src/FDM/JSBSim/models/FGAtmosphere.cpp

   1 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   2
   3  Module:       FGAtmosphere.cpp
   4  Author:       Jon Berndt
   5                Implementation of 1959 Standard Atmosphere added by Tony Peden
   6  Date started: 11/24/98
   7  Purpose:      Models the atmosphere
   8  Called by:    FGSimExec
   9
  10  ------------- Copyright (C) 1999  Jon S. Berndt (jon@jsbsim.org) -------------
  11
  12  This program is free software; you can redistribute it and/or modify it under
  13  the terms of the GNU Lesser General Public License as published by the Free Software
  14  Foundation; either version 2 of the License, or (at your option) any later
  15  version.
  16
  17  This program is distributed in the hope that it will be useful, but WITHOUT
  18  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  19  FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
  20  details.
  21
  22  You should have received a copy of the GNU Lesser General Public License along with
  23  this program; if not, write to the Free Software Foundation, Inc., 59 Temple
  24  Place - Suite 330, Boston, MA  02111-1307, USA.
  25
  26  Further information about the GNU Lesser General Public License can also be found on
  27  the world wide web at http://www.gnu.org.
  28
  29 FUNCTIONAL DESCRIPTION
  30 --------------------------------------------------------------------------------
  31 Models the atmosphere. The equation used below was determined by a third order
  32 curve fit using Excel. The data is from the ICAO atmosphere model.
  33
  34 HISTORY
  35 --------------------------------------------------------------------------------
  36 11/24/98   JSB   Created
  37 07/23/99   TP    Added implementation of 1959 Standard Atmosphere
  38                  Moved calculation of Mach number to FGPropagate
  39                  Later updated to '76 model
  40 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  41 COMMENTS, REFERENCES,  and NOTES
  42 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  43 [1]   Anderson, John D. "Introduction to Flight, Third Edition", McGraw-Hill,
  44       1989, ISBN 0-07-001641-0
  45
  46 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  47 INCLUDES
  48 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
  49
  50 #include "FGAtmosphere.h"
  51 #include "FGAircraft.h"
  52 #include "FGPropagate.h"
  53 #include "FGInertial.h"
  54 #include "FGAuxiliary.h"
  55 #include "FGFDMExec.h"
  56 #include "input_output/FGPropertyManager.h"
  57 #include <iostream>
  58 #include <cstdlib>
  59
  60 using namespace std;
  61
  62 namespace JSBSim {
  63
  64 static const char *IdSrc = "$Id: FGAtmosphere.cpp,v 1.45 2011/05/20 03:18:36 jberndt Exp $";
  65 static const char *IdHdr = ID_ATMOSPHERE;
  66
  67 /*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  68 CLASS IMPLEMENTATION
  69 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
  70
  71 FGAtmosphere::FGAtmosphere(FGFDMExec* fdmex) : FGModel(fdmex)
  72 {
  73   Name = "FGAtmosphere";
  74   lastIndex = 0;
  75   h = 0.0;
  76   psiw = 0.0;
  77   htab[0]=0;
  78   htab[1]= 36089.0;
  79   htab[2]= 65617.0;
  80   htab[3]=104987.0;
  81   htab[4]=154199.0;
  82   htab[5]=167322.0;
  83   htab[6]=232940.0;
  84   htab[7]=278385.0; //ft.
  85
  86   MagnitudedAccelDt = MagnitudeAccel = Magnitude = 0.0;
  87   SetTurbType( ttMilspec );
  88   TurbGain = 1.0;
  89   TurbRate = 10.0;
  90   Rhythmicity = 0.1;
  91   spike = target_time = strength = 0.0;
  92   wind_from_clockwise = 0.0;
  93   SutherlandConstant = 198.72; // deg Rankine
  94   Beta = 2.269690E-08; // slug/(sec ft R^0.5)
  95
  96   T_dev_sl = T_dev = delta_T = 0.0;
  97   StandardTempOnly = false;
  98   first_pass = true;
  99   vGustNED.InitMatrix();
 100   vTurbulenceNED.InitMatrix();
 101
 102   // Milspec turbulence model
 103   windspeed_at_20ft = 0.;
 104   probability_of_exceedence_index = 0;
 105   POE_Table = new FGTable(7,12);
 106   // this is Figure 7 from p. 49 of MIL-F-8785C
 107   // rows: probability of exceedance curve index, cols: altitude in ft
 108   *POE_Table
 109            << 500.0 << 1750.0 << 3750.0 << 7500.0 << 15000.0 << 25000.0 << 35000.0 << 45000.0 << 55000.0 << 65000.0 << 75000.0 << 80000.0
 110     << 1   <<   3.2 <<    2.2 <<    1.5 <<    0.0 <<     0.0 <<     0.0 <<     0.0 <<     0.0 <<     0.0 <<     0.0 <<     0.0 <<     0.0
 111     << 2   <<   4.2 <<    3.6 <<    3.3 <<    1.6 <<     0.0 <<     0.0 <<     0.0 <<     0.0 <<     0.0 <<     0.0 <<     0.0 <<     0.0
