Two-node 3-dimensional dashpot (DASHPOTA)

The dashpot element is defined between two nodes (Figure 74). The force in node 2 amounts to:

$$\boldsymbol{F_2}=-c \left[(\boldsymbol{v_2}-\boldsymbol{v_1}) \cd... ..._2}-\boldsymbol{x_1})}{L} \right] \frac{(\boldsymbol{x_2}-\boldsymbol{x_1})}{L}$$ (8)

where c is the dashpot coefficient, $\boldsymbol{v}$ is the velocity vector, $\boldsymbol{x}$ is the actual location of the nodes and $L$ is the actual distance between them. Notice that $\boldsymbol{F_1} = -\boldsymbol{F_2}$. Right now, only linear dashpots are allowed, i.e. the dashpot coefficient is constant (i.e. it does not depend on the relative velocity. However, it can depend on the temperature). It is defined using the *DASHPOT keyword card.

Figure 74: Definition of a DASHPOTA element

The two-node three-dimensional dashpot 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 dashpot nodes.

The dashpot element can only be used in linear dynamic calculations characterized by the *MODAL DYNAMIC keyword card.