diff --git a/Components/Cylinder.cs b/Components/Cylinder.cs
index 3fc5e8c..ddf460f 100644
--- a/Components/Cylinder.cs
+++ b/Components/Cylinder.cs
@@ -19,15 +19,20 @@ namespace FluidSim.Components
public double ConRodLength { get; }
public double CompressionRatio { get; }
- // Valve timings
+ // Valve timings (degrees, 0 = TDC compression, 720° full cycle)
public double IVO { get; }
public double IVC { get; }
public double EVO { get; }
public double EVC { get; }
- // Valve areas
- public double MaxIntakeArea { get; set; } = 0.0005;
- public double MaxExhaustArea { get; set; } = 0.0005;
+ // Valve geometry
+ public double IntakeValveDiameter { get; set; } = 0.030;
+ public double ExhaustValveDiameter { get; set; } = 0.028;
+ public double IntakeValveLift { get; set; } = 0.005;
+ public double ExhaustValveLift { get; set; } = 0.005;
+
+ public double IntakeValveMaxArea => Math.PI * IntakeValveDiameter * IntakeValveLift;
+ public double ExhaustValveMaxArea => Math.PI * ExhaustValveDiameter * ExhaustValveLift;
// Ignition and combustion
public double SparkAdvance { get; set; } = 20.0;
@@ -40,6 +45,12 @@ namespace FluidSim.Components
public double StoichiometricAFR { get; set; } = 14.7;
public double FuelLowerHeatingValue { get; set; } = 44e6;
+ // Cycle‑to‑cycle randomness
+ /// Fractional variation in fuel energy (±). 0.05 = ±5%.
+ public double EnergyVariationFraction { get; set; } = 0.05;
+ /// Probability of a misfire (0‑1).
+ public double MisfireProbability { get; set; } = 0.01;
+
// Heat loss
public double CylinderWallArea { get; set; } = 0.02;
public double HeatTransferCoefficient { get; set; } = 100.0;
@@ -64,6 +75,10 @@ namespace FluidSim.Components
private bool combustionActive;
private bool fuelInjected;
+ // per‑cycle randomness
+ private double _energyFactor = 1.0; // applied to FuelLowerHeatingValue this cycle
+ private readonly Random _random = new Random();
+
private const double Gamma = 1.4;
private const double GasConstant = 287.0;
@@ -95,6 +110,7 @@ namespace FluidSim.Components
_ports = new[] { IntakePort, ExhaustPort };
}
+ // Derived volumes
private double SweptVolume => Math.PI * 0.25 * Bore * Bore * Stroke;
private double clearanceVolume => SweptVolume / (CompressionRatio - 1.0);
private double CrankRadius => Stroke / 2.0;
@@ -113,24 +129,40 @@ namespace FluidSim.Components
return clearanceVolume + area * x;
}
- public double IntakeValveArea => ValveArea(CrankDeg, IVO, IVC, MaxIntakeArea);
- public double ExhaustValveArea => ValveArea(CrankDeg, EVO, EVC, MaxExhaustArea);
-
- private double ValveArea(double thetaDeg, double opens, double closes, double maxArea)
+ private double ValveLift(double thetaDeg, double opens, double closes, double peakLift)
{
double deg = thetaDeg % 720.0;
if (deg < 0) deg += 720.0;
- if (deg >= opens && deg <= closes)
+
+ double duration = closes - opens;
+ if (duration <= 0) return 0.0;
+
+ double rampDur = duration * 0.25;
+ double holdDur = duration - 2.0 * rampDur;
+
+ if (deg >= opens && deg < opens + rampDur)
{
- double half = (closes - opens) * 0.5;
- double mid = opens + half;
- double frac = 1.0 - Math.Abs(deg - mid) / half;
- frac = Math.Clamp(frac, 0.0, 1.0);
- return maxArea * frac;
+ double t = (deg - opens) / rampDur;
+ return peakLift * t * t * (3.0 - 2.0 * t);
