General testing

.vscode/launch.json

@@ -0,0 +1,26 @@
+{
+    "version": "0.2.0",
+    "configurations": [
+        {
+            // Use IntelliSense to find out which attributes exist for C# debugging
+            // Use hover for the description of the existing attributes
+            // For further information visit https://github.com/dotnet/vscode-csharp/blob/main/debugger-launchjson.md
+            "name": ".NET Core Launch (console)",
+            "type": "coreclr",
+            "request": "launch",
+            "preLaunchTask": "build",
+            // If you have changed target frameworks, make sure to update the program path.
+            "program": "${workspaceFolder}/bin/Debug/net10.0/FluidSim.dll",
+            "args": [],
+            "cwd": "${workspaceFolder}",
+            // For more information about the 'console' field, see https://aka.ms/VSCode-CS-LaunchJson-Console
+            "console": "internalConsole",
+            "stopAtEntry": false
+        },
+        {
+            "name": ".NET Core Attach",
+            "type": "coreclr",
+            "request": "attach"
+        }
+    ]
+}

.vscode/tasks.json

@@ -0,0 +1,41 @@
+{
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "label": "build",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "build",
+                "${workspaceFolder}/FluidSim.csproj",
+                "/property:GenerateFullPaths=true",
+                "/consoleloggerparameters:NoSummary;ForceNoAlign"
+            ],
+            "problemMatcher": "$msCompile"
+        },
+        {
+            "label": "publish",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "publish",
+                "${workspaceFolder}/FluidSim.csproj",
+                "/property:GenerateFullPaths=true",
+                "/consoleloggerparameters:NoSummary;ForceNoAlign"
+            ],
+            "problemMatcher": "$msCompile"
+        },
+        {
+            "label": "watch",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "watch",
+                "run",
+                "--project",
+                "${workspaceFolder}/FluidSim.csproj"
+            ],
+            "problemMatcher": "$msCompile"
+        }
+    ]
+}

Components/Pipe1D.cs

@@ -5,9 +5,10 @@ namespace FluidSim.Components
 {
     public enum BoundaryType
     {
-        VolumeCoupling,
         OpenEnd,
-        ClosedEnd
+        ZeroPressureOpen,   // pressure‑release boundary (strong reflection)
+        ClosedEnd,
+        GhostCell
     }
 
     public class Pipe1D
@@ -21,27 +22,20 @@ namespace FluidSim.Components
         private double _dx, _dt, _gamma, _area, _diameter;
         private double[] _rho, _rhou, _E;
 
-        // Volume‑coupling ghost states for boundaries A and B
-        private double _rhoA, _pA;
-        private double _rhoB, _pB;
-        private bool _aBCSet, _bBCSet;
+        // Ghost cell states
+        private double _rhoGhostL, _uGhostL, _pGhostL;
+        private double _rhoGhostR, _uGhostR, _pGhostR;
+        private bool _ghostLSet, _ghostRSet;
 
-        private BoundaryType _aBCType = BoundaryType.VolumeCoupling;
-        private BoundaryType _bBCType = BoundaryType.VolumeCoupling;
+        private BoundaryType _aBCType = BoundaryType.GhostCell;
+        private BoundaryType _bBCType = BoundaryType.GhostCell;
 
         private double _aAmbientPressure = 101325.0;
         private double _bAmbientPressure = 101325.0;
 
         private const double CflTarget = 0.8;
         private const double ReferenceSoundSpeed = 340.0;
-
-        public int GetCellCount() => _n;
-        public double GetCellDensity(int i) => _rho[i];
-        public double GetCellPressure(int i) => Pressure(i);
-        public double GetCellVelocity(int i) => _rhou[i] / Math.Max(_rho[i], 1e-12);
-
-        public BoundaryType ABCType => _aBCType;
-        public BoundaryType BBCType => _bBCType;
+        private double _lastMassFlow = 0.0;
 
         public Pipe1D(double length, double area, int sampleRate, int forcedCellCount = 0)
         {
@@ -49,9 +43,7 @@ namespace FluidSim.Components
             int nCells;
 
             if (forcedCellCount > 1)
-            {
                 nCells = forcedCellCount;
-            }
             else
             {
                 double dxTarget = ReferenceSoundSpeed * dtGlobal * CflTarget;
@@ -65,8 +57,6 @@ namespace FluidSim.Components
             _dt = dtGlobal;
             _area = area;
             _gamma = 1.4;
-
-            // Hydraulic diameter for a circular pipe
             _diameter = 2.0 * Math.Sqrt(area / Math.PI);
 
             _rho = new double[_n];
@@ -82,6 +72,26 @@ namespace FluidSim.Components
         public void SetAAmbientPressure(double p) => _aAmbientPressure = p;
         public void SetBAmbientPressure(double p) => _bAmbientPressure = p;
 
+        public void SetGhostLeft(double rho, double u, double p)
+        {
+            _rhoGhostL = rho;
+            _uGhostL = u;
+            _pGhostL = p;
+            _ghostLSet = true;
+        }
+        public void SetGhostRight(double rho, double u, double p)
+        {
+            _rhoGhostR = rho;
+            _uGhostR = u;
+            _pGhostR = p;
+            _ghostRSet = true;
+        }
+        public void ClearGhostFlag()
+        {
+            _ghostLSet = false;
+            _ghostRSet = false;
+        }
+
         public void SetUniformState(double rho, double u, double p)
         {
             double e = p / ((_gamma - 1) * rho);
@@ -94,6 +104,46 @@ namespace FluidSim.Components
             }
         }
 
+        public double GetOpenEndMassFlow()
+        {
+            if (_bBCType != BoundaryType.OpenEnd && _bBCType != BoundaryType.ZeroPressureOpen)
+                return 0.0;
+
+            int lastCell = _n - 1;
+            double rho = _rho[lastCell];
+            double u = _rhou[lastCell] / Math.Max(rho, 1e-12);
+            double p = Pressure(lastCell);
+
+            double c = Math.Sqrt(_gamma * p / rho);
+            double uFace = u;
+            double rhoFace = rho;
+            double pFace = p;
+
+            // Subsonic outflow: impose ambient pressure, adjust velocity and density
+            if (uFace > 0 && uFace < c)
+            {
+                double s = p / Math.Pow(rho, _gamma);
+                double rhoAmb = Math.Pow(_bAmbientPressure / s, 1.0 / _gamma);
+                double cAmb = Math.Sqrt(_gamma * _bAmbientPressure / rhoAmb);
+                double J_plus = u + 2.0 * c / (_gamma - 1.0);
+                double uFaceNew = J_plus - 2.0 * cAmb / (_gamma - 1.0);
+                if (uFaceNew > 0) uFace = uFaceNew;
+                if (uFace < 0) uFace = 0;
+                rhoFace = rhoAmb;
+                pFace = _bAmbientPressure;
+            }
+
+            return rhoFace * uFace * _area;
+        }
+
+        public double GetAndStoreMassFlowForDerivative()
+        {
+            double current = GetOpenEndMassFlow();
+            double derivative = (current - _lastMassFlow) / _dt;
+            _lastMassFlow = current;
+            return derivative;
+        }
+
         public void SetCellState(int i, double rho, double u, double p)
         {
             if (i < 0 || i >= _n) return;
@@ -103,22 +153,18 @@ namespace FluidSim.Components
             _E[i] = rho * e + 0.5 * rho * u * u;
         }
 
-        public void SetAVolumeState(double rhoVol, double pVol)
+        public int GetCellCount() => _n;
+        public double GetCellDensity(int i) => _rho[i];
+        public double GetCellPressure(int i) => Pressure(i);
+        public double GetCellVelocity(int i) => _rhou[i] / Math.Max(_rho[i], 1e-12);
+        private double Pressure(int i) => (_gamma - 1.0) * (_E[i] - 0.5 * _rhou[i] * _rhou[i] / Math.Max(_rho[i], 1e-12));
+        public double GetPressureAtFraction(double fraction)
         {
-            _rhoA = rhoVol;
-            _pA = pVol;
-            _aBCSet = true;
+            int i = (int)(fraction * (_n - 1));
+            i = Math.Clamp(i, 0, _n - 1);
+            return Pressure(i);
         }
 
