This is a spring element which is attached to only one node. The direction in which the spring acts has to be defined by the user underneath the *SPRING keyword card by specifying the appropriate degree of freedom. This degree of freedom can be local if the ORIENTATION parameter is used on the *SPRING card. If is the displacement in the spring node and is the spring constant, the force is obtained by:
A nonlinear spring can be defined by specifying a piecewise linear force versus elongation relationship (underneath the *SPRING card).