CERES :: Browsing by Author "Mba, David"

Browsing by Author "Mba, David"

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Open Access
Acoustic emission during run-up and run-down of a power generation turbine.
(Elsevier Science B.V., Amsterdam., 2004-05-01T00:00:00Z) Zuluaga-Giraldo, C.; Mba, David; Smart, M.
The measurement of acoustic emission (AE) activity at the bearings of power generation turbines is evolving into a viable complementary diagnostic technique especially adept at indicating the early stages of shaft-seal rubbing. This paper reports on an ongoing investigation on the application of acoustic emission for shaft-seal rub detection in power generation turbines. A pre- requisite in developing such a technique requires an understanding of the operational AE background noise. The detection of shaft-seal, and blade-case, rubbing with AE has been reported [Electrical Eng. Japan 110 (2) (1990); Joint ASME/IEEE Power Generation Conference, October 4–8, 1981, St. Louis, MI, USA; International Conference on Condition Monitoring. Oxford, UK, July 2–4, 2003]. In these instances, the observations of AE activity were associated with particular dynamic and process conditions known to cause such defects. However, the effect of variations of turbine loading on AE activity is unknown. This report presents observations of AE activity during the run-up and run-down of a 500 MW steam turbine and is the first known document detailing correlations between AE, vibration and turbine load
Open Access
Acoustic Emission for the detection of shaft-to-seal rubbing in large power generation turbines
(2006-01-01T00:00:00Z) Leahy, M.; Mba, David; Cooper, P.; Montgomery, A.; Owen, D.
An empirical investigation is undertaken in order to assess the potential of the AE technique for the detection of seal-to-rotor rubbing in steam turbines. Rubbing was induced at various axial locations along a 4 ½ tonne test rotor, rotating at 3000 rpm and supported by 7” (178mm) journal bearings. This paper examines the capabilities of bearing mounted AE transducers for the detection of seal-torotor rubbi
Open Access
Acoustic Emission Signal Classification in Condition Monitoring Using the Kolmogorov-Smirnov Statistic.
(2001-01-01T00:00:00Z) Hall, L. D.; Mba, David; Bannister, R. H.
Acoustic emission (AE) measurement at the bearings of rotating machinery has become a useful tool for diagnosing incipient fault conditions. In particular, AE can be used to detect unwanted intermittent or partial rubbing between a rotating central shaft and surrounding stationary components. This is a particular problem encountered in gas turbines used for power generation. For successful fault diagnosis, it is important to adopt AE signal analysis techniques capable of distinguishing between various types of rub mechanisms. It is also useful to develop techniques for inferring information such as the severity of rubbing or the type of seal material making contact on the shaft. It is proposed that modelling the cumulative distribution function of rub-induced AE signals with respect to appropriate theoretical distributions, and quantifying the goodness of fit with the Kolmogorov-Smirnov (KS) statistic, offer a suitable signal feature for diagnosis. This paper demonstrates the successful use of the KS feature for discriminating different classes of shaft- seal rubbing. A hierarchical cluster algorithm was employed for grouping extracted KS values. AE rub signals were simulated with various metallic seals and measured at the journal bearings of a test rig rotating at approximately 1500 rev/min. Also, the KS classification results were directly compared withmore established AE feature vectors.
Open Access
Acoustic Emission Waveform Changes for Varying Seeded Defect Sizes.
(2006-01-01T00:00:00Z) Al-Dossary, Saad; Raja, Hamzah R. I.; Mba, David
The investigation reported in this paper was centered on the application of the Acoustic Emissions (AE) technology for characterising the defect sizes on a radially loaded bearing. The aim of this investigation was to ascertain the relationship between the duration of AE transient bursts associated with seeded defects to the actual geometric size of the defect. It is concluded that the geometric defect size can be determined from the AE waveform.
Open Access
Acoustic Emissions and monitoring bearing health
(Taylor & Francis, 2003-01-01T00:00:00Z) Mba, David
Acoustic emission (AE) was originally developed for non-destructive testing of static structures. however, over the years its application has been extended to health monitoring of rotating machines and bearings. It offers the advantage of earlier defect detection in comparison to vibration analysis. Current methodologies of applying AE for bearing diagnosis are reviewed. The investigation reported in this paper was centered on the application of standard acoustic emissions IAE) characteristic parameters on a radially loaded bearing. An experimental test-rig was designed to allow seeded defects on the inner and outer race. It is concluded that irrespective of the radial load, rotational speed and high levels of background noise. simple AE parameters such as e.m.s. and AE counts provided an indication of bearing defect. In addition to validating already established AE techniques, this investigation focuses on establishing an appropriate threshold level for AE counts.
Open Access
Acoustic emissions diagnosis of rotor-stator rubs using the KS statistic.
(Elsevier Science B.V., Amsterdam, 2004-07-01T00:00:00Z) Hall, L. D.; Mba, David
Acoustic emission (AE) measurement at the bearings of rotating machinery has become a useful tool for diagnosing incipient fault conditions. In particular, AE can be used to detect unwanted intermittent or partial rubbing between a rotating central shaft and surrounding stationary components. This is a particular problem encountered in turbines used for power generation. For successful fault diagnosis, it is important to adopt AE signal analysis techniques capable of distinguishing between various types of rub mechanisms. It is also useful to develop techniques for inferring information such as the severity of rubbing or the type of seal material making contact on the shaft. It is proposed that modelling the cumulative distribution function of rub-induced AE signals with respect to appropriate theoretical distributions, and quantifying the goodness of fit with the Kolmogorov–Smirnov (KS) statistic, offers a suitable signal feature for diagnosis. This paper demonstrates the successful use of the KS feature for discriminating different classes of shaft-seal rubbing.
Open Access
An analysis of civil aviation industry safety needs for the introduction of liquid hydrogen propulsion technology
(ASME, 2019-11-05) Benson, C. M.; Ingram, J. M.; Battersby, P. N.; Mba, David; Sethi, Vishal; Rolt, Andrew Martin
Over the next few decades air travel is predicted to grow, with international agencies, manufacturers and governments predicting a considerable increase in aviation use. However, based on current fuel type, International Civil Aviation Organization (ICAO) project emissions from aviation are estimated to be seven to ten times higher in 2050 than in 1990. These conflicting needs are problematic and have led to the EU Flightpath 2050 targeting dramatic emissions reductions for the sector (75% CO2, 90% NOX by 2050). One proposed solution, decreasing carbon emissions without stunting the increase in air travel, is hydrogen propulsion; a technology with clear environmental benefits. However, enabling the safe application of this fuel to aviation systems and industrial infrastructure would be a significant challenge. High-profile catastrophic incidents involving hydrogen, and the flammable and cryogenic nature of liquid hydrogen (LH2) have led to its reputation as a more dangerous substance than existing or alternative fuels. But, where they are used (in industry, transport, energy), with sufficient protocols, hydrogen can have a similar level of safety to other fuels. A knowledge of hazards, risks and the management of these becomes key to the integration of any new technology. Using assessments, and a gap analysis approach, this paper examines the civil aviation industry requirements, from a safety perspective, for the introduction of LH2 fuel use. Specific proposed technology assessments are used to analyze incident likelihood, consequence impact, and ease of remediation for hazards in LH2 systems, and a gap analysis approach is utilized to identify if existing data is sufficient for reliable technology safety assessment. Outstanding industry needs are exposed by both examining challenges that have been identified in transport and industrial areas, and by identifying the gaps in current knowledge that are preventing credible assessment, reliable comparison to other fuels and the development of engineering systems. This paper demonstrates that while hydrogen can be a safe and environmentally friendly fuel option, a significant amount of work is required for the implementation of LH2 technology from a mass market perspective.
