A review on maintenance optimization

To this day, continuous developments of technical systems and increasing reliance on equipment have resulted in a growing importance of effective maintenance activities. During the last couple of decades, a substantial amount of research has been carried out on this topic. In this study we review more than two hundred papers on maintenance modeling and optimization that have appeared in the period 2001 to 2018. We begin by describing terms commonly used in the modeling process. Then, in our classification, we first distinguish single-unit and multi-unit systems. Further sub-classification follows, based on the state space of the deterioration process modeled. Other features that we discuss in this review are discrete and continuous condition monitoring, inspection, replacement, repair, and the various types of dependencies that may exist between units within systems. We end with the main developments during the review period and with potential future research directions

Maintenance models applied to wind turbines. A comprehensive overview

Producción CientíficaWind power generation has been the fastest-growing energy alternative in recent years, however, it still has to compete with cheaper fossil energy sources. This is one of the motivations to constantly improve the efficiency of wind turbines and develop new Operation and Maintenance (O&M) methodologies. The decisions regarding O&M are based on different types of models, which cover a wide range of scenarios and variables and share the same goal, which is to minimize the Cost of Energy (COE) and maximize the profitability of a wind farm (WF). In this context, this review aims to identify and classify, from a comprehensive perspective, the different types of models used at the strategic, tactical, and operational decision levels of wind turbine maintenance, emphasizing mathematical models (MatMs). The investigation allows the conclusion that even though the evolution of the models and methodologies is ongoing, decision making in all the areas of the wind industry is currently based on artificial intelligence and machine learning models

Maintenance optimisation for systems with multi-dimensional degradation and imperfect inspections

In this paper, we develop a maintenance model for systems subjected to multiple correlated degradation processes, where a multivariate stochastic process is used to model the degradation processes, and the covariance matrix is employed to describe the interactions among the processes. The system is considered failed when any of its degradation features hits the pre-specified threshold. Due to the dormancy of degradation-based failures, inspection is implemented to detect the hidden failures. The failed systems are replaced upon inspection. We assume an imperfect inspection, in such a way that a failure can only be detected with a specific probability. Based on the degradation processes, system reliability is evaluated to serve as the foundation, followed by a maintenance model to reduce the economic losses. We provide theoretical boundaries of the cost-optimal inspection intervals, which are then integrated into the optimisation algorithm to relieve the computational burden. Finally, a fatigue crack propagation process is employed as an example to illustrate the effectiveness and robustness of the developed maintenance policy. Numerical results imply that the inspection inaccuracy contributes significantly to the operating cost and it is suggested that more effort should be paid to improve the inspection accuracy

Методики оценивания надежности систем защиты информации от несанкционированного доступа в автоматизированных системах

Современные методы защиты информации от несанкционированного доступа в автоматизированных системах основаны на использовании специализированных систем защиты информации, которые в обязательном порядке включаются в виде дополнительных программных систем в программное обеспечение автоматизированных систем в защищенном исполнении. Данные системы могут разрабатываться не только в процессе проектирования автоматизированных систем, но и дополнять общесистемное программное обеспечение функционирующих систем. Применение систем защиты информации от несанкционированного доступа может снизить надежность автоматизированных систем, если они содержат ошибки, не обнаруживаемые при отладке. Надежность систем защиты информации влияет на эффективность защиты информации (конфиденциальность, целостность и доступность). Методической основой при формировании облика систем защиты информации как в процессе разработки, так и в процессе модернизации автоматизированных систем являются руководящие документы Федеральной службы по техническому и экспортному контролю (ФСТЭК) России. Руководящие документы ФСТЭК России не содержат методических подходов к оценке надежности указанных программных систем. В этой связи актуальна разработка методик оценивания надежности систем защиты информации от несанкционированного доступа автоматизированных систем в защищенном исполнении. Структурная сложность систем защиты информации от несанкционированного доступа и значительное количество выполняемых функций обусловили необходимость использования трех показателей надежности, характеризующих систему при решении задач обеспечения конфиденциальности, целостности и доступности информации. Для разработки методик использованы известные методы оценивания надежности сложных систем, не допускающие их разложение на последовательное и параллельное соединение. Разработанные методики апробированы при оценивании надежности систем защиты информации от несанкционированного доступа, имеющих типовые показатели исходных характеристик. Результаты расчетов и перспективы использования разработанных методик представлены в статье

