Discussion Forum

Hello,

I do most of my modelling using electrostatics steady-state solutions.

One thing that comes up in my models alot is a grounded metal object in a linear, vertical electric field as shown in the attached figure (sorry for MS paint, I am not at a comsol workstation right now).

I have two large horizontal steel plates, 1m apart in an air domain. In the diagram, you can see how the ambient field is set up (by setting the top plate to 100V and the bottom to ground).

In real life, assuming the object and the bottom plate are all connected and made from the same metal, it would take only one connecting wire to ground the whole assembly (i.e. set it all to 0V).

When I apply the BCs (100V to top plate, ground to bottom plate) my metal object does not come out at 0V, but appears 'transparent' to the field like a floating electrode would (it matches the potential of the air around it).

I can of course manually set every boundary of the object to 0V, but it is counter-intuitive to me that I should need to do this. In practice, you would ground a metal assembly just by connecting a wire to a single part of it.

I intend to go on to study electrostatic induction (bringing charged objects up to the metal assembly) and study changes in charge distribution (and thus electric field) in the assembly.

I hope the question is coherent. Thanks in advance for any help.
Kind regards,
Dominic.