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System Degradation and Maintenance
Abstract
Every system (product, plant or infrastructure) is unreliable in the sense that it degrades and eventually fails. Maintenance is needed to compensate for this unreliability. Any decision-making with respect to maintenance requires a proper understanding of the degradation processes over time and the actions of maintenance from a system life cycle perspective.
... On the other hand, the forced degradation is artificially induced by an external agent where component loading gradually increases in response to an increased demand [16,37,52]. Such degradation can be characterized into three categories based on the physics or nature of the component or system: binary degradation, degradation with a finite number of levels, and degradation with an infinite number of levels [106]. [56,73,74,[143][144][145][146], it is assumed that the degradation is proportional to the control effort of actuators and it modifies the failure rate of each actuator. ...
... The condition of a component can be characterised according to the degree of detail given to the degradation process [106]. It could be characterised as a binary condition (see An example of characterisation is an electric bulb where its state changes from working to failing in a very short time which can be assumed to be instantaneous. ...
This thesis presents some contributions to the field of Health-Aware Control (HAC) of dynamic systems. In the first part of this thesis, a review of the concepts and methodologies related to reliability versus degradation and fault-tolerant control versus health-aware control is presented. Firstly, in an attempt to unify concepts, an overview of HAC, degradation, and reliability modelling including some of the most relevant theoretical and applied contributions are given. Moreover, reliability modelling is formalized and exemplified using the structure-function, Bayesian networks (BNs) and Dynamic Bayesian networks (DBNs) as modelling tools in reliability analysis. In addition, some Reliability Importance Measures (RIMs) are presented. In particular, this thesis develops BNs models for overall system reliability analysis by using Bayesian inference techniques. Bayesian networks are powerful tools in system reliability assessment due to their flexibility in modelling the reliability structure of complex systems. For the HAC scheme implementation, this thesis presents and discusses the integration of actuators' health information through RIMs and degradation in Model Predictive Control (MPC) and Linear Quadratic Regulator algorithms. In the proposed strategies, the cost function parameters are tuned using RIMs. The methodology can avoid the occurrence of catastrophic and incipient faults by monitoring the overall system reliability. The proposed HAC strategies are applied to a Drinking Water Network (DWN) and a multirotor UAV system. Moreover, a third approach, which uses MPC and restricts the degradation of the system components is applied to a twin-rotor system. Finally, this thesis presents and discusses two reliability interpretations. These interpretations, namely instantaneous and expected, differ in the manner in which reliability is evaluated and how its evolution along time is considered. This comparison is made within a HAC framework and studies the system reliability under both approaches.
Asphalt roads are gradually deteriorating over time and need road mending to remain in a good state. Inspections are performed to obtain information about the current state of the road; when the damage achieves the established standards, the road is repaired through a maintenance action that is considered as most cost-effective. Because of economies of scale it is to a certain extent economical to limit the number of maintenance services by integrating neighboring segments into a homogeneous section which is completely repaired. In this report we consider the question whether it is economically justified to adopt a maintenance concept in which the road is occasionally regenerated from junction to junction with a distance of several kilometers. The big advantage of junction-to-junction maintenance is that it can be done within special road barrier constructions which reduce the road capacity only slightly, so that the road can be maintained 24 hours a day.
The maintenance of systems in engineering is of increasing concern to managers and designers in all branches of engineering, whether they are producing high-quality products or designing highly-reliable systems. In recent decades, reliability theory has produced many innovations in maintenance policy.
Maintenance Theory of Reliability is a survey of useful and practical maintenance models covering replacement, preventive maintenance and inspection.
The book provides a detailed introduction to maintenance policies, updates the reader on the current status of the field and indicates future directions. The reader will learn the theory of maintenance and how to apply models in practice. The book will serve as an essential reference for graduate students and researchers in reliability theory and a useful guide for reliability engineers engaged in maintenance work.
The Springer Series in Reliability Engineering publishes high-quality books in important areas of current theoretical research and development in reliability, and in areas that bridge the gap between theory and application in areas of interest to practitioners in industry, laboratories, business, and government.
CONTEXT OF RELIABILITY ANALYSIS. An Overview. Illustrative Cases and Data Sets. BASIC RELIABILITY METHODOLOGY. Collection and Preliminary Analysis of Failure Data. Probability Distributions for Modeling Time to Failure. Basic Statistical Methods for Data Analysis. RELIABILITY MODELING, ESTIMATION, AND PREDICTION. Modeling Failures at the Component Level. Modeling and Analysis of Multicomponent Systems. Advanced Statistical Methods for Data Analysis. Software Reliability. Design of Experiments and Analysis of Variance. Model Selection and Validation. RELIABILITY MANAGEMENT, IMPROVEMENT, AND OPTIMIZATION. Reliability Management. Reliability Engineering. Reliability Prediction and Assessment. Reliability Improvement. Maintenance of Unreliable Systems. Warranties and Service Contracts. Reliability Optimization. EPILOGUE. Case Studies. Resource Materials. Appendices. References. Indexes.
