COMSOL 6.2 - Attachment

Attachment

The node is used to define a set of boundaries on a flexible domain which can be used to connect it with other components through a joint in the Multibody Dynamics interface.

There are two formulations of the attachment. In the default formulation, all the selected boundaries behave as if they were connected by a common rigid body. In some cases, this give an unwanted stiffening or unrealistic local stresses. You can then switch to a flexible formulation where the constraint is applied only in an average sense.

Using attachments is optional when connecting a rigid component. It is, however, useful if you consider switching between a rigid and a flexible representation, since you then do not have to change the settings in the joints.

Attachments can be added to boundaries in a Multibody Dynamics or a Solid Mechanics interface, to edges in a Shell or Layered Shell interface, or to points in a Beam interface. This makes it possible to use a joint in the Multibody Dynamics interface for connecting parts modeled in different physics interfaces.


	The use of attachments is discussed in the Attachments section in the Structural Mechanics Modeling chapter.

The node is only available with some COMSOL products (see https://www.comsol.com/products/specifications/). It is available in 3D, 2D, and 2D axisymmetry.

Connection Type

Select or .

When the connection type is rigid, the whole attachment selection acts as a virtual rigid object. This will cause a stiffening of the part with the attachment, and local stress concentrations at the selected boundaries if the domain with the attachment is flexible.

In the flexible formulation, the selected boundaries are allowed to have internal deformations, and the kinematic constraints are fulfilled only in an average sense. This will essentially provide a statically equivalent load distribution over the boundaries.

If a selected boundary is located on a rigid domain, the connection type setting does not matter. The rigid formulation is always used.

Advanced

Select — (default), , or , to choose how to group in the solver sequence the dependent variables added by the feature.


	With the flexible formulation, some extra degrees of freedom are added for each attachment. In order to get good convergence properties for a nonlinear solution, these variables must have a good scaling. When a new solver sequence is generated, then an appropriate manual scaling is automatically set for these variables. If, however, an existing solver sequence was generated while Connection Type was set to Rigid, and you then change to Flexible, no such scaling will be present. In this case, you either have to regenerate the solver sequence, or set the scaling manually under the Dependent Variables node in each study step.

Location in User Interface

Context Menus

Ribbon

Physics tab with selected: