I have been implementing Neumann conditions as essential conditions in FEM schemes with successful results and was wondering whether this type of boundary condition was previously implemented.
I have seen a few papers that discuss the topic which claim their idea is original. However, I have seen in a FEM forum the following sentence:
There are cases where the Dirichlet BC can become a natural BC (Nitsche’s method → related to discontinuous Galerkin method) and Neumann BC can be transformed into an essential condition using the so called mixed methods. But for our “Beginner’s course” we can assume that the Dirichlet BC is an essential BC and the Neumannn a natural one.
https://www.simscale.com/forum/t/the-finite-element-method-fundamentals-physical-problems-2/28665
However, What would be "mixed methods" in this case? Searches on mixed methods did not supply much besides the other papers which claim originality.