-        public void SetBVolumeState(double rhoVol, double pVol)
-        {
-            _rhoB = rhoVol;
-            _pB = pVol;
-            _bBCSet = true;
-        }
-
-        public void ClearBC() => _aBCSet = _bBCSet = false;
-
         public int GetRequiredSubSteps(double dtGlobal, double cflTarget = 0.8)
         {
             double maxW = 0.0;
@@ -141,101 +187,72 @@ namespace FluidSim.Components
             double[] Fp = new double[n + 1];
             double[] Fe = new double[n + 1];
 
-            // ---------- Boundary A (face 0, left) ----------
-            double rhoIntA = _rho[0];
-            double uIntA = _rhou[0] / Math.Max(rhoIntA, 1e-12);
-            double pIntA = Pressure(0);
-
-            switch (_aBCType)
+            // Left boundary (face 0)
+            double rhoL = _rho[0];
+            double uL = _rhou[0] / Math.Max(rhoL, 1e-12);
+            double pL = Pressure(0);
+            if (_aBCType == BoundaryType.GhostCell && _ghostLSet)
+                HLLCFlux(_rhoGhostL, _uGhostL, _pGhostL, rhoL, uL, pL, out Fm[0], out Fp[0], out Fe[0]);
+            else if (_aBCType == BoundaryType.OpenEnd)
+                OpenEndFluxLeft(rhoL, uL, pL, _aAmbientPressure, out Fm[0], out Fp[0], out Fe[0]);
+            else if (_aBCType == BoundaryType.ZeroPressureOpen)
             {
-                case BoundaryType.VolumeCoupling:
-                    if (_aBCSet)
-                    {
-                        HLLCFlux(_rhoA, 0.0, _pA,
-                                 rhoIntA, uIntA, pIntA,
-                                 out Fm[0], out Fp[0], out Fe[0]);
-                    }
-                    else
-                    {
-                        Fm[0] = 0; Fp[0] = pIntA; Fe[0] = 0;
-                    }
-                    break;
-
-                case BoundaryType.OpenEnd:
-                    OpenEndFluxA(rhoIntA, uIntA, pIntA, _aAmbientPressure,
-                                 out Fm[0], out Fp[0], out Fe[0]);
-                    break;
-
-                case BoundaryType.ClosedEnd:
-                    ClosedEndFlux(rhoIntA, uIntA, pIntA, isRightBoundary: false,
-                                  out Fm[0], out Fp[0], out Fe[0]);
-                    break;
+                // Strong reflection: force pressure to ambient, extrapolate density and velocity
+                double rhoFace = rhoL;
+                double uFace = uL;
+                double pFace = _aAmbientPressure;
+                HLLCFlux(rhoFace, uFace, pFace, rhoL, uL, pL, out Fm[0], out Fp[0], out Fe[0]);
             }
+            else if (_aBCType == BoundaryType.ClosedEnd)
+                ClosedEndFlux(rhoL, uL, pL, false, out Fm[0], out Fp[0], out Fe[0]);
+            else
+                { Fm[0] = 0; Fp[0] = pL; Fe[0] = 0; }
 
-            // ---------- Internal faces ----------
+            // Internal faces
             for (int i = 0; i < n - 1; i++)
             {
-                double rhoL = _rho[i];
-                double uL = _rhou[i] / Math.Max(rhoL, 1e-12);
-                double pL = Pressure(i);
-
-                double rhoR = _rho[i + 1];
-                double uR = _rhou[i + 1] / Math.Max(rhoR, 1e-12);
-                double pR = Pressure(i + 1);
-
-                HLLCFlux(rhoL, uL, pL, rhoR, uR, pR,
-                         out Fm[i + 1], out Fp[i + 1], out Fe[i + 1]);
+                double rhoLi = _rho[i];
+                double uLi = _rhou[i] / Math.Max(rhoLi, 1e-12);
+                double pLi = Pressure(i);
+                double rhoRi = _rho[i + 1];
+                double uRi = _rhou[i + 1] / Math.Max(rhoRi, 1e-12);
+                double pRi = Pressure(i + 1);
+                HLLCFlux(rhoLi, uLi, pLi, rhoRi, uRi, pRi, out Fm[i + 1], out Fp[i + 1], out Fe[i + 1]);
             }
 
-            // ---------- Boundary B (face n, right) ----------
-            double rhoIntB = _rho[n - 1];
-            double uIntB = _rhou[n - 1] / Math.Max(rhoIntB, 1e-12);
-            double pIntB = Pressure(n - 1);
-
-            switch (_bBCType)
+            // Right boundary (face n)
+            double rhoR = _rho[n - 1];
+            double uR = _rhou[n - 1] / Math.Max(rhoR, 1e-12);
+            double pR = Pressure(n - 1);
+            if (_bBCType == BoundaryType.GhostCell && _ghostRSet)
+                HLLCFlux(rhoR, uR, pR, _rhoGhostR, _uGhostR, _pGhostR, out Fm[n], out Fp[n], out Fe[n]);
+            else if (_bBCType == BoundaryType.OpenEnd)
+                OpenEndFluxRight(rhoR, uR, pR, _bAmbientPressure, out Fm[n], out Fp[n], out Fe[n]);
+            else if (_bBCType == BoundaryType.ZeroPressureOpen)
             {
-                case BoundaryType.VolumeCoupling:
-                    if (_bBCSet)
-                    {
-                        HLLCFlux(rhoIntB, uIntB, pIntB,
-                                 _rhoB, 0.0, _pB,
-                                 out Fm[n], out Fp[n], out Fe[n]);
-                    }
-                    else
-                    {
-                        Fm[n] = 0; Fp[n] = pIntB; Fe[n] = 0;
-                    }
-                    break;
-
-                case BoundaryType.OpenEnd:
-                    OpenEndFluxB(rhoIntB, uIntB, pIntB, _bAmbientPressure,
-                                 out Fm[n], out Fp[n], out Fe[n]);
-                    break;
-
-                case BoundaryType.ClosedEnd:
-                    ClosedEndFlux(rhoIntB, uIntB, pIntB, isRightBoundary: true,
-                                  out Fm[n], out Fp[n], out Fe[n]);
-                    break;
+                double rhoFace = rhoR;
+                double uFace = uR;
+                double pFace = _bAmbientPressure;
+                HLLCFlux(rhoR, uR, pR, rhoFace, uFace, pFace, out Fm[n], out Fp[n], out Fe[n]);
             }
+            else if (_bBCType == BoundaryType.ClosedEnd)
+                ClosedEndFlux(rhoR, uR, pR, true, out Fm[n], out Fp[n], out Fe[n]);
+            else
+                { Fm[n] = 0; Fp[n] = pR; Fe[n] = 0; }
 
-            // ---- Cell update with linear laminar damping ----
+            // Cell update (linear damping)
             double radius = _diameter / 2.0;
             double mu_air = 1.8e-5;
             double laminarCoeff = DampingMultiplier * 8.0 * mu_air / (radius * radius);
 
             for (int i = 0; i < n; i++)
             {
-                double dM = (Fm[i + 1] - Fm[i]) / _dx;
-                double dP = (Fp[i + 1] - Fp[i]) / _dx;
-                double dE = (Fe[i + 1] - Fe[i]) / _dx;
-
-                _rho[i] -= dtSub * dM;
-                _rhou[i] -= dtSub * dP;
-                _E[i] -= dtSub * dE;
+                _rho[i] -= dtSub * (Fm[i + 1] - Fm[i]) / _dx;
+                _rhou[i] -= dtSub * (Fp[i + 1] - Fp[i]) / _dx;
+                _E[i] -= dtSub * (Fe[i + 1] - Fe[i]) / _dx;
 
                 double rho = Math.Max(_rho[i], 1e-12);
-                double dampingRate = laminarCoeff / rho;
-                double dampingFactor = Math.Exp(-dampingRate * dtSub);
+                double dampingFactor = Math.Exp(-(laminarCoeff / rho) * dtSub);
                 _rhou[i] *= dampingFactor;
 
