[Getdp] Von Neumann misconception?

[John_V]

Consider an electrostatic problem in a cylindrical volume, bottom end cap
(surface) constrained to V=0, source terms in some volume elements, and top
end cap with a von Neumann constraint implemented as shown in the
formulation below. Does the 3rd Galerkin term (the von Neumann term)

a) Require that the electric field through the upper end cap be equal to
Eimposed?
b) Require that the electric field through the upper end cap be equal to the
sum: field produced by charges in SourceDomain + Eimposed?
c) Something else?

Formulation {
  { Name Electrostatics_v; Type FemEquation;
    Quantity {
      { Name v; Type Local; NameOfSpace Hgrad_v_Ele; }
    }
    Equation {
      Galerkin { [ epsr[] * Dof{d v} , {d v} ]; In Domain_Ele;
                 Jacobian Vol; Integration GradGrad; }
      Galerkin { [ -q[]*chargeUnit/eps0/ElementVol[] , {v} ]; In
SourceDomain;
                 Jacobian Vol; Integration GradGrad; }
      Galerkin { [ Eimposed , {v} ]; In UpperEndCap;
                 Jacobian Sur; Integration GradGrad; }
    }
  }
}

The mesh is a cylindrical volume oriented along z. Domain_Ele refers to all
volume elements of my mesh. SourceDomain is a set of volume elements in
which there are charges. (These are near the lower end cap of the
cylindrical mesh.) The 3rd term was meant to impose my von Neumann
condition. When I wrote it I thought I was doing (a) above, but the result
suggests otherwise.

John
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