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Remote Displacement

With the Remote displacement boundary condition, the guided displacement of a face or volume with a remote point can be specified. It provides advantages compared to the classical displacement boundary condition such as:

  • A deformation behavior can be added to the assigned entity,
  • A rotation condition can be applied to the assignment.

In SimScale, the Remote Displacement boundary condition has the following settings:

remote displacement boundary condition panel
Figure 1: Remote displacement boundary condition panel in SimScale

The parameters of the boundary condition to be defined are:

  1. Displacement: For each of the translational direction, the user defines if the displacement should either be unconstrained or predefined. Each predefined value can either be defined, in meters or inches, by a scalar value, a function, or a table. For function or table data the value may depend on time (or frequency in case of harmonic analysis) or the spatial coordinates.
  2. Rotation: For each rotational direction, the rotation can either be predefined or unconstrained. In the case of a predefined rotation, the value is given in radians or degrees. The input methods and possible dependencies are same as for displacement.
  3. External Point: Here the user defines the coordinates of the external point on which the displacement is applied. The coordinates are given in the global coordinate system of the domain.
  4. Deformation behavior: This property defines if the assigned entities (edges or faces) may deform or if they are assumed to be rigid. When set to Deformable, no additional stiffness is generated on the applied entities. When set to Undeformable, the entity behaves like a rigid part. The connection of the point and the entities is a multi-point constraint which blocks all relative displacements between the affected nodes.
  5. Assignment: Set of faces or volumes where the remote displacement deformation will be applied.

Hint

If the deformable option is used and the number of nodes on the assigned entities is large (>1000), it is advised to use either the MUMPS or PETSC solver instead of Multfront since the performance of Multfront is not optimal for this kind of equations.

Supported Analysis Types

The following analysis types support the usage of the pressure boundary condition:

Remote Point Connections

Behind the scenes, the remote point is connected to all the nodes in the assignment with ‘spider web’ elements. As mentioned above, such elements can be completely rigid, in the case of Undeformable behavior, or flexible in the case of Deformable behavior. In the latter case, the remote point is connected to the nodes by RBE3-constraint.

simscale remote displacement connections spider web elements
Figure 2: Illustration of the connections between the assigned nodes and the remote point

The specified degrees of freedom are applied to the remote point and broadcasted to the nodes in the assignment via the ‘spider web’ elements. The result is that this boundary condition allows the assigned face to be treated as a single entity, with its movement described with 6 degrees of freedom, constrained or imposed. For example, if the translation degrees of freedom are set to zero, and one rotational degree of freedom is left unconstrained, the assigned face is free to rotate around such an axis.

Limitations

This is a linear boundary condition, thus it is valid only if small displacements and rotations occur in the area of the applied entity and the remote point itself.

Example Applications

Some cases where the remote displacement boundary condition is often applied are:

  • Simple supports over one face, where the rotation around one axis can be freed
  • Guided displacement or rotation of the assigned faces or volumes

Deformation Behavior

To illustrate the difference in the effect of the deformation behavior, let’s see the example of a beam under imposed displacement, resulting in a deflected shape:

simscale remote displacement example beam deflection
Figure 3: Beam with imposed deflection over the central top face

The deformed shapes for the cases of undeformable and deformable behavior below illustrate the difference between these two conditions. Especially, how in the former case the face deflects with the beam while in the latter it remains flat:

simscale remote displacement undeformable example
Figure 4: Beam deflection applied with an undeformable behavior
simscale remote displacement deformable example
Figure 5: Beam deflection applied with a deformable behavior

It is also notable how the undeformable behavior causes a stress discontinuity with respect to the deformable case, in which stresses are smooth and more in line with traditional beam deflection stress distribution.

Last updated: August 11th, 2021


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