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Nov-01-13 08:31:08
is it possible to change model parameters in a compiled model?

This issue is related to the issue I raised in OpenModelica Programming "Array use leads to excessive compilation times" … ic?id=1030 but is a different question.

Ideally I would like to change parameters in a model without requiring the compilation step to occur every time. I note that there is an OMOptim program but I have been able to get this work with the changes that we are trying to do with our sensitivity study, and from reading the documentation I believe it will recompile the model. The "Simulate" call in the omc API also seems to always recompile.

Is it possible to compile a model and supply an input file or some other technique to change the values of parameters in an OpenModlica model without recompiling the model for every parameter change?

Harley Mackenzie

Oct-31-13 08:27:12
The use of 5 x 501 arrays results in very long compilation times
Category: Programming

I have developed an engine simulation model that includes an object component that allows for the modelling of a complete revolution of an engine cycle. The model works well and as an example, a  simulation of 1440 separate seconds within a day with a 501 element rotational arrays produces good results.

The problem with the model is that if I set the number of rotational elements to a value of 501 elements, the execution time increases as expected, but more significantly the compilation time becomes orders of magnitude longer. This is not an issue when a single simulation is run for an extended period as there is only one compilation process so the compilation time is just a single overhead at the beginning of the total simulation time. However, we would like to run multiple scenarios by varying parameters in the model and so each scenario requires a compilation step and makes the sensitivity study not possible

The included EngineState component has a parameter STEPS set to the number of steps of crank angle in the model. If no rotational analysis is required the number of steps can be set to 0 and as there is a FOR loop in the EngineState component, so STEPS = 0 effectively turns off the rotational analysis and the compilation time then becomes 3-4 seconds. A high number of rotational steps is required by the model , otherwise there are stability issues, so when STEPS = 501 the compilation time increases to about 12 MINUTES and the execution time is about 3 to 4 times longer which is expected and acceptable.

Here is the setting of the number of rotational steps in the included EngineState component:

Parent model


  // rotational
  Bases.EngineState engine_state(STEPS = N, PROP_UNA_STEPS = PROPORTION_UNA_OPEN_STEPS) "Engine state for the current time step";

And here is the EngineState model array definitions:



  // angular variables
  Modelica.SIunits.Angle[STEPS] crank_angles "Crank angle steps in radians";
  Real[STEPS] strokes "Stroke steps";
  Modelica.SIunits.Area[STEPS] exhaust_valve_areas "Exhaust valve open area in m2";
  Modelica.SIunits.Area[STEPS] una_port_areas "Unaflow exhaust port open area in m2";
  Modelica.SIunits.Velocity[STEPS] exit_velocities "Exit velocities in m/s";
  Modelica.SIunits.Pressure[STEPS] pressures "Cylinder pressure in Pa";

I expected the increased execution times and these are acceptable, but I cannot work out why the compilation time increases so much and effectively stops us performing the sensitivity analysis, as I would not have expected 5 501 element arrays to cause any significant increase in compilation time. Changing the size of the number of the arrays directly influences the compilation time, roughly linearly

Is there a reason for the long compilation times?

Can I change the way I define the model to eliminate the problem?

Dr. Harley Mackenzie

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