Support multiple coupling subdomains

[MakisH]

fenics-adapter/fenicsadapter/fenicsadapter.py

Lines 89 to 97 in 7fec6f3

	def configure(self, participant, precice_config_file, mesh, write_data, read_data):
	self._solver_name = participant
	self._interface = PySolverInterface.PySolverInterface(self._solver_name, 0, 1)
	self._interface.configure(precice_config_file)
	self._dimensions = self._interface.getDimensions()
	self._mesh_name = mesh
	self._write_data_name = write_data
	self._read_data_name = read_data

By having the configure() directly inside the Adapter class, we assume that the adapter can only work with one coupling interface. By separating the adapter class (that also handles the time control etc) from the interface itself, we could support multiple coupling interfaces (for example, for Fluid-Solid-Fluid coupling, as in the shell-and-tubes heat exchanger tutorial).

Then, the configure() method would not be called in the adapter itself, but in each coupling interface. The same for the methods to read/write data etc.

[BenjaminRodenberg]

The intended use of the adapter is one interface. In certain situations more than one interface might be needed, but I don't really see the need for this feature now. As a workaround I can imagine that creating two instances of the adapter object might even be sufficient. From a developer's perspective this is also the preferred solution, since supporting N coupling interfaces in the adapter would make the code considerably more complicated for an edge case.

I will close this issue. Feel free to reopen it or comment. Especially related:

• Do you have a use case for the fenics adapter with several coupling interfaces?
• Does the approach mentioned above (creating two instances of the adapter) work?

[MakisH]

Going with "only supporting one interface" is perfectly fine, it is a design decision.

Do you have a use case for the fenics adapter with several coupling interfaces?

Use cases I can think of:

• Heat exchanger (one solid, two fluids)
• Separating membrane (one solid, two fluids)
• Beams connected (multiple solids)
• (if you add support for flows) FSI with two flaps (one fluid, two solids)

Does the approach mentioned above (creating two instances of the adapter) work?

I don't know anything about the FEniCS adapter code, but in the OpenFOAM adapter we have it like this and it works.

[BenjaminRodenberg]

I totally misunderstood the issue. We are talking about coupling_subdomains, not about what we call the interface in the adapter:

fenics-adapter/fenicsprecice/fenicsprecice.py

Lines 267 to 268 in 87e03f8

	coupling_subdomain : Object of class dolfin.cpp.mesh.SubDomain
	SubDomain of mesh which is the physical coupling boundary.

fenics-adapter/fenicsprecice/fenicsprecice.py

Line 57 in 87e03f8

self._interface = precice.Interface(self._config.get_participant_name(), self._config.get_config_file_name(),

This is, of course, a totally valid use-case. We already have several tutorials dealing with this and I can also imagine extending the fenics adapter into this direction, if needed.

note: Naming with interface vs. subdomain is in some places inconsistent and confusing. I will open a PR in a moment to clean this up.