Models atmospheric disturbances: winds, gusts, turbulence, downbursts, etc.
Turbulence
Various turbulence models are available. They are specified via the property atmosphere/turb-type. The following models are available:
- 0: ttNone (turbulence disabled)
- 1: ttStandard
- 2: ttCulp
- 3: ttMilspec (Dryden spectrum)
- 4: ttTustin (Dryden spectrum)
The Milspec and Tustin models are described in the Yeager report cited below. They both use a Dryden spectrum model whose parameters (scale lengths and intensities) are modelled according to MIL-F-8785C. Parameters are modelled differently for altitudes below 1000ft and above 2000ft, for altitudes in between they are interpolated linearly.
The two models differ in the implementation of the transfer functions described in the milspec.
To use one of these two models, set atmosphere/turb-type to 4 resp. 5, and specify values for atmosphere/turbulence/milspec/windspeed_at_20ft_AGL-fps and atmosphere/turbulence/milspec/severity (the latter corresponds to the probability of exceedence curves from Fig. 7 of the milspec, allowable range is 0 (disabled) to 7). atmosphere/psiw-rad is respected as well; note that you have to specify a positive wind magnitude to prevent psiw from being reset to zero.
Reference values (cf. figures 7 and 9 from the milspec):
| Intensity | windspeed_at_20ft_AGL-fps | severity |
| light | 25 (15 knots) | 3 |
| moderate | 50 (30 knots) | 4 |
| severe | 75 (45 knots) | 6 |
Cosine Gust
A one minus cosine gust model is available. This permits a configurable, predictable gust to be input to JSBSim for testing handling and dynamics. Here is how a gust can be entered in a script:
<event name="Introduce gust">
<condition> simulation/sim-time-sec ge 10 </condition>
<set name="atmosphere/cosine-gust/startup-duration-sec" value="5"/>
<set name="atmosphere/cosine-gust/steady-duration-sec" value="1"/>
<set name="atmosphere/cosine-gust/end-duration-sec" value="5"/>
<set name="atmosphere/cosine-gust/magnitude-ft_sec" value="30"/>
<set name="atmosphere/cosine-gust/frame" value="2"/>
<set name="atmosphere/cosine-gust/X-velocity-ft_sec" value="-1"/>
<set name="atmosphere/cosine-gust/Y-velocity-ft_sec" value="0"/>
<set name="atmosphere/cosine-gust/Z-velocity-ft_sec" value="0"/>
<set name="atmosphere/cosine-gust/start" value="1"/>
<notify/>
</event>
The x, y, z velocity components are meant to define the direction vector. The vector will be normalized by the routine, so it does not need to be a unit vector.
The startup duration is the time it takes to build up to full strength (magnitude-ft_sec) from zero. Steady duration is the time the gust stays at the specified magnitude. End duration is the time it takes to dwindle to zero from the specified magnitude. The start and end transients are in a smooth cosine shape.
The frame is specified from the following enum:
enum eGustFrame {gfNone=0, gfBody, gfWind, gfLocal};
That is, if you specify the X, Y, Z gust direction vector in the body frame, frame will be "1". If the X, Y, and Z gust direction vector is in the Wind frame, use frame = 2. If you specify the gust direction vector in the local frame (N-E-D) use frame = 3. Note that an internal local frame direction vector is created based on the X, Y, Z direction vector you specify and the frame at the time the gust is begun. The direction vector is not updated after the initial creation. This is to keep the gust at the same direction independent of aircraft dynamics.
The gust is triggered when the property atmosphere/cosine-gust/start is set to 1. It can be used repeatedly - the gust resets itself after it has completed.
The cosine gust is global: it affects the whole world not just the vicinity of the aircraft.
