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What does it mean to have imaginary part for the force (AC/DC module)?

Posted Mar 1, 2013, 4:13 a.m. EST Version 4.3 5 Replies

Ashraf Atalla
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Hi,

I am running a simulation to calculate the force between two conductors carrying AC current. I used MF with simple two circles of copper and surrounding of air. I set current density 200 in z direction and -200 on z direction for the second coil. The magnetic field looks great and as expected. But you can see the force evaluation in the bottom of the picture, it is complex value!

Does it mean it is sinusoidal? Even if, this means that the average force is zero? this is not true because there should be a net repulsive force.

Please help me with this problem, Thank you.

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5 Replies Last Post Mar 7, 2013, 12:47 a.m. EST
Edgar Kaiser
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Posted: 1 decade ago Mar 1, 2013, 6:11 a.m. EST
Hi,

I am not sure, maybe you have to look at the phase of the solution.

Cheers
Edgar
Hi, I am not sure, maybe you have to look at the phase of the solution. Cheers Edgar
Alexander Kuznetsov
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Posted: 1 decade ago Mar 1, 2013, 3:02 p.m. EST
usually imaginary part of force is related to some kind of damping ("energy loss") in the system
usually imaginary part of force is related to some kind of damping ("energy loss") in the system
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Mar 2, 2013, 2:55 a.m. EST
Hi

in dynamic mode a complex variable means some delay, or damping which are related in "solid"

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Good luck
Ivar
Hi in dynamic mode a complex variable means some delay, or damping which are related in "solid" -- Good luck Ivar
Ashraf Atalla
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Posted: 1 decade ago Mar 6, 2013, 4:24 p.m. EST
So in general, If I want to have a function for the force, How can I use the real and the imaginary parts in this function?
So in general, If I want to have a function for the force, How can I use the real and the imaginary parts in this function?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Mar 7, 2013, 12:47 a.m. EST
Hi

I'm not sure II understand you ;)
You can enter complex values in many fields, and values might be complex when you get them back, but you should do your complex math yourself in your user equations. However a plot in the results section give always the real part

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Good luck
Ivar
Hi I'm not sure II understand you ;) You can enter complex values in many fields, and values might be complex when you get them back, but you should do your complex math yourself in your user equations. However a plot in the results section give always the real part -- Good luck Ivar

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