Cyclic Symmetry Analysis
Cyclic symmetry is a type of symmetry in which a representative (or basic) segment, if patterned circularly about an axis of symmetry would result in the full model.
Structures with symmetry can often be modeled with one representative entity, from which the full structure can be obtained after certain operations (pattern, mirror, rotation, etc.). Such methods can lead to huge savings in modeling effort, computational time, and file storage. Therefore, exploiting symmetry in finite element models could prove to be very advantageous.
 The basic segment could either be the smallest repeating unit in the model or could involve several repeating units.
 Depending on your requirements, a full 360 degree model or a partial (as in, 270 degrees) model could be analyzed by suitably specifying the number of segments in the model definition.
In OptiStruct
In a cyclic symmetry analysis, the boundaries on either side of the modeled base segment which are to be connected to adjacent segments are defined as SIDE 1 and 2. The direction of the axis of symmetry are determined using the righthand thumb rule.
In cyclic symmetry analysis, the solution is internally decomposed as a series of harmonic solutions represented using harmonic indices, and they can be requested by the HARMONICS I/O Option.
The harmonic indices are supposed to be nonnegative and must be no greater than (NSEG is the number of segments of the actual structure).
If NSEG is odd:
If NSEG is even:
Subcase Type  Noncyclic Symmetric Behavior  Cyclic Symmetric Behaviour* 

Linear Static 


Normal Mode 


Nonlinear Static, Nonlinear Transient  N/A 

Preloading/Preloaded Subcase in Prestressed Analyses 


Entry  Purpose  Additional Details 

HARMONICS  Specifies the solution harmonics to be used. 

NOUTPUT  Specifies the segments for which results must be recovered and output. 

Entry  Purpose  Additional Details 

CYAX  Specifies the grids that lie on the axis of symmetry.  This entry is optional for cyclic symmetry analysis. 
CYJOIN  Specifies grid points on the segment boundaries that connect to adjacent segments. 

CYSYM  Specifies the number of segments in the model.  This entry is mandatory for cyclic symmetry analysis. 
LOADCYH  Specifies the loading by harmonics for linear static analysis. 

LOADCYN  Defines the loading by segments for linear static analysis. 

LOAD(ADD)  Defines the loading for implicit nonlinear analyses. 

Support Information
Category  Supported Entities  Additional Details 

Analysis type  Linear static analysis  
Normal modes analysis 


Implicit nonlinear analyses 


Prestressed analysis 


Analysis output  DISPLACEMENT STRESS STRAIN Velocity/Acceleration Plasticity related results Contact results 

Elements  CBEAM CTRIA3, CTRIA6 CQUAD4, CQUAD8 CTETRA, CHEXA, CPENTA CPYRA 

Constraints  SPC MPC RBE2 RBE3 
RBE2 and RBE3 will be generated only for the base segment in the result plot. 
Materials  MAT1 MAT2 MAT9 MATT1 MATT2 MATT9 

Loads  SPCD Forces Pressures GRAV RFORCE TEMP 

Problem Setup
$ *************************************************************
$ EXAMPLE TO DEMONSTRATE A CYCLIC SYMMETRIC ANALYSIS SETUP
$ *************************************************************
.
.
NOUTPUT = ALL
SUBCASE 101
SPC = 1
LOAD = 14
SUBCASE 102
SPC = 1
METHOD(STRUCTURE) = 2
HARMONICS = 102
BEGIN BULK
$1><2><3><4><5><6><7><8><9>
CORD2C 11 0 0.0 0.0 0.0 0.0 0.0 1.0
+ 1.0 0.0 0.0
EIGRL 2 0.0 50 MAX
SET 102 MODE
+ 0 1
CYSYM 4
CYJOIN 1 12 THRU 20
CYJOIN 2 22 THRU 30
GRID …
…
FORCE 51 12 11 1.0 0.0 100.0 1.0
LOADCYN 14 0.1 2 1.0 51
LOADCYN 14 0.1 4 1.0 51
.
.
Example
View Results in Cyclic Symmetry Analysis
Systems referenced by the CD field of grid points in the basic segment (including the basic coordinate system when CD is blank) is cyclically patterned and assigned to corresponding grids in each segment requested by NOUTPUT. This can also be used for viewing the results for each segment in its local coordinate system.
To view results in the basic coordinate system, The “Global coordinate system” option can be selected in HyperView.
Comments
 HyperMesh support for cyclic symmetry analysis would be available in future releases.