핵융합 플라즈마 대면재 텅스텐 재결정화 및 열응력 피로 & 1,000Hz 0-Alloc C# 중성자 취화 수명 예측 서보 엔진

using System;
using System.Runtime.CompilerServices;

namespace ZeliDesk.Stem.Nuclear.FusionMaterials
{
    /// 

    /// 텅스텐 PFC 재결정화 분율 및 열피로 누적 손상도 연산 엔진 (0-Alloc C#)
    /// 
    public ref struct TungstenPfcFatigueEngine
    {
        private const double GasConstantR = 8.314462618; // J/(mol*K)
        private const double QRecrystallization = 400000.0; // 400 kJ/mol
        private const double K0PreExponential = 1.25e11;   // 1/s
        private const double AvramiExponentN = 1.8;

        private readonly double _elasticModulusW; // Pa (~400 GPa)
        private readonly double _thermalExpansionAlpha; // 1/K (~4.5e-6)
        private readonly double _poissonRatio;

        private double _recrystallizedFraction; // 0.0 ~ 1.0
        private double _cumulativeFatigueDamage; // 마이너 누적 손상도
        private double _currentSurfaceTempK;

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public TungstenPfcFatigueEngine(
            double elasticModulusW = 400e9,
            double thermalExpansionAlpha = 4.5e-6,
            double poissonRatio = 0.28)
        {
            _elasticModulusW = elasticModulusW;
            _thermalExpansionAlpha = thermalExpansionAlpha;
            _poissonRatio = poissonRatio;
            _recrystallizedFraction = 0.0;
            _cumulativeFatigueDamage = 0.0;
            _currentSurfaceTempK = 300.0;
        }

        /// 

        /// 표면 열유속(MW/m^2) 및 냉각수 입구 온도로부터 과도 열응력과 누적 피로도를 갱신 (1,000Hz)
        /// 
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void UpdateThermalStep(
            double heatFluxMWPerM2,
            double baseTempK,
            double dtSeconds,
            out double surfaceTempK,
            out double thermalStressMPa,
            out double recrystallizedPct,
            out double remainingLifeCycles)
        {
            // 1D 열전도 근사 표면 온도: Delta T = (q * d) / k (W 전도도 ~120 W/m*K, 두께 12mm)
            double deltaT = (heatFluxMWPerM2 * 1e6 * 0.012) / 120.0;
            _currentSurfaceTempK = baseTempK + deltaT;
            surfaceTempK = _currentSurfaceTempK;

            // 구속 열응력 sigma = (E * alpha * deltaT) / (1 - nu)
            double stressPa = (_elasticModulusW * _thermalExpansionAlpha * deltaT) / (1.0 - _poissonRatio);
            thermalStressMPa = stressPa * 1e-6;

            // 재결정화 속도식 적분 (1,300도 이상 시 급증)
            if (_currentSurfaceTempK > 1473.15) // > 1,200 °C
            {
                double kRate = K0PreExponential * Math.Exp(-QRecrystallization / (GasConstantR * _currentSurfaceTempK));
                double deltaX = kRate * Math.Pow(dtSeconds, AvramiExponentN) * (1.0 - _recrystallizedFraction);
                _recrystallizedFraction = Math.Min(1.0, _recrystallizedFraction + deltaX);
            }
            recrystallizedPct = _recrystallizedFraction * 100.0;

            // 코핀-맨슨 열피로 파손 수명 추정 (ELM 사이클 기준)
            double plasticStrain = Math.Max(0.0, (thermalStressMPa - 500.0) / 400000.0);
            double nFailure = plasticStrain > 1e-5
                ? 0.5 * Math.Pow(plasticStrain / 0.18, -1.8)
                : 1e7;

            // 누적 손상율
            double stepCycles = (heatFluxMWPerM2 > 12.0) ? (dtSeconds * 10.0) : 0.0; // 10Hz ELM 가정
            _cumulativeFatigueDamage += (stepCycles / Math.Max(nFailure, 1.0));

            remainingLifeCycles = Math.Max(0.0, (1.0 - _cumulativeFatigueDamage) * nFailure);
        }

        public double RecrystallizedFraction => _recrystallizedFraction;
        public double CumulativeFatigueDamage => _cumulativeFatigueDamage;
    }
}