A review of asset management literature on multi-asset systems

This article gives an overview of the literature on asset management for multi-unit systems with an emphasis on two multi-asset categories: fleet (a system of homogeneous assets) and portfolio (a system of heterogeneous assets). As asset systems become more complicated, researchers have employed different terms to refer to their specific problems. With an objective to facilitate readers in searching conducive studies to their interests, this paper establishes a novel classification scheme for multi-unit systems in accordance with essential features such as diversity of assets and intervention options. Moreover, discerning differences in characteristics between cross-component and cross-asset interactions, we select three types of potential multi-component dependencies (performance, stochastic, and resource) and extend their notions to be applicable to multi-asset systems. The investigation into these dependencies enables the identification of problems that could exist in real industrial settings but are yet to be determined in academia. Ultimately, we delve into modelling approaches adopted by previous researchers. This comprehensive information allows us to offer the insights into the current trends in multi-asset maintenance. We expect that the output of this review paper will not only stress research gaps on multi-asset systems, but more importantly help systematise future studies on this aspect

Optimization of replacement policy for a one-component system subject to Poisson shocks

In reliability engineering, system failures may occur due to intrinsic or extrinsic factors. For example, drinking water systems may fail due to ageing and deterioration (i.e., intrinsic factors) or flooding (i.e., extrinsic factors). An interesting question is: for such systems, how should preventive maintenance be scheduled? This paper investigates this question. The paper develops a maintenance policy for repairable systems subject to extrinsic shocks. It assumes that a system may fail due to either intrinsic factors or extrinsic factors. Reliability indexes and the expected long run cost rate are then derived. A numerical example is given to illustrate the theoretical results

System Reliability Evaluation Based on Convex Combination Considering Operation and Maintenance Strategy

The approaches to the system reliability evaluation with respect to the cases, where the components are independent or the components have interactive relationships within the system, were proposed in this paper. Starting from the higher requirements on system operational safety and economy, the reliability focused optimal models of multiobjective maintenance strategies were built. For safety-critical systems, the pessimistic maintenance strategies are usually taken, and, in these cases, the system reliability evaluation has also to be tackled pessimistically. For safety-uncritical systems, the optimistic maintenance strategies were usually taken, and, in these circumstances, the system reliability evaluation had also to be tackled optimistically, respectively. Besides, the reasonable maintenance strategies and their corresponding reliability evaluation can be obtained through the convex combination of the above two cases. With a high-speed train system as the example background, the proposed method is verified by combining the actual failure data with the maintenance data. Results demonstrate that the proposed study can provide a new system reliability calculation method and solution to select and optimize the multiobjective operational strategies with the considerations of system safety and economical requirements. The theoretical basis is also provided for scientifically estimating the reliability of a high-speed train system and formulating reasonable maintenance strategies

Improving the profitability, availability and condition monitoring of FPSO terminals

