Bad modeling in Modelica.Mechanics.Translational.Examples.HeatLosses?

[modelica-trac-importer]

Reported by hansolsson on 23 May 2013 12:02 UTC
The friction forces in the massWithStopAndFriction-component in this example cannot be uniquely computed as far as I can tell (solver dependent).

The reason is that the brake-component is close to locking at the start - and the configuration with brake and massWithStopAndFriction is similar to the bad example in:
Modelica.Mechanics.Rotational.UsersGuide.RequirementsForSimulationTool (cannot separate the forces between two friction elements).

Dymola finds that there is a singular linear system (with appropriate debug flags):

Expression brake.fn <= 0 became false ( (brake.fn)-(0) = 1.00013e-010 )
Variable brake.locked = 1 at time 7.95875e-014
System of equations is singular at Time = 7.95875E-014
Linear system of equations number = 1
Variables which cannot be uniquely computed:brake.sa = 0
Simulation continues with minimum norm solution.
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It does not seem to significantly influence the position of the masses.

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Migrated-From: https://trac.modelica.org/Modelica/ticket/1121

[modelica-trac-importer]

Comment by hansolsson on 24 May 2013 09:18 UTC
To clarify: "Solver dependent" mean that the friction forces and the lock-states of the friction elements are solver dependent, since they are not uniquely given by the model.

[modelica-trac-importer]

Comment by ahaumer on 24 May 2013 13:05 UTC
fixed by adc4e12;
please note, that we have to take new reference results (with only slight differences).

[modelica-trac-importer]

Comment by dietmarw on 24 May 2013 13:18 UTC
Could you please also add a small summary to the release notes field. It is not really clear how this was fixed. Thanks.