Guidelines for Cyclic Symmetry

Cyclic symmetry constraints are typically applied to surfaces. When you are making a cyclic symmetry model, you should be careful about applying modeling entities, loads, or constraints to the curves bordering a cyclically constrained curve. Cyclic symmetry boundary geometry should only be associated with surfaces of volumes, curves of surfaces, and points of curves. Geometry not specifically associated with a cyclic symmetry constraint is still available for the assignment of modeling entities.

If you choose to apply loads, constraints, and so on to the perimeter of a cyclically constrained model, you need to be aware of how cyclic symmetry affects their behavior.

• Loads applied to a boundary curve or to the end point of a curve behave as though divided equally between the applied geometry and the corresponding geometry on the other boundary. This means that a load of 100 lb applied to a curve on one boundary will behave as though a 50 lb load has been applied to each boundary.

Heat loads behave in the same way.

• Structure constraints applied to a curve behave as though applied to both the applied geometry and the corresponding boundary geometry, through the rotational transformation defined by the cyclic symmetry constraint.

That is, a constraint restricting X axis displacement for a boundary curve parallel to the X axis of the current coordinate system effectively restricts radial displacement from the cyclic symmetry axis. The corresponding geometry on the other boundary is not constrained with respect to the X axis of the current coordinate system, as might be expected, but it is effectively restricted with respect to radial displacement.

This behavior is true for conflicting constraints applied to corresponding geometry from both boundaries, as well as to enforced displacements.

Thermal boundary conditions behave in the same way.

• Enforced displacements that effectively displace both boundaries of a cyclic symmetry constraint are not permitted, since they may force violation of cyclic symmetry. For example, a surface that shares common border curves with both cyclic symmetry boundary surfaces cannot have an enforced displacement assigned to it. Enforced displacements are generally permitted, provided they do not violate this condition.

• All constraints that touch the cyclic symmetry boundary must be associated with a cylindrical or spherical coordinate system whose axis coincides with the cyclic symmetry axis.

• The stiffness characteristics of your model should be very carefully considered when you use beams, shells, springs, or masses on the cyclic symmetry perimeter. This type of modeling is not recommended.

• No other constraint can share its references with the cyclic symmetry constraint in a constraint set.

• You can create only one cyclic symmetry constraint in a constraint set.

• You cannot use the same geometrical entity as a reference for a cyclic symmetry constraint and a rigid link or a weighted link.

Return to Cyclic Symmetry Constraints.