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flightgear/src/FDM/JSBSim/models/FGGasCell.cpp
Erik Hofman 4a817a6307 Sync. with JSBSim CVS
2011-01-23 15:14:01 +01:00

863 lines
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/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Header: FGGasCell.h
Author: Anders Gidenstam
Date started: 01/21/2006
----- Copyright (C) 2006 - 2008 Anders Gidenstam (anders(at)gidenstam.org) --
This program is free software; you can redistribute it and/or modify it under
the terms of the GNU Lesser 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 Lesser General Public License for more
details.
You should have received a copy of the GNU Lesser 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 Lesser General Public License can also be found on
the world wide web at http://www.gnu.org.
FUNCTIONAL DESCRIPTION
--------------------------------------------------------------------------------
See header file.
HISTORY
--------------------------------------------------------------------------------
01/21/2006 AG Created
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
INCLUDES
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
#include "FGFDMExec.h"
#include "models/FGAuxiliary.h"
#include "models/FGAtmosphere.h"
#include "models/FGInertial.h"
#include "models/FGMassBalance.h"
#include "FGGasCell.h"
#include "input_output/FGXMLElement.h"
#include <iostream>
#include <cstdlib>
using std::cerr;
using std::endl;
using std::cout;
using std::string;
using std::max;
namespace JSBSim {
static const char *IdSrc = "$Id: FGGasCell.cpp,v 1.13 2010/12/29 22:39:25 andgi Exp $";
static const char *IdHdr = ID_GASCELL;
/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
CLASS IMPLEMENTATION
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
/* Constants. */
const double FGGasCell::R = 3.4071; // [lbs ft/(mol Rankine)]
const double FGGasCell::M_air = 0.0019186; // [slug/mol]
const double FGGasCell::M_hydrogen = 0.00013841; // [slug/mol]
const double FGGasCell::M_helium = 0.00027409; // [slug/mol]
FGGasCell::FGGasCell(FGFDMExec* exec, Element* el, int num) : FGForce(exec)
{
string token;
Element* element;
Auxiliary = exec->GetAuxiliary();
Atmosphere = exec->GetAtmosphere();
PropertyManager = exec->GetPropertyManager();
Inertial = exec->GetInertial();
MassBalance = exec->GetMassBalance();
gasCellJ = FGMatrix33();
gasCellM = FGColumnVector3();
Buoyancy = MaxVolume = MaxOverpressure = Temperature = Pressure =
Contents = Volume = dVolumeIdeal = 0.0;
Xradius = Yradius = Zradius = Xwidth = Ywidth = Zwidth = 0.0;
ValveCoefficient = ValveOpen = 0.0;
CellNum = num;
// NOTE: In the local system X points north, Y points east and Z points down.
SetTransformType(FGForce::tLocalBody);
type = el->GetAttributeValue("type");
if (type == "HYDROGEN") Type = ttHYDROGEN;
else if (type == "HELIUM") Type = ttHELIUM;
else if (type == "AIR") Type = ttAIR;
else Type = ttUNKNOWN;
element = el->FindElement("location");
if (element) {
vXYZ = element->FindElementTripletConvertTo("IN");
} else {
cerr << "Fatal Error: No location found for this gas cell." << endl;
exit(-1);
}
if ((el->FindElement("x_radius") || el->FindElement("x_width")) &&
(el->FindElement("y_radius") || el->FindElement("y_width")) &&
(el->FindElement("z_radius") || el->FindElement("z_width"))) {
if (el->FindElement("x_radius")) {
Xradius = el->FindElementValueAsNumberConvertTo("x_radius", "FT");
}
if (el->FindElement("y_radius")) {
Yradius = el->FindElementValueAsNumberConvertTo("y_radius", "FT");
}
if (el->FindElement("z_radius")) {
Zradius = el->FindElementValueAsNumberConvertTo("z_radius", "FT");
}
if (el->FindElement("x_width")) {
Xwidth = el->FindElementValueAsNumberConvertTo("x_width", "FT");
}
if (el->FindElement("y_width")) {
Ywidth = el->FindElementValueAsNumberConvertTo("y_width", "FT");
}
if (el->FindElement("z_width")) {
Zwidth = el->FindElementValueAsNumberConvertTo("z_width", "FT");
}
// The volume is a (potentially) extruded ellipsoid.
// However, currently only a few combinations of radius and width are
// fully supported.
if ((Xradius != 0.0) && (Yradius != 0.0) && (Zradius != 0.0) &&
(Xwidth == 0.0) && (Ywidth == 0.0) && (Zwidth == 0.0)) {
// Ellipsoid volume.
MaxVolume = 4.0 * M_PI * Xradius * Yradius * Zradius / 3.0;
} else if ((Xradius == 0.0) && (Yradius != 0.0) && (Zradius != 0.0) &&
(Xwidth != 0.0) && (Ywidth == 0.0) && (Zwidth == 0.0)) {
// Cylindrical volume.
MaxVolume = M_PI * Yradius * Zradius * Xwidth;
} else {
cerr << "Warning: Unsupported gas cell shape." << endl;
MaxVolume =
(4.0 * M_PI * Xradius * Yradius * Zradius / 3.0 +
M_PI * Yradius * Zradius * Xwidth +
M_PI * Xradius * Zradius * Ywidth +
M_PI * Xradius * Yradius * Zwidth +
2.0 * Xradius * Ywidth * Zwidth +
2.0 * Yradius * Xwidth * Zwidth +
2.0 * Zradius * Xwidth * Ywidth +
Xwidth * Ywidth * Zwidth);
}
} else {
cerr << "Fatal Error: Gas cell shape must be given." << endl;
exit(-1);
}
if (el->FindElement("max_overpressure")) {
MaxOverpressure = el->FindElementValueAsNumberConvertTo("max_overpressure",
"LBS/FT2");
}
if (el->FindElement("fullness")) {
const double Fullness = el->FindElementValueAsNumber("fullness");
if (0 <= Fullness) {
Volume = Fullness * MaxVolume;
} else {
cerr << "Warning: Invalid initial gas cell fullness value." << endl;
}
}
if (el->FindElement("valve_coefficient")) {
ValveCoefficient =
el->FindElementValueAsNumberConvertTo("valve_coefficient",
"FT4*SEC/SLUG");
ValveCoefficient = max(ValveCoefficient, 0.0);
}
// Initialize state
SetLocation(vXYZ);
if (Temperature == 0.0) {
Temperature = Atmosphere->GetTemperature();
}
if (Pressure == 0.0) {
Pressure = Atmosphere->GetPressure();
}
if (Volume != 0.0) {
// Calculate initial gas content.
Contents = Pressure * Volume / (R * Temperature);
// Clip to max allowed value.
const double IdealPressure = Contents * R * Temperature / MaxVolume;
if (IdealPressure > Pressure + MaxOverpressure) {
Contents = (Pressure + MaxOverpressure) * MaxVolume / (R * Temperature);
Pressure = Pressure + MaxOverpressure;
} else {
Pressure = max(IdealPressure, Pressure);
}
} else {
// Calculate initial gas content.
Contents = Pressure * MaxVolume / (R * Temperature);
}
Volume = Contents * R * Temperature / Pressure;
Mass = Contents * M_gas();
// Bind relevant properties
string property_name, base_property_name;
base_property_name = CreateIndexedPropertyName("buoyant_forces/gas-cell", CellNum);
property_name = base_property_name + "/max_volume-ft3";
PropertyManager->Tie( property_name.c_str(), &MaxVolume, false );
PropertyManager->SetWritable( property_name, false );
property_name = base_property_name + "/temp-R";
PropertyManager->Tie( property_name.c_str(), &Temperature, false );
property_name = base_property_name + "/pressure-psf";
PropertyManager->Tie( property_name.c_str(), &Pressure, false );
property_name = base_property_name + "/volume-ft3";
PropertyManager->Tie( property_name.c_str(), &Volume, false );
property_name = base_property_name + "/buoyancy-lbs";
PropertyManager->Tie( property_name.c_str(), &Buoyancy, false );
property_name = base_property_name + "/contents-mol";
PropertyManager->Tie( property_name.c_str(), &Contents, false );
property_name = base_property_name + "/valve_open";
PropertyManager->Tie( property_name.c_str(), &ValveOpen, false );
Debug(0);
// Read heat transfer coefficients
if (Element* heat = el->FindElement("heat")) {
Element* function_element = heat->FindElement("function");
while (function_element) {
HeatTransferCoeff.push_back(new FGFunction(PropertyManager,
function_element));
function_element = heat->FindNextElement("function");
}
}
// Load ballonets if there are any