The main focus of this study is to improve the profitability, availability and condition monitoring of Liquefied Natural Gas (LNG) Floating Production Storage and Offloading platforms (FPSOs). Propane pre-cooled, mixed refrigerant (C3MR) liquefaction is the key process in the production of LNG on FPSOs. LNG liquefaction system equipment has the highest failure rates among the other FPSO equipment, and thus the highest maintenance cost. Improvements in the profitability, availability and condition monitoring were made in two ways: firstly, by making recommendations for the use of redundancy in order to improve system reliability (and hence availability); and secondly, by developing an effective condition-monitoring algorithm that can be used as part of a condition-based maintenance system. C3MR liquefaction system reliability modelling was undertaken using the time-dependent Markov approach. Four different system options were studied, with varying degrees of redundancy. The results of the reliability analysis indicated that the introduction of a standby liquefaction system could be the best option for liquefaction plants in terms of reliability, availability and profitability; this is because the annual profits of medium-sized FPSOs (3MTPA) were estimated to increase by approximately US$296 million, rising from about US$1,190 million to US$1,485.98 million, if redundancy were implemented. The cost-benefit analysis results were based on the average LNG prices (US$500/ton) in 2013 and 2014. Typically, centrifugal turbines, compressors and blowers are the main items of equipment in LNG liquefaction plants. Because centrifugal equipment tops the FPSO equipment failure list, a Condition Monitoring (CM) system for such equipment was proposed and tested to reduce maintenance and shutdown costs, and also to reduce flaring. The proposed CM system was based on a novel FFT-based segmentation, feature selection and fault identification algorithm. A 20 HP industrial air compressor system with a rotational speed of 15,650 RPM was utilised to experimentally emulate five different typical centrifugal equipment machine conditions in the laboratory; this involved training and testing the proposed algorithm with a total of 105 datasets. The fault diagnosis performance of the algorithm was compared with other methods, namely standard FFT classifiers and Neural Network. A sensitivity analysis was performed in order to determine the effect of the time length and position of the signals on the diagnostic performance of the proposed fault identification algorithm. The algorithm was also checked for its ability to identify machine degradation using datasets for which the algorithm was not trained. Moreover, a characterisation table that prioritises the different fault detection techniques and signal features for the diagnosis of centrifugal equipment faults, was introduced to determine the best fault identification technique and signal feature. The results suggested that the proposed automated feature selection and fault identification algorithm is effective and competitive as it yielded a fault identification performance of 100% in 3.5 seconds only in comparison to 57.2 seconds for NN. The sensitivity analysis showed that the algorithm is robust as its fault identification performance was affected by neither the time length nor the position of signals. The characterisation study demonstrated the effectiveness of the AE spectral feature technique over the fault identification techniques and signal features tested in the course of diagnosing centrifugal equipment faults. Moreover, the algorithm performed well in the identification of machine degradation. In summary, the results of this study indicate that the proposed two-pronged approach has the potential to yield a highly reliable LNG liquefaction system with significantly improved availability and profitability profiles

Optimisation des politiques de surveillance par l'intégration du cadenassage/décadenassage dans la gestion de la capacité de production

Ce travail vise à développer une stratégie optimale de gestion de la production dans le but de minimiser les coûts de production tout en tenant compte de l’aspect sécurité par le biais du cadenassage/décadenassage (C/D) durant les étapes de maintenance corrective et préventive. Dans la littérature, des études qui traitent de l’intégration du C/D et de la gestion de production sont presque inexistantes. De plus, dans le contexte actuel de l’industrie, beaucoup de dirigeants et travailleurs pensent, à tort, que la planification et la réalisation des différentes procédures de C/D prend beaucoup de temps. Par conséquent, ce temps de production inactif est perçu comme diminuant la performance de l’entreprise vis-à-vis la cadence de fabrication planifiée. Pour pallier à ce problème le concept novateur de :"mean time to lockout/tagout (MTTLT)" a été développé. Le concept novateur du MTTLT consiste à prendre en considération le temps de C/D en fonction des niveaux d'inventaires pour un système manufacturier afin de trouver une politique optimale. Ce concept permet d'une part de diminuer les coûts totaux de production, comprenant les coûts d’inventaire, de pénurie et de maintenance sur un horizon infini et d'autre part d'augmenter le niveau de sécurité des travailleurs. Cette thèse est présentée en trois (3) phases : En premier lieu, le projet vise à intégrer le concept novateur du MTTLT dans la gestion de la capacité de production sous forme de deux travaux. Tout d'abord, le MTTLT a été assimilé pour un système en redondance passive (deux machines, non-identiques produisant un seul type de pièce). Une modélisation a été faite par la chaîne de Markov homogène, et une résolution numérique à travers des équations différentielles d'Hamilton-Jacoby-Bellman (HJB) a conduit à la solution du système étudié. Nos résultats ont été validés par le biais d’une analyse de sensibilité. En deuxième lieu, l'influence de contrôle du MTTLT a été présenté pour une ligne de production constituée de trois machines (deux machines sous forme redondance passive et une troisième machine en série avec les précédentes) produisant un type de pièce. Une modélisation a été faite par la chaîne de Markov homogène. Les outils utilisés à l'étape précédente ont servi à résoudre ce cas. Le modèle de simulation a été également utilisé afin de déterminer les coûts afférents à chaque combinaison obtenue par le biais du plan d’expérience. Partant de ces coûts, une analyse de régression a été faite pour trouver la nouvelle commande optimale du problème d’optimisation considéré. Et pour illustrer l’utilité de nos résultats, une analyse de sensibilité a été effectuée. En troisième lieu, ce travail s’est concentré sur la modélisation du MTTLT et l'erreur humaine pour un sytème manufacturier flexible (FMS). La modélisation de l'erreur humaine a été effectuée par une chaîne de Markov non-homogène, pour un système en redondance passive produisant une seule pièce. La solution a été exposée par le biais des équations d'HJB et nos résultats ont été confirmés par une analyse de sensibilité

