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Rules for adding circuit terminals

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I am trying to create a simple inductor model based on the tutorial: Modeling of a 3D inductor. I cannot designate the appropriate boundaries as Terminals. In particular, the boundary I want to assign as Ground says "not applicable" in the selection window.

What are the constraints on defining terminals? I am using the end boundaries of a partial copper torus.

I am attaching my model.

I am using version 4.2.0.150

Thank you,

David


2 Replies Last Post May 23, 2012, 4:40 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 May 23, 2012, 2:37 p.m. EDT
Hi

you cannot select the GND node (overriden) bacause you have not selected it at the higher level (Magnetic Isolation)

But I'm not convinced you can make voltage or current appear like that in the middle of the volume as you violate the laws of physics. You need to define a closed loop of current, at worst get it to loop around the external surface of your external boundaries. So I would not really trust the results you get anyhow this way, and at least validate it carefully by a MF simple loop calculation.
I would rather suggest to define a closed thorus with a current looping around sys2.phi of a cylindrical coordinate system sys2 that you define appropriately for the coil loop, and then not use the CIR physics, and in fact use MF instead of MEF as solving for V is a supplementary burden and uses quite some RAM.

Furthermore , if you continue your way, you need to connect your circuit to the terminal (GND is by default connected to node "0" of the circuit).
And I believe you will need a little conductivity (i.e.1[S/m] for your air) to populate the -j*omega*sigma terms of the Amper law equations for a frequency sweep

--
Good luck
Ivar
Hi you cannot select the GND node (overriden) bacause you have not selected it at the higher level (Magnetic Isolation) But I'm not convinced you can make voltage or current appear like that in the middle of the volume as you violate the laws of physics. You need to define a closed loop of current, at worst get it to loop around the external surface of your external boundaries. So I would not really trust the results you get anyhow this way, and at least validate it carefully by a MF simple loop calculation. I would rather suggest to define a closed thorus with a current looping around sys2.phi of a cylindrical coordinate system sys2 that you define appropriately for the coil loop, and then not use the CIR physics, and in fact use MF instead of MEF as solving for V is a supplementary burden and uses quite some RAM. Furthermore , if you continue your way, you need to connect your circuit to the terminal (GND is by default connected to node "0" of the circuit). And I believe you will need a little conductivity (i.e.1[S/m] for your air) to populate the -j*omega*sigma terms of the Amper law equations for a frequency sweep -- Good luck Ivar

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Posted: 1 decade ago May 23, 2012, 4:40 p.m. EDT
Thank you.Not electing it on the higher level was the problem.
Thank you.Not electing it on the higher level was the problem.

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