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 1.38 2010/09/16 11:01:24 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( ttCulp );
  88   SetTurbType( ttNone );
  89   TurbGain = 1.0;
  90   TurbRate = 10.0;
  91   Rhythmicity = 0.1;
  92   spike = target_time = strength = 0.0;
  93   wind_from_clockwise = 0.0;
  94   SutherlandConstant = 198.72; // deg Rankine
  95   Beta = 2.269690E-08; // slug/(sec ft R^0.5)
  96
  97   T_dev_sl = T_dev = delta_T = 0.0;
  98   StandardTempOnly = false;
  99   first_pass = true;
 100   vGustNED.InitMatrix();
 101   vTurbulenceNED.InitMatrix();
 102
 103   // Milspec turbulence model
 104   windspeed_at_20ft = 0.;
 105   probability_of_exceedence_index = 0;
 106   POE_Table = new FGTable(7,12);
 107   // this is Figure 7 from p. 49 of MIL-F-8785C
 108   // rows: probability of exceedance curve index, cols: altitude in ft
 109   *POE_Table
 110            << 500.0 << 1750.0 << 3750.0 << 7500.0 << 15000.0 << 25000.0 << 35000.0 << 45000.0 << 55000.0 << 65000.0 << 75000.0 << 80000.0
 111     << 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
 112     << 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
 113     << 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
 114     << 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
 115     << 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
 116     << 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
 117     << 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;
 118
 119   bind();
 120   Debug(0);
 121 }
 122
 123 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 124
 125 FGAtmosphere::~FGAtmosphere()
 126 {
 127   Debug(1);
 128 }
 129
 130 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 131
 132 bool FGAtmosphere::InitModel(void)
 133 {
 134   if (!FGModel::InitModel()) return false;
 135
 136   UseInternal();  // this is the default
 137
 138   Calculate(h);
 139   StdSLtemperature = SLtemperature = 518.67;
 140   StdSLpressure    = SLpressure = 2116.22;
 141   StdSLdensity     = SLdensity = 0.00237767;
 142   StdSLsoundspeed  = SLsoundspeed = sqrt(SHRatio*Reng*StdSLtemperature);
 143   rSLtemperature = 1.0/StdSLtemperature;
 144   rSLpressure    = 1.0/StdSLpressure;
 145   rSLdensity     = 1.0/StdSLdensity;
 146   rSLsoundspeed  = 1.0/StdSLsoundspeed;
 147
 148   return true;
 149 }
 150
 151 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 152
 153 bool FGAtmosphere::Run(void)
 154 {
 155   if (FGModel::Run()) return true;
 156   if (FDMExec->Holding()) return false;
 157
 158   RunPreFunctions();
 159
 160   T_dev = 0.0;
 161   h = Propagate->GetAltitudeASL();
 162
 163   if (!useExternal) {
 164     Calculate(h);
 165     CalculateDerived();
 166   } else {
 167     CalculateDerived();
 168   }
 169
 170   RunPostFunctions();
 171
 172   Debug(2);
 173   return false;
 174 }
 175
 176 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 177 //
 178 // See reference 1
 179
 180 void FGAtmosphere::Calculate(double altitude)
 181 {
 182   double slope, reftemp, refpress;
 183   int i = lastIndex;
 184
 185   if (altitude < htab[lastIndex]) {
 186     if (altitude <= 0) {
 187       i = 0;
 188       altitude=0;
 189     } else {
 190        i = lastIndex-1;
 191        while (htab[i] > altitude) i--;
 192     }
 193   } else if (altitude > htab[lastIndex+1]) {
 194     if (altitude >= htab[7]) {
 195       i = 7;
 196       altitude = htab[7];
 197     } else {
 198       i = lastIndex+1;
 199       while (htab[i+1] < altitude) i++;
 200     }
 201   }
 202
 203   switch(i) {
 204   case 0: // Sea level
 205     slope     = -0.00356616; // R/ft.
 206     reftemp   = 518.67;   // in degrees Rankine, 288.15 Kelvin
 207     refpress  = 2116.22;    // psf
 208     //refdens   = 0.00237767;  // slugs/cubic ft.