Risk-based shutdown inspection and maintenance for a processing facility

In this research, a risk-based shutdown inspection and maintenance interval optimization for a processing facility is proposed. Often inspection and maintenance activities can’t be performed until the processing unit or plant is taken into a non-operational state, generally known as “shutdown”. Extensive work on inspection and maintenance interval estimation modeling is available in the concerned literature however, no to very limited application on shutdown inspection and maintenance modeling is observed for a continuous operating facility. Majority of the published literature deals to optimize individual equipment inspection and maintenance interval without considering the overall impact of plant unavailability due to shutdown. They all deal to optimize individual equipment inspection and maintenance interval considering cost, risk, availability and reliability. The efforts towards finding an optimal inspection and maintenance interval is not considered in these studies especially when it requires unit or plant to be in shutdown state from an operational state for performing inspection and maintenance. This topic is selected to bridge the existing gap in the available literature and to provide a means to develop a methodology to estimate the shutdown inspection and maintenance interval for a continuous processing unit or plant, rather an inspection and maintenance interval for each piece of equipment considering the overall asset availability, reliability and risk. A component failure due to wear or degradation is a major threat to asset failure in a processing facility. A carefully planned inspection and maintenance strategy not only mitigate the effects of age-based degradation and reduce the threat of failure but also minimize the risk exposure. Generally failure caused by wear or degradation is modeled as a stochastic process. For an effective inspection and maintenance strategy, the stochastic nature of failure has to be taken into consideration. The proposed methodology aims to minimize the risk of exposure considering effect of failure on human life, financial investment and environment by optimizing the interval of process unit shutdown. Risk-based shutdown inspection and maintenance optimization quantifies the risk to which individual equipment are subjected and uses this as a basis for the optimization of a shutdown inspection and maintenance strategy

Методики оценивания надежности систем защиты информации от несанкционированного доступа в автоматизированных системах

Modern methods of protecting information  from unauthorized access in automated systems are based on the use of specialized information security systems from unauthorized access. Security systems are necessarily included in the form of additional software systems in the software as in a secure execution. Information security systems from unauthorized access can be developed not only in a process of automated systems design, but also complement the system-wide software of functioning systems. The use of the information security systems from unauthorized access can reduce a overall reliability of the automated systems, if they contain errors that are not detected during debugging. The reliability of the information security systems affects effectiveness of information security (confidentiality, integrity and availability). Guidelines of the Federal Service for Technical and Export Control (FSTEC) of Russia are a methodological basis for the formation of the information security systems’ image both in the process of development and in the process of modernization of the automated systems. The guidance documents of FSTEC of Russia do not contain methodological approaches to assessing the reliability of these program systems. In this regard, the actual design of techniques of estimating reliability of the information security systems from unauthorized access in automated systems in a secure execution. The structural complexity of the information security systems from unauthorized access and large number of functions performed necessitates the use of three reliability indicators that characterize the system in solving problems of confidentiality, integrity and availability of information. To develop the technique, the known methods of evaluating the reliability of complex systems are used, which do not allow their decomposition into serial and parallel connection. The developed methods were tested in assessing the reliability of the information security systems from unauthorized access with typical indicators of initial characteristics. The results of calculations and prospects of using the developed methods are presented in the paper.Современные методы защиты информации от несанкционированного доступа в автоматизированных системах основаны на использовании специализированных систем защиты информации, которые в обязательном порядке включаются в виде дополнительных программных систем в программное обеспечение автоматизированных систем в защищенном исполнении. Данные системы могут разрабатываться не только в процессе проектирования автоматизированных систем, но и дополнять общесистемное программное обеспечение функционирующих систем. Применение систем защиты информации от несанкционированного доступа может снизить надежность автоматизированных систем, если они содержат ошибки, не обнаруживаемые при отладке. Надежность систем защиты информации влияет на эффективность защиты информации (конфиденциальность, целостность и доступность). Методической основой при формировании облика систем защиты информации как в процессе разработки, так и в процессе модернизации автоматизированных систем являются руководящие документы Федеральной службы по техническому и экспортному контролю (ФСТЭК) России. Руководящие документы ФСТЭК России не содержат методических подходов к оценке надежности указанных программных систем. В этой связи актуальна разработка методик оценивания надежности систем защиты информации от несанкционированного доступа автоматизированных систем в защищенном исполнении. Структурная сложность систем защиты информации от несанкционированного доступа и значительное количество выполняемых функций обусловили необходимость использования трех показателей надежности, характеризующих систему при решении задач обеспечения конфиденциальности, целостности и доступности информации. Для разработки методик использованы известные методы оценивания надежности сложных систем, не допускающие их разложение на последовательное и параллельное соединение. Разработанные методики апробированы при оценивании надежности систем защиты информации от несанкционированного доступа, имеющих типовые показатели исходных характеристик. Результаты расчетов и перспективы использования разработанных методик представлены в статье

