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crum
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Homework Statement
I'm trying to solve Laplace's equation numerically in 3d for a charged sphere in a big box. I'm using Comsol, which solves using the finite elements method. I used neumann BC on the surface of the sphere, and flux=0 BC on the box in which I have the sphere. The result does not converge.
Homework Equations
Laplace's equation \[\nabla^2 \phi=0\]
The Attempt at a Solution
I've tried using derichlet BC instead of neumann, and a fixed potential at the box (instead of flux=0), but the result still doesn't converge. Convergance errors usually appears when the mesh is not fine enough or I'm missing a boundary condition, but I don't see how using neumann at the surface and flux=0 at the box wouldn't be enough boundary conditions. I have used the same BCs using the Poisson-Boltzman eq and it worked fine there.