 209     break;
 210   case 1:     // 36089 ft. or 11 km
 211     slope     = 0;
 212     reftemp   = 389.97; // in degrees Rankine, 216.65 Kelvin
 213     refpress  = 472.763;
 214     //refdens   = 0.000706032;
 215     break;
 216   case 2:     // 65616 ft. or 20 km
 217     slope     = 0.00054864;
 218     reftemp   = 389.97; // in degrees Rankine, 216.65 Kelvin
 219     refpress  = 114.636;
 220     //refdens   = 0.000171306;
 221     break;
 222   case 3:     // 104986 ft. or 32 km
 223     slope     = 0.001536192;
 224     reftemp   = 411.57; // in degrees Rankine, 228.65 Kelvin
 225     refpress  = 18.128;
 226     //refdens   = 1.18422e-05;
 227     break;
 228   case 4:     // 154199 ft. 47 km
 229     slope     = 0;
 230     reftemp   = 487.17; // in degrees Rankine, 270.65 Kelvin
 231     refpress  = 2.316;
 232     //refdens   = 4.00585e-7;
 233     break;
 234   case 5:     // 167322 ft. or 51 km
 235     slope     = -0.001536192;
 236     reftemp   = 487.17; // in degrees Rankine, 270.65 Kelvin
 237     refpress  = 1.398;
 238     //refdens   = 8.17102e-7;
 239     break;
 240   case 6:     // 232940 ft. or 71 km
 241     slope     = -0.00109728;
 242     reftemp   = 386.368; // in degrees Rankine, 214.649 Kelvin
 243     refpress  = 0.0826;
 244     //refdens   = 8.77702e-9;
 245     break;
 246   case 7:     // 278385 ft. or 84.8520 km
 247     slope     = 0;
 248     reftemp   = 336.5; // in degrees Rankine, 186.94 Kelvin
 249     refpress  = 0.00831;
 250     //refdens   = 2.19541e-10;
 251     break;
 252   default:     // sea level
 253     slope     = -0.00356616; // R/ft.
 254     reftemp   = 518.67;   // in degrees Rankine, 288.15 Kelvin
 255     refpress  = 2116.22;    // psf
 256     //refdens   = 0.00237767;  // slugs/cubic ft.
 257     break;
 258
 259   }
 260
 261   // If delta_T is set, then that is our temperature deviation at any altitude.
 262   // If not, then we'll estimate a deviation based on the sea level deviation (if set).
 263
 264   if(!StandardTempOnly) {
 265     T_dev = 0.0;
 266     if (delta_T != 0.0) {
 267       T_dev = delta_T;
 268     } else {
 269       if ((altitude < 36089.239) && (T_dev_sl != 0.0)) {
 270         T_dev = T_dev_sl * ( 1.0 - (altitude/36089.239));
 271       }
 272     }
 273     reftemp+=T_dev;
 274   }
 275
 276   if (slope == 0) {
 277     intTemperature = reftemp;
 278     intPressure = refpress*exp(-Inertial->SLgravity()/(reftemp*Reng)*(altitude-htab[i]));
 279     intDensity = intPressure/(Reng*intTemperature);
 280   } else {
 281     intTemperature = reftemp+slope*(altitude-htab[i]);
 282     intPressure = refpress*pow(intTemperature/reftemp,-Inertial->SLgravity()/(slope*Reng));
 283     intDensity = intPressure/(Reng*intTemperature);
 284   }
 285
 286   lastIndex=i;
 287 }
 288
 289 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 290 // Calculate parameters derived from T, P and rho
 291 // Sum gust and turbulence values in NED frame into the wind vector.
 292
 293 void FGAtmosphere::CalculateDerived(void)
 294 {
 295   T_dev = (*temperature) - GetTemperature(h);
 296
 297   if (T_dev == 0.0) density_altitude = h;
 298   else              density_altitude = 518.67/0.00356616 * (1.0 - pow(GetDensityRatio(),0.235));
 299
 300   if (turbType != ttNone) Turbulence();
 301
 302   vTotalWindNED = vWindNED + vGustNED + vTurbulenceNED;
 303
 304    // psiw (Wind heading) is the direction the wind is blowing towards
 305   if (vWindNED(eX) != 0.0) psiw = atan2( vWindNED(eY), vWindNED(eX) );
 306   if (psiw < 0) psiw += 2*M_PI;
 307
 308   soundspeed = sqrt(SHRatio*Reng*(*temperature));
 309
 310   intViscosity = Beta * pow(intTemperature, 1.5) / (SutherlandConstant + intTemperature);
 311   intKinematicViscosity = intViscosity / intDensity;
 312 }
 313
 314
 315 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 316 // Get the standard atmospheric properties at a specified altitude
 317
 318 void FGAtmosphere::GetStdAtmosphere(double altitude) {
 319   StandardTempOnly = true;
 320   Calculate(altitude);
 321   StandardTempOnly = false;
 322   atmosphere.Temperature = intTemperature;
 323   atmosphere.Pressure = intPressure;
 324   atmosphere.Density = intDensity;
 325
 326   // Reset the internal atmospheric state
 327   Calculate(h);
 328 }
 329
 330 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 331 // Get the standard pressure at a specified altitude
 332
 333 double FGAtmosphere::GetPressure(double altitude) {
 334   GetStdAtmosphere(altitude);
 335   return atmosphere.Pressure;
 336 }
 337
 338 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 339 // Get the standard temperature at a specified altitude
 340
 341 double FGAtmosphere::GetTemperature(double altitude) {
 342   GetStdAtmosphere(altitude);
 343   return atmosphere.Temperature;
 344 }
 345