if (Element* ballonet_element = el->FindElement("ballonet")) {
while (ballonet_element) {
Ballonet.push_back(new FGBallonet(exec,
ballonet_element,
Ballonet.size(),
this));
ballonet_element = el->FindNextElement("ballonet");
}
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
FGGasCell::~FGGasCell()
{
unsigned int i;
for (i = 0; i < HeatTransferCoeff.size(); i++) delete HeatTransferCoeff[i];
HeatTransferCoeff.clear();
for (i = 0; i < Ballonet.size(); i++) delete Ballonet[i];
Ballonet.clear();
Debug(1);
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
void FGGasCell::Calculate(double dt)
{
const double AirTemperature = Atmosphere->GetTemperature(); // [Rankine]
const double AirPressure = Atmosphere->GetPressure(); // [lbs/ft<66>]
const double AirDensity = Atmosphere->GetDensity(); // [slug/ft<66>]
const double g = Inertial->gravity(); // [lbs/slug]
const double OldTemperature = Temperature;
const double OldPressure = Pressure;
unsigned int i;
const unsigned int no_ballonets = Ballonet.size();
//-- Read ballonet state --
// NOTE: This model might need a more proper integration technique.
double BallonetsVolume = 0.0;
double BallonetsHeatFlow = 0.0;
for (i = 0; i < no_ballonets; i++) {
BallonetsVolume += Ballonet[i]->GetVolume();
BallonetsHeatFlow += Ballonet[i]->GetHeatFlow();
}
//-- Gas temperature --
if (HeatTransferCoeff.size() > 0) {
// The model is based on the ideal gas law.
// However, it does look a bit fishy. Please verify.
// dT/dt = dU / (Cv n R)
double dU = 0.0;
for (i = 0; i < HeatTransferCoeff.size(); i++) {
dU += HeatTransferCoeff[i]->GetValue();
}
// Don't include dt when accounting for adiabatic expansion/contraction.
// The rate of adiabatic cooling looks about right: ~5.4 Rankine/1000ft.
if (Contents > 0) {
Temperature +=
(dU * dt - Pressure * dVolumeIdeal - BallonetsHeatFlow) /
(Cv_gas() * Contents * R);
} else {
Temperature = AirTemperature;
}
} else {
// No simulation of complex temperature changes.
// Note: Making the gas cell behave adiabatically might be a better
// option.
Temperature = AirTemperature;
}
//-- Pressure --
const double IdealPressure =
Contents * R * Temperature / (MaxVolume - BallonetsVolume);
if (IdealPressure > AirPressure + MaxOverpressure) {
Pressure = AirPressure + MaxOverpressure;
} else {
Pressure = max(IdealPressure, AirPressure);
}
//-- Manual valving --
// FIXME: Presently the effect of manual valving is computed using
// an ad hoc formula which might not be a good representation
// of reality.
if ((ValveCoefficient > 0.0) && (ValveOpen > 0.0)) {
// First compute the difference in pressure between the gas in the
// cell and the air above it.
// FixMe: CellHeight should depend on current volume.
const double CellHeight = 2 * Zradius + Zwidth; // [ft]
const double GasMass = Contents * M_gas(); // [slug]
const double GasVolume = Contents * R * Temperature / Pressure; // [ft<66>]
const double GasDensity = GasMass / GasVolume;
const double DeltaPressure =
Pressure + CellHeight * g * (AirDensity - GasDensity) - AirPressure;
const double VolumeValved =
ValveOpen * ValveCoefficient * DeltaPressure * dt;
Contents =
max(0.0, Contents - Pressure * VolumeValved / (R * Temperature));
}
//-- Update ballonets. --
// Doing that here should give them the opportunity to react to the
// new pressure.
BallonetsVolume = 0.0;
for (i = 0; i < no_ballonets; i++) {
Ballonet[i]->Calculate(dt);
BallonetsVolume += Ballonet[i]->GetVolume();
}
//-- Automatic safety valving. --
if (Contents * R * Temperature / (MaxVolume - BallonetsVolume) >
AirPressure + MaxOverpressure) {
// Gas is automatically valved. Valving capacity is assumed to be infinite.