Open Access
The application of acoustic emission for detecting incipient cavitation and the best efficiency point of a 60 kW centrifugal pump: case study
(Elsevier Science B.V., Amsterdam., 2005-07-01T00:00:00Z) Alfayez, L; Mba, David; Dyson, G
Pumps play a significant role in industrial plants and need continuous monitoring to minimise loss of production. To date, there is limited published information on the application of acoustic emission (AE) to incipient pump cavitation. This paper presents a case study where AE has been applied for detecting incipient cavitation and determining the best efficiency point (BEP) of a 60 kW centrifugal pump. Results presented are based on net positive suction head (NPSH) and performance tests. In conclusion, the AE technique was shown to offer early detection of incipient cavitation, furthermore, the technique has demonstrated the ability to determine the BEP of a pump.
Open Access
Application of acoustic emission to seeded gear fault detection
(Elsevier Science B.V., Amsterdam., 2005-01-01T00:00:00Z) Toutountzakis, Tim; Tan, Chee Keong; Mba, David
Acoustic emission (AE) is gaining ground as a non-destructive technique for health diagnosis on rotating machinery. There are vast opportunities for development of the AE technique on various forms of rotating machinery, including gearboxes. This paper reviews some recent developments in application of AE to gear defect diagnosis. Furthermore, an experimental investigation that examines the effectiveness of AE for gear defect identification is presented. It is concluded that application of the AE technique to seeded gear defect detection is fraught with difficulties. In addition, the viability of the AE technique for gear defect detection from non-rotating components of a machine is called into question.
Open Access
The application of spectral kurtosis on Acoustic Emission and vibrations from a defective bearing
(Elsevier Science B.V., Amsterdam, 2011-01-31T00:00:00Z) Eftekharnejad, Babak; Carrasco, M. R.; Charnley, B.; Mba, David
The application of Acoustic Emission (AE) technology for machine health monitoring is gaining ground as power tool for health diagnostic of rolling element bearing. This paper provides an investigation that compares the applicability of AE and vibration technologies in monitoring a naturally degraded roller bearing. This research is the first known attempt investigating the comparative effectiveness of applying the Kurtogram to both vibration and AE data from a defective bearing.
Open Access
Assessment of natural crack initiation and its propagation in slow speed bearings
(Taylor & Francis, 2009-09-30T00:00:00Z) Elforjani, Mohamed; Mba, David
Monitoring of bearings is an essential part of most condition monitoring programmes in rotating machinery. This paper demonstrates the use of acoustic emission (AE) measurements to detect, monitor and locate natural defect initiation and propagation in a thrust rolling element bearing. To undertake this task a special purpose test-rig was built that allowed for accelerated natural degradation of a bearing race. It is concluded that sub-surface initiation and subsequent crack propagation can be detected using a range of time and frequency domain analysis techniques on AE's generated from natural degrading bearings. The paper also investigates the source characterisation of AE signals associated with a defective bearing whilst in operation.
Open Access
Bearing defect diagnosis and acoustic emission.
(Professional Engineering Publishing, 2003-01-01T00:00:00Z) Morhain, A.; Mba, David
Acoustic emission (AE) was originally developed for non-destructive testing of static structures, however, over the years its application has been extended to health monitoring of rotating machines and bearings. It offers the advantage of earlier defect detection in comparison to vibration analysis. However, limitations in the successful application of AE technique for monitoring bearings have been partly due to thedifficulty in processing, interpreting and classifying the acquired data. The investigation reported in this paper was centered on the application of standard acoustic emissions (AE) characteristic parameters on a radially loaded bearing. An experimental test-rig was modified such that defects could be seeded onto the inner and outer races of a test bearing. As the test-rig was adapted for this purpose it offered high background acoustic emission noise providing a realistic test for fault diagnosis. In addition to a review of current diagnostic methods for applying AE to bearing diagnosis, the results of this investigation validated the use of r.m.s, amplitude, energy and AE counts for diagnosis. Furthermore, this study determined the most appropriate threshold level for AE count diagnosis, the first known attempt.