 346 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 347 // Get the standard density at a specified altitude
 348
 349 double FGAtmosphere::GetDensity(double altitude) {
 350   GetStdAtmosphere(altitude);
 351   return atmosphere.Density;
 352 }
 353
 354
 355 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 356 // square a value, but preserve the original sign
 357
 358 static inline double square_signed (double value)
 359 {
 360     if (value < 0)
 361         return value * value * -1;
 362     else
 363         return value * value;
 364 }
 365
 366 /// simply square a value
 367 static inline double sqr(double x) { return x*x; }
 368
 369 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 370 //
 371 // psi is the angle that the wind is blowing *towards*
 372
 373 void FGAtmosphere::SetWindspeed(double speed)
 374 {
 375   if (vWindNED.Magnitude() == 0.0) {
 376     psiw = 0.0;
 377     vWindNED(eNorth) = speed;
 378   } else {
 379     vWindNED(eNorth) = speed * cos(psiw);
 380     vWindNED(eEast) = speed * sin(psiw);
 381     vWindNED(eDown) = 0.0;
 382   }
 383 }
 384
 385 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 386
 387 double FGAtmosphere::GetWindspeed(void) const
 388 {
 389   return vWindNED.Magnitude();
 390 }
 391
 392 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 393 //
 394 // psi is the angle that the wind is blowing *towards*
 395
 396 void FGAtmosphere::SetWindPsi(double dir)
 397 {
 398   double mag = GetWindspeed();
 399   psiw = dir;
 400   SetWindspeed(mag);
 401 }
 402
 403 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 404
 405 void FGAtmosphere::Turbulence(void)
 406 {
 407   double DeltaT = rate*FDMExec->GetDeltaT();
 408
 409   switch (turbType) {
 410   case ttStandard: {
 411     // TurbGain = TurbGain * TurbGain * 100.0; // what is this!?
 412
 413     vDirectiondAccelDt(eX) = 1 - 2.0*(double(rand())/double(RAND_MAX));
 414     vDirectiondAccelDt(eY) = 1 - 2.0*(double(rand())/double(RAND_MAX));
 415     vDirectiondAccelDt(eZ) = 1 - 2.0*(double(rand())/double(RAND_MAX));
 416
 417     MagnitudedAccelDt = 1 - 2.0*(double(rand())/double(RAND_MAX)) - Magnitude;
 418                                 // Scale the magnitude so that it moves
 419                                 // away from the peaks
 420     MagnitudedAccelDt = ((MagnitudedAccelDt - Magnitude) /
 421                          (1 + fabs(Magnitude)));
 422     MagnitudeAccel    += MagnitudedAccelDt*TurbRate*DeltaT;
 423     Magnitude         += MagnitudeAccel*DeltaT;
 424     Magnitude          = fabs(Magnitude);
 425
 426     vDirectiondAccelDt.Normalize();
 427
 428                                 // deemphasise non-vertical forces
 429     vDirectiondAccelDt(eX) = square_signed(vDirectiondAccelDt(eX));
 430     vDirectiondAccelDt(eY) = square_signed(vDirectiondAccelDt(eY));
 431
 432     vDirectionAccel += vDirectiondAccelDt*TurbRate*DeltaT;
 433     vDirectionAccel.Normalize();
 434     vDirection      += vDirectionAccel*DeltaT;
 435
 436     vDirection.Normalize();
 437
 438                                 // Diminish turbulence within three wingspans
 439                                 // of the ground
 440     vTurbulenceNED = TurbGain * Magnitude * vDirection;
 441     double HOverBMAC = Auxiliary->GetHOverBMAC();
 442     if (HOverBMAC < 3.0)
 443         vTurbulenceNED *= (HOverBMAC / 3.0) * (HOverBMAC / 3.0);
 444
 445     // I don't believe these next two statements calculate the proper gradient over
 446     // the aircraft body. One reason is because this has no relationship with the
 447     // orientation or velocity of the aircraft, which it must have. What is vTurbulenceGrad
 448     // supposed to represent? And the direction and magnitude of the turbulence can change,
 449     // so both accelerations need to be accounted for, no?
 450
 451     // Need to determine the turbulence change in body axes between two time points.
 452
 453     vTurbulenceGrad = TurbGain*MagnitudeAccel * vDirection;
 454     vBodyTurbGrad = Propagate->GetTl2b()*vTurbulenceGrad;
 455
 456     if (Aircraft->GetWingSpan() > 0) {
 457       vTurbPQR(eP) = vBodyTurbGrad(eY)/Aircraft->GetWingSpan();
 458     } else {
 459       vTurbPQR(eP) = vBodyTurbGrad(eY)/30.0;
 460     }
 461 //     if (Aircraft->GetHTailArm() != 0.0)
 462 //       vTurbPQR(eQ) = vBodyTurbGrad(eZ)/Aircraft->GetHTailArm();
 463 //     else
 464 //       vTurbPQR(eQ) = vBodyTurbGrad(eZ)/10.0;
 465
 466     if (Aircraft->GetVTailArm() > 0)
 467       vTurbPQR(eR) = vBodyTurbGrad(eX)/Aircraft->GetVTailArm();
 468     else
 469       vTurbPQR(eR) = vBodyTurbGrad(eX)/10.0;
 470
 471                                 // Clear the horizontal forces
 472                                 // actually felt by the plane, now
 473                                 // that we've used them to calculate
 474                                 // moments.
