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Introduced automatic sub stepping and pipe cell count

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max
2026-05-03 00:20:17 +02:00
parent 2c338ad7d9
commit 3926ed7ef9
2 changed files with 181 additions and 85 deletions
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242
Components/Pipe1D.cs
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@@ -9,14 +9,19 @@ namespace FluidSim.Components
public Port PortB { get; }
public double Area => _area;
private int _n;
private double _dx, _dt, _gamma = 1.4, _area;
private int _n; // number of cells
private double _dx, _dt, _gamma, _area;
private double[] _rho, _rhou, _E;
// Volume states at boundaries
private double _rhoLeft, _pLeft, _rhoRight, _pRight;
// Volume boundary states, constant during sub‑steps
private double _rhoLeft, _pLeft;
private double _rhoRight, _pRight;
private bool _leftBCSet, _rightBCSet;
// CFL control
private const double CflTarget = 0.8;
private const double ReferenceSoundSpeed = 340.0; // m/s, standard air
public double FrictionFactor { get; set; } = 0.02;
public int GetCellCount() => _n;
@@ -24,12 +29,30 @@ namespace FluidSim.Components
public double GetCellPressure(int i) => Pressure(i);
public double GetCellVelocity(int i) => _rhou[i] / Math.Max(_rho[i], 1e-12);
public Pipe1D(double length, double area, int nCells, int sampleRate)
/// <summary>
/// Creates a 1D pipe.
/// Cell count is automatically determined to satisfy CFL in still air.
/// </summary>
/// <param name="length">Pipe length in metres.</param>
/// <param name="area">Cross‑sectional area in m².</param>
/// <param name="sampleRate">Global simulation sample rate (Hz).</param>
public Pipe1D(double length, double area, int sampleRate)
{
// Desired spatial step to keep CFL ≤ target for still air
double dtGlobal = 1.0 / sampleRate;
double dxTarget = ReferenceSoundSpeed * dtGlobal * CflTarget;
// Number of cells must be at least 2; try to hit dxTarget
int nCells = Math.Max(2, (int)Math.Round(length / dxTarget, MidpointRounding.AwayFromZero));
// Ensure we don't accidentally overshoot dxTarget by more than a factor
while (length / nCells > dxTarget * 1.01 && nCells < int.MaxValue - 1)
nCells++;
_n = nCells;
_dx = length / nCells;
_dt = 1.0 / sampleRate;
_dx = length / _n;
_dt = dtGlobal; // global (audio) time step
_area = area;
_gamma = 1.4;
_rho = new double[_n];
_rhou = new double[_n];
@@ -56,7 +79,6 @@ namespace FluidSim.Components
public double GetLeftDensity() => _rho[0];
public double GetRightDensity() => _rho[_n - 1];
// ★ New: pass both density and pressure from the volume
public void SetLeftVolumeState(double rhoVol, double pVol)
{
_rhoLeft = rhoVol;
@@ -80,95 +102,152 @@ namespace FluidSim.Components
return h + 0.5 * u * u;
}
/// <summary>
/// Advance the pipe over one global time step using sub‑stepping.
/// Must be called once per global simulation cycle.
/// </summary>
public void Simulate()
{
int n = _n;
double[] Fm = new double[n + 1], Fp = new double[n + 1], Fe = new double[n + 1];
// --- Left boundary (face 0) ---
if (_leftBCSet)
{
// Ghost = actual volume state (ρ_vol, u=0, p_vol)
double rhoL = _rhoLeft;
double uL = 0.0;
double pL = _pLeft;
double rhoR = _rho[0];
double uR = _rhou[0] / Math.Max(rhoR, 1e-12);
double pR = Pressure(0);
HLLCFlux(rhoL, uL, pL, rhoR, uR, pR, out Fm[0], out Fp[0], out Fe[0]);
}
else
{
Fm[0] = 0;
Fp[0] = Pressure(0);
Fe[0] = 0;
}
// --- Internal faces ---
for (int i = 0; i < n - 1; i++)
{
double uL = _rhou[i] / Math.Max(_rho[i], 1e-12);
double uR = _rhou[i + 1] / Math.Max(_rho[i + 1], 1e-12);
HLLCFlux(_rho[i], uL, Pressure(i), _rho[i + 1], uR, Pressure(i + 1),
out Fm[i + 1], out Fp[i + 1], out Fe[i + 1]);
}
// --- Right boundary (face n) ---
if (_rightBCSet)
{
double rhoL = _rho[n - 1];
double uL = _rhou[n - 1] / Math.Max(rhoL, 1e-12);
double pL = Pressure(n - 1);
// Ghost = actual volume state (ρ_vol, u=0, p_vol)
double rhoR = _rhoRight;
double uR = 0.0;
double pR = _pRight;
