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Also calculate air pressure and density (while we're at it)

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This commit is contained in:
Erik Hofman 2020-11-19 08:29:31 +01:00
parent 108f2d4328
commit 98a94ecac4
2 changed files with 46 additions and 7 deletions
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48
src/Environment/climate.cxx
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@ -87,6 +87,7 @@ void FGClimate::bind()
// weather properties
_tiedProperties.Tie( "weather-update", &_weather_update);
_tiedProperties.Tie( "pressure-hpa", &_air_pressure);
_tiedProperties.Tie( "relative-humidity", &_relative_humidity_gl);
_tiedProperties.Tie( "relative-humidity-sea-level", &_relative_humidity_sl);
_tiedProperties.Tie( "dewpoint-degc", &_dewpoint_gl);
@ -215,15 +216,15 @@ void FGClimate::update(double dt)
} else {
alt_ft = fgGetDouble("/position/ground-elev-ft");
}
double alt_km = alt_ft*SG_FEET_TO_METER/1000.0;
_alt_km = alt_ft*SG_FEET_TO_METER/1000.0;
// Relative humidity decreases with an average of 4% per kilometer
_relative_humidity_sl = std::min(_relative_humidity_gl + 4.0*alt_km, 100.0);
_relative_humidity_sl = std::min(_relative_humidity_gl + 4.0*_alt_km, 100.0);
// The temperature decreases by about 9.8°C per kilometer
_temperature_sl = _temperature_gl + 9.8*alt_km;
_temperature_mean_sl = _temperature_mean_gl + 9.8*alt_km;
_temperature_seawater = _temperature_water + 9.8*alt_km;
_temperature_sl = _temperature_gl + 9.8*_alt_km;
_temperature_mean_sl = _temperature_mean_gl + 9.8*_alt_km;
_temperature_seawater = _temperature_water + 9.8*_alt_km;
_set(_snow_level, 1000.0*_temperature_mean_sl/9.8);
@ -232,6 +233,7 @@ void FGClimate::update(double dt)
_dewpoint_gl = _temperature_gl - ((100.0 - _relative_humidity_gl)/5.0);
set_environment();
update_air_pressure();
#if REPORT_TO_CONSOLE
report();
@ -282,6 +284,38 @@ void FGClimate::update_season_factor()
else if (_season_transistional > 1.0) _season_transistional = 1.0;
}
// https://en.wikipedia.org/wiki/Density_of_air#Humid_air
void FGClimate::update_air_pressure()
{
// Saturation vapor pressure
double Tc = _temperature_gl;
double Psat = 6.1078*pow(10.0, 7.5*Tc/(Tc+273.3));
// Vapor pressure of water
double Pv = _relative_humidity_gl*Psat;
// pressure at altitude
static const double P0 = 101325.0;
static const double T0 = 288.15;
static const double g = 9.80665;
static const double L = 0.0065;
static const double R = 8.31447;
static const double M = 0.0289654;
double h = _alt_km;
double P = P0*pow(1.0 - L*h/T0, g*M/(R*L));
// partial pressure of dry air
double Pd = P - Pv;
_air_pressure = 0.01*Pd; // hPa
static const double Md = 0.0289654;
static const double Mv = 0.018016;
double Tk = Tc + 273.15;
_air_density = (Pd*Md + Pv*Mv)/(R*Tk);
}
void FGClimate::set_ocean()
{
@ -1073,6 +1107,8 @@ void FGClimate::report()
<< std::endl;
std::cout << " Year (0.25 = spring .. 0.75 = autumn): " << _seasons_year
<< std::endl << std::endl;
td::cout << " Dewpoint: " << _dewpoint_gl << " deg. C."
<< std::endl;
std::cout << " Ground temperature: " << _temperature_gl << " deg. C."
<< std::endl;
std::cout << " Sea level temperature: " << _temperature_sl << " deg. C."
@ -1090,7 +1126,7 @@ void FGClimate::report()
<< std::endl;
std::cout << " Relative humidity: " << _relative_humidity_gl << " %"
<< std::endl;
std::cout << " Dewpoint: " << _dewpoint_gl << " deg. C."
std::cout << " Air PRessuer: " << _air_pressure << " hPa"
<< std::endl;
std::cout << " Wind: " << _wind << " km/h" << std::endl << std::endl;
std::cout << " Snow level: " << _snow_level << " m." << std::endl;

5
src/Environment/climate.hxx
View file

@ -101,6 +101,7 @@ private:
void update_daylight();
void update_day_factor();
void update_season_factor();
void update_air_pressure();
SGPropertyNode_ptr _rootNode;
simgear::TiedPropertyList _tiedProperties;
@ -125,6 +126,7 @@ private:
double _adj_latitude_deg = 0.0; // viewer lat adjusted for sun lat
double _adj_longitude_deg = 0.0; // viewer lat adjusted for sun lon
double _alt_km = 0.0;
double _daytime = 0.0;
double _day_noon = 1.0;
double _day_light = 1.0;
@ -149,7 +151,8 @@ private:
bool _weather_update = false; // enable weather updates
double _relative_humidity_sl = -99999.0;// 0.0 = dry, 1.0 is fully humid
double _relative_humidity_gl = -99999.0;
double _air_pressure = 0.0; // air pressure in hPa
double _air_density = 0.0; // air density in kg/m2
double _dewpoint_gl = -99999.0;
double _dewpoint_sl = -99999.0;
double _temperature_gl = -99999.0; // ground level temperature in deg. C.