SpringDamperSeries

Linear spring and linear damper in series connection acting as line force between frame_a and frame_b:

  frame_a --> damper ----> spring --> frame_b
          |              |
          |-- s_damper --|  (s_damper is the state variable of this system)

A force f is exerted on the origin of frame_b and with opposite sign on the origin of frame_a along the line from the origin of frame_a to the origin of frame_b according to the equations:

   f = c*(s - s_unstretched - s_damper);
   f = d*der(s_damper);

where "c", "s_unstretched" and "d" are parameters, "s" is the distance between the origin of frame_a and the origin of frame_b. "s_damper" is the length of the damper (= an internal state of this force element) and der(s_damper) is the time derivative of s_damper.