Implement quaternion representation of six-degrees-of-freedom equations of motion of custom variable mass with respect to body axes

Equations of Motion/6DOF

For a description of the coordinate system and the translational dynamics, see the block description for the Custom Variable Mass 6DOF (Euler Angles) block.

The integration of the rate of change of the quaternion vector
is given below. The gain *K* drives the norm of the
quaternion state vector to 1.0 should *ε* become
nonzero. You must choose the value of this gain with care, because
a large value improves the decay rate of the error in the norm, but
also slows the simulation because fast dynamics are introduced. An
error in the magnitude in one element of the quaternion vector is
spread equally among all the elements, potentially increasing the
error in the state vector.

$$\begin{array}{l}\left[\begin{array}{c}{\dot{q}}_{0}\\ {\dot{q}}_{1}\\ {\dot{q}}_{2}\\ {\dot{q}}_{3}\end{array}\right]={\scriptscriptstyle \raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}\left[\begin{array}{cccc}0& -p& -q& -r\\ p& 0& r& -q\\ q& -r& 0& p\\ r& q& -p& 0\end{array}\right]\left[\begin{array}{c}{q}_{0}\\ {q}_{1}\\ {q}_{2}\\ {q}_{3}\end{array}\right]+K\epsilon \left[\begin{array}{c}{q}_{0}\\ {q}_{1}\\ {q}_{2}\\ {q}_{3}\end{array}\right]\\ \epsilon =1-({q}_{0}^{2}+{q}_{1}^{2}+{q}_{2}^{2}+{q}_{3}^{2}).\end{array}$$

**Units**Specifies the input and output units:

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

**Mass Type**Select the type of mass to use:

`Fixed`

Mass is constant throughout the simulation.

`Simple Variable`

Mass and inertia vary linearly as a function of mass rate.

`Custom Variable`

Mass and inertia variations are customizable.

The

`Custom Variable`

selection conforms to the previously described equations of motion.**Representation**Select the representation to use:

`Euler Angles`

Use Euler angles within equations of motion.

`Quaternion`

Use quaternions within equations of motion.

The

`Quaternion`

selection conforms to the previously described equations of motion.**Initial position in inertial axes**The three-element vector for the initial location of the body in the flat Earth reference frame.

**Initial velocity in body axes**The three-element vector for the initial velocity in the body-fixed coordinate frame.

**Initial Euler rotation**The three-element vector for the initial Euler rotation angles [roll, pitch, yaw], in radians.

**Initial body rotation rates**The three-element vector for the initial body-fixed angular rates, in radians per second.

**Gain for quaternion normalization**The gain to maintain the norm of the quaternion vector equal to 1.0.

**Include mass flow relative velocity**Select this check box to add a mass flow relative velocity port. This is the relative velocity at which the mass is accreted or ablated.

**Include inertial acceleration**Select this check box to enable an additional output port for the accelerations in body-fixed axes with respect to the inertial frame. You typically connect this signal to the accelerometer.

Input | Dimension Type | Description |
---|---|---|

First | Vector | Contains the three applied forces. |

Second | Vector | Contains the three applied moments. |

Third (Optional) | Vector | Contains one or more rates of change of mass (positive if accreted, negative if ablated). |

Fourth | Scalar | Contains the mass. |

Fifth | 3-by-3 matrix | Contains rate of change of inertia tensor matrix. |

Sixth | 3-by-3 matrix | Contains the inertia tensor matrix. |

Seventh (Optional) | Three-element vector | Contains one or more relative velocities at which the mass is accreted to or ablated from the body in body-fixed axes. |

Output | Dimension Type | Description |
---|---|---|

First | Three-element vector | Contains the velocity in the flat Earth reference frame. |

Second | Three-element vector | Contains the position in the flat Earth reference frame. |

Third | Three-element vector | Contains the Euler rotation angles [roll, pitch, yaw], in radians. |

Fourth | 3-by-3 matrix | Contains the coordinate transformation from flat Earth axes to body-fixed axes. |

Fifth | Three-element vector | Contains the velocity in the body-fixed frame. |

Sixth | Three-element vector | Contains the angular rates in body-fixed axes, in radians per second. |

Seventh | Three-element vector | Contains the angular accelerations in body-fixed axes, in radians per second squared. |

Eighth | Three-element vector | Contains the accelerations in body-fixed axes with respect to body frame. |

Ninth (Optional) | Three-element vector | Contains the accelerations in body-fixed axes with respect to inertial frame (flat Earth). You typically connect this signal to the accelerometer. |

The block assumes that the applied forces are acting at the center of gravity of the body.

Stevens, Brian, and Frank Lewis, *Aircraft Control
and Simulation*, Second Edition, John Wiley & Sons,
2003.

Zipfel, Peter H., *Modeling and Simulation of Aerospace
Vehicle Dynamics*. Second Edition, AIAA Education Series,
2007.

6th Order Point Mass (Coordinated Flight)

Custom Variable Mass 6DOF (Euler Angles)

Custom Variable Mass 6DOF ECEF (Quaternion)

Custom Variable Mass 6DOF Wind (Quaternion)

Custom Variable Mass 6DOF Wind (Wind Angles)

Simple Variable Mass 6DOF (Euler Angles)

Simple Variable Mass 6DOF (Quaternion)

Simple Variable Mass 6DOF ECEF (Quaternion)

Was this topic helpful?