HLLCFlux(rhoL, uL, pL, rhoR, uR, pR, out Fm[n], out Fp[n], out Fe[n]);
}
else
{
Fm[n] = 0;
Fp[n] = Pressure(n - 1);
Fe[n] = 0;
}
// --- Cell update ---
// --- Determine maximum wave speed in the pipe ---
double maxWaveSpeed = 0.0;
for (int i = 0; i < n; i++)
{
double dM = (Fm[i + 1] - Fm[i]) / _dx;
double dP = (Fp[i + 1] - Fp[i]) / _dx;
double dE = (Fe[i + 1] - Fe[i]) / _dx;
_rho[i] -= _dt * dM;
_rhou[i] -= _dt * dP;
_E[i] -= _dt * dE;
if (_rho[i] < 1e-12) _rho[i] = 1e-12;
double kinetic = 0.5 * _rhou[i] * _rhou[i] / _rho[i];
if (_E[i] < kinetic) _E[i] = kinetic;
double rho = Math.Max(_rho[i], 1e-12);
double u = Math.Abs(_rhou[i] / rho);
double c = Math.Sqrt(_gamma * Pressure(i) / rho);
double local = u + c;
if (local > maxWaveSpeed) maxWaveSpeed = local;
}
// --- Friction disabled ---
// if (FrictionFactor > 0) { … }
if (maxWaveSpeed < 1e-8) maxWaveSpeed = 1e-8;
// --- Port flows ---
PortA.MassFlowRate = _leftBCSet ? Fm[0] * _area : 0.0;
PortB.MassFlowRate = _rightBCSet ? -Fm[n] * _area : 0.0;
int nSub = Math.Max(1, (int)Math.Ceiling(_dt * maxWaveSpeed / (CflTarget * _dx)));
double dtSub = _dt / nSub;
PortA.SpecificEnthalpy = GetCellTotalSpecificEnthalpy(0);
PortB.SpecificEnthalpy = GetCellTotalSpecificEnthalpy(_n - 1);
// Accumulators for net mass flows
double sumMdotA = 0.0, sumMdotB = 0.0;
// Accumulators for fluid that ENTERS the volumes (pipe → volume)
double massInA = 0.0, energyInA = 0.0;
double massInB = 0.0, energyInB = 0.0;
for (int step = 0; step < nSub; step++)
{
double[] Fm = new double[n + 1];
double[] Fp = new double[n + 1];
double[] Fe = new double[n + 1];
// Left boundary (face 0)
if (_leftBCSet)
{
HLLCFlux(_rhoLeft, 0.0, _pLeft,
_rho[0], _rhou[0] / Math.Max(_rho[0], 1e-12), Pressure(0),
out Fm[0], out Fp[0], out Fe[0]);
}
else
{
Fm[0] = 0;
Fp[0] = Pressure(0);
Fe[0] = 0;
}
// Internal faces
for (int i = 0; i < n - 1; i++)
{
double uL = _rhou[i] / Math.Max(_rho[i], 1e-12);
double uR = _rhou[i + 1] / Math.Max(_rho[i + 1], 1e-12);
HLLCFlux(_rho[i], uL, Pressure(i),
_rho[i + 1], uR, Pressure(i + 1),
out Fm[i + 1], out Fp[i + 1], out Fe[i + 1]);
}
// Right boundary (face n)
if (_rightBCSet)
{
double rhoL = _rho[n - 1];
double uL = _rhou[n - 1] / Math.Max(rhoL, 1e-12);
double pL = Pressure(n - 1);
HLLCFlux(rhoL, uL, pL,
_rhoRight, 0.0, _pRight,
out Fm[n], out Fp[n], out Fe[n]);
}
else
{
Fm[n] = 0;
Fp[n] = Pressure(n - 1);
Fe[n] = 0;
}
// Cell update
for (int i = 0; i < n; i++)
{
double dM = (Fm[i + 1] - Fm[i]) / _dx;
double dP = (Fp[i + 1] - Fp[i]) / _dx;
double dE = (Fe[i + 1] - Fe[i]) / _dx;
_rho[i] -= dtSub * dM;
_rhou[i] -= dtSub * dP;
_E[i] -= dtSub * dE;
if (_rho[i] < 1e-12) _rho[i] = 1e-12;
double kinetic = 0.5 * _rhou[i] * _rhou[i] / _rho[i];
if (_E[i] < kinetic) _E[i] = kinetic;
}
// Sub‑step mass flow rates (kg/s)
double mdotA_sub = _leftBCSet ? Fm[0] * _area : 0.0; // >0 = into pipe
double mdotB_sub = _rightBCSet ? -Fm[n] * _area : 0.0; // >0 = into pipe from right
sumMdotA += mdotA_sub;
sumMdotB += mdotB_sub;
// Flow FROM pipe INTO volume A: mdotA_sub < 0
if (mdotA_sub < 0 && _leftBCSet)
{
double massRate = -mdotA_sub; // kg/s entering volume A
double h = GetCellTotalSpecificEnthalpy(0);
massInA += massRate * dtSub;
energyInA += massRate * dtSub * h;
}
// Flow FROM pipe INTO volume B: mdotB_sub < 0 (because
// mdotB_sub = -Fm[n], and Fm[n] > 0 is flow to the right)
if (mdotB_sub < 0 && _rightBCSet)
{
double massRate = -mdotB_sub; // kg/s entering volume B
double h = GetCellTotalSpecificEnthalpy(_n - 1);
massInB += massRate * dtSub;
energyInB += massRate * dtSub * h;
}
}
// Averaged net mass flows (sign: positive = into pipe)
PortA.MassFlowRate = sumMdotA / nSub;
PortB.MassFlowRate = sumMdotB / nSub;
// Assign enthalpy ONLY for the fluid that physically entered the volume
if (massInA > 1e-12)
PortA.SpecificEnthalpy = energyInA / massInA;
if (massInB > 1e-12)
PortB.SpecificEnthalpy = energyInB / massInB;
// If no inflow occurred, leave the port’s enthalpy unchanged.
