Rotational
Use Rotation (1 DOF) to determine the rotational motion of boundaries and volumes, explicitly or in a dynamic force balance. Rotational motion is available only in one direction. You can add Rotation (1 DOF) modules, each with its own dynamics, and give each module a different name. The following conditions and parameters are available in the Properties panel:
• Setup Options
• Key Dynamics
• Simulation Method
• Time Definition when you set Simulation Method to Transient (Moving Grid)
• Motion Type
• ODE Time for steady-state run
• Rotational Axis Vector
• Center of Rotation
• Rotational Direction
• Min Angle Displacement
• Max Angle Displacement
When you select Advanced Mode from the Setup Options list, the following options appear in the Properties panel:
• Stability Factor (0-0.9)
• Bounce Model
• ODE Integrator
Motion Type
This determines if the motion for a selected volume or boundary is prescribed explicitly or based on a force balance. The magnitude of the angle of rotation for the rotation (1 DOF) is based on the rotational axis vector and the right-hand rule. According to the rule, if the axis points at an observer, the angle increases in the counter clockwise direction. The motion for a selected volume or boundary is specified as follows:
• Force Balance—Calculates the rotation (1 DOF) dynamics of a volume or boundary as part of the solution. The Force Balance parameters for the rotation (1 DOF) include the following:
◦ Initial Angle Position (deg)—Sets the starting angle at time, t=0 for a volume or boundary. It is independent of the reference theta that you use to define the torsion preload torque and torsion constant. Variables in the force balance equation are measured in rad, or rad/s.
◦ Initial Angular Velocity (rad/s)—Sets the rotational velocity (rad/s) at time, t=0 for a volume or boundary.
◦ Moment of Inertia (kg-m2)—Tendency of a body to resist angular acceleration.
◦ Torsion Constant—Opposes an increase in angle.
◦ Torsion Preload Torque—Based on the position of the associated volume or boundary during model set-up. It does not depend on the value of the initial angle position and opposes an increase in angle.
◦ Damping Coefficient—Rotation (1 DOF) module generates a torque opposite to the angular velocity according to the force balance. The retarding torque due to damping depends on the rotational velocity and the damping coefficient that you specify. The torque associated with the damping coefficient opposes the direction of motion.
◦ Additional Torque on Body—Adds a source of torque to the force balance for rotation (1 DOF) motion. This appears when you select Advanced Mode. The angle and torque are based on the rotational axis vector and the right-hand rule. According to the rule, if the axis points at an observer, the angle increases in the counter clockwise direction. This torque is added to the force balance for rotation (1 DOF).
• Prescribed—Explicitly determines the rotation of a volume or boundary as a function of time. You specify the angle displacement in this option. You can access the specified angle displacement and the associated angular velocity using the expression variables such as rotate_1d.angle and rotate_1d.omega to move a volume or boundary. The unit for angle displacement is deg.
◦ If you specify a constant angle displacement for a transient (moving grid) simulation, the volume or boundary moves directly to that angle at the first time-step.
◦ If you use steady (fixed position) simulation with the Prescribed option, the volume or boundary moves directly to angle displacement corresponding to t=0.
Minimum Angle Displacement
This limits the minimum value of angle displacement specified by the rotation (1 DOF). It is typically used with the Volume remesh under the Common module to limit the minimum degree of rotation of an associated volume or boundary. The unit for minimum angle displacement is deg, which you can consider as a physical limitation or stop.
When the angle displacement rotate_1d[.subname].angle that corresponds to Prescribed or Force Balance reaches the minimum angle displacement:
• Value of rotate_1d[.subname].angle does not decrease below that point.
• Volume or boundary bounces back with an energy corresponding to the selected Bounce Model.
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The default value of -1.#INF means that there is no physical limitation to the motion rotation of the object in the negative direction, where rotate_1d.angle can reach negative infinity.
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Maximum Angle Displacement
This limits the maximum value of angle displacement specified by the rotation (1 DOF). It is typically used with the Volume remesh under the Common module to limit the maximum degree of rotation of an associated volume or boundary. The unit for maximum angle displacement is deg, which you can consider as a physical limitation or stop.
When the angle displacement rotate_1d[.subname].angle that corresponds to Prescribed or Force Balance reaches the maximum angle displacement, the following happens:
• Value ofrotate_1d[.subname].angle does not increase beyond that point.
• Volume or boundary bounces back with an energy that corresponds to the selected bounce model.
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The default value 1.#INF means that there is no physical limitation to motion rotation of the object in the positive direction, where rotate_1d.angle can reach positive infinity.
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