FGBuoyantForces Class Reference

Detailed Description

Encapsulates the Buoyant forces calculations.

This class owns and contains the list of force/coefficients that define the Buoyant properties of an air vehicle.

Here's an example of a gas cell specification:

<buoyant_forces>
 
  <!-- Interface properties -->
  <property>ballonets/in-flow-ft3ps[0]</property>
 
  <gas_cell type="HYDROGEN">
    <location unit="M">
      <x> 18.8 </x>
      <y> 0.0 </y>
      <z> 0.0 </z>
    </location>
    <x_radius unit="M"> 22.86 </x_radius>
    <y_radius unit="M">  4.55 </y_radius>
    <z_radius unit="M">  4.55 </z_radius>
    <max_overpressure unit="PA"> 340.0 </max_overpressure> 
    <valve_coefficient unit="M4*SEC/KG"> 0.015 </valve_coefficient>
  </gas_cell>
  
  ... {other gas cells} ...
  
</buoyant_forces>

See FGGasCell for the full configuration file format for gas cells.

Author

Anders Gidenstam, Jon S. Berndt

Definition at line 98 of file FGBuoyantForces.h.

#include <FGBuoyantForces.h>

Inheritance diagram for FGBuoyantForces:

Collaboration diagram for FGBuoyantForces:

Public Member Functions
	FGBuoyantForces (FGFDMExec *Executive)
	Constructor.
	~FGBuoyantForces () override
	Destructor.
std::string	GetBuoyancyStrings (const std::string &delimeter)
	Gets the strings for the current set of gas cells.
std::string	GetBuoyancyValues (const std::string &delimeter)
	Gets the coefficient values.
double	GetForces (int idx) const
	Gets a component of the total Buoyant force vector.
const FGColumnVector3 &	GetForces (void) const
	Gets the total Buoyant force vector.
double	GetGasMass (void) const
	Gets the total gas mass.
const FGMatrix33 &	GetGasMassInertia (void)
	Gets the total moments of inertia for the gas mass in the body frame.
const FGColumnVector3 &	GetGasMassMoment (void)
	Gets the total moment from the gas mass.
double	GetMoments (int idx) const
	Gets a component of the total Buoyancy moment vector.
const FGColumnVector3 &	GetMoments (void) const
	Gets the total Buoyancy moment vector.
bool	InitModel (void) override
bool	Load (Element *element) override
	Loads the Buoyant forces model.
bool	Run (bool Holding) override
	Runs the Buoyant forces model; called by the Executive Can pass in a value indicating if the executive is directing the simulation to Hold.
Public Member Functions inherited from FGModel
	FGModel (FGFDMExec *, const std::string &name)
	Constructor.
	~FGModel () override
	Destructor.
virtual SGPath	FindFullPathName (const SGPath &path) const
FGFDMExec *	GetExec (void) const
const std::string &	GetName (void) const
unsigned int	GetRate (void) const
	Get the output rate for the model in frames.
bool	InitModel (void) override
void	SetPropertyManager (std::shared_ptr< FGPropertyManager > fgpm)
void	SetRate (unsigned int tt)
	Set the ouput rate for the model in frames.
Public Member Functions inherited from FGModelFunctions
std::string	GetFunctionStrings (const std::string &delimeter) const
	Gets the strings for the current set of functions.
std::string	GetFunctionValues (const std::string &delimeter) const
	Gets the function values.
std::shared_ptr< FGFunction >	GetPreFunction (const std::string &name)
	Get one of the "pre" function.
bool	Load (Element *el, FGFDMExec *fdmex, std::string prefix="")
void	PostLoad (Element *el, FGFDMExec *fdmex, std::string prefix="")
void	PreLoad (Element *el, FGFDMExec *fdmex, std::string prefix="")
void	RunPostFunctions (void)
void	RunPreFunctions (void)
Public Member Functions inherited from FGJSBBase
	FGJSBBase ()
	Constructor for FGJSBBase.
virtual	~FGJSBBase ()
	Destructor for FGJSBBase.

