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Gradient-dependent flux
Posted Jul 4, 2012, 5:59 p.m. EDT Version 4.2a 2 Replies
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Hi there,
I am trying to simulate a gradient-dependent flux in the "Transport of diluted species" module. I added the Flux component from the drop-down menu, and one of the species I want to make it voltage-gradient dependent. It's the Nernst-Planck flux model.
Ji=-D(grad(c)+c * z_1*q*/(kB*T)*grad(V))
D-diffusion constant, c- ion species concentration, z_1 - valency, q-proton charge, kB-Botzmann constant, T-temperature, V-voltage.
how do I have to enter grad(V) and grad(c) in order to have the right thing implemented?
{d(c,x),d(c,y)} and {d(V,x),d(V,y)} seem to be accepted from a syntactic point of view, but then the solver returns an error.
[d(c,x),d(c,y)] and [d(V,x),d(V,y)] yield in having a orange line (as if the units where mismatched), and also the solver stops with an error.
gradient(V) is not working. also ctrl+alt+, (which is the shortcut for the graphic del-symbol) fails.
could you please write a valid expression for this formula?
Thanks,
Dan.
P.S. comsol 4.2a
I am trying to simulate a gradient-dependent flux in the "Transport of diluted species" module. I added the Flux component from the drop-down menu, and one of the species I want to make it voltage-gradient dependent. It's the Nernst-Planck flux model.
Ji=-D(grad(c)+c * z_1*q*/(kB*T)*grad(V))
D-diffusion constant, c- ion species concentration, z_1 - valency, q-proton charge, kB-Botzmann constant, T-temperature, V-voltage.
how do I have to enter grad(V) and grad(c) in order to have the right thing implemented?
{d(c,x),d(c,y)} and {d(V,x),d(V,y)} seem to be accepted from a syntactic point of view, but then the solver returns an error.
[d(c,x),d(c,y)] and [d(V,x),d(V,y)] yield in having a orange line (as if the units where mismatched), and also the solver stops with an error.
gradient(V) is not working. also ctrl+alt+, (which is the shortcut for the graphic del-symbol) fails.
could you please write a valid expression for this formula?
Thanks,
Dan.
P.S. comsol 4.2a
2 Replies Last Post Jul 5, 2012, 6:09 a.m. EDT
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Posted:
1 decade ago
Hi
how do you define your "V", from which physics ?
If it comes from ES, and V is a dependent variable you have the grad components as Vx Vy Vz, they are defined by default by COMSOL for you. Check your "equations" with Preferences turn on Equation viiew" and search therein
but d(V,x) should work as well, as V if a dependent variale is a predefined field V(x,y,z,t)
But there is no vector writing possible, you must write out your equtions in scalar COMPONENT form within your coordinate system choosen
--
Good luck
Ivar
how do you define your "V", from which physics ?
If it comes from ES, and V is a dependent variable you have the grad components as Vx Vy Vz, they are defined by default by COMSOL for you. Check your "equations" with Preferences turn on Equation viiew" and search therein
but d(V,x) should work as well, as V if a dependent variale is a predefined field V(x,y,z,t)
But there is no vector writing possible, you must write out your equtions in scalar COMPONENT form within your coordinate system choosen
--
Good luck
Ivar
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Posted:
1 decade ago
Thanks for the Reply!
Yes V is from the ES module. I know that Vx and Vy are already available. How do I write a component expression? Base vectors I can also not enter!
Do I have to add to flux-objects, one for the x and one for the y direction, or is there a more compact way of writing this?
Thanks,
Dan.
Yes V is from the ES module. I know that Vx and Vy are already available. How do I write a component expression? Base vectors I can also not enter!
Do I have to add to flux-objects, one for the x and one for the y direction, or is there a more compact way of writing this?
Thanks,
Dan.