// FIXME: This could/should be replaced by damage to the gas cell envelope.
Contents =
(AirPressure + MaxOverpressure) *
(MaxVolume - BallonetsVolume) / (R * Temperature);
}
//-- Volume --
Volume = Contents * R * Temperature / Pressure + BallonetsVolume;
dVolumeIdeal =
Contents * R * (Temperature / Pressure - OldTemperature / OldPressure);
//-- Current buoyancy --
// The buoyancy is computed using the atmospheres local density.
Buoyancy = Volume * AirDensity * g;
// Note: This is gross buoyancy. The weight of the gas itself and
// any ballonets is not deducted here as the effects of the gas mass
// is handled by FGMassBalance.
vFn.InitMatrix(0.0, 0.0, - Buoyancy);
// Compute the inertia of the gas cell.
// Consider the gas cell as a shape of uniform density.
// FIXME: If the cell isn't ellipsoid or cylindrical the inertia will
// be wrong.
gasCellJ = FGMatrix33();
const double mass = Contents * M_gas();
double Ixx, Iyy, Izz;
if ((Xradius != 0.0) && (Yradius != 0.0) && (Zradius != 0.0) &&
(Xwidth == 0.0) && (Ywidth == 0.0) && (Zwidth == 0.0)) {
// Ellipsoid volume.
Ixx = (1.0 / 5.0) * mass * (Yradius*Yradius + Zradius*Zradius);
Iyy = (1.0 / 5.0) * mass * (Xradius*Xradius + Zradius*Zradius);
Izz = (1.0 / 5.0) * mass * (Xradius*Xradius + Yradius*Yradius);
} else if ((Xradius == 0.0) && (Yradius != 0.0) && (Zradius != 0.0) &&
(Xwidth != 0.0) && (Ywidth == 0.0) && (Zwidth == 0.0)) {
// Cylindrical volume (might not be valid with an elliptical cross-section).
Ixx = (1.0 / 2.0) * mass * Yradius * Zradius;
Iyy =
(1.0 / 4.0) * mass * Yradius * Zradius +
(1.0 / 12.0) * mass * Xwidth * Xwidth;
Izz =
(1.0 / 4.0) * mass * Yradius * Zradius +
(1.0 / 12.0) * mass * Xwidth * Xwidth;
} else {
// Not supported. Revert to pointmass model.
Ixx = Iyy = Izz = 0.0;
}
// The volume is symmetric, so Ixy = Ixz = Iyz = 0.
gasCellJ(1,1) = Ixx;
gasCellJ(2,2) = Iyy;
gasCellJ(3,3) = Izz;
Mass = mass;
gasCellM.InitMatrix();
gasCellM(eX) +=
GetXYZ(eX) * Mass*slugtolb;
gasCellM(eY) +=
GetXYZ(eY) * Mass*slugtolb;
gasCellM(eZ) +=
GetXYZ(eZ) * Mass*slugtolb;
if (no_ballonets > 0) {
// Add the mass, moment and inertia of any ballonets.
const FGColumnVector3 p = MassBalance->StructuralToBody( GetXYZ() );
for (i = 0; i < no_ballonets; i++) {
Mass += Ballonet[i]->GetMass();
// Add ballonet moments.
gasCellM(eX) +=
Ballonet[i]->GetXYZ(eX) * Ballonet[i]->GetMass()*slugtolb;
gasCellM(eY) +=
Ballonet[i]->GetXYZ(eY) * Ballonet[i]->GetMass()*slugtolb;
gasCellM(eZ) +=
Ballonet[i]->GetXYZ(eZ) * Ballonet[i]->GetMass()*slugtolb;
// Moments of inertia must be converted to the gas cell frame here.