+ }
+ else if (deg >= opens + rampDur && deg < opens + rampDur + holdDur)
+ {
+ return peakLift;
+ }
+ else if (deg >= opens + rampDur + holdDur && deg <= closes)
+ {
+ double t = (deg - (opens + rampDur + holdDur)) / rampDur;
+ return peakLift * (1.0 - t) * (1.0 - t) * (1.0 + 2.0 * t);
}
return 0.0;
}
+ public double IntakeValveArea =>
+ Math.PI * IntakeValveDiameter * ValveLift(CrankDeg, IVO, IVC, IntakeValveLift);
+
+ public double ExhaustValveArea =>
+ Math.PI * ExhaustValveDiameter * ValveLift(CrankDeg, EVO, EVC, ExhaustValveLift);
+
private double Wiebe(double angleSinceSpark)
{
if (angleSinceSpark < WiebeStart) return 0.0;
@@ -147,8 +179,8 @@ namespace FluidSim.Components
double dV = cylinderVolume - prevVolume;
- // ---- Piston torque ----
- double pRel = Pressure - 101325.0; // relative to ambient
+ // Piston torque
+ double pRel = Pressure - 101325.0;
double sinTh = Math.Sin(crankAngleRad);
double cosTh = Math.Cos(crankAngleRad);
double term = Math.Sqrt(1.0 - Obliquity * Obliquity * sinTh * sinTh);
@@ -157,13 +189,12 @@ namespace FluidSim.Components
double torque = pRel * pistonArea * dxdtheta;
Crankshaft.AddTorque(torque);
- // Volume work (done BY gas, positive when expanding)
cylinderEnergy -= Pressure * dV;
double prevDeg = Crankshaft.PreviousAngle * 180.0 / Math.PI % 720.0;
double currDeg = crankAngleRad * 180.0 / Math.PI % 720.0;
- // Intake closing: capture trapped air mass (air only!)
+ // ----- Intake closing: capture trapped air mass and compute fuel -----
if (prevDeg >= IVO && prevDeg < IVC && currDeg >= IVC)
{
trappedAirMass = _airMass;
@@ -171,23 +202,39 @@ namespace FluidSim.Components
fuelInjected = true;
}
- // Spark
+ // ----- Spark ignition (once per cycle, with misfire chance) -----
double sparkAngle = 0.0 - SparkAdvance;
if (sparkAngle < 0) sparkAngle += 720.0;
+
bool crossedSpark = (prevDeg < sparkAngle && currDeg >= sparkAngle) ||
(prevDeg > sparkAngle + 360.0 && currDeg < sparkAngle);
if (crossedSpark && !combustionActive && fuelInjected)
{
- combustionActive = true;
- burnFraction = 0.0;
+ // Decide misfire
+ bool misfire = _random.NextDouble() < MisfireProbability;
+ if (misfire)
+ {
+ combustionActive = false; // no combustion this cycle
+ // fuel is not burned – will remain in cylinder and eventually exit as unburned mixture
+ }
+ else
+ {
+ combustionActive = true;
+ burnFraction = 0.0;
+
+ // Energy variation factor for this cycle
+ double range = EnergyVariationFraction;
+ _energyFactor = 1.0 + range * (2.0 * _random.NextDouble() - 1.0);
+ }
}
- // Combustion progress
+ // ----- Combustion progress -----
if (combustionActive)
{
double angleSinceSpark = currDeg - sparkAngle;
if (angleSinceSpark < 0) angleSinceSpark += 720.0;
double newFraction = Wiebe(angleSinceSpark);
+
if (newFraction >= 1.0 || angleSinceSpark > (WiebeDuration + WiebeStart + SparkAdvance))
{
newFraction = 1.0;
@@ -201,14 +248,14 @@ namespace FluidSim.Components
double dFraction = newFraction - burnFraction;
if (dFraction > 0)
{
- double dQ = fuelMass * FuelLowerHeatingValue * dFraction;
+ double dQ = fuelMass * FuelLowerHeatingValue * _energyFactor * dFraction;
cylinderEnergy += dQ;
- _exhaustMass += fuelMass * dFraction; // burning fuel adds to exhaust
+ _exhaustMass += fuelMass * dFraction;
