Number of intervals is influencing whether simulation run is successful

[Christian Kral <dr.christian.kral@…>]

Please consider the attached example of a controlled DC machine that I am using in my classes. One of my students ran into a problem when simulating this model.

Simulation setting 1 (as attached)

experiment(StartTime = 0, StopTime = 1.5, Tolerance = 1e-06, Interval = 0.00075)

The simulation fails with the error message:

LOG_SUCCESS | info | <p>The initialization finished successfully without homotopy method.</p>
assert | debug | <p>Simulation terminated due to too many, i.e. 20, event iterations.<br>
This could either indicate an inconsistent system or an undersized limit of event iterations.<br>
The limit of event iterations can be specified using the runtime flag '–mei=&lt;value&gt;'.</p>
stdout | error | <p>Simulation process failed. Exited with code 255.</p>

I follow the suggestion and set -mei=1000: This results in:

stdout | error | <p>Simulation process failed. Exited with code 255.</p>

Simulation setting 2

experiment(StartTime = 0, StopTime = 1.5, Tolerance = 1e-06, Interval = 7.5e-05)

The simulation runs fine with some warnings, however.

LOG_SUCCESS | info | <p>The initialization finished successfully without homotopy method.</p>
LOG_NLS_V | warning | <p>Warning: maximal number of iteration reached but no root found</p>

Simulations results are displayed correctly and the simulation looks OK.

Conclusions

I already experienced a couple times, that the actual number of intervals heavily influences the success of a simulation run. This makes it very difficult in a teaching situation to identify the problem and find a proper solution. The attached model now represents a reproducible case of the described issue.

This issue occurred at version 1.12.0 (on Windows machine). I double checked the issue right now at version

OMEdit 1.13.0~dev-101-ga45068d
Connected to OpenModelica 1.13.0~dev-632-g450ec7c

on a Linux 64bit machine.

[Christian Kral <dr.christian.kral@…>]

Example demonstrating the issue