 112     << 3   <<   6.6 <<    6.9 <<    7.4 <<    6.7 <<     4.6 <<     2.7 <<     0.4 <<     0.0 <<     0.0 <<     0.0 <<     0.0 <<     0.0
 113     << 4   <<   8.6 <<    9.6 <<   10.6 <<   10.1 <<     8.0 <<     6.6 <<     5.0 <<     4.2 <<     2.7 <<     0.0 <<     0.0 <<     0.0
 114     << 5   <<  11.8 <<   13.0 <<   16.0 <<   15.1 <<    11.6 <<     9.7 <<     8.1 <<     8.2 <<     7.9 <<     4.9 <<     3.2 <<     2.1
 115     << 6   <<  15.6 <<   17.6 <<   23.0 <<   23.6 <<    22.1 <<    20.0 <<    16.0 <<    15.1 <<    12.1 <<     7.9 <<     6.2 <<     5.1
 116     << 7   <<  18.7 <<   21.5 <<   28.4 <<   30.2 <<    30.7 <<    31.0 <<    25.2 <<    23.1 <<    17.5 <<    10.7 <<     8.4 <<     7.2;
 117
 118   bind();
 119   Debug(0);
 120 }
 121
 122 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 123
 124 FGAtmosphere::~FGAtmosphere()
 125 {
 126   delete(POE_Table);
 127   Debug(1);
 128 }
 129
 130 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 131
 132 bool FGAtmosphere::InitModel(void)
 133 {
 134   UseInternal();  // this is the default
 135
 136   Calculate(h);
 137   StdSLtemperature = SLtemperature = 518.67;
 138   StdSLpressure    = SLpressure = 2116.22;
 139   StdSLdensity     = SLdensity = 0.00237767;
 140   StdSLsoundspeed  = SLsoundspeed = sqrt(SHRatio*Reng*StdSLtemperature);
 141   rSLtemperature = 1.0/StdSLtemperature;
 142   rSLpressure    = 1.0/StdSLpressure;
 143   rSLdensity     = 1.0/StdSLdensity;
 144   rSLsoundspeed  = 1.0/StdSLsoundspeed;
 145
 146   return true;
 147 }
 148
 149 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 150
 151 bool FGAtmosphere::Run(bool Holding)
 152 {
 153   if (FGModel::Run(Holding)) return true;
 154   if (Holding) return false;
 155
 156   RunPreFunctions();
 157
 158   T_dev = 0.0;
 159   h = FDMExec->GetPropagate()->GetAltitudeASL();
 160
 161   if (!useExternal) {
 162     Calculate(h);
 163     CalculateDerived();
 164   } else {
 165     CalculateDerived();
 166   }
 167
 168   RunPostFunctions();
 169
 170   Debug(2);
 171   return false;
 172 }
 173
 174 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 175 //
 176 // See reference 1
 177
 178 void FGAtmosphere::Calculate(double altitude)
 179 {
 180   double slope, reftemp, refpress;
 181   int i = lastIndex;
 182
 183   if (altitude < htab[lastIndex]) {
 184     if (altitude <= 0) {
 185       i = 0;
 186       altitude=0;
 187     } else {
 188        i = lastIndex-1;
 189        while (htab[i] > altitude) i--;
 190     }
 191   } else if (altitude > htab[lastIndex+1]) {
 192     if (altitude >= htab[7]) {
 193       i = 7;
 194       altitude = htab[7];
 195     } else {
 196       i = lastIndex+1;
 197       while (htab[i+1] < altitude) i++;
 198     }
 199   }
 200
 201   switch(i) {
 202   case 0: // Sea level
 203     slope     = -0.00356616; // R/ft.
 204     reftemp   = 518.67;   // in degrees Rankine, 288.15 Kelvin
 205     refpress  = 2116.22;    // psf
 206     //refdens   = 0.00237767;  // slugs/cubic ft.
 207     break;
 208   case 1:     // 36089 ft. or 11 km
 209     slope     = 0;
 210     reftemp   = 389.97; // in degrees Rankine, 216.65 Kelvin
 211     refpress  = 472.763;
 212     //refdens   = 0.000706032;
 213     break;
 214   case 2:     // 65616 ft. or 20 km
 215     slope     = 0.00054864;
 216     reftemp   = 389.97; // in degrees Rankine, 216.65 Kelvin
 217     refpress  = 114.636;
 218     //refdens   = 0.000171306;
 219     break;
 220   case 3:     // 104986 ft. or 32 km
 221     slope     = 0.001536192;
 222     reftemp   = 411.57; // in degrees Rankine, 228.65 Kelvin
 223     refpress  = 18.128;
 224     //refdens   = 1.18422e-05;
 225     break;
 226   case 4:     // 154199 ft. 47 km
 227     slope     = 0;
 228     reftemp   = 487.17; // in degrees Rankine, 270.65 Kelvin
 229     refpress  = 2.316;
 230     //refdens   = 4.00585e-7;
 231     break;
 232   case 5:     // 167322 ft. or 51 km
 233     slope     = -0.001536192;
 234     reftemp   = 487.17; // in degrees Rankine, 270.65 Kelvin
 235     refpress  = 1.398;
 236     //refdens   = 8.17102e-7;
 237     break;
 238   case 6:     // 232940 ft. or 71 km
 239     slope     = -0.00109728;
 240     reftemp   = 386.368; // in degrees Rankine, 214.649 Kelvin
 241     refpress  = 0.0826;
 242     //refdens   = 8.77702e-9;
 243     break;
 244   case 7:     // 278385 ft. or 84.8520 km
 245     slope     = 0;
 246     reftemp   = 336.5; // in degrees Rankine, 186.94 Kelvin
 247     refpress  = 0.00831;
 248     //refdens   = 2.19541e-10;
 249     break;
 250   default:     // sea level
 251     slope     = -0.00356616; // R/ft.
