Defining Flow-Driven Orbital Motion

Flow-driven Orbital motion is also affected by driving and resistive forces and torque.

The origins of such forces 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 topic, the Direction of Rotation of the object are referenced. These are the directions specified on the Motion task dialog.

To open the Motion Editor:

1. On the Motion quick edit dialog, set the Type to Orbital. (If Flow-Driven is checked for Orbital and Angular, both motion types are flow-driven.)
2. Click Edit... on the Edit Motion line.

To Define Flow-Driven Orbital Motion

1. Define each of the Orbital properties by first clicking on the desired property button: Initial Angular Velocity, Driving Force, and Resistive Force. (It is not required to specify any or all of the properties.)
2. For each property, select the Variation Method.
3. Enter the appropriate values.
4. Click the Apply button.
5. Repeat for the Rotation properties.
6. Click OK when all information is entered to close the dialog.

Note that forces (instead of torques) are used to describe the Orbital motion. This is done because the orbit is really a displacement motion, so force, displacements, and velocities are more applicable than torque, angular displacements, and angular velocities.

The relationship between torque and force for the orbit is expressed in terms of the eccentricity radius (eps):

• Torque = force * eps
• Omega = velocity / eps
• Theta = displacement /eps

Variation Methods

The orbital motion element uses forces, and the angular rotation element uses torque. Follow these links for information about the variation methods for Flow-Driven Orbital motion:

Orbital

Initial Angular Velocity: Constant

Driving Force: Table

Resistive Force: Table

Rotational

Initial Angular Velocity: Constant

Driving Torque: Table

Resistive Torque: Table