심해 열수분출공(Hydrothermal Vent) 초임계 유체 & 1,000Hz 0-Alloc C# 음향 도플러 유속계(ADCP) 난류 추적 서보 제어기

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

namespace ZeliDesk.Stem.OceanPhysics
{
    /// 

    /// ADCP 4개 빔 도플러 복소 원시 데이터 프레임
    /// 
    [StructLayout(LayoutKind.Sequential)]
    public readonly struct AdcpRawFrame
    {
        public readonly uint PingTimestampUs;
        public readonly float DopplerShiftHz1; // Beam 1
        public readonly float DopplerShiftHz2; // Beam 2
        public readonly float DopplerShiftHz3; // Beam 3
        public readonly float DopplerShiftHz4; // Beam 4
        public readonly float SoundSpeedMps;   // 심해 염분/수온 보정 음속 (~1520 m/s)

        public AdcpRawFrame(uint timestamp, float d1, float d2, float d3, float d4, float soundSpeed = 1520.0f)
        {
            PingTimestampUs = timestamp;
            DopplerShiftHz1 = d1;
            DopplerShiftHz2 = d2;
            DopplerShiftHz3 = d3;
            DopplerShiftHz4 = d4;
            SoundSpeedMps = soundSpeed;
        }
    }

    /// 

    /// 1,000Hz 0-Alloc 심해 열수 플룸 ADCP 난류 추적 서보 엔진
    /// 
    public ref struct HydrothermalVentAdcpServo
    {
        private const float TransmitFreqHz = 300_000.0f; // 300 kHz 초음파 소나
        private const float BeamAngleRad = 0.349066f;     // 20도 (야누스 빔 각도)
        private static readonly float SinBeam = MathF.Sin(BeamAngleRad);
        private static readonly float CosBeam = MathF.Cos(BeamAngleRad);

        private Vector3 _meanVelocity;
        private float _tkeHistory;
        private int _tickCount;

        public HydrothermalVentAdcpServo(bool initialize = true)
        {
            _meanVelocity = Vector3.Zero;
            _tkeHistory = 0.0f;
            _tickCount = 0;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public bool ProcessPing(in AdcpRawFrame frame, out Vector3 currentVelocity, out float turbulenceEnergy, out Vector3 thrusterCompVector)
        {
            float factor = frame.SoundSpeedMps / (2.0f * TransmitFreqHz * CosBeam);

            // 1. 4개 빔 시선 속도 (Radial Velocity) 계산
            float vb1 = frame.DopplerShiftHz1 * factor;
            float vb2 = frame.DopplerShiftHz2 * factor;
            float vb3 = frame.DopplerShiftHz3 * factor;
            float vb4 = frame.DopplerShiftHz4 * factor;

            // 2. 야누스 직교 변환 (Janus Orthogonal Transform - 0-Alloc 스택 연산)
            float u = (vb1 - vb2) / (2.0f * SinBeam);
            float v = (vb3 - vb4) / (2.0f * SinBeam);
            float w = (vb1 + vb2 + vb3 + vb4) / (4.0f * CosBeam);
            float errorVel = ((vb1 + vb2) - (vb3 + vb4)) / (2.828427f * SinBeam);

            currentVelocity = new Vector3(u, v, w);

            // 3. 순간 속도 요동 및 난류 운동에너지(TKE) 산출
            _meanVelocity = Vector3.Lerp(_meanVelocity, currentVelocity, 0.05f);
            Vector3 fluctuation = currentVelocity - _meanVelocity;
            float instantTke = 0.5f * fluctuation.LengthSquared();
            _tkeHistory = (0.9f * _tkeHistory) + (0.1f * instantTke);
            turbulenceEnergy = _tkeHistory;

            _tickCount++;

            // 4. AUV 호버링 슬러스터 역추력 벡터 합성
            // 상승 열수류(Updraft w) 및 난류 요동에 대한 즉각 반작용 생성
            thrusterCompVector = new Vector3(
                -currentVelocity.X * 150.0f,
                -currentVelocity.Y * 150.0f,
                -(currentVelocity.Z * 300.0f) - (_tkeHistory * 500.0f) // 강한 상승 부력 억제
            );

            // 오차 속도가 과도하게 크면 소나 빔 폐색(기포/입자군) 판정
            return MathF.Abs(errorVel) < 0.5f;
        }
    }
}