flightgear/src/FDM/JSBSim/FGAtmosphere.cpp

/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

 Module:       FGAtmosphere.cpp
 Author:       Jon Berndt
               Implementation of 1959 Standard Atmosphere added by Tony Peden 
 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
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

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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"
#include "FGDefs.h"
#include "FGMatrix.h"

static const char *IdSrc = "$Id$";
static const char *IdHdr = ID_ATMOSPHERE;

extern short debug_lvl;

/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
CLASS IMPLEMENTATION
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/


FGAtmosphere::FGAtmosphere(FGFDMExec* fdmex) : FGModel(fdmex),
                                               vWindNED(3)
{
  Name = "FGAtmosphere";
  h = 0;
  Calculate(h);
  SLtemperature = temperature;
  SLpressure    = pressure;
  SLdensity     = density;
  SLsoundspeed  = sqrt(SHRATIO*Reng*temperature);
  useExternal=false;

  if (debug_lvl & 2) cout << "Instantiated: " << Name << endl;
}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

FGAtmosphere::~FGAtmosphere()
{
  if (debug_lvl & 2) cout << "Destroyed:    FGAtmosphere" << endl;
}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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;
    }

    if (vWindNED(1) != 0.0) psiw = atan2( vWindNED(2), vWindNED(1) );

    if (psiw < 0) psiw += 2*M_PI;

    soundspeed = sqrt(SHRATIO*Reng*temperature);
    //cout << "Atmosphere: soundspeed: " << soundspeed << endl;
    State->Seta(soundspeed);

  } else {                               // skip Run() execution this time
  }
  return false;
}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

void FGAtmosphere::Calculate(float altitude)
{
  //see reference [1]

  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;
  if (altitude <= htab[0]) {
    altitude=0;
  } else if (altitude >= htab[7]){
    i = 7;
    altitude = htab[7];
  } else {
    while (htab[i+1] < altitude) {
      i++;
    }
  }

  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;
  case 1:     // 36089 ft.
    slope     = 0;
    reftemp   = 389.988;
    refpress  = 474.1;
    refdens   = 0.0007078;
    break;
  case 2:     // 82020 ft.
    slope     = 0.00164594;
    reftemp   = 389.988;
    refpress  = 52.7838;
    refdens   = 7.8849E-5;
    break;
  case 3:     // 154198 ft.
    slope     = 0;
    reftemp   = 508.788;
    refpress  = 2.62274;
    refdens   = 3.01379E-6;
    break;
  case 4:     // 173882 ft.
    slope     = -0.00246891;
    reftemp   = 508.788;
    refpress  = 1.28428;
    refdens   = 1.47035e-06;
    break;
  case 5:     // 259183 ft.
    slope     = 0;
    reftemp   = 298.188;
    refpress  = 0.0222008;
    refdens   = 4.33396e-08;
    break;
  case 6:     // 295272 ft.
    slope     = 0.00219459;
    reftemp   = 298.188;
    refpress  = 0.00215742;
    refdens   = 4.21368e-09;
    break;
  case 7:     // 344484 ft.
    slope     = 0;
    reftemp   = 406.188;
    refpress  = 0.000153755;
    refdens   = 2.20384e-10;
    break;
  }

  if (slope == 0) {
    temperature = reftemp;
    pressure = refpress*exp(-GRAVITY/(reftemp*Reng)*(altitude-htab[i]));
    density = refdens*exp(-GRAVITY/(reftemp*Reng)*(altitude-htab[i]));
  } else {
    temperature = reftemp+slope*(altitude-htab[i]);
    pressure = refpress*pow(temperature/reftemp,-GRAVITY/(slope*Reng));
    density = refdens*pow(temperature/reftemp,-(GRAVITY/(slope*Reng)+1));
  }

  //cout << "Atmosphere:  h=" << altitude << " rho= " << density << endl;

}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

void FGAtmosphere::Debug(void)
{
    //TODO: Add your source code here
}