Discussion Forum

Hi,

Allow me to give some partial answers to the questions you raise:

1) To set the current density in a non-circular coil, I resorted to an
approach in which I specified the spatial distribution of the
current density vector. This approach has limited applicability,
and possibly alternatives easier to apply do exist.

2) To model a winding (also called stranded conductor) you indeed
need to set the conductivity equal to zero. Different people have
succesfully applied this in Comsol Multiphysics and I could send
you example models if of interest to you.
The issue to pay attention to in solving a 3D transient model with
zero-conductivity is that one has to enforce the cauging
condition at each time step in over to enforce the magnetic
flux to remain divergence free. This can be done by solving
simultaneously for vector and scalar potential.

3) I suggest to solve the model using a direct solver first, and worry
about an iterative solution technique in a second stage.

I share your interest in eddy-current computations.

Bye, Domenico Lahaye.

Hello Domenico Lahaye,

Thanks for your answer and help!

Yes you have right, i think also that the spatial distribution of the current density vector in the subdomain area are limited for symmetries geometries. For 2 years i work with the Ansoft Maxwell Software. In this Software was it easy to specify the current density for a non-circular coil. I only set a current density terminal + Current source and i can set the skin effect off with one click but comsol makes it not so easy to me. I try many to specified the current density but with zero conductivity i see no alternatives to apply the current source.

2) Im very interest for an example with stranded conductor, then I can find out whether my model is correct and can study more with stranded conductor models. Thanks for your offer! It is possible to create a 3D "transient" model with a frequency of 1 MHz?
I know the gauge fixing problem in 3D and read many article and books about it, but I'm not sure whether I've understood the theory correctly.
Mean you with simultaneously solving the variables "psi" and "tAxAyAz10..."?

3)Yes you have right, the iterative solver are not easy to use but it could help to save much memory.
My model have often more as 100000 DOF, because i can exploit in the geometry only one symmetry.
Furthermore i make experimental with infinity elements for a better accurate solution

I'm fascinated by Comsol Multiphysics!

Bye, Matthias

Hola Matthias,

There is number of issues to reply you with:

1) a) Setting the spatial distribution of the current density can be done for the coils
of the TEAM problem you are interested in: indeed, J is essentially plus or
minus one on the straight side and equal to the circular coil J in the bend
corners.
b) Possibly one can copy the Ansys trick in Comsol by solving a PDE for the
components of J in a seperate application mode (did not yet understand the
details myself though, support?).
c) The modeling of voltage driven stranded conductors and current driven
solid conductors is discussed in Chapter 2 of my thesis (available from my
home page). Essentially you supply the PDE with an ODE modeling the
electrical excitation (mail me for details).

2) a) I am working on notes explaining one and other. Attached you will find
a pre-release of these notes, including some example in 2D for time being.

b) I do not understand your 3D transient 1Mhz question. The AC/DC module
comes with an example modeling skin-effect you might want to look into.

c) By gauge fixing I do indeed mean what you understood.

Do you still plan to make your hands durty with that TEAM problem?

Bye, Domenico.

Hi Domenico,

I'm having the same problem as Matthias, however with a different coil. I'd like you to send me some examples about the stranded coil solved in multiphisics. I'm trying to solve first the electrical circuit and then the magnetic problem, but I don't know what I am doing wrong.

Thanks,
Iker.