noEvent(x>0) fails to guard against sqrt(x) for x<0

[Michael Wetter]

Hi

The regression test

Buildings.Fluid.FixedResistances.Examples.FixedResistancesExplicit

fails with "Model error: Argument of sqrt(res22.dp) was -5 should be >= 0"

This is triggered from

m_flow := if noEvent(dp>dp_turbulent) then k*sqrt(dp)
             elseif noEvent(dp<-dp_turbulent) then -k*sqrt(-dp)
             else (k^2*5/4/m_flow_turbulent)*dp-k/4/(m_flow_turbulent/k)^5*dp^3;

According to the Modelica specification, this is the correct implementation. However, when reformulating as

m_flow := if noEvent(dp>dp_turbulent) then k*sqrt(abs(dp))
             elseif noEvent(dp<-dp_turbulent) then -k*sqrt(abs(-dp))
             else (k^2*5/4/m_flow_turbulent)*dp-k/4/(m_flow_turbulent/k)^5*dp^3;

the example works. Hence, this looks like the implementation of noEvent is wrong in OpenModelica.

This fix makes the following tests work:

simulate(Buildings.Fluid.Examples.Performance.Example1v1);
simulate(Buildings.Fluid.Examples.Performance.Example1v2);
simulate(Buildings.Fluid.Examples.Performance.Example2);
simulate(Buildings.Fluid.HeatExchangers.Examples.DryCoilCounterFlowPControl);
simulate(Buildings.Fluid.FixedResistances.Examples.FixedResistancesExplicit);
simulate(Buildings.Fluid.Examples.ResistanceVolumeFlowReversal);