How do I fix the error, “Model is structurally singular, error found sorting equations”

[KieranF <kieran.fung@…>]

This is one of the most common errors I receive when working with OpenModelica Software.

I already understand how this error is usually triggered; when system parameters are conflicting and disagree with one another. I only recieve this error upon simulation. Leading up to that point, my model is able to be checked and instantiated.

I've already tried omitting system parameters that I've deemed not an necessity to my system however nothing seems to fix the error. This was an attempt to get rid of system parameters that might be conflicting with one another.

My system is already very simple to begin with. Currently, I'm working on a sub-assembly verification process in order to correctly build a working Rankine Power model. The sub assembly focuses on a (1) of (2) heat exchangers that would be used in a dual HX system incorporating a reheat process in between the High Pressure and Low Pressure turbines.

This sub assembly is trying to describe water coming from a pump at a condensed liquid state where it will travel through a heat exchanger "super heater" where it will change the state from a compressed liquid to a superheated vapor. This vapor will then be fed into the High Pressure turbine and return into a Pressure Sink.

I've already completed a hand calculated thermodynamic analysis of my system and know outlet temperatures and enthalpies. However, these outlet parameters are some of which I chose to remove for I felt I would let the system solve for them instead of telling it what it should calculate. Removing these values to solve the error did not work as well.

If you have any thoughts, advice or considerations please let me know! Below I've posted the code to what I have been working on. Thanks again!

[Francesco Casella]

@kieran, as I understand this is not a problem involving parameters, but rather involving singular system configuration. For example, if you connect two ideal pump models in series, each one trying to set its own mass flow rate, the model is balanced, checks successfully, and can actually be flattened, but as soon as structural analysis is applied, it is found to be ill posed. Ditto if you connect two ideal pressure sources together. I guess you have something similar in your system.

[KieranF <kieran.fung@…>]

I do have (2) sourcemassflow components within my model but they are both running to their own pressure sinks.

I'm confused as to why this model wont run because the model iteration prior to the one posted above, was the exact same thing excluding the steam turbine and generator that were added was able to simulate with results. The more simpler version of this model did not really have components within the model that made it structurally singular as you put it. However, I am assuming this because it was able to run and simulate before it became more complex to how it is now.

Let me know what you Casella. Thanks.

[Anonymous]

Even the Example PumpingSystem from the MSL suffers actually from this behavior. It errors with the same message. But it was working a few weeks before.

Tested with:
OMEdit - OpenModelica Connection Editor
OMEdit v1.14.0-dev.62+g21f82a33
Connected to OMCompiler v1.14.0-dev.237+gdd336f954
Connected to OMSimulator v2.1.0-dev-91-g2561eda-linux

Ulrich