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Treating complex data from time-harmonic analysis

Posted Oct 24, 2013, 4:38 a.m. EDT Parameters, Variables, & Functions Version 4.3b 2 Replies

Kristoffer Menzel
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Hi there,

I just started to learn how time-harmonic analysis work in order to include eddy current effects in my simulations (of a magnetic field). So I started a simulation using mef physics from the AC/DC module. What I get out of it is (of course) a complex-valued magnetic field. Now, I was wondering if I understand the data correctly by treating the field as B(t)=B_0*exp(iwt+phi). So for instance, if I want to get the field at a certain instant of time I use the following expression: abs(mef.By)*sin(2*pi*50*t+arg(mef.By)) .
Is this correct or is there a paragraph in the COMSOL documentation about it?

Thanks in advance,
Kristoffer
2 Replies Last Post Oct 24, 2013, 12:01 p.m. EDT
Sven Friedel COMSOL Employee

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Posted: 1 decade ago Oct 24, 2013, 6:52 a.m. EDT
Dear Kristoffer,

have a look at the COMSOL Help system searching for the word "phasor".

Just to illustrate - if you open the library model coil_above_plate.mph and you visualize
mf.Jphi the plot will show actually the real part of this quantity real(mf.Jphi).
Alternatively you can display imag(mf.Jphi) which is the out-of phase component or the current
at the time t=T/4.

The same result you would get by plotting mf.Jphi*exp(i*pi/2).

Using an arbitrary phase angle in the above expression you can inspect the solution at any time within one period. Note also that there are special postprocessing options.

You can easily animate the plot group for the surface current by pressing the "Player button" note that you need to select "Dynamic Data Extension" to get a movie in phase (or time as you want). The default would be to generate a movie for all frequencies in a sweep.

In my attached model I have also added a 1D plot group where you see the current in different point over the phase.

Let me know if those hints could help to answer your question.

Best regards,
Sven Friedel
Dear Kristoffer, have a look at the COMSOL Help system searching for the word "phasor". Just to illustrate - if you open the library model coil_above_plate.mph and you visualize mf.Jphi the plot will show actually the real part of this quantity real(mf.Jphi). Alternatively you can display imag(mf.Jphi) which is the out-of phase component or the current at the time t=T/4. The same result you would get by plotting mf.Jphi*exp(i*pi/2). Using an arbitrary phase angle in the above expression you can inspect the solution at any time within one period. Note also that there are special postprocessing options. You can easily animate the plot group for the surface current by pressing the "Player button" note that you need to select "Dynamic Data Extension" to get a movie in phase (or time as you want). The default would be to generate a movie for all frequencies in a sweep. In my attached model I have also added a 1D plot group where you see the current in different point over the phase. Let me know if those hints could help to answer your question. Best regards, Sven Friedel
Kristoffer Menzel
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Posted: 1 decade ago Oct 24, 2013, 12:01 p.m. EDT
Hi Sven,

this reply is fine for me. Thanks a lot. I was thinking that it's the way you described above but I did not find it in the manual.

BR
Kristoffer
Hi Sven, this reply is fine for me. Thanks a lot. I was thinking that it's the way you described above but I did not find it in the manual. BR Kristoffer

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