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 the user’s 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 a cyclic symmetry analysis, the response of the full model is determined from a linear combination of several independent basic responses, known as solution harmonics. They are represented using indices called harmonic indices and they could be selected by the user during the modeling process.
The harmonic indices are supposed to be nonnegative and must be no greater than (NSEG is the number of segments to be modeled).
Analysis Type  Comments 

Linear Static Analysis with Cyclicsymmetric loading 

Linear Static Analysis with Noncyclicsymmetric loading  In this case, only the 0^{th} Harmonic will be used, and all other harmonics will be disregarded. 
Normal Modes Analysis  Removing some harmonics will only lead to some missing mode shapes, without any loss in accuracy. 
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 harmonic coefficients of loading. 

LOADCYN  Defines the loading. 

Support Information
Category  Supported Entities  Additional Details 

Analysis type  Linear static analysis Normal modes analysis 
In normal modes analysis, only Lanczos eigensolver (EIGRL) is supported. 
Analysis output  DISPLACEMENT STRESS STRAIN 

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

Constraints  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  Enforced displacement (only via nonzero
SPC) Forces Pressures GRAV RFORCE TEMP 

Preloading  Preloaded linear static and normal modes analysis are supported  The following restrictions apply to the subcase that
preloads:

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
CYAX 100
CYJOIN 1 12 THRU 20
CYJOIN 2 22 THRU 30
FORCE 51 12 11 1.0 0.0 100.0 1.0
LOADCYN 14 0.1 1.0 51
.
.
Example
Comments
 HyperMesh support for cyclic symmetry analysis would be available in future releases.