Types of Symmetry

There are three types of symmetry that provide a modeling advantage in finite element analyses, as follows:

Full Symmetry: All geometry, constraints, physical loads, and thermal loads are symmetrical about one or more planes of symmetry. Constrain the following degree of freedom (DOF) at the faces lying along a plane of full symmetry:
- Translation in the direction normal to the symmetry plane

Note: If a plane of symmetry does not align with a global plane (XY, YZ, or XZ), you can apply a Frictionless Constraint to prevent translation in the normal direction only.

The following image is another example of a model that is fully symmetrical about all three global planes:

shackle full example

Figure 2a: Full model of a shackle.

shackle eight-symmetry example

Figure 2b: Eighth-symmetry model of the same shackle.

Note: The (X), (Y), and (Z) labels indicate the faces that should be constrained against translation in the global X, Y, and Z direction, respectively. This constraint scheme produces the same behavior as the full model. The eight-symmetry model is statically stable, whereas the full model is difficult to constrain correctly. You would have to split many faces of the full CAD assembly to provide edges along the symmetry planes for constraining motion.