burnFraction = newFraction;
}
}
- // Heat loss
+ // ----- Heat loss to cylinder walls -----
double dQ_loss = HeatTransferCoefficient * CylinderWallArea *
(Temperature - AmbientTemperature) * dt;
cylinderEnergy -= dQ_loss;
@@ -250,7 +297,6 @@ namespace FluidSim.Components
double V = Math.Max(cylinderVolume, 1e-12);
- // Safety clamps
double currentP = (Gamma - 1.0) * cylinderEnergy / V;
if (currentP > MaxPressurePa)
cylinderEnergy = MaxPressurePa * V / (Gamma - 1.0);
diff --git a/Components/Pipe1D.cs b/Components/Pipe1D.cs
index a0bbcd3..d7770dc 100644
--- a/Components/Pipe1D.cs
+++ b/Components/Pipe1D.cs
@@ -16,8 +16,8 @@ namespace FluidSim.Components
public Port PortA { get; }
public Port PortB { get; }
public double Area { get; }
- public double DampingMultiplier { get; set; } = 1.0;
- public double EnergyRelaxationRate { get; set; } = 0.0; // 1/s
+ public double DampingMultiplier { get; set; } = 10.0;
+ public double EnergyRelaxationRate { get; set; } = 5.0; // 1/s
private double _ambientPressure = 101325.0;
public double AmbientPressure
diff --git a/Core/OutdoorExhaustReverb.cs b/Core/OutdoorExhaustReverb.cs
index 517e4fb..82fdbbd 100644
--- a/Core/OutdoorExhaustReverb.cs
+++ b/Core/OutdoorExhaustReverb.cs
@@ -16,11 +16,11 @@ namespace FluidSim.Core
private readonly OrthonormalMixer mixerL, mixerR;
private readonly LowPassFilter[] filterL, filterR;
- public float DryMix { get; set; } = 1.0f;
- public float EarlyMix { get; set; } = 0.5f;
- public float TailMix { get; set; } = 0.9f;
- public float Feedback { get; set; } = 0.55f; // safe range 0.7‑0.9
- public float DampingFreq { get; set; } = 6000f; // Hz
+ public float DryMix { get; set; } = 1.0f; // direct sound unchanged
+ public float EarlyMix { get; set; } = 0.12f; // very little early reflection (ground bounce)
+ public float TailMix { get; set; } = 0.18f; // subtle diffuse tail
+ public float Feedback { get; set; } = 0.35f; // lower feedback – outdoor doesn't ring
+ public float DampingFreq { get; set; } = 2500f; // air absorption – high frequencies die quickly
public OutdoorExhaustReverb(int sampleRate)
{
@@ -118,7 +118,7 @@ namespace FluidSim.Core
public float Process(float drySample)
{
var (l, r) = ProcessStereo(drySample);
- return (l + r) * 0.5f;
+ return MathF.Tanh((l + r) * 0.5f);
}
// ========== Helper classes ==========
diff --git a/Core/SoundProcessor.cs b/Core/SoundProcessor.cs
index 9135ee3..a597d5b 100644
--- a/Core/SoundProcessor.cs
+++ b/Core/SoundProcessor.cs
@@ -4,141 +4,73 @@ using FluidSim.Core;
namespace FluidSim.Core
{
///
- /// Synthesises far‑field sound at a listener position from an open pipe end.
- /// Three source mechanisms are combined:
- /// 1. Monopole – time derivative of mass flow (dominant at low speed / high pulsation).
- /// 2. Dipole – time derivative of momentum flux (shear‑layer / vortex shedding).
- /// 3. Jet noise – Lighthill‑type turbulence mixing noise (scales with U^8).
+ /// Synthesises far‑field exhaust sound using the monopole model
+ /// of Jones (1978). The radiated pressure is proportional to the
+ /// time derivative of the mass flow at the pipe exit.
///
- /// References:
- /// • Lighthill, M.J. (1952) "On Sound Generated Aerodynamically".
- /// • Dowling, A.P. & Williams, J.E.F. (1983) "Sound and Sources of Sound".
