• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.1
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• pp.76-84
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• 2009

The vibration and stability of thin, flexible corotating disks in an enclosed compressible fluid is investigated analytically and compared with the results of a single rotating disk. The discretized dynamical system of the corotating disks is derived in the compact form of a classical gyroscopic system similar with a single disk. For the undamped system, coupled structure-acoustic traveling waves destabilize through mode coalescence leading to flutter instability. However, it is found that the flutter regions of the corotating disks are wider than those of a single disk. A detailed investigation of the effects of dissipation arising from acoustic or disk damping is also performed. Finally, in the presence of both acoustic and disk dampings, the instability regions are found and compared with those of a single disk. Although this study does not allow a radial clearance between the disk and the enclosure, the computational frame work of the problem can be expanded to the system having the radial clearance in an enclosure.

• Structural Engineering and Mechanics
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• v.50 no.1
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• pp.19-36
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• 2014

This paper focuses on a model order reduction (MOR) for large-scale rotordynamic systems by using finite element discretization. Typical rotor-bearing systems consist of a rotor, built-on parts, and a support system. These systems require careful consideration in their dynamic analysis modeling because they include unsymmetrical stiffness, localized nonproportional damping, and frequency-dependent gyroscopic effects. Because of this complex geometry, the finite element model under consideration may have a very large number of degrees of freedom. Thus, the repeated dynamic analyses used to investigate the critical speeds, stability, and unbalanced response are computationally very expensive to complete within a practical design cycle. In this study, we demonstrate that a Krylov subspace-based MOR via moment matching significantly speeds up the rotordynamic analyses needed to check the whirling frequencies and critical speeds of large rotor systems. This approach is very efficient, because it is possible to repeat the dynamic simulation with the help of a reduced system by changing the operating rotational speed, which can be preserved as a parameter in the process of model reduction. Two examples of rotordynamic systems show that the suggested MOR provides a significant reduction in computational cost for a Campbell diagram analysis, while maintaining accuracy comparable to that of the original systems.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.2 s.257
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• pp.152-159
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• 2007

A study on the control of free vibration and stability characteristics of rotating hollow circular shafts subjected to compressive axial forces is presented in this paper. Both passive structural tailoring technique and active control scheme via collocated piezoelectric sensing and actuation are used in the study Gyroscopic and centrifugal forces combined with the compressive axial force contribute to the occurrence of divergence and flutter instabilities of the rotating shaft. The dual methodology based on the passive and active control schemes shows a high degree of efficiency toward postponement of these instabilities and expansion of the domain of stability of the system. The structural model of the shaft is based on an advanced thin-walled beam structure that includes the non-classical effects of transverse shear, anisotropy of constituent materials and rotatory inertia.

• Composites Research
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• v.19 no.6
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• pp.8-15
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• 2006

In this study, computational rotor dynamic analyses of a composite roller used for large LCD panel manufacturing process have been conducted. The present computational method is based on the general finite element method with rotating gyroscopic effects of rotor systems. General purpose commercial finite element code, SAMCEF which has special rotordynamics analysis module is applied. For the purpose of numerical verification, comparison study for a benchmark dual rotor model with support bearings is also presented. Detailed finite element models for composite roller with optimized lamination angles are constructed and analyzed considering gravity effect in order to investigate vibration characteristics in actual operation environment. As results of the present study, rotor stability diagrams and mass unbalance responses are presented for different rotating conditions.