OpenSimHub · dietmarw · Feb 10, 2026 · Feb 9, 2026 · Feb 9, 2026 · Feb 10, 2026
diff --git a/OpenHPL/Types/FrictionMethod.mo b/OpenHPL/Types/FrictionMethod.mo
@@ -0,0 +1,5 @@
+within OpenHPL.Types;
+type FrictionMethod = enumeration(
+    PipeRoughness "Direct pipe roughness height (p_eps)",
+    MoodyFriction "Moody friction factor (f)",
+    ManningFriction "Manning roughness coefficient (M or n)") "Enumeration defining method for specifying pipe friction";
diff --git a/OpenHPL/Types/package.order b/OpenHPL/Types/package.order
@@ -1,4 +1,5 @@
 DraftTube
 Fitting
+FrictionMethod
 Lambda
 SurgeTank
diff --git a/OpenHPL/Waterway/Pipe.mo b/OpenHPL/Waterway/Pipe.mo
@@ -13,8 +13,21 @@ model Pipe "Model of a pipe"
     Dialog(group = "Geometry"));
   parameter SI.Diameter D_o = D_i "Diameter of the outlet side" annotation (
     Dialog(group = "Geometry"));
-  parameter SI.Height p_eps = data.p_eps "Pipe roughness height" annotation (
-    Dialog(group = "Geometry"));
+
+  // Friction specification:
+  parameter Types.FrictionMethod friction_method = Types.FrictionMethod.PipeRoughness "Method for specifying pipe friction" annotation (
+    Dialog(group = "Friction"));
+  parameter SI.Height p_eps_input = data.p_eps "Pipe roughness height (absolute)" annotation (
+    Dialog(group = "Friction", enable = friction_method == Types.FrictionMethod.PipeRoughness));
+  parameter Real f_moody(min=0) = 0.02 "Moody friction factor (dimensionless, typically 0.01-0.05)" annotation (
+    Dialog(group = "Friction", enable = friction_method == Types.FrictionMethod.MoodyFriction));
+  parameter Real m_manning(unit="m(1/3)/s", min=0) = 40 "Manning M (Strickler) coefficient M=1/n (typically 60-110 for steel, 30-60 for rock tunnels)" annotation (
+    Dialog(group = "Friction", enable = friction_method == Types.FrictionMethod.ManningFriction and not use_n));
+  parameter Boolean use_n = false "If true, use Mannings coefficient n (=1/M) instead of Manning's M (Strickler)" annotation (
+    Dialog(group = "Friction", enable = friction_method == Types.FrictionMethod.ManningFriction), choices(checkBox=true));
+  parameter Real n_manning(unit="s/m(1/3)", min=0) = 0.025 "Manning's n coefficient (typically 0.009-0.017 for steel/concrete, 0.017-0.030 for rock tunnels)" annotation (
+    Dialog(group = "Friction", enable = friction_method == Types.FrictionMethod.ManningFriction and use_n));
+
 
   // Steady state:
   parameter Boolean SteadyState=data.SteadyState "If true, starts in steady state" annotation (Dialog(group="Initialization"));
@@ -29,6 +42,10 @@ model Pipe "Model of a pipe"
   SI.VolumeFlowRate Vdot "Volume flow rate";
 
 protected
+    parameter Real n_eff = if use_n then n_manning else 1/m_manning "Effective Manning's n coefficient";
+    parameter SI.Height p_eps = if friction_method == Types.FrictionMethod.PipeRoughness then p_eps_input
+                                 elseif friction_method == Types.FrictionMethod.MoodyFriction then 3.7 * D_ * 10^(-1/(2*sqrt(f_moody)))
+                                 else D_*3.0971 *exp(-0.118/n_eff) "Equivalent pipe roughness height";
     parameter SI.Diameter D_ = ( D_i + D_o)  / 2 "Average diameter";
     parameter SI.Area A_i = D_i ^ 2 * C.pi / 4 "Inlet cross-sectional area";
     parameter SI.Area A_o = D_o ^ 2 * C.pi / 4 "Outlet cross-sectional area";
@@ -56,8 +73,7 @@ equation
   mdot = i.mdot "Inlet direction for mdot";
 
   annotation (
-    Documentation(info= "<html>
-    <p>The simple model of the pipe gives possibilities
+    Documentation(info="<html><p>The simple model of the pipe gives possibilities
     for easy modelling of different conduit: intake race, penstock, tail race, etc.</p>
     <p>This model is described by the momentum differential equation, which depends
     on pressure drop through the pipe together with friction and gravity forces.
@@ -72,8 +88,29 @@ equation
     <p>If the pipe is slightly tapered then this can be taken into account by adjusting
     <code>K_c</code> based on your taper geometry: 0.05–0.15 for gentle cones,
       up to 0.6 for sharp contractions.</p>
+    <h5>Friction Specification</h5>
+    <p>The pipe friction can be specified using one of three methods via the <code>friction_method</code> parameter:</p>
+    <ul>
+    <li><strong>Pipe Roughness (p_eps)</strong>: Direct specification of absolute pipe roughness height (m).
+    Typical values: 0.0001-0.001 m for steel pipes, 0.001-0.003 m for concrete.</li>
+    <li><strong>Moody Friction Factor (f)</strong>: Dimensionless friction factor from Moody diagram.
+    Typical values: 0.01-0.05. Converted to equivalent roughness using fully turbulent flow approximation:
+    p_eps = 3.7·D·10<sup>-1/(2√f)</sup></li>
+    <li><strong>Manning Coefficient</strong>: Two notations are supported:
+    <ul>
+    <li><strong>Manning's M coefficient (Strickler)</strong> [m<sup>1/3</sup>/s]: M = 1/n, typical values 60-110 for steel,
+    30-60 for rock tunnels.</li>
+    <li><strong>Manning's n coefficient</strong> [s/m<sup>1/3</sup>]: Typical values 0.009-0.013 for smooth steel,
+    0.012-0.017 for concrete, 0.017-0.030 for rock tunnels.  Use checkbox <code>use_n</code> to enable this notation.</li>
+    </ul>
+    These are then converted using: p_eps = D_h·3.097·e<sup>(-0.118/n)</sup> empirically derived from the&nbsp;Karman-Prandtl equation.</li>
+    </ul>
+    <p>The conversions are simplified for hydropower applications assuming fully turbulent flow,
+    so they depend only on fixed pipe dimensions and the chosen friction coefficient.</p>
+
+    <h5>More info</h5>
     <p>More info about the pipe model can be found in
         <a href=\"modelica://OpenHPL.UsersGuide.References\">[Vytvytskyi2017]</a>
-    and <a href=\"modelica://OpenHPL.UsersGuide.References\">[Splavska2017a]</a>.</p><p>Updated formulation for non-equal inlet- and outlet diameter.</p><p><br></p><p><br></p>
+    and <a href=\"modelica://OpenHPL.UsersGuide.References\">[Splavska2017a]</a>.</p>
     </html>"));
 end Pipe;