 252     reftemp   = 518.67;   // in degrees Rankine, 288.15 Kelvin
 253     refpress  = 2116.22;    // psf
 254     //refdens   = 0.00237767;  // slugs/cubic ft.
 255     break;
 256
 257   }
 258
 259   // If delta_T is set, then that is our temperature deviation at any altitude.
 260   // If not, then we'll estimate a deviation based on the sea level deviation (if set).
 261
 262   if(!StandardTempOnly) {
 263     T_dev = 0.0;
 264     if (delta_T != 0.0) {
 265       T_dev = delta_T;
 266     } else {
 267       if ((altitude < 36089.239) && (T_dev_sl != 0.0)) {
 268         T_dev = T_dev_sl * ( 1.0 - (altitude/36089.239));
 269       }
 270     }
 271     reftemp+=T_dev;
 272   }
 273
 274   if (slope == 0) {
 275     intTemperature = reftemp;
 276     intPressure = refpress*exp(-FDMExec->GetInertial()->SLgravity()/(reftemp*Reng)*(altitude-htab[i]));
 277     intDensity = intPressure/(Reng*intTemperature);
 278   } else {
 279     intTemperature = reftemp+slope*(altitude-htab[i]);
 280     intPressure = refpress*pow(intTemperature/reftemp,-FDMExec->GetInertial()->SLgravity()/(slope*Reng));
 281     intDensity = intPressure/(Reng*intTemperature);
 282   }
 283
 284   lastIndex=i;
 285 }
 286
 287 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 288 // Calculate parameters derived from T, P and rho
 289 // Sum gust and turbulence values in NED frame into the wind vector.
 290
 291 void FGAtmosphere::CalculateDerived(void)
 292 {
 293   T_dev = (*temperature) - GetTemperature(h);
 294
 295   if (T_dev == 0.0) density_altitude = h;
 296   else              density_altitude = 518.67/0.00356616 * (1.0 - pow(GetDensityRatio(),0.235));
 297
 298   if (turbType != ttNone) Turbulence();
 299
 300   vTotalWindNED = vWindNED + vGustNED + vTurbulenceNED;
 301
 302    // psiw (Wind heading) is the direction the wind is blowing towards
 303   if (vWindNED(eX) != 0.0) psiw = atan2( vWindNED(eY), vWindNED(eX) );
 304   if (psiw < 0) psiw += 2*M_PI;
 305
 306   soundspeed = sqrt(SHRatio*Reng*(*temperature));
 307
 308   intViscosity = Beta * pow(intTemperature, 1.5) / (SutherlandConstant + intTemperature);
 309   intKinematicViscosity = intViscosity / intDensity;
 310 }
 311
 312
 313 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 314 // Get the standard atmospheric properties at a specified altitude
 315
 316 void FGAtmosphere::GetStdAtmosphere(double altitude) {
 317   StandardTempOnly = true;
 318   Calculate(altitude);
 319   StandardTempOnly = false;
 320   atmosphere.Temperature = intTemperature;
 321   atmosphere.Pressure = intPressure;
 322   atmosphere.Density = intDensity;
 323
 324   // Reset the internal atmospheric state
 325   Calculate(h);
 326 }
 327
 328 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 329 // Get the standard pressure at a specified altitude
 330
 331 double FGAtmosphere::GetPressure(double altitude) {
 332   GetStdAtmosphere(altitude);
 333   return atmosphere.Pressure;
 334 }
 335
 336 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 337 // Get the standard temperature at a specified altitude
 338
 339 double FGAtmosphere::GetTemperature(double altitude) {
 340   GetStdAtmosphere(altitude);
 341   return atmosphere.Temperature;
 342 }
 343
 344 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 345 // Get the standard density at a specified altitude
 346
 347 double FGAtmosphere::GetDensity(double altitude) {
 348   GetStdAtmosphere(altitude);
 349   return atmosphere.Density;
 350 }
 351
 352
 353 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 354 // square a value, but preserve the original sign
 355
 356 static inline double square_signed (double value)
 357 {
 358     if (value < 0)
 359         return value * value * -1;
 360     else
 361         return value * value;
 362 }
 363
 364 /// simply square a value
 365 static inline double sqr(double x) { return x*x; }
 366
 367 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 368 //
 369 // psi is the angle that the wind is blowing *towards*
 370
 371 void FGAtmosphere::SetWindspeed(double speed)
 372 {
 373   if (vWindNED.Magnitude() == 0.0) {
 374     psiw = 0.0;
 375     vWindNED(eNorth) = speed;
 376   } else {
 377     vWindNED(eNorth) = speed * cos(psiw);
 378     vWindNED(eEast) = speed * sin(psiw);
 379     vWindNED(eDown) = 0.0;
 380   }
 381 }
 382
 383 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 384
 385 double FGAtmosphere::GetWindspeed(void) const
 386 {
 387   return vWindNED.Magnitude();
 388 }
 389
 390 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 391 //
 392 // psi is the angle that the wind is blowing *towards*
 393
 394 void FGAtmosphere::SetWindPsi(double dir)
 395 {
 396   double mag = GetWindspeed();
 397   psiw = dir;
 398   SetWindspeed(mag);
 399 }
 400
 401 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 402
 403 void FGAtmosphere::Turbulence(void)
 404 {
 405   const double DeltaT = rate*FDMExec->GetDeltaT();
 406   const double wingspan = FDMExec->GetAircraft()->GetWingSpan();
 407   const double HOverBMAC = FDMExec->GetAuxiliary()->GetHOverBMAC();
 408   const FGMatrix33& Tl2b = FDMExec->GetPropagate()->GetTl2b();
 409   const double HTailArm = FDMExec->GetAircraft()->GetHTailArm();
 410   const double VTailArm = FDMExec->GetAircraft()->GetVTailArm();
 411
 412   switch (turbType) {
 413   case ttStandard: {
 414     // TurbGain = TurbGain * TurbGain * 100.0; // what is this!?