FGColumnVector3 v =
MassBalance->StructuralToBody( Ballonet[i]->GetXYZ() ) - p;
// Body basis is in FT.
const double mass = Ballonet[i]->GetMass();
gasCellJ += Ballonet[i]->GetInertia() +
FGMatrix33( 0, - mass*v(1)*v(2), - mass*v(1)*v(3),
- mass*v(2)*v(1), 0, - mass*v(2)*v(3),
- mass*v(3)*v(1), - mass*v(3)*v(2), 0 );
}
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// The bitmasked value choices are as follows:
// unset: In this case (the default) JSBSim would only print
// out the normally expected messages, essentially echoing
// the config files as they are read. If the environment
// variable is not set, debug_lvl is set to 1 internally
// 0: This requests JSBSim not to output any messages
// whatsoever.
// 1: This value explicity requests the normal JSBSim
// startup messages
// 2: This value asks for a message to be printed out when
// a class is instantiated
// 4: When this value is set, a message is displayed when a
// FGModel object executes its Run() method
// 8: When this value is set, various runtime state variables
// are printed out periodically
// 16: When set various parameters are sanity checked and
// a message is printed out when they go out of bounds
void FGGasCell::Debug(int from)
{
if (debug_lvl <= 0) return;
if (debug_lvl & 1) { // Standard console startup message output
if (from == 0) { // Constructor
cout << " Gas cell holds " << Contents << " mol " <<
type << endl;
cout << " Cell location (X, Y, Z) (in.): " << vXYZ(eX) << ", " <<
vXYZ(eY) << ", " << vXYZ(eZ) << endl;
cout << " Maximum volume: " << MaxVolume << " ft3" << endl;
cout << " Relief valve release pressure: " << MaxOverpressure <<
" lbs/ft2" << endl;
cout << " Manual valve coefficient: " << ValveCoefficient <<
" ft4*sec/slug" << endl;
cout << " Initial temperature: " << Temperature << " Rankine" <<
endl;
cout << " Initial pressure: " << Pressure << " lbs/ft2" << endl;
cout << " Initial volume: " << Volume << " ft3" << endl;
cout << " Initial mass: " << GetMass() << " slug mass" << endl;
cout << " Initial weight: " << GetMass()*lbtoslug << " lbs force" <<
endl;
cout << " Heat transfer: " << endl;
}
}
if (debug_lvl & 2 ) { // Instantiation/Destruction notification
if (from == 0) cout << "Instantiated: FGGasCell" << endl;
if (from == 1) cout << "Destroyed: FGGasCell" << endl;
}
if (debug_lvl & 4 ) { // Run() method entry print for FGModel-derived objects
}
if (debug_lvl & 8 ) { // Runtime state variables
cout << " " << type << " cell holds " << Contents << " mol " << endl;
cout << " Temperature: " << Temperature << " Rankine" << endl;
cout << " Pressure: " << Pressure << " lbs/ft2" << endl;
cout << " Volume: " << Volume << " ft3" << endl;
cout << " Mass: " << GetMass() << " slug mass" << endl;
cout << " Weight: " << GetMass()*lbtoslug << " lbs force" << endl;
}
if (debug_lvl & 16) { // Sanity checking
}
if (debug_lvl & 64) {
if (from == 0) { // Constructor
cout << IdSrc << endl;
cout << IdHdr << endl;
}
}
}
/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
CLASS IMPLEMENTATION
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
const double FGBallonet::R = 3.4071; // [lbs ft/(mol Rankine)]
const double FGBallonet::M_air = 0.0019186; // [slug/mol]
const double FGBallonet::Cv_air = 5.0/2.0; // [??]
FGBallonet::FGBallonet(FGFDMExec* exec, Element* el, int num, FGGasCell* parent)
{
string token;
Element* element;
Auxiliary = exec->GetAuxiliary();
Atmosphere = exec->GetAtmosphere();
PropertyManager = exec->GetPropertyManager();
Inertial = exec->GetInertial();
ballonetJ = FGMatrix33();
MaxVolume = MaxOverpressure = Temperature = Pressure =
Contents = Volume = dVolumeIdeal = dU = 0.0;
Xradius = Yradius = Zradius = Xwidth = Ywidth = Zwidth = 0.0;
ValveCoefficient = ValveOpen = 0.0;
BlowerInput = NULL;
CellNum = num;
Parent = parent;
// NOTE: In the local system X points north, Y points east and Z points down.
