Periodic Condition
Use a Periodic Condition to prescribe that the displacements on two different sets of boundaries with the same geometrical shape are related, as in a periodic structure.
Several different types of periodicity properties of the solution can be prescribed using this boundary condition.
The Continuity, Antiperiodicity, and User defined periodic conditions directly prescribe relations between displacements and can be used for any type of study.
The Floquet periodicity can be used for frequency domain problems with a spatial periodicity of the geometry and solution. The modeled structure is typically a unit cell of a repetitive structure.
The Cyclic symmetry is a special case of a Floquet condition, intended for structures which consist of a number of sectors which are identical when rotated around a common axis, like in a fan.
The Floquet periodicity and Cyclic symmetry options are available only with some COMSOL products (see http://www.comsol.com/products/specifications/).
The two sets of boundaries between which there is a periodicity condition are called the source and destination. It is not required to have the same mesh on the source and destination, but the local accuracy of the solution at the boundaries will be better if you use the same mesh.
Boundary Selection
Select both the source and destination boundaries.
The software automatically identifies the boundaries as either source boundaries or destination boundaries. This works fine for cases like opposing parallel boundaries. In more general cases, use the Destination Selection subnode to specify the boundaries which constitute the destination. By default this node contains the selection that COMSOL Multiphysics has identified.
In cases where the periodic boundary is split into several boundaries within the geometry, it might be necessary to apply separate periodic conditions to each pair of geometry boundaries for the matching to work properly.
Periodicity Settings
With Type of periodicity you select the form of periodicity that your solution should have.
For Continuity the displacements on the destination are set equal to the displacements on the source; . If the source and destination boundaries are rotated with respect to each other, a transformation is automatically performed, so that corresponding displacement components are connected.
For Antiperiodicity the displacements on the destination are set equal to the displacements on the source with the sign reversed; . If the source and destination boundaries are rotated with respect to each other, a transformation is automatically performed, so that corresponding displacement components are connected.
For Floquet periodicity enter a k-vector for Floquet periodicity kF. This is the wave number vector for the excitation.
For Cyclic symmetry choose how to define the sector angle that the geometry represents using Sector angle. If Automatic is selected, the program attempts to find out how many full repetitions of the geometry there will be on a full revolution. If User defined is selected, enter a value for the sector angle θS. In both cases, also enter an Azimuthal mode number for the mode to be studied. It can vary from 0 to N/2, where N is the total number of sectors on a full revolution.
For User defined select the check box for any of the displacement components as needed. Then for each selection, choose the Type of periodicityContinuity or Antiperiodicity. Each selected displacement component will be connected by or . If the source and destination boundaries are rotated with respect to each other, a transformation is automatically performed, so that corresponding displacement components are connected.
Constraint Settings
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box.
In the COMSOL Multiphysics Reference Manual:
Orientation of Source
For information about the Orientation of Source section, see Orientation of Source and Destination in the COMSOL Multiphysics Reference Manual.
Vibrations of an Impeller: Application Library path Structural_Mechanics_Module/Dynamics_and_Vibration/impeller
Location in User Interface
Context Menus
Ribbon
Physics tab with Solid Mechanics selected:
Physics tab with Periodic Condition node selected in the model tree: