Can FEniCS handle individual PDEs on coupled regions (like conjugate heat transfer)?

Question

Hello,
I would like to solve physical models that involve separate regions (meshes) described by different PDEs, like conjugate heat transfer between a fluid and a solid region. For better convergence all DOFs should be included in the same equation system instead of solving the solid and fluid region in turns and iterate them with underrelaxation. (The duplicated DOFs for the coupled variable (temperature) on the inner boundary need to be accounted for, of course)

Basically the same question remained unanswered here:
https://fenicsproject.org/pipermail/fenics-support/2014-May/000549.html
Then it was rephrased here:
https://fenicsproject.org/pipermail/fenics-support/2014-May/000569.html
with an answer "Mixing different meshes in single form is not yet supported with full
generality but rapid development is currently taking place in this
area."

Do any examples exist for similar problems?
Or can somebody comment, whether it would be reasonable to just append the equation system of the fluid region after the solid region and additionally equate the boundary temperatures on the congruent nodes from both meshes?

(As a side note, I am not looking for solutions like adding weighted PDEs:
"isOnMesh1PDEsys1+(1-isOnMesh1)PDEsys2)",
which switches on and off different PDEs depending on a weighting function that is either 1 or 0 in each region. This approach is problematic with nontrivial inner boundary conditions, and also rather inefficient.)

Thank you
Herrmann

Comments

Hello everybody,
unfortunately, there was no reply on my question. May I ask, why?
Is the question unclear?
Can somebody confirm that it is impossible to couple different equation systems on different meshes using the current FEniCS? Then I will work on a modification of the underlying matrices.

Thank you
Herrmann