ssShipMotion Class Reference

This class defines the ship's motion in the selected sea states. More...

Public Member Functions
	ssShipMotion ()
	Default Constructor.
void	setShipPerformance (ssShipPerformance *shipPerfomance)
	Set a pointer to the ShipPerformance object that this class should use to get performance data for the specific size of this ship and the current sea state.
ssShipPerformance *	getShipPerformance ()
	Get a pointer to the ShipPerformance object that this class should use to get performance data for the specific size of this ship and the current sea state.
void	setNatoSeaState (int natoSeaState)
	Sets the NATO Sea State.
int	getNatoSeaState ()
	Gets the NATO sea state that is currently being used by this class.
void	setWindSpeed (float wind_knots)
	Internally this class uses the NATO sea state for computation.
float	getWindSpeed ()
	Returns the last wind speed that was provided.
void	setShipSize (float beam_length_m, float length_between_perp_m, float roll_const_sec_per_sqrt_m, float metacentric_height_m)
	Set the data that defines the size of this ship.
void	getShipSize (float &beam_length_m, float &length_between_perp_m, float &roll_const_sec_per_sqrt_m, float &metacentric_height_m)
	Get the data that defines the size of this ship.
void	setWorldOrientation (float heading, float pitch, float roll)
	Set the orientation of the ship without any wave motion.
void	getWorldOrientation (float &heading, float &pitch, float &roll)
	Get the orientation of the ship without any wave motion.
void	getOffsetOrientation (double time_sec, float &heading, float &pitch, float &roll)
	Get the offset orientation of the ship.
void	setWorldPosition (double x, double y, double z)
	Set the position of the ship without any wave motion.
void	getWorldPosition (double &x, double &y, double &z)
	Get the position of the ship without any wave motion.
void	getOffsetTranslation (double time_sec, float &x, float &y, float &z)
	Get the current offset translation of the ship.
VECTOR	getUnitTangentialVelocity (double time_sec)
	Calculates the ship motion instantaneous unit tangential direction velocity (at radius = 1).
VECTOR	getAngularVelocity (double time_sec, VECTOR shippoint)
	Calculates the ship motion instantaneous angular velocity direction vector.
rotmatrix	getSensorMotionMatrix (double time_sec)
	Calculates the sensor motion rotation matrix.
void	getAverageRotation (double time_start, double time_end, double &heading, double &pitch, double &roll, double &heading_rate, double &pitch_rate, double &roll_rate)
	getAverageRotation : Returns average orientation and rate of orientation change during time interval
float	getEstimatedRotationPotential ()
	Estimated Rotation Potential (not an established industry quantity)

Private Member Functions
void	updatePerformanceData ()
	Update the performance data used by this ship.
double	SHMOscillations (double time_sec, double amplitude, double ang_freq_rad_per_sec, double phase_rad)
	Simple Harmonic Motion equation for ship motion.
double	SHMOscillations_time_deriv (double time_sec, double amplitude, double ang_freq_rad_per_sec, double phase_rad)
	Simple Harmonic Motion equation for ship motion.
void	getMotionAngles (double time_sec, double &pitch, double &roll)
	Calculates the Ship Motion Rotation Angles.
void	getMotionRates (double time_sec, double &pitchrate, double &rollrate)
	Return pitch and roll time derivatives.

Private Attributes
float	m_windSpeed
int	m_seaState
float	m_beamLength
float	m_lengthBetweenPerpendicular
float	m_rollConstant
float	m_metacentricHeight
float	m_rollAmplitude
float	m_rollPeriod
float	m_pitchAmplitude
float	m_pitchPeriod
float	m_initialHeading
float	m_initialPitch
float	m_initialRoll
double	m_positionX
double	m_positionY
double	m_positionZ
ssShipPerformance *	m_shipPerformance

Detailed Description

This class defines the ship's motion in the selected sea states.

It uses the sea state behaviors (DOD-STD-1399/301). Motion is defined by calculation of rotation matrices.

Constructor & Destructor Documentation

ssShipMotion::ssShipMotion

(

)

Default Constructor.

Member Function Documentation

void ssShipMotion::setShipPerformance

(

ssShipPerformance *

shipPerfomance

)

Set a pointer to the ShipPerformance object that this class should use to get performance data for the specific size of this ship and the current sea state.

Parameters

shipPerformance

- pointer to a class that contains and can provides ship performance data.

ssShipPerformance* ssShipMotion::getShipPerformance ( )

inline

Get a pointer to the ShipPerformance object that this class should use to get performance data for the specific size of this ship and the current sea state.

void ssShipMotion::setNatoSeaState

(

int

natoSeaState

)

Sets the NATO Sea State.