element = el->FindElement("location");
if (element) {
vXYZ = element->FindElementTripletConvertTo("IN");
} else {
cerr << "Fatal Error: No location found for this ballonet." << endl;
exit(-1);
}
if ((el->FindElement("x_radius") || el->FindElement("x_width")) &&
(el->FindElement("y_radius") || el->FindElement("y_width")) &&
(el->FindElement("z_radius") || el->FindElement("z_width"))) {
if (el->FindElement("x_radius")) {
Xradius = el->FindElementValueAsNumberConvertTo("x_radius", "FT");
}
if (el->FindElement("y_radius")) {
Yradius = el->FindElementValueAsNumberConvertTo("y_radius", "FT");
}
if (el->FindElement("z_radius")) {
Zradius = el->FindElementValueAsNumberConvertTo("z_radius", "FT");
}
if (el->FindElement("x_width")) {
Xwidth = el->FindElementValueAsNumberConvertTo("x_width", "FT");
}
if (el->FindElement("y_width")) {
Ywidth = el->FindElementValueAsNumberConvertTo("y_width", "FT");
}
if (el->FindElement("z_width")) {
Zwidth = el->FindElementValueAsNumberConvertTo("z_width", "FT");
}
// The volume is a (potentially) extruded ellipsoid.
// FIXME: However, currently only a few combinations of radius and
// width are fully supported.
if ((Xradius != 0.0) && (Yradius != 0.0) && (Zradius != 0.0) &&
(Xwidth == 0.0) && (Ywidth == 0.0) && (Zwidth == 0.0)) {
// Ellipsoid volume.
MaxVolume = 4.0 * M_PI * Xradius * Yradius * Zradius / 3.0;
} else if ((Xradius == 0.0) && (Yradius != 0.0) && (Zradius != 0.0) &&
(Xwidth != 0.0) && (Ywidth == 0.0) && (Zwidth == 0.0)) {
// Cylindrical volume.
MaxVolume = M_PI * Yradius * Zradius * Xwidth;
} else {
cerr << "Warning: Unsupported ballonet shape." << endl;
MaxVolume =
(4.0 * M_PI * Xradius * Yradius * Zradius / 3.0 +
M_PI * Yradius * Zradius * Xwidth +
M_PI * Xradius * Zradius * Ywidth +
M_PI * Xradius * Yradius * Zwidth +
2.0 * Xradius * Ywidth * Zwidth +
2.0 * Yradius * Xwidth * Zwidth +
2.0 * Zradius * Xwidth * Ywidth +
Xwidth * Ywidth * Zwidth);
}
} else {
cerr << "Fatal Error: Ballonet shape must be given." << endl;
exit(-1);
}
if (el->FindElement("max_overpressure")) {
MaxOverpressure = el->FindElementValueAsNumberConvertTo("max_overpressure",
"LBS/FT2");
}
if (el->FindElement("fullness")) {
const double Fullness = el->FindElementValueAsNumber("fullness");
if (0 <= Fullness) {
Volume = Fullness * MaxVolume;
} else {
cerr << "Warning: Invalid initial ballonet fullness value." << endl;
}
}
if (el->FindElement("valve_coefficient")) {
ValveCoefficient =
el->FindElementValueAsNumberConvertTo("valve_coefficient",
"FT4*SEC/SLUG");
ValveCoefficient = max(ValveCoefficient, 0.0);
}
// Initialize state
if (Temperature == 0.0) {
Temperature = Parent->GetTemperature();
}
if (Pressure == 0.0) {
Pressure = Parent->GetPressure();
}
if (Volume != 0.0) {
// Calculate initial air content.
Contents = Pressure * Volume / (R * Temperature);
// Clip to max allowed value.
const double IdealPressure = Contents * R * Temperature / MaxVolume;
if (IdealPressure > Pressure + MaxOverpressure) {
Contents = (Pressure + MaxOverpressure) * MaxVolume / (R * Temperature);
Pressure = Pressure + MaxOverpressure;
} else {
Pressure = max(IdealPressure, Pressure);
}
} else {
// Calculate initial air content.
