This is a spring element which is attached to two nodes (Figure 79). The directions and determining the action of the spring have to be defined by the user underneath the *SPRING keyword card by specifying the appropriate degrees of freedom. These degrees of freedom can be local if the ORIENTATION parameter is used on the *SPRING card. Usually, it does not make sense to take a different degree of freedom in node 1 and node2. If is the displacement in node 1 (and similar for node 2) and is the spring constant, the force in node 1 is obtained by:
and the force in node 2 by:
A nonlinear spring can be defined by specifying a piecewise linear force versus elongation relationship (underneath the *SPRING card).