Application of acoustic emission in diagnostic of bearing faults within a helicopter gearbox

AbstractAcoustics Emissions (AE) technology has emerged as a promising diagnostic approach. AE was originally developed for non-destructive testing of static structures, however, in recent times its application has been extended to health monitoring of rotating machines. This paper introduces a novel method for application of AE in monitoring of helicopter gearboxes. In addition this paper investigates the application of signal separation techniques in detection of bearing faults within the epicyclic module of a large helicopter (CS-29) main gearbox using Acoustic Emissions (AE). The results showed successful of AE in detection bearing fault within the helicopter gearbox. Detection of the small bearing defect gives the AE an indisputable diagnosis advantage and prove ability of application of AE in helicopter gearboxes

HIV clinical stage progression of patients at 241 outpatient clinics in Democratic Republic of Congo: Disparities by gender, TB status and rurality

Background: HIV clinical care programs are increasingly cognizant of the importance of customizing services according to patients’ clinical stage progression (WHO\u27s four-tiered staging) and other risk assessments. Understanding factors associated with Persons Living with HIV (PLHIV) patients’ progression through the treatment cascade and clinical stages is essential for programs to provide patient-centered, evidence-based services. Methods and materials: To analyze patient characteristics associated with disease progression stages for PLHIV on antiretroviral therapy (ART), this quantitative study used data, from January 2014–June 2019, from 49,460 PLHIV on ART from 241 HIV/AIDS outpatient clinics in 23 health zones in Haut-Katanga and Kinshasa provinces, Democratic Republic of Congo. To assess bivariate and multivariate associations, we performed Chi-square and multinomial logistic regression. Results: Among PLHIV receiving ART, 4.4% were at stage 4, and 30.7% at stage 3. Those at the less severe stages 2 and 1 constituted 22.9% and 41.9%. After controlling for covariates, patients with no TB were significantly more likely than those with TB (p\u3c = .05) to be at stage 1, rather than 3 or 4 (adjusted odds ratio or AOR, 5.73; confidence interval or CI, 4.98–6.59). Other characteristics significantly associated with higher odds of being at stage 1 included being female (AOR, 1.35; CI, 1.29–1.42), and shorter duration on ART (vs. \u3e 40.37 months); for ART duration less than 3.23 months the AOR was 2.47, for 3.23–14.52 months duration the AOR was 2.60, and for 14.53–40.37 months duration the AOR was 1.77 (quartile cut points used). Compared to patients in urban health zones, those in rural (AOR, 0.32) and semi-rural health zones (AOR, 0.79) were less likely to be at stage 1. Conclusion: Significant and substantial variation in HIV clinical progression stage by geographic location and demographic characteristics existed, indicative of the need for targeted efforts to improve the effectiveness of HIV care. Patients with TB coinfection compared to those without coinfection had a much greater risk of being at stage 3 or 4, implying a need for customized approaches and clinical regimens for this high-risk population

Linear friction weld process monitoring of fixture cassette deformations using empirical mode decomposition

Due to its inherent advantages, linear friction welding is a solid-state joining process of increasing importance to the aerospace, automotive, medical and power generation equipment industries. Tangential oscillations and forge stroke during the burn-off phase of the joining process introduce essential dynamic forces, which can also be detrimental to the welding process. Since burn-off is a critical phase in the manufacturing stage, process monitoring is fundamental for quality and stability control purposes. This study aims to improve workholding stability through the analysis of fixture cassette deformations. Methods and procedures for process monitoring are developed and implemented in a fail-or-pass assessment system for fixture cassette deformations during the burn-off phase. Additionally, the de-noised signals are compared to results from previous production runs. The observed deformations as a consequence of the forces acting on the fixture cassette are measured directly during the welding process. Data on the linear friction-welding machine are acquired and de-noised using empirical mode decomposition, before the burn-off phase is extracted. This approach enables a direct, objective comparison of the signal features with trends from previous successful welds. The capacity of the whole process monitoring system is validated and demonstrated through the analysis of a large number of signals obtained from welding experiments

A comparative study of the effectiveness of vibration and acoustic emission in diagnosing a defective bearing in a planetry gearbox

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 pat

Planetary bearing defect detection in a commercial helicopter main gearbox with vibration and acoustic emission