- See also
- Yeager, Jessie C.: "Implementation and Testing of Turbulence Models for
the F18-HARV" (pdf), NASA CR-1998-206937, 1998
-
MIL-F-8785C: Military Specification: Flying Qualities of Piloted Aircraft
Definition at line 166 of file FGWinds.h.
|
| enum | eGustFrame { gfNone =0
, gfBody
, gfWind
, gfLocal
} |
| |
| enum | tType {
ttNone
, ttStandard
, ttCulp
, ttMilspec
,
ttTustin
} |
| |
| 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...
|
| |
|
| | FGWinds (FGFDMExec *) |
| | Constructor.
|
| |
| | ~FGWinds () |
| | Destructor.
|
| |
| virtual void | EndGustDuration (double dur) |
| | Specifies the length of time it takes for the gust to return to zero velocity.
|
| |
| virtual double | GetGustNED (int idx) const |
| | Retrieves a gust component in NED frame.
|
| |
| virtual const FGColumnVector3 & | GetGustNED (void) const |
| | Retrieves the gust components in NED frame.
|
| |
| virtual int | GetProbabilityOfExceedence () const |
| |
| virtual double | GetRhythmicity () const |
| |
| virtual double | GetTotalWindNED (int idx) const |
| | Retrieves a total wind component in NED frame.
|
| |
| virtual const FGColumnVector3 & | GetTotalWindNED (void) const |
| | Retrieves the total wind components in NED frame.
|
| |
| virtual double | GetTurbDirection (void) const |
| |
| virtual double | GetTurbGain () const |
| |
| virtual double | GetTurbMagnitude (void) const |
| |
| virtual double | GetTurbNED (int idx) const |
| | Retrieves a turbulence component in NED frame.
|
| |
| virtual double | GetTurbPQR (int idx) const |
| |
| virtual const FGColumnVector3 & | GetTurbPQR (void) const |
| |
| virtual double | GetTurbRate () const |
| |
| virtual tType | GetTurbType () const |
| |
| virtual double | GetWindNED (int idx) const |
| | Retrieves a wind component in NED frame.
|
| |
| virtual const FGColumnVector3 & | GetWindNED (void) const |
| | Retrieves the wind components in NED frame.
|
| |
| virtual double | GetWindPsi (void) const |
| | Retrieves the direction that the wind is coming from.
|
| |
| virtual double | GetWindspeed (void) const |
| |
| virtual double | GetWindspeed20ft () const |
| |
| virtual void | GustFrame (eGustFrame gFrame) |
| | Specifies the frame that the gust direction vector components are specified in.
|
| |
| virtual void | GustMagnitude (double mag) |
| | Specifies the magnitude of the gust in feet/second.
|
| |
| virtual void | GustXComponent (double x) |
| | Specifies the X component of velocity in the specified gust frame (ft/sec).
|
| |
| virtual void | GustYComponent (double y) |
| | Specifies the Y component of velocity in the specified gust frame (ft/sec).
|
| |
| virtual void | GustZComponent (double z) |
| | Specifies the Z component of velocity in the specified gust frame (ft/sec).
|
| |
| bool | InitModel (void) override |
| |
| void | NumberOfUpDownburstCells (int num) |
| |
| bool | Run (bool Holding) override |
| | Runs the winds model; called by the Executive Can pass in a value indicating if the executive is directing the simulation to Hold.
|
| |
| virtual void | SetGustNED (double gN, double gE, double gD) |
| | Sets the gust components in NED frame.
|
| |
| virtual void | SetGustNED (int idx, double gust) |
| | Sets a gust component in NED frame.
|
| |
| virtual void | SetProbabilityOfExceedence (int idx) |
| | allowable range: 0-7, 3=light, 4=moderate, 6=severe turbulence
|
| |
| virtual void | SetRhythmicity (double r) |
| |
| virtual void | SetTurbGain (double tg) |
| |
| virtual void | SetTurbNED (int idx, double turb) |
| | Sets a turbulence component in NED frame.
|
| |
| virtual void | SetTurbRate (double tr) |
| |
| virtual void | SetTurbType (tType tt) |
| | Turbulence models available: ttNone, ttStandard, ttBerndt, ttCulp, ttMilspec, ttTustin.
|
| |
| virtual void | SetWindNED (const FGColumnVector3 &wind) |
| | Sets the wind components in NED frame.
|
| |
| virtual void | SetWindNED (double wN, double wE, double wD) |
| | Sets the wind components in NED frame.
|
| |
| virtual void | SetWindNED (int idx, double wind) |
| | Sets a wind component in NED frame.
|
| |
| virtual void | SetWindPsi (double dir) |
| | Sets the direction that the wind is coming from.
