Improvement Modal Testing in Dynamics Revolves Structures to Investigate the Gyroscope Effect Performance

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Author(s) Hisham A. H. Al-Khazali | Mohamad R. Askari
Pages 151-163
Volume 1
Issue 3
Date March, 2012
Keywords Campbell diagram; Whirl motion; Modal test; Gyroscopic effect; Finite element method.
Abstract

Revolve dynamic systems require careful consideration in their dynamic models as they include localized non-proportional damping and frequency-dependent gyroscopic effects. Devices such as engines, motors, disc drives and turbines all develop characteristic inertia effects that can be analyzed to improve the design and decrease the possibility of failure. At higher speeds, the inertia effects of the rotating parts must be represented in order to predict the rotor behavior. The natural frequency versus the spin-speed diagram or the interference diagram, often known as the Campbell diagram, is one of the important design tools to obtain critical speeds of rotating machineries. It is basically the graphical representation of the speed-dependent frequency equation. This variation is important when the effect of the gyroscopic couple is considered, which causes coupling of the rotor motion in two orthogonal planes. Campbell diagrams are commonly plotted either through numerical analyses or through modal testing methods and whirl orbital motion can be detected in this research. It is important to identify all the critical speeds within the range of operation and analyse the damping effects, stiffness and other phenomena also their effects in the safe operation. There are several phenomena need to be detected such as gyroscopic effect which would create complexity in the mathematical procedures in modal analysis which need to be addressed and interpreted appropriately before they could be used in modal testing of rotating machinery. The experimental technique used thus far is called Modal Testing. The technique has recently been applied to rotating structures and some research papers been published, however the full implementation of Modal Testing in active structures and the implications are not fully understood and are therefore in need of much further and more in depth investigations. Mathematical model of the system from the test data can be assembled. The raw data obtained from experiment was used in finite element (FE) model for comparison. It has good capability for Eigen analysis and also good graphical facility and obtained good result.

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