DC current flow

Hengre

Hello all,
I have tried to carry out an analysis of the current distribution in a brass body (housing). The resulting power density should be used in a second step for an analysis of the Joule heating. In principle, I managed to do this kind of calculation. But I have some doubts about the results.

I made a first attempt to find the power density by defining one area with +potential (called "plus") and 4 smaller areas with 0 potential (called "zero"), and then solving. The calculation was done. When I compare the surface normal integral of the current density of the surface "plus" with that of the surface "zero", I get different current values. For "zero" it is only ~9350A and for "plus" ~16000A.

In a second approach I applied a current to these surfaces. +15000 A to the surface "plus" and -15000 A to the surface "zero".
After solving this configuration, I got 15000 A for "plus" and only 13542 A for "zero" from the surface normal integrals of the current density.

Does anyone have an explanation of what I am doing wrong?

Best regards

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Victor

Hello Hengre. I don't think you're doing anything wrong. It's just that discretization error can be significant when integrating a field variable that changes rapidly over individual elements, as it does here. EDIT: The error is in the current density itself not the integral.

With the fixed potential BCs, the current is highly localized in one corner of a cavity, but the electric current BC distributes normal current density uniformly over the whole surface, so the discretization error at the corners is less significant.

I'm not sure if this will have any effect on Joule heating.

You could refine the mesh in the corners but I suspect they might be current density singularities.

Hengre

Hello Victor,
thank you for the quick response. Good to know that I am going the right way.

Hengre

Hello

I am about to continue my heating project. I was able to calculate the current distribution. But now I get the following error message during the heating calculation "Element has incorrect topology" (see picture). Unfortunately, the erroneous element is not selected. How can I find and select that element, or how can I correct the error?

Victor

You can find it with Edit -> Select elements by... and enter its number.

First thing may be to delete the element and see if the solver then complains about a different one. There might be many of them.

You may see that it's distorted. If it's quadratic, move the midside nodes to the midpoints of the corner nodes. Alternatively, regenerate the mesh with different parameters, perhaps finer in that region.