6DOF Wind (Quaternion)

Implement quaternion representation of six-degrees-of-freedom equations of motion with respect to wind axes

Libraries:
Aerospace Blockset / Equations of Motion / 6DOF

Description

The 6DOF Wind (Quaternion) block considers the rotation of a wind-fixed coordinate frame (X_w, Y_w, Z_w) about an flat Earth reference frame (X_e, Y_e, Z_e). For more information on the wind-fixed coordinate frame, see Algorithms.

Aerospace Blockset™ uses quaternions that are defined using the scalar-first convention.

Limitations

The block assumes that the applied forces act at the center of gravity of the body, and that the mass and inertia are constant.

Ports

Input

expand all

F_xyz(N) — Applied forces
three-element vector

Applied forces, specified as a three-element vector.

Data Types: double

M_xyz(N-m) — Applied moments
three-element vector

Applied moments, specified as a three-element vector.

Data Types: double

Output

expand all

V_e — Velocity in flat Earth reference frame
three-element vector

Velocity in the flat Earth reference frame, returned as a three-element vector.

Data Types: double

X_e — Position in flat Earth reference frame
three-element vector

Position in the flat Earth reference frame, returned as a three-element vector.

Data Types: double

μ γ x (rad) — Wind rotation angles
three-element vector

Wind rotation angles [bank, flight path, heading], returned as a three-element vector, in radians.

Data Types: double

DCM_we — Coordinate transformation
3-by-3 matrix

Coordinate transformation from flat Earth axes to wind-fixed axes, returned as a 3-by-3 matrix.

Data Types: double

V_w — Velocity in wind-fixed frame
three-element vector

Velocity in wind-fixed frame, returned as a three-element vector.

Data Types: double

α β (rad) — Angle of attack and sideslip angle
two-element vector

Angle of attack and sideslip angle, returned as a two-element vector, in radians.

Data Types: double

dα/dt dβ/dt — Rate of change of angle of attack and rate of change of sideslip angle
two-element vector

Rate of change of angle of attack and rate of change of sideslip angle, returned as a two-element vector, in radians per second.

Data Types: double

ω_b (rad/s) — Angular rates in body-fixed axes
three-element vector

Angular rates in body-fixed axes, returned as a three-element vector.

Data Types: double

dω_b/dt — Angular accelerations in body-fixed axes
three-element vector

Angular accelerations in body-fixed axes, returned as a three-element vector, in radians per second squared.

Data Types: double

A_bb — Accelerations in body-fixed axes
three-element vector

Accelerations in body-fixed axes with respect to body frame, returned as a three-element vector.

Data Types: double

A_be — Accelerations with respect to inertial frame
three-element vector

Accelerations in body-fixed axes with respect to inertial frame (flat Earth), returned as a three-element vector. You typically connect this signal to the accelerometer.

Dependencies

To enable this point, select Include inertial acceleration.

Data Types: double

Parameters

expand all

Main

Units — Input and output units
`Metric (MKS)` (default) | `English (Velocity in ft/s)` | `English (Velocity in kts)`

Input and output units, specified as Metric (MKS), English (Velocity in ft/s), or English (Velocity in kts).

Units	Forces	Moment	Acceleration	Velocity	Position	Mass	Inertia
`Metric (MKS)`	Newton	Newton-meter	Meters per second squared	Meters per second	Meters	Kilogram	Kilogram meter squared
`English (Velocity in ft/s)`	Pound	Foot-pound	Feet per second squared	Feet per second	Feet	Slug	Slug foot squared
`English (Velocity in kts)`	Pound	Foot-pound	Feet per second squared	Knots	Feet	Slug	Slug foot squared

Programmatic Use

Block Parameter: units

Type: character vector

Values: Metric (MKS) | English (Velocity in ft/s) | English (Velocity in kts)

Default: Metric (MKS)

Mass Type — Mass type
`Fixed` (default) | `Simple Variable` | `Custom Variable`

Mass type, specified according to the following table.