The different sea states are defined in (DOD-STD-1399/301)

Parameters

natoSeaState

- The NATO Sea State to use

int ssShipMotion::getNatoSeaState ( )

inline

Gets the NATO sea state that is currently being used by this class.

Returns

The NATO Sea State

void ssShipMotion::setWindSpeed

(

float

wind_knots

)

Internally this class uses the NATO sea state for computation.

This method is a convenience method that will convert the provided wind speed into a NATO sea state.

Parameters

wind_knots

- The wind speed in knots

float ssShipMotion::getWindSpeed ( )

inline

Returns the last wind speed that was provided.

Note: The wind speed this method returns might not match the current NATO sea state if the sea state was set directly.

Returns

The wind speed in knots

void ssShipMotion::setShipSize	(	float	beam_length_m,
		float	length_between_perp_m,
		float	roll_const_sec_per_sqrt_m,
		float	metacentric_height_m
	)

Set the data that defines the size of this ship.

This should be called by the ssShipFactory based on the data read from a ship definition configuration file.

Parameters

beam_length_m	- the maximum beam at or below the waterline in meters
length_between_perp_m	- the length between perpendiculars of the ship in meters (along the long axis of the ship)
roll_const_sec_per_sqrt_m	- is a roll constant based upon experimental results from similar ships - usual range 0.69 to 0.89 [sec/sqrt(meter)]
metacentric_height_m	- the maximum metacentric height in meters

void ssShipMotion::getShipSize ( float &  beam_length_m, float &  length_between_perp_m, float &  roll_const_sec_per_sqrt_m, float &  metacentric_height_m  )

inline

Get the data that defines the size of this ship.

Parameters

beam_length_m	- the maximum beam at or below the waterline in meters
length_between_perp_m	- the length between perpendiculars of the ship in meters (along the long axis of the ship)
roll_const_sec_per_sqrt_m	- is a roll constant based upon experimental results from similar ships - usual range 0.69 to 0.89 [sec/sqrt(meter)]
metacentric_height_m	- the maximum metacentric height in meters

void ssShipMotion::setWorldOrientation ( float  heading, float  pitch, float  roll  )

inline

Set the orientation of the ship without any wave motion.

This would be the resting orientation or calm sea orientation of this ship.

Parameters

heading	- The heading in radians of the ship relative to north
pitch	- The pitch in radians of the ship relative to the horizon
roll	- The roll in radians of the ship relative to level

void ssShipMotion::getWorldOrientation ( float &  heading, float &  pitch, float &  roll  )

inline

Get the orientation of the ship without any wave motion.

This would be the resting orientation or calm sea orientation of this ship.

Parameters

heading	- The heading in radians of the ship relative to north
pitch	- The pitch in radians of the ship relative to the horizon
roll	- The roll in radians of the ship relative to level

void ssShipMotion::getOffsetOrientation	(	double	time_sec,
		float &	heading,
		float &	pitch,
		float &	roll
	)

Get the offset orientation of the ship.

This is the rotational motion computed due to the current sea state.

Parameters

time_sec	- The current simulation time in seconds
heading	- The heading offset in radians
pitch	- The pitch offset in radians
roll	- The roll offset in radians

void ssShipMotion::setWorldPosition ( double  x, double  y, double  z  )

inline

Set the position of the ship without any wave motion.

This would be the resting position or calm sea position of this ship.

Parameters

x	- The x component of the position of this ship.
y	- The y component of the position of this ship.
z	- The z component of the position of this ship.

void ssShipMotion::getWorldPosition ( double &  x, double &  y, double &  z  )

inline

Get the position of the ship without any wave motion.

This would be the resting position or calm sea position of this ship.

Parameters

x	- The x component of the position of this ship.
y	- The y component of the position of this ship.
z	- The z component of the position of this ship.

void ssShipMotion::getOffsetTranslation	(	double	time_sec,
		float &	x,
		float &	y,
		float &	z
	)

Get the current offset translation of the ship.

This is the heave, sway, and surge from the current sea state. This capability is not currently implemented, but could be in the future.

Parameters

time_sec	- The current simulation time in seconds
x	- The x component of the offset of this ship.
y	- The y component of the offset of this ship.
z	- The z component of the offset of this ship.

VECTOR ssShipMotion::getUnitTangentialVelocity

(

double

time_sec

)

Calculates the ship motion instantaneous unit tangential direction velocity (at radius = 1).

This method assumes ship coordinate origin are set at the metacentric height, Ship length lies along the x-axis, and z-axis is vertical.

