src/FDM/SP/BalloonSim.cpp

   1 /*****************************************************************************
   2
   3  Module:       BalloonSim.cpp
   4  Author:       Christian Mayer
   5  Date started: 01.09.99
   6  Called by:
   7
   8  -------- Copyright (C) 1999 Christian Mayer (fgfs@christianmayer.de) --------
   9
  10  This program is free software; you can redistribute it and/or modify it under
  11  the terms of the GNU General Public License as published by the Free Software
  12  Foundation; either version 2 of the License, or (at your option) any later
  13  version.
  14
  15  This program is distributed in the hope that it will be useful, but WITHOUT
  16  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  17  FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
  18  details.
  19
  20  You should have received a copy of the GNU General Public License
  21  along with this program; if not, write to the Free Software
  22  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  23
  24  Further information about the GNU General Public License can also be found on
  25  the world wide web at http://www.gnu.org.
  26
  27 FUNCTIONAL DESCRIPTION
  28 ------------------------------------------------------------------------------
  29 A hot air balloon simulator
  30
  31 HISTORY
  32 ------------------------------------------------------------------------------
  33 01.09.1999 Christian Mayer      Created
  34 03.10.1999 Christian Mayer      cleaned  the code  by moveing  WeatherDatabase
  35                                 calls inside the update()
  36 *****************************************************************************/
  37
  38 /****************************************************************************/
  39 /* INCLUDES                                                                 */
  40 /****************************************************************************/
  41
  42 #ifdef HAVE_CONFIG_H
  43 #  include "config.h"
  44 #endif
  45
  46 #include <stdio.h>
  47 #include <math.h>
  48
  49 #include <simgear/constants.h>
  50
  51 #include <Aircraft/aircraft.hxx>
  52
  53 #include "BalloonSim.h"
  54
  55 /****************************************************************************/
  56 /********************************** CODE ************************************/
  57 /****************************************************************************/
  58
  59 /****************************************************************************/
  60 /*                                                                          */
  61 /*  Constructor:                                                            */
  62 /*  Set the balloon model to some values that seem reasonable as I haven't  */
  63 /*  got much original values                                                */
  64 /*                                                                          */
  65 /****************************************************************************/
  66 balloon::balloon()
  67 {
  68     dt = 0.1;
  69     ground_level = 3400.0;
  70
  71     gravity_vector = SGVec3f(0.0, 0.0, -9.81);
  72     velocity = SGVec3f(0.0, 0.0, 0.0);
  73     position = SGVec3f(0.0, 0.0, 0.0);
  74     hpr = SGVec3f(0.0, 0.0, 0.0);
  75
  76     /************************************************************************/
  77     /* My balloon  has a  radius of  8.8 metres  as that  gives a  envelope */
  78     /* volume of about 2854 m^3  which is  about 77000 ft^3,  a very common */
  79     /* size for hot air balloons                                            */
  80     /************************************************************************/
  81
  82     balloon_envelope_area = 4.0 * (8.8 * 8.8) * SGD_PI;
  83     balloon_envelope_volume = (4.0/3.0) * (8.8 * 8.8 * 8.8) * SGD_PI;
  84
  85     wind_facing_area_of_balloon = SGD_PI * (8.8 * 8.8);
  86     wind_facing_area_of_basket = 2.0;   //guessed: 2 m^2
  87
  88     cw_envelope=0.45;                   //a sphere in this case
  89     cw_basket=0.8;
  90
  91     weight_of_total_fuel = 40.0;        //big guess
  92     weight_of_envelope = 200.0;         //big guess
  93     weight_of_basket = 40.0;            //big guess
  94     weight_of_cargo = 750.0;            //big guess
  95
  96     fuel_left=1.0;
  97     max_flow_of_fuel_per_second=10.0*1.0/3600.0; //assuming 10% of one hour of total burn time
  98     current_burner_strength = 0.0;      //the throttle
  99
 100     lambda = 0.15;                      //for plasic
 101     l_of_the_envelope = 1.0/1000.0;     //the thickness of the envelope (in m): 1mm
 102
 103     T = 273.16 + 130.6;                 //Temperature in the envelope => still at ground level
 104 }
 105
 106 void balloon::update()
 107 {
 108     /************************************************************************/
 109     /* I'm  simplifying  the  balloon by  reducing the  simulation  to  two */
 110     /* points:                                                              */
 111     /* the center of the basket (CB) and the center of the envelope (CE)    */
 112     /*                                                                      */
 113     /*                                 ce                                   */
 114     /*                                 I                                    */
 115     /*                                 I                                    */