                 if (_rho[i] < 1e-12) _rho[i] = 1e-12;
@@ -244,139 +261,10 @@ namespace FluidSim.Components
                 double eMin = pMin / ((_gamma - 1) * _rho[i]) + kinetic;
                 if (_E[i] < eMin) _E[i] = eMin;
             }
-
-            // ---------- Port quantities ----------
-            double mdotA_sub = _aBCType == BoundaryType.VolumeCoupling && _aBCSet ? Fm[0] * _area : 0.0;
-            double mdotB_sub = _bBCType == BoundaryType.VolumeCoupling && _bBCSet ? -Fm[n] * _area : 0.0;
-
-            PortA.MassFlowRate = mdotA_sub;
-            PortB.MassFlowRate = mdotB_sub;
-            PortA.Pressure = pIntA;
-            PortB.Pressure = pIntB;
-            PortA.Density = _rho[0];
-            PortB.Density = _rho[n - 1];
-
-            // Corrected enthalpy for both directions
-            if (_aBCType == BoundaryType.VolumeCoupling && _aBCSet)
-            {
-                PortA.SpecificEnthalpy = mdotA_sub < 0
-                    ? GetCellTotalSpecificEnthalpy(0)
-                    : (_gamma / (_gamma - 1.0)) * _pA / Math.Max(_rhoA, 1e-12);
-            }
-            if (_bBCType == BoundaryType.VolumeCoupling && _bBCSet)
-            {
-                PortB.SpecificEnthalpy = mdotB_sub < 0
-                    ? GetCellTotalSpecificEnthalpy(_n - 1)
-                    : (_gamma / (_gamma - 1.0)) * _pB / Math.Max(_rhoB, 1e-12);
-            }
         }
 
-        private double GetCellTotalSpecificEnthalpy(int i)
-        {
-            double rho = Math.Max(_rho[i], 1e-12);
-            double u = _rhou[i] / rho;
-            double p = Pressure(i);
-            double h = _gamma / (_gamma - 1.0) * p / rho;
-            return h + 0.5 * u * u;
-        }
-
-        private double Pressure(int i) =>
-            (_gamma - 1.0) * (_E[i] - 0.5 * _rhou[i] * _rhou[i] / Math.Max(_rho[i], 1e-12));
-
-        // ========== Characteristic‑based Open End ==========
-        private void OpenEndFluxA(double rhoInt, double uInt, double pInt, double pAmb,
-                                  out double fm, out double fp, out double fe)
-        {
-            double cInt = Math.Sqrt(_gamma * pInt / Math.Max(rhoInt, 1e-12));
-
-            // Subsonic inflow (uInt ≤ 0, so flow inside pipe ←)
-            if (uInt <= -cInt)   // supersonic inflow – use interior state as ghost
-            {
-                fm = rhoInt * uInt;
-                fp = rhoInt * uInt * uInt + pInt;
-                fe = (rhoInt * (pInt / ((_gamma - 1) * rhoInt) + 0.5 * uInt * uInt) + pInt) * uInt;
-                return;
-            }
-            else if (uInt <= 0)   // subsonic inflow
-            {
-                // Reservoir condition: p = pAmb, T = 300K, u = 0
-                double T0 = 300.0;
-                double R = 287.0;
-                double rhoGhost = pAmb / (R * T0);
-                HLLCFlux(rhoGhost, 0.0, pAmb, rhoInt, uInt, pInt, out fm, out fp, out fe);
-                return;
-            }
-            else   // subsonic outflow (uInt > 0)
-            {
-                // Ghost pressure forced to pAmb
-                double s = pInt / Math.Pow(rhoInt, _gamma);
-                double rhoGhost = Math.Pow(pAmb / s, 1.0 / _gamma);
-                double cGhost = Math.Sqrt(_gamma * pAmb / rhoGhost);
-
-                // Outgoing Riemann invariant J⁻ = uInt - 2*cInt/(γ-1) (for left boundary)
-                double J_minus = uInt - 2.0 * cInt / (_gamma - 1.0);
-                double uGhost = J_minus + 2.0 * cGhost / (_gamma - 1.0);
-
-                // Prevent spurious inflow by clipping to zero
-                if (uGhost < 0) uGhost = 0;
-
-                HLLCFlux(rhoGhost, uGhost, pAmb, rhoInt, uInt, pInt, out fm, out fp, out fe);
-            }
-        }
-
-        private void OpenEndFluxB(double rhoInt, double uInt, double pInt, double pAmb,
-                                  out double fm, out double fp, out double fe)
-        {
-            double cInt = Math.Sqrt(_gamma * pInt / Math.Max(rhoInt, 1e-12));
-
-            if (uInt >= cInt)   // supersonic outflow (extrapolation)
-            {
-                fm = rhoInt * uInt;
-                fp = rhoInt * uInt * uInt + pInt;
-                fe = (rhoInt * (pInt / ((_gamma - 1) * rhoInt) + 0.5 * uInt * uInt) + pInt) * uInt;
-                return;
-            }
-            else if (uInt >= 0)   // subsonic outflow
-            {
-                double s = pInt / Math.Pow(rhoInt, _gamma);
-                double rhoGhost = Math.Pow(pAmb / s, 1.0 / _gamma);
-                double cGhost = Math.Sqrt(_gamma * pAmb / rhoGhost);
-
-                // Outgoing Riemann invariant J⁺ = uInt + 2*cInt/(γ-1) (for right boundary)
-                double J_plus = uInt + 2.0 * cInt / (_gamma - 1.0);
-                double uGhost = J_plus - 2.0 * cGhost / (_gamma - 1.0);
-
-                // Clip to zero to prevent inflow
-                if (uGhost > 0) uGhost = 0;
-
-                HLLCFlux(rhoInt, uInt, pInt, rhoGhost, uGhost, pAmb, out fm, out fp, out fe);
-            }
-            else   // subsonic inflow
-            {
-                double T0 = 300.0;
-                double R = 287.0;
-                double rhoGhost = pAmb / (R * T0);
-                HLLCFlux(rhoInt, uInt, pInt, rhoGhost, 0.0, pAmb, out fm, out fp, out fe);
-            }
-        }
-
-        // ========== Closed end (mirror) ==========
-        private void ClosedEndFlux(double rhoInt, double uInt, double pInt, bool isRightBoundary,
-                                   out double fm, out double fp, out double fe)
-        {
-            double rhoGhost = rhoInt;
-            double pGhost = pInt;
-            double uGhost = -uInt;   // mirror velocity
-
-            if (isRightBoundary)
-                HLLCFlux(rhoInt, uInt, pInt, rhoGhost, uGhost, pGhost, out fm, out fp, out fe);
-            else
-                HLLCFlux(rhoGhost, uGhost, pGhost, rhoInt, uInt, pInt, out fm, out fp, out fe);
-        }
-
-        // ========== Standard HLLC flux ==========
-        private void HLLCFlux(double rL, double uL, double pL,
-                              double rR, double uR, double pR,
+        // ---------- HLLC Riemann solver ----------
+        private void HLLCFlux(double rL, double uL, double pL, double rR, double uR, double pR,
                               out double fm, out double fp, out double fe)
         {
             double cL = Math.Sqrt(_gamma * pL / Math.Max(rL, 1e-12));
@@ -385,7 +273,6 @@ namespace FluidSim.Components
             double ER = pR / ((_gamma - 1) * rR) + 0.5 * uR * uR;
             double SL = Math.Min(uL - cL, uR - cR);
             double SR = Math.Max(uL + cL, uR + cR);
-
             double Ss = (pR - pL + rL * uL * (SL - uL) - rR * uR * (SR - uR))
                       / (rL * (SL - uL) - rR * (SR - uR));
 
@@ -404,17 +291,76 @@ namespace FluidSim.Components
             else
             {
                 double rsR = rR * (SR - uR) / (SR - Ss);
-                double ps = pL + rL * (SL - uL) * (Ss - uL);
+                double ps = pR + rR * (SR - uR) * (Ss - uR);
                 double EsR = ER + (Ss - uR) * (Ss + pR / (rR * (SR - uR)));
                 fm = rsR * Ss; fp = rsR * Ss * Ss + ps; fe = (rsR * EsR + ps) * Ss;
             }
         }
 
