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Introduce a new equation

Posted May 28, 2010, 5:37 a.m. EDT 6 Replies

Pablo Briones
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Hi,

I'm working with the comsol and I want to introcude a new equation for calculate the potencial in a Battery.
The equation is like this:

E = E1 + A * Log(c_A*(6800-c_A)/c_B)

Where E1 and A are constant and c_A, c_B are output variables concentrations of the other equation (Convention and Diffusion),
So I need this for calculate E, but i don't know how can i do it. I'm triying to work woth the PDE equation but is not working.

I'll really apreciate your help

regards

Pablo
6 Replies Last Post May 28, 2010, 11:43 a.m. EDT
Danial Tz
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Posted: 1 decade ago May 28, 2010, 8:01 a.m. EDT
How about entering them in Scalar expressions? Options -> Expressions -> Scalar expressions

once you entered, update your model (under Solve menu)
How about entering them in Scalar expressions? Options -> Expressions -> Scalar expressions once you entered, update your model (under Solve menu)
Pablo Briones
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Posted: 1 decade ago May 28, 2010, 10:23 a.m. EDT
The problem is that i need to introduce this equation and obtain the visual representation of this equation in all of the material.

I don't know if that is possible only with the scalar equation because I don't find this variable in the plot parameters.

what can i do?

The problem is that i need to introduce this equation and obtain the visual representation of this equation in all of the material. I don't know if that is possible only with the scalar equation because I don't find this variable in the plot parameters. what can i do?
Danial Tz
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Posted: 1 decade ago May 28, 2010, 10:43 a.m. EDT
Then define it in subdomain expressions, and just write the variable in the surface plot manually; if I got you correctly.
Then define it in subdomain expressions, and just write the variable in the surface plot manually; if I got you correctly.
Pablo Briones
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Posted: 1 decade ago May 28, 2010, 11:18 a.m. EDT
Write the variable in the surface plot manually?
How can i do that?
Write the variable in the surface plot manually? How can i do that?
Danial Tz
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Posted: 1 decade ago May 28, 2010, 11:27 a.m. EDT
well, let's say I have a variable called reaction_rate, which is equal to c*k, where c is the concentration and k a constant.
Write reaction_rate = k*c in the subdomain expression. Then update your model through solve menu. Next, type reaction_rate in the surface plot where the expression box is.
well, let's say I have a variable called reaction_rate, which is equal to c*k, where c is the concentration and k a constant. Write reaction_rate = k*c in the subdomain expression. Then update your model through solve menu. Next, type reaction_rate in the surface plot where the expression box is.
Pablo Briones
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Posted: 1 decade ago May 28, 2010, 11:43 a.m. EDT
Thanks a lot for your help!!

The program is running in this seccion now.

regards

Pablo
Thanks a lot for your help!! The program is running in this seccion now. regards Pablo

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