 415
 416     vDirectiondAccelDt(eX) = 1 - 2.0*(double(rand())/double(RAND_MAX));
 417     vDirectiondAccelDt(eY) = 1 - 2.0*(double(rand())/double(RAND_MAX));
 418     vDirectiondAccelDt(eZ) = 1 - 2.0*(double(rand())/double(RAND_MAX));
 419
 420     MagnitudedAccelDt = 1 - 2.0*(double(rand())/double(RAND_MAX)) - Magnitude;
 421                                 // Scale the magnitude so that it moves
 422                                 // away from the peaks
 423     MagnitudedAccelDt = ((MagnitudedAccelDt - Magnitude) /
 424                          (1 + fabs(Magnitude)));
 425     MagnitudeAccel    += MagnitudedAccelDt*TurbRate*DeltaT;
 426     Magnitude         += MagnitudeAccel*DeltaT;
 427     Magnitude          = fabs(Magnitude);
 428
 429     vDirectiondAccelDt.Normalize();
 430
 431                                 // deemphasise non-vertical forces
 432     vDirectiondAccelDt(eX) = square_signed(vDirectiondAccelDt(eX));
 433     vDirectiondAccelDt(eY) = square_signed(vDirectiondAccelDt(eY));
 434
 435     vDirectionAccel += vDirectiondAccelDt*TurbRate*DeltaT;
 436     vDirectionAccel.Normalize();
 437     vDirection      += vDirectionAccel*DeltaT;
 438
 439     vDirection.Normalize();
 440
 441                                 // Diminish turbulence within three wingspans
 442                                 // of the ground
 443     vTurbulenceNED = TurbGain * Magnitude * vDirection;
 444     if (HOverBMAC < 3.0)
 445         vTurbulenceNED *= (HOverBMAC / 3.0) * (HOverBMAC / 3.0);
 446
 447     // I don't believe these next two statements calculate the proper gradient over
 448     // the aircraft body. One reason is because this has no relationship with the
 449     // orientation or velocity of the aircraft, which it must have. What is vTurbulenceGrad
 450     // supposed to represent? And the direction and magnitude of the turbulence can change,
 451     // so both accelerations need to be accounted for, no?
 452
 453     // Need to determine the turbulence change in body axes between two time points.
 454
 455     vTurbulenceGrad = TurbGain*MagnitudeAccel * vDirection;
 456     vBodyTurbGrad = Tl2b*vTurbulenceGrad;
 457
 458     if (wingspan > 0) {
 459       vTurbPQR(eP) = vBodyTurbGrad(eY)/wingspan;
 460     } else {
 461       vTurbPQR(eP) = vBodyTurbGrad(eY)/30.0;
 462     }
 463 //     if (HTailArm != 0.0)
 464 //       vTurbPQR(eQ) = vBodyTurbGrad(eZ)/HTailArm;
 465 //     else
 466 //       vTurbPQR(eQ) = vBodyTurbGrad(eZ)/10.0;
 467
 468     if (VTailArm > 0)
 469       vTurbPQR(eR) = vBodyTurbGrad(eX)/VTailArm;
 470     else
 471       vTurbPQR(eR) = vBodyTurbGrad(eX)/10.0;
 472
 473                                 // Clear the horizontal forces
 474                                 // actually felt by the plane, now
 475                                 // that we've used them to calculate
 476                                 // moments.
 477                                 // Why? (JSB)
 478 //    vTurbulenceNED(eX) = 0.0;
 479 //    vTurbulenceNED(eY) = 0.0;
 480
 481     break;
 482   }
 483
 484   case ttCulp: {
 485
 486     vTurbPQR(eP) = wind_from_clockwise;
 487     if (TurbGain == 0.0) return;
 488
 489     // keep the inputs within allowable limts for this model
 490     if (TurbGain < 0.0) TurbGain = 0.0;
 491     if (TurbGain > 1.0) TurbGain = 1.0;
 492     if (TurbRate < 0.0) TurbRate = 0.0;
 493     if (TurbRate > 30.0) TurbRate = 30.0;
 494     if (Rhythmicity < 0.0) Rhythmicity = 0.0;
 495     if (Rhythmicity > 1.0) Rhythmicity = 1.0;
 496
 497     // generate a sine wave corresponding to turbulence rate in hertz
 498     double time = FDMExec->GetSimTime();
 499     double sinewave = sin( time * TurbRate * 6.283185307 );
 500
 501     double random = 0.0;
 502     if (target_time == 0.0) {
 503       strength = random = 1 - 2.0*(double(rand())/double(RAND_MAX));
 504       target_time = time + 0.71 + (random * 0.5);
 505     }
 506     if (time > target_time) {
 507       spike = 1.0;
 508       target_time = 0.0;
 509     }
 510
 511     // max vertical wind speed in fps, corresponds to TurbGain = 1.0
 512     double max_vs = 40;
 513
 514     vTurbulenceNED(1) = vTurbulenceNED(2) = vTurbulenceNED(3) = 0.0;
 515     double delta = strength * max_vs * TurbGain * (1-Rhythmicity) * spike;
 516
 517     // Vertical component of turbulence.