 116     /*                                 cg (=center of gravity)              */
 117     /*                                 I                                    */
 118     /*                                 cb                                   */
 119     /*                                                                      */
 120     /* On each center  are forces acting:  gravity and  wind resitance.  CE */
 121     /* additionally got the lift  (=> I need to calculate the weight of the */
 122     /* air inside, too)                                                     */
 123     /*                                                                      */
 124     /* The weight of the air  in the envelope is  dependant of the tempera- */
 125     /* ture. This temperature is decreasing over the time that is dependant */
 126     /* of the insulation  of the envelope  material (lambda),  the gas used */
 127     /* (air) and the wind speed. For a plane surface it's for air:          */
 128     /*                                                                      */
 129     /*    alpha = 4.8 + 3.4*v   with v < 5.0 m/s                            */
 130     /*                                                                      */
 131     /* The value k that takes all of that into account is defined as:       */
 132     /*                                                                      */
 133     /*    1 / k = 1 / alpha1 + 1 / alpha2 + l / lambda                      */
 134     /*                                                                      */
 135     /* with 'l' beeing the 'length' i.e. thickness of the insulator, alpha1 */
 136     /* the air inside and alpha2 the air outside of the envelope.  So our k */
 137     /* is:                                                                  */
 138     /*                                                                      */
 139     /*    k = 1 / [1/4.8 + 1/(4.8+3.4v) + l/lambda]                         */
 140     /*                                                                      */
 141     /* The energy lost by this process is defined as:                       */
 142     /*                                                                      */
 143     /*    dQ = k * A * t * dT                                               */
 144     /*                                                                      */
 145     /* with Q being  the energy,  k that value  defined above,  A the total */
 146     /* area of the envelope,  t the time (in hours)  and dT the temperature */
 147     /* difference between the inside and the outside.                       */
 148     /* To get the temperature of the air in the inside I need the formula:  */
 149     /*                                                                      */
 150     /*    dQ = cAir * m * dT                                                */
 151     /*                                                                      */
 152     /* with cAir being the specific heat capacity(?)  of air (= 1.00 kcal / */
 153     /* kg * degree),  m the mass of the air and  dT the temperature change. */
 154     /* As the envelope is open I'm  assuming that the  same air pressure is */
 155     /* inside and  outside of  it  (practical there  should  be  a slightly */
 156     /* higher air pressure  in the inside or the envelope  would collapse). */
 157     /* So it's easy to calculate the density of the air inside:             */
 158     /*                                                                      */
 159     /*    rho = p / R * T                                                   */
 160     /*                                                                      */
 161     /* with p being  the pressure,  R the gas constant(?)  which is for air */
 162     /* 287.14 N * m / kg * K and T the absolute temperature.                */
 163     /*                                                                      */
 164     /* The value returned by this function is the displacement of the CB    */
 165     /************************************************************************/
 166
 167     /************************************************************************/
 168     /* NOTE:  This is the simplified version:  I'm assuming that  the whole */
 169     /* balloon consists only of the envelope.I will improove the simulation */
 170     /* later, but currently was my main concern to get it going...          */
 171     /************************************************************************/
 172
 173    // I realy don't think there is a solution for this without WeatherCM
 174    // but this is a hack, and it's working -- EMH
 175    double mAir = 1;
 176    float Q = 0;
 177
 178     // gain of energy by heating:
 179     if (fuel_left > 0.0)        //but only with some fuel left ;-)
 180     {
 181         float fuel_burning = current_burner_strength * max_flow_of_fuel_per_second * dt * weight_of_total_fuel; //in kg
 182
 183         //convert to cubemetres (I'm wrongly assuming 'normal' conditions; but that's correct for my special case)
 184         float cube_metres_burned = fuel_burning / 2.2;  //2.2 is the density for propane
 185
 186         fuel_left -= fuel_burning / weight_of_total_fuel;
 187
 188         // get energy through burning.
 189         Q += 22250.0 * cube_metres_burned;  //22250 for propan, 29500 would be butane and if you dare: 2580 would be hydrogen...