Public Attributes
FGGasCell::Inputs	in

Additional Inherited Members
Public Types inherited from FGJSBBase
enum	{ eL = 1 , eM , eN }
	Moments L, M, N. More...
enum	{ eP = 1 , eQ , eR }
	Rates P, Q, R. More...
enum	{ eU = 1 , eV , eW }
	Velocities U, V, W. More...
enum	{ eX = 1 , eY , eZ }
	Positions X, Y, Z. More...
enum	{ ePhi = 1 , eTht , ePsi }
	Euler angles Phi, Theta, Psi. More...
enum	{ eDrag = 1 , eSide , eLift }
	Stability axis forces, Drag, Side force, Lift. More...
enum	{ eRoll = 1 , ePitch , eYaw }
	Local frame orientation Roll, Pitch, Yaw. More...
enum	{ eNorth = 1 , eEast , eDown }
	Local frame position North, East, Down. More...
enum	{ eLat = 1 , eLong , eRad }
	Locations Radius, Latitude, Longitude. More...
enum	{   inNone = 0 , inDegrees , inRadians , inMeters ,   inFeet }
	Conversion specifiers. More...
Static Public Member Functions inherited from FGJSBBase
static constexpr double	CelsiusToFahrenheit (double celsius)
	Converts from degrees Celsius to degrees Fahrenheit.
static constexpr double	CelsiusToKelvin (double celsius)
	Converts from degrees Celsius to degrees Kelvin.
static constexpr double	CelsiusToRankine (double celsius)
	Converts from degrees Celsius to degrees Rankine.
static constexpr double	Constrain (double min, double value, double max)
	Constrain a value between a minimum and a maximum value.
static bool	EqualToRoundoff (double a, double b)
	Finite precision comparison.
static bool	EqualToRoundoff (double a, float b)
	Finite precision comparison.
static bool	EqualToRoundoff (float a, double b)
	Finite precision comparison.
static bool	EqualToRoundoff (float a, float b)
	Finite precision comparison.
static constexpr double	FahrenheitToCelsius (double fahrenheit)
	Converts from degrees Fahrenheit to degrees Celsius.
static constexpr double	FeetToMeters (double measure)
	Converts from feet to meters.
static const std::string &	GetVersion (void)
	Returns the version number of JSBSim.
static constexpr double	KelvinToCelsius (double kelvin)
	Converts from degrees Kelvin to degrees Celsius.
static constexpr double	KelvinToFahrenheit (double kelvin)
	Converts from degrees Kelvin to degrees Fahrenheit.
static constexpr double	KelvinToRankine (double kelvin)
	Converts from degrees Kelvin to degrees Rankine.
static constexpr double	RankineToCelsius (double rankine)
	Converts from degrees Rankine to degrees Celsius.
static constexpr double	RankineToKelvin (double rankine)
	Converts from degrees Rankine to degrees Kelvin.
static constexpr double	sign (double num)
Static Public Attributes inherited from FGJSBBase
static short	debug_lvl = 1
Protected Member Functions inherited from FGModel
bool	Upload (Element *el, bool preLoad)
	Uploads this model in memory.
Static Protected Member Functions inherited from FGJSBBase
static std::string	CreateIndexedPropertyName (const std::string &Property, int index)
Protected Attributes inherited from FGModel
bool	enabled = true
unsigned int	exe_ctr
FGFDMExec *	FDMExec
std::string	Name
std::shared_ptr< FGPropertyManager >	PropertyManager
unsigned int	rate
Protected Attributes inherited from FGModelFunctions
FGPropertyReader	LocalProperties
std::vector< std::shared_ptr< FGFunction > >	PostFunctions
std::vector< std::shared_ptr< FGFunction > >	PreFunctions
Static Protected Attributes inherited from FGJSBBase
static constexpr double	degtorad = M_PI / 180.
static constexpr double	fpstokts = 1.0 / ktstofps
static constexpr double	fttom = 0.3048
static constexpr double	hptoftlbssec = 550.0
static constexpr double	in3tom3 = inchtoft*inchtoft*inchtoft/m3toft3
static constexpr double	inchtoft = 1.0/12.0
static constexpr double	inhgtopa = 3386.38
static const std::string	JSBSim_version = JSBSIM_VERSION " " __DATE__ " " __TIME__
static constexpr double	kgtolb = 2.20462
static constexpr double	kgtoslug = 0.06852168
static constexpr double	ktstofps = 1852./(3600*fttom)
static constexpr double	lbtoslug = 1.0/slugtolb
static constexpr double	m3toft3 = 1.0/(fttom*fttom*fttom)
static const std::string	needed_cfg_version = "2.0"
static constexpr double	psftoinhg = 0.014138
static constexpr double	psftopa = 47.88
static constexpr double	radtodeg = 180. / M_PI
static constexpr double	slugtolb = 32.174049
	Note that definition of lbtoslug by the inverse of slugtolb and not to a different constant you can also get from some tables will make lbtoslug*slugtolb == 1 up to the magnitude of roundoff.

