No description available.

In the oil and gas industry, statistical methods have been used for corrosion analysis for various asset systems such as pipelines, storage tanks, and so on. However, few industrial standards and guidelines provide comprehensive stepwise procedures for the usage of statistical approaches for corrosion analysis. For example, the UK HSE (2002) report "Guidelines for the use of statistics for analysis of sample inspection of corrosion" demonstrates how statistical methods can be used to evaluate corrosion samples, but the methods explained in the document are very basic and do not consider risk factors such as pressure, temperature, design, external factors and other factors for the analyses. Furthermore, often the industrial practice that uses linear approximation on localised corrosion such as pitting is considered inappropriate as pitting growth is not uniform. The aim of this research is to develop an approach that models the stochastic behaviour of localised corrosion and demonstrate how the influencing factors can be linked to the corrosion analyses, for predicting the remaining useful life of components in oil and gas plants. This research addresses a challenge in industry practice. Non-destructive testing (NDT) and inspection techniques have improved in recent years making more and more data available to asset operators. However, this means that these data need to be processed to extract meaningful information. Increasing computer power has enabled the use of statistics for such data processing. Statistical software such as R and OpenBUGS is available to users to explore new and pragmatic statistical methods (e.g. regression models and stochastic models) and fully use the available data in the field. In this thesis, we carry out extreme value analysis to determine maximum defect depth of an offshore conductor pipe and simulate the defect depth using geometric Brownian motion in Chapter 2. In Chapter 3, we introduce a Weibull density regression that is based on a gamma transformation proportional hazards model to analyse the corrosion data of piping deadlegs. The density regression model takes multiple influencing factors into account; this model can be used to extrapolate the corrosion density of inaccessible deadlegs with data available from other piping systems. In Chapter 4, we demonstrate how the corrosion prediction models in Chapters 2 and 3 could be used to predict the remaining useful life of these components. Chapter 1 sets the background to the techniques used, and Chapter 5 presents concluding remarks based on the application of the techniques.

Yes / Diagnostics and prognostics have significant roles in the reliability enhancement of systems and are focused topics of active research. Engineered systems are becoming more complex and are subjected to miscellaneous failure modes that impact adversely their performability. This everincreasing complexity makes fault diagnostics and prognostics challenging for the system-level functions. A significant number of successes have been achieved and acknowledged in some review papers; however, these reviews rarely focused on the application of complex engineered systems nor provided a systematic review of diverse techniques and approaches to address the related challenges. To bridge the gap, this paper firstly presents a review to systematically cover the general concepts and recent development of various diagnostics and prognostics approaches, along with their strengths and shortcomings for the application of diverse engineered systems. Afterward, given the characteristics of complex systems, the applicability of different techniques and methods that are capable to address the features of complex systems are reviewed and discussed, and some of the recent achievements in the literature are introduced. Finally, the unaddressed challenges are discussed by taking into account the characteristics of automotive systems as an example of complex systems. In addition, future development and potential research trends are offered to address those challenges. Consequently, this review provides a systematic view of the state of the art and case studies with a reference value for scholars and practitioners.

We consider the prediction algorithm and performance evaluation for prognostics and health management (PHM) problems, especially the prediction of remaining useful life (RUL) for the milling machine cutter and lithium ‐ ion battery. We modeled battery as a voltage source and internal resisters. By analyzing voltage change trend during discharge, we made the prediction of battery remain discharge time in one discharge cycle. By analyzing internal resistance change trend during multiple cycles, we were able to predict the battery remaining useful time during its life time. We showed that the battery rest profile is correlated with the RUL. Numerical results using the realistic battery aging data from NASA prognostics data repository yielded satisfactory performance for battery prognosis as measured by certain performance metrics. We built a battery test platform and simulated more usage pattern and verified the prediction algorithm. Prognostic performance metrics were used to compare different algorithms.

Le pronostic industriel vise à étendre le cycle de vie d’un dispositif physique, tout en réduisant les couts d’exploitation et de maintenance. Pour cette raison, le pronostic est considéré comme un processus clé avec des capacités de prédiction. En effet, des estimations précises de la durée de vie avant défaillance d’un équipement, Remaining Useful Life (RUL), permettent de mieux définir un plan d’action visant à accroitre la sécurité, réduire les temps d’arrêt, assurer l’achèvement de la mission et l’efficacité de la production.Des études récentes montrent que les approches guidées par les données sont de plus en plus appliquées pour le pronostic de défaillance. Elles peuvent être considérées comme des modèles de type boite noire pour l’ étude du comportement du système directement `a partir des données de surveillance d’ état, pour définir l’ état actuel du système et prédire la progression future de défauts. Cependant, l’approximation du comportement des machines critiques est une tâche difficile qui peut entraîner des mauvais pronostic. Pour la compréhension de la modélisation du pronostic guidé par les données, on considère les points suivants. 1) Comment traiter les données brutes de surveillance pour obtenir des caractéristiques appropriées reflétant l’ évolution de la dégradation? 2) Comment distinguer les états de dégradation et définir des critères de défaillance (qui peuvent varier d’un cas `a un autre)? 3) Comment être sûr que les modèles définis seront assez robustes pour montrer une performance stable avec des entrées incertaines s’ écartant des expériences acquises, et seront suffisamment fiables pour intégrer des données inconnues (c’est `a dire les conditions de fonctionnement, les variations de l’ingénierie, etc.)? 4) Comment réaliser facilement une intégration sous des contraintes et des exigence industrielles? Ces questions sont des problèmes abordés dans cette thèse. Elles ont conduit à développer une nouvelle approche allant au-delà des limites des méthodes classiques de pronostic guidé par les données. / Prognostics and Health Management (PHM) aims at extending the life cycle of engineerin gassets, while reducing exploitation and maintenance costs. For this reason,prognostics is considered as a key process with future capabilities. Indeed, accurateestimates of the Remaining Useful Life (RUL) of an equipment enable defining furtherplan of actions to increase safety, minimize downtime, ensure mission completion andefficient production.Recent advances show that data-driven approaches (mainly based on machine learningmethods) are increasingly applied for fault prognostics. They can be seen as black-boxmodels that learn system behavior directly from Condition Monitoring (CM) data, usethat knowledge to infer its current state and predict future progression of failure. However,approximating the behavior of critical machinery is a challenging task that canresult in poor prognostics. As for understanding, some issues of data-driven prognosticsmodeling are highlighted as follows. 1) How to effectively process raw monitoringdata to obtain suitable features that clearly reflect evolution of degradation? 2) Howto discriminate degradation states and define failure criteria (that can vary from caseto case)? 3) How to be sure that learned-models will be robust enough to show steadyperformance over uncertain inputs that deviate from learned experiences, and to bereliable enough to encounter unknown data (i.e., operating conditions, engineering variations,etc.)? 4) How to achieve ease of application under industrial constraints andrequirements? Such issues constitute the problems addressed in this thesis and have ledto develop a novel approach beyond conventional methods of data-driven prognostics.

This thesis focuses on obtaining better estimates of remaining life for on-condition (OC) parts in aircraft engines. Aircraft engine components are commonly classified into three categories, life-limited parts (LLP), OC-parts and consumables. Engine maintenance typi-cally accounts for 10% to 20% of aircraft-related operating cost. Current methods to esti-mate remaining life for OC parts have been found insufficient and this thesis aims to devel-op a method that obtains better life estimates of OC part. Improved life estimates are es-sential to facilitate more reliable maintenance plans and lower maintenance costs. In the thesis, OC parts that need a better life estimates are identified and suitable prognosis methodologies for estimating the remaining life are presented. Three papers are appended to the thesis. The first paper lays out the main principles of air-craft engine maintenance and identifies the potential for improving maintenance planning by improving the remaining life estimation for the OC parts. The paper concludes that re-search is needed to find better estimates so that the right amount of maintenance is per-formed at each maintenance occasion. The second paper describes the aircraft and its engine from a system of system perspective. The aim of the paper is to show that no system is stronger than its weakest part and that there is a potential to increase the availability and readiness of the complete system, the aircraft engine, by introducing better life estimates for OC parts. Furthermore, a review of all engine parts, no matter if they are life-limited or on-condition, which needs to be incor-porated in a replacement model for maintenance optimization, is given. The paper con-cludes that the reliability of the complete aircraft engine would be increased if better life estimates are presented also for the OC parts. The third paper includes an evolved analysis of the subject and the analysis moves deeper in to a subsystem/module of the engine, the low pressure turbine. The specific subsys-tem/module is further analyzed to show the potential of increased reliability for the subsys-tem/module and the complete system, the aircraft engine, if better life estimates for the OC parts are obtained. Methods on how to estimate remaining life is discussed in this paper. It is stated that life estimates can be based on visual inspections, available testing methods (e.g. non destructive testing ) or new techniques that may be need to be developed based on remaining useful life estimations. To estimate the remaining life for the OC parts well es-tablished prognostic techniques such as physic-based, data-driven, symbolic, hybrid, or context awareness approaches that combine contextual/situation information awareness will be considered.