Contents = Pressure * MaxVolume / (R * Temperature);
}
Volume = Contents * R * Temperature / Pressure;
// Bind relevant properties
string property_name, base_property_name;
base_property_name = CreateIndexedPropertyName("buoyant_forces/gas-cell", Parent->GetIndex());
base_property_name = CreateIndexedPropertyName(base_property_name + "/ballonet", CellNum);
property_name = base_property_name + "/max_volume-ft3";
PropertyManager->Tie( property_name, &MaxVolume, false );
PropertyManager->SetWritable( property_name, false );
property_name = base_property_name + "/temp-R";
PropertyManager->Tie( property_name, &Temperature, false );
property_name = base_property_name + "/pressure-psf";
PropertyManager->Tie( property_name, &Pressure, false );
property_name = base_property_name + "/volume-ft3";
PropertyManager->Tie( property_name, &Volume, false );
property_name = base_property_name + "/contents-mol";
PropertyManager->Tie( property_name, &Contents, false );
property_name = base_property_name + "/valve_open";
PropertyManager->Tie( property_name, &ValveOpen, false );
Debug(0);
// Read heat transfer coefficients
if (Element* heat = el->FindElement("heat")) {
Element* function_element = heat->FindElement("function");
while (function_element) {
HeatTransferCoeff.push_back(new FGFunction(PropertyManager,
function_element));
function_element = heat->FindNextElement("function");
}
}
// Read blower input function
if (Element* blower = el->FindElement("blower_input")) {
Element* function_element = blower->FindElement("function");
BlowerInput = new FGFunction(PropertyManager,
function_element);
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
FGBallonet::~FGBallonet()
{
unsigned int i;
for (i = 0; i < HeatTransferCoeff.size(); i++) delete HeatTransferCoeff[i];
HeatTransferCoeff.clear();
delete BlowerInput;
BlowerInput = NULL;
Debug(1);
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
void FGBallonet::Calculate(double dt)
{
const double ParentPressure = Parent->GetPressure(); // [lbs/ft<66>]
const double AirPressure = Atmosphere->GetPressure(); // [lbs/ft<66>]
const double OldTemperature = Temperature;
const double OldPressure = Pressure;
unsigned int i;
//-- Gas temperature --
// The model is based on the ideal gas law.
// However, it does look a bit fishy. Please verify.
// dT/dt = dU / (Cv n R)
dU = 0.0;
for (i = 0; i < HeatTransferCoeff.size(); i++) {
dU += HeatTransferCoeff[i]->GetValue();
}
// dt is already accounted for in dVolumeIdeal.
if (Contents > 0) {
Temperature +=
(dU * dt - Pressure * dVolumeIdeal) / (Cv_air * Contents * R);
} else {
Temperature = Parent->GetTemperature();
}
//-- Pressure --
const double IdealPressure = Contents * R * Temperature / MaxVolume;
// The pressure is at least that of the parent gas cell.
Pressure = max(IdealPressure, ParentPressure);
//-- Blower input --
if (BlowerInput) {
const double AddedVolume = BlowerInput->GetValue() * dt;
if (AddedVolume > 0.0) {
Contents += Pressure * AddedVolume / (R * Temperature);
}
}
//-- Pressure relief and manual valving --
// FIXME: Presently the effect of valving is computed using
// an ad hoc formula which might not be a good representation
// of reality.
if ((ValveCoefficient > 0.0) &&
((ValveOpen > 0.0) || (Pressure > AirPressure + MaxOverpressure))) {
const double DeltaPressure = Pressure - AirPressure;
const double VolumeValved =
((Pressure > AirPressure + MaxOverpressure) ? 1.0 : ValveOpen) *
ValveCoefficient * DeltaPressure * dt;
// FIXME: Too small values of Contents sometimes leads to NaN.
// Currently the minimum is restricted to a safe value.
Contents =
max(1.0, Contents - Pressure * VolumeValved / (R * Temperature));
}
//-- Volume --
Volume = Contents * R * Temperature / Pressure;
dVolumeIdeal =
Contents * R * (Temperature / Pressure - OldTemperature / OldPressure);
// Compute the inertia of the ballonet.
// Consider the ballonet as a shape of uniform density.
// FIXME: If the ballonet isn't ellipsoid or cylindrical the inertia will
// be wrong.
ballonetJ = FGMatrix33();
const double mass = Contents * M_air;
double Ixx, Iyy, Izz;
if ((Xradius != 0.0) && (Yradius != 0.0) && (Zradius != 0.0) &&
(Xwidth == 0.0) && (Ywidth == 0.0) && (Zwidth == 0.0)) {
// Ellipsoid volume.