-        public double GetPressureAtFraction(double fraction)
+        // ---------- Characteristic open‑end boundaries ----------
+        private void OpenEndFluxLeft(double rhoInt, double uInt, double pInt, double pAmb,
+                                     out double fm, out double fp, out double fe)
         {
-            int i = (int)(fraction * (_n - 1));
-            i = Math.Clamp(i, 0, _n - 1);
-            return Pressure(i);
+            double cInt = Math.Sqrt(_gamma * pInt / Math.Max(rhoInt, 1e-12));
+            if (uInt <= -cInt)  // supersonic inflow
+            {
+                fm = rhoInt * uInt;
+                fp = rhoInt * uInt * uInt + pInt;
+                fe = (rhoInt * (pInt / ((_gamma - 1) * rhoInt) + 0.5 * uInt * uInt) + pInt) * uInt;
+                return;
+            }
+            if (uInt <= 0)  // subsonic inflow
+            {
+                double T0 = 300.0, R = 287.0;
+                double ghost_Rho = pAmb / (R * T0);
+                HLLCFlux(ghost_Rho, 0.0, pAmb, rhoInt, uInt, pInt, out fm, out fp, out fe);
+                return;
+            }
+            // subsonic outflow
+            double s = pInt / Math.Pow(rhoInt, _gamma);
+            double ghostRho = Math.Pow(pAmb / s, 1.0 / _gamma);
+            double cGhost = Math.Sqrt(_gamma * pAmb / ghostRho);
+            double J_minus = uInt - 2.0 * cInt / (_gamma - 1.0);
+            double uGhost = J_minus + 2.0 * cGhost / (_gamma - 1.0);
+            if (uGhost < 0) uGhost = 0;
+            HLLCFlux(ghostRho, uGhost, pAmb, rhoInt, uInt, pInt, out fm, out fp, out fe);
+        }
+
+        private void OpenEndFluxRight(double rhoInt, double uInt, double pInt, double pAmb,
+                                      out double fm, out double fp, out double fe)
+        {
+            double cInt = Math.Sqrt(_gamma * pInt / Math.Max(rhoInt, 1e-12));
+            if (uInt >= cInt)  // supersonic outflow
+            {
+                fm = rhoInt * uInt;
+                fp = rhoInt * uInt * uInt + pInt;
+                fe = (rhoInt * (pInt / ((_gamma - 1) * rhoInt) + 0.5 * uInt * uInt) + pInt) * uInt;
+                return;
+            }
+            if (uInt >= 0)  // subsonic outflow
+            {
+                double s = pInt / Math.Pow(rhoInt, _gamma);
+                double ghost_Rho = Math.Pow(pAmb / s, 1.0 / _gamma);
+                double cGhost = Math.Sqrt(_gamma * pAmb / ghost_Rho);
+                double J_plus = uInt + 2.0 * cInt / (_gamma - 1.0);
+                double uGhost = J_plus - 2.0 * cGhost / (_gamma - 1.0);
+                if (uGhost > 0) uGhost = 0;
+                HLLCFlux(rhoInt, uInt, pInt, ghost_Rho, uGhost, pAmb, out fm, out fp, out fe);
+            }
+            // subsonic inflow
+            double T0 = 300.0, R = 287.0;
+            double ghostRho = pAmb / (R * T0);
+            HLLCFlux(rhoInt, uInt, pInt, ghostRho, 0.0, pAmb, out fm, out fp, out fe);
+        }
+
+        private void ClosedEndFlux(double rhoInt, double uInt, double pInt, bool isRight,
+                                   out double fm, out double fp, out double fe)
+        {
+            double rhoGhost = rhoInt, pGhost = pInt, uGhost = -uInt;
+            if (isRight)
+                HLLCFlux(rhoInt, uInt, pInt, rhoGhost, uGhost, pGhost, out fm, out fp, out fe);
+            else
+                HLLCFlux(rhoGhost, uGhost, pGhost, rhoInt, uInt, pInt, out fm, out fp, out fe);
         }
     }
 }

Components/Volume0D.cs

@@ -1,21 +1,17 @@
 using System;
-using FluidSim.Interfaces;
-using FluidSim.Utils;
 
 namespace FluidSim.Components
 {
     public class Volume0D
     {
-        public Port Port { get; private set; }
-
-        public double Mass { get; private set; }
-        public double InternalEnergy { get; private set; }
+        public double Mass { get; set; }
+        public double InternalEnergy { 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; }
+        public double Dvdt { get; set; }
 
         private double _dt;
 
@@ -24,6 +20,9 @@ namespace FluidSim.Components
         public double Temperature => Pressure / (Density * GasConstant);
         public double SpecificEnthalpy => Gamma / (Gamma - 1.0) * Pressure / Density;
 
+        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)
@@ -31,54 +30,38 @@ namespace FluidSim.Components
             GasConstant = gasConstant;
             Gamma = gamma;
             Volume = initialVolume;
-            dVdt = 0.0;
+            Dvdt = 0.0;
             _dt = 1.0 / sampleRate;
 
             double rho0 = initialPressure / (GasConstant * initialTemperature);
             Mass = rho0 * Volume;
             InternalEnergy = (initialPressure * Volume) / (Gamma - 1.0);
-
-            Port = new Port();
-            PushStateToPort();
         }
 
-        public void PushStateToPort()
-        {
-            Port.Pressure = Pressure;
-            Port.Density = Density;
-            Port.Temperature = Temperature;
-            Port.SpecificEnthalpy = SpecificEnthalpy;
-        }
-
-        // Original integrate (uses the constructor’s sample rate)
-        public void Integrate()
-        {
-            Integrate(_dt);
-        }
-
-        public void SetPressure(double newPressure)
-        {
-            InternalEnergy = newPressure * Volume / (Gamma - 1.0);
-            // Mass stays the same, so density is unchanged
-        }
-
-        // New overload: integrate with a custom time step (for sub‑steps)
         public void Integrate(double dtOverride)
         {
-            double mdot = Port.MassFlowRate;
-            double h_in = Port.SpecificEnthalpy;
-
-            double dm = mdot * dtOverride;
-            double dE = (mdot * h_in) * dtOverride - Pressure * dVdt * dtOverride;
+            double dm = MassFlowRateIn * dtOverride;
+            double dE = (MassFlowRateIn * SpecificEnthalpyIn) * dtOverride - Pressure * Dvdt * dtOverride;
 
             Mass += dm;
             InternalEnergy += dE;
 
-            // Hard physical bounds – prevent NaN and unphysical states
-            if (Mass < 1e-12) Mass = 1e-12;
-            if (InternalEnergy < 1e-12) InternalEnergy = 1e-12;
+            // Safety: if mass becomes extremely small, reset internal energy to zero
+            if (Mass < 1e-12)
+            {
+                Mass = 0.0;
+                InternalEnergy = 0.0;
+            }
+            else if (InternalEnergy < 1e-12)
+            {
+                InternalEnergy = 0.0;
+            }
 
-            PushStateToPort();
+            // Avoid negative mass/energy
+            if (Mass < 0.0) Mass = 0.0;
+            if (InternalEnergy < 0.0) InternalEnergy = 0.0;
         }
+
+        public void Integrate() => Integrate(_dt);
     }
 }

Core/NozzleFlow.cs

@@ -0,0 +1,46 @@
+using System;
+using FluidSim.Components;
+
+namespace FluidSim.Core
+{
+    public static class NozzleFlow
+    {
+        public static void Compute(Volume0D vol, double area, double downstreamPressure,
+                                   out double massFlow, out double rhoFace, out double uFace, out double pFace,
+                                   double gamma = 1.4)
+        {
+            // Default fallback (no flow)
+            massFlow = 0.0;
+            rhoFace = 0.0;
+            uFace = 0.0;
+            pFace = 0.0;
+
+            if (vol == null || vol.Mass <= 0 || vol.Volume <= 0)
+                return;
+
+            double p0 = vol.Pressure;
+            double T0 = vol.Temperature;
+            double R = vol.GasConstant;
+            double rho0 = vol.Density;
+
+            if (double.IsNaN(p0) || double.IsNaN(T0) || double.IsNaN(rho0) ||
+                p0 <= 0 || T0 <= 0 || rho0 <= 0)
+                return;
+
+            double pr = downstreamPressure / p0;
+            double choked = Math.Pow(2.0 / (gamma + 1.0), gamma / (gamma - 1.0));
+            if (pr < choked) pr = choked;
+
+            double M = Math.Sqrt((2.0 / (gamma - 1.0)) * (Math.Pow(pr, -(gamma - 1.0) / gamma) - 1.0));
+            if (double.IsNaN(M)) return;
+
+            uFace = M * Math.Sqrt(gamma * R * T0);
+            rhoFace = rho0 * Math.Pow(pr, 1.0 / gamma);
+            pFace = p0 * pr;
+
+            massFlow = rhoFace * uFace * area;
+            if (double.IsNaN(massFlow) || double.IsInfinity(massFlow))
+                massFlow = 0.0;
+        }
+    }
+}