 475                                 // Why? (JSB)
 476 //    vTurbulenceNED(eX) = 0.0;
 477 //    vTurbulenceNED(eY) = 0.0;
 478
 479     break;
 480   }
 481   case ttBerndt: { // This is very experimental and incomplete at the moment.
 482
 483     vDirectiondAccelDt(eX) = GaussianRandomNumber();
 484     vDirectiondAccelDt(eY) = GaussianRandomNumber();
 485     vDirectiondAccelDt(eZ) = GaussianRandomNumber();
 486 /*
 487     MagnitudedAccelDt = GaussianRandomNumber();
 488     MagnitudeAccel    += MagnitudedAccelDt * DeltaT;
 489     Magnitude         += MagnitudeAccel * DeltaT;
 490 */
 491     Magnitude         += GaussianRandomNumber() * DeltaT;
 492
 493     vDirectiondAccelDt.Normalize();
 494     vDirectionAccel += TurbRate * vDirectiondAccelDt * DeltaT;
 495     vDirectionAccel.Normalize();
 496     vDirection      += vDirectionAccel*DeltaT;
 497
 498     // Diminish z-vector within two wingspans of the ground
 499     double HOverBMAC = Auxiliary->GetHOverBMAC();
 500     if (HOverBMAC < 2.0) vDirection(eZ) *= HOverBMAC / 2.0;
 501
 502     vDirection.Normalize();
 503
 504     vTurbulenceNED = TurbGain*Magnitude * vDirection;
 505     vTurbulenceGrad = TurbGain*MagnitudeAccel * vDirection;
 506
 507     vBodyTurbGrad = Propagate->GetTl2b() * vTurbulenceGrad;
 508     vTurbPQR(eP) = vBodyTurbGrad(eY) / Aircraft->GetWingSpan();
 509     if (Aircraft->GetHTailArm() > 0)
 510       vTurbPQR(eQ) = vBodyTurbGrad(eZ) / Aircraft->GetHTailArm();
 511     else
 512       vTurbPQR(eQ) = vBodyTurbGrad(eZ) / 10.0;
 513
 514     if (Aircraft->GetVTailArm() > 0)
 515       vTurbPQR(eR) = vBodyTurbGrad(eX) / Aircraft->GetVTailArm();
 516     else
 517       vTurbPQR(eR) = vBodyTurbGrad(eX)/10.0;
 518
 519     break;
 520   }
 521   case ttCulp: {
 522
 523     vTurbPQR(eP) = wind_from_clockwise;
 524     if (TurbGain == 0.0) return;
 525
 526     // keep the inputs within allowable limts for this model
 527     if (TurbGain < 0.0) TurbGain = 0.0;
 528     if (TurbGain > 1.0) TurbGain = 1.0;
 529     if (TurbRate < 0.0) TurbRate = 0.0;
 530     if (TurbRate > 30.0) TurbRate = 30.0;
 531     if (Rhythmicity < 0.0) Rhythmicity = 0.0;
 532     if (Rhythmicity > 1.0) Rhythmicity = 1.0;
 533
 534     // generate a sine wave corresponding to turbulence rate in hertz
 535     double time = FDMExec->GetSimTime();
 536     double sinewave = sin( time * TurbRate * 6.283185307 );
 537
 538     double random = 0.0;
 539     if (target_time == 0.0) {
 540       strength = random = 1 - 2.0*(double(rand())/double(RAND_MAX));
 541       target_time = time + 0.71 + (random * 0.5);
 542     }
 543     if (time > target_time) {
 544       spike = 1.0;
 545       target_time = 0.0;
 546     }
 547
 548     // max vertical wind speed in fps, corresponds to TurbGain = 1.0
 549     double max_vs = 40;
 550
 551     vTurbulenceNED(1) = vTurbulenceNED(2) = vTurbulenceNED(3) = 0.0;
 552     double delta = strength * max_vs * TurbGain * (1-Rhythmicity) * spike;
 553
 554     // Vertical component of turbulence.
 555     vTurbulenceNED(3) = sinewave * max_vs * TurbGain * Rhythmicity;
 556     vTurbulenceNED(3)+= delta;
 557     double HOverBMAC = Auxiliary->GetHOverBMAC();
 558     if (HOverBMAC < 3.0)
 559         vTurbulenceNED(3) *= HOverBMAC * 0.3333;
 560
 561     // Yaw component of turbulence.
 562     vTurbulenceNED(1) = sin( delta * 3.0 );
 563     vTurbulenceNED(2) = cos( delta * 3.0 );
 564
 565     // Roll component of turbulence. Clockwise vortex causes left roll.
