대한민국 해군 장보고-III(KSS-III) 잠수함 무반향 타일(Anechoic Tile) 수중 음향 흡수 다공성 점탄성 층 음향 임피던스 정합 및 1,000Hz 0-Alloc C# 능동 소음 상쇄(ANC) 스텔스 엔진

using System;
using System.Runtime.CompilerServices;

namespace ZeliDesk.Defense.Navy.SubmarineAcoustics
{
    public readonly record struct SonarPingSample(
        float FrequencyKhz,
        float IncidentPressurePa,
        float SeawaterTempCelsius,
        float DepthMeters,
        float SalinityPsu
    );

    public ref struct AcousticStealthResponse
    {
        public float EstimatedSeawaterSoundSpeedMps;
        public float TargetTileImpedanceKgM2S;
        public float EchoReductionDb;
        public float AncAntiPhaseAmplitudePa;
        public bool AcousticStealthOptimized;
    }

    public static class Kss3AcousticStealthCore
    {
        private const float NominalWaterDensity = 1025.0f; // kg/m^3
        private const float AnechoicTileNominalDensity = 1180.0f;
        private const float TileThicknessMeters = 0.065f; // 65mm 타일

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static void ComputeAcousticStealth(
            ref readonly SonarPingSample sample,
            ref AcousticStealthResponse response)
        {
            // 1. Mackenzie 수중 음속 공식 간략화 계산
            float cWater = 1448.96f + (4.591f * sample.SeawaterTempCelsius) 
                         - (0.05304f * sample.SeawaterTempCelsius * sample.SeawaterTempCelsius)
                         + (1.340f * (sample.SalinityPsu - 35.0f)) 
                         + (0.0163f * sample.DepthMeters);
            response.EstimatedSeawaterSoundSpeedMps = cWater;

            // 2. 해수 음향 특성 임피던스 산출 (Z = rho * c)
            float zWater = NominalWaterDensity * cWater;
            response.TargetTileImpedanceKgM2S = zWater;

            // 3. 입사 주파수에 따른 점탄성 타일 감쇠율 산출 (10kHz~50kHz 능동소나 대역)
            float freqHz = sample.FrequencyKhz * 1000.0f;
            float attenuationAlpha = 0.0025f * (float)Math.Sqrt(freqHz);
            float totalDamping = attenuationAlpha * TileThicknessMeters * 2.0f;

            // 4. 에코 감소율 (Echo Reduction) dB 연산
            float echoRatio = (float)Math.Exp(-totalDamping);
            float erDb = -20.0f * (float)Math.Log10(Math.Max(echoRatio, 0.001f));
            response.EchoReductionDb = erDb;

            // 5. 저주파 잔류 진동 능동 상쇄 (ANC) 역위상 음압 산출
            response.AncAntiPhaseAmplitudePa = -sample.IncidentPressurePa * 0.12f;
            response.AcousticStealthOptimized = erDb >= 15.0f;
        }
    }
}