Core/PipeVolumeConnection.cs

@@ -0,0 +1,20 @@
+using FluidSim.Components;
+
+namespace FluidSim.Core
+{
+    public class PipeVolumeConnection
+    {
+        public Volume0D Volume { get; }
+        public Pipe1D Pipe { get; }
+        public bool IsPipeLeftEnd { get; }
+        public double OrificeArea { get; set; }
+
+        public PipeVolumeConnection(Volume0D vol, Pipe1D pipe, bool isPipeLeftEnd, double orificeArea)
+        {
+            Volume = vol;
+            Pipe = pipe;
+            IsPipeLeftEnd = isPipeLeftEnd;
+            OrificeArea = orificeArea;
+        }
+    }
+}

Core/Solver.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using FluidSim.Components;
-using FluidSim.Interfaces;
 
 namespace FluidSim.Core
 {
@@ -9,162 +8,80 @@ namespace FluidSim.Core
     {
         private readonly List<Volume0D> _volumes = new();
         private readonly List<Pipe1D> _pipes = new();
-        private readonly List<Connection> _connections = new();
+        private readonly List<PipeVolumeConnection> _connections = new();
 
         private double _dt;
+        private double _ambientPressure = 101325.0;
 
+        public void SetAmbientPressure(double p) => _ambientPressure = p;
         public void AddVolume(Volume0D v) => _volumes.Add(v);
         public void AddPipe(Pipe1D p) => _pipes.Add(p);
-        public void AddConnection(Connection c) => _connections.Add(c);
+        public void AddConnection(PipeVolumeConnection c) => _connections.Add(c);
         public void SetTimeStep(double dt) => _dt = dt;
 
-        /// <summary>
-        /// Set boundary type for a pipe end. isA = true for port A (left), false for port B (right).
-        /// </summary>
         public void SetPipeBoundary(Pipe1D pipe, bool isA, BoundaryType type, double ambientPressure = 101325.0)
         {
             if (isA)
             {
                 pipe.SetABoundaryType(type);
-                if (type == BoundaryType.OpenEnd)
-                    pipe.SetAAmbientPressure(ambientPressure);
+                if (type == BoundaryType.OpenEnd) pipe.SetAAmbientPressure(ambientPressure);
             }
             else
             {
                 pipe.SetBBoundaryType(type);
-                if (type == BoundaryType.OpenEnd)
-                    pipe.SetBAmbientPressure(ambientPressure);
+                if (type == BoundaryType.OpenEnd) pipe.SetBAmbientPressure(ambientPressure);
             }
         }
 
         public float Step()
         {
-            // 1. Volumes publish state
-            foreach (var v in _volumes)
-                v.PushStateToPort();
-
-            // 2. Set volume BCs for volume‑coupled ends
+            // 1. Compute nozzle flows and update volumes (once per audio sample)
             foreach (var conn in _connections)
             {
-                if (IsPipePort(conn.PortA) && IsVolumePort(conn.PortB))
-                {
-                    var pipe = GetPipe(conn.PortA);
-                    bool isA = pipe.PortA == conn.PortA;
-                    if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
-                        (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
-                        SetVolumeBC(conn.PortA, conn.PortB);
-                }
-                else if (IsVolumePort(conn.PortA) && IsPipePort(conn.PortB))
-                {
-                    var pipe = GetPipe(conn.PortB);
-                    bool isA = pipe.PortB == conn.PortB;
-                    if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
-                        (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
-                        SetVolumeBC(conn.PortB, conn.PortA);
-                }
+                double downstreamPressure = conn.IsPipeLeftEnd
+                    ? conn.Pipe.GetCellPressure(0)
+                    : conn.Pipe.GetCellPressure(conn.Pipe.GetCellCount() - 1);
+
+                NozzleFlow.Compute(conn.Volume, conn.OrificeArea, downstreamPressure,
+                                out double mdot, out double rhoFace, out double uFace, out double pFace,
+                                gamma: conn.Volume.Gamma);
+
+                // Limit mass flow to available mass
+                double maxMdot = conn.Volume.Mass / _dt;
+                if (mdot > maxMdot) mdot = maxMdot;
+                if (mdot < -maxMdot) mdot = -maxMdot;
+
+                conn.Volume.MassFlowRateIn = -mdot;
+                conn.Volume.SpecificEnthalpyIn = (conn.Volume.Gamma / (conn.Volume.Gamma - 1.0)) *
+                                                (conn.Volume.Pressure / Math.Max(conn.Volume.Density, 1e-12));
+                conn.Volume.Integrate(_dt);
+
+                if (conn.IsPipeLeftEnd)
+                    conn.Pipe.SetGhostLeft(rhoFace, uFace, pFace);
+                else
+                    conn.Pipe.SetGhostRight(rhoFace, uFace, pFace);
             }
 
-            // 3. Sub‑steps
+            // 2. Determine required sub‑steps
             int nSub = 1;
             foreach (var p in _pipes)
                 nSub = Math.Max(nSub, p.GetRequiredSubSteps(_dt));
             double dtSub = _dt / nSub;
 
+            // 3. Sub‑step loop for pipes
             for (int sub = 0; sub < nSub; sub++)
-            {
                 foreach (var p in _pipes)
                     p.SimulateSingleStep(dtSub);
 
-                foreach (var conn in _connections)
-                {
-                    if (IsPipePort(conn.PortA) && IsVolumePort(conn.PortB))
-                    {
-                        var pipe = GetPipe(conn.PortA);
-                        bool isA = pipe.PortA == conn.PortA;
-                        if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
-                            (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
-                            TransferAndIntegrate(conn.PortA, conn.PortB, dtSub);
-                    }
-                    else if (IsVolumePort(conn.PortA) && IsPipePort(conn.PortB))
-                    {
-                        var pipe = GetPipe(conn.PortB);
-                        bool isA = pipe.PortB == conn.PortB;
-                        if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
-                            (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
-                            TransferAndIntegrate(conn.PortB, conn.PortA, dtSub);
-                    }
-                }
-
-                if (sub < nSub - 1)
-                {
-                    foreach (var v in _volumes)
-                        v.PushStateToPort();
-
-                    foreach (var conn in _connections)
-                    {
-                        if (IsPipePort(conn.PortA) && IsVolumePort(conn.PortB))
-                        {
-                            var pipe = GetPipe(conn.PortA);
-                            bool isA = pipe.PortA == conn.PortA;
-                            if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
-                                (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
-                                SetVolumeBC(conn.PortA, conn.PortB);
-                        }
-                        else if (IsVolumePort(conn.PortA) && IsPipePort(conn.PortB))
-                        {
-                            var pipe = GetPipe(conn.PortB);
-                            bool isA = pipe.PortB == conn.PortB;
-                            if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
-                                (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
-                                SetVolumeBC(conn.PortB, conn.PortA);
-                        }
-                    }
-                }
-            }
-
-            // 5. Audio samples (none for now, but placeholder)
-            var audioSamples = new List<float>();
-            foreach (var conn in _connections)
-            {
-                if (conn is SoundConnection sc)
-                    audioSamples.Add(sc.GetAudioSample());
-            }
-
-            // 6. Clear BC flags
+            // 4. Clear ghost flags
             foreach (var p in _pipes)
-                p.ClearBC();
+                p.ClearGhostFlag();
 
-            return SoundProcessor.MixAndClip(audioSamples.ToArray());
-        }
+            // 5. Return raw mass flow from the first pipe’s open end (assumed exhaust tailpipe)
+            if (_pipes.Count > 0)
+                return (float)_pipes[0].GetOpenEndMassFlow();
 
