Symmetry Constraints
When the loads, constraints, and geometry of a model are symmetrical, you can take advantage of symmetry to analyze a portion of the model instead of the entire model. Symmetric constraints work by preventing the model from deforming through the plane(s) of symmetry. There are two types of symmetry constraints that can be created in Mechanica: Mirror and Cyclic. We will focus on Cyclic symmetry in this topic.
Cyclic symmetry is applied to models that are symmetrical about an axis. This is different from axisymmetric models in that the model does not have to be a body of revolution. The model can have patterns of features that are repeated at the same interval about an axis. Using cyclic symmetry requires that the user create a cut feature that reduces the model to a single "slice."
Best Practices
- It should be noted that symmetry can only be used when the model, loads, and constraints are symmetrical. If only the model is symmetrical, then the results generated will not be correct, or may be correct for stress but not displacement, or vice versa. The symmetry requirement for loads and constraints is often overlooked.
- In cyclic symmetry, the angular dimension of the "slice" being used must return an integer when 360 degrees is divided by the dimension. Therefore dimensions such as 15, 18, 30, 45, 60 are all valid. In addition, the surfaces selected for cyclic symmetry must map to one another.
- Finally, users should note that when taking advantage of symmetry in models, a modal analysis or buckling analysis will only report the modes that are symmetrical. As such, not all modes may be captured. For such analyses it is recommended to not use symmetry.