 190     }
 191
 192     // calculate the new temperature in the inside:
 193     T += Q / (1.00 * mAir);
 194
 195     //calculate the masses of the envelope and the basket
 196     float mEnvelope = mAir + weight_of_envelope;
 197     float mBasket   = weight_of_total_fuel*fuel_left + weight_of_basket + weight_of_cargo;
 198
 199     float mTotal = mEnvelope + mBasket;
 200
 201     //calulate the forces
 202     SGVec3f fTotal, fFriction, fLift;
 203
 204     fTotal = mTotal*gravity_vector;
 205
 206     // fTotal += fLift;     //FIXME: uninitialized fLift
 207     // fTotal += fFriction; //FIXME: uninitialized fFriction
 208
 209     //claculate acceleration: a = F / m
 210     SGVec3f aTotal, vTotal, dTotal;
 211
 212     aTotal = (1.0 / mTotal)*fTotal;
 213
 214     //integrate the displacement: d = 0.5 * a * dt**2 + v * dt + d
 215     vTotal = dt*velocity;
 216     dTotal = (0.5*dt*dt)*aTotal; dTotal += vTotal;
 217
 218     //integrate the velocity to 'velocity': v = a * dt + v
 219     vTotal = dt*aTotal; velocity += vTotal;
 220
 221     /************************************************************************/
 222     /* VERY WRONG STUFF: it's just here to get some results to start with   */
 223     /************************************************************************/
 224
 225     // care for the ground
 226     if (position[2] < (ground_level+0.001) )
 227         position[2] = ground_level;
 228
 229     //return results
 230     position += dTotal;
 231
 232     //cout << "BallonSim: T: " << (T-273.16) << " alt: " << position[2] << " ground: " << ground_level << " throttle: " << current_burner_strength << "\n";
 233 }
 234
 235 void balloon::set_burner_strength(const float bs)
 236 {
 237     if ((bs>=0.0) && (bs<=1.0))
 238     current_burner_strength = bs;
 239 }
 240
 241 void balloon::getVelocity(SGVec3f& v) const
 242 {
 243     v = velocity;
 244 }
 245
 246 void balloon::setVelocity(const SGVec3f& v)
 247 {
 248     velocity = v;
 249 }
 250
 251 void balloon::getPosition(SGVec3f& v) const
 252 {
 253     v = position;
 254 }
 255
 256 void balloon::setPosition(const SGVec3f& v)
 257 {
 258     position = v;
 259 }
 260
 261 void balloon::getHPR(SGVec3f& angles) const //the balloon isn't allways exactly vertical
 262 {
 263     angles = hpr;
 264 }
 265
 266 void balloon::setHPR(const SGVec3f& angles)  //the balloon isn't allways exactly vertical
 267 {
 268     hpr = angles;
 269 }
 270
 271 void balloon::setGroundLevel(const float altitude)
 272 {
 273     ground_level = altitude;
 274 }
 275
 276 float balloon::getTemperature(void) const
 277 {
 278     return T;
 279 }
 280
 281 float balloon::getFuelLeft(void) const
 282 {
 283     return fuel_left;
 284 }
 285
 286 /*
 287 void main(void)
 288 {
 289     bool burner = true;
 290     balloon bal;
 291     bool exit = false;
 292     sgVec3 pos={0.0, 0.0, 0.0};
 293     char c;
 294     float acc_dt = 0.0;
 295     float alt;
 296
 297 bool hysteresis = false; // moving up
 298     for (;!exit;)
 299     {
 300         for (int i=0; i<100; i++)
 301         {
 302             bal.update(0.1); acc_dt += 0.1;
 303             bal.getPosition(pos);
 304             alt = pos[2];
 305
 306             if (alt > 3010)
 307             {
 308                 hysteresis = true;
 309                 burner = false;
 310             }
 311             if ((alt < 2990) && (hysteresis == true))
 312             {
 313                 hysteresis = false;
 314                 burner = true;
 315             }
 316             if ((bal.getTemperature()-273.16)>250.0)
 317                 burner = false; //emergency
 318         }
 319
 320         // toogle burner
 321         c = getch();
 322         if (c==' ')
 323             burner=!burner;
 324         //if (c=='s')
 325         //    show=!show;
 326
 327         //printf("Position: (%f/%f/%f), dP: (%f/%f/%f), burner: ", pos[0], pos[1], pos[2], dp[0], dp[1], dp[2]);
 328         printf("%f         \t%f         \t%f         \t%f\n", acc_dt/60.0, bal.getTemperature()-273.16, pos[2], bal.getFuelLeft());
 329         if (burner==true)
 330         {
 331             //printf("on\n");
 332             bal.set_burner_strength(1.0);
 333         }
 334         else
 335         {
 336             //printf("off\n");
 337             bal.set_burner_strength(0.0);
 338         }
 339
 340     }
 341 }
 342 */