Creating a Sector Model and Applying Symmetry Constraints

Making use of the Symmetry feature requires an understanding of the geometry symmetry and the symmetry of loading and boundary conditions. If geometric symmetry exists, and the loading and boundary conditions are suitable, then the model can be simplified to just the symmetry sector of the model.

You can use the inherent geometric symmetry of a body to model only a portion or sector of the body for simulation. When your geometry, loading conditions, and supports are symmetrical, using symmetry provides the following benefits:

  • faster solution run times
  • less use of system resources
  • simplified mesh refinement
  • more stabilized models

Here are two simple examples of symmetry models:

A rectangular shell under a uniform normal pressure can be simplified by modeling only ¼ of the geometry by taking advantage of two symmetry planes.

  

An axisymmetric impeller under a uniform rotational velocity can be simplified by modeling only a sector of the geometry.
 

Shell

Shell 1/4 Sector

Impeller

Impeller 1/8 Sector

 

A symmetric structural boundary condition means that out-of-plane displacements and in-plane rotations are set to zero. Structural symmetry is applicable to solid and surface bodies. You can model a symmetry constraint by using a frictionless support.

 

Constructing a Symmetry Model

Create Symmetry Model

Any CAD program can create symmetry models that can be imported into ANSYS Workbench. Symmetry models are created by splitting the parts at symmetry regions. One must first determine the planes in which the model geometry and boundary conditions are symmetrical. Looking at the axisymmetrical impeller blade above, the model is symmetrical about its axis and can be sectored into 1/8th sections. Planes can be created in the CAD model and the model can be sliced about the sector planes.

Apply Symmetry Conditions

Import your symmetry model into ANSYS Workbench Simulation and create a structural simulation analysis. Apply a frictionless support at the cut faces or symmetry faces. The out-of-plane displacements and in-plane rotations are set to zero.

 

View Animation of Symmetry Model