-        private bool IsVolumePort(Port p) => _volumes.Exists(v => v.Port == p);
-        private bool IsPipePort(Port p) => _pipes.Exists(pp => pp.PortA == p || pp.PortB == p);
-        private Pipe1D GetPipe(Port p) => _pipes.Find(pp => pp.PortA == p || pp.PortB == p);
-        private Volume0D GetVolume(Port p) => _volumes.Find(v => v.Port == p);
-
-        private void SetVolumeBC(Port pipePort, Port volPort)
-        {
-            var pipe = GetPipe(pipePort);
-            if (pipe == null) return;
-            bool isA = pipe.PortA == pipePort;
-            if (isA)
-                pipe.SetAVolumeState(volPort.Density, volPort.Pressure);
-            else
-                pipe.SetBVolumeState(volPort.Density, volPort.Pressure);
-        }
-
-        private void TransferAndIntegrate(Port pipePort, Port volPort, double dtSub)
-        {
-            double mdot = pipePort.MassFlowRate;
-            volPort.MassFlowRate = -mdot;
-
-            if (mdot < 0)  // pipe → volume
-            {
-                volPort.SpecificEnthalpy = pipePort.SpecificEnthalpy;
-            }
-            // else volume’s own enthalpy (from PushStateToPort) is used
-
-            GetVolume(volPort)?.Integrate(dtSub);
+            return 0f;
         }
     }
 }

Core/SoundProcessor.cs

@@ -1,23 +1,155 @@
-namespace FluidSim.Core
-{
-    /// <summary>
-    /// Mixes multiple audio samples and applies a soft‑clipping tanh.
-    /// </summary>
-    public static class SoundProcessor
-    {
-        /// <summary>Overall gain applied after mixing (before tanh).</summary>
-        public static float MasterGain { get; set; } = 0.01f;
+using System;
 
-        /// <summary>
-        /// Mixes an array of raw audio samples and returns a single sample in [‑1, 1].
-        /// </summary>
-        public static float MixAndClip(params float[] samples)
+namespace FluidSim.Core
+{
+    public class SoundProcessor
+    {
+        // Monopole state
+        private double lastMassFlow = 0.0;
+        private double dt;
+
+        // Resonant band‑pass filter (second‑order)
+        private double b0, b1, b2, a1, a2;
+        private double x1 = 0, x2 = 0, y1 = 0, y2 = 0;
+        private double pipeLength;
+
+        // Reverb (outdoor)
+        private float[] delayLine;
+        private int writeIndex;
+        private float feedback = 0.50f;
+        private float lowpassCoeff = 0.70f;
+        private float lastFeedbackSample = 0f;
+
+        // Turbulence (pink noise scaled by U³)
+        private PinkNoiseGenerator pinkNoise;
+        private float turbulenceGain = 0.05f;
+        private double pipeArea;
+        private double ambientPressure = 101325.0;
+
+        // Gains
+        private float masterGain = 0.0005f;
+        private float pressureGain = 0.12f;
+
+        public SoundProcessor(int sampleRate, double pipeLengthMeters, double pipeDiameterMeters = 0.04, float reverbTimeMs = 200.0f)
         {
+            dt = 1.0 / sampleRate;
+            pipeLength = pipeLengthMeters;
+            pipeArea = Math.PI * Math.Pow(pipeDiameterMeters / 2.0, 2.0);
+
+            // Design resonant filter at pipe fundamental frequency
+            double c = 340.0;
+            double f0 = c / (4.0 * pipeLength);
+            double Q = 15.0;
+            double omega = 2.0 * Math.PI * f0;
+            double alpha = Math.Sin(omega * dt) / (2.0 * Q);
+            double norm = 1.0 / (1.0 + alpha);
+            b0 = alpha * norm;
+            b1 = 0.0;
+            b2 = -alpha * norm;
+            a1 = -2.0 * Math.Cos(omega * dt) * norm;
+            a2 = (1.0 - alpha) * norm;
+
+            // Reverb delay line
+            int delaySamples = (int)(sampleRate * reverbTimeMs / 1000.0);
+            delayLine = new float[delaySamples];
+            writeIndex = 0;
+
+            pinkNoise = new PinkNoiseGenerator();
+        }
+
+        public float MasterGain
+        {
+            get => masterGain;
+            set => masterGain = value;
+        }
+
+        public float PressureGain
+        {
+            get => pressureGain;
+            set => pressureGain = value;
+        }
+
+        public float TurbulenceGain
+        {
+            get => turbulenceGain;
+            set => turbulenceGain = value;
+        }
+
+        public void SetAmbientPressure(double p) => ambientPressure = p;
+        public void SetPipeDiameter(double diameterMeters) => pipeArea = Math.PI * Math.Pow(diameterMeters / 2.0, 2.0);
+
+        public float Process(float massFlow, float pipeEndPressure)
+        {
+            // 1. Monopole source: d(mdot)/dt
+            double derivative = (massFlow - lastMassFlow) / dt;
+            lastMassFlow = massFlow;
+            float monopole = (float)(derivative * masterGain);
+
+            // 2. Pressure difference (low‑frequency component)
+            float pressureDiff = (float)((pipeEndPressure - ambientPressure) / ambientPressure) * pressureGain;
+            float mixed = monopole + pressureDiff;
+            // DO NOT clamp here – let the filter and final clamp handle dynamics
+
+            // 3. Resonant band‑pass filter
+            double y = b0 * mixed + b1 * x1 + b2 * x2 - a1 * y1 - a2 * y2;
+            x2 = x1; x1 = mixed;
+            y2 = y1; y1 = y;
+            float resonant = (float)Math.Clamp(y, -1f, 1f);
+
+            // 4. Turbulence noise: amplitude ∝ U³ (empirical for low speeds)
+            double velocity = massFlow / (pipeArea * 1.225);
+            double Uref = 100.0;
+            double turbulenceAmp = Math.Pow(Math.Abs(velocity) / Uref, 3.0);
+            float pink = pinkNoise.Next() * turbulenceGain * (float)turbulenceAmp;
+
+            resonant += pink;
+            resonant = Math.Clamp(resonant, -1f, 1f);
+
+            // 5. Outdoor reverb
+            float delayed = delayLine[writeIndex];
+            float filteredDelay = delayed * lowpassCoeff + lastFeedbackSample * (1f - lowpassCoeff);
+            lastFeedbackSample = filteredDelay;
+            float wet = delayed + filteredDelay * feedback;
+            delayLine[writeIndex] = resonant + filteredDelay * feedback;
+            writeIndex = (writeIndex + 1) % delayLine.Length;
+
+            // 6. Dry/wet mix
+            float output = resonant * 0.7f + wet * 0.3f;
+            output = Math.Clamp(output, -1f, 1f);
+            return output;
+        }
+    }
+
+    internal class PinkNoiseGenerator
+    {
+        private readonly Random random = new Random();
+        private readonly float[] whiteNoise = new float[7];
+        private int currentIndex = 0;
+
+        public PinkNoiseGenerator()
+        {
+            for (int i = 0; i < 7; i++)
+                whiteNoise[i] = (float)(random.NextDouble() * 2.0 - 1.0);
+        }
+
+        public float Next()
+        {
+            whiteNoise[0] = (float)(random.NextDouble() * 2.0 - 1.0);
+            currentIndex = (currentIndex + 1) & 0x7F;
+            int updateMask = 0;
+            int temp = currentIndex;
+            for (int i = 0; i < 7; i++)
+            {
+                if ((temp & 1) == 0)
+                    updateMask |= (1 << i);
+                temp >>= 1;
+            }
+            for (int i = 1; i < 7; i++)
+                if ((updateMask & (1 << i)) != 0)
+                    whiteNoise[i] = (float)(random.NextDouble() * 2.0 - 1.0);
             float sum = 0f;
-            foreach (float s in samples)
-                sum += s;
-            sum *= MasterGain;
-            return sum;
+            for (int i = 0; i < 7; i++) sum += whiteNoise[i];
+            return sum / 3.5f;
         }
     }
 }

Program.cs

@@ -13,23 +13,23 @@ public class Program
     private static Scenario scenario;
 
     // Speed control
-    //private static double desiredSpeed = 1.0;
     private static double desiredSpeed = 0.0001;
+    //private static double desiredSpeed = 1;
     private static double currentSpeed = desiredSpeed;
     private const double MinSpeed = 0.0001;
     private const double MaxSpeed = 1.0;
     private const double ScrollFactor = 1.1;
 