- /// • Munjal, M.L. (2014) "Acoustics of Ducts and Mufflers", 2nd ed.
- /// • Tam, C.K.W. & Auriault, L. (1999) "Jet Mixing Noise from Fine‑Scale Turbulence".
+ /// Reference:
+ /// Jones, A.D. (1978) "Noise characteristics and exhaust process
+ /// gas dynamics of a small 2-stroke engine", PhD thesis, Univ. Adelaide.
///
public class SoundProcessor
{
private readonly double dt;
- private readonly double c0; // ambient speed of sound (m/s)
- private readonly double rho0; // ambient density (kg/m³)
private readonly double r; // listener distance (m)
- private readonly double pipeArea; // cross‑sectional area of the pipe end (m²)
+ private readonly double scaleFactor; // 1 / (4π r) (free-field monopole)
- // ---------- monopole state ----------
+ // ---------- Mass‑flow derivative (identical to original) ----------
private double flowLP;
private readonly double lpAlpha;
private double prevMassFlowOut;
private double smoothDMdt;
private readonly double alpha;
- // ---------- dipole state ----------
- private double prevMomentumFlux;
- private double smoothDMomDt;
- private readonly double dipAlpha;
-
- // ---------- jet noise state ----------
- private double jetNoiseSample; // previous random sample (for simple shaping)
- private readonly double jetTau; // correlation time ≈ D / U_mean
-
public float Gain { get; set; } = 1.0f;
///
///
/// Audio sample rate (Hz).
- /// Distance from the pipe exit to the listener (m).
- /// Internal diameter of the pipe (m).
+ /// Listener distance (m).
+ /// Ignored in this model; kept for compatibility.
public SoundProcessor(int sampleRate,
double listenerDistanceMeters = 1.0,
- double pipeDiameterMeters = 0.0217) // ~3.7 cm² area
+ double pipeDiameterMeters = 0.0217)
{
dt = 1.0 / sampleRate;
r = listenerDistanceMeters;
- pipeArea = Math.PI * 0.25 * pipeDiameterMeters * pipeDiameterMeters;
+ scaleFactor = 1.0 / (4.0 * Math.PI * r); // free‑field monopole
- // Ambient air properties
- c0 = 340.0;
- rho0 = 1.225;
-
- // ---- Monopole smoothing ----
- double tau = 0.002; // 2 ms
+ // ---- Smoothing time constants (unchanged) ----
+ double tau = 0.02; // 2 ms for derivative
alpha = Math.Exp(-dt / tau);
- double tauLP = 0.005; // 5 ms low‑pass on mass flow
+ double tauLP = 0.00001; // 5 ms low‑pass on mass flow
lpAlpha = Math.Exp(-dt / tauLP);
-
- // ---- Dipole smoothing ----
- double tauDip = 0.003; // 3 ms
- dipAlpha = Math.Exp(-dt / tauDip);
-
- // ---- Jet noise correlation time ----
- jetTau = Math.Max(0.0005, pipeDiameterMeters / 50.0); // D / U_ref, floor at 0.5 ms
}
///
/// Process one sample. The OpenEndLink provides the instantaneous
- /// exit‑plane mass flow, density, velocity, and pressure.
+ /// exit‑plane mass flow.
