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how to switch boundary conditions between float potential and ground?

Posted Sep 24, 2013, 12:40 p.m. EDT Low-Frequency Electromagnetics, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.3a 5 Replies

Lian Yi
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Hey
I was trying to switch the voltage between ground and float to a boundary in electric current physics. I can either apply floating or grounding condition to a boundary, but not able to switch these two conditions.

Does anyone know how to switch them? Or anyone knows discrete function in comsol that can be applied as the voltage to that boundary?

Regards
Lian

5 Replies Last Post Sep 25, 2013, 5:08 p.m. EDT
Jens Krause
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Posted: 1 decade ago Sep 25, 2013, 7:03 a.m. EDT
Hallo Lian,

maybe there are other ways, but what I do with success is to connect the domain to ground in
an external circuit with an resistor. Then I can change the resistance from 0 (=grounded) to
a very big value (= inf = floating). You can even do in a transient simulation using a step function.
You need to verify that in the floating case the current flowing through the resistor is small enough
to be neglect. Otherwise increase the resistance until happy.

Regards

Jens
Hallo Lian, maybe there are other ways, but what I do with success is to connect the domain to ground in an external circuit with an resistor. Then I can change the resistance from 0 (=grounded) to a very big value (= inf = floating). You can even do in a transient simulation using a step function. You need to verify that in the floating case the current flowing through the resistor is small enough to be neglect. Otherwise increase the resistance until happy. Regards Jens
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Sep 25, 2013, 8:50 a.m. EDT
Lian,

you can also apply a potential BC and use any time dependent function to apply the potential, e.g. a step function to switch from 0V (ground) to a non-zero potential.
If you need floating potential, then Jens' solution is a good one.

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
Lian, you can also apply a potential BC and use any time dependent function to apply the potential, e.g. a step function to switch from 0V (ground) to a non-zero potential. If you need floating potential, then Jens' solution is a good one. Cheers Edgar -- Edgar J. Kaiser emPhys Physical Technology
Lian Yi
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Posted: 1 decade ago Sep 25, 2013, 11:26 a.m. EDT
Dear Jens:
Many thanks for your suggestion and it is exactly how the relay works on my experimental setup.

I was wondering how you connect a external circuit with a resistor to it? Do I need to use a different physics for that external circuit? Now I am using electric currents and creeping flow for simulation of microfluidic channels.

Regards
Lian
Dear Jens: Many thanks for your suggestion and it is exactly how the relay works on my experimental setup. I was wondering how you connect a external circuit with a resistor to it? Do I need to use a different physics for that external circuit? Now I am using electric currents and creeping flow for simulation of microfluidic channels. Regards Lian
Lian Yi
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Posted: 1 decade ago Sep 25, 2013, 5:05 p.m. EDT
Hello Jens:
I figured out how to connect a resistor with either a constant(ground) or zero(float) conductivity to that boundary. I tested square wave, step and piecewise function. They are all good when I used a simple model electric currents. Thank you for your suggestion. It really helps.

However, if I go to my complicated model with creeping flow, electric currents and transport of diluted species, the study is not able to go through the step change. An error happens when it went to the change point: repeated error test failures. May have reached a singularity. Time.... Last time step is not converged.

I was wondering if you have any experience dealing with it?
Thanks

Regards
Lian
Hello Jens: I figured out how to connect a resistor with either a constant(ground) or zero(float) conductivity to that boundary. I tested square wave, step and piecewise function. They are all good when I used a simple model electric currents. Thank you for your suggestion. It really helps. However, if I go to my complicated model with creeping flow, electric currents and transport of diluted species, the study is not able to go through the step change. An error happens when it went to the change point: repeated error test failures. May have reached a singularity. Time.... Last time step is not converged. I was wondering if you have any experience dealing with it? Thanks Regards Lian
Lian Yi
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Posted: 1 decade ago Sep 25, 2013, 5:08 p.m. EDT
Dear Edgar:
thank you for your suggestion.

I am doing step function for the conductivity now, which can switch between float and ground, but encountered singularity error continuously. If you are interested or have any experience, please let me know.

Thanks

Regards
Lian
Dear Edgar: thank you for your suggestion. I am doing step function for the conductivity now, which can switch between float and ground, but encountered singularity error continuously. If you are interested or have any experience, please let me know. Thanks Regards Lian

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