FluidSim/Scenarios/TestScenario.cs

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

namespace FluidSim.Tests
{
    public class TestScenario : Scenario
    {
        private Solver solver;
        private Pipe1D pipe;
        private OrificeLink closedEnd;    // left end – closed wall
        private OpenEndLink openEndLink;  // right end – atmosphere
        private SoundProcessor soundProcessor;
        private OutdoorExhaustReverb reverb;
        private int stepCount;
        private double simTime;            // elapsed simulation time (seconds)
        private double pulseInterval = 0.1; // seconds between pulses
        private double nextPulseTime;
        private double dt;

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

            soundProcessor = new SoundProcessor(sampleRate, 1);
            soundProcessor.Gain = 10;

            reverb = new OutdoorExhaustReverb(sampleRate);

            solver = new Solver();
            solver.SetTimeStep(dt);

            // Pipe: 2 m long, 1 cm² area, 200 cells
            pipe = new Pipe1D(length: 2, area: 1e-4, cellCount: 100);
            solver.AddComponent(pipe);

            // Initially pipe at ambient conditions
            pipe.SetUniformState(1.225, 0.0, 101325.0);

            // Left end: closed wall (area = 0 → reflective)
            closedEnd = new OrificeLink(null, pipe, isPipeLeftEnd: true, areaProvider: () => 0.0);
            solver.AddOrificeLink(closedEnd);

            // Right end: open to atmosphere
            openEndLink = new OpenEndLink(pipe, isLeftEnd: false)
            {
                AmbientPressure = 101325.0,
                Gamma = 1.4
            };
            solver.AddOpenEndLink(openEndLink);

            stepCount = 0;
            simTime = 0.0;
            nextPulseTime = pulseInterval;   // first pulse at 100 ms

            Console.WriteLine("Pulse reflection test – closed left, open right");
            Console.WriteLine("Pulse injected every 100 ms at left end (cell 0)");
        }

        public override float Process()
        {
            solver.Step();
            stepCount++;
            simTime += dt;

            // ---- Inject a pressure pulse at the closed end every 100 ms ----
            if (simTime >= nextPulseTime)
            {
                // Apply a Gaussian pulse to the first few cells
                double ambientPressure = 101325.0;
                double pulseAmplitude = 20 * ambientPressure;   // 0.5 atm overpressure
                double pulseWidth = 0.05;   // m (spread over a few cells)
                int n = pipe.CellCount;
                double dx = 2.0 / n;

                // Only modify cells within 2*pulseWidth from the left end
                int maxCell = Math.Min(5, n - 1);   // at most the first 5 cells
                for (int i = 0; i <= maxCell; i++)
                {
                    double x = (i + 0.5) * dx;
                    double P = pulseAmplitude * Math.Exp(-x * x / (pulseWidth * pulseWidth));
                    double currentP = pipe.GetCellPressure(i);
                    double newP = P;
                    // Update pressure, keeping density and velocity unchanged
                    // We recompute total energy accordingly
                    double rho = pipe.GetCellDensity(i);
                    double u = pipe.GetCellVelocity(i);
                    double e = newP / ((1.4 - 1.0) * rho);
                    double E = rho * e + 0.5 * rho * u * u;
                    pipe.SetCellState(i, rho, u, newP);
                }
                Console.WriteLine($"Pulse injected at t = {simTime:F3} s");
                nextPulseTime += pulseInterval;
            }

            // Audio from open‑end mass flow
            float sample = soundProcessor.Process(openEndLink);

            // Log every 200 steps
            if (stepCount % 1000 == 0)
            {
                int leftIdx = 0;
                int midIdx = pipe.CellCount / 2;
                int rightIdx = pipe.CellCount - 1;
                double pL = pipe.GetCellPressure(leftIdx);
                double pM = pipe.GetCellPressure(midIdx);
                double pR = pipe.GetCellPressure(rightIdx);

                Console.WriteLine($"Step {stepCount}: P_left={pL:F1} Pa, P_mid={pM:F1} Pa, P_right={pR:F1} Pa");
            }

            if (double.IsNaN(pipe.GetCellPressure(0)))
            {
                Console.WriteLine("NaN detected – stopping simulation.");
                return 0f;
            }

            return reverb.Process(sample);
        }

        public override void Draw(RenderWindow target)
        {
            float winWidth = target.GetView().Size.X;
            float winHeight = target.GetView().Size.Y;
            float pipeCenterY = winHeight / 2f;
            float margin = 60f;
            float pipeStartX = margin;
            float pipeEndX = winWidth - margin;
            DrawPipe(target, pipe, pipeCenterY, pipeStartX, pipeEndX);
        }
    }
}