Open Access
Bearing signal separation of commercial helicopter main gearbox
(Elsevier, 2017-03-02) Elasha, Faris; Greaves, Matthew J.; Mba, David
Gears are significant component in a multiplicity of industrial applications such as machine tool and gearboxes. An unforeseen failure of gear may result in significant economic losses. Therefore this research propose fault detection improvement throught series of vibration signal processing techuiques. These techniques have been tested experimentally using vibration data collected from the transmission system of a CS-29 ‘Category A’ helicopter gearbox under different bearing damage severity of the second planetary stage. Results showed successful improvement of bearing fault detection.
Open Access
Bearing time-to-failure estimation using spectral analysis features
(Sage Publications, 2014-02-19T00:00:00Z) Reuben, Lim Chi Keong; Mba, David
With the increasing use of health usage monitoring systems on helicopters, a lot of research has been undertaken for diagnosis of transmission components. However, most of these works are performed in laboratory environments and there are hardly any published works on in-service application. In this study, we present an experience in diagnosis of a helicopter gearbox bearing using actual service data gathered from AH64D helicopters belonging to the Republic of Singapore Air Force. A number of helicopters have been found with grease leak and radial play in the tail rotor gearbox output shaft during field maintenance. Subsequent tear-down inspections of the tail rotor gearboxes revealed that they had similar defects of bearing race spalling and widespread pitting of the rolling elements. Spectral analysis was carried out on the accelerometer data from these helicopters and correlated with the tear-down inspection findings. The fault patterns exhibited correspond well to progressing stages of bearing wear and are consistent across defective gearboxes from different helicopters. It is demonstrated that simple spectral analysis can be effective in tracking progressive stages of bearing damage using both low-frequency and high-frequency bandwidths. The observed fault patterns are extracted as features for diagnosis and used to determine the bearings' estimated time to failure for maintenance planning.
Open Access
Buckling and vibration analysis of functionally graded composite structures using the finite element method
(Elsevier Science B.V., Amsterdam., 2009-06-30T00:00:00Z) Oyekoya, Oyedele O.; Mba, David; El-Zafrany, A. M.
The authors [Oyekoya OO, Mba DU, El-Zafrany AM. Structural integrity of functionally graded composite structure using Mindlin-type finite elements. ICCES 2008:172(l): 1-6] have previously written a paper Oil Structural integrity of functionally graded composite (FGC) structure using Mindlin-type finite elements. In this paper, the Mindlin-type element and Reissner-type element have been further developed for the modelling of FGC plate Subjected to buckling and free vibration. The Mindlin-type element formulation is based on averaging Of transverse shear distribution over plate thickness using Lagrangian interpolation. The Reissner-type element formulation is based on parabolic transverse shear distribution over plate thickness using Lagrangian and Hermitian interpolation. The composite plate considered in this paper is functionally graded in the longitudinal direction only, but the FE code developed is capable of analysing composite plates with functional gradation in transverse and radial direction as well. This Study was able to show that the structural integrity enhancement and strength maximisation of composite Structures are achievable through functional gradation of material properties over the structure.
Open Access
Canonical variate analysis for performance degradation under faulty conditions
(Elsevier, 2016-06-01) Ruiz Cárcel, Cristóbal; Lao, Liyun; Cao, Yi; Mba, David
Condition monitoring of industrial processes can minimize maintenance and operating costs while increasing the process safety and enhancing the quality of the product. In order to achieve these goals it is necessary not only to detect and diagnose process faults, but also to react to them by scheduling the maintenance and production according to the condition of the process. The objective of this investigation is to test the capabilities of canonical variate analysis (CVA) to estimate performance degradation and predict the behavior of a system affected by faults. Process data was acquired from a large-scale experimental multiphase flow facility operated under changing operational conditions where process faults were seeded. The results suggest that CVA can be used effectively to evaluate how faults affect the process variables in comparison to normal operation. The method also predicted future process behavior after the appearance of faults, modeling the system using data collected during the early stages of degradation.
Open Access
Combination of process and vibration data for improved condition monitoring of industrial systems working under variable operating conditions
(Elsevier, 2015-06-19) Ruiz Cárcel, Cristóbal; Jaramillo, Víctor H.; Mba, David; Ottewill, James R.; Cao, Yi
The detection and diagnosis of faults in industrial processes is a very active field of research due to the reduction in maintenance costs achieved by the implementation of process monitoring algorithms such as Principal Component Analysis, Partial Least Squares or more recently Canonical Variate Analysis (CVA). Typically the condition of rotating machinery is monitored separately using vibration analysis or other specific techniques. Conventional vibration-based condition monitoring techniques are based on the tracking of key features observed in the measured signal. Typically steady-state loading conditions are required to ensure consistency between measurements. In this paper, a technique based on merging process and vibration data is proposed with the objective of improving the detection of mechanical faults in industrial systems working under variable operating conditions. The capabilities of CVA for detection and diagnosis of faults were tested using experimental data acquired from a compressor test rig where different process faults were introduced. Results suggest that the combination of process and vibration data can effectively improve the detectability of mechanical faults in systems working under variable operating conditions.
Open Access
A comparative experimental study on the diagnostic and prognostic capabilities of acoustics emission, vibration and spectrometric oil analysis for spur gears.
(Elsevier Science B.V., Amsterdam, 2007-01-01T00:00:00Z) Tan, Chee Keong; Irving, Phil E.; Mba, David
Prognosis of gear life using the acoustic emission (AE) technique is relatively new in condition monitoring of rotating machinery. This paper describes an experimental investigation on spur gears in which natural pitting was allowed to occur. Throughout the test period, AE, vibration and spectrometric oil samples were monitored continuously in order to correlate and compare these techniques to natural life degradation of the gears. It was observed that based on the analysis of root mean square (rms) levels only the AE technique was more sensitive in detecting and monitoring pitting than either the vibration or spectrometric oil analysis (SOA) techniques. It is concluded that as AE exhibited a direct relationship with pitting progression, it offers the opportunity for prognosis.
Open Access
A comparative experimental study on the use of acoustic emission and vibration analysis for bearing defect identification and estimation of defect size
(Elsevier Science B.V., Amsterdam, 2006-01-01T00:00:00Z) Al-Ghamd, Abdullah M; Mba, David
Vibration monitoring of rolling element bearings is probably the most established diagnostic technique for rotating machinery. The application of acoustic emission (AE) for bearing diagnosis is gaining ground as a complementary diagnostic tool, however, limitations in the successful application of the AE technique have been partly due to the difficulty in processing, interpreting and classifying the acquired data. Furthermore, the extent of bearing damage has eluded the diagnostician. The experimental investigation reported in this paper was centred on the application of the AE technique for identifying the presence and size of a defect on a radially loaded bearing. An experimental test rig was designed such that defects of varying sizes could be seeded onto the outer race of a test bearing. Comparisons between AE and vibration analysis over a range of speed and load conditions are presented. In addition, the primary source of AE activity from seeded defects is investigated. It is concluded that AE offers earlier fault detection and improved identification capabilities than vibration analysis. Furthermore, the AE technique also provided an indication of the defect size, allowing the user to monitor the rate of degradation on the bearing; unachievable with vibration analysis.
Open Access
A comparative study of the effectiveness of vibration and acoustic emission in diagnosing a defective bearing in a planetry gearbox
(Elsevier, 2016-09-12) Elasha, Faris; Greaves, Matthew J.; Mba, David; Fang, Duan
Whilst vibration analysis of planetary gearbox faults is relatively well established, the application of Acoustic Emission (AE) to this field is still in its infancy. For planetary-type gearboxes it is more challenging to diagnose bearing faults due to the dynamically changing transmission paths which contribute to masking the vibration signature of interest. The present study is aimed to reduce the effect of background noise whilst extracting the fault feature from AE and vibration signatures. This has been achieved through developing of internal AE sensor for helicopter transmission system. In addition, series of signal processing procedure has been developed to improved detection of incipient damage. Three signal processing techniques including an adaptive filter, spectral kurtosis and envelope analysis, were applied to AE and vibration data acquired from a simplified planetary gearbox test rig with a seeded bearing defect. The results show that AE identified the defect earlier than vibration analysis irrespective of the tortuous transmission path