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Basic electrostatic: FEM vs my interpretation
Posted 11.10.2012, 10:53 GMT-4 2 Replies
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Hi everybody,
I am confused by a very simple electrostatic problem illustrated in the attached drawing. My model (2D) consists in a first circle (1) defining the limits of the computation domain. A surface charge boundary is applied on a second circle (2) which is centered on the same point than circle 1. A third circle (3) is also present inside circle 1.
I simulated two situations: in the first case, a ground boundary is applied on circle 1 while a floating potential boundary is applied on circle 3. In the second case, this is the opposite: ground is on circle 3 while circle 1 is a floating potential.
The electrical field computed by Comsol is different in these two situations. From my basic understanding of electrostatics, I expected the two situations to be totally equivalent one to the other, i.e. the electrical field does not depend on which of the two equipotential surface the reference potential is set. Is it a numerical related issue or am I incorrect in my understanding?
I am confused by a very simple electrostatic problem illustrated in the attached drawing. My model (2D) consists in a first circle (1) defining the limits of the computation domain. A surface charge boundary is applied on a second circle (2) which is centered on the same point than circle 1. A third circle (3) is also present inside circle 1.
I simulated two situations: in the first case, a ground boundary is applied on circle 1 while a floating potential boundary is applied on circle 3. In the second case, this is the opposite: ground is on circle 3 while circle 1 is a floating potential.
The electrical field computed by Comsol is different in these two situations. From my basic understanding of electrostatics, I expected the two situations to be totally equivalent one to the other, i.e. the electrical field does not depend on which of the two equipotential surface the reference potential is set. Is it a numerical related issue or am I incorrect in my understanding?
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2 Replies Last Post 11.10.2012, 13:16 GMT-4
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Posted:
1 decade ago
Hi
is it this you get ? I do not really see why the two should look the same, as the floating potential fixes a constant potential along the border and its not infinite large.
But I'm neither not aleways right needs some more thoughts ;)
--
Good luck
Ivar
is it this you get ? I do not really see why the two should look the same, as the floating potential fixes a constant potential along the border and its not infinite large.
But I'm neither not aleways right needs some more thoughts ;)
--
Good luck
Ivar
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Posted:
1 decade ago
Mmmmhhhh, you're right finally Ivar.
The physical situation that I want to model is just made of a surface charge (circle 2) and a floating conductor (circle 3). I was wrongly assuming that circles centered on circle 2 were isopotential. This is true when the conductor is not present, but this is wrong when it is included. This is the reason why the two situations are not equivalent.
The physical situation that I want to model is just made of a surface charge (circle 2) and a floating conductor (circle 3). I was wrongly assuming that circles centered on circle 2 were isopotential. This is true when the conductor is not present, but this is wrong when it is included. This is the reason why the two situations are not equivalent.