Attachment

The node is used to define a set of boundaries on a flexible or rigid component, which can be used to connect it with other components through a joint or Spring-Damper 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 interface, and to points in a Beam interface. This makes it possible to use a joint for connecting to parts modeled in different physics interfaces.

Connection Type

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


	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.

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The Solid Mechanics Interface, The Shell and Plate Interfaces, and The Beam Interface in the Structural Mechanics Module User’s Guide.

Location in User Interface

Physics tab with selected: