WindTypes.hpp

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// Wind Model Types and Utilities
// Common types for all wind models - MIL-F-8785C / MIL-HDBK-1797 compliant
#pragma once
 
#include <janus/janus.hpp>
 
namespace vulcan::wind {
 
// ============================================================================
// Wind Vector Representation
// ============================================================================

template <typename Scalar> struct WindVector {
    Scalar north; 
    Scalar east;  
    Scalar down;  

    Scalar horizontal_speed() const {
        return janus::sqrt(north * north + east * east);
    }

    Scalar speed() const {
        return janus::sqrt(north * north + east * east + down * down);
    }

    Scalar direction_from() const { return janus::atan2(east, north); }
};

template <typename Scalar> struct GustVelocity {
    Scalar u_g; 
    Scalar v_g; 
    Scalar w_g; 
};

template <typename Scalar> struct GustAngularRate {
    Scalar p_g; 
    Scalar q_g; 
    Scalar r_g; 
};
 
// ============================================================================
// Turbulence Parameters
// ============================================================================

template <typename Scalar = double> struct TurbulenceParams {
    Scalar sigma_u; 
    Scalar sigma_v; 
    Scalar sigma_w; 
    Scalar L_u;     
    Scalar L_v;     
    Scalar L_w;     
};

enum class TurbulenceSeverity {
    Light,    
    Moderate, 
    Severe    
};
 
// ============================================================================
// MIL-Spec Parameter Calculation
// ============================================================================
 
namespace detail {

inline constexpr double W20_LIGHT = 7.5;     // [m/s] (~15 knots)
inline constexpr double W20_MODERATE = 15.0; // [m/s] (~30 knots)
inline constexpr double W20_SEVERE = 30.0;   // [m/s] (~60 knots)
 
} // namespace detail

inline TurbulenceParams<double> mil_spec_params(double altitude,
                                                TurbulenceSeverity severity) {
    // Convert altitude to feet for MIL-spec equations
    constexpr double M_TO_FT = 3.28084;
    constexpr double FT_TO_M = 0.3048;
    double h_ft = altitude * M_TO_FT;
 
    // Wind speed at 20 ft based on severity
    double W20 = 0.0;
    switch (severity) {
    case TurbulenceSeverity::Light:
        W20 = detail::W20_LIGHT;
        break;
    case TurbulenceSeverity::Moderate:
        W20 = detail::W20_MODERATE;
        break;
    case TurbulenceSeverity::Severe:
        W20 = detail::W20_SEVERE;
        break;
    }
 
    TurbulenceParams<double> params;
 
    if (h_ft < 1000.0) {
        // Low altitude model
        // Ensure minimum altitude of 10 ft for numerical stability
        h_ft = std::max(h_ft, 10.0);
 
        // Scale lengths (in feet, then convert)
        double denom = std::pow(0.177 + 0.000823 * h_ft, 1.2);
        params.L_w = h_ft * FT_TO_M;
        params.L_u = (h_ft / denom) * FT_TO_M;
        params.L_v = params.L_u;
 
        // Turbulence intensities
        params.sigma_w = 0.1 * W20;
        double denom2 = std::pow(0.177 + 0.000823 * h_ft, 0.4);
        params.sigma_u = params.sigma_w / denom2;
        params.sigma_v = params.sigma_u;
    } else {
        // Medium/high altitude model
        // Scale lengths are constant at 1750 ft = 533.4 m
        params.L_u = 533.4;
        params.L_v = 533.4;
        params.L_w = 533.4;
 
        // Intensities based on probability of exceedance
        // Using simplified model: σ increases with severity
        switch (severity) {
        case TurbulenceSeverity::Light:
            params.sigma_u = params.sigma_v = params.sigma_w = 1.5;
            break;
        case TurbulenceSeverity::Moderate:
            params.sigma_u = params.sigma_v = params.sigma_w = 3.0;
            break;
        case TurbulenceSeverity::Severe:
            params.sigma_u = params.sigma_v = params.sigma_w = 7.0;
            break;
        }
    }
 
    return params;
}
 
} // namespace vulcan::wind