id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
5642	The frontends do not handle actualStream correctly	Francesco Casella	Per Östlund	"Please flatten the attached {{{TestActualStream}}} model. 

The [https://github.com/modelica/ModelicaStandardLibrary/blob/8642c8de8b65ad90905a680932a2cab2b369cf43/Modelica/Fluid/Machines.mo#L458 PartialPump] models contains:
{{{
Hb_flow = port_a.m_flow*actualStream(port_a.h_outflow) +
          port_b.m_flow*actualStream(port_b.h_outflow);
}}}
When flattening these equations, the OF returns
{{{
pump.Hb_flow = 
  pump.port_a.m_flow * smooth(0, pipe.port_b.h_outflow) +
  pump.port_b.m_flow * smooth(0, pump.port_b.h_outflow);
}}}
while the NF returns
{{{
pump.Hb_flow = 
  pump.port_a.m_flow * smooth(0, pipe.port_b.h_outflow) +
  pump.port_b.m_flow * smooth(0, if pump.port_b.m_flow > 0.0
                                 then sink.ports[1].h_outflow
                                 else pump.port_b.h_outflow);
}}}
According to [https://specification.modelica.org/v3.4/Ch15.html#stream-operator-actualstream Section 15.3 of the specification]
{{{
actualStream(c.h_outflow) = if c.m_flow > 0 
  then inStream(c.h_outflow)
  else c.h_outflow;
}}}
Additionally, whenever {{{actualStream}}} is multiplied by its corresponding flow variable, the corresponding expression turns out to be continuous (but not differentiable) even in the presence of a conditional expression, so it should be surrounded by {{{smooth(0, ...)}}}.

Notice that if the flow variable (or some of its aliases) has a {{{min = 0}}} or {{{max = 0}}}, then one of the two branches of the conditional expression will never be triggered, so one can replace the entire conditional expression by the always active branch. At that point, {{{smooth}}} ''is no longer necessary'', because there is no longer any potentially discontinuous expression to declare as actually continuous. Since {{{system.allowFlowReversal = false}}}, these min/max values are indeed set.

So, the output of the NF is wrong for two reasons:

First, 
{{{
pump.port_b.m_flow * smooth(0, if pump.port_b.m_flow > 0.0
                                 then sink.ports[1].h_outflow
                                 else pump.port_b.h_outflow);
}}}
should rather be
{{{
smooth(0, pump.port_b.m_flow * (if pump.port_b.m_flow > 0.0
                                 then sink.ports[1].h_outflow
                                 else pump.port_b.h_outflow));
}}}

Second, given that {{{pump.port_b.m_flow.max = 0}}}, i.e., water always flows out of the port, likewise that expression can be simplified by only keeping the active branch, which also means an explicit {{{smooth}}} annotation is no longer needed, because the conditional expression is also gone. Hence,
{{{
pump.port_b.m_flow*(
  if pump.port_b.m_flow > 0.0 
  then sink.ports[1].h_outflow
  else pump.port_b.h_outflow)
}}}
shoud be simplified into 
{{{
pump.port_b.m_flow*pump.port_b.h_outflow
}}}
without any need of a {{{smooth()}}} operator.

If the {{{TestActualStreamFlowReversal}}} model, which has {{{system.allowFlowReversal = false}}}, is flattened, then instead of getting
{{{
pump.Hb_flow =
  pump.port_a.m_flow * 
  smooth(0, if pump.port_a.m_flow > 0.0
            then pipe.port_b.h_outflow
            else pump.port_a.h_outflow) +
  pump.port_b.m_flow * 
  smooth(0, if pump.port_b.m_flow > 0.0
            then sink.ports[1].h_outflow
            else pump.port_b.h_outflow);
}}}

one should get
{{{
pump.Hb_flow =
  smooth(0, pump.port_a.m_flow * 
              if pump.port_a.m_flow > 0.0
              then pipe.port_b.h_outflow
              else pump.port_a.h_outflow) +
  smooth(0, pump.port_b.m_flow * 
              if pump.port_b.m_flow > 0.0
              then sink.ports[1].h_outflow
              else pump.port_b.h_outflow);
}}}

Implementing this feature correctly is crucial for the success of a few MSL example cases, so I'd try to fix it in time for 1.14.0. I won't bother fixing the OF, unless it is a trivial fix.
"	defect	new	blocker	1.14.0	New Instantiation				Karim Adbdelhak