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Wade A Smith

Wade A Smith
UNSW Sydney | UNSW · School of Mechanical and Manufacturing Engineering

PhD

About

103
Publications
83,219
Reads
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2,213
Citations
Introduction
I'm an experienced research engineer specialising in machine condition monitoring and vibration analysis. I have over 14 years' research experience and have lectured extensively on vibration, dynamics and machine condition monitoring at both the University of New South Wales and the University of Technology, Sydney. I am currently looking for new opportunities (academia or industry) in the predictive maintenance or vibration analysis fields.
Additional affiliations
January 2017 - December 2019
UNSW Sydney
Position
  • Research Associate
October 2011 - December 2016
UNSW Sydney
Position
  • Research Associate

Publications

Publications (103)
Article
This paper proposes a gear diagnostic method denoted as the angle cepstrum comb liftering (ACCL) method. It uses comb liftering in the cepstrum of the order tracked acceleration signal to select all rahmonics of the gearmesh quefrency of a particular meshing gear pair. When converted to the equivalent log spectrum, it thus contains only the harmoni...
Article
Signal models of rolling-element bearings have been a fundamental tool for the development and justification of new bearing signal processing techniques. A cyclostationary model proposed twenty years ago is still the most common reference for physically-justified bearing diagnostics. Surprisingly, a pseudo-cyclostationary bearing model proposed jus...
Article
Gear transmission error (TE) has been acknowledged as a prominent diagnostic tool in condition monitoring. Its advantages vs vibration include being closer to the source and less affected by transmission path effects. TE has recently demonstrated its enormous capabilities in gear wear severity assessment. For crack diagnostics, despite some promisi...
Article
Gear wear often results in both tooth profile changes caused by abrasive wear, and fatigue pitting. Being able to accurately monitor and predict the profile change (i.e., the wear depth in the direction normal to the gear surface) and surface pitting propagation can bring enormous benefits to industrial practice. However, there is a lack of efficie...
Article
Wind-turbine gearboxes mostly work under varying speed conditions. With the increased need for cost-saving and installation difficulties in many applications, vibration-based speed estimation approaches have attracted more attention recently. However, the authors have observed that instantaneous speed or phase estimates from planetary gearbox vibra...
Article
Spalling caused by fatigue is the most common reason for rolling element bearing failure, and spall size can be a good indicator to predict the remaining useful life of the bearing. Previous studies reported that, in the acceleration signal, a low-frequency step response is caused by de-stressing or re-stressing of the rolling element during its en...
Article
A smartphone is a low-cost pocket wireless multichannel multiphysical data acquisition system: the use of such a device for noise and vibration analysis is a challenging task. To what extent is it possible to carry out relevant analysis from it? The Survishno conference, held in Lyon in July 2019, proposed a contest to participants based on this su...
Article
Gear transmission error (TE) has become a promising diagnostic tool due to the fact that, compared with vibration responses, it is much less affected by the transfer path from the source to the measurement, and it can be measured conveniently using shaft encoders installed on the input and output of a gear stage. It is also the direct cause of vibr...
Article
Having the ability to predict the gear surface wear progression can bring significant benefits in safety and cost to various industries. Gear wear can result in a change in the working surface geometry of the gear tooth, which affects the tooth surface load distribution. The altered load distribution in turn promotes the progression of gear wear. T...
Article
Fatigue pitting and abrasive wear are the most common wear mechanisms in lubricated gears, and they have different effects on the gear transmission system. To develop effective methods for online gear wear monitoring, in this paper, a vibration-based wear mechanism identification procedure is proposed, and then the wear evolution is tracked using a...
Conference Paper
Full-text available
For constant speed gearboxes, a number of techniques have been developed to separate gear signals from bearing fault signals, but operation at variable speed emphasises the differences between gears and bearings. With gears, fault signals are directly tied to shaft speed, and are best extracted in the harmonic order domain, whereas bearing fault si...
Article
Demodulation methods are widely used for bearing diagnostics, based often on the (Squared) Envelope Spectrum after band pass filtering. One of the main challenges of these methods is the detection of a suitable band for signal demodulation under varying speed conditions. Angular resampling methods may synchronize the impulsive nature of bearing dam...
Article
This paper proposes a model-based surface roughness estimation method using acoustic emission (AE) signals. Two powerful theoretical AE generation models are modified in this method to provide a comparative study. The proposed method extracts for the first time the theoretical relationship between surface roughness and the mechanism of AE generatio...
Article
Acoustic emission (AE) techniques play a key role in machine condition monitoring and wear/fault diagnosis. Understanding the impact of friction and wear on the generation of AE signals is essential to building a reliable wear monitoring system. However, existing papers focus on only one or two factors in specific contact conditions. This paper aim...