No description available.

Ces dernières années ont vu apparaître sur le marché les premiers transistors de puissance de type MOSFET en carbure de silicium. Ce type de composant est particulièrement adapté à la réalisation d’équipement électrique à haut rendement et capable de fonctionner à haute température. Néanmoins, la question de la fiabilité doit être posée avant de pouvoir envisager la mise en œuvre de ces composants dans des applications aéronautiques ou spatiales. Les mécanismes de défaillance liés à l’oxyde de grille ont pendant longtemps retardé la mise sur le marché des transistors à grille isolée en carbure de silicium. Cette étude s’attache donc à estimer la durée de vie des MOSFET SiC de 1ére génération. Dans un premier temps, le mécanisme connu sous le nom de Time Dependent Dielectric Breakdown(TDDB) a été étudié au travers de résultats expérimentaux issus de la bibliographie. Notre analyse nous a permis de justifier de l’emploi d’une loi de Weibull pour modéliser la distribution des temps à défaillance issue de ces tests. Les résultats nous ont également permis de confirmer l’amélioration significative de la fiabilité de ces structures vis-à-vis de ce mécanisme. Dans un second temps, l’impact du mécanisme d’instabilité de la tension de seuil sur la fiabilité a été quantifié au travers de tests de vieillissement de type HTGB. Les données de dégradation ainsi collectées ont été modélisées à l’aide d’un processus gamma non-homogène, qui nous a permis de prendre en compte la variabilité entre les composants testés dans des conditions identiques et de proposer des facteurs d’accélération en tension et en température pour ce mécanisme. Enfin, ces travaux ont permis d’ouvrir la voie à la mise en œuvre d’outils de pronostic de la durée de vie résiduelle pour les équipements électriques. / Recent years have seen SiC MOSFET reach the industrial market. This type of device is particularly adapted to the design of power electronics equipment with high efficiency and high reliability capable to operate in high ambient temperature. Nevertheless the question of the SiC MOSFET reliability has to be addressed prior to considering the implementation of such devices in an aeronautic application. The failure mechanisms linked to the gate oxide of the SiC MOSFET have for a long time prevented the introduction of the device. In this manuscript we propose to study the reliability of the first generation of SiC MOSFET. First, the mechanism known as the Time–Dependent Dielectric Breakdown is studied through experimental results extracted from literature. Our study shows the successful application of a Weibull law to model the time-to-failure distribution extracted from the accelerated tests. The results show also a significant improvement of the SiC MOSFET structure with respect to this phenomenon. In a second step, the impact of the threshold voltage instability is quantified through accelerated tests known as High Temperature Gate Bias. The collected degradation data are modeled using a non-homogeneous Gamma process. This approach allows taking into account the variability between devices tested under the same conditions. Acceleration factors have been proposed with respect to temperature and gate voltage. Eventually the study delivers a primary estimation of the remaining useful lifetime of the SiC MOSFET in a typical aeronautic application.

In the year of 2000 the European Commission adopted a communication called EU Financial Reporting Strategy: the Way Forward. The communication intended to make all listed companies within the EU arrange their financial statements in accordance with International Accounting Standards by 2005 at the latest. When the amendments of IFRS 3 was introduced in March 2004 it meant that companies from that moment on, when acquiring another company, have to allocate the part of the purchase price assignable to customer contracts and the related customer relationships as an intangible asset. IFRS 3 does not give any guidance whatsoever on how to accomplish the above described allocation and estimate a true and fair value of customer contracts and relationships. Let alone any direction regarding the establishment of the remaining useful life of the customer relationships and contracts, which constitutes the foundation of the fair valuation but also a true and fair view regarding amortizations. The purpose of this thesis is to examine how the establishments regarding remaining useful life of customer relationships and contracts have been done. Furthermore, the purpose of this thesis is to explain the decision process and motives that results in why management choose to apply the specific remaining useful life of customer relationships and contracts they do. This study has been carried out with a qualitative approach involving two listed group companies within three different industries, hence, six companies are involved in this thesis. Semi-structured telephone interviews have been made with the companies and the annual reports have been examined. In order to explain the actions behind the valuation and establishment process, the positive accounting theory has been used. None of the six companies taking part in this study have applied an outspoken method for the establishment of the remaining useful life of the customer relationships and contracts and only half of the companies have identified different customer groups. A relation can be identified between using an external consultant and applying different remaining lives for different customer groups. All companies amortize the customer relationships and contracts on a straight-line basis. This can be explained by the positive accounting theory to some extent. All companies applied straight-line amortization even though some of them actually admit that a declining balance would provide a fairer view. Furthermore, long amortization plans are used in some companies in order to decrease the amortization costs and hence increase the net income. Positive accounting has been applied in order to shift reported earnings. / Under år 2000 beslutade den Europeiska kommissionen om att anta ett förslag som hette EU Financial Reporting Strategy: the Way Forward. Antagandet av förslaget innebar att alla noterade bolag inom EU skulle presentera sin redovisning och sina årsredovisningar i linje med bestämmelserna i IAS – International Accounting Standards senast år 2005. När lagändringarna i IFRS 3 introducerades i mars 2004 innebar det att noterade bolag vid företagsförvärv fortsättningsvis skulle allokera den del av köpeskillingen som är hänförlig till kundkontrakt och relaterade kundrelationer som immateriell tillgång i balansräkningen. IFRS 3 ger ingen vägledning överhuvudtaget med avseende på hur bolagen ska genomföra den ovan beskrivna allokeringen och uppskatta ett rättvist värde på kundkontrakt och kundrelationer. Inte heller finns det någon anvisning angående fastställandet av livslängd på kundkontrakt och kundrelationer som i sin tur ligger till grund för en rättvis värdering och en rättvis avskrivningsplan. Syftet med den här uppsatsen är att undersöka hur fastställandet av livslängden på kundrelationer och kundkontrakt har utförts. Syftet är även att förklara beslutsprocessen och de bakomliggande motiven till varför företagsledningen väljer att använda den livslängd på kundrelationer och kundkontrakt de faktiskt gör. Studien har genomförts med en kvalitativ ansats som har involverat två noterade koncernbolag inom tre olika branscher, totalt har alltså sex bolag medverkat i uppsatsen. Semistrukturerade telefonintervjuer har gjorts med de involverade bolagen och även deras årsredovisningar har undersökts. För att kunna förklara handlandet angående värderingsprocessen och livslängdsprocessen har den positiva redovisningsteorin använts. Inget av de sex bolagen som medverkat i studien har använt sig av någon etablerad metod för att fastställa den återstående livslängden av kundrelationerna och kundkontrakten, och endast hälften av företagen har identifierat olika grupper av kunder. Ett samband har identifierats mellan att använda sig av en extern konsult vid fastställandet och att använda sig av olika återstående livslängder för olika kundgrupper. Alla sex företagen använder sig av linjär avskrivning på kundkontrakten och kundrelationerna. Detta kan till en viss gräns förklaras med positiv redovisningsteori. Alla företagen har använt sig av linjär avskrivning även om vissa av företagen till och med medger att degressiv avskrivning skulle ge en mer rättvis bild. Dessutom har långa avskrivningstider använts i en del av företagen för att sänka avskrivningskostnaderna som i sin tur ökar resultatet. Positiv redovisningsteori har alltså använts för att flytta vinster till innevarande år.

