Periodic Condition

The node adds a periodic boundary condition that can be used to reduce the model size by using symmetries and periodicities in the geometry and physics interfaces being modeled. This feature works well for cases like opposing parallel boundaries. In other cases, use the section to control the destination. By default, it contains the selection that COMSOL Multiphysics identifies.

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 option is selected in the context menu for the node. You can only select destination boundaries from the union of all source and destination boundaries.

Periodicity Settings

Select a : (the default), , (Bloch periodicity), or .

•

For , also known as Bloch periodicity, enter a kF (SI unit: rad/m) for the , , and coordinates (3D components), the and coordinates (2D axisymmetric components), or and coordinates (2D components).

This condition is used to model infinite periodic structures with nonnormal incident pressure fields or excitations. Use it to model, for example, a large perforated plate with an oblique incident wave with wave vector k (and set kF = k) by only analyzing one hole or one subset of holes that is periodic.

•

For select a : (the default) or . For enter a value for θS (SI unit: rad). Enter an m (dimensionless).

This condition is used to model any geometry that has a cyclic periodic structure such as a microphone or a loudspeaker driver. Setting the azimuthal mode number determines which mode that is analyzed. The response of the full system to an external excitation is in general a linear combination of many different modes.

In the time domain, both the and the boundary conditions reduce to the continuity condition.


	To get correct behavior of the Periodic Condition, in particular the Floquet periodicity and the Cyclic symmetry conditions, it is recommended that the source and destination meshes are identical. This can be achieved using the Identical Mesh mesh feature. When the Periodic Condition stretches across regions with a mix of default material models, PMLs, background pressure fields, or background acoustic fields, it is recommended to add one Periodic Condition for each set of such boundaries.


	The Porous Absorber model uses Floquet periodic boundary conditions to model an infinite porous absorber used for sound proofing. Application Library path Acoustics_Module/Building_and_Room_Acoustics/porous_absorber

Constraint Settings

To display this section, click the button (

) and select in the dialog box. For information about the section, see Constraint Settings in the COMSOL Multiphysics Reference Manual.

Excluded Edges

To display this section, select in the dialog box.

Excluded Points

To display this section, select in the dialog box.

For more information about the and sections, see Excluded Surfaces, Excluded Edges, and Excluded Points in the COMSOL Multiphysics Reference Manual.

Orientation of Source

To display this section, click the button (

) and select in the dialog box. For information about the section, see Orientation of Source and Destination in the COMSOL Multiphysics Reference Manual.

Orientation of Destination

This section appears if the setting for in the section is changed from the default value, , and is selected in the dialog box. For information about the section, see Orientation of Source and Destination in the COMSOL Multiphysics Reference Manual.

Mapping Between Source and Destination

To display this section, click the button (

) and select in the dialog box. For information about the section, see Mapping Between Source and Destination in the COMSOL Multiphysics Reference Manual.