 518     vTurbulenceNED(3) = sinewave * max_vs * TurbGain * Rhythmicity;
 519     vTurbulenceNED(3)+= delta;
 520     if (HOverBMAC < 3.0)
 521         vTurbulenceNED(3) *= HOverBMAC * 0.3333;
 522
 523     // Yaw component of turbulence.
 524     vTurbulenceNED(1) = sin( delta * 3.0 );
 525     vTurbulenceNED(2) = cos( delta * 3.0 );
 526
 527     // Roll component of turbulence. Clockwise vortex causes left roll.
 528     vTurbPQR(eP) += delta * 0.04;
 529
 530     spike = spike * 0.9;
 531     break;
 532   }
 533   case ttMilspec:
 534   case ttTustin: {
 535     double V = FDMExec->GetAuxiliary()->GetVt(); // true airspeed in ft/s
 536
 537     // an index of zero means turbulence is disabled
 538     // airspeed occurs as divisor in the code below
 539     if (probability_of_exceedence_index == 0 || V == 0) {
 540       vTurbulenceNED(1) = vTurbulenceNED(2) = vTurbulenceNED(3) = 0.0;
 541       vTurbPQR(1) = vTurbPQR(2) = vTurbPQR(3) = 0.0;
 542       return;
 543     }
 544
 545     // Turbulence model according to MIL-F-8785C (Flying Qualities of Piloted Aircraft)
 546     double
 547       h = FDMExec->GetPropagate()->GetDistanceAGL(),
 548       b_w = wingspan,
 549       L_u, L_w, sig_u, sig_w;
 550
 551       if (b_w == 0.) b_w = 30.;
 552
 553     // clip height functions at 10 ft
 554     if (h <= 10.) h = 10;
 555
 556     // Scale lengths L and amplitudes sigma as function of height
 557     if (h <= 1000) {
 558       L_u = h/pow(0.177 + 0.000823*h, 1.2); // MIL-F-8785c, Fig. 10, p. 55
 559       L_w = h;
 560       sig_w = 0.1*windspeed_at_20ft;
 561       sig_u = sig_w/pow(0.177 + 0.000823*h, 0.4); // MIL-F-8785c, Fig. 11, p. 56
 562     } else if (h <= 2000) {
 563       // linear interpolation between low altitude and high altitude models
 564       L_u = L_w = 1000 + (h-1000.)/1000.*750.;
 565       sig_u = sig_w = 0.1*windspeed_at_20ft
 566                     + (h-1000.)/1000.*(POE_Table->GetValue(probability_of_exceedence_index, h) - 0.1*windspeed_at_20ft);
 567     } else {
 568       L_u = L_w = 1750.; //  MIL-F-8785c, Sec. 3.7.2.1, p. 48
 569       sig_u = sig_w = POE_Table->GetValue(probability_of_exceedence_index, h);
 570     }
 571
 572     // keep values from last timesteps
 573     // TODO maybe use deque?
 574     static double
 575       xi_u_km1 = 0, nu_u_km1 = 0,
 576       xi_v_km1 = 0, xi_v_km2 = 0, nu_v_km1 = 0, nu_v_km2 = 0,
 577       xi_w_km1 = 0, xi_w_km2 = 0, nu_w_km1 = 0, nu_w_km2 = 0,
 578       xi_p_km1 = 0, nu_p_km1 = 0,
 579       xi_q_km1 = 0, xi_r_km1 = 0;
 580
 581
 582     double
 583       T_V = DeltaT, // for compatibility of nomenclature
 584       sig_p = 1.9/sqrt(L_w*b_w)*sig_w, // Yeager1998, eq. (8)
 585       sig_q = sqrt(M_PI/2/L_w/b_w), // eq. (14)
 586       sig_r = sqrt(2*M_PI/3/L_w/b_w), // eq. (17)
 587       L_p = sqrt(L_w*b_w)/2.6, // eq. (10)
 588       tau_u = L_u/V, // eq. (6)
 589       tau_w = L_w/V, // eq. (3)
 590       tau_p = L_p/V, // eq. (9)
 591       tau_q = 4*b_w/M_PI/V, // eq. (13)
 592       tau_r =3*b_w/M_PI/V, // eq. (17)
 593       nu_u = GaussianRandomNumber(),
 594       nu_v = GaussianRandomNumber(),
 595       nu_w = GaussianRandomNumber(),
 596       nu_p = GaussianRandomNumber(),
 597       xi_u=0, xi_v=0, xi_w=0, xi_p=0, xi_q=0, xi_r=0;
 598
 599     // values of turbulence NED velocities
 600
 601     if (turbType == ttTustin) {
 602       // the following is the Tustin formulation of Yeager's report
 603       double
 604         omega_w = V/L_w, // hidden in nomenclature p. 3
 605         omega_v = V/L_u, // this is defined nowhere
 606         C_BL  = 1/tau_u/tan(T_V/2/tau_u), // eq. (19)
 607         C_BLp = 1/tau_p/tan(T_V/2/tau_p), // eq. (22)
 608         C_BLq = 1/tau_q/tan(T_V/2/tau_q), // eq. (24)
 609         C_BLr = 1/tau_r/tan(T_V/2/tau_r); // eq. (26)
 610
 611       // all values calculated so far are strictly positive, except for
 612       // the random numbers nu_*. This means that in the code below, all
 613       // divisors are strictly positive, too, and no floating point
 614       // exception should occur.
