Can boundary conditions be functions of state variables

[AmbroiseJuston]

Check these boxes if you have followed the posting rules.

• Q&A General is the most appropriate section for my question
• I have consulted the posting Guidelines on the Discussions front page
• I have searched the Discussions forum and my question has not been asked before
• I have searched the MOOSE website and the documentation does not answer my question
• I have formatted my post following the posting guidelines (screenshots as a last resort, triple back quotes around pasted text)

Question

I have been looking at the FunctionBC___ boundary conditions and i have q question about its capabilities. I would like to create a boundary condition that is a function of a state variable V. That is to say the two state variable of this siimulation are c and V and i would like a boundary condition of c to be a function of the gradient of V.

The bellow figure shows a diagram of what i am tryign to achieve. I am just showing a subset of the conditions but it should give you an idea. Is it possible to use a variable calculated from within the model as an input to a function as to iteratively solve the system? Is it also possible to use a variable calculated from an Aux kernel and vector quantities? The function shown is just for illustration.

Continuing on i would like to then add some more domains onto the model (if the previous question is a yes) and define a BC at the interface of domains. Bellow shows an expanded view. Can this be done in a single app or is a multi-app aproach necessary for such conditions?

[GiudGiud]

Hello

I would like to create a boundary condition that is a function of a state variable V

Functions are supposed to only depend on space and time, not other variables.
So what you want to look at is either BCs using "Functor" or the "Coupled"... / MatchedValue BCs.

The former can evaluate any kind of functor, which includes variables
The latter are dedicated to coupling variables together.

Continuing on i would like to then add some more domains onto the model (if the previous question is a yes) and define a BC at the interface of domains. Bellow shows an expanded view. Can this be done in a single app or is a multi-app aproach necessary for such conditions?

It looks to me like you can try a single app. With either the fully coupled or the multiple-system approach for solving the nonlinear equations