Hard-coding elemVolVars in flux laws (Fick's law, Fourier's law, ...) prohibits reuse
There are certain situations where one would like to evaluate fluxes using e.g., Darcy's law, Ficks's law, etc. For instance, coupling free flow with Darcy requires calculating the diffusive fluxes across the interface as coupling condition.
Unfortunately, one cannot just use
FicksLaw and pass the current
elemVolVars to it because the latter do not contain
outsideVolVars since the coupling boundary is considered as a
neumann boundary (therefore, no outside volvars exist for TPFA).
The problem basically always arises when I would like to calculate a flux within a
The problem could be solved by making
elemVolVars a template in
FicksLaw and passing some custom
pseudoElemVolVars (containing the relevant outside data, see !2398 ).
Another option would be to make
elemVolVars themselves more flexible, allowing the user to manually add
outsideVolVars with given input primary variables.