 615       xi_u = -(1 - C_BL*tau_u)/(1 + C_BL*tau_u)*xi_u_km1
 616            + sig_u*sqrt(2*tau_u/T_V)/(1 + C_BL*tau_u)*(nu_u + nu_u_km1); // eq. (18)
 617       xi_v = -2*(sqr(omega_v) - sqr(C_BL))/sqr(omega_v + C_BL)*xi_v_km1
 618            - sqr(omega_v - C_BL)/sqr(omega_v + C_BL) * xi_v_km2
 619            + sig_u*sqrt(3*omega_v/T_V)/sqr(omega_v + C_BL)*(
 620                  (C_BL + omega_v/sqrt(3.))*nu_v
 621                + 2/sqrt(3.)*omega_v*nu_v_km1
 622                + (omega_v/sqrt(3.) - C_BL)*nu_v_km2); // eq. (20) for v
 623       xi_w = -2*(sqr(omega_w) - sqr(C_BL))/sqr(omega_w + C_BL)*xi_w_km1
 624            - sqr(omega_w - C_BL)/sqr(omega_w + C_BL) * xi_w_km2
 625            + sig_w*sqrt(3*omega_w/T_V)/sqr(omega_w + C_BL)*(
 626                  (C_BL + omega_w/sqrt(3.))*nu_w
 627                + 2/sqrt(3.)*omega_w*nu_w_km1
 628                + (omega_w/sqrt(3.) - C_BL)*nu_w_km2); // eq. (20) for w
 629       xi_p = -(1 - C_BLp*tau_p)/(1 + C_BLp*tau_p)*xi_p_km1
 630            + sig_p*sqrt(2*tau_p/T_V)/(1 + C_BLp*tau_p) * (nu_p + nu_p_km1); // eq. (21)
 631       xi_q = -(1 - 4*b_w*C_BLq/M_PI/V)/(1 + 4*b_w*C_BLq/M_PI/V) * xi_q_km1
 632            + C_BLq/V/(1 + 4*b_w*C_BLq/M_PI/V) * (xi_w - xi_w_km1); // eq. (23)
 633       xi_r = - (1 - 3*b_w*C_BLr/M_PI/V)/(1 + 3*b_w*C_BLr/M_PI/V) * xi_r_km1
 634            + C_BLr/V/(1 + 3*b_w*C_BLr/M_PI/V) * (xi_v - xi_v_km1); // eq. (25)
 635
 636     } else if (turbType == ttMilspec) {
 637       // the following is the MIL-STD-1797A formulation
 638       // as cited in Yeager's report
 639       xi_u = (1 - T_V/tau_u)  *xi_u_km1 + sig_u*sqrt(2*T_V/tau_u)*nu_u;  // eq. (30)
 640       xi_v = (1 - 2*T_V/tau_u)*xi_v_km1 + sig_u*sqrt(4*T_V/tau_u)*nu_v;  // eq. (31)
 641       xi_w = (1 - 2*T_V/tau_w)*xi_w_km1 + sig_w*sqrt(4*T_V/tau_w)*nu_w;  // eq. (32)
 642       xi_p = (1 - T_V/tau_p)  *xi_p_km1 + sig_p*sqrt(2*T_V/tau_p)*nu_p;  // eq. (33)
 643       xi_q = (1 - T_V/tau_q)  *xi_q_km1 + M_PI/4/b_w*(xi_w - xi_w_km1);  // eq. (34)
 644       xi_r = (1 - T_V/tau_r)  *xi_r_km1 + M_PI/3/b_w*(xi_v - xi_v_km1);  // eq. (35)
 645     }
 646
 647     // rotate by wind azimuth and assign the velocities
 648     double cospsi = cos(psiw), sinpsi = sin(psiw);
 649     vTurbulenceNED(1) =  cospsi*xi_u + sinpsi*xi_v;
 650     vTurbulenceNED(2) = -sinpsi*xi_u + cospsi*xi_v;
 651     vTurbulenceNED(3) = xi_w;
 652
 653     vTurbPQR(1) =  cospsi*xi_p + sinpsi*xi_q;
 654     vTurbPQR(2) = -sinpsi*xi_p + cospsi*xi_q;
 655     vTurbPQR(3) = xi_r;
 656
 657     // vTurbPQR is in the body fixed frame, not NED
 658     vTurbPQR = Tl2b*vTurbPQR;
 659
 660     // hand on the values for the next timestep
 661     xi_u_km1 = xi_u; nu_u_km1 = nu_u;
 662     xi_v_km2 = xi_v_km1; xi_v_km1 = xi_v; nu_v_km2 = nu_v_km1; nu_v_km1 = nu_v;
 663     xi_w_km2 = xi_w_km1; xi_w_km1 = xi_w; nu_w_km2 = nu_w_km1; nu_w_km1 = nu_w;
 664     xi_p_km1 = xi_p; nu_p_km1 = nu_p;
 665     xi_q_km1 = xi_q;
 666     xi_r_km1 = xi_r;
 667
 668   }
 669   default:
 670     break;
 671   }
 672 }
 673
 674 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 675
 676 void FGAtmosphere::UseExternal(void)
 677 {
 678   temperature=&exTemperature;
 679   pressure=&exPressure;
 680   density=&exDensity;
 681   useExternal=true;
 682 }
 683
 684 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 685
 686 void FGAtmosphere::UseInternal(void)
 687 {
 688   temperature=&intTemperature;
 689   pressure=&intPressure;
 690   density=&intDensity;
 691   useExternal=false;
 692 }
 693
 694 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 695
 696 void FGAtmosphere::bind(void)
 697 {
 698   typedef double (FGAtmosphere::*PMF)(int) const;
 699   typedef double (FGAtmosphere::*PMFv)(void) const;
 700   typedef int (FGAtmosphere::*PMFt)(void) const;
 701   typedef void   (FGAtmosphere::*PMFd)(int,double);
