Roller

The node adds a roller constraint as the boundary condition; that is, the displacement is zero in the direction perpendicular (normal) to the boundary, but the boundary is free to move in the tangential direction. A condition is similar to a Symmetry condition, but the latter has some other options. The constraint is not available in 1D and 1D axisymmetry; use a instead.

Coordinate System Selection

By selecting a coordinate system, you can simplify the description of axis orientations when using the or options in the section.

Roller Constraint

The default roller constraint acts along a normal to the selected boundaries, which is computed numerically. For a certain mesh node, this direction is kept constant during the analysis, so it cannot represent finite sliding on a curved boundary. You can however, for some important cases, prescribe that the boundary slides on an analytical surface. There are two situations where you may want to do this:

•

The geometry or mesh representation of the actual boundary is imperfect. This can lead to unexpected locking of the deformation, since the computed normals do not have the intended directions.

•

In a geometrically nonlinear analysis, the use of an analytical surface makes it possible to model finite sliding also along curved boundaries.

Select a — , , , or .

For , the constraint is applied in the direction normal to the boundary, as represented by the mesh. This orientation is not updated during the analysis.

For , select — , , , or to describe the constraint direction. When is used, enter the vector en, pointing along the normal to the plane along which the boundary is sliding. The orientation is interpreted in the coordinate system given in the section.

For , select — , , , or to describe the orientation of the cylinder. When is used, enter the vector es, pointing along the axis of the cylinder. The orientation is interpreted in the coordinate system given in the section. Enter the location of a , Xc, in order fix the location of the cylinder. The constraints will act radially from the cylinder axis. If the analysis is geometrically nonlinear, each mesh node is assumed to maintain its distance from the cylinder axis.

For , enter the location of the , Xc. The constraints will act radially from this point. If the analysis is geometrically nonlinear, each mesh node is assumed to maintain its distance from the center of the sphere.

Constraint Settings

To display this section, click the button (

) and select in the dialog box.

In the theory section of the Structural Mechanics User’s Guide:

•

Rigid Connector

In the COMSOL Multiphysics Reference Manual:

•

Constraint Reaction Terms

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Constraint Settings

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Weak Constraints

Excluded Edges, Excluded Points

To display these sections ( in 3D geometries only), click the button (

) and select in the dialog box. For more information about these sections, see Excluded Surfaces, Excluded Edges, and Excluded Points in the COMSOL Multiphysics Reference Manual.


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

Location in User Interface

Context Menus

Ribbon

Physics tab with selected:

Physics tab with node selected in the model tree: