is: Dc/Dx = A*Dphi/Dx, where A is a constant.

I tried to use the 'Flux/Source' Boundary Condition. I can type in the equation, but this BC actually doesn't work.
Do I need to define such kinds of BC in a diferrent manner?

Hope someone can help me.
Thanks.
3 Replies Last Post 9 ago 2016, 03:58 GMT-4
Sunny Wang
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Posted: 8 years ago 8 ago 2016, 23:24 GMT-4
Actually, I hope that someone can tell me whether such a boundary condition can work:
Flux of c = A*d(phi,x)
c and phi are the variables I defined.
Actually, I hope that someone can tell me whether such a boundary condition can work: Flux of c = A*d(phi,x) c and phi are the variables I defined.
Lasse Murtomäki
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Posted: 8 years ago 9 ago 2016, 01:35 GMT-4
What are you trying to simulate? The boundary condition you present I have not encountered earlier.

BR
Lasse
What are you trying to simulate? The boundary condition you present I have not encountered earlier. BR Lasse
Sunny Wang
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Posted: 8 years ago 9 ago 2016, 03:58 GMT-4

What are you trying to simulate? The boundary condition you present I have not encountered earlier.

BR
Lasse


I am simulating the transport and reaction of electron and ion in a mixed conductor.
Both kinds of species have diffusion and drift, their transport are described by Nernst-Planck equation.
The electric field is determined by Poisson equation.
For simplification, I first apply charge neutrality everywhere, so that the Poisson equation becomes Laplace equation.
I am trying to repeat the results of an article, and the boundary conditions are from that paper.

I will send you that paper and my simulation file. (I cannot attach file in my reply, but when I use 'send private message', I am able to attach the file, I don't know why...)
[QUOTE] What are you trying to simulate? The boundary condition you present I have not encountered earlier. BR Lasse [/QUOTE] I am simulating the transport and reaction of electron and ion in a mixed conductor. Both kinds of species have diffusion and drift, their transport are described by Nernst-Planck equation. The electric field is determined by Poisson equation. For simplification, I first apply charge neutrality everywhere, so that the Poisson equation becomes Laplace equation. I am trying to repeat the results of an article, and the boundary conditions are from that paper. I will send you that paper and my simulation file. (I cannot attach file in my reply, but when I use 'send private message', I am able to attach the file, I don't know why...)

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