 566     vTurbPQR(eP) += delta * 0.04;
 567
 568     spike = spike * 0.9;
 569     break;
 570   }
 571   case ttMilspec:
 572   case ttTustin: {
 573     // an index of zero means turbulence is disabled
 574     if (probability_of_exceedence_index == 0) {
 575       vTurbulenceNED(1) = vTurbulenceNED(2) = vTurbulenceNED(3) = 0.0;
 576       vTurbPQR(1) = vTurbPQR(2) = vTurbPQR(3) = 0.0;
 577       return;
 578     }
 579
 580     // Turbulence model according to MIL-F-8785C (Flying Qualities of Piloted Aircraft)
 581     double
 582       h = Propagate->GetDistanceAGL(),
 583       V = Auxiliary->GetVt(), // true airspeed in ft/s
 584       b_w = Aircraft->GetWingSpan(),
 585       L_u, L_w, sig_u, sig_w;
 586
 587     // clip height functions at 10 ft
 588     if (h <= 10.) h = 10;
 589
 590     // Scale lengths L and amplitudes sigma as function of height
 591     if (h <= 1000) {
 592       L_u = h/pow(0.177 + 0.000823*h, 1.2); // MIL-F-8785c, Fig. 10, p. 55
 593       L_w = h;
 594       sig_w = 0.1*windspeed_at_20ft;
 595       sig_u = sig_w/pow(0.177 + 0.000823*h, 0.4); // MIL-F-8785c, Fig. 11, p. 56
 596     } else if (h <= 2000) {
 597       // linear interpolation between low altitude and high altitude models
 598       L_u = L_w = 1000 + (h-1000.)/1000.*750.;
 599       sig_u = sig_w = 0.1*windspeed_at_20ft
 600                     + (h-1000.)/1000.*(POE_Table->GetValue(probability_of_exceedence_index, h) - 0.1*windspeed_at_20ft);
 601     } else {
 602       L_u = L_w = 1750.; //  MIL-F-8785c, Sec. 3.7.2.1, p. 48
 603       sig_u = sig_w = POE_Table->GetValue(probability_of_exceedence_index, h);
 604     }
 605
 606     // keep values from last timesteps
 607     // TODO maybe use deque?
 608     static double
 609       xi_u_km1 = 0, nu_u_km1 = 0,
 610       xi_v_km1 = 0, xi_v_km2 = 0, nu_v_km1 = 0, nu_v_km2 = 0,
 611       xi_w_km1 = 0, xi_w_km2 = 0, nu_w_km1 = 0, nu_w_km2 = 0,
 612       xi_p_km1 = 0, nu_p_km1 = 0,
 613       xi_q_km1 = 0, xi_r_km1 = 0;
 614
 615
 616     double
 617       T_V = DeltaT, // for compatibility of nomenclature
 618       sig_p = 1.9/sqrt(L_w*b_w)*sig_w, // Yeager1998, eq. (8)
 619       sig_q = sqrt(M_PI/2/L_w/b_w), // eq. (14)
 620       sig_r = sqrt(2*M_PI/3/L_w/b_w), // eq. (17)
 621       L_p = sqrt(L_w*b_w)/2.6, // eq. (10)
 622       tau_u = L_u/V, // eq. (6)
 623       tau_w = L_w/V, // eq. (3)
 624       tau_p = L_p/V, // eq. (9)
 625       tau_q = 4*b_w/M_PI/V, // eq. (13)
 626       tau_r =3*b_w/M_PI/V, // eq. (17)
 627       nu_u = GaussianRandomNumber(),
 628       nu_v = GaussianRandomNumber(),
 629       nu_w = GaussianRandomNumber(),
 630       nu_p = GaussianRandomNumber(),
 631       xi_u, xi_v, xi_w, xi_p, xi_q, xi_r;
 632
 633     // values of turbulence NED velocities
 634
 635     if (turbType == ttTustin) {
 636       // the following is the Tustin formulation of Yeager's report
 637       double
 638         omega_w = V/L_w, // hidden in nomenclature p. 3
 639         omega_v = V/L_u, // this is defined nowhere
 640         C_BL  = 1/tau_u/tan(T_V/2/tau_u), // eq. (19)
 641         C_BLp = 1/tau_p/tan(T_V/2/tau_p), // eq. (22)
 642         C_BLq = 1/tau_q/tan(T_V/2/tau_q), // eq. (24)
 643         C_BLr = 1/tau_r/tan(T_V/2/tau_r); // eq. (26)
 644
 645       xi_u = -(1 - C_BL*tau_u)/(1 + C_BL*tau_u)*xi_u_km1
 646            + sig_u*sqrt(2*tau_u/T_V)/(1 + C_BL*tau_u)*(nu_u + nu_u_km1); // eq. (18)
 647       xi_v = -2*(sqr(omega_v) - sqr(C_BL))/sqr(omega_v + C_BL)*xi_v_km1
 648            - sqr(omega_v - C_BL)/sqr(omega_v + C_BL) * xi_v_km2
 649            + sig_u*sqrt(3*omega_v/T_V)/sqr(omega_v + C_BL)*(
 650                  (C_BL + omega_v/sqrt(3.))*nu_v
 651                + 2/sqrt(3.)*omega_v*nu_v_km1