     // Space‑toggle state
-    private static double lastDesiredSpeed = 0.1;   // remembers the last non‑1.0 scroll speed
-    private static bool isRealTime = true;          // true when desiredSpeed == 1.0
+    private static double lastDesiredSpeed = 0.1;   // remembers the last non‑1.0 speed
+    private static bool isRealTime = false;         // starts in slow‑mo (desiredSpeed != 1.0)
 
     private static volatile bool running = true;
 
     public static void Main()
     {
         var mode = new VideoMode(new Vector2u(1280, 720));
-        var window = new RenderWindow(mode, "Pipe Resonator");
+        var window = new RenderWindow(mode, "FluidSim - Helmholtz Resonator");
         window.SetVerticalSyncEnabled(true);
         window.Closed += (_, _) => { running = false; window.Close(); };
         window.MouseWheelScrolled += OnMouseWheel;
@@ -39,9 +39,11 @@ public class Program
         soundEngine.Volume = 70;
         soundEngine.Start();
 
-        //scenario = new PipeResonatorScenario();
+        // Choose one scenario. The Helmholtz resonator is fully updated.
         //scenario = new HelmholtzResonatorScenario();
-        scenario = new SodShockTubeScenario();
+        //scenario = new PipeResonatorScenario();   // needs update to new API
+        //scenario = new SodShockTubeScenario();    // needs update to new API
+        scenario = new EngineScenario();          // also works (provided earlier)
 
         scenario.Initialize(SampleRate);
 
@@ -51,9 +53,10 @@ public class Program
         double lastSpeedUpdateTime = stopwatch.Elapsed.TotalSeconds;
 
         // Resampling buffer
-        List<float> simBuffer = new List<float>(4096);
+        var simBuffer = new List<float>(4096);
         double readIndex = 0.0;
 
+        // Prime the buffer with a few samples
         for (int i = 0; i < 4; i++)
             simBuffer.Add(scenario.Process());
 
@@ -73,7 +76,6 @@ public class Program
             lastSpeedUpdateTime = currentRealTime;
 
             // Smoothly transition currentSpeed → desiredSpeed
-            // When toggling, desiredSpeed jumps, but currentSpeed follows with a smooth lerp
             double smoothingRate = 8.0;   // higher = faster catch‑up
             currentSpeed += (desiredSpeed - currentSpeed) * (1.0 - Math.Exp(-smoothingRate * dtSpeed));
 
@@ -122,7 +124,7 @@ public class Program
                     break;
             }
 
-            // ---------- Drawing & title ----------
+            // ---------- Drawing & window title ----------
             if (currentRealTime - lastDrawTime >= drawInterval)
             {
                 double actualSpeed = totalOutputSamples / (currentRealTime * SampleRate);
@@ -156,7 +158,7 @@ public class Program
 
         desiredSpeed = Math.Clamp(desiredSpeed, MinSpeed, MaxSpeed);
 
-        // Update the remembered slow-mo speed (unless we are exactly at 1.0)
+        // Update the remembered slow‑mo speed (unless we are exactly at 1.0)
         if (!wasRealTime || Math.Abs(desiredSpeed - 1.0) > 1e-6)
             lastDesiredSpeed = desiredSpeed;
 

