FluidSim/Scenarios/EngineScenario.cs

using System;
using FluidSim.Components;
using SFML.Graphics;
using SFML.System;

namespace FluidSim.Core
{
    public class EngineScenario : Scenario
    {
        private Solver solver;
        private Crankshaft crankshaft;
        private EngineCylinder engineCyl;
        private Pipe1D exhaustPipe;
        private PipeVolumeConnection coupling;
        private SoundProcessor soundProcessor;

        private double dt;
        private double ambientPressure = 101325.0;
        private double time;
        private int stepCount = 0;
        private const int LogInterval = 10000;

        // Throttle 0..1 → target combustion pressure
        public double Throttle { get; set; } = 0.05;  // tiny throttle to keep idle
        private const double IdlePeakPressure = 5.0 * 101325.0;    // 5 bar
        private const double MaxPeakPressure  = 50.0 * 101325.0;   // 50 bar

        public override void Initialize(int sampleRate)
        {
            dt = 1.0 / sampleRate;

            // Crankshaft (inertia + friction)
            crankshaft = new Crankshaft(initialRPM: 100.0)   // starter speed
            {
                Inertia = 0.05,
                FrictionConstant = 1.0,
                FrictionViscous = 0.01
            };

            // Pipe
            double pipeLength = 0.5;
            double pipeRadius = 0.1;
            double pipeArea = Math.PI * pipeRadius * pipeRadius;
            exhaustPipe = new Pipe1D(pipeLength, pipeArea, sampleRate, forcedCellCount: 60);
            exhaustPipe.SetUniformState(1.225, 0.0, ambientPressure);
            exhaustPipe.EnergyRelaxationRate = 0f; 
            exhaustPipe.DampingMultiplier = 0;

            // Cylinder (coupled to crankshaft)
            engineCyl = new EngineCylinder(crankshaft,
                bore: 0.065, stroke: 0.0565, compressionRatio: 10.0,
                pipeArea: pipeArea, sampleRate: sampleRate);

            // Coupling (valve → pipe)
            coupling = new PipeVolumeConnection(engineCyl.Cylinder, exhaustPipe, true, orificeArea: 0.0);

            // Solver
            solver = new Solver();
            solver.SetTimeStep(dt);
            solver.AddVolume(engineCyl.Cylinder);
            solver.AddPipe(exhaustPipe);
            solver.AddConnection(coupling);
            solver.SetPipeBoundary(exhaustPipe, false, BoundaryType.OpenEnd, ambientPressure);

            // Sound (your tuned gains)
            soundProcessor = new SoundProcessor(sampleRate, pipeRadius * 2, reverbTimeMs: 500.0f);
            soundProcessor.MasterGain       = 0.0f; //0.00001f;
            soundProcessor.PressureGain     = 0.1f;
            soundProcessor.TurbulenceGain   = 0.0f;
            soundProcessor.Turbulence       = 0.001f;
            soundProcessor.SetAmbientPressure(ambientPressure);

            Console.WriteLine("=== EngineScenario (torque‑driven RPM, throttle = pressure) ===");
            Console.WriteLine($"Crankshaft inertia: {crankshaft.Inertia}, friction: {crankshaft.FrictionConstant} + {crankshaft.FrictionViscous}*ω");
            Console.WriteLine($"Throttle range: {IdlePeakPressure/101325:F0} – {MaxPeakPressure/101325:F0} bar");
            Console.WriteLine($"Pipe: {pipeLength} m, fundamental: {340/(4*pipeLength):F1} Hz");
        }

        public override float Process()
        {
            // 1. Map throttle to target peak pressure
            double targetPressure = IdlePeakPressure + Throttle * (MaxPeakPressure - IdlePeakPressure);
            engineCyl.TargetPeakPressure = targetPressure;

            // 2. Step the cylinder (adds torque to crankshaft, updates valve)
            engineCyl.Step(dt);

            // 3. Integrate crankshaft (applies friction, updates RPM)
            crankshaft.Step(dt);

            // 4. Set orifice area for coupling
            coupling.OrificeArea = engineCyl.OrificeArea;

            // 5. Fluid solver step
            float massFlow = solver.Step();
            float endPressure = (float)exhaustPipe.GetCellPressure(exhaustPipe.GetCellCount() - 1);

            // 6. Audio
            float audioSample = soundProcessor.Process(massFlow, endPressure);

            time += dt;
            stepCount++;
            if (stepCount % LogInterval == 0) {
                Console.WriteLine(audioSample);
            }

            if (stepCount % 1000 == 0 && false)
            {
                Console.WriteLine($"{time,5:F3}  {crankshaft.AngularVelocity*60/(2*Math.PI),5:F0} RPM  " +
                                  $"Thr:{Throttle:F2}  P_target:{targetPressure/101325:F1} bar  " +
                                  $"mflow:{massFlow,14:E4}  Comb#{engineCyl.CombustionCount}  Mis#{engineCyl.MisfireCount}");
            }

            return audioSample;
        }

        // ---- Drawing (unchanged) ----
        public override void Draw(RenderWindow target)
        {
            float winW = target.GetView().Size.X;
            float winH = target.GetView().Size.Y;
            float centerY = winH / 2f;

            const float T_ambient = 293.15f;
            const float T_hot     = 1500f;
            const float T_cold    = 0f;
            const float R         = 287.05f;
            float deltaHot  = T_hot - T_ambient;
            float deltaCold = T_ambient - T_cold;

            float NormaliseTemperature(double T)
            {
                double t;
                if (T >= T_ambient)
                    t = (T - T_ambient) / deltaHot;
                else
                    t = (T - T_ambient) / deltaCold;
                return (float)Math.Clamp(t, -1.0, 1.0);
            }

            float cylW = 80f, cylH = 150f;
            var cylRect = new RectangleShape(new Vector2f(cylW, cylH));
            cylRect.Position = new Vector2f(40f, centerY - cylH / 2f);

            double tempCyl = engineCyl.Cylinder.Temperature;
            float tnCyl = NormaliseTemperature(tempCyl);
            byte rC = (byte)(tnCyl > 0 ? 255 * tnCyl : 0);
            byte bC = (byte)(tnCyl < 0 ? -255 * tnCyl : 0);
            byte gC = (byte)(255 * (1 - Math.Abs(tnCyl)));
            cylRect.FillColor = new Color(rC, gC, bC);
            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];
            float ambPress = 101325f;

            for (int i = 0; i < n; i++)
            {
                float x = pipeStartX + i * dx;
                double p   = exhaustPipe.GetCellPressure(i);
                double rho = exhaustPipe.GetCellDensity(i);
                double T   = p / (rho * R);

                float r = baseRadius * 0.3f * (float)(1.0 + (p - ambPress) / ambPress);
                if (r < 2f) r = 2f;

                float tn = NormaliseTemperature(T);
                byte rCol = (byte)(tn > 0 ? 255 * tn : 0);
                byte bCol = (byte)(tn < 0 ? -255 * tn : 0);
                byte gCol = (byte)(255 * (1 - Math.Abs(tn)));
                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);
        }
    }
}