Prescribed Displacement/Rotation
The Prescribed Displacement/Rotation subnode can be used to selectively constrain or prescribe degrees the of freedom of a Rigid Domain:
The prescribed values that you specify are interpreted in the selected coordinate system.
The Fixed Constraint and Prescribed Displacement/Rotation subnodes cannot be combined for a Rigid Domain.
Center of Rotation
The selection of the center of rotation only affects the prescribed displacements, not the rotations.
Select an option from the list: From parent, Centroid of selected entities, or User defined.
For From parent, the center of rotation is taken as the one defined in the parent Rigid Domain node.
For Centroid of selected entities select an Entity levelBoundary, Edge, or Point. The available choices depend on physics interface and geometrical dimension. The constraints act at the centroid of the selected entities, which do not need to be related to rigid domain itself. As a special case, you can select a single point, and thus constrain that point
For User defined, enter the Global coordinates of center of rotation, Xc, in the table.
Select the Offset check box to add an optional offset vector to the definition of the center of rotation. Enter values for the offset vector Xoffset.
The center of rotation used is the sum of the vector obtained from any of the input methods and the offset vector.
Prescribed Displacement at Center of Rotation
Select one or several of the Prescribed in x direction, Prescribed in y direction, and Prescribed in z direction (3D components only) check boxes. Then enter a value or expression for u0x, u0y, and u0z (3D components).
Prescribed Rotation
Select an option from the By list: Free, Constrained rotation, or Prescribed rotation.
For 2D components, and if Prescribed rotation is selected, enter a value or expression for the Angle of rotation φ0.
For Constrained rotation select one or several of the Constrain rotation around x-axis, Constrain rotation around y-axis, and Constrain rotation around z-axis check boxes.
For Prescribed rotation enter values or expressions in the table for the Axis of rotation Ω . Then enter a value or expression for the Angle of rotation φ0.
You can add a Harmonic Perturbation subnode for specifying a harmonic variation of the values of the prescribed displacements and rotations in a frequency domain analysis of perturbation type.
You can activate and deactivate this boundary condition by assigning it to a constraint group. See Load Cases in the Structural Mechanics Modeling chapter. Note that constraint groups only can be used when the constraints are pointwise, but not for weak constraints. This means that if Evaluate reaction forces is selected, any constraint group settings are ignored.
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.
Select Apply reaction only on rigid body 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.
Location in User Interface
Context Menus
Ribbon
Physics tab with Rigid Domain node selected in the model tree:
When this node has been added once, it is no longer available for selection in the context menu or ribbon.