Scenarios/EngineScenario.cs

@@ -0,0 +1,238 @@
+using System;
+using FluidSim.Components;
+using SFML.Graphics;
+using SFML.System;
+
+namespace FluidSim.Core
+{
+    public class EngineScenario : Scenario
+    {
+        private Solver solver;
+        private Volume0D cylinder;
+        private Pipe1D exhaustPipe;
+        private PipeVolumeConnection coupling;
+        private SoundProcessor soundProcessor;
+
+        private double dt;
+        private double ambientPressure = 101325.0;
+        private double time;
+
+        // Crankshaft
+        private double crankAngle = 0.0;
+        private const double TargetRPM = 4000.0;
+        private double angularVelocity;
+
+        // Combustion
+        private const double CombustionPressure = 8.0 * 101325.0;
+        private const double CombustionTemperature = 1800.0;
+
+        // Valve timing
+        private const double ValveOpenStart = 120.0 * Math.PI / 180.0;
+        private const double ValveOpenEnd   = 480.0 * Math.PI / 180.0;
+        private const double ValveRampWidth = 30.0 * Math.PI / 180.0;
+
+        private double maxOrificeArea;
+
+        // Misfire
+        private Random rand = new Random();
+        private const double MisfireProbability = 0.02;
+        private bool isMisfiring = false;
+
+        // Low‑pass filter for pressure
+        private double lastFilteredPressure;
+        private const double PressureCutoffHz = 50.0;
+
+        // Logging
+        private int stepCount = 0;
+        private const int LogStepInterval = 1000;
+        private int combustionCount = 0;
+        private int misfireCount = 0;
+
+        public override void Initialize(int sampleRate)
+        {
+            dt = 1.0 / sampleRate;
+            angularVelocity = TargetRPM * 2.0 * Math.PI / 60.0;
+
+            // Cylinder: 0.5 litre, initially at ambient
+            double cylVolume = 0.5e-3;
+            double initialPressure = ambientPressure;
+            double initialTemperature = 300.0;
+            cylinder = new Volume0D(cylVolume, initialPressure, initialTemperature, sampleRate)
+            {
+                Gamma = 1.4,
+                GasConstant = 287.0
+            };
+
+            // Exhaust pipe: length 2.5 m, radius 2 cm
+            double pipeLength = 2.5;
+            double pipeRadius = 0.02;
+            double pipeArea = Math.PI * pipeRadius * pipeRadius;
+            maxOrificeArea = pipeArea;
+            exhaustPipe = new Pipe1D(pipeLength, pipeArea, sampleRate, forcedCellCount: 70);
+            exhaustPipe.SetUniformState(1.225, 0.0, ambientPressure);
+
+            // Coupling (valve starts closed)
+            coupling = new PipeVolumeConnection(cylinder, exhaustPipe, true, orificeArea: 0.0);
+
+            solver = new Solver();
+            solver.SetTimeStep(dt);
+            solver.AddVolume(cylinder);
+            solver.AddPipe(exhaustPipe);
+            solver.AddConnection(coupling);
+            // Use ZeroPressureOpen for strong reflections
+            solver.SetPipeBoundary(exhaustPipe, false, BoundaryType.ZeroPressureOpen, ambientPressure);
+
+            // Sound processor (tuned to pipe length)
+            soundProcessor = new SoundProcessor(sampleRate, pipeLength, pipeRadius * 2, reverbTimeMs: 200.0f);
+            soundProcessor.MasterGain = 0.02f;      // boosted from 0.0008
+            soundProcessor.PressureGain = 4.0f;     // boosted from6 0.12
+            soundProcessor.TurbulenceGain = 0.0002f; // reduced from 0.02
+            soundProcessor.SetAmbientPressure(ambientPressure);
+
+            lastFilteredPressure = ambientPressure;
+
+            Console.WriteLine("=== EngineScenario (ZeroPressureOpen, boosted gains) ===");
+            Console.WriteLine($"Target RPM: {TargetRPM}, Misfire prob: {MisfireProbability * 100:F1}%");
+            Console.WriteLine($"Pipe length: {pipeLength} m, fundamental: {340/(4*pipeLength):F1} Hz");
+            Console.WriteLine($"Valve opens at {ValveOpenStart*180/Math.PI:F0}°, closes at {ValveOpenEnd*180/Math.PI:F0}°, ramp {ValveRampWidth*180/Math.PI:F0}°");
+            Console.WriteLine($"Sample rate: {sampleRate} Hz, dt = {dt*1000:F3} ms");
+            Console.WriteLine("Time[s]  Crank[°]  Valve[%]  MassFlow[kg/s]  Comb#  Misfire");
+            Console.WriteLine("---------------------------------------------------------");
+        }
+
+        private double ValveOpenRatio(double crankRad)
+        {
+            double cycleAngle = crankRad % (4.0 * Math.PI);
+            double openStart = ValveOpenStart;
+            double openEnd = ValveOpenEnd;
+
+            if (cycleAngle < openStart || cycleAngle > openEnd)
+                return 0.0;
+
+            double fullOpenWindow = openEnd - openStart;
+            double closedWindow = 2.0 * ValveRampWidth;
+            if (fullOpenWindow <= closedWindow)
+                return 1.0;
+
+            double tmid = (openStart + openEnd) / 2.0;
+            double dist = Math.Abs(cycleAngle - tmid);
+            double rampHalf = (fullOpenWindow - closedWindow) / 2.0;
+            if (dist <= rampHalf)
+                return 1.0;
+            else
+            {
+                double frac = (dist - rampHalf) / ValveRampWidth;
+                frac = Math.Clamp(frac, 0.0, 1.0);
+                double lift = Math.Cos(frac * Math.PI / 2.0);
+                return lift * lift;
+            }
+        }
+
+        public override float Process()
+        {
+            // Update crank angle
+            crankAngle += angularVelocity * dt;
+            if (crankAngle >= 2.0 * Math.PI)
+            {
+                crankAngle -= 2.0 * Math.PI;
+                isMisfiring = rand.NextDouble() < MisfireProbability;
+            }
+
+            // Power stroke at TDC
+            if (crankAngle < angularVelocity * dt && crankAngle >= 0.0)
+            {
+                if (isMisfiring)
+                {
+                    double vol = cylinder.Volume;
+                    double R = cylinder.GasConstant;
+                    double T0 = 300.0;
+                    double newMass = ambientPressure * vol / (R * T0);
+                    double newInternalEnergy = ambientPressure * vol / (cylinder.Gamma - 1.0);
+                    cylinder.Mass = newMass;
+                    cylinder.InternalEnergy = newInternalEnergy;
+                    misfireCount++;
+                }
+                else
+                {
+                    double volume = cylinder.Volume;
+                    double gamma = cylinder.Gamma;
+                    double newInternalEnergy = CombustionPressure * volume / (gamma - 1.0);
+                    double R = cylinder.GasConstant;
+                    double newMass = CombustionPressure * volume / (R * CombustionTemperature);
+                    cylinder.InternalEnergy = newInternalEnergy;
+                    cylinder.Mass = newMass;
+                    combustionCount++;
+                }
+            }
+
+            // Update valve area
+            double valveOpen = ValveOpenRatio(crankAngle);
+            coupling.OrificeArea = maxOrificeArea * valveOpen;
+
+            float massFlow = solver.Step();
+            float endPressure = (float)exhaustPipe.GetCellPressure(exhaustPipe.GetCellCount() - 1);
+
+            // Low‑pass filter the pressure (emphasise low frequencies)
+            double rc = 1.0 / (2.0 * Math.PI * PressureCutoffHz);
+            double alpha = dt / (rc + dt);
+            double filteredPressure = alpha * endPressure + (1.0 - alpha) * lastFilteredPressure;
+            lastFilteredPressure = filteredPressure;
+
+            float audioSample = soundProcessor.Process(massFlow, (float)filteredPressure);
+            time += dt;
+            stepCount++;
+
+            // Logging
+            if (stepCount % LogStepInterval == 0 || (crankAngle < angularVelocity * dt * 2 && !isMisfiring && combustionCount > 0))
+            {
+                Console.WriteLine($"{time,7:F3}  {crankAngle * 180.0 / Math.PI,6:F1}   " +
+                                  $"{valveOpen * 100,6:F1}   {massFlow,10:F4}   " +
+                                  $"{combustionCount,3}     {(isMisfiring ? "X" : "")}");
+            }
+
+            return audioSample;
+        }
+
+        public override void Draw(RenderWindow target)
+        {
+            float winW = target.GetView().Size.X;
+            float winH = target.GetView().Size.Y;
+            float centerY = winH / 2f;
+
+            float cylW = 80f, cylH = 150f;
+            var cylRect = new RectangleShape(new Vector2f(cylW, cylH));
+            cylRect.Position = new Vector2f(40f, centerY - cylH / 2f);
+            double pNorm = (cylinder.Pressure - ambientPressure) / ambientPressure;
+            if (double.IsNaN(pNorm)) pNorm = 0;
+            byte red = (byte)(Math.Clamp(pNorm * 128, 0, 255));
+            byte blue = (byte)(Math.Clamp(-pNorm * 128, 0, 255));
+            cylRect.FillColor = new Color(red, 0, blue);
+            target.Draw(cylRect);
+
+            int n = exhaustPipe.GetCellCount();
+            float pipeStartX = 120f, pipeEndX = winW - 60f;
+            float pipeLen = pipeEndX - pipeStartX;
+            float dx = pipeLen / (n - 1);
+            float baseRadius = 20f;
+            var vertices = new Vertex[n * 2];
+            for (int i = 0; i < n; i++)
+            {
+                float x = pipeStartX + i * dx;
+                double p = exhaustPipe.GetCellPressure(i);
+                float r = baseRadius * (float)(1.0 + (p - ambientPressure) / ambientPressure);
+                if (r < 2f) r = 2f;
+
+                double t = (p - ambientPressure) / ambientPressure;
+                t = Math.Clamp(t, -1.0, 1.0);
+                byte rCol = (byte)(t > 0 ? 255 * t : 0);
+                byte bCol = (byte)(t < 0 ? -255 * t : 0);
+                byte gCol = (byte)(255 * (1 - Math.Abs(t)));
+                var col = new Color(rCol, gCol, bCol);
+
+                vertices[i * 2] = new Vertex(new Vector2f(x, centerY - r), col);
+                vertices[i * 2 + 1] = new Vertex(new Vector2f(x, centerY + r), col);
+            }
+            target.Draw(vertices, PrimitiveType.TriangleStrip);
+        }
+    }
+}

Scenarios/HelmholtzResonatorScenario.cs

@@ -1,6 +1,5 @@
 using System;
 using FluidSim.Components;
-using FluidSim.Interfaces;
 using FluidSim.Utils;
 using SFML.Graphics;
 using SFML.System;
@@ -12,7 +11,7 @@ namespace FluidSim.Core
         private Solver solver;
         private Volume0D cavity;
         private Pipe1D neck;
-        private Connection coupling;
+        private PipeVolumeConnection coupling;
         private int stepCount;
         private double time;
         private double dt;
@@ -38,12 +37,8 @@ namespace FluidSim.Core
             neck = new Pipe1D(neckLength, neckArea, sampleRate, forcedCellCount: 40);
             neck.SetUniformState(1.225, 0.0, ambientPressure);
 
-            coupling = new Connection(neck.PortA, cavity.Port)
-            {
-                Area = neckArea,
-                DischargeCoefficient = 0.62,
-                Gamma = 1.4
-            };
+            // Create the coupling between cavity and left end of the neck (PortA)
+            coupling = new PipeVolumeConnection(cavity, neck, isPipeLeftEnd: true, orificeArea: neckArea);
 
             solver = new Solver();
             solver.SetTimeStep(dt);
@@ -51,8 +46,8 @@ namespace FluidSim.Core
             solver.AddPipe(neck);
             solver.AddConnection(coupling);
 
-            // Port A (left) = volume coupling, Port B (right) = open end
-            solver.SetPipeBoundary(neck, isA: true, BoundaryType.VolumeCoupling);
+            // Left boundary (PortA) is volume‑coupled via ghost cell, right boundary (PortB) is open end
+            solver.SetPipeBoundary(neck, isA: true, BoundaryType.GhostCell);
             solver.SetPipeBoundary(neck, isA: false, BoundaryType.OpenEnd, ambientPressure);
         }
 
@@ -68,11 +63,11 @@ namespace FluidSim.Core
             if (stepCount % 20 == 0)
             {
                 double pCav = cavity.Pressure;
-                double mdotA = neck.PortA.MassFlowRate;   // positive = into pipe (leaving cavity)
+                // Mass flow rate is not directly available – we can compute from pressure difference or skip
                 Console.WriteLine(
                     $"t={time * 1e3:F2} ms step={stepCount} " +
                     $"P_cav={pCav:F1} Pa, P_open={pOpen:F1} Pa, " +
-                    $"mdot_A={mdotA * 1e3:F4} g/s, audio={audio:F4}");
+                    $"audio={audio:F4}");
             }
 
             return audio;
@@ -100,7 +95,7 @@ namespace FluidSim.Core
             float dx = neckLenPx / (n - 1);
             float baseRadius = 20f;
 
-            Vertex[] vertices = new Vertex[n * 2];
+            var vertices = new Vertex[n * 2];
             for (int i = 0; i < n; i++)
             {
                 float x = neckStartX + i * dx;