 702   typedef void   (FGAtmosphere::*PMFi)(int);
 703   PropertyManager->Tie("atmosphere/T-R", this, (PMFv)&FGAtmosphere::GetTemperature);
 704   PropertyManager->Tie("atmosphere/rho-slugs_ft3", this, (PMFv)&FGAtmosphere::GetDensity);
 705   PropertyManager->Tie("atmosphere/P-psf", this, (PMFv)&FGAtmosphere::GetPressure);
 706   PropertyManager->Tie("atmosphere/a-fps", this, &FGAtmosphere::GetSoundSpeed);
 707   PropertyManager->Tie("atmosphere/T-sl-R", this, &FGAtmosphere::GetTemperatureSL);
 708   PropertyManager->Tie("atmosphere/rho-sl-slugs_ft3", this, &FGAtmosphere::GetDensitySL);
 709   PropertyManager->Tie("atmosphere/P-sl-psf", this, &FGAtmosphere::GetPressureSL);
 710   PropertyManager->Tie("atmosphere/a-sl-fps", this, &FGAtmosphere::GetSoundSpeedSL);
 711   PropertyManager->Tie("atmosphere/theta", this, &FGAtmosphere::GetTemperatureRatio);
 712   PropertyManager->Tie("atmosphere/sigma", this, &FGAtmosphere::GetDensityRatio);
 713   PropertyManager->Tie("atmosphere/delta", this, &FGAtmosphere::GetPressureRatio);
 714   PropertyManager->Tie("atmosphere/a-ratio", this, &FGAtmosphere::GetSoundSpeedRatio);
 715   PropertyManager->Tie("atmosphere/psiw-rad", this, &FGAtmosphere::GetWindPsi, &FGAtmosphere::SetWindPsi);
 716   PropertyManager->Tie("atmosphere/delta-T", this, &FGAtmosphere::GetDeltaT, &FGAtmosphere::SetDeltaT);
 717   PropertyManager->Tie("atmosphere/T-sl-dev-F", this, &FGAtmosphere::GetSLTempDev, &FGAtmosphere::SetSLTempDev);
 718   PropertyManager->Tie("atmosphere/density-altitude", this, &FGAtmosphere::GetDensityAltitude);
 719
 720   PropertyManager->Tie("atmosphere/wind-north-fps", this, eNorth, (PMF)&FGAtmosphere::GetWindNED,
 721                                                           (PMFd)&FGAtmosphere::SetWindNED);
 722   PropertyManager->Tie("atmosphere/wind-east-fps",  this, eEast, (PMF)&FGAtmosphere::GetWindNED,
 723                                                           (PMFd)&FGAtmosphere::SetWindNED);
 724   PropertyManager->Tie("atmosphere/wind-down-fps",  this, eDown, (PMF)&FGAtmosphere::GetWindNED,
 725                                                           (PMFd)&FGAtmosphere::SetWindNED);
 726   PropertyManager->Tie("atmosphere/wind-mag-fps", this, &FGAtmosphere::GetWindspeed,
 727                                                         &FGAtmosphere::SetWindspeed);
 728   PropertyManager->Tie("atmosphere/total-wind-north-fps", this, eNorth, (PMF)&FGAtmosphere::GetTotalWindNED);
 729   PropertyManager->Tie("atmosphere/total-wind-east-fps",  this, eEast,  (PMF)&FGAtmosphere::GetTotalWindNED);
 730   PropertyManager->Tie("atmosphere/total-wind-down-fps",  this, eDown,  (PMF)&FGAtmosphere::GetTotalWindNED);
 731
 732   PropertyManager->Tie("atmosphere/gust-north-fps", this, eNorth, (PMF)&FGAtmosphere::GetGustNED,
 733                                                           (PMFd)&FGAtmosphere::SetGustNED);
 734   PropertyManager->Tie("atmosphere/gust-east-fps",  this, eEast, (PMF)&FGAtmosphere::GetGustNED,
 735                                                           (PMFd)&FGAtmosphere::SetGustNED);
 736   PropertyManager->Tie("atmosphere/gust-down-fps",  this, eDown, (PMF)&FGAtmosphere::GetGustNED,
 737                                                           (PMFd)&FGAtmosphere::SetGustNED);
 738
 739   PropertyManager->Tie("atmosphere/turb-north-fps", this, eNorth, (PMF)&FGAtmosphere::GetTurbNED,
 740                                                           (PMFd)&FGAtmosphere::SetTurbNED);
 741   PropertyManager->Tie("atmosphere/turb-east-fps",  this, eEast, (PMF)&FGAtmosphere::GetTurbNED,
 742                                                           (PMFd)&FGAtmosphere::SetTurbNED);
 743   PropertyManager->Tie("atmosphere/turb-down-fps",  this, eDown, (PMF)&FGAtmosphere::GetTurbNED,
 744                                                           (PMFd)&FGAtmosphere::SetTurbNED);
