These conditions are legacy and should not be considered for general
use. They require specific, unintuitive mesh structuring (i.e.,
duplicated boundary faces) that only PDRMesh can now create.
If an an interface is needed which opens or closes based on modelling
criteria, then this should be implemented as an extension of NCC. That
would be more flexible, parallelisable, and would not require
modification of the underlying polyheral mesh.
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