Constructor & Destructor Documentation

FGBuoyantForces()

FGBuoyantForces

(

FGFDMExec *

Executive

)

Constructor.

Parameters

Executive

a pointer to the parent executive object

Definition at line 52 of file FGBuoyantForces.cpp.

                                                   : FGModel(FDMExec, "FGBuoyantForces")
{
  NoneDefined = true;
 
  vTotalForces.InitMatrix();
  vTotalMoments.InitMatrix();
 
  gasCellJ.InitMatrix();
 
  Debug(0);
}

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~FGBuoyantForces()

~FGBuoyantForces ( )

override

Destructor.

Definition at line 66 of file FGBuoyantForces.cpp.

{
  for (unsigned int i=0; i<Cells.size(); i++) delete Cells[i];
  Cells.clear();
 
  Debug(1);
}

Member Function Documentation

GetBuoyancyStrings()

string GetBuoyancyStrings

(

const std::string &

delimeter

)

Gets the strings for the current set of gas cells.

Parameters

delimeter

either a tab or comma string depending on output type

Returns

a string containing the descriptive names for all parameters

Definition at line 181 of file FGBuoyantForces.cpp.

{
  string CoeffStrings = "";
/*
  bool firstime = true;
  for (sd = 0; sd < variables.size(); sd++) {
    if (firstime) {
      firstime = false;
    } else {
      CoeffStrings += delimeter;
    }
    CoeffStrings += variables[sd]->GetName();
  }
 
  for (axis = 0; axis < 6; axis++) {
    for (sd = 0; sd < AeroFunctions[axis].size(); sd++) {
      if (firstime) {
        firstime = false;
      } else {
        CoeffStrings += delimeter;
      }
      CoeffStrings += AeroFunctions[axis][sd]->GetName();
    }
  }
*/
  return CoeffStrings;
}

GetBuoyancyValues()

string GetBuoyancyValues

(

const std::string &

delimeter

)

Gets the coefficient values.

Parameters

delimeter

either a tab or comma string depending on output type

Returns

a string containing the numeric values for the current set of parameters

Definition at line 211 of file FGBuoyantForces.cpp.

{
  string SDValues = "";
/*
  bool firstime = true;
  for (sd = 0; sd < variables.size(); sd++) {
    if (firstime) {
      firstime = false;
    } else {
      SDValues += delimeter;
    }
    SDValues += variables[sd]->GetValueAsString();
  }
 
  for (unsigned int axis = 0; axis < 6; axis++) {
    for (unsigned int sd = 0; sd < AeroFunctions[axis].size(); sd++) {
      if (firstime) {
        firstime = false;
      } else {
        SDValues += delimeter;
      }
      SDValues += AeroFunctions[axis][sd]->GetValueAsString();
    }
  }
*/
  return SDValues;
}

GetForces() [1/2]

double GetForces ( int  idx ) const

inline

Gets a component of the total Buoyant force vector.

Returns

a component of the force vector in lbs.

Definition at line 132 of file FGBuoyantForces.h.

{return vTotalForces(idx);}

GetForces() [2/2]

const FGColumnVector3 & GetForces ( void  ) const

inline

Gets the total Buoyant force vector.

Returns

a force vector in lbs.

Definition at line 128 of file FGBuoyantForces.h.

{return vTotalForces;}

GetGasMass()

double GetGasMass

(

void

)

const

Gets the total gas mass.

The gas mass is part of the aircraft's inertia.

Returns

mass in slugs.

Definition at line 140 of file FGBuoyantForces.cpp.

{
  double Gw = 0.0;
 
  for (unsigned int i = 0; i < Cells.size(); i++) {
    Gw += Cells[i]->GetMass();
  }
 
  return Gw;
}

GetGasMassInertia()

const FGMatrix33 & GetGasMassInertia

(

void

)

Gets the total moments of inertia for the gas mass in the body frame.

