극초음속 비행체 스크램제트(Scramjet) 흡입구 경사 충격파(Oblique Shock) 압축 & 1,000Hz 0-Alloc C# 초음속 연소 유동 제어 엔진

using System;
using System.Runtime.CompilerServices;

namespace ZeliDesk.Stem.Hypersonics;

public readonly ref struct ScramjetInletState
{
    public readonly double ShockAngleBetaRad;
    public readonly double DownstreamMach;
    public readonly double StaticPressureRatio;
    public readonly double TotalPressureRecovery;
    public readonly bool IsUnstartRisk;

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public ScramjetInletState(double beta, double m2, double pRatio, double ptRecovery, bool unstart)
    {
        ShockAngleBetaRad = beta;
        DownstreamMach = m2;
        StaticPressureRatio = pRatio;
        TotalPressureRecovery = ptRecovery;
        IsUnstartRisk = unstart;
    }
}

public ref struct ScramjetInletController
{
    private const double Gamma = 1.4;
    private double _currentRampAngleRad;

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public ScramjetInletController(double initialRampDeg = 12.0)
    {
        _currentRampAngleRad = initialRampDeg * (Math.PI / 180.0);
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public ScramjetInletState Evaluate(double flightMach, double ambientPressurePa)
    {
        if (flightMach < 1.5)
            throw new ArgumentException("Flight Mach must be supersonic (M > 1.5).");

        double theta = _currentRampAngleRad;
        double beta = SolveBetaNewtonRaphson(flightMach, theta);

        double sinBeta = Math.Sin(beta);
        double mn1 = flightMach * sinBeta;
        double mn1Sq = mn1 * mn1;

        // 랭킨-위고니오 정압비
        double pRatio = 1.0 + (2.0 * Gamma / (Gamma + 1.0)) * (mn1Sq - 1.0);

        // 하류 수직 마하수 및 하류 마하수
        double mn2Sq = (2.0 + (Gamma - 1.0) * mn1Sq) / (2.0 * Gamma * mn1Sq - (Gamma - 1.0));
        double mn2 = Math.Sqrt(Math.Max(0.01, mn2Sq));
        double m2 = mn2 / Math.Sin(beta - theta);

        // 전압력 회복률 (Pt2 / Pt1)
        double term1 = Math.Pow((Gamma + 1.0) / (2.0 * Gamma * mn1Sq - (Gamma - 1.0)), 1.0 / (Gamma - 1.0));
        double term2 = Math.Pow(((Gamma + 1.0) * mn1Sq) / ((Gamma - 1.0) * mn1Sq + 2.0), Gamma / (Gamma - 1.0));
        double ptRecovery = term1 * term2;

        // 언스타트(Unstart) 위험성 판정: 연소실 유입 마하수가 아음속으로 떨어지거나 압력비가 지나치게 급증할 때
        bool unstart = m2 < 1.3 || ptRecovery < 0.45;

        // 가변 지오메트리 램프 능동 적응
        if (unstart && _currentRampAngleRad > 8.0 * (Math.PI / 180.0))
        {
            _currentRampAngleRad -= 0.001; // 램프 각도 감소 (충격파 완화)
        }
        else if (!unstart && m2 > 3.0 && _currentRampAngleRad < 18.0 * (Math.PI / 180.0))
        {
            _currentRampAngleRad += 0.0005; // 램프 각도 증대 (압축비 증강)
        }

        return new ScramjetInletState(beta, m2, pRatio, ptRecovery, unstart);
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static double SolveBetaNewtonRaphson(double m, double theta)
    {
        // 초기 추정값 (약충격파 해)
        double beta = Math.Asin(1.0 / m) + theta * 1.1;
        double tanTheta = Math.Tan(theta);
        double mSq = m * m;

        for (int iter = 0; iter < 12; iter++)
        {
            double sinB = Math.Sin(beta);
            double cosB = Math.Cos(beta);
            double cotB = cosB / sinB;
            double cos2B = Math.Cos(2.0 * beta);

            double num = mSq * sinB * sinB - 1.0;
            double den = mSq * (Gamma + cos2B) + 2.0;

            double f = 2.0 * cotB * (num / den) - tanTheta;
            if (Math.Abs(f) < 1e-7) break;

            // 수치 미분 df/dbeta
            double dBeta = 1e-5;
            double sinB2 = Math.Sin(beta + dBeta);
            double cosB2 = Math.Cos(beta + dBeta);
            double cotB2 = cosB2 / sinB2;
            double cos2B2 = Math.Cos(2.0 * (beta + dBeta));
            double num2 = mSq * sinB2 * sinB2 - 1.0;
            double den2 = mSq * (Gamma + cos2B2) + 2.0;
            double f2 = 2.0 * cotB2 * (num2 / den2) - tanTheta;
            double df = (f2 - f) / dBeta;

            if (Math.Abs(df) > 1e-9)
            {
                beta -= f / df;
            }
        }
        return beta;
    }
}