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Helicopter gearboxes significantly differ from other transmission types and exhibit unique behaviors that reduce the effectiveness of traditional fault diagnostics methods. In addition, due to lack of redundancy, helicopter transmission failure can lead to catastrophic accidents. Bearing faults in helicopter gearboxes are difficult to discriminate due to the low signal to noise ratio (SNR) in the presence of gear vibration. In addition, the vibration response from the planet gear bearings must be transmitted via a time-varying path through the ring gear to externally mounted accelerometers, which cause yet further bearing vibration signal suppression. This research programme has resulted in the successful proof of concept of a broadband wireless transmission sensor that incorporates power scavenging whilst operating within a helicopter gearbox. In addition, this paper investigates the application of signal separation techniques in detection of bearing faults within the epicyclic module of a large helicopter (CS-29) main gearbox using vibration and Acoustic Emissions (AE). It compares their effectiveness for various operating conditions. Three signal processing techniques including an adaptive filter, spectral kurtosis and envelope analysis, were combined for this investigation. In addition, this research discusses the feasibility of using AE for helicopter gearbox monitoring

Detection of sub-surface damage in wind turbine bearings using acoustic emissions and probabilistic modelling

Bearings are the culprit of a large quantity of Wind Turbine (WT) gearbox failures and account for a high percentage of the total of global WT downtime. Damage within rolling element bearings have been shown to initiate beneath the surface which defies detection by conventional vibration monitoring as the geometry of the rolling surface is unaltered. However, once bearing damage reaches the surface, it generates spalling and quickly drives the deterioration of the entire gearbox through the introduction of debris into the oil system. There is a pressing need for performing damage detection before damage reaches the bearing surface. This paper presents a methodology for detecting sub-surface damage using Acoustic Emission (AE) measurements. AE measurements are well known for their sensitivity to incipient damage. However, the background noise and operational variations within a bearing necessitate the use of a principled statistical procedure for damage detection. This is addressed here through the use of probabilistic modelling, more specifically Gaussian mixture models. The methodology is validated using a full-scale rig of a WT bearing. The bearings are seeded with sub-surface and early-stage surface defects in order to provide a comparison of the detectability at each level of a fault progression

Analyse spectrale singulière des signaux vibratoires et Machine Learning pour la surveillance d'usure d'outils

Cette étude explore l'utilisation des techniques de Machine Learning pour la classification de l'état d'outils en usinage. Une analyse spectrale singulière (ASS) pseudo-locale des signaux vibratoires relevés sur le porte-outil, couplée à un filtrage passe-bande a permis la définition et la mise en évidence d'indicateurs très sensibles à l'évolution de l'état de l'outil. Ces indicateurs sont définis à partir des sommes des raies spectrales des signaux reconstruits par ASS et de leurs résidus, dans des gammes de fréquence judicieusement choisies. Les taux de reconnaissance de l'usure sont très bons et dépassent les 80 %. Cette étude met en évidence deux aspects importants : la forte richesse en information des composantes hautes fréquences des signaux vibratoires et la possibilité de s'affranchir du bruit inutile par la combinaison de l'ASS et d'un filtrage passe-bande

Evaluation of the performance of infrared thermography for on-line condition monitoring of rotating machines

peer reviewedThis study evaluated the possibility of infrared thermography to measure accurately the temperature of elements of a rotating device, within the scope of condition monitoring. The tested machine was a blower coupled to a 500 kW electric motor, that operated in multiples regimes. The thermograms were acquired by a fixed thermographic camera and were processed and recorded every 15 minutes. Because the normal temperature variations could easily mask a drift caused by a failure, a corrected temperature was computed using autorecursive models. It was shown that an efficient temperature correction should compensate for the variations of the process, and for the ambient temperatures variations, either daily or seasonal. The standard deviation of the corrected temperature was of a few tenth of degree, making possible the detection of a drift of less than one degree and the prediction of potential failure.FiaM

Recherche-action en milieu scolaire à Bukavu: l'éducation par les pairs pour prévenir l'infection à VIH

