ibpsa · mwetter · Oct 22, 2024 · Oct 14, 2024 · Oct 14, 2024 · Oct 14, 2024
diff --git a/IBPSA/Fluid/BaseClasses/FlowModels/basicFlowFunction_dp_der.mo b/IBPSA/Fluid/BaseClasses/FlowModels/basicFlowFunction_dp_der.mo
@@ -11,7 +11,7 @@ function basicFlowFunction_dp_der
     "Mass flow rate where transition to turbulent flow occurs";
   input Real dp_der
     "Derivative of pressure difference between port_a and port_b (= port_a.p - port_b.p)";
-  output Real m_flow_der(unit="kg/s2")
+  output Real m_flow_der
     "Derivative of mass flow rate in design flow direction";
 protected
   Modelica.Units.SI.PressureDifference dp_turbulent=(m_flow_turbulent/k)^2
@@ -30,8 +30,14 @@ Documentation(info="<html>
 <p>
 Function that implements the first order derivative of
 <a href=\"modelica://IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp\">
-IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp</a>
-with respect to the mass flow rate.
+IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp</a>,
+assuming a constant flow coefficient.
+</p>
+<p>
+When called with <code>dp_der=der(dp)</code>, this function returns
+the time derivative of <code>m_flow</code>.
+When called with <code>dp_der=1</code>, this function returns
+the derivative of <code>m_flow</code> with respect to <code>dp</code>.
 </p>
 </html>",
 revisions="<html>

diff --git a/IBPSA/Fluid/BaseClasses/FlowModels/basicFlowFunction_dp_der2.mo b/IBPSA/Fluid/BaseClasses/FlowModels/basicFlowFunction_dp_der2.mo
@@ -1,6 +1,6 @@
 within IBPSA.Fluid.BaseClasses.FlowModels;
 function basicFlowFunction_dp_der2
-  "2nd derivative of flow function2nd derivative of function that computes mass flow rate for given pressure drop"
+  "2nd derivative of function that computes mass flow rate for given pressure drop"
   extends Modelica.Icons.Function;
 
   input Modelica.Units.SI.PressureDifference dp(displayUnit="Pa")
@@ -35,8 +35,16 @@ Documentation(info="<html>
 <p>
 Function that implements the second order derivative of
 <a href=\"modelica://IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp\">
-IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp</a>
-with respect to the mass flow rate.
+IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp</a>,
+assuming a constant flow coefficient.
+</p>
+<p>
+When called with <code>dp_der=der(dp)</code> and <code>dp_der2=der(dp_der)</code>,
+this function returns the second order derivative of <code>m_flow</code>
+with respect to time.
+When called with <code>dp_der=1</code> and <code>dp_der2=0</code>,
+this function returns the second order derivative of <code>m_flow</code>
+with respect to <code>dp</code>.
 </p>
 </html>",
 revisions="<html>

diff --git a/IBPSA/Fluid/BaseClasses/FlowModels/basicFlowFunction_m_flow_der.mo b/IBPSA/Fluid/BaseClasses/FlowModels/basicFlowFunction_m_flow_der.mo
@@ -9,7 +9,7 @@ function basicFlowFunction_m_flow_der
     "Flow coefficient, k=m_flow/sqrt(dp), with unit=(kg.m)^(1/2)";
   input Modelica.Units.SI.MassFlowRate m_flow_turbulent(min=0)
     "Mass flow rate where transition to turbulent flow occurs";
-  input Real m_flow_der(unit="kg/s2")
+  input Real m_flow_der
     "Derivative of mass flow rate in design flow direction";
   output Real dp_der
     "Derivative of pressure difference between port_a and port_b (= port_a.p - port_b.p)";
@@ -31,8 +31,14 @@ Documentation(info="<html>
 <p>
 Function that implements the first order derivative of
 <a href=\"modelica://IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow\">
-IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow</a>
-with respect to the mass flow rate.
+IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow</a>,
+assuming a constant flow coefficient.
+</p>
+<p>
+When called with <code>m_flow_der=der(m_flow)</code>, this function returns
+the time derivative of <code>dp</code>.
+When called with <code>m_flow_der=1</code>, this function returns
+the derivative of <code>dp</code> with respect to <code>m_flow</code>.
 </p>
 </html>",
 revisions="<html>

