### 5.6.1. Using Domain Interfaces

The following points should be considered when using domain interfaces:

- Domain interfaces are always required when multiple assemblies are used within a domain or across multiple domains. If you do not create the required domain interfaces, the regions will remain part of the default wall boundary condition.

- Domain interfaces are also always required when multiple domains are created within a single assembly. If you do not create the required domain interfaces, default domain interfaces will be created which may or may not be appropriate.

- Domain interfaces are not required when multiple 3D regions within the same assembly are selected for a single domain.

- Any given domain must contain at least one node that is not used in a domain interface. Domains defined only by interface nodes will not be accepted by the CFX-Solver.

- You cannot use Mesh Adaption when a simulation contains domain interfaces.

Information on the implementation of GGI connections is available in GGI and MFR Theory in the CFX-Solver Theory Guide.

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