Symmetric constraint

When a part is symmetric and contains symmetric support and loading conditions, you can often simplify the problem by cutting the model in half and analyzing only half of the model. This technique is very efficient because it reduces the size of the model's stiffness matrix, which decreases the solve time.

To correctly model the problem, however, you must apply the correct boundary conditions to account for the deleted half of the model. The boundary conditions you apply must force the displacements on the plane of symmetry of the half model to be the same as the displacements that would have occurred in the whole model. If you could place a mirror at the plane of symmetry (if the structure and the loads are symmetric), you would see the same thing in the mirror as what is behind the mirror (the same model, deflection, and stresses).

These degrees of freedom (DOF) are free:

• Translation along X and Y axes

• Rotation about the Z axis

These DOF are fixed:

• Translation along Z axis

• Rotation about X and Y axes

When you apply symmetric constraint to a planar face, a local nodal Cartesian coordinate system is defined, with its Z axis normal to the plane.

Note:

When you define a symmetric constraint on geometry, a local coordinate system is created and applied to the underlying nodes. If local coordinate systems already exist at these nodes, the constraint's coordinate system may overwrite them. For example, if you define a constraint on a location where spring elements are defined, the constraint's coordinate system may overwrite the spring element definitions.

For information about symmetric constraints in the Simcenter Samcef environment, see Simcenter Samcef environment.

Where do I find it?

Application	Pre/Post
Prerequisite	A Simulation file as the work part and displayed partSimcenter Nastran, MSC Nastran, Abaqus, or ANSYS as the specified solver
Command Finder	Symmetric Constraint
Simulation Navigator	Right-click Constraint Container→New Constraint→Symmetric Constraint

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Symmetric constraint, Simcenter 3D 2021.1 Series

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