Ixx = (1.0 / 5.0) * mass * (Yradius*Yradius + Zradius*Zradius);
Iyy = (1.0 / 5.0) * mass * (Xradius*Xradius + Zradius*Zradius);
Izz = (1.0 / 5.0) * mass * (Xradius*Xradius + Yradius*Yradius);
} else if ((Xradius == 0.0) && (Yradius != 0.0) && (Zradius != 0.0) &&
(Xwidth != 0.0) && (Ywidth == 0.0) && (Zwidth == 0.0)) {
// Cylindrical volume (might not be valid with an elliptical cross-section).
Ixx = (1.0 / 2.0) * mass * Yradius * Zradius;
Iyy =
(1.0 / 4.0) * mass * Yradius * Zradius +
(1.0 / 12.0) * mass * Xwidth * Xwidth;
Izz =
(1.0 / 4.0) * mass * Yradius * Zradius +
(1.0 / 12.0) * mass * Xwidth * Xwidth;
} else {
// Not supported. Revert to pointmass model.
Ixx = Iyy = Izz = 0.0;
}
// The volume is symmetric, so Ixy = Ixz = Iyz = 0.
ballonetJ(1,1) = Ixx;
ballonetJ(2,2) = Iyy;
ballonetJ(3,3) = Izz;
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// The bitmasked value choices are as follows:
// unset: In this case (the default) JSBSim would only print
// out the normally expected messages, essentially echoing
// the config files as they are read. If the environment
// variable is not set, debug_lvl is set to 1 internally
// 0: This requests JSBSim not to output any messages
// whatsoever.
// 1: This value explicity requests the normal JSBSim
// startup messages
// 2: This value asks for a message to be printed out when
// a class is instantiated
// 4: When this value is set, a message is displayed when a
// FGModel object executes its Run() method
// 8: When this value is set, various runtime state variables
// are printed out periodically
// 16: When set various parameters are sanity checked and
// a message is printed out when they go out of bounds
void FGBallonet::Debug(int from)
{
if (debug_lvl <= 0) return;
if (debug_lvl & 1) { // Standard console startup message output
if (from == 0) { // Constructor
cout << " Ballonet holds " << Contents << " mol air" << endl;
cout << " Location (X, Y, Z) (in.): " << vXYZ(eX) << ", " <<
vXYZ(eY) << ", " << vXYZ(eZ) << endl;
cout << " Maximum volume: " << MaxVolume << " ft3" << endl;
cout << " Relief valve release pressure: " << MaxOverpressure <<
" lbs/ft2" << endl;
cout << " Relief valve coefficient: " << ValveCoefficient <<
" ft4*sec/slug" << endl;
cout << " Initial temperature: " << Temperature << " Rankine" <<
endl;
cout << " Initial pressure: " << Pressure << " lbs/ft2" << endl;
cout << " Initial volume: " << Volume << " ft3" << endl;
cout << " Initial mass: " << GetMass() << " slug mass" << endl;
cout << " Initial weight: " << GetMass()*lbtoslug <<
" lbs force" << endl;
cout << " Heat transfer: " << endl;
}
}
if (debug_lvl & 2 ) { // Instantiation/Destruction notification
if (from == 0) cout << "Instantiated: FGBallonet" << endl;
if (from == 1) cout << "Destroyed: FGBallonet" << endl;
}
if (debug_lvl & 4 ) { // Run() method entry print for FGModel-derived objects
}
if (debug_lvl & 8 ) { // Runtime state variables
cout << " Ballonet holds " << Contents <<
" mol air" << endl;
cout << " Temperature: " << Temperature << " Rankine" << endl;
cout << " Pressure: " << Pressure << " lbs/ft2" << endl;
cout << " Volume: " << Volume << " ft3" << endl;
cout << " Mass: " << GetMass() << " slug mass" << endl;
cout << " Weight: " << GetMass()*lbtoslug << " lbs force" << endl;
}
if (debug_lvl & 16) { // Sanity checking
}
if (debug_lvl & 64) {
if (from == 0) { // Constructor
cout << IdSrc << endl;
cout << IdHdr << endl;
}
}
}
}
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