Two-node 3-dimensional spring (SPRINGA) next up previous contents
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Two-node 3-dimensional spring (SPRINGA)

This is a spring element defined between two nodes (Figure 64). The force needed in node 2 to extend the spring with original length $ L_0$ to a final length $ L$ is given by:

$\displaystyle \boldsymbol{F}=k(L-L_0) \boldsymbol{n},$ (9)

where k is the spring stiffness and $ \boldsymbol{n}$ is a unit vector pointing from node 1 to node 2. The force in node 1 is $ \boldsymbol{-F}$. This formula applies if the spring stiffness is constant. It is defined using the *SPRING keyword card. Alternatively, a nonlinear spring can be defined by providing a graph of the force versus the elongation. In calculations in which NLGEOM is active (nonlinear geometric calculations) the motion of nodes 1 and 2 induces a change of $ \boldsymbol{n}$.

Figure 64: Definition of a SPRINGA element
\begin{figure}\epsfig{file=spring.eps,width=5cm}\end{figure}

The two-node three-dimensional spring element is considered as a genuine three-dimensional element. Consequently, if it is connected to a 2D element with special restraints on the third direction (plane stress, plane strain or axisymmetric elements) the user has to take care of the third dimension does not induce rigid body motions in the spring nodes. An example of how to restrain the spring is given in test example spring4.


next up previous contents
Next: One-node coupling element (DCOUP3D) Up: Element Types Previous: Two-node 3-dimensional dashpot (DASHPOTA)   Contents
guido dhondt 2012-10-06