Defining Flow-Driven Nutation

Flow-driven nutation is influenced by the flow as well as user-specified driving and resistive torques.

The origins of such torques do not have to be included in the analysis model--they act on the object in a user-prescribed manner to either accelerate the object or to slow it down.

In several places in this section, the direction of nutation of the object is referenced. This is the nutation direction determined by the direction of the Tilt Axis or the Axis of Nutation (as defined on the Motion task dialog.) Because the true nutation direction of flow-driven motion is not always known prior to the analysis, this direction is really the reference positive direction.

Note: Directions of driving and resistance forces are then relative to this direction.

Flow-driven objects may start off with an initial nutation velocity, and either speed up or slow down based on their interaction with the surrounding fluid (and applied forces).

To open the Motion Editor:

1. On the Motion quick edit dialog, set the Type to Nutating, and check Flow-Driven.
2. Click Edit... on the Edit Motion line.

To Define Flow-Driven Nutating Motion

1. Three properties are available for specification, but entries are not required: Initial Nutation Velocity, Driving Torque, and Resistive Torque.
2. For each property, select the Variation Method, and enter the appropriate values. The Variation Methods are described below for each property.
3. Click Apply.
4. Click OK.

Initial Nutation Velocity

The object will nutate at this velocity at the beginning of the analysis, and will react to the flow forces appropriately. If the object is to start from rest, leave this value specified as 0.

Driving Torque Variation Methods

A driving torque is positive when applied in the reference direction of motion (as applied on the Motion task dialog). A negative driving force will act in the opposite direction.

Examples of driving torque include electromagnetic and other body torques as well as torque imposed by objects omitted from the analysis geometry. The torque will act in the same direction as the direction of motion (as specified on the Motion task dialog).

Constant

Enter a constant torque value to apply an unchanging torque to the object throughout the entire analysis.

Table

A driving torque that varies with time is specified using the table of torque vs. time. As with all table entries, values can be retrieved from an Excel “.csv” file or saved to one.

Resistive Torque Variation Methods

Applied resistive torque affects the nutation of the object by acting against its specified nutation direction, impeding its progress. A positive value of a resistive torque acts in the opposite direction of nutation; a negative value acts in the direction of nutation.

Constant

Enter a constant torque value to apply an unchanging resistive torque to the object throughout the entire motion.

Table

If a resistive torque is to vary with time, enter the time history as a table of torque and time. As with all table entries, values can be retrieved from an Excel “.csv” file or saved to one.