Symmetry Constraints

In many cases symmetry of the geometry and loads can be used to your advantage in modeling. Symmetries can often greatly reduce the size of a model and hence reduce the memory requirements and solution time. When a structure exhibits axial symmetry, use the axisymmetric physics interfaces. A solid that is generated by rotating a planar shape about an axis is said to have axial symmetry. In order to make use of the axisymmetric physics interfaces, all loads and constraints must also be the same around the circumference.

For other types of symmetry, use the predefined symmetry and antisymmetry constraints. This means that no expressions need to be entered—instead just add the type of constraint to apply to the model.


	Physics Interface Axial Symmetry Node in the COMSOL Multiphysics Reference Manual

If the geometry exhibits two symmetry planes (Figure 2-6), model a quarter of the geometry by using the Symmetry node for the two selected surfaces.

Figure 2-6: If the geometry exhibits two symmetry planes, model a quarter of the geometry by using the Symmetry feature for the two selected surfaces.


	Both geometric symmetry and loads are important when selecting the correct constraints for a model.


	In an eigenfrequency or buckling analysis, the eigenmodes might be non-symmetric even if the structure is symmetric.

Figure 2-7 shows symmetric and antisymmetric loading of a symmetric geometry. When modeling half of the geometry, the correct constraint for the face at the middle of the object would be Antisymmetry in the case of antisymmetric loading and Symmetry in the case of symmetric loading of the object.

Figure 2-7: Symmetry plane (left) and antisymmetry plane (right).