Comme dans un bon nombre de pays d’Afrique sub-saharienne, l’infection par le virus du sida constitue un problème de santé publique majeur en République Démocratique du Congo. La question opérationnelle à laquelle la présente recherche propose de répondre est de savoir si la recherche, en particulier les théories de l’éducation et de la promotion de la santé peuvent, au Congo, alimenter et accompagner, c’est-à-dire servir de support à l’organisation des interventions éducatives en direction des jeunes, qui connaissant une activité sexuelle intense, constituent un des groupes vulnérables. L’objectif principal de la recherche consiste en effet à construire un cadre de référence pertinent permettant de développer une méthodologie adéquate d’intervention éducative en direction des jeunes congolais et ainsi favoriser l’adoption de comportements de protection et faire reculer l’épidémie. Après une discussion sur les perspectives théoriques de la recherche, nous avons développé une stratégie méthodologique en trois point : l’analyse de la littérature afin d’identifier les facteurs de vulnérabilité au sida, la mise en œuvre au cours d’une phase empirique d’une recherche-action dans les écoles au Congo, et son évaluation. Les résultats de cette recherche soulignent l’importance des variables socio-comportementales dans les déterminants de la vulnérabilité au sida chez les jeunes scolarisés de Bukavu. Ces derniers constituent un public prioritaire qu’il faut atteindre par des interventions éducatives adéquates et culturellement adaptées. Quoique les principaux modes de transmission du sida soient connus, de nombreuses croyances persistent au sujet des situations om un risque de contamination existe ; ces croyances sont significativement plus souvent présentes chez les élèves du primaire par rapport à leurs aînés du secondaire. En raison de ces croyances et des stéréotypes religieux en rapport avec les représentations associées au sida et à la sexualité, la proximité des personnes séropositives est redoutée et le recours au préservatif et au test de dépistage du sida est faible. Le fait que de nombreux jeunes perçoivent le sida comme une menace éloignée de leur environnement de vie habituel favorise le déni du sida et une prise importante de risque, et constitue un obstacle à des pratiques sexuelles sécuritaires. Les questions liées à la sexualité, à la santé, au sida prennent rarement place dans le contexte du dialogue familial les parents n’imaginent pas une telle initiative qui est, en fait, contraire aux mœurs locales. Les jeunes attendent ce genre d’informations de leurs copains/copines et des professionnels de la santé, considérés comme étant des sources crédibles. D’une manière générale, l’action mise en place dans les écoles de Bukavu a été bien accueillie et comporte un impact positif chez les relais en termes d’amélioration de l’estime de soi, des connaissances, des représentations et d’attitudes en matière de sida. C’est une expérience intéressante que de nombreux relais sont prêts à poursuivre surtout s’ils peuvent bénéficier du support des adultes (enseignants, parents, professionnels de santé, leaders religieux) bien au fait de l’actualité. L’approche par les pairs est bien réalisable dans le contexte congolais et peut s’appliquer à la prévention de l’infection à VIH. Cette approche est congruente avec la démarche de promotion de la santé qui vise au total à développer un processus d’empowerment individuel et communautaire. Elle favorise l’ouverture au dialogue et à la communication au sujet du sida, notamment en créant un espace de parole tel que les jeunes puissent parler entre eux et s’exprimer sans gêne sur tout ce qui concerne le sida, la sexualité, la santé. Les jeunes relais peuvent donc s’avérer des communicateurs efficaces des messages de prévention aussi bien en direction des jeunes de leur âge qu’auprès d’autres publics. La participation des parents et des enseignants, jugée actuellement insuffisante, est essentielle pour conférer plus de crédibilité et d’adéquation culturelle aux messages et à la qualité des outils de prévention. Au total, ces résultats confortent notre thèse à savoir qu’une approche globale de prévention de l’infection à VIH auprès des jeunes, qui se construit à partir d’un cadre de référence inspiré des théories de l’éducation pour la santé et de la promotion de la santé, et qui se structure autour d’une démarche participative, favorisant l’empowerment individuel et communautaire et le changement social, est faisable, efficace et acceptable dans le contexte congolais. Dès lors, pour pouvoir rencontrer les besoins et les demandes des jeunes (et de l’ensemble de la communauté) en matière de prévention du l’infection à VIH et de la santé de la reproduction en général, diverses interventions devront être menées tant sur le plan de la politique sanitaire et de la politique éducative, qu’au niveau de l’organisation communautaireThèse de doctorat en sciences de la santé publique (éducation pour la santé) (ESP 3) --UCL, 199

Early detection of bearing damage by means of decision trees

This paper presents a procedure for early detection of rolling bearing damages on the basis of vibration measurements. First, an envelope analysis is performed on bandpass filtered signals. For each frequency range, a feature indicator is defined as sum of spectral lines. These features are passed through a principal component model to generate a single variable, which allows tracking change in the bearing health. Thresholds and rules for early detection are learned thanks to decision trees. Experimental results demonstrate that this procedure enables early detection of bearing defects