A Collection of Technical Papers

Papers presented at the 6th Space Logistics Symposium covered such areas as: The International Space Station; The Hubble Space Telescope; Launch site computer simulation; Integrated logistics support; The Baikonur Cosmodrome; Probabalistic tools for high confidence repair; A simple space station rescue vehicle; Integrated Traffic Model for the International Space Station; Packaging the maintenance shop; Leading edge software support; Storage information management system; Consolidated maintenance inventory logistics planning; Operation concepts for a single stage to orbit vehicle; Mission architecture for human lunar exploration; Logistics of a lunar based solar power satellite scenario; Just in time in space; NASA acquisitions/logistics; Effective transition management; Shuttle logistics; and Revitalized space operations through total quality control management

AVAILABILITY MODEL FOR A COG EN ERA TION SYSTEM SUBJECTED TO REDUNDANCY

The main emphasis of cogeneration system is to provide electrical energy, steam, hot and chilled water to their customers. The failure of this system could lead to the disruption of the supply of these items. If failure occurs, it will result in reduction of availability as well as economic loss. In order to mitigate such effects, it is required to study availability of the cogeneration system together with associated economic loss. However, there are factors which affect the availability assessment of the cogeneration system. These factors are system redundancy and limitation of maintenance data. Use of redundancy in cogeneration helps to achieve higher availability but the operation cost of redundancy is expensive due to maximum demand charge cost. Thus, it is important to consider the economic effect of redundancy

Mathematical Modeling and Simulation in Mechanics and Dynamic Systems

The present book contains the 16 papers accepted and published in the Special Issue “Mathematical Modeling and Simulation in Mechanics and Dynamic Systems” of the MDPI “Mathematics” journal, which cover a wide range of topics connected to the theory and applications of Modeling and Simulation of Dynamic Systems in different field. These topics include, among others, methods to model and simulate mechanical system in real engineering. It is hopped that the book will find interest and be useful for those working in the area of Modeling and Simulation of the Dynamic Systems, as well as for those with the proper mathematical background and willing to become familiar with recent advances in Dynamic Systems, which has nowadays entered almost all sectors of human life and activity

Analysis and Preliminary Design of an Advanced Technology Transport Flight Control System

The analysis and preliminary design of an advanced technology transport aircraft flight control system using avionics and flight control concepts appropriate to the 1980-1985 time period are discussed. Specifically, the techniques and requirements of the flight control system were established, a number of candidate configurations were defined, and an evaluation of these configurations was performed to establish a recommended approach. Candidate configurations based on redundant integration of various sensor types, computational methods, servo actuator arrangements and data-transfer techniques were defined to the functional module and piece-part level. Life-cycle costs, for the flight control configurations, as determined in an operational environment model for 200 aircraft over a 15-year service life, were the basis of the optimum configuration selection tradeoff. The recommended system concept is a quad digital computer configuration utilizing a small microprocessor for input/output control, a hexad skewed set of conventional sensors for body rate and body acceleration, and triple integrated actuators