FluidSim/Core/OrificeLink.cs

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

namespace FluidSim.Core
{
    /// <summary>
    /// Connects a port (volume or atmosphere) to one end of a pipe via an orifice.
    /// The area can be dynamic (Func<double>).
    /// </summary>
    public class OrificeLink
    {
        public Port VolumePort { get; }
        public Pipe1D Pipe { get; }
        public bool IsPipeLeftEnd { get; }
        public Func<double> AreaProvider { get; set; }
        public double DischargeCoefficient { get; set; } = 0.62;
        public double Gamma { get; set; } = 1.4;
        public double GasConstant { get; set; } = 287.0;

        // Last resolved state (for audio/monitoring)
        public double LastMassFlowRate { get; private set; }
        public double LastFaceDensity { get; private set; }
        public double LastFaceVelocity { get; private set; }
        public double LastFacePressure { get; private set; }

        public OrificeLink(Port volumePort, Pipe1D pipe, bool isPipeLeftEnd, Func<double> areaProvider)
        {
            VolumePort = volumePort ?? throw new ArgumentNullException(nameof(volumePort));
            Pipe = pipe ?? throw new ArgumentNullException(nameof(pipe));
            IsPipeLeftEnd = isPipeLeftEnd;
            AreaProvider = areaProvider ?? throw new ArgumentNullException(nameof(areaProvider));
        }

        /// <summary>
        /// Resolve the coupling for one sub‑step. Computes nozzle flow (isentropic)
        /// and sets the pipe ghost cell and the port flow rates.
        /// </summary>
        public void Resolve(double dtSub)
        {
            double area = AreaProvider();
            if (area < 1e-12)
            {
                SetClosedWall();
                return;
            }

            // Retrieve volume state
            double volP = VolumePort.Pressure;
            double volRho = VolumePort.Density;
            double volT = VolumePort.Temperature;
            double volH = VolumePort.SpecificEnthalpy;

            // Retrieve pipe interior state at the connected end
            (double pipeRho, double pipeU, double pipeP) = IsPipeLeftEnd
                ? Pipe.GetInteriorStateLeft()
                : Pipe.GetInteriorStateRight();

            // Determine upstream/downstream: if volume pressure > pipe pressure, flow is out of volume (negative into volume).
            bool flowOutOfVolume = volP > pipeP;
            double pUp, rhoUp, TUp, pDown;
            if (flowOutOfVolume)
            {
                pUp = volP; rhoUp = volRho; TUp = volT; pDown = pipeP;
            }
            else
            {
                // Pipe is upstream
                pUp = pipeP; rhoUp = pipeRho; TUp = pipeP / (pipeRho * GasConstant); // temperature from pipe
                pDown = volP;
            }

            // Compute isentropic nozzle flow
            IsentropicOrifice.Compute(pUp, rhoUp, TUp, Gamma, GasConstant, pDown, area, DischargeCoefficient,
                                      out double mdotUpstreamToDown, out double rhoFace, out double uFace, out double pFace);

            // mdotUpstreamToDown is positive from upstream to downstream.
            // Convert to mass flow into volume (positive mdot = into volume).
            double mdotVolume;
            if (flowOutOfVolume)
                mdotVolume = -mdotUpstreamToDown;   // out of volume is negative
            else
                mdotVolume = mdotUpstreamToDown;    // into volume is positive

            // Clamp mass flow to available mass in volume (if it is a Volume0D)
            if (VolumePort.Owner is Volume0D vol)
            {
                double maxMdot = vol.Mass / dtSub;
                if (mdotVolume > maxMdot) mdotVolume = maxMdot;
                if (mdotVolume < -maxMdot) mdotVolume = -maxMdot;
            }

            // Apply ghost state to pipe
            if (IsPipeLeftEnd)
                Pipe.SetGhostLeft(rhoFace, uFace, pFace);
            else
                Pipe.SetGhostRight(rhoFace, uFace, pFace);

            // Store results
            LastMassFlowRate = mdotVolume;
            LastFaceDensity = rhoFace;
            LastFaceVelocity = uFace;
            LastFacePressure = pFace;

            // Set port flow rates for volume integration
            VolumePort.MassFlowRate = mdotVolume;
            if (mdotVolume >= 0)
            {
                // Inflow: enthalpy comes from upstream (pipe)
                double pPipe = pipeP;
                double rhoPipe = pipeRho;
                VolumePort.SpecificEnthalpy = Gamma / (Gamma - 1.0) * pPipe / rhoPipe;
            }
            else
            {
                // Outflow: volume's own specific enthalpy
                VolumePort.SpecificEnthalpy = volH;
            }
        }

        private void SetClosedWall()
        {
            var (rInt, uInt, pInt) = IsPipeLeftEnd
                ? Pipe.GetInteriorStateLeft()
                : Pipe.GetInteriorStateRight();

            if (IsPipeLeftEnd)
                Pipe.SetGhostLeft(rInt, -uInt, pInt);
            else
                Pipe.SetGhostRight(rInt, -uInt, pInt);

            LastMassFlowRate = 0.0;
            LastFaceDensity = rInt;
            LastFaceVelocity = 0.0;
            LastFacePressure = pInt;
            VolumePort.MassFlowRate = 0.0;
            // Keep specific enthalpy as is (not used)
        }
    }
}