A unified methodology of maintenance management for repairable systems based on optimal stopping theory

This dissertation focuses on the study of maintenance management for repairable systems based on optimal stopping theory. From reliability engineering’s point of view, all systems are subject to deterioration with age and usage. System deterioration can take various forms, including wear, fatigue, fracture, cracking, breaking, corrosion, erosion and instability, any of which may ultimately cause the system to fail to perform its required function. Consequently, controlling system deterioration through maintenance and thus controlling the risk of system failure becomes beneficial or even necessary. Decision makers constantly face two fundamental problems with respect to system maintenance. One is whether or when preventive maintenance should be performed in order to avoid costly failures. The other problem is how to make the choice among different maintenance actions in response to a system failure. The whole purpose of maintenance management is to keep the system in good working condition at a reasonably low cost, thus the tradeoff between cost and condition plays a central role in the study of maintenance management, which demands rigorous optimization. The agenda of this research is to develop a unified methodology for modeling and optimization of maintenance systems. A general modeling framework with six classifying criteria is to be developed to formulate and analyze a wide range of maintenance systems which include many existing models in the literature. A unified optimization procedure is developed based on optimal stopping, semi-martingale, and lambda-maximization techniques to solve these models contained in the framework. A comprehensive model is proposed and solved in this general framework using the developed procedure which incorporates many other models as special cases. Policy comparison and policy optimality are studied to offer further insights. Along the theoretical development, numerical examples are provided to illustrate the applicability of the methodology. The main contribution of this research is that the unified modeling framework and systematic optimization procedure structurize the pool of models and policies, weed out non-optimal policies, and establish a theoretical foundation for further development

Supporting group maintenance through prognostics-enhanced dynamic dependability prediction

Condition-based maintenance strategies adapt maintenance planning through the integration of online condition monitoring of assets. The accuracy and cost-effectiveness of these strategies can be improved by integrating prognostics predictions and grouping maintenance actions respectively. In complex industrial systems, however, effective condition-based maintenance is intricate. Such systems are comprised of repairable assets which can fail in different ways, with various effects, and typically governed by dynamics which include time-dependent and conditional events. In this context, system reliability prediction is complex and effective maintenance planning is virtually impossible prior to system deployment and hard even in the case of condition-based maintenance. Addressing these issues, this paper presents an online system maintenance method that takes into account the system dynamics. The method employs an online predictive diagnosis algorithm to distinguish between critical and non-critical assets. A prognostics-updated method for predicting the system health is then employed to yield well-informed, more accurate, condition-based suggestions for the maintenance of critical assets and for the group-based reactive repair of non-critical assets. The cost-effectiveness of the approach is discussed in a case study from the power industry

Maintenance Optimization and Inspection Planning of Wind Energy Assets: Models, Methods and Strategies

Designing cost-effective inspection and maintenance programmes for wind energy farms is a complex task involving a high degree of uncertainty due to diversity of assets and their corresponding damage mechanisms and failure modes, weather-dependent transport conditions, unpredictable spare parts demand, insufficient space or poor accessibility for maintenance and repair, limited availability of resources in terms of equipment and skilled manpower, etc. In recent years, maintenance optimization has attracted the attention of many researchers and practitioners from various sectors of the wind energy industry, including manufacturers, component suppliers, maintenance contractors and others. In this paper, we propose a conceptual classification framework for the available literature on maintenance policy optimization and inspection planning of wind energy systems and structures (turbines, foundations, power cables and electrical substations). The developed framework addresses a wide range of theoretical and practical issues, including the models, methods, and the strategies employed to optimise maintenance decisions and inspection procedures in wind farms. The literature published to date on the subject of this article is critically reviewed and several research gaps are identified. Moreover, the available studies are systematically classified using different criteria and some research directions of potential interest to operational researchers are highlighted

The Theorem of Proportionality in Mainstream Capital Theory: An Assessment of its Applicability

This paper surveys and assesses the empirical literature that bears on the applicability of the theorem of proportionality, which asserts that depreciation is proportional to the outstanding capital stock. All available evidence shows that: a) the rates of depreciation and retirements vary from year to year in response to changes in conventional economic forces like utilization, maintenance and repair, the prices of new capital goods, etc., and b) while the approximation of the distribution of depreciation rates by a single parameter may be characterized by simplicity and ease of use, at the same time it thwarts the advances that can be achieved by returning to a general equilibrium model centered on the time structure of capital and the useful lives of its components. For this reason, it is concluded that, the sooner this theorem is replaced by an endogenous theory of depreciation and replacement, the better for economic theory and policy.Capital longevity, replacement, depreciation, scrappage, maintenance, utilization, obsolescence

Subsidising consumer services: effects on employment, welfare and the informal economy

It is widely agreed that the opportunities for expansion of aggregate employment in the OECD area must be sought mainly in the private service sector. Thus,because of budgetary problems and voter resistance to higher tax rates, the scope for further expansion of public sector employment seems limited in most OECD countries. Furthermore, the primary sector will undoubtedly continue to release labour resources and, with normal growth rates, there is little prospect of a secular rise in manufacturing employment, since the increase in demand for manufactures is likely to be met through increases in labour productivity. In particular, the ongoing shifts in the international division of labour and the associated transition to the ‘knowledge-based economy’ within the OECD are likely to destroy a large number of manufacturing jobs for unskilled and lowskilled workers in the OECD area.

Modeling Information Reliability and Maintenance: A Systematic Literature Review

Operating a business efficiently depends on effective everyday decision-making. In turn, those decisions are influenced by the quality of data used in the decision-making process, and maintaining good data quality becomes more challenging as a business expands. Protecting the quality of the data and the information it generates is a challenge faced by many companies across all industrial sectors. As companies begin to use data from these large data bases they will need to begin to develop strategies for maintaining and assessing the reliability of the information they generate using this data. A considerable amount of literature exists on data quality but minimal amounts of information exist on information reliability and maintenance. For these reasons, it is important to study the current methods used by businesses to maintain desired levels of data and information quality. The purpose of this paper is to describe and assess the available knowledge relating data quality, reliability and maintenance by performing a systematic literature review in these areas

Optimal maintenance and replacement decisions under technological change with consideration of spare parts inventories

International audienceClassical spare parts inventory models assume that the same vintage of technology will be utilized throughout the planning horizon. However, replacement often occurs in the form of a new technology that renders existing spare parts inventories obsolete. This paper aims to study the impact of spare parts inventory on maintenance and replacement decisions under technological change via a Markov decision process formulation. The replacement decision is complex in that one must decide with which technology available on the market to replace the current asset. Under technological change, the do nothing and repair options have significantly more value as they allow the appearance of even better technologies in the future