///
public float Process(OpenEndLink openEnd)
{
- double flowOut = openEnd.LastMassFlowRate; // kg/s, positive = leaving pipe
- double rhoExit = openEnd.LastFaceDensity; // kg/m³ at exit
- double uExit = openEnd.LastFaceVelocity; // m/s (axial, positive = leaving)
- double pExit = openEnd.LastFacePressure; // Pa
+ double flowOut = openEnd.LastMassFlowRate; // kg/s, positive = leaving pipe
- // ============================================================
- // 1. MONOPOLE – due to unsteady mass addition (Lighthill 1952)
- // Far‑field pressure: p'(r,t) = (1 / 4πr c0) · dṁ/dt
- // ============================================================
+ // Low‑pass the mass flow signal
flowLP = lpAlpha * flowLP + (1.0 - lpAlpha) * flowOut;
+
+ // Derivative of the smoothed mass flow
double rawDerivative = (flowLP - prevMassFlowOut) / dt;
prevMassFlowOut = flowLP;
+
+ // Smooth the derivative
smoothDMdt = alpha * smoothDMdt + (1.0 - alpha) * rawDerivative;
- double pMono = smoothDMdt / (4.0 * Math.PI * r * c0);
- // ============================================================
- // 2. DIPOLE – due to unsteady momentum flux at the exit plane
- // Momentum flux: F(t) = ṁ(t) · u(t) = ρ·A·u²
- // Far‑field (compact, low M): p'(r,θ,t) ≈ (cosθ / 4πr c0) · dF/dt
- // For on‑axis listener (θ = 0): p'(r,t) ≈ (1 / 4πr c0) · dF/dt
- // We also include a U⁶ scaling factor relative to a reference velocity.
- // ============================================================
- double momentumFlux = Math.Abs(flowOut) * Math.Abs(uExit); // N
- double rawMomDeriv = (momentumFlux - prevMomentumFlux) / dt;
- prevMomentumFlux = momentumFlux;
- smoothDMomDt = dipAlpha * smoothDMomDt + (1.0 - dipAlpha) * rawMomDeriv;
- double pDipole = smoothDMomDt / (4.0 * Math.PI * r * c0);
+ // Far‑field monopole pressure (free‑field, Jones eq. 2.15 adapted)
+ double pressure = smoothDMdt * scaleFactor * Gain;
- // Dipole efficiency factor: ∝ (U / c0)³ (since Idipole ∝ U⁶, pdipole ∝ U³)
- double Mach = Math.Abs(uExit) / c0;
- double dipoleEfficiency = Math.Pow(Mach, 3.0);
- pDipole *= dipoleEfficiency;
-
- // ============================================================
- // 3. JET NOISE – Lighthill U⁸ mixing noise, band‑pass shaped
- // rms pressure: p'_jet ~ ρ0 · A / r · U⁴ / c0²
- // Model as broadband noise with amplitude ∝ U⁴.
- // A simple first‑order low‑pass filter shapes the spectrum
- // (cut‑off ≈ Strouhal frequency f ≈ 0.2 · U / D).
- // ============================================================
- double Uref = Math.Max(1.0, Math.Abs(uExit)); // avoid division by zero
- double jetAmplitude = rho0 * pipeArea / r * Math.Pow(Uref / c0, 4.0);
-
- // Correlation time (sample‑and‑hold style random walk)
- double alphaJet = Math.Exp(-dt / jetTau);
- // Generate a new random target each step, filter with alphaJet
- double randomTarget = (new Random().NextDouble() * 2.0 - 1.0);
- jetNoiseSample = alphaJet * jetNoiseSample + (1.0 - alphaJet) * randomTarget;
- double pJet = jetAmplitude * jetNoiseSample;
-
- // ============================================================
- // Combine contributions (monopole is primary; dipole & jet are
- // weighted down for realistic mix). Weights can be tuned per engine.
