Model TestReheater fails during initialization in OpenModelica

[casella]

Model Test.UnitTest.WaterSteam.HeatExchangers.TestReheater fails during initialization in OpenModelica.

The Newton solver fails while trying to solve system 156, which has the following iteration variables:

[1] Real sink_hot_CondSteam.basicTransport.h_in(start=100000, nominal=500000)
[2] Real sink_hot_CondSteam.h_in(start=100000, nominal=500000)
[3] Real Reheater.Kth_cond(start=2000, nominal=1)
[4] Real Reheater.S_deh(start=250, nominal=1)
[5] Real Reheater.condensing_hot.h_out(start=100000, nominal=500000)
[6] Real Reheater.condensing_hot.h_in(start=100000, nominal=500000)
[7] Real Reheater.deheating_hot.h_in(start=100000, nominal=500000)
[8] Real sink_hot_CondSteam.Q_in(start=500, nominal=1)
[9] Real source_hot_SatSteam.basicTransport.h_in(start=100000, nominal=500000)

The solution found by Dymola is very far from these start values. In particular:

• enthalpies are in the range of wet or superheated steam (1-2 MJ/kg), not cold water (100 kJ/kg)
• S_deh turns out to be zero
• Kth_cond is much higher than the start value, at about 70 kW/m2K
• Q_in is much lower than the start value, at 44 kg/s

It is probably advisable to provide some default values which are appropriate for steam enthalpies (e.g. 1e6 instead of 1e5).

Also the presence of noEvent could be questionable - it could be replaced by smooth(0, ).

One thing worth investigating is that Dymola splits the computation in two cascaded sub-systems, the second computing only S_cond, S_deh, Kth_cond, Kth_deh, while OpenModelica keeps this computation together with the computation of the enthalpies. In principle, strong component analysis should give the same results in both tools, even though the individual strong components may be solved differently.

[casella]

We should investigate the structural analysis issue further with the OMC development team

[AndreaBartolini]

This is out of scope for the current contract, can be considered for the next work.