Article
Data integrity has become more critical with the growth in remote semi-automated machine health monitoring. The mounted resonance frequency of an accelerometer, if correctly mounted on a flat surface, is normally quite repeatable, for example at different locations on the same object. A method has recently been developed which largely separates for...
Article
Rolling element bearing fault diagnostics has been a topic of intensive research in recent decades, as they are critical components of rotating machinery and therefore their failure may result in sudden breakdown of machines and industrial installations. The early and accurate detection of incipient faults on bearings can reduce the production cost...
Article
The demodulation of machine signals is a key step for the diagnostics and prognostics of components such as rolling element bearings. Whereas diagnostic approaches could perform a cyclostationary analysis over the full spectral band (i.e. using cyclic-spectral maps), in order to extract time domain and statistical features for prognostics, a pre-pr...
Article
The Teager Kaiser Energy Operator (TKEO) was originally proposed for use in speech analysis as representing the total energy (i.e. kinetic plus potential energy) in a signal. It was shown that for a mono-component carrier, with slowly changing amplitude and frequency, the TKEO is approximately equal to the product of the squares of the instantaneou...
Article
This paper aims at establishing a correlation between gear wear in spur gears and the statistical properties of AE signals. A generalised Gaussian cyclostationary model is proposed for AE signals measured on gears. This choice is motivated by the characteristics of lubricated contact in spur gears, combining non-stationarity (i.e. cyclostationarity...
Conference Paper
The use of traditional features (e.g. kurtosis, RMS, and envelope spectra) combined with machine learning technology has proven successful in the detection of bearing faults. The extension of this approach to fault severity assessment is however questionable. Cyclostationary features (e.g. based on the envelope signal) and statistical indices targe...
Conference Paper
Full-text available
Transmission error (TE) has long been thought to be a major contributor to gear vibration and noise, but insufficient consideration has been given to the different types of TE and how they generate vibrations. TE is defined as the difference in torsional vibration of two meshing gears, scaled so as to represent linear motion along the line of actio...
Article
Planetary gearboxes have a wide range of applications, but due to their complex layout, the diagnostics of planetary gearboxes is more challenging than that of fixed-axis gearboxes. This is especially so for planet gears, as multiple planets mesh simultaneously, share the same rotating speed and are in mesh with both the sun and ring gears. To enab...
Article
Gear wear is a critical degradation process in many applications and its monitoring is important to ensure safe operation of machines. The case study presents a novel approach to obtain comprehensive and high-resolution wear information for monitoring the evolution of gear wear. This is achieved through the combination of a moulding method and non-...
Article
Gear wear introduces geometric deviations in gear teeth and alters the load distribution across the tooth surface. Wear also increases the gear transmission error, generally resulting in increased vibration, noise and dynamic loads. This altered loading in turn promotes wear, forming a feedback loop between gear surface wear and vibration. Having t...
Article
In this study, a mesh phasing-based approach is developed to locate the positions of faulty planet gears using external vibration measurements. Previous studies have illustrated how this can be achieved using internal vibration measurements recorded from a sensor placed on the planet carrier. It was shown in these studies that the timing of identif...
Article
Full-text available
The cepstrum has a very long history, since the first paper was published in 1963, two years before the publication of the FFT algorithm. The first application was to the determination of echo delay time, but it was quickly applied to speech analysis for two reasons. Firstly, it was able to detect voiced speech, and measure the voice pitch, and sec...
Conference Paper
The components of a helicopter gearbox are vulnerable to fatigue defects and therefore Health and Usage Monitoring Systems have been developed, focusing towards early, accurate and on time fault detection with limited false alarms and missed detections. The main aim of HUMs is to enhance the helicopters’ operational reliability and functionality an...
Conference Paper
Full-text available
It was shown many years ago that gear transmission error (TE) could be measured very accurately using high quality shaft encoders on the free ends of the shafts on which the gears are mounted. TE is defined as the difference in torsional vibration of the gears, scaled so as to represent linear motion along the line of action. The torsional vibratio...
Article
It is a challenge to determine by vibration analysis which planet gear carries a fault due to the complex layout of planetary gearboxes. In this study, we explain for the first time the possibility of using mesh phasing for distinguishing between faults on different planet gears. It has been found that, due to mesh phasing relationships, the vibrat...
Article
The last decade has witnessed spectacular advances in vibration-based fault detection of rotating machines and, in particular, rolling element bearings. Nowadays, the related state of the art can be considered mature thanks to a set of powerful signal processing techniques able to denoise and process the vibration signal to detect fault symptoms. A...
Chapter
This paper presents the results of transmission error (TE) analysis of spur planetary gearboxes using finite element methods. Two subsystem models were established to study changes in the transmission error caused by planet gear tooth root cracks and spalls. The simulation results reveal that a tooth crack gives changes twice in a planet revolution...
Chapter
Bearing failures not only increase the cost due to production loss and need for repair or replacement, but also threaten the personnel safety. Manufacturers of rotating machinery tend to adopt new health monitoring services, using regular inspections or embedding sensors for health monitoring systems within each unit. Early failure signs of a beari...
Chapter
Wear in gears can usually be detected from the vibration signal once the wear has reached a ‘macro’ level—millimetre-scale variations from the original involute profile. Macro level wear is often preceded and accompanied by micro-level surface roughness changes (micrometre scale), arising from either abrasive wear or contact fatigue pitting. These...
Chapter
The instantaneous speed of a machine can be accurately determined by frequency demodulation of a tacho or shaft encoder signal, but can often be determined by frequency demodulation of a machine shaft order in a response vibration signal. It has recently been realised that the latter is not necessarily the same as the speed variation of the machine...
Chapter
Condition monitoring of rotating machinery is a field of intensive research being closely related to the technological evolution in the area of energy, manufacturing and transport. The fault detection and diagnosis of planetary gearbox bearings present an interesting challenge even under steady operating conditions as often the relatively weak bear...
Article
Full-text available
This article aims at developing a new framework to identify and assess progressive structural damage. The method relies solely on output measurements to establish the frequency response functions of a structure using cepstrum-based operational modal analysis. Two different damage indicative features are constructed using the established frequency r...
Conference Paper
Full-text available
Data integrity has become more critical with the growth in remote semi-automated machine health monitoring. The mounted resonance frequency of an accelerometer, if correctly mounted on a flat surface, is normally quite repeatable, for example at different locations on the same object. A method has recently been developed which largely separates for...
Conference Paper
Full-text available
In this study, we develop a mesh phasing based approach to locate the position of faulty planet gears using external vibration measurements. Previous studies have illustrated how this can be done using internal vibration measurements recorded from a sensor placed on the planet carrier. It was shown in those studies that the timing of identifiable f...
Conference Paper
Full-text available
In the diagnostics of variable speed machines, it is often important to know the instantaneous speed very accurately. This can be done by frequency demodulation of a tacho signal, but in some cases it can be determined by frequency demodulation of a response vibration signal. However, it has recently been realised that the result of the latter depe...
Conference Paper
Full-text available
Rolling element bearings are among the most common components which lead to machinery breakdown. Lately, focus has been targeted to cyclostationary-based tools that show a good performance in describing and detecting the bearing vibration signatures and early damage diagnosis. The Cyclic Spectral Correlation (CSC) and Coherence (CSCoh) describe the...
Conference Paper
Full-text available
Rolling element bearings are common but crucial components of rotating machines being the interface among steady and rotating parts and are responsible for many machine failures and breakdowns. Condition monitoring of machinery using vibration analysis often provides insight and early detection of damage on the bearings. The most widespread method...
Article
Full-text available
All vibration-based machine condition monitoring uses response signals, which are a mixture of forcing function and transfer function effects, and often an assumption is made as to whether a change is due to one or the other. Operational modal analysis (OMA) is one way of determining the dynamic properties of a structure or machine from the respons...
Article
This paper proposes a new statistical model to characterise acoustic emission (AE) signals generated from surfaces in sliding contact. Such signals have traditionally been assessed using simple metrics such as RMS or kurtosis, but these metrics assume the signal is both (approximately) Gaussian and stationary, neither of which hold in many practica...
Conference Paper
Full-text available
A common problem with operational modal analysis (OMA) is that response signals are often contaminated by forcing functions, which can mask the modal information in various ways. This is particularly the case for machine structures, where deterministic forcing functions associated with rotating shafts often dominate the responses. Where the machine...
Conference Paper
Wear in gears can usually be detected from the vibration signal once the wear has reached a 'macro' level – millimetre-scale variations from the original involute profile. Macro level wear is often preceded and accompanied by micro-level surface roughness changes (micrometre scale), arising from either abrasive wear or contact fatigue pitting. Thes...
Conference Paper
Full-text available
This paper presents the development of a new indicator designed to locate faults on planet gears. Although the condition monitoring of planetary gearboxes has attracted much attention, it is still a challenge to diagnose and especially to locate faults on planet gears. This paper explains the differences in the vibration responses collected by an i...
Conference Paper
Full-text available
All vibration-based machine condition monitoring uses response signals, which are a mixture of forcing function and transfer function effects, and often an assumption is made as to whether a change is due to one or the other. Operational modal analysis (OMA) is one way of determining the dynamic properties of a structure or machine from the respons...
Conference Paper
Full-text available
Most traditional gear diagnostic indicators were developed for constant speed operation and are based on the spectral amplitudes of the gearmesh component and its harmonics, as well as those of the sidebands spaced at integer multiples of shaft speed around the meshing harmonics. In variable speed operation, it is common to perform order tracking t...