Introduction Experimental Designs for ALT Parametric Models Used in ALT Nonparametric Models Used in ALT Problems
A model that recognizes the advantages of coordinated group maintenance planning is established. The maintenance policy that is investigated calls for group maintenance to be conducted at time T or upon m failures, whichever comes first. This policy combines the best features of the well-known T-age and m-failure replacement policies. Using a renewal approach the economic objective is to minimize the long-run (expected) average cost per unit time. General cost structures and failure time distributions are allowed. An algorithm that does not require unimodality properties is provided for computing optimal policies for general failure time distribution and cost structures.
Optimum group maintenance policies for a set of N machines subjected to stochastic failures under continuous and periodic inspections are considered. Under very general conditions it is shown that a control limit policy minimizes the expected cost per unit time over an infinite horizon, when costs are incurred due to loss of production and repair only. It is also shown how to explicitly compute this control limit. When additional costs are incurred due to inspection, a characterization of an optimal periodic inspection/repair policy that minimizes the expected cost per unit time over an infinite horizon is given.
In Australia, routine road maintenance activities such as pavement patching, drainage works, litter collection, etc. are usualy carried out by maintenance patrols who work from depots located throughout the road network. In general, the location of these depots has largely been determined on historic grounds. This paper outlines a systematic, analytic framework for examining decisions concerning the location and size of maintenance depots. A model system is described which formulates the depot location problem as an optimisation problem. Results are presented for one sub-region of the rural road network in Victoria. The scope for consolidating patrols into fewer, larger depots is highlighted by the results and the benefits of this consolidation for the road authority and its employees are discussed.
This paper proposes a two-phase maintenance policy for a group of identical repairable units. We define the time-interval (0, T] as the first phase, and the time interval (T, T + W ] as the second phase. As individual units fail individual units have two types of failures. Type I failures (minor failures) are removed by minimal repairs (in both phases), whereas Type II failures (catastrophic failures) are removed by replacements (in the first phase) or are left idle (in the second phase). A group maintenance is conducted at time T + W or upon the kth idle, whichever comes first. The optimal policy is to select to minimize the expected cost per unit time for an infinite time span. Various special cases are considered. Numerical examples are given to illustrate the method.
In this article we describe a Decision Support Model, based on Operational Research methods, for the multi-period planning of maintenance of bituminous pavements. This model is a tool for the road manager to assist in generating an optimal maintenance plan for a road. Optimal means: minimising the Net Present Value of maintenance costs, while the plan is acceptable in terms of technical admissibility, resulting quality, etc. Global restrictions such as budget restrictions can also be imposed.Adequate grouping of maintenance activities in view of quantity discounts is an important aspect of our model. Our approach is to reduce the complexity of the optimisation by hierarchical structuring in four levels. In the lowest two levels maintenance per lane sector is considered, first with an unbounded planning horizon and next with a bounded planning horizon and time-windows for maintenance. The grouping of maintenance activities for a specific road is the topic of the third level. At the fourth level, which we will not consider in this article, the problem of optimal assignment of the available maintenance budgets over a set of roads or road sections takes place. Here, some results are presented to demonstrate the effects of grouping and to show that this hierarchical approach gives rise to improvements compared with previous work.
A determining factor in efficient use of fleets of equipment is
effective maintenance planning. Managing the maintenance of a fleet of
equipment is a complex problem for a variety of reasons. In this paper,
the requirements of a comprehensive strategy for effectively managing
the maintenance of an equipment fleet are presented. In addition, the
mathematical modeling domains required for developing such a strategy
are defined. These domains include equipment-level maintenance
scheduling, predictive maintenance, opportunistic maintenance policies,
impacts of new technology, equipment retirement, and maintenance
resource allocation. We explore these modeling domains as part of a
collaborative research project
The authors propose a new block replacement policy for a group of
nominally identical units. Each unit is individually replaced on failure
during a specified time interval. Beyond the failure replacement
interval, failed units are left idle until a specified number of
failures occur, then a block replacement is performed. The average cost
rate for this two-phase block replacement policy is derived and
analyzed. The policy yields lower cost rate than two block replacement
policies published previously. Numerical examples demonstrate the
results
Bituminous road deterioration, highway development and management (HDM-4). The World Bank
- R Archondo-Callao