About Identity and Contact Pairs
Identity Pairs
An identity pair (Identity Boundary Pair ()) is a pair that, by default, makes the fields across two connected boundaries (one from each connecting object in an assembly) continuous. This is equivalent to the continuity that is obtained by default on interior boundaries in a geometry created by forming a union. Some physics provide special boundary conditions for identity pairs to model “slit conditions” such as resistive layers. You can specify boundary conditions for these pairs from the Pairs submenu at the bottom of the boundary condition part of the context menu for the physics feature node. The nodes in the Model Builder that represent pair boundary conditions use an icon with a pair symbol in the lower-left corner: . There are also similar Identity Edge Pair () and Identity Point Pair () pair nodes.
Contact Pairs
A contact pair () is a pair that define boundaries where the parts can come into contact but cannot penetrate each other under deformation for modeling of structural contact and multiphysics contact.
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Contact pair modeling requires the Structural Mechanics Module or MEMS Module. Details about this pair type can be found in the respective product’s user’s guide.
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In a continuity feature, it is possible to select either an identity pair or a contact pair. Selecting a contact pair is only meaningful in conjunction with a structural mechanics interface containing a Contact node in which the contact state for the pair is computed. If the boundaries are in contact, then the continuity is also active.
Fallback Boundary Conditions on NonOverlapping Parts
For pairs where parts of the boundaries do not overlap you need to specify boundary conditions for the non-overlapping parts, which typically represent exterior boundaries outside of the overlapping area. These boundary conditions (fallback boundary conditions) appear as subnodes to the pair’s boundary condition node in the Model Builder. By default, the default boundary condition for exterior boundaries is added to the nonoverlapping parts. If you want to use another boundary condition for any of the nonoverlapping parts, right-click the pair’s boundary condition node (Continuity, for example) and select any of the standard boundary conditions from the Fallback Features submenu. In the Settings window, the selection includes all applicable boundaries by default, but a separate boundary condition can be added for only a subset of the pair boundaries. In the following illustration, which shows a simple example with two partially overlapping rectangles, there is one identity pair that consists of two boundaries, each with a nonoverlapping part. You can right-click the pair’s boundary condition node and, from the Fallback Features submenu, add one fallback boundary condition for the top boundary and another fallback boundary condition for the bottom boundary if desired.
The options for the available fallback conditions are based on the physics interface and the license type (see Figure 5-5).
With only a few exceptions for the Solid Mechanics interface or other physics interfaces using Solid Mechanics functionality, all subnodes to pairs are fallback nodes.
When additional fallback feature nodes are added, the node has an indicator in the lower-left corner () identifying it as a fallback feature node.
Figure 5-5: An example of the Fallback Features submenu for a Continuity pair added to the Solid Mechanics interface.
To add Pairs to any Component:
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In the Definitions toolbar, select features from the Pairs menu, or
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Right-click the Definitions () node and choose an option from the Pairs submenu.
Go to Pair Name for information about the Settings window Pair name. Also see Settings and Properties Windows for Feature Nodes.