FluidSim/Core/Simulation.cs

using System;
using FluidSim.Components;
using FluidSim.Interfaces;
using FluidSim.Utils;

namespace FluidSim.Core
{
    public static class Simulation
    {
        private static Solver solver;
        private static Pipe1D pipe;
        private static int stepCount;
        private static double time;
        private static double dt;
        private static float sample;
        private static double ambientPressure = 1.0 * Units.atm;

        private static bool enableLogging = false;

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

            double length = 2;
            double radius = 20 * Units.mm;
            double area = Units.AreaFromDiameter(radius);

            pipe = new Pipe1D(length, area, sampleRate, forcedCellCount: 80);
            pipe.SetUniformState(1.225, 0.0, ambientPressure);

            solver = new Solver();
            solver.SetTimeStep(dt);
            solver.AddPipe(pipe);
            solver.SetPipeBoundary(pipe, isLeft: true, BoundaryType.OpenEnd, ambientPressure);
            solver.SetPipeBoundary(pipe, isLeft: false, BoundaryType.ClosedEnd);

            // Excite the pipe with an initial pressure pulse near the open end
            int pulseCells = 5;
            double pulsePressure = 4 * ambientPressure;
            for (int i = 0; i < pulseCells; i++)
                pipe.SetCellState(i, 1.225, 0.0, pulsePressure);
        }

        public static float Process()
        {
            sample = solver.Step();
            time += dt;
            stepCount++;

            // Override the audio sample with mid-pipe pressure deviation
            double pMid = pipe.GetPressureAtFraction(0.5);
            sample = (float)((pMid - ambientPressure) / ambientPressure);

            Log();
            return sample;
        }

        public static void Log()
        {
            if (!enableLogging) return;
            if (stepCount % 10 == 0 && stepCount < 1000)
            {
                double pMid = pipe.GetPressureAtFraction(0.5);
                double pOpen = pipe.GetCellPressure(0);
                double pClosed = pipe.GetCellPressure(pipe.GetCellCount() - 1);
                Console.WriteLine(
                    $"t = {time * 1e3:F3} ms  Step {stepCount:D4}: " +
                    $"Sample: = {sample:F3}, " +
                    $"P_mid = {pMid:F2} Pa ({pMid / ambientPressure:F4} atm), " +
                    $"P_open = {pOpen:F2} Pa, P_closed = {pClosed:F2} Pa");
            }
        }
    }
}