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Use local gravity, Use a more accurate way to calculate saturation vapor pressure.

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This commit is contained in:
Erik Hofman 2020-11-19 11:21:25 +01:00
parent 98a94ecac4
commit ef9636c8e5
2 changed files with 26 additions and 16 deletions
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41
src/Environment/climate.cxx
View file

@ -46,6 +46,11 @@
// the dewpoint temperature in moist air: A simple conversion and
// applications. Bull. Amer. Meteor. Soc., 86, 225-233.
// doi: http://dx.doi.org/10.1175/BAMS-86-2-225
//
// * A Simple Accurate Formula for Calculating Saturation Vapor Pressure of
// Water and Ice. Jianhua Huang, J. Appl. Meteor. Climatol. (2018) 57 (6):
// 1265–1272. https://doi.org/10.1175/JAMC-D-17-0334.1
#define HOUR (0.5/24.0)
#define MONTH (1.0/12.0)
@ -72,6 +77,7 @@ void FGClimate::init()
_positionLongitudeNode= fgGetNode("/position/longitude-deg", true);
_ground_elev_node = fgGetNode("/environment/terrain/area[0]/enabled", true);
_gravityNode = fgGetNode("/environment/gravitational-acceleration-mps2", true);
}
void FGClimate::bind()
@ -194,7 +200,7 @@ void FGClimate::update(double dt)
color = image->getColor(s, t);
// convert from color shades to koppen-classicfication
_code = static_cast<int>(255.0f*color[0]/4.0f);
_code = static_cast<int>((255.0f*color[0]+0.5)/4.0f);
if (_code == 0) set_ocean();
else if (_code < 5) set_tropical();
@ -287,33 +293,36 @@ void FGClimate::update_season_factor()
// https://en.wikipedia.org/wiki/Density_of_air#Humid_air
void FGClimate::update_air_pressure()
{
// Saturation vapor pressure
// saturation vapor pressure for water, Jianhua Huang:
double Tc = _temperature_gl;
double Psat = 6.1078*pow(10.0, 7.5*Tc/(Tc+273.3));
double Psat = exp(34.494 - 4924.99/(Tc+237.1))/pow(Tc + 105.0, 1.57);
// Vapor pressure of water
double Pv = _relative_humidity_gl*Psat;
// vapor pressure of water
double Pv = 0.01*_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;
static const double R0 = 8.314462618; // Universal gas constant
static const double P0 = 101325.0; // Sea level standard atm. pressure
static const double T0 = 288.15; // Sea level standard temperature
static const double L = 0.0065; // Temperature lapse rate
static const double M = 0.0289654; // Molar mass of dry air
double h = _alt_km;
double P = P0*pow(1.0 - L*h/T0, g*M/(R*L));
double g = _gravityNode->getDoubleValue();
double P = P0*pow(1.0 - L*h/T0, g*M/(L*R0));
// partial pressure of dry air
double Pd = P - Pv;
_air_pressure = 0.01*Pd; // hPa
// air pressure
_air_pressure = 0.01*(Pd+Psat); // hPa
// air density
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);
_air_density = (Pd*Md + Pv*Mv)/(Tk*R0);
}
@ -1107,7 +1116,7 @@ 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::cout << " Dewpoint: " << _dewpoint_gl << " deg. C."
<< std::endl;
std::cout << " Ground temperature: " << _temperature_gl << " deg. C."
<< std::endl;
@ -1126,7 +1135,7 @@ void FGClimate::report()
<< std::endl;
std::cout << " Relative humidity: " << _relative_humidity_gl << " %"
<< std::endl;
std::cout << " Air PRessuer: " << _air_pressure << " hPa"
std::cout << " Air Pressure: " << _air_pressure << " hPa"
<< std::endl;
std::cout << " Wind: " << _wind << " km/h" << std::endl << std::endl;
std::cout << " Snow level: " << _snow_level << " m." << std::endl;

1
src/Environment/climate.hxx
View file

@ -107,6 +107,7 @@ private:
simgear::TiedPropertyList _tiedProperties;
SGPropertyNode_ptr _monthNode;
SGPropertyNode_ptr _gravityNode;
SGPropertyNode_ptr _metarSnowLevelNode;
SGPropertyNode_ptr _positionLatitudeNode;
SGPropertyNode_ptr _positionLongitudeNode;