Spring and Damping Forces
The spring force is proportional to the spring constant
k
:
If
k
depends on the extension, so that the spring is nonlinear, it should be interpreted as a secant stiffness, that is
You can also specify the spring force as function of extension explicitly, as
To create the expression for the function, use the built-in variable for the spring extension. It has the form <
physicsTag>.<SpringNodeTag>
.
dl
, for example
mbd.spd1.dl
.
In a dynamic analysis, the viscous damping force is computed as
where
c
is the viscous damping coefficient.
The magnitude of the total force is
The total forces in the global coordinate system, acting on the destination and source points are
In a geometrically linear case, the orientation of the force is kept fixed, so that
The contribution to the virtual work is
