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Current not being conserved in AC/DC.
Posted 29.04.2013, 20:42 GMT-4 Low-Frequency Electromagnetics, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.3a 3 Replies
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The model is two parallel pieces of copper and a small piece of aluminum between them. I add either a voltage or current source at the end of one piece of copper and a ground or current sink at the end of the other. Basically I am making current from through one piece of copper, through the aluminum block and out the other copper piece.
I have been setting the normal current density source at the ends such that exactly 100000 amps (arbitrary) runs into and out the ends of the copper. I then solve the system and do a surface integral of the normalized current density at the interface between the copper and aluminum pieces. I get a total current of over 100000 amps, Something 1.5 times as much. If I do a cut plane in the middle of the aluminum piece however and integrate over the current density there I get something like 99999 amps (good enough since its a numerical solver). I tried cranking up my mesh at the boundries of the aluminum and copper interface but it is still the same.
According to Kirchhoff I should be getting 100000 amps at any slice through my model. There is no way I can have 150000 amps running through anywhere in the system if all I input is 100000. Or if I do a voltage source at the end of the pieces I should get the same integrated current through any slice of the model.
Any ideas? Thanks
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no particular idea as for my cases so far the current flow is mostly within 5-10% ,
so perhaps some singularity (sharpe edge that overestimates grossly the current calculation), or are you in 2D-axi and you have added manually and via the selection markl the 2*pi*r (but then the units should not match) ?
Without seeing the model it's difficult to say much more
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Good luck
Ivar
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There is definitely current build up on the corners/edges at the interface between the parts. But it is something I want to see and model accurately. Is there a way to get comsol to make more accurate calculations there and not over calculate? I am away from my workstation but can post screenshots/the model tomorrow.
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try filleting off and rounding corners hen the derivatives along these round corners will be better defined and the integration should give less errors. But you cannot always easily "round-off" all corners, all depends on the model
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Good luck
Ivar