Define cyclic symmetry in Abaqus using the Automatic method

The automatic cyclic symmetry method lets you select the source region faces and the software automatically determines the target region faces.

1. Choose Home tab→Loads and Conditions group→Simulation Object Type list→Cyclic Symmetry .

2. In the Cyclic Symmetry dialog box, from the type list, select Automatic Cyclic Symmetry Pairing.

3. In the Automatic Face Pair Creation group, click Create Face Pairs .

4. In the Create Automatic Face Pairs dialog box, do the following: In the Properties group, from the Grouping Option list, select one of the following to determine how the face pairs are grouped.ToSelectCreate a single region for all source faces, a single region for all target faces, and a single pair using the source and target regionsOneDivide the resulting regions and pairs according to the solid bodies to which the source region belongsPer Body PairsDivide the resulting regions according to the faces to which the source region belongs.Per Face PairsIn the Direction group, from CSYS list, select a coordinate system or select User-Defined Cylindrical to create your own. The coordinate system you select must be cylindrical and its Z-axis must be collinear with the global cyclic analysis coordinate system. If you set CSYS to User-Defined Cylindrical, from the Local list, select a method and create the coordinate system. For more information, see CSYS dialog box.(Optional) To have the software assign the specified coordinate system as the nodal displacement coordinate system for nodes included in the target and source regions, select the Set Displacement CSYS check box.(Optional) In the Segments group, set the tolerances.Note: The software automatically computes the segment angle and the number of segments. It uses the distance and angle tolerances during the computation to determine if your modeled segment is appropriate for cyclic symmetry. Ideally, the topology of your source and target geometry match, and your modeled segment is an even division of 360°. Models that are less than ideal may require increased tolerance or geometry corrections. Before you increase the tolerances, make sure you defined the global cyclic analysis coordinate system correctly. In the Distance Tolerance box, type a distance tolerance.The software uses sample points to compute bounding boxes in the source and target regions. The bounding boxes must be identical within the distance tolerance you specify. In addition, the software rotates the source into the target region. It uses the distance tolerance to compare whether the source and target have matching topology. Caution: Modeling non-cyclic symmetric features is not an ideal modeling scenario.Features, such as holes or slots, that are present in one region but not in the other can cause the regions to fail the compatibility check. When this occurs, the software cannot compute the number of segments (NSEG). In the Angle Tolerance box, type a value.The software computes the difference between the actual segment angle as it is modeled, and the segment angle computed using the closest integer NSEG in a full circumference. These angles should match within the angle tolerance. For example, if you model the geometry as a 20.5° segment, the closest integer number of segments in a full circumference is 18, which corresponds to a 20° segment. The value for Angle Tolerance, in this case, must be larger than (20.5 – 20) = .5°. Review the results of the face pair. Click Preview to view the face pairs, and if necessary, modify the tolerance values to generate more or fewer pairs.In the Segments section of the dialog box, review the computed values. The value in the Calculated Segment Angle box is the angle between the faces, and the value in the Calculated Number of Segments box is the number of segments (360° divided by the angle between the faces). For example, if the angle is 10°, the calculated number of segments is 36. The software uses the modeled geometry to automatically compute the angle and the calculated number of segments. For example, if your model is a 20.5° segment, the software displays 20.5 in the Angle box. The software also computes the number of segments based on the modeled geometry as 360/20.5 = 17.56 and displays the value in the Calculated Number of Segments box. The value in the Number of Segments box is the value computed in the Calculated Number of Segments box rounded to the closest integer. For example, if the angle is a 20.57° segment, the software displays 18 (360/20.5 = 17.56, then rounded to 18). Click OK to return to the Cyclic Symmetry dialog box.

5. To override the global cyclic analysis coordinate system set in the FEM and specify a user-defined coordinate system, select the Override CSYS check box.

6. (Optional) In the Optional Parameters group, specify whether to move all tied nodes on the slave surface onto the master surface in the initial configuration, without any strain. You can then set a position tolerance that calculates a cutoff distance used to determine which nodes on the slave surface are tied to the master surface. You can also let the solver determine the position tolerance. From the Adjust Slave Nodes, set one of the following:To move all tied nodes on the slave surface onto the master surface in the initial configuration, without any strain, select Yes.To leave the slave nodes and not move them, select No.To not specify a value for Adjust Slave Nodes, select Default.If you set Adjust Slave Nodes to Yes, select whether to let the solver determine the position tolerance or enter your own. To use the position tolerance set by the solver, select the Use Position Tolerance Computed by Solver check box. To enter your own position tolerance, clear the selection of the Use Position Tolerance Computed by Solver check box and type a cutoff distance in the Position Tolerance box.

7. (Optional) To use the face pairs that are generated by the automatic face pair recipe, select the Associate Automatic Pair Recipe check box. Note: The automatic pair recipe is the set of parameters in the Create Automatic Face Pairs dialog box that determine how to compute and group face pairs. When the Automatic Pair Recipe check box is selected, the generated contact pairs appear in the Simulation Navigator with the prefix Auto. If the master part is updated, the software recalculates the face pairs and updates the boundary condition. When the Automatic Pair Recipe check box is cleared, the generated contact pairs are not associated with the face pair recipe. These contact pairs behave the same as manually created contact pairs.

8. Click OK.

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