// (It will be set to the volume’s static enthalpy by PushStateToPort
// or overwritten by TransferPipeToVolume if flow reverses later.)
_leftBCSet = _rightBCSet = false;
}
double Pressure(int i) =>
// Pressure and HLLC flux unchanged
private double Pressure(int i) =>
(_gamma - 1.0) * (_E[i] - 0.5 * _rhou[i] * _rhou[i] / Math.Max(_rho[i], 1e-12));
void HLLCFlux(double rL, double uL, double pL, double rR, double uR, double pR,
out double fm, out double fp, out double fe)
private void HLLCFlux(double rL, double uL, double pL,
double rR, double uR, double pR,
out double fm, out double fp, out double fe)
{
double cL = Math.Sqrt(_gamma * pL / Math.Max(rL, 1e-12));
double cR = Math.Sqrt(_gamma * pR / Math.Max(rR, 1e-12));
@@ -176,6 +255,7 @@ namespace FluidSim.Components
double ER = pR / ((_gamma - 1) * rR) + 0.5 * uR * uR;
double SL = Math.Min(uL - cL, uR - cR);
double SR = Math.Max(uL + cL, uR + cR);
double Ss = (pR - pL + rL * uL * (SL - uL) - rR * uR * (SR - uR))
/ (rL * (SL - uL) - rR * (SR - uR));

24
Core/Simulation.cs
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@@ -19,15 +19,14 @@ namespace FluidSim.Core
dt = 1.0 / sampleRate;
double V = 5.0 * Units.L;
volA = new Volume0D(V, 1.1 * Units.atm, Units.Celsius(20), sampleRate);
volA = new Volume0D(V, 2.0 * Units.atm, Units.Celsius(20), sampleRate);
volB = new Volume0D(V, 1.0 * Units.atm, Units.Celsius(20), sampleRate);
double length = 150 * Units.mm;
double diameter = 25 * Units.mm;
double area = Units.AreaFromDiameter(25, Units.mm);
int nCells = 10;
pipe = new Pipe1D(length, area, nCells, sampleRate);
pipe = new Pipe1D(length, area, sampleRate);
pipe.SetUniformState(volA.Density, 0.0, volA.Pressure);
pipe.FrictionFactor = 0.02;
@@ -54,13 +53,30 @@ namespace FluidSim.Core
public static void Log()
{
if (stepCount <= 50 || stepCount % 200 == 0)
bool logPipe = true;
if ((stepCount <= 10 || (stepCount <= 1000 && stepCount % 100 == 0)) || stepCount % 1000 == 0 && stepCount < 10000)
{
// Summary line
Console.WriteLine(
$"t = {time * 1e3:F3} ms Step {stepCount:D4}: " +
$"PA = {volA.Pressure / 1e5:F6} bar, " +
$"PB = {volB.Pressure / 1e5:F6} bar, " +
$"FlowA = {pipe.PortA.MassFlowRate * 1e3:F2} g/s");
// Per‑cell state
if (logPipe && stepCount <= 1000)
{
int n = pipe.GetCellCount();
for (int i = 0; i < n; i++)
{
double rho = pipe.GetCellDensity(i);
double p = pipe.GetCellPressure(i);
double u = pipe.GetCellVelocity(i);
Console.WriteLine(
$" Cell {i,2}: ρ={rho,8:F4} kg/m³, p={p,10:F2} Pa, u={u,8:F3} m/s");
}
}
}
}
}