Added small pressure losses to DynamicPipeEnergyConservationCheck2 to…

… avoid index reduction with the fixed pressure boundary.

Changed to explicit steady state initialization to avoid unspecified initial conditions
Fixes modelica#4424

ModelicaTest/Fluid/TestComponents/Pipes/DynamicPipeEnergyConservationCheck2.mo

@@ -25,7 +25,7 @@ model DynamicPipeEnergyConservationCheck2
     modelStructure=Modelica.Fluid.Types.ModelStructure.av_b,
     useInnerPortProperties=true)
     annotation (Placement(transformation(extent={{-10,40},{10,60}})));
-  inner Modelica.Fluid.System system
+  inner Modelica.Fluid.System system(energyDynamics=Modelica.Fluid.Types.Dynamics.SteadyStateInitial)
     annotation (Placement(transformation(extent={{-100,80},{-80,100}})));
   Modelica.Fluid.Sources.MassFlowSource_h boundary(
     nPorts=1,
@@ -59,9 +59,9 @@ model DynamicPipeEnergyConservationCheck2
     redeclare package Medium = Modelica.Media.Air.DryAirNasa,
     m_flow=1) annotation (Placement(transformation(extent={{-40,0},{-20,20}})));
   Modelica.Fluid.Sources.FixedBoundary boundary7(
-    nPorts=1,
     redeclare package Medium = Modelica.Media.Air.DryAirNasa,
-    p=100000) annotation (Placement(transformation(extent={{40,0},{20,20}})));
+    p=100000,
+    nPorts=1) annotation (Placement(transformation(extent={{70,0},{50,20}})));
   Modelica.Fluid.Pipes.DynamicPipe pipeAV_VB(
     length=100,
     redeclare package Medium = Modelica.Media.Air.DryAirNasa,
@@ -86,9 +86,9 @@ model DynamicPipeEnergyConservationCheck2
     redeclare package Medium = Modelica.Media.Air.DryAirNasa,
     m_flow=1) annotation (Placement(transformation(extent={{-40,-40},{-20,-20}})));
   Modelica.Fluid.Sources.FixedBoundary boundary13(
-    nPorts=1,
     redeclare package Medium = Modelica.Media.Air.DryAirNasa,
-    p=100000) annotation (Placement(transformation(extent={{40,-40},{20,-20}})));
+    p=100000,
+    nPorts=1) annotation (Placement(transformation(extent={{70,-40},{50,-20}})));
   Modelica.Fluid.Pipes.DynamicPipe pipeA_V_B(
     length=100,
     redeclare package Medium = Modelica.Media.Air.DryAirNasa,
@@ -116,6 +116,14 @@ model DynamicPipeEnergyConservationCheck2
     nPorts=1,
     redeclare package Medium = Modelica.Media.Air.DryAirNasa,
     p=100000) annotation (Placement(transformation(extent={{40,-80},{20,-60}})));
+  Modelica.Fluid.Fittings.GenericResistances.VolumeFlowRate loss1(
+    redeclare package Medium = Modelica.Media.Air.DryAirNasa,
+    a=0,
+    b=2.3e3) annotation (Placement(transformation(extent={{22,0},{42,20}})));
+  Modelica.Fluid.Fittings.GenericResistances.VolumeFlowRate loss2(
+    redeclare package Medium = Modelica.Media.Air.DryAirNasa,
+    a=0,
+    b=2.3e3) annotation (Placement(transformation(extent={{20,-40},{40,-20}})));
 equation
   total_AV_B_a = pipeAV_B.H_flows[1] + pipeAV_B.m_flows[1]*pipeAV_B.flowModel.vs[1]^2/2;
   total_AV_B_b = pipeAV_B.H_flows[end] + pipeAV_B.m_flows[end]*pipeAV_B.flowModel.vs[end]^2/2;
@@ -135,16 +143,20 @@ equation
     annotation (Line(points={{10,50},{20,50}}, color={0,127,255}));
   connect(boundary6.ports[1], pipeA_VB.port_a)
     annotation (Line(points={{-20,10},{-10,10}}, color={0,127,255}));
-  connect(pipeA_VB.port_b, boundary7.ports[1])
-    annotation (Line(points={{10,10},{20,10}}, color={0,127,255}));
   connect(boundary12.ports[1], pipeAV_VB.port_a)
     annotation (Line(points={{-20,-30},{-10,-30}}, color={0,127,255}));
-  connect(pipeAV_VB.port_b, boundary13.ports[1])
-    annotation (Line(points={{10,-30},{20,-30}}, color={0,127,255}));
   connect(boundary18.ports[1], pipeA_V_B.port_a)
     annotation (Line(points={{-20,-70},{-10,-70}}, color={0,127,255}));
   connect(pipeA_V_B.port_b, boundary19.ports[1])
     annotation (Line(points={{10,-70},{20,-70}}, color={0,127,255}));
+  connect(pipeA_VB.port_b, loss1.port_a)
+    annotation (Line(points={{10,10},{22,10}}, color={0,127,255}));
+  connect(boundary7.ports[1], loss1.port_b)
+    annotation (Line(points={{50,10},{42,10}}, color={0,127,255}));
+  connect(pipeAV_VB.port_b, loss2.port_a)
+    annotation (Line(points={{10,-30},{20,-30}}, color={0,127,255}));
+  connect(boundary13.ports[1], loss2.port_b)
+    annotation (Line(points={{50,-30},{40,-30}}, color={0,127,255}));
   annotation (experiment(StopTime=500),
   Documentation(info="<html>
   Test of energy conservation in dynamic pipes.