Mass Type	Description	Default For
`Fixed`	Mass is constant throughout the simulation.	6DOF (Euler Angles) 6DOF (Quaternion) 6DOF Wind (Wind Angles) 6DOF Wind (Quaternion) 6DOF ECEF (Quaternion)
`Simple Variable`	Mass and inertia vary linearly as a function of mass rate.	Simple Variable Mass 6DOF (Euler Angles) Simple Variable Mass 6DOF (Quaternion) Simple Variable Mass 6DOF Wind (Wind Angles) Simple Variable Mass 6DOF Wind (Quaternion) Simple Variable Mass 6DOF ECEF (Quaternion)
`Custom Variable`	Mass and inertia variations are customizable.	Custom Variable Mass 6DOF (Euler Angles) Custom Variable Mass 6DOF (Quaternion) Custom Variable Mass 6DOF Wind (Wind Angles) Custom Variable Mass 6DOF Wind (Quaternion) Custom Variable Mass 6DOF ECEF (Quaternion)

The Simple Variable selection conforms to the previously described equations of motion.

Programmatic Use

Block Parameter: mtype

Type: character vector

Values: Fixed | Simple Variable | Custom Variable

Default: Simple Variable

Representation — Equations of motion representation
`Quaternion` (default) | `Wind Angles`

Equations of motion representation, specified according to the following table.

Representation	Description
`Quaternion`	Use quaternions within equations of motion.
`Wind Angles`	Use wind angles within equations of motion.

The Quaternion selection conforms to the equations of motion in Algorithms.

Programmatic Use

Block Parameter: rep

Type: character vector

Values: Wind Angles | Quaternion

Default: 'Wind Angles'

Initial position in inertial axes [Xe,Ye,Ze] — Position in inertial axes
`[0 0 0]` (default) | three-element vector

Initial location of the body in the flat Earth reference frame, specified as a three-element vector.

Programmatic Use

Block Parameter: xme_0

Type: character vector

Values: '[0 0 0]' | three-element vector

Default: '[0 0 0]'

Initial airspeed, angle of attack, and sideslip angle [V,alpha,beta] — Initial airspeed, angle of attack, and sideslip angle
`[0 0 0]` (default) | three-element vector

Initial airspeed, angle of attack, and sideslip angle, specified as a three-element vector.

Programmatic Use

Block Parameter: Vm_0

Type: character vector

Values: '[0 0 0]' | three-element vector

Default: '[0 0 0]'

Initial wind orientation [bank angle,flight path angle,heading angle] — Initial wind orientation
`[0 0 0]` (default) | three-element vector

Initial wind angles [bank, flight path, and heading], specified as a three-element vector in radians.

Programmatic Use

Block Parameter: wind_0

Type: character vector

Values: '[0 0 0]' | three-element vector

Default: '[0 0 0]'

Initial body rotation rates [p,q,r] — Initial body rotation
`[0 0 0]` (default) | three-element vector

Initial body-fixed angular rates with respect to the NED frame, specified as a three-element vector, in radians per second.

Programmatic Use

Block Parameter: pm_0

Type: character vector

Values: '[0 0 0]' | three-element vector

Default: '[0 0 0]'

Initial mass — Initial mass
`1.0` (default) | scalar

Initial mass of the rigid body, specified as a double scalar.

Programmatic Use

Block Parameter: mass_0

Type: character vector

Values: '1.0' | double scalar

Default: '1.0'

Inertia in body axis — Inertia of body
`eye(3)` (default) | scalar

Inertia of the body, specified as a double scalar.

Programmatic Use

Block Parameter: inertia

Type: character vector

Values: 'eye(3)' | double scalar

Default: 'eye(3)'

Include inertial acceleration — Include inertial acceleration port
`off` (default) | `on`

Select this check box to add an inertial acceleration port.

Dependencies

To enable the A_{b ff} port, select this parameter.

Programmatic Use

Block Parameter: abi_flag

Type: character vector

Values: 'off' | 'on'

Default: off

State Attributes

Assign a unique name to each state. You can use state names instead of block paths during linearization.

