Two-node unidirectional gap element (GAPUNI)

This is a standard gap element defined between two nodes. The clearance $d$ of the gap and its direction $\boldsymbol{n}$ are defined by using the *GAP card. Let the displacement vector of the first node of the GAPUNI element be $\boldsymbol{u_1}$ and the displacement vector of the second node $\boldsymbol{u_2}$. Then, the gap condition is defined by (Figure 77):

$$d+\boldsymbol{n} \cdot (\boldsymbol{u_2} -\boldsymbol{u_1}) \ge 0.$$ (13)

Figure 77: Definition of a GAPUNI element