11.2. How to Create Coupled Degree-of-Freedom Sets

You can use several different methods to create a coupled degree-of-freedom set, including CP and other commands such as CPNGEN, CPINTF, CPLGEN, and CPSGEN.

In addition to the methods discussed here, you can use the internal multipoint constraint (MPC) feature of certain contact elements (CONTA172, CONTA174, CONTA175, and CONTA177) to model coupling constraints. By this method, the program builds MPC equations internally based on the contact kinematics. See Multipoint Constraints and Assemblies in the Contact Technology Guide for more information on how to use this feature.

 

11.2.1. Creating and Modifying Coupled Sets at Specified Nodes

Use the CP command to define (or modify) a set of coupled degrees of freedom.

After creating a coupled set of nodes, you can include more nodes in that set by simply performing an additional coupling operation (be sure to use the same set reference number). You can also use selecting logic to couple "ALL" of the selected nodes. Nodes can be deleted from a coupled set by inputting them as negative node numbers on the CP command. To modify a coupled degree-of-freedom set (that is, add or delete nodes, or change the degree-of-freedom label), use the CPNGEN command. (You cannot access the CPNGEN command directly in the GUI.)

 

11.2.2. Coupling Coincident Nodes

The CPINTF command couples coincident nodes in a model by generating one coupled set for each specified degree-of-freedom label at every pair of coincident nodes. This operation is useful for "buttoning" together several pairs of nodes (such as at a seam).

Instead of coupling coincident nodes, you can use one of these alternative methods to force the nodes to behave in the same way:

  • If all degrees of freedom are to be coupled for coincident nodes, it is usually more efficient to simply merge those nodes together via NUMMRG.

  • You can connect coincident pairs of nodes by creating two-node elements between them via EINTF.

  • To tie together two regions having dissimilar mesh patterns, issue CEINTF. This operation generates constraint equations that connect the selected nodes of one region to the selected elements of the other region.

 

11.2.3. Generating More Coupled Sets

After one or more coupled sets exist, you can generate additional sets as follows:

  • To generate new coupled sets using the same node numbers, but different degree-of-freedom labels, as an existing "pattern" set, use CPLGEN.

  • To generate new coupled sets using different (uniformly incremented) node numbers, but the same degree-of-freedom labels as an existing set, use CPSGEN.

 

11.2.4. Listing, Deleting, and Selecting Coupled Sets

You can perform these other operations to manage coupled sets:

  • Use CPLIST to list coupled degree-of-freedom sets.

  • Use CPDELE to delete entire coupled degree-of-freedom sets.

  • Use CPNGEN or CP to delete specific nodes from coupled sets.

  • Use CPSEL to select coupled degree-of-freedom sets.