diff --git a/IBPSA/Fluid/BaseClasses/FlowModels/basicFlowFunction_m_flow_der2.mo b/IBPSA/Fluid/BaseClasses/FlowModels/basicFlowFunction_m_flow_der2.mo
@@ -9,9 +9,9 @@ function basicFlowFunction_m_flow_der2
     "Flow coefficient, k=m_flow/sqrt(dp), with unit=(kg.m)^(1/2)";
   input Modelica.Units.SI.MassFlowRate m_flow_turbulent(min=0)
     "Mass flow rate where transition to turbulent flow occurs";
-  input Real m_flow_der(unit="kg/s2")
+  input Real m_flow_der
     "1st derivative of mass flow rate in design flow direction";
-  input Real m_flow_der2(unit="kg/s3")
+  input Real m_flow_der2
     "2nd derivative of mass flow rate in design flow direction";
   output Real dp_der2
     "2nd derivative of pressure difference between port_a and port_b (= port_a.p - port_b.p)";
@@ -35,8 +35,16 @@ Documentation(info="<html>
 <p>
 Function that implements the second order derivative of
 <a href=\"modelica://IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow\">
-IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow</a>
-with respect to the mass flow rate.
+IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow</a>,
+assuming a constant flow coefficient.
+</p>
+<p>
+When called with <code>m_flow_der=der(m_flow)</code> and <code>m_flow_der2=der(m_flow_der)</code>,
+this function returns the second order derivative of <code>dp</code>
+with respect to time.
+When called with <code>m_flow_der=1</code> and <code>m_flow_der2=0</code>,
+this function returns the second order derivative of <code>dp</code>
+with respect to <code>m_flow</code>.
 </p>
 </html>",
 revisions="<html>

