atmospheric_math.c

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/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 * for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, see <http://www.gnu.org/licenses/>
 */

#include "math.h"

#include "atmospheric_math.h"           /* API declarations */
#include "physical_constants.h"

float air_density_from_altitude(float altitude, struct AirParameters *air)
{
        float pressure = air_pressure_from_altitude(altitude, air);
        float rho = pressure*air->M / (air->univ_gas_constant*(air->air_temperature_at_surface - air->temperature_lapse_rate*altitude));

        return rho;
}

float air_pressure_from_altitude(float altitude, struct AirParameters *air)
{
        float pressure = air->sea_level_press* powf(1 - air->temperature_lapse_rate*altitude / air->air_temperature_at_surface, GRAVITY*air->M / (air->univ_gas_constant*air->temperature_lapse_rate));

        return pressure;
}

float cas2tas(float CAS, float altitude, struct AirParameters *air)
{
        float rho=air_density_from_altitude(altitude, air);
        float TAS = CAS * sqrtf(air->air_density_at_surface/rho);

        return TAS;
}

float tas2cas(float TAS, float altitude, struct AirParameters *air)
{
        float rho=air_density_from_altitude(altitude, air);
        float CAS = TAS / sqrtf(air->air_density_at_surface/rho);

        return CAS;
}


struct AirParameters initialize_air_structure()
{
        struct AirParameters air;

        air.sea_level_press = STANDARD_AIR_SEA_LEVEL_PRESSURE;
        air.air_density_at_surface = STANDARD_AIR_DENSITY;
        air.air_temperature_at_surface = STANDARD_AIR_TEMPERATURE;
        air.temperature_lapse_rate = STANDARD_AIR_LAPSE_RATE;
        air.univ_gas_constant = UNIVERSAL_GAS_CONSTANT;
        air.dry_air_constant = DRY_AIR_CONSTANT;
        air.relative_humidity = STANDARD_AIR_RELATIVE_HUMIDITY;
        air.M = STANDARD_AIR_MOLS2KG;

        return air;
}