Safety and Reliability - Safe Societies in a Changing World

The contributions cover a wide range of methodologies and application areas for safety and reliability that contribute to safe societies in a changing world. These methodologies and applications include: - foundations of risk and reliability assessment and management - mathematical methods in reliability and safety - risk assessment - risk management - system reliability - uncertainty analysis - digitalization and big data - prognostics and system health management - occupational safety - accident and incident modeling - maintenance modeling and applications - simulation for safety and reliability analysis - dynamic risk and barrier management - organizational factors and safety culture - human factors and human reliability - resilience engineering - structural reliability - natural hazards - security - economic analysis in risk managemen

Integrated Workload Allocation and Condition-based Maintenance Threshold Optimisation

Effective asset management is considered key to reducing total costs of asset ownership while enhancing machine availability, guaranteeing security, and increasing productivity. Amongst all the activities involved in asset management, maintenance has been one of the major focus areas of academic research due to its potential in helping manufacturers to generate the most value from their assets. The emergence of condition-based maintenance (CBM) in which decisions are made based on the real-time condition of assets, has opened up new possibilities in developing more comprehensive approaches to improve the performance of production systems. For instance, a trend has been observed where attempts are made to couple CBM decisions with those on other production-related factors such as inventory control, spare parts management, and labour routing. The intrinsic link between the degradation behaviour of and the workload allocated to an asset, however, has not been sufficiently studied. Consequently, the potential benefits of intervening in machine degradation, either in the context of a single asset or a fleet of assets, are rarely explored. It is therefore essential that a systematic approach is at hand to improve system performance by exploiting the inter-relationship between production and maintenance. This thesis is dedicated to developing a dynamic integrated decision-making model to improve the system-level performance of a fleet of parallel assets. The aim of the model is to realise the potential benefits, mainly in the form of lower maintenance costs and reduced penalty costs incurred due to loss of production, by simultaneously optimising workload allocation and the CBM threshold. The decision-making model is implemented using an agent-based system involving two types of agents - 1) machine agents that reside within each individual machine; and 2) a coordinator agent that oversees the entire system. The integrated decision-making model is constituted of two components - 1) a workload-dependent condition-based maintenance optimisation model based on Gamma Process at the asset level through a machine agent; and 2) a workload allocation strategy at the system level implemented by a coordinator agent. Numerical analysis is performed to demonstrate the rationale behind the decision-making process, which is to reach the most desirable balance between maintenance costs and penalty costs incurred by loss of production. The capability of the model to reduce total costs is demonstrated via comparison with traditional strategies such as uniform and random workload allocation. Additionally, the sensitivity analysis conducted has helped to reveal the respective factors that impact the potential reduction in maintenance costs and that in penalty costs, which include the sensitivity of asset degradation to workloads, heterogeneity of assets, penalty cost for a unit of production loss, redundancy of the system, etc. The model presented in this study not only assists operation and maintenance managers to make decisions on the optimal combination of workload allocation and maintenance plans for assets in a production system, but also provides guidance on whether they should invest in workload control capabilities. Furthermore, the proposed approach allows practitioners to evaluate the long-term impacts of sudden events such as an increase in demand, a decrease in the number of redundant machines, and a change in the cost of maintenance actions

Use, Operation and Maintenance of Renewable Energy Systems:Experiences and Future Approaches

The aim of this book is to put the reader in contact with real experiences, current and future trends in the context of the use, exploitation and maintenance of renewable energy systems around the world. Today the constant increase of production plants of renewable energy is guided by important social, economical, environmental and technical considerations. The substitution of traditional methods of energy production is a challenge in the current context. New strategies of exploitation, new uses of energy and new maintenance procedures are emerging naturally as isolated actions for solving the integration of these new aspects in the current systems of energy production. This book puts together different experiences in order to be a valuable instrument of reference to take into account when a system of renewable energy production is in operation