Dirichlet & Neumann Boundary

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1

Hi,

is it possible to use a dirichlet & neumann boundary condition at the same node?
It seems that if i mark the node as “dirichlet”, the neumann condition gets ignored/overwritten.

thanks a lot,
joey

2

quick answer: that’s not allowed with standard FEM, it is as you have observed.

moderate answer: if you are asking for reason of flux conservation issues at vertices where Dirichlet and Neumann bc come together, consider HDG methods: there boundary conditions are applied for edges (or faces in 3D), and not for vertices.

long answer: if you really want to solve an ill-conditioned Cauchy-problem, and you are aware of what you are asking, we should talk extra.

Joachim