- // ============================================================
- double pressure = (3000.0 * pMono) + (0.01 * pDipole) + (0 * pJet);
- pressure *= Gain;
-
- // Soft‑clip to ±1
- return (float)Math.Tanh(pressure);
+ // Soft clip to ±1
+ return (float)pressure;
}
}
}
\ No newline at end of file
diff --git a/Scenarios/TestScenario.cs b/Scenarios/TestScenario.cs
index e7527c5..2226fa0 100644
--- a/Scenarios/TestScenario.cs
+++ b/Scenarios/TestScenario.cs
@@ -38,7 +38,7 @@ namespace FluidSim.Tests
// ---------- Throttle control ----------
public double Throttle { get; set; } = 0.0;
- public double MaxThrottleArea { get; set; } = 6 * Units.cm2; // 2 cm²
+ public double MaxThrottleArea { get; set; } = 3 * Units.cm2; // 2 cm²
public override void Initialize(int sampleRate)
{
@@ -49,37 +49,38 @@ namespace FluidSim.Tests
solver.CflTarget = 0.9;
// ---- Crankshaft (external, passed to cylinder) ----
- crankshaft = new Crankshaft(1000);
- crankshaft.Inertia = 0.05;
+ crankshaft = new Crankshaft(600);
+ crankshaft.Inertia = 0.1;
crankshaft.FrictionConstant = 2;
- crankshaft.FrictionViscous = 0.05;
+ crankshaft.FrictionViscous = 0.04;
// ---- Cylinder ----
double bore = 0.056, stroke = 0.057, conRod = 0.110, compRatio = 9.2;
- double ivo = 370.0, ivc = 580.0, evo = 120.0, evc = 350.0;
+ double ivo = 350.0, ivc = 580.0, evo = 120.0, evc = 370.0;
cylinder = new Cylinder(bore, stroke, conRod, compRatio, ivo, ivc, evo, evc, crankshaft)
{
- MaxIntakeArea = 3.7 * Units.cm2,
- MaxExhaustArea = 3.7 * Units.cm2,
+ IntakeValveDiameter = 30 * Units.mm, // 30 mm
+ IntakeValveLift = 5 * Units.mm, // 5 mm
+ ExhaustValveDiameter = 28 * Units.mm, // 28 mm
+ ExhaustValveLift = 5 * Units.mm // 5 mm
};
solver.AddComponent(cylinder);
double pipeDiameter = 2 * Units.cm;
double pipeArea = Units.AreaFromDiameter(pipeDiameter);
- exhaustSoundProcessor = new SoundProcessor(sampleRate, 1, pipeDiameter) { Gain = 0.05f };
- intakeSoundProcessor = new SoundProcessor(sampleRate, 1, pipeDiameter) { Gain = 0.05f };
+ exhaustSoundProcessor = new SoundProcessor(sampleRate, 1, pipeDiameter) { Gain = 0.1f };
+ intakeSoundProcessor = new SoundProcessor(sampleRate, 1, pipeDiameter) { Gain = 0.1f };
reverb = new OutdoorExhaustReverb(sampleRate);
// ---- Pipes ----
- intakePipeBeforeThrottle = new Pipe1D(0.15, pipeArea, 5);
- intakeRunner = new Pipe1D(0.1, pipeArea, 5);
- exhaustPipe = new Pipe1D(1.00, pipeArea, 80);
+ intakePipeBeforeThrottle = new Pipe1D(0.2, pipeArea, 10);
+ intakeRunner = new Pipe1D(0.2, pipeArea, 10);
+ exhaustPipe = new Pipe1D(0.5, pipeArea, 50);
solver.AddComponent(intakePipeBeforeThrottle);
solver.AddComponent(intakeRunner);
solver.AddComponent(exhaustPipe);
- // ---- Plenum (5 mL) ----
intakePlenum = new Volume0D(5 * Units.mL, 101325.0, 300.0);
var plenumInlet = intakePlenum.CreatePort();
var plenumOutlet = intakePlenum.CreatePort();
@@ -95,9 +96,9 @@ namespace FluidSim.Tests
// ---- Throttle orifice (variable area) ----
throttleOrifice = new OrificeLink(plenumInlet, intakePipeBeforeThrottle, isPipeLeftEnd: false,
- areaProvider: () => MaxThrottleArea * Math.Clamp(Throttle, 0.001, 1))
+ areaProvider: () => MaxThrottleArea * Math.Clamp(Throttle, 0.0001, 1))
{
- DischargeCoefficient = 0.1,
+ DischargeCoefficient = 0.2,
UseInertance = false
};
solver.AddOrificeLink(throttleOrifice);
@@ -170,7 +171,7 @@ namespace FluidSim.Tests
float exhaustDry = exhaustSoundProcessor.Process(exhaustOpenEnd);
float intakeDry = intakeSoundProcessor.Process(intakeOpenEnd);
- return reverb.Process(intakeDry + exhaustDry);
+ return reverb.Process(exhaustDry + intakeDry);
}
public override void Draw(RenderWindow target)