[Bug] Embedded failures break local balance

[pierre-eliep-met]

Describe the bug

Several components (Pipes, all heat exchangers) can be declared as faulty, giving access to some failure modes (fouling, water_level_rise, etc.)
But currently, those failure modes are used in the model as :

if not faulty then
  fouling = 0;
end if;

Which means that in a faulty=true model, each failure variable should be declared as a connector input, right ? How can we take that into account ?

Additional context

I tried to define a fouling class, with only one connector input, fouling, and extend this class in Pipe for instance but it did not solve the local balance issue...

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[casella]

@pepmts it is not clear to me what you mean by "failure mode". Is fouling an integer variable (0: OK, 1: faulty, 2: irreparably broken) or is is a Real parameter?

[casella]

If it is a Real parameter, this can be done by giving a default binding to it:

model HeatExchanger
  Real fouling = 0;
  ...

If you use the model as it is, fouling = 0. However, you can make it faulty by changing the binding equation when instantiating

HeatExchanger hex(fouling = 0.1);

[pierre-eliep-met]

fouling is a real variable, but we want to be able to define inputs in faulty models, that are assigned to this "failure variable".
For instance :

model SimplePlant
   ... // no faulty parameters, variables, etc. involved, okay with binding equation ✔️ 
end SimplePlant

And then :

model SimplePlant_faulty
  extends SimplePlant(
    heat_exchanger(faulty=true, fouling=Failure_fouling) // okay with binding equation ?
  
  input Real Failure_fouling;
equation
  Failure_fouling = time*10; // for instance
end SimplePlant

[casella]

fouling is a real variable, but we want to be able to define inputs in faulty models, that are assigned to this "failure variable".

The only way I see to have well-balanced models with inputs having default values is not to have them as inputs, but as regular variables with default binding equations, that can be changed upon instantiation or inheritance.

So

model HeatExchanger
  Real fouling = 0;
  ...
end HeatExchanger;

model SimplePlant
  HeatExchanger hex;  
   ... // no faults, default binding applies
end SimplePlant;

model SimplePlant_faulty
  extends SimplePlant(
    hex(fouling=Failure_fouling);
    Real Failure_fouling;
 equation
   Failure_fouling = time*10; // for instance
end SimplePlant

BTW, if you write the equation for Failure_fouling inside the model, then Failure_fouling needs to to be a plain Real variable, not input Real, otherwise the SimplePlant_faulty model won't be balanced.

[pierre-eliep-met]

BTW, if you write the equation for Failure_fouling inside the model, then Failure_fouling needs to to be a plain Real variable, not input Real, otherwise the SimplePlant_faulty model won't be balanced.

Agreed, I made a wrong example. So you would say that this is not balanced ? :

model SimplePlant_faulty
  extends SimplePlant(
    hex(fouling=Failure_fouling);
    input Real Failure_fouling;
equation
  // No binding equation on Failure_fouling
end SimplePlant

[pierre-eliep-met]

It works great for me, with both your case (which is what we do in our unit tests) and mine, which is what we do in our methodology, so it seems fine to me !

[casella]

Agreed, I made a wrong example. So you would say that this is not balanced ? :

model SimplePlant_faulty
  extends SimplePlant(
    hex(fouling=Failure_fouling);
    input Real Failure_fouling;
equation
  // No binding equation on Failure_fouling
end SimplePlant

This looks balanced to me.

SimplePlant is balanced, thanks to the default binding fouling = 0.

SimplePlant_fouling adds one variable Failure_fouling and one equation because of the input prefix. The binding in hex doesn't change the number of equations, because it replaces an existing one. So it is balance, but it requires you to instantiate it and give a binding equation to its input (see