Parameters

time_sec

- elapsed time in seconds

Returns

- the instantaneous unit tangential velocity vector

VECTOR ssShipMotion::getAngularVelocity	(	double	time_sec,
		VECTOR	shippoint
	)

Calculates the ship motion instantaneous angular velocity direction vector.

This class assumes that the ship coordinate origin is set at the metacentric height, the ship length lies along the x-axis, and the z-axis is vertical

Parameters

time_sec	- elapsed time in seconds
xpos	- x position of point under rotation wrt origin at meta-center of ship
ypos	- y position of point under rotation wrt origin at meta-center of ship
zpos	- z position of point under rotation wrt origin at meta-center of ship

Returns

Ship motion instantaneous angular velocity direction vector in (x, y, z) ship coordinates. Note that it has been normalized, so is a unit vector

rotmatrix ssShipMotion::getSensorMotionMatrix

(

double

time_sec

)

Calculates the sensor motion rotation matrix.

Equivalent motion of a sensor wrt ship initial position. Assumes ship coordinate origin is set at the metacentric height, the ship length lies along the x-axis, and z-axis is vertical

Parameters

time_sec

- elapsed time in seconds

Returns

Sensor motion rotation matrix in homogeneous coordinates

void ssShipMotion::getAverageRotation	(	double	time_start,
		double	time_end,
		double &	heading,
		double &	pitch,
		double &	roll,
		double &	heading_rate,
		double &	pitch_rate,
		double &	roll_rate
	)

getAverageRotation : Returns average orientation and rate of orientation change during time interval

float ssShipMotion::getEstimatedRotationPotential

(

)

Estimated Rotation Potential (not an established industry quantity)

void ssShipMotion::updatePerformanceData ( )

private

Update the performance data used by this ship.

This data is based on the currently assigned ship size and sea state. The updated performance data will be used when computing motion data for this ship.

Parameters

state	- NATO Sea State
beam_length_m	- the maximum beam at or below the waterline in meters
length_between_perp_m	- the length between perpendiculars of the ship in meters (along the long axis of the ship)
roll_const_sec_per_sqrt_m	- is a roll constant based upon experimental results from similar ships - usual range 0.69 to 0.89 [sec/sqrt(meter)]
metacentric_height_m	- the maximum metacentric height in meters

double ssShipMotion::SHMOscillations ( double  time_sec, double  amplitude, double  ang_freq_rad_per_sec, double  phase_rad  )

private

Simple Harmonic Motion equation for ship motion.

double ssShipMotion::SHMOscillations_time_deriv ( double  time_sec, double  amplitude, double  ang_freq_rad_per_sec, double  phase_rad  )

private

Simple Harmonic Motion equation for ship motion.

void ssShipMotion::getMotionAngles ( double  time_sec, double &  pitch, double &  roll  )

private

Calculates the Ship Motion Rotation Angles.

This method assumes ship coordinate origin are set at the metacentric height, Ship length lies along the x-axis, z-axis is vertical.

Parameters

time_sec	- elapsed time in seconds
pitch	[rad] - the amount the ship is pitching at the provided time
roll	[rad] - the amount the ship is rolling at the provided time

void ssShipMotion::getMotionRates ( double  time_sec, double &  pitchrate, double &  rollrate  )

private

Return pitch and roll time derivatives.

This method assumes ship coordinate origin are set at the metacentric height, Ship length lies along the x-axis, z-axis is vertical.

Parameters

time_sec	- elapsed time in seconds
pitchrate	[rad/s] - the rate at which the ship is pitching at the provided time
rollrate	[rad/s] - the rate at which the ship is rolling at the provided time

Member Data Documentation

float ssShipMotion::m_windSpeed

private

int ssShipMotion::m_seaState

private

float ssShipMotion::m_beamLength

private

float ssShipMotion::m_lengthBetweenPerpendicular

private

float ssShipMotion::m_rollConstant

private

float ssShipMotion::m_metacentricHeight

private

float ssShipMotion::m_rollAmplitude

private

float ssShipMotion::m_rollPeriod

private

float ssShipMotion::m_pitchAmplitude

private

float ssShipMotion::m_pitchPeriod

private

float ssShipMotion::m_initialHeading

private

float ssShipMotion::m_initialPitch

private

float ssShipMotion::m_initialRoll

private

double ssShipMotion::m_positionX

private

double ssShipMotion::m_positionY

private

double ssShipMotion::m_positionZ

private

ssShipPerformance* ssShipMotion::m_shipPerformance

private

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

• ssShipMotion.h