 652                + (omega_v/sqrt(3.) - C_BL)*nu_v_km2); // eq. (20) for v
 653       xi_w = -2*(sqr(omega_w) - sqr(C_BL))/sqr(omega_w + C_BL)*xi_w_km1
 654            - sqr(omega_w - C_BL)/sqr(omega_w + C_BL) * xi_w_km2
 655            + sig_w*sqrt(3*omega_w/T_V)/sqr(omega_w + C_BL)*(
 656                  (C_BL + omega_w/sqrt(3.))*nu_w
 657                + 2/sqrt(3.)*omega_w*nu_w_km1
 658                + (omega_w/sqrt(3.) - C_BL)*nu_w_km2); // eq. (20) for w
 659       xi_p = -(1 - C_BLp*tau_p)/(1 + C_BLp*tau_p)*xi_p_km1
 660            + sig_p*sqrt(2*tau_p/T_V)/(1 + C_BLp*tau_p) * (nu_p + nu_p_km1); // eq. (21)
 661       xi_q = -(1 - 4*b_w*C_BLq/M_PI/V)/(1 + 4*b_w*C_BLq/M_PI/V) * xi_q_km1
 662            + C_BLq/V/(1 + 4*b_w*C_BLq/M_PI/V) * (xi_w - xi_w_km1); // eq. (23)
 663       xi_r = - (1 - 3*b_w*C_BLr/M_PI/V)/(1 + 3*b_w*C_BLr/M_PI/V) * xi_r_km1
 664            + C_BLr/V/(1 + 3*b_w*C_BLr/M_PI/V) * (xi_v - xi_v_km1); // eq. (25)
 665
 666     } else if (turbType == ttMilspec) {
 667       // the following is the MIL-STD-1797A formulation
 668       // as cited in Yeager's report
 669       xi_u = (1 - T_V/tau_u)  *xi_u_km1 + sig_u*sqrt(2*T_V/tau_u)*nu_u;  // eq. (30)
 670       xi_v = (1 - 2*T_V/tau_u)*xi_v_km1 + sig_u*sqrt(4*T_V/tau_u)*nu_v;  // eq. (31)
 671       xi_w = (1 - 2*T_V/tau_w)*xi_w_km1 + sig_w*sqrt(4*T_V/tau_w)*nu_w;  // eq. (32)
 672       xi_p = (1 - T_V/tau_p)  *xi_p_km1 + sig_p*sqrt(2*T_V/tau_p)*nu_p;  // eq. (33)
 673       xi_q = (1 - T_V/tau_q)  *xi_q_km1 + M_PI/4/b_w*(xi_w - xi_w_km1);  // eq. (34)
 674       xi_r = (1 - T_V/tau_r)  *xi_r_km1 + M_PI/3/b_w*(xi_v - xi_v_km1);  // eq. (35)
 675     }
 676
 677     // rotate by wind azimuth and assign the velocities
 678     double cospsi = cos(psiw), sinpsi = sin(psiw);
 679     vTurbulenceNED(1) =  cospsi*xi_u + sinpsi*xi_v;
 680     vTurbulenceNED(2) = -sinpsi*xi_u + cospsi*xi_v;
 681     vTurbulenceNED(3) = xi_w;
 682
 683     vTurbPQR(1) =  cospsi*xi_p + sinpsi*xi_q;
 684     vTurbPQR(2) = -sinpsi*xi_p + cospsi*xi_q;
 685     vTurbPQR(3) = xi_r;
 686
 687     // vTurbPQR is in the body fixed frame, not NED
 688     vTurbPQR = Propagate->GetTl2b()*vTurbPQR;
 689
 690     // hand on the values for the next timestep
 691     xi_u_km1 = xi_u; nu_u_km1 = nu_u;
 692     xi_v_km2 = xi_v_km1; xi_v_km1 = xi_v; nu_v_km2 = nu_v_km1; nu_v_km1 = nu_v;
 693     xi_w_km2 = xi_w_km1; xi_w_km1 = xi_w; nu_w_km2 = nu_w_km1; nu_w_km1 = nu_w;
 694     xi_p_km1 = xi_p; nu_p_km1 = nu_p;
 695     xi_q_km1 = xi_q;
 696     xi_r_km1 = xi_r;
 697
 698   }
 699   default:
 700     break;
 701   }
 702 }
 703
 704 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 705
 706 void FGAtmosphere::UseExternal(void)
 707 {
 708   temperature=&exTemperature;
 709   pressure=&exPressure;
 710   density=&exDensity;
 711   useExternal=true;
 712 }
 713
 714 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 715
 716 void FGAtmosphere::UseInternal(void)
 717 {
 718   temperature=&intTemperature;
 719   pressure=&intPressure;
 720   density=&intDensity;
 721   useExternal=false;
 722 }
 723
 724 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 725
 726 void FGAtmosphere::bind(void)
 727 {
 728   typedef double (FGAtmosphere::*PMF)(int) const;
 729   typedef double (FGAtmosphere::*PMFv)(void) const;
 730   typedef int (FGAtmosphere::*PMFt)(void) const;
 731   typedef void   (FGAtmosphere::*PMFd)(int,double);
 732   typedef void   (FGAtmosphere::*PMFi)(int);
 733   PropertyManager->Tie("atmosphere/T-R", this, (PMFv)&FGAtmosphere::GetTemperature);
 734   PropertyManager->Tie("atmosphere/rho-slugs_ft3", this, (PMFv)&FGAtmosphere::GetDensity);
 735   PropertyManager->Tie("atmosphere/P-psf", this, (PMFv)&FGAtmosphere::GetPressure);
