Browsing by Subject "Maintenance"
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Item Open Access An adaptive bayesian replacement policy with minimal repair(Institute for Operations Research and the Management Sciences (INFORMS), 2002) Gürler, Ü.; Dayanık, S.In this study, an adaptive Bayesian decision model is developed to determine the optimal replacement age for the systems maintained according to a general age-replacement policy. It is assumed that when a failure occurs, it is either critical with probability p or noncritical with probability1−p, independently. A maintenance policy is considered where the noncritical failures are corrected with minimal repair and the system is replaced either at the first critical failure or at age , whichever occurs first. The aim is to find the optimal value of that minimizes the expected cost per unit time. Two adaptive Bayesian procedures that utilize different levels of information are proposed for sequentiallyupdating the optimal replacement times. Posterior density/mass functions of the related variables are derived when the time to failure for the system can be expressed as a Weibull random variable. Some simulation results are also presented for illustration purposes.Item Open Access Analysis of maintenance policies for M machines with deteriorating performance(Taylor & Francis, 2000) Berk, E.; Moinzadeh, K.In this paper, we consider the maintenance scheduling of a group of M identical machines, the performance of which deteriorates with usage. Examples of such situations are frequently found in the heavy machine tooling, petro-chemical and semi-conductor industries among others. Assuming a limited maintenance resource and that the maintenance times are i.i.d., we propose a dynamic maintenance policy which utilities the information about the number of operating machines and their ages. We analyze the system for the special cases of constant and exponentially distributed maintenance times. We investigate the impact of maintenance time variability on system performance and evaluate the performance of various maintenance policies within the proposed policy class when the expected profit rate is maximized.Item Open Access An approximate analytical method of analysis of a threshold maintenance policy for a multiphase multicomponent model(Springer, 2003) Anisimov, V. V.; Gürler, Ü.A multicomponent system is investigated that consists of n identical unreliable components whose nonfailure operating time consists of a number of sequential phases with exponential times. A maintenance policy is studied that proposes the instant replacement of all the components as soon as the number of components that are in some doubtful state (before a failure) amounts to a predefined threshold value. A cost function averaged over a large period is studied. For a fixed n, an analytical approach is considered. If n increases, a new approximate analytical approach is proposed, which is based on results of the type of the averaging principle for recurrent semi-Markovian processes. The conditions of existence and properties of the optimal strategy are studied. An example is considered and possibilities of generalizations are discussed.Item Open Access Capital maintenance versus technology adoption under embodied technical progress(B E Press, 2006) Boucekkine, R.; Martínez, B.; Saglam, C.We study an optimal growth model with one-hoss-shay vintage capital, where labor resources can be allocated freely either to production, technology adoption or capital maintenance. Technological progress is partly embodied. Adoption labor increases the level of embodied technical progress. First, we are able to disentangle the amplification-propagation role of maintenance in business fluctuations: in the short run, the response of the model to transitory shocks on total factor productivity in the final good sector are definitely much sharper compared to the counterpart model without maintenance but with the same average depreciation rate. Moreover, the one-hoss shay technology is shown to reinforce this amplification-propagation mechanism. We also find that accelerations in embodied technical progress should be responded by a gradual adoption effort, and capital maintenance should be the preferred instrument in the short run. Copyright © 2006 The Berkeley Electronic Press. All rights reserved.Item Open Access Effects of endogenous depreciation on the optimal timing of technology adoption(Bilkent University, 2006) Karaşahin, RamazanIn this thesis, we use two stage optimal control techniques to analyze optimal timing of technology adoption under embodied technical change taking into account the endogenous nature of depreciation. We show that a more efficient maintenance service reducing the depreciation rate postpones the optimal timing of technology adoption. In this respect, we study to what extent can maintenance of the existing capital stock be a substitute for adoption of new technologies.Item Open Access Evaluation of army corps food supply system using simulation(IEEE, 2003) Pembe, O.; Sabuncuoğlu, İhsanThe Food Supply System is one of the main elements of the Army Logistics System. The ultimate objective in a food supply system is to provide the food at the right time and in the right amount at the right place. If this objective is achieved, the morale, the health, and the strength of the soldiers on the battlefield will enormously enhanced. The purposes of this study are to test if the existing food supply system of the Turkish Army operates properly under the war conditions; to identify the potential problem areas; and establish time standards for different scenarios. We use simulation as the modelling and analysis tool to answer the above questions. The proposed simulation model of the Army Corps Food Supply System is built in Arena and the results are analyzed statistically.Item Open Access A maintanence policy for a system with multi-state components: an approximate solution(Elsevier, 2002) Gürler, Ü.; Kaya, A.For maintenance and quality assessment purposes, various performance levels for both systems and components are identified, usually as a function of the deterioration. In this study, we consider a multicomponent system where the lifetime of each component is described by several stages, (0,…,S), which are further classified as good, doubtful, preventive maintenance due (PM due) and down. A control policy is suggested where the system is replaced when a component enters a PM due or a down state and the number of components in the doubtful states (K,…,S−2) is at least N. All maintenance activities are assumed to take negligible time. The exact description of the underlying stochastic model under the policy is very complicated. We therefore propose some approximations, which allow an explicit expression for the long run average cost function, which is minimized w.r.t. (K,N) by numerical methods. Sensitivity of the model to system parameters and the performance of the approximation are investigated through several examples.Item Open Access Performance evaluation of track association and maintenance for a MFPAR with doppler velocity measurements(2010) Kural, F.; Arikan, F.; Arıkan, Orhan; Efe, M.This study investigates the effects of incorporating Doppler velocity measurements directly into track association and maintenance parts for single and multiple target tracking unit in a multi function phased array radar (MFPAR). Since Doppler velocity is the major discriminant of clutter from a desired target, the measurement set has been expanded from range, azimuth and elevation angles to include Doppler velocity measurements. We have developed data association and maintenance part of a well known tracking method, Interacting Multiple Model Probabilistic Data Association.Item Open Access Progreso técnico incorporado, adopción y mantenimiento(Ministerio de Industria, Turismo Y Comercio, 2006) Boucekkine, R.; Martínez, B.; Saglam, C.We study the properties of an optimal growth model of a developing economy with one-hoss shay vintage capital, where the scarce (skilled) labor resources can be allocated freely either to production, technology adoption or capital maintenance. Technological progress is partly embodied. Technology adoption features a kind of catching up law of motion according to a Nelson-Phelps scheme. We first analytically characterize the balanced growth paths of the economy. Second, we numerically investigate the short run dynamics of the model. Among numerous findings, we find that under exogenous technological accelerations, intensive technology adoption should be delayed, and maintenance acts as an optimal transitory substitute to adoption.Item Open Access View maintenance in object-oriented databases(Springer, 1996-09) Alhajj, Reda; Polat, F.in this paper, we present a model that facilitates view maintenance within object-oriented databases. For that purpose, we differentiate between two categories of classes, base classes and brother classes. While the former constitute the actual database, the latter are introduced to hold virtual database, i.e., views derived from base classes. To achieve incremental view update, we introduce a modification list into each base class. A series of algorithms are developed to serve the purpose. Finally it happened that, view maintenance within object-oriented databases subsumes that within the nested and hence conventional relational models.