Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

where is the B field?

Please login with a confirmed email address before reporting spam


I have an axial current in 2D in the ACDC mf mode. External current in z direction.

Results: current in z direction, no B field in surrounding air.

I realized maybe the circuit is not closed so I tried various boundaries with no luck

help anyone


9 Replies Last Post 19 juil. 2011, 21:21 UTC−4

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 13 juil. 2011, 05:32 UTC−4
Hello David,

without having seen your model: I think you should define the domain as a "single turn coil domain" and choose the current there.
I think the problem with the external current density is, as you said, that the loop is not closed.
Do you get any Resistant losses with the ext. current density? I don't think so.
With the single turn coil domain you get them and the field.

Greetings
Hello David, without having seen your model: I think you should define the domain as a "single turn coil domain" and choose the current there. I think the problem with the external current density is, as you said, that the loop is not closed. Do you get any Resistant losses with the ext. current density? I don't think so. With the single turn coil domain you get them and the field. Greetings

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 13 juil. 2011, 06:52 UTC−4

Hi

Thanks but the single coil domain is for azimuthal currents and I have an axial current
Hi Thanks but the single coil domain is for azimuthal currents and I have an axial current

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 13 juil. 2011, 09:00 UTC−4
Hi David,

I don't think you must close an external current inside the model. You should indeed see a magnetic field with a phi component (in axial symmetry) or x and y components in planar symmetry.

Cheers
Edgar
Hi David, I don't think you must close an external current inside the model. You should indeed see a magnetic field with a phi component (in axial symmetry) or x and y components in planar symmetry. Cheers Edgar

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 13 juil. 2011, 19:07 UTC−4

Hi

Thanks but the single coil domain is for azimuthal currents and I have an axial current


Hey,

to be sure we don't talk at cross purposes:
Are you trying to simulate it in a 2D axis symmetric system or a normal 2D system?
I understood it as a normal 2D system.

When you say "axial current", do you mean a current flowing into z-direction, or do you mean a tangential (phi-direction) flowing current (for example around the z-axis)?
Because I understood it as a flow into z-direction.
When you say "external current", do you mean "external current density", or do you couple your model with e.g. the electrical circuit physics?

IF you want to let it flow into z-direction in 2D, a "single turn coil domain" works (Az and Resistant Losses are not zero) [not only at azimuthal currents]. As far as I know, the "external current density" doesn't work here (Az and Resistant Losses are zero).
IF you want to let it flow around the z-axis, you can define it with only a phi- component in a cylindrical system, or stay in cartesian coordinates and use parametric circle equations.

Perhaps I'm just having a wrong image of you model in my mind. Could you maybe attach it?



Greetings
[QUOTE] Hi Thanks but the single coil domain is for azimuthal currents and I have an axial current [/QUOTE] Hey, to be sure we don't talk at cross purposes: Are you trying to simulate it in a 2D axis symmetric system or a normal 2D system? I understood it as a normal 2D system. When you say "axial current", do you mean a current flowing into z-direction, or do you mean a tangential (phi-direction) flowing current (for example around the z-axis)? Because I understood it as a flow into z-direction. When you say "external current", do you mean "external current density", or do you couple your model with e.g. the electrical circuit physics? IF you want to let it flow into z-direction in 2D, a "single turn coil domain" works (Az and Resistant Losses are not zero) [not only at azimuthal currents]. As far as I know, the "external current density" doesn't work here (Az and Resistant Losses are zero). IF you want to let it flow around the z-axis, you can define it with only a phi- component in a cylindrical system, or stay in cartesian coordinates and use parametric circle equations. Perhaps I'm just having a wrong image of you model in my mind. Could you maybe attach it? Greetings

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 14 juil. 2011, 08:59 UTC−4
Hi

thanks for your interest

the system is 2D axisymmetric, the current flows in the z direction, I am trying to see the B field surrounding this current.

attached is a file with the simple geometry, I inject external current density but see no B field.

thanks

David
Hi thanks for your interest the system is 2D axisymmetric, the current flows in the z direction, I am trying to see the B field surrounding this current. attached is a file with the simple geometry, I inject external current density but see no B field. thanks David


Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 14 juil. 2011, 09:01 UTC−4
Hi

thanks for your interest

the system is 2D axisymmetric, the current flows in the z direction, I am trying to see the B field surrounding this current.

attached is a file with the simple geometry, I inject external current density but see no B field.

thanks

David
Hi thanks for your interest the system is 2D axisymmetric, the current flows in the z direction, I am trying to see the B field surrounding this current. attached is a file with the simple geometry, I inject external current density but see no B field. thanks David


Ruud Borger COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 16 juil. 2011, 02:45 UTC−4
Dear David,

In a 2D-Axisymmetric analysis, z is the height on your screen (up-down), and phi is the vector that goes into your screen. This is the component that you want: set Jphi to some non-zero value.

I have two more tips for your model:

1. Create a large rectangle around the block so that the surrounding field can be calculated correctly. Make sure that there is enough space for the field to be reduced to 5-10% of their maximum value, preferably more.
2: Refine your mesh.

I hope that helps.

Best regards,

Ruud
Dear David, In a 2D-Axisymmetric analysis, z is the height on your screen (up-down), and phi is the vector that goes into your screen. This is the component that you want: set Jphi to some non-zero value. I have two more tips for your model: 1. Create a large rectangle around the block so that the surrounding field can be calculated correctly. Make sure that there is enough space for the field to be reduced to 5-10% of their maximum value, preferably more. 2: Refine your mesh. I hope that helps. Best regards, Ruud

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 18 juil. 2011, 09:52 UTC−4
Ruud,

I think he wants a current in z-direction, not phi. This should generate a Bphi field, but it doesn't in the model.

Is it possible to set an external current density in z direction?

Cheers
Edgar
Ruud, I think he wants a current in z-direction, not phi. This should generate a Bphi field, but it doesn't in the model. Is it possible to set an external current density in z direction? Cheers Edgar

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 19 juil. 2011, 21:21 UTC−4
Can it model a moving magnet with a stationary coil to produce current (Induced)???
Can it model a moving magnet with a stationary coil to produce current (Induced)???

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.