To assign a name to a single state, enter a unique name between quotes, for example, 'velocity'.
To assign names to multiple states, enter a comma-separated list surrounded by braces, for example, {'a', 'b', 'c'}. Each name must be unique.
If a parameter is empty (' '), no name is assigned.
The state names apply only to the selected block with the name parameter.
The number of states must divide evenly among the number of state names.
You can specify fewer names than states, but you cannot specify more names than states.
For example, you can specify two names in a system with four states. The first name applies to the first two states and the second name to the last two states.
To assign state names with a variable in the MATLAB^® workspace, enter the variable without quotes. A variable can be a character vector, cell array, or structure.

Position: e.g., {'Xe', 'Ye', 'Ze'} — Position state name
`''` (default) | comma-separated list surrounded by braces

Position state names, specified as a comma-separated list surrounded by braces.

Programmatic Use

Block Parameter: xme_statename

Type: character vector

Values: '' | comma-separated list surrounded by braces

Default: ''

Velocity: e.g., 'V' — Velocity state name
`''` (default) | character vector

Velocity state names, specified as a character vector.

Programmatic Use

Block Parameter: Vm_statename

Type: character vector

Values: '' | character vector

Default: ''

Incidence angle e.g., 'alpha' — Incidence angle state name
`''` (default) | character vector

Incidence angle state name, specified as a character vector.

Programmatic Use

Block Parameter: alpha_statename

Type: character vector

Values: ''

Default: ''

Sideslip angle e.g., 'beta' — Sideslip angle state name
`''` (default) | character vector

Sideslip angle state name, specified as a character vector.

Programmatic Use

Block Parameter: beta_statename

Type: character vector

Values: ''

Default: ''

Wind orientation e.g., {'mu', 'gamma', 'chi'} — Wind orientation state names
`''` (default) | comma-separated list surrounded by braces

Wind orientation state names, specified as a comma-separated list surrounded by braces.

Programmatic Use

Block Parameter: wind_statename

Type: character vector

Values: ''

Default: ''

Quaternion vector: e.g., {'qr', 'qi', 'qj', 'qk'} — Quaternion vector state name
`''` (default) | comma-separated list surrounded by braces

Quaternion vector state names, specified as a comma-separated list surrounded by braces.

Programmatic Use

Block Parameter: quat_statename

Type: character vector

Values: '' | comma-separated list surrounded by braces

Default: ''

Body rotation rates: e.g., {'p', 'q', 'r'} — Body rotation state names
`''` (default) | comma-separated list surrounded by braces

Body rotation rate state names, specified comma-separated list surrounded by braces.

Programmatic Use

Block Parameter: pm_statename

Type: character vector

Values: '' | comma-separated list surrounded by braces

Default: ''

Mass: e.g., 'mass' — Mass state name
`''` (default) | character vector

Mass state name, specified as a character vector.

Programmatic Use

Block Parameter: mass_statename

Type: character vector

Values: '' | character vector

Default: ''

Algorithms

The origin of the wind-fixed coordinate frame is the center of gravity of the body, and the body is assumed to be rigid, an assumption that eliminates the need to consider the forces acting between individual elements of mass. The flat Earth reference frame is considered inertial, an excellent approximation that allows the forces due to the Earth's motion relative to the “fixed stars” to be neglected.

Flat Earth reference frame

The translational motion of the wind-fixed coordinate frame is given below, where the applied forces [F_x F_y F_z]^Tare in the wind-fixed frame, and the mass of the body m is assumed constant.

$\begin{array}{l} {\bar{F}}_{w} = [\begin{matrix} F_{x} \\ F_{y} \\ F_{z} \end{matrix}] = m ({\dot{\bar{V}}}_{w} + {\bar{ω}}_{w} \times {\bar{V}}_{w}) \\ A_{b e} = D C M_{w b} \frac{{\bar{F}}_{w}}{m} \\ {\bar{V}}_{w} = [\begin{matrix} V \\ 0 \\ 0 \end{matrix}], {\bar{ω}}_{w} = [\begin{matrix} p_{w} \\ q_{w} \\ r_{w} \end{matrix}] = D C M_{w b} [\begin{matrix} p_{b} - \dot{β} \sin α \\ q_{b} - \dot{α} \\ r_{b} + \dot{β} \cos α \end{matrix}], {\bar{ω}}_{b} = [\begin{matrix} p_{b} \\ q_{b} \\ r_{b} \end{matrix}] \\ A_{b b} = [\begin{matrix} {\dot{u}}_{b} \\ {\dot{v}}_{b} \\ {\dot{w}}_{b} \end{matrix}] = D C M_{w b} [\frac{{\bar{F}}_{w}}{m} - {\bar{ω}}_{w} \times {\bar{V}}_{w}] \end{array}$