Conference Paper
Full-text available
The detection and diagnostics of faults in planet gear bearings constitute a problem in the diagnostics of planetary gearboxes, possibly because of the tortuous and time varying path the signals must take in reaching externally mounted accelerometers. The problem is made even more difficult when the speed of the machine is continuously varying, suc...
Article
Full-text available
Direct measurement of wear in IC engine bearings is a tedious activity. Vibration signals are known to carry substantial information about engine condition and correlate well with bearing clearance, but have not been well utilised for wear analysis. This paper presents a new method to simulate wear in IC engine bearings by integrating vibration and...
Conference Paper
Full-text available
Planetary gearboxes present a challenging case for condition monitoring, and planet bearing faults in particular are often extremely difficult to diagnose. In addition, two of the most common uses of planetary gearboxes – in wind turbine and helicopter transmissions – involve mostly variable speed operation, rendering most of the conventional diagn...
Conference Paper
Full-text available
Wear is known to be the cause of most failures in machine components. A major challenge associated with direct and regular wear monitoring is the need for extensive and recurring inspection. This work presents a simulation based method to predict the wear profile through integrating wear and vibration based data, which can be used to predict remain...
Conference Paper
Full-text available
The Teager Kaiser Energy Operator (TKEO) was originally developed for tracking the " energy " in speech signals, including both potential and kinetic energy, where for real-time it can be calculated very efficiently from three adjacent time samples. It has recently been shown that the TKEO is equal to the squared envelope of the derivative of the m...
Conference Paper
Full-text available
This paper explains the problem of electromagnetic interference (EMI) in vibration signals, and how it can affect bearing diagnostics. The particular focus is on the EMI generated from variable frequency drives (VFDs) – very common components in rotating machinery. This type of EMI is very impulsive and wideband, with a complex but well-structured...
Conference Paper
Full-text available
The symptoms of faults in both gears and rolling element bearings are tied to machine speed, but the actual mechanisms of vibration signal generation are quite different. Gear vibrations are inherently deterministic, and can be extracted from extraneous vibrations for each gear separately using synchronous averaging with respect to that particular...
Conference Paper
Full-text available
For diagnostics of variable speed machines such as wind turbines, it is essential to have a measure of instantaneous speed, preferably extracted from the response signal to avoid the need for a tacho signal. The Teager Kaiser Energy Operator (TKEO) was first proposed by Teager, and refined by Kaiser. It is analogous to the total (kinetic and potent...
Article
Full-text available
The selection of the optimal demodulation frequency band is a significant step in bearing fault diagnosis because it determines whether the fault information can be extracted from the demodulated signal via envelope analysis. Two well-known methods for selecting the demodulation band are the Fast Kurtogram, based on the kurtosis of the filtered tim...
Article
Full-text available
Discrete frequency components such as machine shaft orders can disrupt the operation of normal Operational Modal Analysis (OMA) algorithms. With constant speed machines, they have been removed using time synchronous averaging (TSA). This paper compares two approaches for varying speed machines. In one method, signals are transformed into the order...
Article
Full-text available
Operational modal analysis (OMA) seeks to determine a structure׳s dynamic characteristics from response-only measurements, which comprise both excitation and transmission path effects. The cepstrum has been used successfully in a number of applications to separate these source and path effects, after which the poles and zeros of the transfer functi...
Article
Full-text available
Gear tooth wear is an inevitable phenomenon and has a significant influence on gear dynamic features. Although vibration analysis has been widely used to diagnose localised gear tooth faults, its techniques for gear wear monitoring have not been well-established. This paper aims at developing a vibration indicator to evaluate the effects of wear on...
Conference Paper
Full-text available
Fatigue-induced fault propagation is the most common cause of failure in rolling element bearings. As most classic diagnostic indicators do not trend monotonically with wear development, the ability to assess fault severity remains limited at present. This paper aims to expand current understanding and establish a correlation between the vibration...
Conference Paper
Full-text available
The detection of gear wear from vibration signals is generally achievable once the wear has progressed to a ‘macro’ level, in which the tooth profile has changed appreciably. A typical example is the ‘double scalloped’ wear pattern – involving substantial material loss either side of the (largely unaffected) pitchline – which is diagnosable from an...
Conference Paper
Full-text available
Condition monitoring of wind turbines is very important to minimise maintenance costs (virtually the only costs once they are installed), and to maximise production. New diagnostic techniques have had to be developed to deal with the varying speed and load of the most efficient turbines, but these are greatly aided by having a measure of the speed....
Conference Paper
Full-text available
Cepstrum-based operational modal analysis (OMA) relies on identifying the transfer function poles and zeros in the response measurement, and then summing (in log magnitude) the individual pole/zero contributions to regenerate the corresponding frequency response function (FRF). Yet this regenerated FRF will be subject to magnitude distortion from t...