 736   PropertyManager->Tie("atmosphere/a-fps", this, &FGAtmosphere::GetSoundSpeed);
 737   PropertyManager->Tie("atmosphere/T-sl-R", this, &FGAtmosphere::GetTemperatureSL);
 738   PropertyManager->Tie("atmosphere/rho-sl-slugs_ft3", this, &FGAtmosphere::GetDensitySL);
 739   PropertyManager->Tie("atmosphere/P-sl-psf", this, &FGAtmosphere::GetPressureSL);
 740   PropertyManager->Tie("atmosphere/a-sl-fps", this, &FGAtmosphere::GetSoundSpeedSL);
 741   PropertyManager->Tie("atmosphere/theta", this, &FGAtmosphere::GetTemperatureRatio);
 742   PropertyManager->Tie("atmosphere/sigma", this, &FGAtmosphere::GetDensityRatio);
 743   PropertyManager->Tie("atmosphere/delta", this, &FGAtmosphere::GetPressureRatio);
 744   PropertyManager->Tie("atmosphere/a-ratio", this, &FGAtmosphere::GetSoundSpeedRatio);
 745   PropertyManager->Tie("atmosphere/psiw-rad", this, &FGAtmosphere::GetWindPsi, &FGAtmosphere::SetWindPsi);
 746   PropertyManager->Tie("atmosphere/delta-T", this, &FGAtmosphere::GetDeltaT, &FGAtmosphere::SetDeltaT);
 747   PropertyManager->Tie("atmosphere/T-sl-dev-F", this, &FGAtmosphere::GetSLTempDev, &FGAtmosphere::SetSLTempDev);
 748   PropertyManager->Tie("atmosphere/density-altitude", this, &FGAtmosphere::GetDensityAltitude);
 749
 750   PropertyManager->Tie("atmosphere/wind-north-fps", this, eNorth, (PMF)&FGAtmosphere::GetWindNED,
 751                                                           (PMFd)&FGAtmosphere::SetWindNED);
 752   PropertyManager->Tie("atmosphere/wind-east-fps",  this, eEast, (PMF)&FGAtmosphere::GetWindNED,
 753                                                           (PMFd)&FGAtmosphere::SetWindNED);
 754   PropertyManager->Tie("atmosphere/wind-down-fps",  this, eDown, (PMF)&FGAtmosphere::GetWindNED,
 755                                                           (PMFd)&FGAtmosphere::SetWindNED);
 756   PropertyManager->Tie("atmosphere/wind-mag-fps", this, &FGAtmosphere::GetWindspeed,
 757                                                         &FGAtmosphere::SetWindspeed);
 758   PropertyManager->Tie("atmosphere/total-wind-north-fps", this, eNorth, (PMF)&FGAtmosphere::GetTotalWindNED);
 759   PropertyManager->Tie("atmosphere/total-wind-east-fps",  this, eEast,  (PMF)&FGAtmosphere::GetTotalWindNED);
 760   PropertyManager->Tie("atmosphere/total-wind-down-fps",  this, eDown,  (PMF)&FGAtmosphere::GetTotalWindNED);
 761
 762   PropertyManager->Tie("atmosphere/gust-north-fps", this, eNorth, (PMF)&FGAtmosphere::GetGustNED,
 763                                                           (PMFd)&FGAtmosphere::SetGustNED);
 764   PropertyManager->Tie("atmosphere/gust-east-fps",  this, eEast, (PMF)&FGAtmosphere::GetGustNED,
 765                                                           (PMFd)&FGAtmosphere::SetGustNED);
 766   PropertyManager->Tie("atmosphere/gust-down-fps",  this, eDown, (PMF)&FGAtmosphere::GetGustNED,
 767                                                           (PMFd)&FGAtmosphere::SetGustNED);
 768
 769   PropertyManager->Tie("atmosphere/turb-north-fps", this, eNorth, (PMF)&FGAtmosphere::GetTurbNED,
 770                                                           (PMFd)&FGAtmosphere::SetTurbNED);
 771   PropertyManager->Tie("atmosphere/turb-east-fps",  this, eEast, (PMF)&FGAtmosphere::GetTurbNED,
 772                                                           (PMFd)&FGAtmosphere::SetTurbNED);
 773   PropertyManager->Tie("atmosphere/turb-down-fps",  this, eDown, (PMF)&FGAtmosphere::GetTurbNED,
 774                                                           (PMFd)&FGAtmosphere::SetTurbNED);
 775
 776   PropertyManager->Tie("atmosphere/p-turb-rad_sec", this,1, (PMF)&FGAtmosphere::GetTurbPQR);
 777   PropertyManager->Tie("atmosphere/q-turb-rad_sec", this,2, (PMF)&FGAtmosphere::GetTurbPQR);
 778   PropertyManager->Tie("atmosphere/r-turb-rad_sec", this,3, (PMF)&FGAtmosphere::GetTurbPQR);
 779   PropertyManager->Tie("atmosphere/turb-type", this, (PMFt)&FGAtmosphere::GetTurbType, (PMFi)&FGAtmosphere::SetTurbType);
 780   PropertyManager->Tie("atmosphere/turb-rate", this, &FGAtmosphere::GetTurbRate, &FGAtmosphere::SetTurbRate);
 781   PropertyManager->Tie("atmosphere/turb-gain", this, &FGAtmosphere::GetTurbGain, &FGAtmosphere::SetTurbGain);
 782   PropertyManager->Tie("atmosphere/turb-rhythmicity", this, &FGAtmosphere::GetRhythmicity,
 783                                                             &FGAtmosphere::SetRhythmicity);
 784
 785   PropertyManager->Tie("atmosphere/turbulence/milspec/windspeed_at_20ft_AGL-fps",
 786                        this, &FGAtmosphere::GetWindspeed20ft,
 787                              &FGAtmosphere::SetWindspeed20ft);
 788   PropertyManager->Tie("atmosphere/turbulence/milspec/severity",
 789                        this, &FGAtmosphere::GetProbabilityOfExceedence,
 790                              &FGAtmosphere::SetProbabilityOfExceedence);
 791
 792 }
 793
 794 //%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 795 //    The bitmasked value choices are as follows:
 796 //    unset: In this case (the default) JSBSim would only print
 797 //       out the normally expected messages, essentially echoing
 798 //       the config files as they are read. If the environment
 799 //       variable is not set, debug_lvl is set to 1 internally
 800 //    0: This requests JSBSim not to output any messages
 801 //       whatsoever.
 802 //    1: This value explicity requests the normal JSBSim
 803 //       startup messages
 804 //    2: This value asks for a message to be printed out when
 805 //       a class is instantiated
 806 //    4: When this value is set, a message is displayed when a
 807 //       FGModel object executes its Run() method
 808 //    8: When this value is set, various runtime state variables
 809 //       are printed out periodically
 810 //    16: When set various parameters are sanity checked and
 811 //       a message is printed out when they go out of bounds
 812
 813 void FGAtmosphere::Debug(int from)
 814 {
 815   if (debug_lvl <= 0) return;
 816
 817   if (debug_lvl & 1) { // Standard console startup message output
 818     if (from == 0) { // Constructor
 819     }
 820   }
 821   if (debug_lvl & 2 ) { // Instantiation/Destruction notification
 822     if (from == 0) cout << "Instantiated: FGAtmosphere" << endl;
 823     if (from == 1) cout << "Destroyed:    FGAtmosphere" << endl;
 824   }
 825   if (debug_lvl & 4 ) { // Run() method entry print for FGModel-derived objects
 826   }
 827   if (debug_lvl & 8 ) { // Runtime state variables
 828   }
 829   if (debug_lvl & 16) { // Sanity checking
 830   }
 831   if (debug_lvl & 128) { // Turbulence
 832     if (first_pass && from == 2) {
 833       first_pass = false;
 834       cout << "vTurbulenceNED(X), vTurbulenceNED(Y), vTurbulenceNED(Z), "
 835            << "vTurbulenceGrad(X), vTurbulenceGrad(Y), vTurbulenceGrad(Z), "
 836            << "vDirection(X), vDirection(Y), vDirection(Z), "
 837            << "Magnitude, "
 838            << "vTurbPQR(P), vTurbPQR(Q), vTurbPQR(R), " << endl;
 839     }
 840     if (from == 2) {
 841       cout << vTurbulenceNED << ", " << vTurbulenceGrad << ", " << vDirection << ", " << Magnitude << ", " << vTurbPQR << endl;
 842     }
 843   }
 844   if (debug_lvl & 64) {
 845     if (from == 0) { // Constructor
 846       cout << IdSrc << endl;
 847       cout << IdHdr << endl;
 848     }
 849   }
 850 }
 851
 852 } // namespace JSBSim