One other thought I just had is maybe the reason my initialize to steady state does not work is that our initial position is too far from the steady solution. You can try moving the masses close and then try it.

Here is the model with the bar and mass flying off.

Attachments:

DetachableMasses.mo

Mor,

The way to model a detaching mass is as a lineforce combined with a stiff spring representing the rigid translation. By editing a spring component, you can make the spring "give up" and apply no force when a boolean variable changes.

Here is an example system:

The detachable spring is coded:

model DetachableSpring
  import SI = Modelica.SIunits;
  extends Modelica.Mechanics.Translational.Interfaces.PartialCompliant;
  parameter SI.TranslationalSpringConstant c(final min = 0, start = 1) "spring constant ";
  parameter SI.Distance s_rel0 = 0 "unstretched spring length";
  Modelica.Blocks.Interfaces.BooleanInput attached annotation(Placement(visible = true, transformation(origin = {-100.0, 68.0}, extent = {{-20.0, -20.0}, {20.0, 20.0}}, rotation = 0), iconTransformation(origin = {0.0, 120.0}, extent = {{-20.0, -20.0}, {20.0, 20.0}}, rotation = -90)));
equation
  f = if attached then c * (s_rel - s_rel0) else 0;
end DetachableSpring;

The simulation looks like this (note the distance between the masses is plotted in the background showing the release at 3.5 seconds.

The full model is attached.

Regards,

Neil

Attachments:

DetachableMasses.mo