Create and Edit Gaps
A gap element is an element created in a space between two nodes, or between a node and an element, of a model where contact may occur. Use a gap element when you want to impose a nonlinear constraint on a model; this constraint will limit the amount of movement possible during analysis.
For more information on creating and updating gaps, see either the Gaps Panel - HyperWorks or the Gaps Panel - OptiStruct topic.