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Electrostatic model
Posted 01.12.2010, 14:13 GMT-5 6 Replies
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Hello all,
Hopefully this is a simple question. I'm trying to calculate some forces in the electrostatic model and I've been running into trouble. This is a rotationally symmetric model consisting of an electrode at a fixed voltage in vacuum above a dielectric material over a ground plane.
To debug the problems that I've been having, I've tried to simply perform a surface integral over the electrode of the surface charge.
Value of surface integral: 1.694352e-18 [C], Expression: -(Dz_emes*nz + Dr_emes*nr), Boundary: 8
Value of surface integral: 3.388705e-18 [C], Expression: nD_emes, Boundary: 8
these are the results. According to documentation, the surface charge nD_emes is calculated by finding -n dot D, which is what is on the first line above.
I'm wondering why the two results are not the same?
Thanks,
Everet
Hopefully this is a simple question. I'm trying to calculate some forces in the electrostatic model and I've been running into trouble. This is a rotationally symmetric model consisting of an electrode at a fixed voltage in vacuum above a dielectric material over a ground plane.
To debug the problems that I've been having, I've tried to simply perform a surface integral over the electrode of the surface charge.
Value of surface integral: 1.694352e-18 [C], Expression: -(Dz_emes*nz + Dr_emes*nr), Boundary: 8
Value of surface integral: 3.388705e-18 [C], Expression: nD_emes, Boundary: 8
these are the results. According to documentation, the surface charge nD_emes is calculated by finding -n dot D, which is what is on the first line above.
I'm wondering why the two results are not the same?
Thanks,
Everet
6 Replies Last Post 04.12.2010, 07:33 GMT-5
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Posted:
1 decade ago
Hi
you have a very good question there,
but as the difference looks like a factor "2" could it be a rms value or simply a true bug, there were a few typos in the equations in ACDC for 4.0a, corrected now in 4.1
Take a look at the equtions beneath and check if you find something wrong, check the model in 4.1 (if you are not already with the latest patch of 4.1) if still there report it to "support" they shpould be able to explain
--
Good luck
Ivar
you have a very good question there,
but as the difference looks like a factor "2" could it be a rms value or simply a true bug, there were a few typos in the equations in ACDC for 4.0a, corrected now in 4.1
Take a look at the equtions beneath and check if you find something wrong, check the model in 4.1 (if you are not already with the latest patch of 4.1) if still there report it to "support" they shpould be able to explain
--
Good luck
Ivar
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Posted:
1 decade ago
Actually the particular machine I'm using is running v3.5. I think there are some computers with a different version - I'll check them out.
Thanks for your input
Thanks for your input
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Posted:
1 decade ago
Hi
you can still look at the equations (in 3,5), you need to find the correct path via the windows and pull down menus.
But I cannot remember of any equation typos in 3.5 so I suspect you are doing something slightly different for the two cases, and you are missing a 0.5 or a 2 somewhere
--
Good luck
Ivar
you can still look at the equations (in 3,5), you need to find the correct path via the windows and pull down menus.
But I cannot remember of any equation typos in 3.5 so I suspect you are doing something slightly different for the two cases, and you are missing a 0.5 or a 2 somewhere
--
Good luck
Ivar
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Posted:
1 decade ago
Hi,
Interesting but
I have tried the same thing as you (in my own model): These are my results
Value of surface integral: -3.613317e-17 [C], Expression: -(Dz_emes*nz + Dr_emes*nr), Boundary: 2
Value of surface integral: -3.613317e-17 [C], Expression: nD_emes, Boundary: 2
Check your model again!!
Good luck
Interesting but
I have tried the same thing as you (in my own model): These are my results
Value of surface integral: -3.613317e-17 [C], Expression: -(Dz_emes*nz + Dr_emes*nr), Boundary: 2
Value of surface integral: -3.613317e-17 [C], Expression: nD_emes, Boundary: 2
Check your model again!!
Good luck
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Posted:
1 decade ago
Thanks for your thoughts.
I just tried this again, with different (but inconsistent) results. I built the model again, meshed and solved it then performed the surface integral over the electrode.
Value of surface integral: 1.045e-18 [C], Expression: -(Dz_emes*nz + Dr_emes*nr), Boundaries: 8, 10, 12
Value of surface integral: 8.467133e-18 [C], Expression: nD_emes, Boundaries: 8, 10, 12
I looked at the equations and found that nD_emes = unr*(down(Dr_emes)-up(Dr_emes))+unz*(down(Dz_emes)-up(Dz_emes))
To be perfectly honest, I don't see how nD_emes = -del dot D. To be fair though, I don't think I fully understand what the up() and down() functions are for.
Insight may be all I need,
Thanks for all the help,
Everet
I just tried this again, with different (but inconsistent) results. I built the model again, meshed and solved it then performed the surface integral over the electrode.
Value of surface integral: 1.045e-18 [C], Expression: -(Dz_emes*nz + Dr_emes*nr), Boundaries: 8, 10, 12
Value of surface integral: 8.467133e-18 [C], Expression: nD_emes, Boundaries: 8, 10, 12
I looked at the equations and found that nD_emes = unr*(down(Dr_emes)-up(Dr_emes))+unz*(down(Dz_emes)-up(Dz_emes))
To be perfectly honest, I don't see how nD_emes = -del dot D. To be fair though, I don't think I fully understand what the up() and down() functions are for.
Insight may be all I need,
Thanks for all the help,
Everet
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Posted:
1 decade ago
Hi
up and down are the normal of a boundary looking into one and the other domains. If you have physicsl flux continuity at the boundary they should give you similar results (up to a +/- sign definition) but if you have a discontinuity at the boundary your results would only be correct if you consder the differences of each domain, that is what the specific "up" and "down" are for.
plot them out for different cases (when they exist) and you will rapidly catch their interest
--
Good luck
Ivar
up and down are the normal of a boundary looking into one and the other domains. If you have physicsl flux continuity at the boundary they should give you similar results (up to a +/- sign definition) but if you have a discontinuity at the boundary your results would only be correct if you consder the differences of each domain, that is what the specific "up" and "down" are for.
plot them out for different cases (when they exist) and you will rapidly catch their interest
--
Good luck
Ivar