160 lines
4.8 KiB
C++
160 lines
4.8 KiB
C++
// atmosphere.hxx -- routines to model the air column
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//
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// Written by David Megginson, started February 2002.
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// Modified by John Denker to correct physics errors in 2007
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//
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// Copyright (C) 2002 David Megginson - david@megginson.com
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//
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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License as
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// published by the Free Software Foundation; either version 2 of the
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// License, or (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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//
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// $Id$
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#ifndef _ATMOSPHERE_HXX
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#define _ATMOSPHERE_HXX
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#include <simgear/compiler.h>
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#include <simgear/math/interpolater.hxx>
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#include <cmath>
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#include <utility>
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using namespace std;
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/**
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* Model the atmosphere in a way consistent with the laws
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* of physics.
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*
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* Each instance of this class models a particular air mass.
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* You may freely move up, down, or sideways in the air mass.
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* In contrast, if you want to compare different air masses,
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* you should use a separate instance for each one.
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*
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* See also ./environment.hxx
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*/
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#define SCD(name,val) const double name(val)
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namespace atmodel {
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SCD(g, 9.80665); // [m/s/s] acceleration of gravity
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SCD(mm, .0289644); // [kg/mole] molar mass of air (dry?)
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SCD(Rgas, 8.31432); // [J/K/mole] gas constant
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SCD(inch, 0.0254); // [m] definition of inch
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SCD(foot, 12 * inch); // [m]
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SCD(inHg, 101325.0 / 760 * 1000 * inch); // [Pa] definition of inHg
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SCD(mbar, 100.); // [Pa] definition of millibar
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SCD(freezing, 273.15); // [K] centigrade - kelvin offset
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SCD(nm, 1852); // [m] nautical mile (NIST)
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SCD(sm, 5280*foot); // [m] nautical mile (NIST)
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namespace ISA {
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SCD(P0, 101325.0); // [pascals] ISA sea-level pressure
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SCD(T0, 15. + freezing); // [K] ISA sea-level temperature
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SCD(lam0, .0065); // [K/m] ISA troposphere lapse rate
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}
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}
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#undef SCD
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class ISA_layer {
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public:
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double height;
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double temp;
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double lapse;
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ISA_layer(int, double h, double, double, double, double t, double,
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double l=-1, double=0)
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: height(h), // [meters]
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temp(t), // [kelvin]
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lapse(l) // [K/m]
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{}
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};
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extern const ISA_layer ISA_def[];
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std::pair<double,double> PT_vs_hpt(
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const double hh,
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const double _p0 = atmodel::ISA::P0,
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const double _t0 = atmodel::ISA::T0);
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double P_layer(const double height, const double href,
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const double Pref, const double Tref, const double lapse );
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double T_layer(const double height, const double href,
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const double Pref, const double Tref, const double lapse );
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// The base class is little more than a namespace.
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// It has no constructor, no destructor, and no variables.
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class FGAtmo {
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public:
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double a_vs_p(const double press, const double qnh = atmodel::ISA::P0);
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double fake_T_vs_a_us(const double h_ft,
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const double Tsl = atmodel::ISA::T0) const;
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double fake_dp_vs_a_us(const double dpsl, const double h_ft);
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void check_one(const double height);
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// Altimeter setting _in pascals_
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// ... caller gets to convert to inHg or millibars
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// Field elevation in m
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// Field pressure in pascals
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// Valid for fields within the troposphere only.
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double QNH(const double field_elev, const double field_press);
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/**
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* Invert the QNH calculation to get the field pressure from a metar
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* report. Valid for fields within the troposphere only.
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* @param field_elev field elevation in m
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* @param qnh altimeter setting in pascals
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* @return field pressure _in pascals_. Caller gets to convert to inHg
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* or millibars
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*/
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static double fieldPressure(const double field_elev, const double qnh);
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};
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class FGAtmoCache : FGAtmo {
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friend class FGAltimeter;
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SGInterpTable * a_tvs_p; // _tvs_ means "tabulated versus"
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public:
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FGAtmoCache();
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~FGAtmoCache();
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void tabulate();
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void cache();
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void check_model(); // debug
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};
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class FGAltimeter : public FGAtmoCache {
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double kset;
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double kft;
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public:
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FGAltimeter();
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double reading_ft(const double p_inHg,
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const double set_inHg = atmodel::ISA::P0/atmodel::inHg);
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inline double press_alt_ft(const double p_inHg) {
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return a_tvs_p->interpolate(p_inHg);
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}
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inline double kollsman_ft(const double set_inHg) {
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return a_tvs_p->interpolate(set_inHg);
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}
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// debug
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void dump_stack();
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void dump_stack1(const double Tref);
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};
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#endif // _ATMOSPHERE_HXX
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