6-DOF Body Reports Reference

Reports for the Component of a Quantity along a Specified Direction

The following reports calculate the component of a quantity along a specified direction (see Eqn. (4966)):

For each of these reports, the available properties define:

Additionally, the 6-DOF Body Force and 6-DOF Body Moment reports have the following properties:

6-DOF Body Dissipated Energy

Calculates the energy that is dissipated by the body due to mechanical friction (contact couplings), damping forces, and damping moments.

6-DOF Body Orientation

Calculates the Euler angles that define the orientation of a body with respect to the initial orientation.

The report properties specify the bodies for which the report is calculated, the units for the rotation angle, and the following:

• Angle Report Option—specifies the axis of the coordinate system relative to which rotation is measured. For fixed axes, the axes of the Laboratory coordinate system are used. For moving axes, the corresponding rotated axes of the Laboratory system are used.
• Euler Angle Convention—specifies the order of the rotations describing the orientation of the body (see Euler Angle Convention). For fixed axes, the first rotation is around the first axis of the lab system in the option (giving the first Euler Angle). The second rotation is around the second mentioned axis of the lab system (giving the second Euler Angle). The third rotation is around the last axis of the lab system (giving the third Euler angle). For moving axes, read the order of rotation from back to front.
• Offset—adds an offset value to the selected Euler angle.
• Constrained Angle Range—when activated, the angle is constrained in the interval $[-\pi ,\pi ]$ or $[-\frac{\pi }{2},\frac{\pi }{2}]$ , depending on the selected Angle Report Option and Euler Angle Convention. When deactivated, the angle of rotation is unconstrained to reflect the full rotation of the body. Using unconstrained angles is advantageous in cases with large angular motions of the body (for example, a body undergoing multiple revolutions around an axis). When choosing the unconstrained angle option, the reported rotation angle reflects the full rotation of the body. For example, if the body has made two revolutions, the reported angle is $4\pi$ . The default option is to report the unconstrained angle.

In non-trivial case with complex 3D rotations, Euler angles do not directly describe the real rotational motion of the body. Euler angles are a commonly used measure for describing the change in orientation of the body with respect to its original orientation, independent of which motion actually accomplished the change.

Consider a body which rotates in the following way: -90 deg about laboratory Y axis, -90 deg about laboratory Z axis. There is no rotation about X axis at any point, but the Euler angle about laboratory X axis is -90 deg (using Euler convention "Rotation X-Z-Y Axis").

In cases such as the one above, the Euler angle notation can return a non-zero rotation about axes for which rotation is frozen. Nevertheless, there is no rotational motion about the frozen axes. This can be seen when using a 6-DOF body angular velocity report which gives the instantaneous angular velocity about an axis.

6-DOF Body Rotation Angle

For motions with only one axis of rotation (One-DOF Rotating Motion in 2D or 3D and Free Motion in 2D), the orientation of the body is defined by a single rotation angle. In this case, the report calculates the angle of rotation relative to the initial orientation. Offset adds an offset value to the angle of rotation.

For all other types of motion, this report is not appropriate, as the orientation of the body is defined by multiple angles. In this case, use the 6-DOF Body Orientation report, which determines the orientation in terms of Euler angles.

The report properties specify the relevant bodies and the rotation angle units.

6-DOF Body Rotational Energy

Calculates the rotational energy of the body according to Eqn. (4969)

The report properties specify the relevant bodies and the rotational energy units.

6-DOF Body Spring Elongation

For linear spring connections, this report calculates the elongation of the spring.

The report properties specify the preferred length units, as well as the following:

• Linear Spring Coupling—the linear spring couplings for which the report is calculated.
• Total Length—when activated, the report calculates the total length of the spring (Eqn. (4970)). When deactivated, the relaxation length of the spring is subtracted from the total length (Eqn. (4971)).

6-DOF Body Total Distance

Calculates the total distance between two specified points (see Eqn. (4972)).

The report properties specify the preferred units, the position vectors of the two points, and the coordinate systems with respect to which the positions are defined.

6-DOF Catenary Length

For catenary couplings, this report calculates the length of the catenary.

The report properties specify the preferred length units, as well as the following:

6-DOF Component Distance

Calculates the distance between two points along a specified direction (see Eqn. (4975)).

The report properties specify the preferred units, the position vectors of the two points, the coordinate systems with respect to which the positions are specified (Coordinate System 1 and Coordinate System 2), the direction vector, and the coordinate system with respect to which the direction vector is defined (Coordinate System).

6-DOF Constraint Deviation

Calculates the maximum normalized deviation from the constraint equations (see Constraint Stabilization). The maximum normalized deviation is the maximum value of all mechanical joints that are defined in the simulation. You typically use this report when performing a multi-body DFBI simulation.

Depending on the type of mechanical joint, the deviations are translational or angular. A spherical joint can have translational deviations only. A revolute joint can have translational and angular deviations. Translational deviations are normalized by the extent of the smallest of the two bodies that are attached to the joint. The angular deviation for a revolute joint is the sine of the angle between the two rotation axes that characterize the revolute joint (one axis for each of the attached bodies).

For example, a reported value of ${10}^{-5}$ means that all translational deviations (normalized per joint by the smallest of the attached bodies) and all angular deviations (sine of deviation angles) are below or equal to ${10}^{-5}$ .

Typically, a value $<{10}^{-3}$ indicates a well assembled multi-body system.