Equivalencing is the process of reducing all nodes that coexist at a point to a single node. This change is propagated through any existing FEM definition (element connectivity definitions, MPC equations, loads and boundary conditions), geometry definition and groups.

By default, a red highlight circle is drawn over each retained node causing the deletion of neighboring nodes. For example, if nodes 2 and 3 are deleted because of their proximity to node 1, then a circle is drawn over node 1. If node labels are active, a highlight label appears indicating the selected ID.

The removal of a node by equivalencing causes all occurrences of that node in the FEM definition to be replaced with the surviving node, which is usually the coincident node with the lowest ID. The surviving node remains associated with whatever geometric entity it was associated with prior to equivalencing. However, the effect on groups are additive. For example, if equivalencing removes a node which belongs to group1, in favor of a surviving node which belongs to group2, then the surviving node is associated with both groups.

The selection of the retained node among a set of coincident nodes is guided by two principles:

Therefore, Patran always retains the coincident node with the lowest ID, unless one of the coincident nodes belongs to an MPC or a zero length element edge, and the MPC or element contains at least two nodes in the set of nodes for which equivalencing has been requested. (In the Equivalence-All option, for example, that set is the set of all nodes in the model.) Furthermore, if nodes 1, 2, and 3 are coincident and nodes 2 and 3 are connected by an MPC equation, then if the Equivalence-All option is chosen, all references to node 1 will be replaced with node 2. However, if the Equivalence-List option is used with a node list of “Node 1:2”, then all references to node 2 will be replaced with node 1. The MPC is ignored here because only one of its nodes is in the user-specified set.

The automated equivalencing method available in Patran is called Geometric Equivalencing. Geometric Equivalencing is based upon the physical coordinates of the node points. The proximity is compared with a user definable tolerance parameter called the Equivalencing Tolerance.

Equivalencing can be delayed until the completion of the model, but it is generally recommended that equivalencing be performed before loads and boundary conditions are defined. In this way, diagnostics which may be issued for loads and boundary conditions will have more significance since Patran will be implementing the values of nodal attributes at common nodes at the time of loads and
boundary specification.

Equivalencing should always be performed prior to the optimization of element connectivity and the generation of the neutral file output file.

The model, or any portion of the model, can be equivalenced more than once. When the new component is completed and equivalenced, only those nodes which are newly equivalenced as a result of this second equivalencing will be circled.

It is necessary to perform local equivalencing whenever a modification is made to a region’s mesh. Only the new nodes will be subject to equivalencing.

If the INTERRUPT button is selected during equivalencing, the search for equivalent nodes is immediately terminated. If any changes have been made to the node numbering sequence, they will
be reversed.

The results of equivalencing can be verified by bringing up the “Verify⁄Element⁄Boundaries” form.