diff --git a/IBPSA/Fluid/FixedResistances/CheckValve.mo b/IBPSA/Fluid/FixedResistances/CheckValve.mo
@@ -27,48 +27,85 @@ model CheckValve "Check valve that avoids flow reversal"
     else 0
     "Flow coefficient of fixed resistance that may be in series with valve,
     k=m_flow/sqrt(dp), with unit=(kg.m)^(1/2).";
-
-  Real k(min=Modelica.Constants.small)
-    "Flow coefficient of valve and pipe in series in allowed/forward direction,
-    k=m_flow/sqrt(dp), with unit=(kg.m)^(1/2).";
-
 protected
-  Real a
-    "Scaled pressure variable";
-  Real cv
-    "Twice differentiable Heaviside check valve characteristic";
-  Real kCv
-    "Smoothed restriction characteristic";
-
+  parameter Real k_min=if dpFixed_nominal > Modelica.Constants.eps then
+    sqrt(1 / (1 / kFixed ^ 2 + 1 /(l * Kv_SI) ^ 2)) else l * Kv_SI
+    "Minimum flow coefficient (valve closed)";
+  parameter Real k_max=if dpFixed_nominal > Modelica.Constants.eps then
+    sqrt(1 / (1 / kFixed ^ 2 + 1 / Kv_SI ^ 2)) else Kv_SI
+    "Maximum flow coefficient (valve fully open)";
+  parameter Modelica.Units.SI.MassFlowRate m1_flow = 0
+    "Flow rate through closed valve with zero pressure drop";
+  parameter Modelica.Units.SI.MassFlowRate m2_flow =
+    IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp(
+      dp=dpValve_closing,
+      k=k_max,
+      m_flow_turbulent=m_flow_turbulent)
+    "Flow rate through fully open valve exposed to dpValve_closing";
+  parameter Real dm1_flow_dp =
+    IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp_der(
+      dp=0,
+      k=k_min,
+      m_flow_turbulent=m_flow_turbulent,
+      dp_der=1)
+    "Derivative of closed valve flow function at dp=0";
+  parameter Real dm2_flow_dp =
+    IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp_der(
+      dp=dpValve_closing,
+      k=k_max,
+      m_flow_turbulent=m_flow_turbulent,
+      dp_der=1)
+    "Derivative of open valve flow function at dp=dpValve_closing";
+  parameter Real d2m1_flow_dp =
+    IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp_der2(
+      dp=0,
+      k=k_min,
+      m_flow_turbulent=m_flow_turbulent,
+      dp_der=1,
+      dp_der2=0)
+    "Second derivative of closed valve flow function at dp=0";
+  parameter Real d2m2_flow_dp =
+    IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp_der2(
+      dp=dpValve_closing,
+      k=k_max,
+      m_flow_turbulent=m_flow_turbulent,
+      dp_der=1,
+      dp_der2=0)
+    "Second derivative of open valve flow function at dp=dpValve_closing";
+  Modelica.Units.SI.MassFlowRate m_flow_smooth
+    "Smooth interpolation result between two flow regimes";
 initial equation
-  assert(dpFixed_nominal > -Modelica.Constants.eps,
-    "In " + getInstanceName() + ": We require dpFixed_nominal >= 0.
+  assert(dpFixed_nominal > - Modelica.Constants.eps, "In " + getInstanceName() +
+    ": We require dpFixed_nominal >= 0.
     Received dpFixed_nominal = " + String(dpFixed_nominal) + " Pa.");
-  assert(l > -Modelica.Constants.eps,
-    "In " + getInstanceName() + ": We require l >= 0. Received l = " + String(l));
+  assert(l > - Modelica.Constants.eps, "In " + getInstanceName() +
+    ": We require l >= 0. Received l = " + String(l));
 equation
-  a = dp/dpValve_closing;
-  cv = smooth(2, max(0, min(1, a^3*(10+a*(-15+6*a)))));
-  kCv = Kv_SI*(cv*(1-l) + l);
-
-  if (dpFixed_nominal > Modelica.Constants.eps) then
-    k = sqrt(1/(1/kFixed^2 + 1/kCv^2));
-  else
-    k = kCv;
-  end if;
-
+  m_flow_smooth=noEvent(smooth(2,
+    if dp <= 0 then IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp(
+      dp=dp,
+      k=k_min,
+      m_flow_turbulent=m_flow_turbulent)
+    elseif dp >= dpValve_closing then IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp(
+      dp=dp,
+      k=k_max,
+      m_flow_turbulent=m_flow_turbulent)
+    else IBPSA.Utilities.Math.Functions.quinticHermite(
+      x=dp,
+      x1=0,
+      x2=dpValve_closing,
+      y1=0,
+      y2=m2_flow,
+      y1d=dm1_flow_dp,
+      y2d=dm2_flow_dp,
+      y1dd=d2m1_flow_dp,
+      y2dd=d2m2_flow_dp)));
   if homotopyInitialization then
-    m_flow = homotopy(
-      actual=IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp(
-            dp = dp,
-            k = k,
-            m_flow_turbulent = m_flow_turbulent),
-      simplified = m_flow_nominal_pos*dp/dp_nominal_pos);
+    m_flow=homotopy(
+      actual=m_flow_smooth,
+      simplified=m_flow_nominal_pos * dp / dp_nominal_pos);
   else
-    m_flow = IBPSA.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp(
-        dp = dp,
-        k = k,
-        m_flow_turbulent = m_flow_turbulent);
+    m_flow=m_flow_smooth;
   end if;
   annotation (Icon(coordinateSystem(preserveAspectRatio=true, extent={{-100,-100},
             {100,100}}), graphics={
@@ -103,7 +140,7 @@ defaultComponentName="cheVal",
 Documentation(info="<html>
 <p>
 Implementation of a hydraulic check valve.
-Note that the small reverse flows can still occur with this model.
+Note that small reverse flows can still occur with this model.
 </p>
 <h4>Main equations</h4>
 <p>
@@ -113,26 +150,22 @@ The basic flow function
   m&#775; = sign(&Delta;p) k  &radic;<span style=\"text-decoration:overline;\">&nbsp;&Delta;p &nbsp;</span>,
 </p>
 <p>
-with regularization near the origin, is used to compute the pressure drop.
-The flow coefficient
-</p>
-<p align=\"center\" style=\"font-style:italic;\">
-  k = m&#775; &frasl; &radic;<span style=\"text-decoration:overline;\">&nbsp;&Delta;p &nbsp;</span>
-</p>
-<p>
-is increased from <code>l*KV_Si</code> to <code>KV_Si</code>,
-where <code>KV_Si</code> is equal to <code>Kv</code> but in SI units.
-Therefore, the flow coefficient <code>k</code> is set to a value close to zero for negative pressure differences, thereby
-restricting reverse flow to a small value.
-The flow coefficient <code>k</code> saturates to its maximum value at the pressure <code>dpValve_closing</code>.
-For larger pressure drops, the pressure drop is a quadratic function of the flow rate.
+with regularization near the origin, is used to compute the mass flow rate
+through the fully closed and fully open valve, respectively.
+The valve is considered fully closed when subjected to a negative pressure drop,
+and its flow coefficient <i>k</i> is then equal to <code>l * Kv_SI</code>,
+where <code>Kv_SI</code> is equal to <code>Kv</code> but in SI units.
+The valve is considered fully open when the pressure drop exceeds
+<code>dpValve_closing</code>,
+and its flow coefficient <i>k</i> is then equal to <code>Kv_SI</code>.
+For valve positions between these two extremes, a quintic spline interpolation
+is applied to determine the mass flow rate as a function of
+the pressure drop across the valve.
 </p>
 <h4>Typical use and important parameters</h4>
 <p>
 The parameters <code>m_flow_nominal</code> and <code>dpValve_nominal</code>
-determine the flow coefficient of the check valve when it is fully opened.
-A typical value for a nominal flow rate of <i>1</i> m/s is
-<code>dpValve_nominal = 3400 Pa</code>.
+determine the flow coefficient of the check valve when it is fully open.
 The leakage ratio <code>l</code> determines the minimum flow coefficient,
 for negative pressure differences.
 The parameter <code>dpFixed_nominal</code> allows to include a series
@@ -156,8 +189,13 @@ by default.
 </html>", revisions="<html>
 <ul>
 <li>
+October 14, 2024, by Antoine Gautier:<br/>
+Refactored using a spline interpolation. This is for
+<a href=\"https://github.com/ibpsa/modelica-ibpsa/issues/1937\">issue 1937</a>.
+</li>
+<li>
 February 3, 2023, by Michael Wetter:<br/>
-Corrected grahpical annotation.
+Corrected graphical annotation.
 </li>
 <li>
 September 16, 2019, by Kristoff Six and Filip Jorissen:<br/>