Some models fails in OpenModelica due to theirs parameters are assigned by using start attribute

AndreaBartolini commented 6 months ago

Some models in the Buildings library fails to simulate under OpenModelica because some parameters are assigned by using theirs start attribute instead of a binding (an example is given in https://github.com/OpenModelica/OpenModelica/issues/12305).

This modus-operandi is allowed by the Modelica Specification and the issue is under fixing in OpenModelica (see https://github.com/OpenModelica/OpenModelica/issues/12304) but in general it is better to use modifiers to assign the values to the parameters.

Please consider the possibility to update the Models listed in the https://github.com/OpenModelica/OpenModelica/issues/12305 by adding proper modifiers to assign the parameters that currently have only the start attribute.

keeping @casella in the loop

mwetter commented 6 months ago

@AntoineGautier : Can you please look into this issue that is used in the Templates package.

AntoineGautier commented 6 months ago

Context

We use this implementation pattern systematically in the Buildings library for parameters that are used in conditional or replaceable components. All these parameter declarations have

an enable annotation, and
an explicit start attribute.

From the language specification:

If enable = false, the input field may be disabled and no input can be given.

If the enable attribute evaluates to false, you'll notice that these parameters are actually not used in the flat equation system – after removing the conditional components with false condition and taking into account all redeclarations. We use the start attribute to provide a "placeholder" value that has no impact whatsoever on the simulation results.

All this is due to the fact that conditional components cannot be used outside of connect equations in Modelica.
You will find more insight on this in section 6 of the paper HVAC and Control Templates for the Modelica Buildings Library, as well as the alternative approaches that were tested and the reason why they were rejected.

Outside of MBL

The same feature is used for example in the model Modelica.Electrical.Machines.BasicMachines.SynchronousMachines.SM_ElectricalExcited.

  parameter SI.Temperature TrRef(start=293.15)
    "Reference temperature of damper resistances in d- and q-axis"
    annotation (Dialog(
      tab="Nominal resistances and inductances",
      group="Damper cage",
      enable=useDamperCage));
...
  Machines.BasicMachines.Components.DamperCage damperCage(
    final Lrsigmad=Lrsigmad,
    final Lrsigmaq=Lrsigmaq,
    final Rrd=Rrd,
    final Rrq=Rrq,
    final T_ref=TrRef,
    final alpha=Machines.Thermal.convertAlpha(alpha20r, TrRef),
    final useHeatPort=true) if useDamperCage

In any instance of this model, if useDamperCage=false, the parameter TrRef may be left unassigned.

Support by other tools

This feature is fully supported by Dymola. For example, translating Buildings.Templates.Plants.HeatPumps.Components.Validation.ValvesIsolation yields the following info message – but not a warning as in the case where a parameter assignment relies on the start attribute and no enable attribute is used.

The following parameters have enable=false and don't have any value, only a start value:

Modelon is working on supporting this feature as well in Optimica (ticket #2022110739000228).

Conclusion

We believe that the lack of conditional declarations of parameters is the biggest obstacle to the development of complex system templates and makes the parametric polymorphism of the Modelica language cumbersome in practice. We plan to raise the issue to the Modelica Association and motivate an evolution of the language specification to support the use of conditional components outside of connect statements (at least for parameters). In the meantime, and as described in the paper on HVAC templates, we see no satisfying alternative other than using the start attribute together with enable.

Can this be supported by OMC in the near future?

AndreaBartolini commented 6 months ago

Can this be supported by OMC in the near future?

@casella can you please answer about this point?

casella commented 6 months ago

@AntoineGautier, thanks for the in-depth analysis.

According to the currently available specifications, all the models using start attributes only for parameters are legal and should work, this will be fixed in #12305
Suppressing the warning in case the parameter has an annotation(Dialog(enable = false)) definitely makes sense, although this should be stated in the specification explicitly - the rule in MLS 18.7 that no input can be given if the parameter dialog is disabled doesn't necessarily complement what is stated in Section 8.6 about parameter values with no binding. We can implement that feature, but strongly support the action of amending the MLS accordingly. Are you going to open a ticket about that or should I do that for you?
We also support further MLS amendments to better support models with conditional components and are open to discussion and test implementation of that.

AntoineGautier commented 6 months ago

@casella It would be great if you could open a ticket to improve the MLS concerning parameters with annotation(Dialog(enable = false)) and no binding.

On my end I will open a ticket for supporting the use of conditional parameters in binding equations, which is more of a long-term feature enhancement. I talked about this with Hans Olsson at the Modelica conference last year and now I really need to follow up on that.

We also support further MLS amendments to better support models with conditional components and are open to discussion and test implementation of that.

Great! I'll keep you in the loop.

lbl-srg / modelica-buildings