Spring-Damper
Use a Spring-Damper to model — between two points — an elastic spring, a viscous damper, or both. By adding a Truss interface with this material model, you can add springs and dashpots to any other structural mechanics physics interface.
Spring-Damper
Select a Spring typeSpring constant or Force as function of extension.
For Spring constant enter a value for the spring constant k.
For Force as function of extension enter an expression for the spring force Fs. The expression must be a function of the extension of the spring. The built-in variable for the spring extension has the form <physicsName>.<SpringNodeTag>.dl, for example truss.spd1.dl. The default expression is (1[N/m])*truss.spd1.dl, which corresponds to a linear spring with the stiffness 1 N/m.
To add viscous damping in a dynamic analysis, enter a value or expression for the Damping coefficient c.
To add loss factor damping, enter a value for the Loss factor damping η.
Free Length
The free length is the distance between the connection points when there is no force in the spring. Select an option from the list — Specify initial extension or Specify free length.
For Specify initial extension enter a value for Δl0. The free length is computed as lf = l0 − Δl0, where l0 is the initial distance between the connection points.
For Specify free length enter a value for lf.
Activation Condition
Select a Spring actionBidirectional, Tension only, or Compression only.
Select the Deactivation condition check box to enter a Deactivation indicator expression idac. The expression is treated as a boolean expression, so that when it is evaluated to a nonzero value, the spring or damper is deactivated.
Select the Permanently deactivate check box if the spring is supposed to be removed permanently from the simulation once the deactivation condition is fulfilled for the first time.
As an example, if the spring should break at a certain extension, you can write an expression like truss.spd1.dl>0.12[m], and select the Permanently deactivate check box. If the check box is not selected, the spring would become active again when its connection points come close enough to each other.
Location in User Interface
Context Menus
Ribbon
Physics tab with Truss selected: