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Integration to find current

Posted 2 janv. 2012, 21:30 UTC−5 Low-Frequency Electromagnetics, Materials, Parameters, Variables, & Functions Version 4.2a 6 Replies

Bahar
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Hi everybody

I am a bit confused by the current measurement in Comsol.

if I use 2D, should i use surface integration, or line integration of current density for finding current?
what about 3D?

6 Replies Last Post 20 juil. 2012, 06:18 UTC−4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 3 janv. 2012, 01:22 UTC−5
Hi Bahar

For integration in COMSOL it all depends, what you want, the units are there to give a good hint.

i.e. in 3D you normally look for total current passing a boundary (2D surface for a 3D model) so you do a surface integration of a current density in [A/m^2] (*dx*dy) which ends up in [A] (note the *dx*dy is implicit in a 2D integration

in 2D and 2D axi you have 2 cases, either the floe is going "out of the paper/screen" then you do a domain integration in 2D (a 2D surface again as above), or you have a current flowing in the screen plane crossing a boundary (a 1D line in 2D). But as COMSOL always calculates in 3D assuming generally by default a 1[m] deep geometry, you current flowing through a boundary in 2D (=1D line) is also in [A/m^2] and when you do a line integration on this boundary you end up with a current density [A/m] (from the [A/m^2](*dx)=[A/m]. and this tells you its "per meter". To get an absolute value you need to do the line integration of [A/m^2]*1[m]*dx = [A]

Now in certain physics you can decide the true thickness and use a different value than the default 1[m], in which case you must use this thickness often referred to by the variable name "d" with the physics prefix

I hope I made myself clear, have fun Comsoling

--
Good luck
Ivar
Hi Bahar For integration in COMSOL it all depends, what you want, the units are there to give a good hint. i.e. in 3D you normally look for total current passing a boundary (2D surface for a 3D model) so you do a surface integration of a current density in [A/m^2] (*dx*dy) which ends up in [A] (note the *dx*dy is implicit in a 2D integration in 2D and 2D axi you have 2 cases, either the floe is going "out of the paper/screen" then you do a domain integration in 2D (a 2D surface again as above), or you have a current flowing in the screen plane crossing a boundary (a 1D line in 2D). But as COMSOL always calculates in 3D assuming generally by default a 1[m] deep geometry, you current flowing through a boundary in 2D (=1D line) is also in [A/m^2] and when you do a line integration on this boundary you end up with a current density [A/m] (from the [A/m^2](*dx)=[A/m]. and this tells you its "per meter". To get an absolute value you need to do the line integration of [A/m^2]*1[m]*dx = [A] Now in certain physics you can decide the true thickness and use a different value than the default 1[m], in which case you must use this thickness often referred to by the variable name "d" with the physics prefix I hope I made myself clear, have fun Comsoling -- Good luck Ivar
Bahar
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Posted: 1 decade ago 3 janv. 2012, 10:58 UTC−5
Dear Ivar

I appreciate you full, and helpful reply. That is exactly the hints that I was looking for.

Best
Bahareh
Dear Ivar I appreciate you full, and helpful reply. That is exactly the hints that I was looking for. Best Bahareh
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 3 janv. 2012, 11:08 UTC−5
Hi
that is nice to hear, but you know, you can also try it out with a simple example, i.e. calculate the area of a cylinder in 3D and of a cylinder in 2D-axi view and compare. Some time you discover sum "bug" to like that ;)

--
Good luck
Ivar
Hi that is nice to hear, but you know, you can also try it out with a simple example, i.e. calculate the area of a cylinder in 3D and of a cylinder in 2D-axi view and compare. Some time you discover sum "bug" to like that ;) -- Good luck Ivar
Bahar
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Posted: 1 decade ago 4 janv. 2012, 16:38 UTC−5
Thanks I will follow your advice :)
Thanks I will follow your advice :)
Murali Venkatraman
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Posted: 1 decade ago 15 févr. 2012, 22:33 UTC−5
Dear Ivar and Bhar,

I have raised a question today in these lines here:

www.comsol.com/community/forums/general/thread/26157/

Could you please give me your inputs ?

Thanks
Murali
Dear Ivar and Bhar, I have raised a question today in these lines here: http://www.comsol.com/community/forums/general/thread/26157/ Could you please give me your inputs ? Thanks Murali
Anahita Zargarani
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Posted: 1 decade ago 20 juil. 2012, 06:18 UTC−4
Hi Bahare

Have you ever tried comsol in 3D? or ever simulated with frequency? if so Id be glad to have your help



Best Regards
Hi Bahare Have you ever tried comsol in 3D? or ever simulated with frequency? if so Id be glad to have your help Best Regards

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