 745
 746   PropertyManager->Tie("atmosphere/p-turb-rad_sec", this,1, (PMF)&FGAtmosphere::GetTurbPQR);
 747   PropertyManager->Tie("atmosphere/q-turb-rad_sec", this,2, (PMF)&FGAtmosphere::GetTurbPQR);
 748   PropertyManager->Tie("atmosphere/r-turb-rad_sec", this,3, (PMF)&FGAtmosphere::GetTurbPQR);
 749   PropertyManager->Tie("atmosphere/turb-type", this, (PMFt)&FGAtmosphere::GetTurbType, (PMFi)&FGAtmosphere::SetTurbType);
 750   PropertyManager->Tie("atmosphere/turb-rate", this, &FGAtmosphere::GetTurbRate, &FGAtmosphere::SetTurbRate);
 751   PropertyManager->Tie("atmosphere/turb-gain", this, &FGAtmosphere::GetTurbGain, &FGAtmosphere::SetTurbGain);
 752   PropertyManager->Tie("atmosphere/turb-rhythmicity", this, &FGAtmosphere::GetRhythmicity,
 753                                                             &FGAtmosphere::SetRhythmicity);
 754
 755   PropertyManager->Tie("atmosphere/turbulence/milspec/windspeed_at_20ft_AGL-fps",
 756                        this, &FGAtmosphere::GetWindspeed20ft,
 757                              &FGAtmosphere::SetWindspeed20ft);
 758   PropertyManager->Tie("atmosphere/turbulence/milspec/severity",
 759                        this, &FGAtmosphere::GetProbabilityOfExceedence,
 760                              &FGAtmosphere::SetProbabilityOfExceedence);
 761
 762 }
 763
 764 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 765 //    The bitmasked value choices are as follows:
 766 //    unset: In this case (the default) JSBSim would only print
 767 //       out the normally expected messages, essentially echoing
 768 //       the config files as they are read. If the environment
 769 //       variable is not set, debug_lvl is set to 1 internally
 770 //    0: This requests JSBSim not to output any messages
 771 //       whatsoever.
 772 //    1: This value explicity requests the normal JSBSim
 773 //       startup messages
 774 //    2: This value asks for a message to be printed out when
 775 //       a class is instantiated
 776 //    4: When this value is set, a message is displayed when a
 777 //       FGModel object executes its Run() method
 778 //    8: When this value is set, various runtime state variables
 779 //       are printed out periodically
 780 //    16: When set various parameters are sanity checked and
 781 //       a message is printed out when they go out of bounds
 782
 783 void FGAtmosphere::Debug(int from)
 784 {
 785   if (debug_lvl <= 0) return;
 786
 787   if (debug_lvl & 1) { // Standard console startup message output
 788     if (from == 0) { // Constructor
 789     }
 790   }
 791   if (debug_lvl & 2 ) { // Instantiation/Destruction notification
 792     if (from == 0) cout << "Instantiated: FGAtmosphere" << endl;
 793     if (from == 1) cout << "Destroyed:    FGAtmosphere" << endl;
 794   }
 795   if (debug_lvl & 4 ) { // Run() method entry print for FGModel-derived objects
 796   }
 797   if (debug_lvl & 8 ) { // Runtime state variables
 798   }
 799   if (debug_lvl & 16) { // Sanity checking
 800   }
 801   if (debug_lvl & 128) { // Turbulence
 802     if (first_pass && from == 2) {
 803       first_pass = false;
 804       cout << "vTurbulenceNED(X), vTurbulenceNED(Y), vTurbulenceNED(Z), "
 805            << "vTurbulenceGrad(X), vTurbulenceGrad(Y), vTurbulenceGrad(Z), "
 806            << "vDirection(X), vDirection(Y), vDirection(Z), "
 807            << "Magnitude, "
 808            << "vTurbPQR(P), vTurbPQR(Q), vTurbPQR(R), " << endl;
 809     }
 810     if (from == 2) {
 811       cout << vTurbulenceNED << ", " << vTurbulenceGrad << ", " << vDirection << ", " << Magnitude << ", " << vTurbPQR << endl;
 812     }
 813   }
 814   if (debug_lvl & 64) {
 815     if (from == 0) { // Constructor
 816       cout << IdSrc << endl;
 817       cout << IdHdr << endl;
 818     }
 819   }
 820 }
 821
 822 } // namespace JSBSim