Mirror Symmetry Constraints

A mirror symmetry constraint fixes the translational degrees of freedom normal to the symmetry plane, and frees the rotational degrees of freedom around the axis normal to the symmetry plane. Note that for solid models, the software disregards the rotational settings, because solids have only three degrees of freedom. However, the software uses the rotational settings for shell and beam models.

You can use mirror symmetry constraints in Structure when you want to analyze a segment of a model and project the results to the entire model. Using mirror symmetry allows you to take advantage of your model's symmetry to reduce meshing and analysis time. Mirror symmetry constraints are not available in FEM mode.

To use mirror symmetry successfully to analyze your model, your part or assembly must exhibit reflective symmetry through a plane. In other words, the geometry and modeling entities on one side of the plane must be matched in size and location by the geometry and modeling entities on the other side. If your model has mirror symmetry you should be able to visualize folding it along the mirror plane and obtaining two identical geometries with loads and other displacement constraints exhibiting the same placement and orientation.

If you run a modal analysis on a model with mirror symmetry constraints or a representative segment of that model, the results will not include any nonsymmetric modes. To determine whether there are nonsymmetric modes, run the modal analysis with the entire model without mirror symmetry constraints.

To define a mirror symmetry constraint, you must select sufficient geometric references on your model to define a plane. Keep the following in mind when selecting references:

• The references must be coplanar.

• You can use combinations of points, curves, edges, or surfaces that lie on the plane of symmetry.

• You cannot use reference combinations that are collinear.

• You cannot use the same geometric entities as references for different mirror symmetry constraints in a constraint set.

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

• If you define more than one mirror symmetry constraint in a constraint set, they must be either parallel or orthogonal to each other. A mirror symmetry constraint must be orthogonal to any cyclic symmetry constraint in a constraint set.

• The symmetry planes for multiple mirror constraints in the same model must be either parallel or orthogonal to each other.

Return to Symmetry Constraints.