Merge pull request #1622 from ibpsa/issue1621_negativeFanPower

Issue1621 negative fan power
ibpsa · Sep 28, 2022 · 50b5b93 · 50b5b93
2 parents 36b9a23 + 46d1c6f
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diff --git a/IBPSA/Fluid/Movers/BaseClasses/FlowMachineInterface.mo b/IBPSA/Fluid/Movers/BaseClasses/FlowMachineInterface.mo
@@ -484,7 +484,10 @@ equation
   end if;
 
   // Flow work
-  WFlo = dp_internal*V_flow;
+  WFlo = IBPSA.Utilities.Math.Functions.smoothMax(
+           x1=dp_internal*V_flow,
+           x2=0,
+           deltaX=1E-4*dpMax*V_flow_max);
 
   // Power consumption
   if per.use_powerCharacteristic then
@@ -665,10 +668,25 @@ point is added and where two additional points are added.
 The parameter <code>curve</code> causes the correct data record
 to be used during the simulation.
 </p>
+<p>
+In order to prevent the model from producing negative mover power
+when either the flow rate or pressure rise is forced to be negative,
+the flow work <i>W&#775;<sub>flo</sub></i> is constrained to be non-negative.
+The regularisation starts around 0.01% of the characteristic maximum power
+<i>W&#775;<sub>max</sub> = V&#775;<sub>max</sub> &Delta;p<sub>max</sub></i>.
+See discussions and an example of this situation in
+<a href=\"https://github.com/ibpsa/modelica-ibpsa/issues/1621\">IBPSA, #1621</a>.
+</p>
 </html>",
 revisions="<html>
 <ul>
 <li>
+June 6, 2022, by Hongxiang Fu:<br/>
+Added a constraint that <i>W<sub>flo</sub> = V&#775; &Delta;p &ge; 0</i>.<br/>
+This is for
+<a href=\"https://github.com/ibpsa/modelica-ibpsa/issues/1621\">IBPSA, #1621</a>.
+</li>
+<li>
 April 14, 2020, by Michael Wetter:<br/>
 Changed <code>homotopyInitialization</code> to a constant.<br/>
 This is for

diff --git a/IBPSA/Fluid/Movers/UsersGuide.mo b/IBPSA/Fluid/Movers/UsersGuide.mo
@@ -432,6 +432,15 @@ the hydraulic power input <i>W<sub>hyd</sub></i>, the flow work
 <p>
 where <i>V&#775;</i> is the volume flow rate and
 <i>&Delta;p</i> is the pressure rise.
+In order to prevent the model from producing negative mover power
+when either the flow rate or pressure rise is forced to be negative,
+the flow work <i>W&#775;<sub>flo</sub></i> is constrained to be non-negative.
+The regularisation starts around 0.01% of the characteristic maximum power
+<i>W&#775;<sub>max</sub> = V&#775;<sub>max</sub> &Delta;p<sub>max</sub></i>.
+See discussions and an example of this situation in
+<a href=\"https://github.com/ibpsa/modelica-ibpsa/issues/1621\">IBPSA, #1621</a>.
+</p>
+<p>
 The heat dissipated into the medium is as follows:
 If the motor is cooled by the fluid, as indicated by
 <code>per.motorCooledByFluid=true</code>, then the heat dissipated into the medium is

