Discussion Forum

I have a simple 5 domain model, composed of roughly concentric spheres. I am modeling a transmembrane potential on the 3rd domain using the General Form PDE physics. This part is working correctly. I am then trying to use that potential to compute the magnetic and electric fields at the inner boundary of the outermost domain.

This was implemented pretty simply in COMSOL 3.5, using Conductive Media DC and QuasiStatics to find the electric and magnetic fields sequentially. The only inputs were the conductivities and the external current density from the PDE simulation. I'm not having any luck reimplementing it in 4.3.

With COMSOL 4.3, I'm using the Magnetic and Electric Fields physics. The transmembrane potential is used in the MEF physics in the expression for the external current density on the 3rd domain. I have a study with two steps - a time-dependent and a stationary step. The PDE physics are active in the first, the MEF physics in the second. For the stationary step, I tell it to use all the solutions from the time-dependent step for the variables not solved for.

My most recent error message is:
Failed to find a solution.
Divergence of the linear iterations.
Returned solution is not converged.

When I look at the convergence plot, the error steadily decreases until it hits a floor, and then it stays constant until COMSOL gives up after 10000 iterations.

Any suggestions on what's causing this?

(As a side note, these ask for permittivities and permeabilities that I didn't need before - why? Is there a way around this?)