One-node 3-dimensional spring (SPRING1)

This is a spring element which is attached to only one node. The direction $\boldsymbol{n}$ 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 $\boldsymbol{u}$ is the displacement in the spring node and $K$ is the spring constant, the force is obtained by:

$$\boldsymbol{F}=K (\boldsymbol{u} \cdot \boldsymbol{n}) \boldsymbol{n}.$$ (15)

A nonlinear spring can be defined by specifying a piecewise linear force versus elongation relationship (underneath the *SPRING card).