Periodic Condition
The Periodic Condition node can be used to define periodicity for the phase transport between two sets of boundaries. The node prescribes continuity in the volume fractions and mass fluxes between the “source” and “destination” side respectively. Note that these names are arbitrary and do not influence the direction in which mass is transported. It is dictated by the phase transport equations in the adjacent domains.
The node can be activated on more than two boundaries, in which case the feature tries to identify two separate surfaces that each consist of one or several connected boundaries.
For more complex geometries, it might be necessary to add the Destination Selection selection, with which you can specify the boundaries that constitute the destination surfaces.
Boundary Selection
The software usually automatically identifies the boundaries as either source boundaries or destination boundaries, as indicated in the selection list. This works fine for cases like opposing parallel boundaries. In other cases, right-click Periodic Condition and select Manual Destination Selection to control the destination. By default it contains the selection that COMSOL Multiphysics identifies.
Destination Selection
This section is available for specifying the destination boundaries, if needed, when the Manual Destination Selection option is selected in the context menu for the Periodic Condition node. You can only select destination boundaries from the union of all source and destination boundaries.
Constraint Settings
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog. The Constraints settings can be set to Use pointwise constraints (default) or to Use DG constraints (if possible). This latter option uses DG constraints as long as the selected boundaries are not adjacent to a porous domain. If the boundary selection contains boundaries adjacent to a porous domain, pointwise constraints are used instead. DG constraints are recommended on boundaries adjacent to a Fluid feature, especially when the mesh vertices do not match across the source and destination boundaries.
Depending on the constraint method selected, the following settings are available:
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Apply reaction terms on can be set to Individual dependent variables (default) or All physics (symmetric). This setting is not available when Use DG constraints (if possible) is selected.
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Select Elemental (default) or Nodal under Constraint method. This setting is available for Use pointwise constraints.
Orientation of Source
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog. For information about the Orientation of Source section, see Orientation of Source and Destination in the COMSOL Multiphysics Reference Manual.
Orientation of Destination
This section appears if the setting for Transform to intermediate map in the Orientation of Source section is changed from the default value, Automatic, and Advanced Physics Options is selected in the Show More Options dialog. For information about the Orientation of Destination section, see Orientation of Source and Destination in the COMSOL Multiphysics Reference Manual.
Mapping Between Source and Destination
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog. For information about the Mapping Between Source and Destination section, see Mapping Between Source and Destination in the COMSOL Multiphysics Reference Manual.