The rotational dynamics of the body-fixed frame are given below, where the applied moments are [L M N]^T, and the inertia tensor I is with respect to the origin O. Inertia tensor I is easier to define in body-fixed frame.

$\begin{array}{l} {\bar{M}}_{b} = [\begin{matrix} L \\ M \\ N \end{matrix}] = I {\dot{\bar{ω}}}_{b} + {\bar{ω}}_{b} \times (I {\bar{ω}}_{b}) \\ I = [\begin{matrix} I_{x x} & - I_{x y} & - I_{x z} \\ - I_{y x} & I_{y y} & - I_{y z} \\ - I_{z x} & - I_{z y} & I_{z z} \end{matrix}] \end{array}$

The integration of the rate of change of the quaternion vector is given below.

$[\begin{matrix} {\dot{q}}_{0} \\ {\dot{q}}_{1} \\ {\dot{q}}_{2} \\ {\dot{q}}_{3} \end{matrix}] = - \frac{1}{2} [\begin{matrix} 0 & p & q & r \\ - p & 0 & - r & q \\ - q & r & 0 & - p \\ - r & - q & p & 0 \end{matrix}] [\begin{matrix} q_{0} \\ q_{1} \\ q_{2} \\ q_{3} \end{matrix}]$

References

[1] Stevens, Brian, and Frank Lewis. Aircraft Control and Simulation. New York: John Wiley & Sons, 1992.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2006a

6DOF Wind (Quaternion)

Description

Limitations

Ports

Input

Fxyz(N) — Applied forces three-element vector

Mxyz(N-m) — Applied moments three-element vector

Output

Ve — Velocity in flat Earth reference frame three-element vector

Xe — Position in flat Earth reference frame three-element vector

μ γ x (rad) — Wind rotation angles three-element vector

DCMwe — Coordinate transformation 3-by-3 matrix

Vw — Velocity in wind-fixed frame three-element vector

α β (rad) — Angle of attack and sideslip angle two-element vector

dα/dt dβ/dt — Rate of change of angle of attack and rate of change of sideslip angle two-element vector

ωb (rad/s) — Angular rates in body-fixed axes three-element vector

dωb/dt — Angular accelerations in body-fixed axes three-element vector

Abb — Accelerations in body-fixed axes three-element vector

Abe — Accelerations with respect to inertial frame three-element vector

Dependencies

Parameters

Main

Units — Input and output units Metric (MKS) (default) | English (Velocity in ft/s) | English (Velocity in kts)

Programmatic Use

Mass Type — Mass type Fixed (default) | Simple Variable | Custom Variable

Programmatic Use

Representation — Equations of motion representation Quaternion (default) | Wind Angles

Programmatic Use

Initial position in inertial axes [Xe,Ye,Ze] — Position in inertial axes [0 0 0] (default) | three-element vector

Programmatic Use

Initial airspeed, angle of attack, and sideslip angle [V,alpha,beta] — Initial airspeed, angle of attack, and sideslip angle [0 0 0] (default) | three-element vector

Programmatic Use

Initial wind orientation [bank angle,flight path angle,heading angle] — Initial wind orientation [0 0 0] (default) | three-element vector

Programmatic Use

Initial body rotation rates [p,q,r] — Initial body rotation [0 0 0] (default) | three-element vector

Programmatic Use

Initial mass — Initial mass 1.0 (default) | scalar

Programmatic Use

Inertia in body axis — Inertia of body eye(3) (default) | scalar

Programmatic Use

Include inertial acceleration — Include inertial acceleration port off (default) | on

