Rigid Domain
Add the Rigid Domain node and select one or more domains to make them a rigid body.
These subnodes are described in the Structural Mechanics Module User’s Guide:
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Fixed Constraint (Rigid Domain)
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Prescribed Displacement/Rotation
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Applied Force (Rigid Domain)
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Applied Moment (Rigid Domain)
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Mass and Moment of Inertia (Rigid Domain)
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Spring Foundation (Rigid Domain)
Rigid Domain
The default Density ρ is taken From material. In this case, the material assignment for the domain supplies the mass density. For User defined, enter another value or expression.
The density is needed for dynamic analysis. It is also used when computing mass forces for gravitational or rotating frame loads, and when computing mass properties (Computing Mass Properties).
Center of Rotation
Select a Center of Rotation — Center of mass, Centroid of selected entities, or User defined. The center of rotation affects how displacements are interpreted and is also used as the default in various subnodes.
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For Center of mass, the center of rotation is taken as the center of mass of the rigid domain.
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For Centroid of selected entities select an Entity level — Boundary, Edge, or Point. The available choices depend on geometrical dimension. The center of rotation is located 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 use that point as center of rotation.
Once chosen, a default Center of Rotation: Boundary, Center of Rotation: Edge, or Center of Rotation: Point subnode is automatically added.
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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.
Initial Values
Select From physics interface node or Locally defined.
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When From physics interface node is selected, initial values for rigid body displacement, rotation, and velocities are inherited from the physics interface level.
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When Locally defined is selected, an Initial Values subnode is automatically added, in which you can initialize the rigid domain degrees of freedom.
Select a Consistent initialization — Default or Force initial values to enforce that the exact values given in this node should be maintained through the consistent initialization process. The default when the given initial values are inconsistent is to make them adapt to each other by adjusting all initial values. For Force initial values, click to select the applicable check boxes — Translation along first axis, Translation along second axis, Translation along third axis, and Total rotation. Only the selected degrees of freedom have the initial values fixed during the consistent initialization process.
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The optional subnode is described in Initial Values (Rigid Domain).
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For details about the input expressions at the physics interface level, see Initial Values.
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See Rigid Domain Model in the Structural Mechanics Module User’s Guide for more information.
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For details about the initialization process, see Initialization in Time-Dependent Studies.
Location in User Interface
Context Menus
 Multibody Dynamics>Rigid Domain
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Physics tab with Multibody Dynamics selected:
Domains>Multibody Dynamics>Rigid Domain
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Physics tab with Multibody Dynamics selected:
Domains>Multibody Dynamics>Initial Values