Creating a rotational symmetry restriction

You can specify a rotational symmetry geometric restriction for a shape optimization. A rotational symmetry geometric restriction forces selected faces of the optimized model to be symmetric about a specified axis. You choose the axis of symmetry by specifying the starting and ending coordinates of a vector representing the axis. You can use the global coordinate system, or you can create a datum coordinate system (see Methods for creating a datum coordinate system, for more information).

See Also
Creating a geometric restriction in a topology or sizing optimization
Creating a geometric restriction in a shape optimization

Context:

The mesh must be approximately symmetric around the axis of symmetry before the optimization starts so that the Optimization module can identify the group of nodes that sit on a selected face in a plane normal to the axis of symmetry. By default, the main node is the node in the group that the optimization moves out the most (the most growth) or moves in the least (the least shrinkage). The optimization displaces the main node, and the symmetry condition applies an equal displacement to the rest of the nodes in the group (the secondary nodes) so that they remain symmetrical about the axis. If you are trying to optimize surfaces that are in contact, you can force the Optimization module to select the main node as the node to which the optimization is applying the least growth or the most amount of shrinkage. Alternatively, you can select a single point that will be used as the main node by all other nodes. The optimization determines how much the main node is displaced, and all other nodes are moved the same amount so that they remain symmetric about the selected axis.

  1. From the main menu bar, select Geometric RestrictionCreate.

    The Create Geometric Restriction dialog box appears.

    Tip: You can initiate the Create procedure in two other ways:

    • Click Create in the Geometric Restriction Manager. (You can display the Geometric Restriction Manager by selecting Geometric RestrictionManager from the main menu bar.)

    • Click the tool in the Optimization module toolbox.

  2. From the Create Geometric Restriction dialog box that appears, enter the name of the geometric restriction.
  3. Select Rotational symmetry (Shape) from the list of geometric restrictions, and click Continue.
  4. From the viewport, select the faces in which the rotational symmetry will be enforced. For more information, see Using the face curvature method to select multiple faces.

    If you would rather select from a list of existing sets, do the following:

    1. Click Sets on the right side of the prompt area.

      Abaqus/CAE displays the Region Selection dialog box containing a list of available sets.

    2. Select the set of interest, and click Continue.

    Note:

    The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Sets on the right side of the prompt area.

  5. When you have finished selecting faces, click Done in the prompt area.

    The Edit Geometric Restriction dialog box appears.

  6. Enter the coordinates of the starting point and the ending point of a vector representing the axis of symmetry.
  7. Toggle on Create a repeating pattern, and enter the angle over which the pattern created by the optimization will be repeated. The value must be between 0° and 360°. A value of 0° implies the secondary nodes are symmetric about the axis of symmetry, but the optimization does not create a repeating pattern.
  8. If desired, toggle on Allow nonsymmetric mesh (default) to use the rotational symmetry geometric restriction for nonsymmetric meshes as well. Toggle off Allow nonsymmetric mesh to use the rotational symmetry geometric restriction with symmetric meshes only. When you allow nonsymmetric meshes, you can pick the Start point of the repeating pattern.
  9. Select the method that the optimization will use to determine the main point. In most cases you should select Determine from most growth and least shrinkage. You should select Determine from least growth and most shrinkage only if you are trying to optimize faces that are involved in contact.

    Alternatively, you can select Region and select a vertex that will be used to represent the main node.

  10. Enter the tolerance that will be used to determine symmetric points in the X-, Y-, and Z-axes.

    The Optimization module uses the tolerance to identify the nodes on the surface that lie on a plane normal to the axis of symmetry and are equidistant from the axis of symmetry.

  11. If desired, toggle on Ignore in first design cycle (default). When the optimization starts, it assumes the faces are already symmetric about the axis. If the faces are not symmetric, the Optimization module issues a warning and tries to continue. If you toggle off Ignore in first design cycle and the faces are not symmetric, the Optimization module issues an error message and stops execution.
  12. Click OK to create the rotational symmetry geometric restriction and to exit the editor.