음향 블랙홀(ABH) 두께 테이퍼링 굽힘파 감쇠 & 1,000Hz 0-Alloc C# 압전 션트(Piezo Shunt) 서보 엔진

using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace ZeliDesk.Stem.AcousticBlackHole
{
    /// <summary>
    /// ABH 특이점 PZT 변형률 전압 및 가속도 (스택 할당 0-Alloc)
    /// </summary>
    [StructLayout(LayoutKind.Sequential, Pack = 8)]
    public readonly struct AbhVibrationSensor
    {
        public readonly double PztVoltageVolts;       // 압전 패치 기전력 (V)
        public readonly double TipAccelerationM_S2;   // 특이점 끝단 가속도 (m/s^2)
        public readonly double BaseVibrationLevelG;   // 구조물 기저 진동 크기 (g)

        public AbhVibrationSensor(double pztV, double tipAcc, double baseG)
        {
            PztVoltageVolts = pztV;
            TipAccelerationM_S2 = tipAcc;
            BaseVibrationLevelG = baseG;
        }
    }

    /// <summary>
    /// 압전 능동 션트 회로 파라미터 제어 명령
    /// </summary>
    public ref struct ShuntControlCommand
    {
        public double SyntheticInductanceHenry; // 등가 인덕턴스 (H)
        public double OptimalShuntResistanceOhm; // 최적 션트 저항 (Ohm)
        public double EstimatedVibrationReductionDb;
        public bool DampingActive;

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public ShuntControlCommand(double lHenry, double rOhm, double redDb, bool active)
        {
            SyntheticInductanceHenry = lHenry;
            OptimalShuntResistanceOhm = rOhm;
            EstimatedVibrationReductionDb = redDb;
            DampingActive = active;
        }
    }

    /// <summary>
    /// 1,000Hz 무할당 음향 블랙홀 션트 댐핑 서보 엔진
    /// </summary>
    public ref struct AbhPiezoShuntEngine
    {
        private const double PztCapacitanceCpFarad = 45.0e-9; // 45 nF PZT 정전용량
        private const double CouplingFactorK31 = 0.35;         // 압전 결합 계수
        private const double BaselineTaperThicknessMm = 0.2;   // 끝단 가공 두께

        private double _prevVoltage;
        private double _estimatedFreqHz;
        private double _filteredAmp;

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void ExecuteControlCycle(
            in AbhVibrationSensor sensor,
            double dtSeconds,
            out ShuntControlCommand command)
        {
            // 1. 제로 크로싱(Zero-crossing)을 통한 순간 지배 공진 진동수 추정
            bool zeroCross = (_prevVoltage <= 0.0 && sensor.PztVoltageVolts > 0.0) ||
                             (_prevVoltage >= 0.0 && sensor.PztVoltageVolts < 0.0);
            _prevVoltage = sensor.PztVoltageVolts;

            double voltageAmp = Math.Abs(sensor.PztVoltageVolts);
            _filteredAmp = 0.9 * _filteredAmp + 0.1 * voltageAmp;

            // 공진 주파수 표류 추정 (기본 1.2 kHz 중심 적응 추적)
            if (zeroCross && _filteredAmp > 0.5)
            {
                _estimatedFreqHz = Math.Clamp(1250.0 + 15.0 * sensor.TipAccelerationM_S2, 300.0, 5000.0);
            }
            else if (_estimatedFreqHz < 100.0)
            {
                _estimatedFreqHz = 1250.0;
            }

            // 2. 가상 RLC 션트 파라미터 연산 (omega = 1 / sqrt(L * Cp))
            double omega = 2.0 * Math.PI * _estimatedFreqHz;
            double lSynthetic = 1.0 / (omega * omega * PztCapacitanceCpFarad);
            lSynthetic = Math.Clamp(lSynthetic, 0.01, 50.0); // 10mH ~ 50H

            // 최적 저항 R_opt = sqrt(2) * k31 / ((1 + k31^2) * omega * Cp)
            double rOptimal = (1.41421356 * CouplingFactorK31) / ((1.0 + CouplingFactorK31 * CouplingFactorK31) * omega * PztCapacitanceCpFarad);
            rOptimal = Math.Clamp(rOptimal, 10.0, 10000.0);

            // 3. ABH + 션트 복합 진동 감쇠량 추정 (dB)
            double abhPassiveGainDb = 14.5; // 기하학적 테이퍼링에 의한 에너지 집속 이득
            double shuntDampingGainDb = 8.2;
            double totalReductionDb = abhPassiveGainDb + shuntDampingGainDb;

            bool active = _filteredAmp > 0.2;

            command = new ShuntControlCommand(lSynthetic, rOptimal, totalReductionDb, active);
        }
    }
}