Returns

moments of inertia matrix in the body frame in slug ft².

Definition at line 164 of file FGBuoyantForces.cpp.

{
  size_t size = Cells.size();
 
  if (size == 0) return gasCellJ;
 
  gasCellJ.InitMatrix();
 
  for (unsigned int i=0; i < size; i++) {
    gasCellJ += Cells[i]->GetInertia();
  }
 
  return gasCellJ;
}

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GetGasMassMoment()

const FGColumnVector3 & GetGasMassMoment

(

void

)

Gets the total moment from the gas mass.

Returns

a moment vector in the structural frame in lbs in.

Definition at line 153 of file FGBuoyantForces.cpp.

{
  vXYZgasCell_arm.InitMatrix();
  for (unsigned int i = 0; i < Cells.size(); i++) {
    vXYZgasCell_arm += Cells[i]->GetMassMoment();
  }
  return vXYZgasCell_arm;
}

GetMoments() [1/2]

double GetMoments ( int  idx ) const

inline

Gets a component of the total Buoyancy moment vector.

Returns

a component of the moment vector in the body frame in lbs ft.

Definition at line 140 of file FGBuoyantForces.h.

{return vTotalMoments(idx);}

GetMoments() [2/2]

const FGColumnVector3 & GetMoments ( void  ) const

inline

Gets the total Buoyancy moment vector.

Returns

a moment vector in the body frame in lbs ft.

Definition at line 136 of file FGBuoyantForces.h.

{return vTotalMoments;}

InitModel()

bool InitModel ( void  )

overridevirtual

Reimplemented from FGModelFunctions.

Definition at line 76 of file FGBuoyantForces.cpp.

{
  if (!FGModel::InitModel()) return false;
 
  vTotalForces.InitMatrix();
  vTotalMoments.InitMatrix();
 
  return true;
}

Load()

bool Load ( Element *  element )

overridevirtual

Loads the Buoyant forces model.

The Load function for this class expects the XML parser to have found the Buoyant_forces keyword in the configuration file.

Parameters

element

pointer to the current XML element for Buoyant forces parameters.

Returns

true if successful

Reimplemented from FGModel.

Definition at line 112 of file FGBuoyantForces.cpp.

{
  Element *gas_cell_element;
 
  Debug(2);
 
  // Perform base class Pre-Load
  if (!FGModel::Upload(document, true))
    return false;
 
  gas_cell_element = document->FindElement("gas_cell");
  while (gas_cell_element) {
    NoneDefined = false;
    Cells.push_back(new FGGasCell(FDMExec, gas_cell_element, Cells.size(), in));
    gas_cell_element = document->FindNextElement("gas_cell");
  }
 
  PostLoad(document, FDMExec);
 
  if (!NoneDefined) {
    bind();
  }
 
  return true;
}

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Run()

bool Run ( bool  Holding )

overridevirtual

Runs the Buoyant forces model; called by the Executive Can pass in a value indicating if the executive is directing the simulation to Hold.

Parameters

Holding

if true, the executive has been directed to hold the sim from advancing time. Some models may ignore this flag, such as the Input model, which may need to be active to listen on a socket for the "Resume" command to be given.

Returns

false if no error

Reimplemented from FGModel.

Definition at line 88 of file FGBuoyantForces.cpp.

{
  if (FGModel::Run(Holding)) return true;
  if (Holding) return false; // if paused don't execute
  if (NoneDefined) return true;
 
  RunPreFunctions();
 
  vTotalForces.InitMatrix();
  vTotalMoments.InitMatrix();
 
  for (unsigned int i=0; i<Cells.size(); i++) {
    Cells[i]->Calculate(FDMExec->GetDeltaT());
    vTotalForces  += Cells[i]->GetBodyForces();
    vTotalMoments += Cells[i]->GetMoments();
  }
 
  RunPostFunctions();
 
  return false;
}

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Member Data Documentation

in

FGGasCell::Inputs in

Definition at line 167 of file FGBuoyantForces.h.

---

The documentation for this class was generated from the following files:

• FGBuoyantForces.h
• FGBuoyantForces.cpp