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flightgear/src/FDM/JSBSim/FGAtmosphere.cpp

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/*******************************************************************************
Module: FGAtmosphere.cpp
Author: Jon Berndt
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Implementation of 1959 Standard Atmosphere added by Tony Peden
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Date started: 11/24/98
Purpose: Models the atmosphere
Called by: FGSimExec
------------- Copyright (C) 1999 Jon S. Berndt (jsb@hal-pc.org) -------------
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 2 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, write to the Free Software Foundation, Inc., 59 Temple
Place - Suite 330, Boston, MA 02111-1307, USA.
Further information about the GNU General Public License can also be found on
the world wide web at http://www.gnu.org.
FUNCTIONAL DESCRIPTION
--------------------------------------------------------------------------------
Models the atmosphere. The equation used below was determined by a third order
curve fit using Excel. The data is from the ICAO atmosphere model.
HISTORY
--------------------------------------------------------------------------------
11/24/98 JSB Created
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07/23/99 TP Added implementation of 1959 Standard Atmosphere
Moved calculation of Mach number to FGTranslation
********************************************************************************
COMMENTS, REFERENCES, and NOTES
********************************************************************************
[1] Anderson, John D. "Introduction to Flight, Third Edition", McGraw-Hill,
1989, ISBN 0-07-001641-0
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********************************************************************************
INCLUDES
*******************************************************************************/
#include "FGAtmosphere.h"
#include "FGState.h"
#include "FGFDMExec.h"
#include "FGFCS.h"
#include "FGAircraft.h"
#include "FGTranslation.h"
#include "FGRotation.h"
#include "FGPosition.h"
#include "FGAuxiliary.h"
#include "FGOutput.h"
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#include "FGDefs.h"
#include "FGMatrix.h"
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/*******************************************************************************
************************************ CODE **************************************
*******************************************************************************/
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FGAtmosphere::FGAtmosphere(FGFDMExec* fdmex) : FGModel(fdmex),
vWindNED(3),
vWindUVW(3)
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{
Name = "FGAtmosphere";
h = 0;
Calculate(h);
SLtemperature = temperature;
SLpressure = pressure;
SLdensity = density;
SLsoundspeed = sqrt(SHRATIO*Reng*temperature);
useExternal=false;
vWindUVW(1)=0;vWindUVW(2)=0;vWindUVW(3)=0;
vWindNED(1)=0;vWindNED(2)=0;vWindNED(3)=0;
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}
FGAtmosphere::~FGAtmosphere()
{
}
bool FGAtmosphere::Run(void)
{
//cout << "In FGAtmosphere::Run(void)" << endl;
if (!FGModel::Run()) { // if false then execute this Run()
//do temp, pressure, and density first
if (!useExternal) {
//cout << "Atmosphere: Using internal model, altitude= ";
h = Position->Geth();
Calculate(h);
} else {
density = exDensity;
pressure = exPressure;
temperature = exTemperature;
//switch sign of wind components so that they are
//in aircraft reference frame. The classic example is
//takeoff or landing where you always want to fly
//into the wind. Suppose that an aircraft is
//taking off into the wind on the runway heading
//of pure north. Into the wind means the wind is
//flowing to the south (or negative) direction,
//and we know that headwinds increase the relative
//velocity, so to make a positive delta U from the
//southerly wind the sign must be switched.
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vWindNED *= -1;
vWindUVW = State->GetTl2b()*vWindNED;
}
soundspeed = sqrt(SHRATIO*Reng*temperature);
//cout << "Atmosphere: soundspeed: " << soundspeed << endl;
State->Seta(soundspeed);
} else { // skip Run() execution this time
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}
return false;
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}
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void FGAtmosphere::Calculate(float altitude)
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{
//see reference [1]
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float slope,reftemp,refpress,refdens;
int i=0;
float htab[]={0,36089,82020,154198,173882,259183,295272,344484}; //ft.
// cout << "Atmosphere: h=" << altitude << " rho= " << density << endl;
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if (altitude <= htab[0]) {
altitude=0;
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} else if (altitude >= htab[7]){
i = 7;
altitude = htab[7];
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} else {
while (htab[i+1] < altitude) {
i++;
}
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}
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switch(i) {
case 0: // sea level
slope = -0.0035662; // R/ft.
reftemp = 518.688; // R
refpress = 2116.17; // psf
refdens = 0.0023765; // slugs/cubic ft.
break;
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case 1: // 36089 ft.
slope = 0;
reftemp = 389.988;
refpress = 474.1;
refdens = 0.0007078;
break;
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case 2: // 82020 ft.
slope = 0.00164594;
reftemp = 389.988;
refpress = 52.7838;
refdens = 7.8849E-5;
break;
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case 3: // 154198 ft.
slope = 0;
reftemp = 508.788;
refpress = 2.62274;
refdens = 3.01379E-6;
break;
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case 4: // 173882 ft.
slope = -0.00246891;
reftemp = 508.788;
refpress = 1.28428;
refdens = 1.47035e-06;
break;
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case 5: // 259183 ft.
slope = 0;
reftemp = 298.188;
refpress = 0.0222008;
refdens = 4.33396e-08;
break;
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case 6: // 295272 ft.
slope = 0.00219459;
reftemp = 298.188;
refpress = 0.00215742;
refdens = 4.21368e-09;
break;
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case 7: // 344484 ft.
slope = 0;
reftemp = 406.188;
refpress = 0.000153755;
refdens = 2.20384e-10;
break;
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}
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if (slope == 0) {
temperature = reftemp;
pressure = refpress*exp(-GRAVITY/(reftemp*Reng)*(altitude-htab[i]));
density = refdens*exp(-GRAVITY/(reftemp*Reng)*(altitude-htab[i]));
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} else {
temperature = reftemp+slope*(altitude-htab[i]);
pressure = refpress*pow(temperature/reftemp,-GRAVITY/(slope*Reng));
density = refdens*pow(temperature/reftemp,-(GRAVITY/(slope*Reng)+1));
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}
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//cout << "Atmosphere: h=" << altitude << " rho= " << density << endl;
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}