Rigid Connector
The Rigid Connector is a boundary condition for modeling rigid regions and kinematic constraints such as prescribed rigid rotations. The selected points will move as a single rigid object.
You can add the Rigid Connector node at the edge (2D: boundary) and point levels.
If the study step is geometrically nonlinear, the rigid connector takes finite rotations into account.
The feature is similar to the rigid connectors in the Solid Mechanics and Shell interfaces. Rigid connectors from Beam, Pipe Mechanics, Shell, and Solid Mechanics interfaces can be attached to each other.
You can add functionality to the rigid connector through the following subnodes:
Applied Force (Rigid Connector) to apply a force in given point.
Mass and Moment of Inertia (Rigid Connector) to add extra mass and moment of inertia in a given point.
Spring Foundation (Rigid Connector) to add a translational or rotational spring or damper in a given point.
When physics symbols are shown, a rigid connector is represented by a symbol at the center of rotation, together with a set of lines connecting the center of rotation with the centers of gravity of the selected entities.
This section is present when the Rigid Connector node has been added at the edge level. Select one or more edges to be part of the rigid region.
This section is present when the Rigid Connector node has been added at the boundary level. Select one or more edges to be part of the rigid region.
Point Selection
This section is always present.
When the Rigid Connector is added at the point level, select a number of points that form the rigid region.
When the Rigid Connector is added at the edge (2D: boundary) level, this section is initially collapsed. Here, you can add optional points to the rigid region. The points cannot be adjacent to the selected boundaries or edges.
Coordinate System Selection
The Global coordinate system is selected by default. The Coordinate system list contains any additional coordinate systems that the model includes. Prescribed displacements or rotations are specified along the axes of this coordinate system. It is also used for defining the axis directions of the moment of inertia tensor of the Mass and Moment of Inertia subnode.
Center of Rotation
The center of rotation serves two purposes.
Select a Center of rotation Automatic, Centroid of selected entities, or User defined.
For Automatic the center of rotation is at the geometrical center of the selected points. The constraints are applied at the center of rotation.
For Centroid of selected entities a subnode for selection of the points is added to the Model Builder.
For User defined, in the Global coordinates of center of rotation XC table enter coordinates based on space dimension.
Once Centroid of selected entities is chosen, a default Center of Rotation: Point subnode is added.
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
To define a prescribed displacement at the center of rotation for each space direction, select one or several of the available check boxes then enter values or expressions for the prescribed displacements. The direction coordinate names can vary depending on the selected coordinate system.
For 3D components: Prescribed in z direction u0z
Prescribed Rotation at Center of Rotation
Specify the rotation at the center of rotation. Select from the By list: Free (the default), Constrained rotation, or Prescribed rotation at center of rotation.
For 2D components, the Constrained rotation and Prescribed rotation at center of rotation is always about the z-axis, so no component selection is necessary.
Constrained Rotation (3D Components)
For Constrained rotation select one or more of the available check boxes to enforce zero rotation about the corresponding axis in the selected coordinate system:
Constrain rotation about x-axis
Constrain rotation about y-axis
Constrain rotation about z-axis
Prescribed Rotation at Center of Rotation
For Prescribed rotation at center of rotation enter an Angle of rotation φ0. For 3D components also enter an Axis of rotation Ω for the x, y, and z coordinates.
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.
Reaction Force Settings
Select Evaluate reaction forces to compute the reaction force caused by a 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 a 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.
Constraint Settings
On the points where the rigid connector is coupled to a flexible material, all nodes are constrained to move as a rigid body. As a default, these constraints are implemented as pointwise constraints. If you want to use a weak constraint formulation, select Use weak constraints for rigid-flexible connection.
Advanced
It is possible to couple rigid connectors to each other. In the Connect to list, you can select any rigid connector defined in the Solid Mechanics, Multibody Dynamics, or Shell interfaces as being rigidly connected to the current one.
Location in User Interface
Context Menus
Ribbon
Physics tab with Beam selected: