A. Seshadri Sekhar

Department of Mechanical Engineering

Differential equations

Fatigue of materials

Machine vibrations

Mathematical models

Rotating machinery

ROTORS

CRACKED ROTOR

TRANSIENT VIBRATION RESPONSE

Crack propagation

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of Sound and Vibration

Faults such as misalignment, rotor cracks and rotor to stator rub can exist collectively in rotor bearing systems. It is an important task for rotor dynamic personnel to monitor and detect faults in rotating machinery. In this paper, the rotor startup vibrations are utilized to solve the fault identification problem using time frequency techniques. Numerical simulations are performed through finite element analysis of the rotor bearing system with individual and collective combinations of faults as mentioned above. Three signal processing tools namely Short Time Fourier Transform (STFT), Continuous Wavelet Transform (CWT) and Hilbert Huang Transform (HHT) are compared to evaluate their detection performance. The effect of addition of Signal to Noise ratio (SNR) on three time frequency techniques is presented. The comparative study is focused towards detecting the least possible level of the fault induced and the computational time consumed. The computation time consumed by HHT is very less when compared to CWT based diagnosis. However, for noisy data CWT is more preferred over HHT. To identify fault characteristics using wavelets a procedure to adjust resolution of the mother wavelet is presented in detail. Experiments are conducted to obtain the run-up data of a rotor bearing setup for diagnosis of shaft misalignment and rotor stator rubbing faults. © 2015 Elsevier Ltd. All rights reserved.

Mechanical Systems and Signal Processing

Fault detection in rotor bearing systems using time frequency techniques

High speed rotating machinery operating with higher load capacity in extreme working conditions can induce fatigue crack into the systems. To avoid failure of the system, it has to be monitored continuously for cracks before it becomes critical. There is a need for the newer techniques that can detect even small cracks. The aim of the present work is to identify the crack in a rotor-bearing system using the concept of operational deflection shape and using kurtosis of vibration response. In the literature kurtosis is used for identifying bearing and gearbox defects. Higher kurtosis means more of the variance is due to infrequent extreme deviations, as opposed to frequent modestly sized deviations. In this study kurtosis deviation curve and amplitude deviation curves are also used for shaft crack detection. It has been noted that the kurtosis changes are significant when the crack is closer to the bearing locations. Single cracks and two cracks have been identified. The rotational laser vibrometer has been used to measure the response from the rotating system. The simulation results of crack detection compare well with experimental results. © The Author(s) 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

JVC/Journal of Vibration and Control

Crack detection in a rotor by operational deflection shape and kurtosis using laser vibrometer measurements

The dynamics and diagnostics of cracked rotors have been gaining importance in recent years. Relatively few authors have addressed the problem of multi-crack assessment for rotors. In many cases there exist more than one crack on the shaft. Then the solutions or the combinations of parameters characterizing the cracks are more and the problem becomes more complicated. In this study, a new technique called amplitude deviation curve (ADC) or slope deviation curve (SDC) has been developed, which is a modification of the operational deflection shape (ODS). The effectiveness of the SDC over ODS for small cracks detection has been demonstrated in the present paper. © 2008 Elsevier Ltd. All rights reserved.

Detection of two cracks in a rotor-bearing system using amplitude deviation curve

The dynamics and diagnostics of a cracked rotor have been gaining importance in the recent years. Vibration monitoring during start-up or shut-down is as important as during steady-state operations to detect cracks especially for machines such as aircraft engines which start and stop quite frequently and run at high speeds. In the present study a relatively new signal processing technique namely Hilbert-Huang transform (HHT) has been applied to transient response of a cracked rotor and few interesting results have been observed. And in all cases it has been found that HHT appears to be a better tool compared to fast Fourier transform and continuous wavelet transform for crack detection in a transient rotor. © 2007 Elsevier Ltd. All rights reserved.

Hilbert-Huang transform for detection and monitoring of crack in a transient rotor

In the present study a simple Laval rotor with a transverse crack is considered. The analysis assumes that the vibrations remain small in comparison to the sag of the rotor under its own weight. If a cracked shaft rotates slowly under the load of its own weight, then the crack will open and close once per revolution, i.e. it breathes. Considering a simple hinge model which is a very good model for small cracks with the breathing action of crack, the transient vibration response of a cracked rotor passing through its critical speed is analysed, as an attempt for crack detection and monitoring. Effects of different factors such as crack depth, unbalance eccentricity with phase and acceleration influencing vibration are investigated. © 1998 Elsevier Science Ltd. All rights reserved.

Journal	Journal of Sound and Vibration
ISSN	0022460X
Open Access	No