Periodic Condition
The Periodic Condition 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 a Destination Selection subnode to control the destination. By default it contains the selection that COMSOL Multiphysics identifies.
Periodicity Settings
Select a Type of periodicity: Continuity (the default), Floquet periodicity (Bloch periodicity), or Cyclic symmetry, or Antiperiodicity.
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For Floquet periodicity, also known as Bloch periodicity, enter a k-vector for Floquet periodicity kF (SI unit: rad/m) for the x, y, and z coordinates (3D components), or the r and z coordinates (2D axisymmetric components), or x and y coordinates (2D components).
This condition is used to model infinite periodic structures with non-normal 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.
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For Cyclic symmetry select a Sector angle: Automatic (the default), or User defined. For User defined enter a value for θS (SI unit: rad). Enter an Azimuthal mode number 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 what mode 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 Cyclic symmetry and the Floquet periodicity boundary conditions reduce to the continuity condition.
To optimize the performance of the Floquet periodicity and the Cyclic symmetry conditions, it is recommended that the source and destination meshes are identical. This can be achieved by first meshing the source boundary or edge and then copy the mesh to the destination boundary or edge. 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 such boundaries.
Constraint Settings
To display this section, click the Show button () and select Advanced Physics Options.
Orientation of Source
For information about the Orientation of Source section, see Orientation of Source and Destination in the COMSOL Multiphysics Reference Manual.
The Porous Absorber model uses Floquet periodic boundary conditions to model an infinite porous absorber used for sound proofing. The Application Library path is Acoustics_Module/Building_and_Room_Acoustics/porous_absorber