Improper aligning of shafts through couplings often leads to severe vibration problems in many rotating machines. The rotor-bearing system is modelled using higher order finite elements by considering deflection, slope, shear force, bending moment with eight degrees of freedom per node. The reaction forces, moments developed due to flexible coupling misalignment are derived and introduced in the model. The imbalance response in two harmonics is evaluated. The increase in harmonics with misalignment can easily be modelled by using FEM analysis. The location of the coupling with respect to the bending mode shape has a strong influence on the vibrations. © 1995 Academic Press. All rights reserved.

A. Seshadri Sekhar

Department of Mechanical Engineering

Alignment

Bending (deformation)

Degrees of freedom (mechanics)

finite element method

FLEXIBLE COUPLINGS

Harmonic analysis

Loads (forces)

Mathematical models

Rotating machinery

ROTORS

Shafts (machine components)

Bending moment

Harmonics

IMBALANCE RESPONSE

MISALIGNMENT

Reaction forces

Shear force

Slope

Machine vibrations

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

Rotor faults such as misalignment, shaft crack, rotor rub, bearing fault etc. lead to high vibration and are major cause of machinery shut down. Misalignment in rotating machinery shafts develops reaction forces and moments at the coupling. Conventionally, misalignment diagnosis is carried through vibration measurements. Especially, the existence of strong 2x component is widely accepted. However, there are other rotor-bearing faults which lead to significant 2x vibrations. Hence distinguishing misalignment is a challenging task using vibration signals alone. In view of these limitations by employing vibrations signals, present study focuses on torque measurements for misalignment diagnosis. Experimental results using torque sensor for different cases of misalignment at different frequency of operation are reported. Fourier and wavelet transforms are used to detect the misalignment fault. The variation of the fault characteristics with respect to time are reported for sampled signals using wavelet transforms. The study shows the possibilities of using torque measurements as useful and additional technique for the detection and monitoring of coupling misalignment. © 2014 Elsevier Ltd. All rights reserved.

Measurement: Journal of the International Measurement Confederation

Detection and monitoring of coupling misalignment in rotors using torque measurements

Precise detection of the misalignment can reduce maintenance cost, power loss and improve life of rotating machinery. In this paper, Hilbert Huang Transform (HHT) of the run-up response of a rotor is used to detect coupling misalignment. A finite element analysis is carried out to simulate desirable level of possible parallel and angular misalignment. All the best conventional detection techniques like Fourier spectrum analysis, Continuous Wavelet Transform are compared with results obtained by HHT. The effect of Signal to Noise Ratio and angular acceleration on all the methods to detect misalignment is discussed. The comparison of the methods is oriented towards detecting least possible misalignment level. Finally, experiments are performed on a test rotor rig to detect induced misalignment using the proposed method. It is observed that this method is sensitive to low misalignment, and consumes less testing time. Copyright © 2014 by ASME.

Proceedings of the ASME Turbo Expo

Detection and monitoring of shaft misalignment in rotors using hilbert huang transform

After unbalance, coupling misalignment is the most common fault present in rotating machines. However, limited research has been carried out on coupling misalignment and its effects. The present study aims to explore the research on coupling misalignment by briefly summarizing the research work done so far on different modelling techniques, effects on the system behaviour, fault identification and condition monitoring techniques.

Noise and Vibration Worldwide

Coupling misalignment in rotating machines: Modelling, effects and monitoring

Mechanical malfunctions such as, rotor unbalance and shaft misalignment are the most common causes of vibration in rotating machineries. Vibration is the most widely used parameter to monitor and asses the machine health condition. In this work, the Coast Down Time (CDT), which is an indicator of faults, is used to assess the condition of the rotating machine as a condition monitoring parameter. CDT is the total time taken by the system to dissipate the momentum acquired during sustained operation. Extensive experiments were conducted on Forward Curved Centrifugal Blower Test Rig at selected cutoff speeds for several combinations of combined horizontal and vertical parallel misalignment, combined parallel and angular misalignment, as well as for various unbalance conditions. As mechanical faults increase, a drastic decrease in CDT is found and this is represented as CDT reduction percentage. A specific correlation between the CDT reduction percentage, level of mechanical faults, and rotational cutoff speeds is observed. The results are analyzed and compared with vibration analysis for potential use of CDT as one of the condition monitoring parameter.

Fulltext

International Journal of Rotating Machinery

Condition Monitoring of Forward Curved Centrifugal Blower Using Coast Down Time Analysis

Couplings and Joints

Elastomeric Couplings

Machinery Failure Analysis and Troubleshooting Practical Machinery Management for Process Plants

Machinery Troubleshooting

Tribology International

International conference on flexible couplings for high powers and speeds

The Lancet

FIFTH DAY. Wednesday, March 17, 1837. MEMBERS PRESENT. Baines, Mr. Hume, Mr. Estcourt, Mr. Miles, Mr. W. Freemantle, Sir T. Mosley, Sir O. Gordon, Mr. Ponsonby, Mr. Graham, Sir J. Scrope, Mr. Harvey, Mr. Villiers, Mr. Hodges, Mr. Walter, Mr. Mr. FAZAKERLEY in the Chair,

Effects of coupling misalignment on vibrations of rotating machinery

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