|
| |
| virtual void | SetWindspeed (double speed) |
| |
| virtual void | SetWindspeed20ft (double ws) |
| |
| virtual void | StartGust (bool running) |
| | Initiates the execution of the gust.
|
| |
| virtual void | StartupGustDuration (double dur) |
| | Specifies the duration of the startup portion of the gust.
|
| |
| virtual void | SteadyGustDuration (double dur) |
| | Specifies the length of time that the gust is at a steady, full strength.
|
| |
| | 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.
|
| |
| virtual bool | Load (Element *el) |
| |
| void | SetPropertyManager (std::shared_ptr< FGPropertyManager > fgpm) |
| |
| void | SetRate (unsigned int tt) |
| | Set the ouput rate for the model in frames.
|
| |
| 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) |
| |
| | FGJSBBase () |
| | Constructor for FGJSBBase.
|
| |
| virtual | ~FGJSBBase () |
| | Destructor for FGJSBBase.
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| |
| void | disableHighLighting (void) |
| | Disables highlighting in the console output.
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| |
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| static const std::string & | GetVersion (void) |
| | Returns the version number of JSBSim.
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| |
| static constexpr double | KelvinToFahrenheit (double kelvin) |
| | Converts from degrees Kelvin to degrees Fahrenheit.
|
| |
| static constexpr double | CelsiusToRankine (double celsius) |
| | Converts from degrees Celsius to degrees Rankine.
|
| |
| static constexpr double | RankineToCelsius (double rankine) |
| | Converts from degrees Rankine to degrees Celsius.
|
| |
| static constexpr double | KelvinToRankine (double kelvin) |
| | Converts from degrees Kelvin to degrees Rankine.
|
| |
| static constexpr double | RankineToKelvin (double rankine) |
| | Converts from degrees Rankine to degrees Kelvin.
|
| |
| static constexpr double | FahrenheitToCelsius (double fahrenheit) |
| | Converts from degrees Fahrenheit to degrees Celsius.
|
| |
| 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 | KelvinToCelsius (double kelvin) |
| | Converts from degrees Kelvin to degrees Celsius.
|
| |
| static constexpr double | FeetToMeters (double measure) |
| | Converts from feet to meters.
|
| |
| static bool | EqualToRoundoff (double a, double b) |
| | Finite precision comparison.
|
| |
| static bool | EqualToRoundoff (float a, float b) |
| | Finite precision comparison.
|
| |
| static bool | EqualToRoundoff (float a, double b) |
| | Finite precision comparison.
|
| |
| static bool | EqualToRoundoff (double a, float b) |
| | Finite precision comparison.
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| |
| 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 char | highint [5] = {27, '[', '1', 'm', '\0' } |
| | highlights text
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| |
| static char | halfint [5] = {27, '[', '2', 'm', '\0' } |
| | low intensity text
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| |
| static char | normint [6] = {27, '[', '2', '2', 'm', '\0' } |
| | normal intensity text
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| |
| static char | reset [5] = {27, '[', '0', 'm', '\0' } |
| | resets text properties
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| |
| static char | underon [5] = {27, '[', '4', 'm', '\0' } |
| | underlines text
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| |
| 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
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| |
| static char | fggreen [6] = {27, '[', '3', '2', 'm', '\0' } |
| | green text
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| |
| static char | fgdef [6] = {27, '[', '3', '9', 'm', '\0' } |
| | default text
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| |
| static short | debug_lvl = 1 |
| |
| bool | Upload (Element *el, bool preLoad) |
| | Uploads this model in memory.
|
| |
| static std::string | CreateIndexedPropertyName (const std::string &Property, int index) |
| |
| unsigned int | exe_ctr |
| |
| FGFDMExec * | FDMExec |
| |
| std::string | Name |
| |
| std::shared_ptr< FGPropertyManager > | PropertyManager |
| |
| unsigned int | rate |
| |
| FGPropertyReader | LocalProperties |
| |
| std::vector< std::shared_ptr< FGFunction > > | PostFunctions |
| |
| std::vector< std::shared_ptr< FGFunction > > | PreFunctions |
| |
| 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.
|
| |
| 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__ |
| |
Inheritance diagram for FGWinds:
1.9.8 
