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Floating Potential incomplete description?
Posted 25 set 2015, 10:46 GMT-4 3 Replies
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I'm a bit confused about the description of the Floating Potential boundary condition in the Electric Currents mode. It says that the integral of the current into the surface is 0 (or another user-defined value) and while this is true it doesn't seem to properly define what the boundary condition actually is used for. I use it to put an unknown electric potential that is identical everywhere on a surface (i.e. the current PARALLELL to the surface is 0) which is representative to surfaces that are good conductors compared to the surrounding. As far as I can see, electric insulation would also satisfy the boundary condition as described in Comsol as it also results in a integral of 0 for the electric current normal to the surface but this give a varying electric potential over the surface. So is the 0 parallell current constraint missing from the documentation or am I misunderstanding something here?
3 Replies Last Post 28 set 2015, 10:59 GMT-4
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Posted:
9 years ago
The Floating Potential boundary condition will make the potential constant over the assigned boundaries and the resulting potential will depend on the integral current source, "I0", specified (default: I0=0). The effect is indeed also that the tangential electric field and tangential current density will become zero so for clarity it would be a good idea to state that also in the equation display (besides that the integral current source is I0). The Electric Insulation boundary condition is different as it states that the normal current density is zero locally but the tangential electric field and current density may still be large.
If you read the feature documentation (press F1 when having the Floating Potential feature seleceted), it states that:
"The Floating Potential node is useful when modeling a metallic electrode at floating potential. This is a good approximation when the conductivity of the electrode is many orders of magnitude larger than that of the surrounding medium. "
which tries to give an engineering picture of in what situation to use the feature.
Best regards,
Magnus
If you read the feature documentation (press F1 when having the Floating Potential feature seleceted), it states that:
"The Floating Potential node is useful when modeling a metallic electrode at floating potential. This is a good approximation when the conductivity of the electrode is many orders of magnitude larger than that of the surrounding medium. "
which tries to give an engineering picture of in what situation to use the feature.
Best regards,
Magnus
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Posted:
9 years ago
Maybe I should add that in the case of anisotropic conductivity, the floating potential condition will only guarantee that the tangential electric field, "E", is zero, that is:
n x E = n x (-grad(V)) = 0
but as the electric field and the current density, "J", are not parallel, the tangential current density will become non zero.
--
Magnus
n x E = n x (-grad(V)) = 0
but as the electric field and the current density, "J", are not parallel, the tangential current density will become non zero.
--
Magnus
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Posted:
9 years ago
Thank you! I too believe it would be good to add the "n x E = 0" in the equation description for the boundary condition.