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Complex result after integration of real variable?
Posted Dec 23, 2015, 10:02 a.m. EST 2 Replies
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Hello everyone,
I have an electrical problem similar to a parallel plate capacitor. After solving for V, if I carry out a line integral from one electrode to the other I get the potential difference between the electrodes, as expected.
However, if I integrate V*rect1(z) instead of just V (where rect1(z) is a rectangular function that selects only a certain range of z for the integration), I get a complex number as a result. As far as I can see, the real part of the result is what I expect, but the inclusion of an imaginary component in the result bothers me.
After some tests, I see that I also get complex results if I carry out a volume integral of the voltage (not that I need that, just wanted to see what happens).
Why am I getting complex results if I am integrating a real variable?
Thank you for your help.
I have an electrical problem similar to a parallel plate capacitor. After solving for V, if I carry out a line integral from one electrode to the other I get the potential difference between the electrodes, as expected.
However, if I integrate V*rect1(z) instead of just V (where rect1(z) is a rectangular function that selects only a certain range of z for the integration), I get a complex number as a result. As far as I can see, the real part of the result is what I expect, but the inclusion of an imaginary component in the result bothers me.
After some tests, I see that I also get complex results if I carry out a volume integral of the voltage (not that I need that, just wanted to see what happens).
Why am I getting complex results if I am integrating a real variable?
Thank you for your help.
2 Replies Last Post Jan 8, 2016, 4:42 a.m. EST
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Posted:
9 years ago
Hi
you do not say much about your model. A complex potential in ACDC is not uncommon, COMSOL uses the "phasor" representation, and you could well have some phase lag in the results.
Normally COMSOL only plots real values, so with complex results you need to separate or use the abs() operator
--
Good luck
Ivar
you do not say much about your model. A complex potential in ACDC is not uncommon, COMSOL uses the "phasor" representation, and you could well have some phase lag in the results.
Normally COMSOL only plots real values, so with complex results you need to separate or use the abs() operator
--
Good luck
Ivar
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Posted:
9 years ago
Thank you for your reply.
Yes, I am using the ACDC module. I am not sure what the phase in the voltage and the field is supposed to mean though. In the quasi-static approximation there should not be any phase difference between two values of the same time-varying variable evaluated at different points since the system is assumed to be at equilibrium at all times. Perhaps the phase in the voltage is related to the lag between voltage and current due to the complex impedance? But then I don't see why the electric field should also show phase differences when evaluated at different points.
Perhaps somebody could shed some light into this?
Thank you.
Yes, I am using the ACDC module. I am not sure what the phase in the voltage and the field is supposed to mean though. In the quasi-static approximation there should not be any phase difference between two values of the same time-varying variable evaluated at different points since the system is assumed to be at equilibrium at all times. Perhaps the phase in the voltage is related to the lag between voltage and current due to the complex impedance? But then I don't see why the electric field should also show phase differences when evaluated at different points.
Perhaps somebody could shed some light into this?
Thank you.