diff --git a/IBPSA/Fluid/Movers/Validation/NegativePressureOrFlow.mo b/IBPSA/Fluid/Movers/Validation/NegativePressureOrFlow.mo
@@ -0,0 +1,75 @@
+within IBPSA.Fluid.Movers.Validation;
+model NegativePressureOrFlow
+  "A validation model that tests the mover behaviour when the pressure rise or flow is negative"
+  extends Modelica.Icons.Example;
+
+  package Medium = IBPSA.Media.Air;
+
+  parameter Modelica.Units.SI.MassFlowRate m_flow_nominal=0.1
+    "Nominal mass flow rate";
+  parameter Modelica.Units.SI.PressureDifference dp_nominal=sou.p*0.1
+    "Nominal pressure difference";
+
+  IBPSA.Fluid.Movers.SpeedControlled_y fan(
+    redeclare package Medium = Medium,
+    per(pressure(V_flow={0,m_flow_nominal,2*m_flow_nominal}/1.2,
+                 dp={0.5*dp_nominal,0.25*dp_nominal,0})),
+    energyDynamics=Modelica.Fluid.Types.Dynamics.FixedInitial) "Fan"
+    annotation (Placement(transformation(extent={{-10,-10},{10,10}})));
+  IBPSA.Fluid.Sources.Boundary_pT sou(
+    redeclare package Medium = Medium,
+    use_p_in=false,
+    p(displayUnit="Pa") = 101325,
+    T=293.15,
+    nPorts=1) "Source with constant pressure"
+              annotation (Placement(transformation(extent={{-80,-10},{-60,10}})));
+  IBPSA.Fluid.Sources.Boundary_pT sin(
+    redeclare package Medium = Medium,
+    use_p_in=true,
+    T=293.15,
+    nPorts=1) "Sink with varying pressure"
+    annotation (Placement(transformation(extent={{80,-10},{60,10}})));
+  Modelica.Blocks.Sources.Constant one(k=1) "Constant one"
+    annotation (Placement(transformation(extent={{-40,20},{-20,40}})));
+  Modelica.Blocks.Sources.Ramp ram(
+    height=-sou.p*0.5,
+    duration=3600,
+    offset=sou.p*1.25) "Ramp signal"
+    annotation (Placement(transformation(extent={{40,20},{60,40}})));
+equation
+  connect(one.y, fan.y)
+    annotation (Line(points={{-19,30},{0,30},{0,12}}, color={0,0,127}));
+
+  connect(ram.y, sin.p_in)
+    annotation (Line(points={{61,30},{88,30},{88,8},{82,8}}, color={0,0,127}));
+  connect(fan.port_b, sin.ports[1])
+    annotation (Line(points={{10,0},{60,0}}, color={0,127,255}));
+  connect(sou.ports[1], fan.port_a)
+    annotation (Line(points={{-60,0},{-10,0}}, color={0,127,255}));
+annotation(__Dymola_Commands(file="modelica://IBPSA/Resources/Scripts/Dymola/Fluid/Movers/Validation/NegativePressureOrFlow.mos"
+        "Simulate and plot"),
+   experiment(
+      StopTime=3600,
+      Tolerance=1e-06),
+   Documentation(info="<html>
+<p>
+Without the constraint that
+<i>W<sub>flo</sub> = V&#775; &Delta;p &ge; 0</i>,
+this validation model would produce negative computed mover power
+when the pressure rise or the flow rate is forced to be negative,
+as shown below.
+</p>
+<p align=\"center\">
+<img alt=\"image\" src=\"modelica://IBPSA/Resources/Images/Fluid/Movers/Validation/NegativePressureOrFlow.png\"/>
+</p>
+</html>", revisions="<html>
+<ul>
+<li>
+June 6, 2022, by Hongxiang Fu:<br/>
+First implementation.<br/>
+This is for
+<a href=\"https://github.com/ibpsa/modelica-ibpsa/issues/1621\">IBPSA, #1621</a>.
+</li>
+</ul>
+</html>"));
+end NegativePressureOrFlow;
diff --git a/IBPSA/Fluid/Movers/Validation/package.order b/IBPSA/Fluid/Movers/Validation/package.order
@@ -3,6 +3,7 @@ ControlledFlowMachineDynamic
 FlowControlled_dp
 FlowControlled_dpSystem
 FlowControlled_m_flow
+NegativePressureOrFlow
 PowerExact
 PowerSimplified
 PumpCurveConstruction

diff --git a/IBPSA/Resources/Images/Fluid/Movers/Validation/NegativePressureOrFlow.png b/IBPSA/Resources/Images/Fluid/Movers/Validation/NegativePressureOrFlow.png