Automatic coupling

Use Automatic Coupling to automatically create coupled degrees of freedom between offset or symmetric meshes. The offset or symmetry condition can be in terms of any of the three coordinate system types. A coupled degree of freedom is a set of nodes linked together in specific directions and rotations. For example, you can use Automatic Coupling to couple the nodal degrees of freedom on a part that is a rotational cyclic symmetry equivalent of a full circular model.

With Automatic Coupling, the software pairs the nodes on the independent side of the model with nodes on the dependent side of the model using a coordinate system and nodal search tolerance you specify. The software searches for nodes based on the translation from a designated independent node to a designated dependent node using the search tolerance. Optionally, the software modifies the displacement coordinate system of all the nodes that participate in the coupling to use the designated coordinate system. You specify the directions and rotations in which the software couples the nodes.

Note:

An Automatic Coupling is categorized as a constraint in the Nastran or Simcenter Samcef environments. It is categorized as a solver-specific Simulation object in the ANSYS and Abaqus environments.

Understanding the Automatic Coupling process

With Automatic Coupling, the software automatically searches your model for valid pairs of nodes to couple based upon criteria you specify. In the Automatic Coupling dialog box, you first select a node or vertex from the independent side of the model (the independent node) and a node or vertex from the dependent side of the model (the dependent node). These two nodes or vertices should represent a matching and logical pair. You must specify a reference coordinate system, which is the coordinate system the software uses to search for the node pairs. You also have the option to explicitly specify an edge or face that is associated with the independent node. This helps the software more easily identify all the nodes on the independent side of the model.

Note:

If you select vertices to define the Automatic Coupling rather than individual nodes, the software is able to update the coupling if the underlying mesh changes. If you select nodes and the underlying mesh changes, the associated Automatic Coupling becomes inactive until you redefine the target sets.

With Automatic Coupling, the software first searches for all valid nodes on the independent side of the model. With those identified, it searches for the matching nodes on the dependent side. The software determines a point location by translating from each independent node a distance equal to the translation between the specified independent and dependent nodes. Therefore, the distance between the selected independent and dependent nodes controls the translation of all the nodes in the reference coordinate system. With each point location, the software creates a search sphere whose radius is equal to the specified Node Match Tolerance. If the software finds a node within the sphere, it pairs that node with the independent node and couples their degrees of freedom as specified on the Automatic Coupling dialog box.

Setting an appropriate Node Match Tolerance

If the value for the Node Match Tolerance is set too high, the software may find multiple matching nodes. In this case, the software's node matching algorithm attempts to choose the closest node on a free face. However, there are cases in which the software may not be able to determine the appropriate match for a node. To help avoid this issue, in general, you should keep the specified Node Match Tolerance to less than 50% of the defined element size.

Specifying the reference coordinate system

By default, when you create an Automatic Coupling, the software modifies the displacement coordinate system of the independent and dependent nodes to use the specified reference coordinate system. If you are creating coupled degrees-of-freedom in a rotational or cyclic symmetry model, the nodal displacement coordinate system must be cylindrical.

Where do I find it?

Application	Pre/Post
Prerequisite	A Simulation file as the work part and displayed partSimcenter Nastran, MSC Nastran, Abaqus, ANSYS, LS-DYNA, or Simcenter Samcef as the specified solver
Command Finder	Automatic Coupling
Simulation Navigator	Right-click Constraint Container→New Constraint→Automatic CouplingFor Abaqus and ANSYS, under a Solution, right-click Simulation Objects→New Simulation Object→Automatic Coupling

How do I

Define an automatic coupling

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Automatic coupling, Simcenter 3D 2021.1 Series

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