The Prescribed Displacement/Rotation node adds a point, edge, boundary, or domain condition to a model where the displacements and rotations are prescribed in one or more directions.
This setting is used in conjunction with a Local edge system and
Shell Local System. If displacement or rotations is prescribed for an edge or point which is shared between boundaries, the local system can be ambiguous. Select the boundary which should define the local system. The default is
Use face with lowest number.
If any displacement component is set to Limited, an additional section
Limited Displacement is visible. Select the
Method used to implement the weak inequality constraint —
Penalty or
Augmented Lagrangian. For both methods, enter a
Penalty factor kp.
By default, the Penalty method is suggested, which in principle enforces the maximum and minimum limits for the displacement by adding nonlinear springs with a stiffness equal to
kp when the limits are exceeded. This method is usually robust, but the accuracy is directly dependent on the chosen penalty factor.
The Augmented Lagrangian method adds extra degrees of freedom to improve the accuracy of the constraint. Here, the penalty factor is a numerical parameter, and has less impact on the accuracy of the constraint compared to when using the penalty method. The implementation of the augmented Lagrangian method puts no restrictions on the solver sequence, but for good convergence, proper scaling of the extra degrees of freedom can be important.
The default value for the Penalty factor kp depends on to what type of entity the
Prescribed Displacement/Rotation node is added. In the expressions below,
<phys> is the tag of the physics interface, and
<pd> is the tag of the
Prescribed Displacement/Rotation node.
Here, the terms point, edge, and boundary refer to the actual physical entities represented by the chosen
geometric entities. For instance, in a 2D axisymmetric component, the circumferential direction is only implicitly modeled, and thus the physical entity level of the shell is interpreted as one level higher than the chosen geometric entity level. The highest entity level in the 2D Plate interface is interpreted as a boundary.
The variable <phys>.<pd>.charLen is equal to thickness of the shell or plate.
For geometric linearity, select one or both of the Free rotation around t1 direction and
Free rotation around t2 direction check boxes to remove the constraint for the corresponding rotation component. If unchecked, the rotations are constrained to either the input value or to the default zero rotation. The status of the check boxes has no effect when the geometric nonlinearity is activated under the study settings. This is because the constraints for different rotation components are not independent of each other in the case of finite rotations.
) and select Advanced Physics Options in the Show More Options dialog box.