<p>In the year of 2000 the European Commission adopted a communication</p><p>called EU Financial Reporting Strategy: the Way Forward. The communication intended to make all listed companies within the EU arrange their financial statements in accordance with</p><p>International Accounting Standards by 2005 at the latest. When the amendments of IFRS 3 was introduced in March 2004 it meant that companies from that moment on, when acquiring another company, have to allocate the part of the purchase price assignable to customer contracts and the related customer relationships as an intangible asset. IFRS 3 does not give any guidance whatsoever on how to</p><p>accomplish the above described allocation and estimate a true and fair value of customer contracts and relationships. Let alone any direction regarding the establishment of the remaining useful life of the customer relationships and contracts, which constitutes the</p><p>foundation of the fair valuation but also a true and fair view regarding amortizations. The purpose of this thesis is to examine how the establishments regarding remaining useful life of customer relationships and contracts have been done. Furthermore, the purpose of this thesis is to explain the decision process and motives that results in why management choose to apply the specific remaining useful life of customer relationships and contracts they do. This study has been carried out with a qualitative approach involving two listed group companies within three different industries, hence, six companies are involved in this thesis. Semi-structured telephone interviews have been made with the companies and the annual reports have been examined. In order to explain the actions behind the valuation and establishment process, the positive accounting theory has been used. None of the six companies taking part in this study have applied an outspoken method for the establishment of the remaining useful life of the customer relationships and contracts and only half of the companies have identified different customer groups. A relation can be identified between using an external consultant</p><p>and applying different remaining lives for different customer groups. All companies amortize the customer relationships and contracts on a straight-line basis. This can be explained by the positive accounting theory to some extent. All companies applied straight-line amortization even though some of them actually admit that a declining</p><p>balance would provide a fairer view. Furthermore, long amortization plans are used in some companies in order to decrease the amortization costs and hence increase the net income. Positive accounting has been applied in order to shift reported earnings.</p> / <p>Under år 2000 beslutade den Europeiska kommissionen om att anta ett</p><p>förslag som hette EU Financial Reporting Strategy: the Way Forward. Antagandet av förslaget innebar att alla noterade bolag inom EU skulle presentera sin redovisning och sina årsredovisningar i linje med bestämmelserna i IAS – International Accounting Standards senast år 2005. När lagändringarna i IFRS 3 introducerades i mars 2004 innebar det att noterade bolag vid företagsförvärv fortsättningsvis skulle allokera den del av köpeskillingen som är hänförlig till kundkontrakt och relaterade kundrelationer som immateriell tillgång i</p><p>balansräkningen. IFRS 3 ger ingen vägledning överhuvudtaget med avseende på hur bolagen ska genomföra den ovan beskrivna allokeringen och uppskatta ett rättvist värde på kundkontrakt och kundrelationer. Inte heller finns det någon anvisning angående fastställandet av livslängd på kundkontrakt och kundrelationer som i sin tur ligger till grund för en rättvis värdering och en rättvis avskrivningsplan.</p><p>Syftet med den här uppsatsen är att undersöka hur fastställandet av livslängden på kundrelationer och kundkontrakt har utförts. Syftet är även att förklara beslutsprocessen och de bakomliggande motiven till varför företagsledningen väljer att använda den livslängd på kundrelationer och kundkontrakt de faktiskt gör. Studien har genomförts med en kvalitativ ansats som har involverat två noterade</p><p>koncernbolag inom tre olika branscher, totalt har alltså sex bolag medverkat i uppsatsen. Semistrukturerade telefonintervjuer har gjorts med de involverade bolagen och även deras årsredovisningar har undersökts. För att kunna förklara handlandet angående värderingsprocessen och livslängdsprocessen har den positiva redovisningsteorin använts. Inget av de sex bolagen som medverkat i studien har använt sig av någon etablerad metod för att fastställa den återstående livslängden av kundrelationerna och kundkontrakten, och endast hälften av företagen har identifierat olika grupper av kunder. Ett samband har identifierats mellan att använda sig av en extern konsult vid fastställandet och att använda sig av olika återstående livslängder för olika kundgrupper. Alla sex företagen använder sig av linjär avskrivning på kundkontrakten och kundrelationerna. Detta kan till en viss gräns förklaras med positiv redovisningsteori. Alla företagen har använt sig av linjär avskrivning även om vissa av företagen till och med medger att</p><p>degressiv avskrivning skulle ge en mer rättvis bild. Dessutom har långa avskrivningstider använts i en del av företagen för att sänka avskrivningskostnaderna som i sin tur ökar resultatet. Positiv redovisningsteori har alltså använts för att flytta vinster till innevarande år.</p>