refactoring (broken right now)

Components/Volume0D.cs

@@ -1,69 +1,109 @@
 using System;
+using System.Collections.Generic;
+using FluidSim.Interfaces;
 
 namespace FluidSim.Components
 {
-    public class Volume0D
+    /// <summary>
+    /// Zero‑dimensional control volume with arbitrary number of ports.
+    /// Integrates mass and energy fluxes from all ports.
+    /// Safeguards keep a tiny amount of gas to avoid negative states.
+    /// </summary>
+    public class Volume0D : IComponent
     {
-        public double Mass { get; set; }
-        public double InternalEnergy { get; set; }
+        public List<Port> Ports { get; } = new List<Port>();
 
+        public double Mass { get; private set; }
+        public double InternalEnergy { get; private set; }
+        public double Volume { get; set; }
+        public double Dvdt { get; set; }
         public double Gamma { get; set; } = 1.4;
         public double GasConstant { get; set; } = 287.0;
 
-        public double Volume { get; set; }
-        public double Dvdt { get; set; }
-
-        private double _dt;
+        // Ambient pressure used for emergency refill – default 101325 Pa
+        public double AmbientPressure { get; set; } = 101325.0;
 
+        // Derived quantities
         public double Density => Mass / Math.Max(Volume, 1e-12);
         public double Pressure => (Gamma - 1.0) * InternalEnergy / Math.Max(Volume, 1e-12);
         public double Temperature => Pressure / Math.Max(Density * GasConstant, 1e-12);
         public double SpecificEnthalpy => Gamma / (Gamma - 1.0) * Pressure / Math.Max(Density, 1e-12);
 
-        public double MassFlowRateIn { get; set; }
-        public double SpecificEnthalpyIn { get; set; }
-
         public Volume0D(double initialVolume, double initialPressure,
-                        double initialTemperature, int sampleRate,
-                        double gasConstant = 287.0, double gamma = 1.4)
+                        double initialTemperature, double gasConstant = 287.0, double gamma = 1.4)
         {
             GasConstant = gasConstant;
             Gamma = gamma;
             Volume = initialVolume;
             Dvdt = 0.0;
-            _dt = 1.0 / sampleRate;
 
             double rho0 = initialPressure / (GasConstant * initialTemperature);
             Mass = rho0 * Volume;
             InternalEnergy = (initialPressure * Volume) / (Gamma - 1.0);
         }
 
-        public void Integrate(double dtOverride)
+        /// <summary>Add a new port and initialise it to the volume's current state.</summary>
+        public Port CreatePort()
         {
-            double dm = MassFlowRateIn * dtOverride;
-            double dE = (MassFlowRateIn * SpecificEnthalpyIn) * dtOverride - Pressure * Dvdt * dtOverride;
+            var port = new Port { Owner = this };
+            // Set the port state immediately to avoid a mismatch before the first integration
+            port.Pressure = Pressure;
+            port.Density = Density;
+            port.Temperature = Temperature;
+            port.SpecificEnthalpy = SpecificEnthalpy;
+            Ports.Add(port);
+            return port;
+        }
+
+        /// <summary>
+        /// Integrate over dt using the MassFlowRate and SpecificEnthalpy
+        /// that have been set on each port during the coupling resolution phase.
+        /// </summary>
+        public void UpdateState(double dt)
+        {
+            double totalMdot = 0.0;
+            double totalEdot = 0.0;
+
+            foreach (var port in Ports)
+            {
+                totalMdot += port.MassFlowRate;
+                // mdot * h gives energy flow: positive mdot = inflow, negative = outflow
+                totalEdot += port.MassFlowRate * port.SpecificEnthalpy;
+            }
+
+            double dm = totalMdot * dt;
+            double dE = totalEdot * dt - Pressure * Dvdt * dt;   // piston work
 
             Mass += dm;
             InternalEnergy += dE;
 
-            // ---- ABSOLUTE SAFEGUARD: keep at least 1 µg of gas at ambient pressure ----
-            double minMass = 1e-9;
+            // Safeguards: keep at least 1 µg of gas at a small pressure
             double V = Math.Max(Volume, 1e-12);
-            if (Mass < minMass)
+            if (Mass < 1e-9)
             {
-                Mass = minMass;
-                InternalEnergy = 5000.0 * V / (Gamma - 1.0);   // 0.05 bar, not ambient
+                Mass = 1e-9;
+                InternalEnergy = AmbientPressure * V / (Gamma - 1.0);
             }
             else if (InternalEnergy < 0.0)
             {
-                InternalEnergy = 101325.0 * V / (Gamma - 1.0);
+                InternalEnergy = AmbientPressure * V / (Gamma - 1.0);
             }
 
-            // Final non‑negative clamp
-            if (Mass < 0.0) Mass = 0.0;
-            if (InternalEnergy < 0.0) InternalEnergy = 0.0;
+            // Final non‑negative clamps (should not be needed after above)
+            if (Mass < 0.0) Mass = 1e-9;
+            if (InternalEnergy < 0.0) InternalEnergy = AmbientPressure * V / (Gamma - 1.0);
+
+            // Push updated state back to all ports
+            double p = Pressure, rho = Density, T = Temperature, h = SpecificEnthalpy;
+            foreach (var port in Ports)
+            {
+                port.Pressure = p;
+                port.Density = rho;
+                port.Temperature = T;
+                port.SpecificEnthalpy = h;   // will be overwritten by couplings for inflow, but this is the default
+            }
         }
 
-        public void Integrate() => Integrate(_dt);
+        IReadOnlyList<Port> IComponent.Ports => Ports;
     }
 }