Defining cyclic symmetry analysis in Abaqus

You use the Cyclic Symmetry simulation object to define cyclic symmetry in the Abaqus environment.

Segment creation methods

To apply the cyclic symmetry constraints, in the Cyclic Symmetry dialog box, you define a pair of corresponding surfaces on each side of a single sector of the model, which in Abaqus is called the datum sector.

You can select to use the automatic or manual method to define the segments.

• Automatic cyclic symmetry pairing — Using the automatic method, you select faces on a source region and the software automatically finds the matching target faces. The grouping option controls how the software creates the regions and pairs. You can preview the matching faces and the calculated segment properties.

• Manual cyclic symmetry — Using the manual method, you create and pair the source and target regions. The regions can contain multiple disjoint faces.

The source region must be able to rotate into the target region in the positive theta direction. The Z-axis of the selected cyclic analysis coordinate system and the right-hand rule determine the positive theta direction.

After you use either method to create face pairs, you can modify the regions or create additional manual pairings to specify additional regions.

Axis of cyclic symmetry

In the Direction group of the Cyclic Symmetry dialog box, you define the axis of cyclic symmetry. You can define a user-defined cylindrical coordinate system or select the global cyclic analysis coordinate system defined in the FEM. The selected coordinate system defines the axis of cyclic symmetry (data line in the *CYCLIC SYMMETRIC MODEL keyword).

For more information about the global cyclic analysis coordinate system, see Simulation coordinate systems.

Number of segments

If you selected to manually define the segments, after creating the regions, you can do one of the following using the options in the Segments group of the Cyclic Symmetry dialog box:

• Specify the number of segments in the 360° model.

• Request that the software calculate the number of segments automatically by specifying the distance and angle tolerances.

The first surface of each pair specified is the slave surface, and all degrees of freedom of the nodes in the surface are represented by multi-point constraint equations (MPCs) that the software generates. The second surface of each pair is a master surface.

The number of segments corresponds to the N parameter in the *CYCLIC SYMMETRIC MODEL keyword.

Additional slave node adjustments and tolerances

You can use the Adjust Slave Nodes list in the Optional Parameters group of the Cyclic Symmetry dialog box to select to move all tied nodes on the slave surface onto the master surface in the initial configuration, without any strain or leave them.

You can then select the Use Position Tolerance Computed by Solver check box to specify a position tolerance that determines which nodes on the slave surface are tied to the master surface. You can also let the software determine the tolerance. The calculation of the distance between the slave and master surface for a particular slave node depends on the shell element thickness, whether the segments are node- or element-based, the types of surfaces involved, and more.

The software does not tie slave nodes that do not lie within the position tolerance to the master surface.

Processing natural frequencies and corresponding eigenmodes

You can create a Frequency Perturbation solution step in a Structural analysis to extract the natural frequencies and corresponding eigenmodes of a cyclic symmetric structure.

The Cyclic Symmetry Modes tab of the Solution Step dialog box lets you specify the cyclic symmetry modes for which the software is to perform eigenfrequency analysis. You can specify to use only the even cyclic symmetry modes and specify the lowest and highest cyclic symmetry modes to be used in the analysis.

The software sorts the natural frequencies in ascending order. It also does the following:

• For each natural frequency, it reports the symmetry mode number.

• For each user-specified segment, it saves the eigenmodes in the order corresponding to the natural frequencies.

Where do I find it?

Cyclic symmetry solution options

Application	Pre/Post
Prerequisites	A Simulation file as the work part and the displayed partAbaqus as the specified solverStructural or Thermal as the specified analysis typeFor Structural, Static Perturbation, Visco, or Frequency Perturbation as the specified solution typeFor Thermal, Heat Transfer as the specified solution typeA solution containing a Cyclic Symmetry simulation object

Processing natural frequencies and corresponding eigenmodes

Application	Pre/Post
Prerequisites	A Simulation file as the work part and the displayed partAbaqus as the specified solverStructural as the specified analysis typeFrequency Perturbation as the specified solution typeA solution containing a Cyclic Symmetry simulation object
Location in dialog box	Solution Step dialog box→Cyclic Symmetry Modes tab

Cyclic Symmetry options

Application	Pre/Post
Prerequisites	A Simulation file as the work part and the displayed partAbaqus as the specified solverStructural or Thermal as the specified analysis typeFor Structural, Static Perturbation, Visco, or Frequency Perturbation as the specified solution typeFor Thermal, Heat Transfer as the specified solution typeA solution containing a Cyclic Symmetry simulation object
Command Finder	Cyclic Symmetry
Simulation Navigator	Right-click Simulation Object container node→New Simulation Object list→Cyclic Symmetry

How do I

Define cyclic symmetry in Abaqus using the Automatic method

Define cyclic symmetry in Abaqus using the Manual method

Learn more

Cyclic symmetry analysis in Abaqus

Abaqus workflow—cyclic symmetric analysis

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