OS-E: 6005 Modal Complex Eigenvalue Analysis

This example demonstrates the Rotor Dynamics modal complex eigenvalue analysis using two coaxial rotors.



Figure 1. FE Model

Model Description

This example consists of two coaxial rotors modeled using 1D elements. One end of each rotor is constrained, the same end is attached to stator using rigid elements and on the other end is attached to the stator through Spring and Damper elements. Static loading condition, due to centrifugal force, is applied to the rotors, also relative spin between the two rotors are defined. Synchronous and Asynchronous analysis are performed at different maximum rotor speeds. The complex modes are extracted for the structure to determine the critical frequencies and Campbell diagram is generated.
FE Model 1D Elements
Rotor
CBAR, CONM2
Stator
SPC, CDAMP, CELAS
Junction
RBE2 Elements
Material Material MAT1 Rotor:
Young’s modulus
2×107
Poisson ratio
0.3
Initial density
1×10-3
Reference Guide Entries Keywords RGYRO, ROTORG, RSPINR, DDVAL, RFORCE, RSPEED, EIGC, EIGRL

Results



Figure 2. Campbell Diagram Plot for the Asynchronous Analysis


Figure 3. Critical Frequencies Identified from the Synchronous Analysis. which are matching with the critical speeds calculated using the Campbell diagram from the asynchronous analysis
Note: OptiStruct always prints the complex pairs for the frequency and damping, and only the one with positive imaginary Eigenvalue is taken into consideration here.

Model Files

The model files used in this example include:
  • <install_directory>/hwsolvers/demos/optistruct/examples/RD_MCEIG.fem