Dependencies

Programmatic Use

State Attributes

Position: e.g., {'Xe', 'Ye', 'Ze'} — Position state name '' (default) | comma-separated list surrounded by braces

Programmatic Use

Velocity: e.g., 'V' — Velocity state name '' (default) | character vector

Programmatic Use

Incidence angle e.g., 'alpha' — Incidence angle state name '' (default) | character vector

Programmatic Use

Sideslip angle e.g., 'beta' — Sideslip angle state name '' (default) | character vector

Programmatic Use

Wind orientation e.g., {'mu', 'gamma', 'chi'} — Wind orientation state names '' (default) | comma-separated list surrounded by braces

Programmatic Use

Quaternion vector: e.g., {'qr', 'qi', 'qj', 'qk'} — Quaternion vector state name '' (default) | comma-separated list surrounded by braces

Programmatic Use

Body rotation rates: e.g., {'p', 'q', 'r'} — Body rotation state names '' (default) | comma-separated list surrounded by braces

Programmatic Use

Mass: e.g., 'mass' — Mass state name '' (default) | character vector

Programmatic Use

Algorithms

References

Extended Capabilities

C/C++ Code Generation Generate C and C++ code using Simulink® Coder™.

Version History

See Also

F_xyz(N) — Applied forces
three-element vector

M_xyz(N-m) — Applied moments
three-element vector

V_e — Velocity in flat Earth reference frame
three-element vector

X_e — Position in flat Earth reference frame
three-element vector

μ γ x (rad) — Wind rotation angles
three-element vector

DCM_we — Coordinate transformation
3-by-3 matrix

V_w — Velocity in wind-fixed frame
three-element vector

α β (rad) — Angle of attack and sideslip angle
two-element vector

dα/dt dβ/dt — Rate of change of angle of attack and rate of change of sideslip angle
two-element vector

ω_b (rad/s) — Angular rates in body-fixed axes
three-element vector

dω_b/dt — Angular accelerations in body-fixed axes
three-element vector

A_bb — Accelerations in body-fixed axes
three-element vector

A_be — Accelerations with respect to inertial frame
three-element vector

Units — Input and output units
`Metric (MKS)` (default) | `English (Velocity in ft/s)` | `English (Velocity in kts)`

Mass Type — Mass type
`Fixed` (default) | `Simple Variable` | `Custom Variable`

Representation — Equations of motion representation
`Quaternion` (default) | `Wind Angles`

Initial position in inertial axes [Xe,Ye,Ze] — Position in inertial axes
`[0 0 0]` (default) | three-element vector

Initial airspeed, angle of attack, and sideslip angle [V,alpha,beta] — Initial airspeed, angle of attack, and sideslip angle
`[0 0 0]` (default) | three-element vector

Initial wind orientation [bank angle,flight path angle,heading angle] — Initial wind orientation
`[0 0 0]` (default) | three-element vector

Initial body rotation rates [p,q,r] — Initial body rotation
`[0 0 0]` (default) | three-element vector

Initial mass — Initial mass
`1.0` (default) | scalar

Inertia in body axis — Inertia of body
`eye(3)` (default) | scalar

Include inertial acceleration — Include inertial acceleration port
`off` (default) | `on`

Position: e.g., {'Xe', 'Ye', 'Ze'} — Position state name
`''` (default) | comma-separated list surrounded by braces

Velocity: e.g., 'V' — Velocity state name
`''` (default) | character vector

Incidence angle e.g., 'alpha' — Incidence angle state name
`''` (default) | character vector

Sideslip angle e.g., 'beta' — Sideslip angle state name
`''` (default) | character vector

Wind orientation e.g., {'mu', 'gamma', 'chi'} — Wind orientation state names
`''` (default) | comma-separated list surrounded by braces

Quaternion vector: e.g., {'qr', 'qi', 'qj', 'qk'} — Quaternion vector state name
`''` (default) | comma-separated list surrounded by braces

Body rotation rates: e.g., {'p', 'q', 'r'} — Body rotation state names
`''` (default) | comma-separated list surrounded by braces

Mass: e.g., 'mass' — Mass state name
`''` (default) | character vector

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.