FGExternalReactions Class Reference

Detailed Description

Manages the external and/or arbitrary forces and moments.

The external reactions capability in JSBSim really should be named "arbitrary forces and moments", because this feature can be used to model a wide variety of forces and moments that act on a vehicle. Some examples include: parachutes, catapult, arresting hook, and tow line.

This class acts similarly to the other "manager classes" (FGPropulsion, FGFCS, FGGroundReactions, FGAerodynamics) because it manages collections of constituent elements. The individual forces and moments are implemented with the FGExternalForce class.

The format of the optional external reactions section in the config file is as follows:

<external_reactions>
 
  <!-- Interface properties, a.k.a. property declarations -->
  <property> ... </property>
    
  <force name="name" frame="BODY | LOCAL | WIND">
    ...
  </force>
  <moment name="name" frame="BODY | LOCAL | WIND">
    ...
  </moment>
 
  <!-- Additional force and moment definitions may follow -->
  <force name="name" frame="BODY | LOCAL | WIND">
    ...
  </force>
  <moment name="name" frame="BODY | LOCAL | WIND">
    ...
  </moment>
 
</external_reactions>

See the FGExternalForce class for more information on the format of the force and moment specifications.

When force or moment elements are encountered in the configuration file, a new instance of the FGExternalForce class is created and a pointer to the class is pushed onto the Forces vector.

This class is one of a few of the manager classes that allows properties to be "declared". In code, these are represented by the interface_properties vector. Properties that have not yet been created in an already parsed section of the configuration file and that are used in the definition of an external force or moment should be declared in the external_reactions section because they will not be created automatically, and so would cause an error, since the property cannot be found to exist.

See the FGExternalForce documentation for details on how forces and moments are actually calculated.

Definition at line 121 of file FGExternalReactions.h.

#include <FGExternalReactions.h>

Inheritance diagram for FGExternalReactions:

Collaboration diagram for FGExternalReactions:

Public Member Functions
	FGExternalReactions (FGFDMExec *fdmex)
	Constructor. More...
	~FGExternalReactions (void) override
	Destructor. More...
double	GetForces (int idx) const
const FGColumnVector3 &	GetForces (void) const
	Retrieves the total forces defined in the external reactions. More...
double	GetMoments (int idx) const
const FGColumnVector3 &	GetMoments (void) const
	Retrieves the total moment resulting from the forces defined in the external reactions. More...
bool	InitModel (void) override
bool	Load (Element *el) override
	Loads the external forces from the XML configuration file. More...
bool	Run (bool Holding) override
	Sum all the constituent forces for this cycle. More...
Public Member Functions inherited from FGModel
	FGModel (FGFDMExec *)
	Constructor.
	~FGModel () override
	Destructor.
virtual SGPath	FindFullPathName (const SGPath &path) const
FGFDMExec *	GetExec (void)
const std::string &	GetName (void)
unsigned int	GetRate (void)
	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. More...
std::string	GetFunctionValues (const std::string &delimeter) const
	Gets the function values. More...
std::shared_ptr< FGFunction >	GetPreFunction (const std::string &name)
	Get one of the "pre" function. More...
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.
void	disableHighLighting (void)
	Disables highlighting in the console output.

Additional Inherited Members
Public Types inherited from FGJSBBase
enum	{ eL = 1 , eM , eN }
	Moments L, M, N.
enum	{ eP = 1 , eQ , eR }
	Rates P, Q, R.
enum	{ eU = 1 , eV , eW }
	Velocities U, V, W.
enum	{ eX = 1 , eY , eZ }
	Positions X, Y, Z.
enum	{ ePhi = 1 , eTht , ePsi }
	Euler angles Phi, Theta, Psi.
enum	{ eDrag = 1 , eSide , eLift }
	Stability axis forces, Drag, Side force, Lift.
enum	{ eRoll = 1 , ePitch , eYaw }
	Local frame orientation Roll, Pitch, Yaw.
enum	{ eNorth = 1 , eEast , eDown }
	Local frame position North, East, Down.
enum	{ eLat = 1 , eLong , eRad }
	Locations Radius, Latitude, Longitude.
enum	{   inNone = 0 , inDegrees , inRadians , inMeters ,   inFeet }
	Conversion specifiers.
Static Public Member Functions inherited from FGJSBBase
static const std::string &	GetVersion (void)
	Returns the version number of JSBSim. More...
static constexpr double	KelvinToFahrenheit (double kelvin)
	Converts from degrees Kelvin to degrees Fahrenheit. More...
static constexpr double	CelsiusToRankine (double celsius)
	Converts from degrees Celsius to degrees Rankine. More...
static constexpr double	RankineToCelsius (double rankine)
	Converts from degrees Rankine to degrees Celsius. More...
static constexpr double	KelvinToRankine (double kelvin)
	Converts from degrees Kelvin to degrees Rankine. More...
static constexpr double	RankineToKelvin (double rankine)
	Converts from degrees Rankine to degrees Kelvin. More...
static constexpr double	FahrenheitToCelsius (double fahrenheit)
	Converts from degrees Fahrenheit to degrees Celsius. More...
static constexpr double	CelsiusToFahrenheit (double celsius)
	Converts from degrees Celsius to degrees Fahrenheit. More...
static constexpr double	CelsiusToKelvin (double celsius)
	Converts from degrees Celsius to degrees Kelvin. More...
static constexpr double	KelvinToCelsius (double kelvin)
	Converts from degrees Kelvin to degrees Celsius. More...
static constexpr double	FeetToMeters (double measure)
	Converts from feet to meters. More...
static bool	EqualToRoundoff (double a, double b)
	Finite precision comparison. More...
static bool	EqualToRoundoff (float a, float b)
	Finite precision comparison. More...
static bool	EqualToRoundoff (float a, double b)
	Finite precision comparison. More...
static bool	EqualToRoundoff (double a, float b)
	Finite precision comparison. More...
static constexpr double	Constrain (double min, double value, double max)
	Constrain a value between a minimum and a maximum value.
static constexpr double	sign (double num)
Static Public Attributes inherited from FGJSBBase
static char	highint [5] = {27, '[', '1', 'm', '\0' }
	highlights text
static char	halfint [5] = {27, '[', '2', 'm', '\0' }
	low intensity text
static char	normint [6] = {27, '[', '2', '2', 'm', '\0' }
	normal intensity text
static char	reset [5] = {27, '[', '0', 'm', '\0' }
	resets text properties
static char	underon [5] = {27, '[', '4', 'm', '\0' }
	underlines text
static char	underoff [6] = {27, '[', '2', '4', 'm', '\0' }
	underline off
static char	fgblue [6] = {27, '[', '3', '4', 'm', '\0' }
	blue text
static char	fgcyan [6] = {27, '[', '3', '6', 'm', '\0' }
	cyan text
static char	fgred [6] = {27, '[', '3', '1', 'm', '\0' }
	red text
static char	fggreen [6] = {27, '[', '3', '2', 'm', '\0' }
	green text
static char	fgdef [6] = {27, '[', '3', '9', 'm', '\0' }
	default text
static short	debug_lvl = 1
Protected Member Functions inherited from FGModel
bool	Upload (Element *el, bool preLoad)
	Uploads this model in memory. More...
Static Protected Member Functions inherited from FGJSBBase
static std::string	CreateIndexedPropertyName (const std::string &Property, int index)
Protected Attributes inherited from FGModel
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	radtodeg = 180. / M_PI
static constexpr double	degtorad = M_PI / 180.
static constexpr double	hptoftlbssec = 550.0
static constexpr double	psftoinhg = 0.014138
static constexpr double	psftopa = 47.88
static constexpr double	fttom = 0.3048
static constexpr double	ktstofps = 1852./(3600*fttom)
static constexpr double	fpstokts = 1.0 / ktstofps
static constexpr double	inchtoft = 1.0/12.0
static constexpr double	m3toft3 = 1.0/(fttom*fttom*fttom)
static constexpr double	in3tom3 = inchtoft*inchtoft*inchtoft/m3toft3
static constexpr double	inhgtopa = 3386.38
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. More...
static constexpr double	lbtoslug = 1.0/slugtolb
static constexpr double	kgtolb = 2.20462
static constexpr double	kgtoslug = 0.06852168
static const std::string	needed_cfg_version = "2.0"
static const std::string	JSBSim_version = JSBSIM_VERSION " " __DATE__ " " __TIME__

Constructor & Destructor Documentation

FGExternalReactions()

FGExternalReactions

(

FGFDMExec *

fdmex

)

Constructor.

Parameters

fdmex

pointer to the main executive class.

Definition at line 51 of file FGExternalReactions.cpp.

                                                         : FGModel(fdmex)
{
  Debug(0);
}

~FGExternalReactions()

~FGExternalReactions ( void  )

override

Destructor.

Within the destructor the Forces and interface_properties vectors are cleared out and the items pointed to are deleted.

Definition at line 93 of file FGExternalReactions.cpp.

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

Member Function Documentation

GetForces()

const FGColumnVector3& GetForces ( void  ) const

inline

Retrieves the total forces defined in the external reactions.

Returns

the total force in pounds.

Definition at line 157 of file FGExternalReactions.h.

{return vTotalForces;}

GetMoments()

const FGColumnVector3& GetMoments ( void  ) const

inline

Retrieves the total moment resulting from the forces defined in the external reactions.

Returns

the total moment in foot-pounds.

Definition at line 163 of file FGExternalReactions.h.

{return vTotalMoments;}

Load()

bool Load ( Element *  el )

overridevirtual

Loads the external forces from the XML configuration file.

If the external_reactions section is encountered in the vehicle configuration file, this Load() method is called. All external forces will be parsed, and a FGExternalForce object will be instantiated for each force definition.

Parameters

el	a pointer to the XML element holding the external reactions definition.

Reimplemented from FGModel.

Definition at line 58 of file FGExternalReactions.cpp.

{
  // Call the base class Load() function to load interface properties.
  if (!FGModel::Upload(el, true))
    return false;
 
  Debug(2);
 
  // Parse force elements
 
  Element* force_element = el->FindElement("force");
  while (force_element) {
    Forces.push_back(new FGExternalForce(FDMExec));
    Forces.back()->setForce(force_element);
    force_element = el->FindNextElement("force");
  }
 
  // Parse moment elements
 
  Element* moment_element = el->FindElement("moment");
  while (moment_element) {
    Forces.push_back(new FGExternalForce(FDMExec));
    Forces.back()->setMoment(moment_element);
    moment_element = el->FindNextElement("moment");
  }
 
  PostLoad(el, FDMExec);
 
  if (!Forces.empty()) bind();
 
  return true;
}

Here is the call graph for this function:

Run()

bool Run ( bool  Holding )

overridevirtual

Sum all the constituent forces for this cycle.

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

true always.

Reimplemented from FGModel.

Definition at line 114 of file FGExternalReactions.cpp.

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

Here is the call graph for this function:

---

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

• FGExternalReactions.h
• FGExternalReactions.cpp