Hi Hans,

Your usage of reinit is not valid, since the variable being reinitialized must be of type Real. Unfortunately we don't check this yet. But I think the real problem is that reinit is not counted as one equation, since a state variable should already have another equation associated with it. So from PartialCompliant you get 6 unknown and 5 equations, and then you introduce 1 unknown and 1 equation in your model. So you need to also supply an equation for broken to make the model balanced.

Unfortunately I'm not a modeler, so I'm not sure how to solve this problem. Hopefully someone else will be able to help you with that.

Thanks for your feedback!
I think I could replace the Boolean 'broken' with a Real (and check if it is larger or smaller than zero for example) to solve one of the problems.

However, I want to assign a value to it which *lasts* and which only is changed at certain events. For example, I don't want the 'broken' variable to depend directly on the force, because then the link would magically heal itself when the force would be small enough again.

Maybe a person with modeling experience has an idea for this? Unfortunately I couldn't find an example for this in the MSL.

Note that reinit() has to be applied to a state variable, so you would need der(broken) somewhere even if it is a real.

So, I would have to add

der(broken) = 0;

?

Or is there any other Modelica language item that I could use to set the state of a model? (I mean, to assign a state and to change it at a certain event)

Using a Boolean type just seems to be more "right" to me, but Modelica forces me to use a Real in this case.

For clarity: I updated the model to the following code

model breakableElasticConnection

  extends Modelica.Mechanics.Translational.Interfaces.PartialCompliant;

  parameter Modelica.SIunits.Area contactArea;

  parameter Modelica.SIunits.Stress adhesiveStrength = 250000000.0 "Yield strength";

  parameter Modelica.SIunits.ModulusOfElasticity E = 1500000000.0 "Young's modulus";

  parameter Modelica.SIunits.Length t = 0.0005 "Glue layer thickness";

  Real broken(start = -1.0) "adhesive state variable";

equation

  der(broken) = 0.0;

  when f / contactArea > adhesiveStrength then

      reinit(broken, 1.0);  

  end when;

  f = if broken < 0.0 then (s_rel * E * contactArea) / t else 0 "Hooke's law or zero";

end breakableElasticConnection;

The complaint about a lacking equation is still there...

I used this spring model I don't see the error.

@yzh89: you're right, using the new model it works. I must have made some mistake during testing.

Thank you all for your feedback!