Rigid Connector

The 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 node at the edge (2D: boundary) and point levels.

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When added at the edge level you can connect edges and points as long as at least one edge is selected. Selecting points is optional.

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When added at the point level, you can connect a set of points to each other.

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:

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Applied Force (Rigid Connector) to apply a force in given point.

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Applied Moment (Rigid Connector) to apply a moment.

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Mass and Moment of Inertia (Rigid Connector) to add extra mass and moment of inertia in a given point.

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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.

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When the rigid connector is added at the edge level, such symbols are shown only for the selected edges, but not for auxiliary selections of points.

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Because of the way physics symbols are evaluated, as a lightweight operation when moving between physics nodes in the model builder tree, it is sometimes not possible to determine the center of rotation. In particular, if an offset is supplied, it will not be taken into account.


	Edge Selection 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.


	Boundary Selection 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.

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When the is added at the point level, select a number of points that form the rigid region.

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When the 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 is selected by default. The 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 subnode.

Center of Rotation

The center of rotation serves two purposes.

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If you prescribe the displacement of the rigid connector, this is the place where it is fixed.

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Results are interpreted with respect to the center of rotation.

Select a — , , or .

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For the center of rotation is at the geometrical center of the selected points. The constraints are applied at the center of rotation.

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For a subnode for selection of the points is added to the Model Builder.

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For , in the XC table enter coordinates based on space dimension.

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Once is chosen, a default Center of Rotation: Point subnode is added.

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The center of rotation is located at the centroid of the selected points, which do not need to be related to the objects to which the rigid connector is attached. The points do not even have to belong to the physics interface. As a special case, you can select a single point, and thus locate the center of rotation at a certain point.

Select the 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.

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u0x

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u0y

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For 3D components: u0z

Prescribed Rotation at Center of Rotation

Specify the rotation at the center of rotation. Select from the list: (the default), , or .


	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 select one or more of the available check boxes to enforce zero rotation about the corresponding axis in the selected coordinate system:

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Prescribed Rotation at Center of Rotation

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For enter an φ0. For 3D components also enter an Ω for the , , and coordinates.

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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.

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You can activate and deactivate the rigid connector by assigning it to a constraint group. See Load Cases in the Structural Mechanics Modeling chapter.

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You can assign the value of the prescribed displacement and rotation to a load group. See Load Cases in the Structural Mechanics Modeling chapter.

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Rigid Connector Theory

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Harmonic Perturbation

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Load Cases

Reaction Force Settings

Select 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 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 .

Advanced

It is possible to couple rigid connectors to each other. In the 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.


	When coupling rigid connectors to each other, you must be careful not to add conflicting settings. Typically, you should only assign constraints to one of the connectors, and it is recommended to use a common center of rotation. It is, however, possible to deviate from these recommendations and create other meaningful combinations.


	Rigid Connector Theory

Location in User Interface

Context Menus

Ribbon

Physics tab with selected: