Behavior DASHPOT#

Definition#

Behavior DASHPOT is a law that allows to introduce a form of damping into quasistatic calculations. To activate it you must use the keyword RELATION =” DASHPOT “. At each moment of calculation \({t}_{i}\), it links the nodal force \(F({t}_{i})\) to the displacement increment \({\mathrm{\Delta }}_{x}({t}_{i})\) (and not to the total displacement as the law ELAS does) in the following way: \(F({t}_{i})=K{\mathrm{\Delta }}_{x}({t}_{i})\) where \(K\) is a stiffness parameter provided by the user via the command AFFE_CARA_ELEM [U4.42.01] ( CARA =” K_T_D_L “or” K_T_D_N “).

This law does not really make physical sense; it is used in some complex calculations where we need to limit the movements of rigid bodies while reducing the intensity of the restoring force in the discrete element. The idea is to limit the undesirable effects due to these recall forces as much as possible.

The specificities of the Quasi-Static Dashpot formulation are:

  • Unlike elastic springs, the model does not take into account the history of loading at the beginning of the time step;

  • The Dashpot adapts to sudden kinematic changes (movement jumps); if the movement increment is large, the recall force is large. On the other hand, if the increment is small, the return force is small; this has the consequence of introducing more regular force control than the springs;

  • The almost static Dashpot model implemented in the code is not sensitive to the effects associated with small time steps;

  • In cases where you have a single time step and you are not in reuse mode of a previous non-linear calculation, the Dashpot is reduced to an elastic spring.

Internal variables#

This behavior has no internal variables.