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Frequency domain with two input variables

Posted Jan 24, 2013, 9:38 a.m. EST Low-Frequency Electromagnetics, Structural Mechanics Version 4.2a, Version 4.3 4 Replies

James
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Dear all

If I add a external force on one end of a silicon beam while let the other end fixed, is it possible to put a constant voltage across this beam in frequency domain simulation? It seems COMSOL4.2a set both external force and the voltage to AC (e.g. sinusoidal) form in default frequency domain simulation. But I want to keep the voltage unchanged. Does anyone know how to realize it? Thanks.

Regards

James
4 Replies Last Post Sep 29, 2015, 8:45 p.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 24, 2013, 10:16 a.m. EST
Hi

in frequency domain all right hand side components are turned into sinus excitation components. But you have (at least in the last versions) some special solver cases (very physics dependent) that allow to either use an offset + frequency domain, or harmonic perturbations on top of typically a larger static BC condition. Check your doc

--
Good luck
Ivar
Hi in frequency domain all right hand side components are turned into sinus excitation components. But you have (at least in the last versions) some special solver cases (very physics dependent) that allow to either use an offset + frequency domain, or harmonic perturbations on top of typically a larger static BC condition. Check your doc -- Good luck Ivar
James
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Posted: 1 decade ago Jan 24, 2013, 8:14 p.m. EST

Hi

in frequency domain all right hand side components are turned into sinus excitation components. But you have (at least in the last versions) some special solver cases (very physics dependent) that allow to either use an offset + frequency domain, or harmonic perturbations on top of typically a larger static BC condition. Check your doc

--
Good luck
Ivar


Thanks Ivar.
[QUOTE] Hi in frequency domain all right hand side components are turned into sinus excitation components. But you have (at least in the last versions) some special solver cases (very physics dependent) that allow to either use an offset + frequency domain, or harmonic perturbations on top of typically a larger static BC condition. Check your doc -- Good luck Ivar [/QUOTE] Thanks Ivar.
Ashraf Atalla
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Posted: 1 decade ago Mar 1, 2013, 3:53 a.m. EST
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.
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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Daniel F. Daza
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Posted: 9 years ago Sep 29, 2015, 8:45 p.m. EDT
Hi, Ashraf, sadly it's been around two years since you posted your question. I'm currently working with obtaining electromagnetic forces in a frequency domain study too. A frequency domain study implies a phasor representation of field variables, which adds a complex exponential to their values. However, their actual values should be evaluated by taking their real part. This applies to forces, as well.
On the other hand, there are two ways to compute electromagnetic forces in Comsol. One of them is readily available as the electromagnetic force, which is the one you are using as I can infer from the picture you attached. The other one involves a surface integral of the Lorentz contribution, over the domain of interest. These two can give different results.
I'd like to hear if you continued or concluded your work and about your experience.
Hi, Ashraf, sadly it's been around two years since you posted your question. I'm currently working with obtaining electromagnetic forces in a frequency domain study too. A frequency domain study implies a phasor representation of field variables, which adds a complex exponential to their values. However, their actual values should be evaluated by taking their real part. This applies to forces, as well. On the other hand, there are two ways to compute electromagnetic forces in Comsol. One of them is readily available as the electromagnetic force, which is the one you are using as I can infer from the picture you attached. The other one involves a surface integral of the Lorentz contribution, over the domain of interest. These two can give different results. I'd like to hear if you continued or concluded your work and about your experience.

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