Prescribed Motion
Use the Prescribed Motion subnode to prescribe the relative motion on a joint. You can also prescribe the motion by giving the time derivatives of the joint degrees of freedom, for example, velocity for translation motion and angular velocity for rotational motion. Activation conditions can be used to prescribe the motion for only a certain duration. Axis directions are interpreted in the selected coordinate system.
The Prescribed Motion subnode can be added to the Prismatic Joint, Hinge Joint, Cylindrical Joint, Screw Joint, Planar Joint, Ball Joint, Slot Joint, and Reduced Slot Joint. The contents of the settings sections will differ between different joint types
The Theory for Prescribed Motion on Joints section describes the theory for each of the different types of prescribed motion: translational and rotational.
Prescribed Translational Motion
This section is available for the Prismatic Joint, Cylindrical Joint, Screw Joint, Planar Joint, Slot Joint, and Reduced Slot Joint nodes.
Select an option from the Prescribed motion through list — Displacement or Velocity.
For Displacement enter a value or expression for up.
For Velocity enter a value or expression for vp.
Select an Activation conditionAlways active or Conditionally active. For Conditionally active enter a De-activation indicator expression iup. For the joints having more than one degree of freedom (Cylindrical Joint, Screw Joint, Planar Joint, Slot Joint, and Reduced Slot Joint), Never active is also an option.
For the Planar Joint, enter values or expressions for the Initial prescribed motion axis ep0.
Prescribed Rotational Motion
This section is available for the Hinge Joint, Cylindrical Joint, Screw Joint, Planar Joint, Ball Joint, Slot Joint, and Reduced Slot Joint nodes.
For the Ball Joint and Slot Joint, enter values or expressions for the Initial prescribed motion axis ep0.
Select an option from the Prescribed motion through list — Rotation or Angular velocity.
For Rotation enter a value or expression for θp. In this case, the variable name is φp for the Ball Joint and Slot Joint.
For Angular velocity enter a value or expression for ωp.
Select an Activation conditionAlways active or Conditionally active. For Conditionally active enter a De-activation indicator expression iθp. (In this case, the variable name is iφp for the Ball Joint and Slot Joint). For the joints having more than one degree of freedom (Cylindrical Joint, Screw Joint, Planar Joint, Slot Joint, and Reduced Slot Joint), Never active is also an option.
Reaction Force Settings
Select Evaluate reaction forces to compute the reaction force caused by the prescribed motion. The default is to not compute the reaction force. When selected, the prescribed motion is implemented as a weak constraint. If the prescribed motion is not active all through the study step, because Activation condition is Conditionally active, this setting is ignored. Reaction forces are never computed in that case.
Select Apply reaction only on joint variables to use a unidirectional constraint for enforcing the prescribed motion. The default is that bidirectional constraints are used. This setting is useful in a situation where a bidirectional constraint would give an unwanted coupling in the equations. This would happen if the prescribed value of the motion is a variable solved for in other equations.
If the motion is prescribed as a velocity, the reaction force is applied on the joint variables only (unidirectional constraint) irrespective of the setting of this control.
Location in User Interface
Context Menus
Multibody Dynamics>Prismatic Joint>Prescribed Motion
Multibody Dynamics>Hinge Joint>Prescribed Motion
Multibody Dynamics>Cylindrical Joint>Prescribed Motion
Multibody Dynamics>Screw Joint>Prescribed Motion
Multibody Dynamics>Planar Joint>Prescribed Motion
Multibody Dynamics>Ball Joint>Prescribed Motion
Multibody Dynamics>Slot Joint>Prescribed Motion
Multibody Dynamics>Reduced Slot Joint>Prescribed Motion
Ribbon
Physics tab with Prismatic Joint, Hinge Joint, Cylindrical Joint, Screw Joint, Planar Joint, Ball Joint, Slot Joint, or Reduced Slot Joint selected in the model tree:
Attributes>Prescribed Motion