• 산업경영시스템학회지
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• 제17권32호
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• pp.209-220
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• 1994

In this paper, we study the timing and equipment of replacement. Those affect both available possibility and technological levels of new equipments in the future. These problems are classified according to technological levels and in consequence generated four circumstance. Models are formulated in this research. These are able to make us decision which we replace equipment at the first time. A method is suggested to find the optimal age for replacement at given each circumstance. A solution procedure and numerical example are given.

• 한국국방경영분석학회지
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• 제15권1호
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• pp.54-62
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• 1989

This paper presents a corrective maintenance model to determine either type of maintenance actions upon failure of the system. Types of maintenance actions considered are minimal repair and replacement. Minimal repair cost is assumed to be random, whereas replacement cost is fixed. A policy, B(t), which determines the type of maintenance action based on the estimated minimal repair cost when the system fails at time t is adopted. To obtain an optimal policy, an expected maintenance cost per unit time is derived and is minimized with respect to B(t).

• 품질경영학회지
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• 제19권2호
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• pp.78-85
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• 1991

In this paper, an inspection and replacement policy in a redundant system is considered. It is assumed that the state of the redundant system is known by inspection. When the system is inspected, it is preventively replaced only if the number of failed units exceeds the predetermined limit. Otherwise, the system is inspected after a inspection interval which depends on the number of failed units. We obtain the optimal number of redundant units, inspection intervals and replacement limit minimizing the expected cost rate.

• 한국국방경영분석학회지
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• 제3권1호
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• pp.109-114
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• 1977

There are some factors which cause the profits from the production to be decreased or increased. They are, for example, the rise in efficiency of production facilities resulting from the development of the scientific technique, the changes of purchase price of those, and the drop in efficiency of those owing to there long-term operation. In this connection, an manager can get the highest profit by deciding the proper time of new facilities replacement for those in operation or in being planned, which leads to good management planning of his manufactaring business for a given period or a long time. Main purpose of this is the study of how we decide the optimal time or facilities replacement in order to maximize the total profits for a given period by considering them as continous function as to the time in the case where a machineng is set. The results are following: 1. The definition of profit function is in duced in consideration of the breakdowns caused from continous operation of the machinery. 2. The necessary conditions are obtained for the optimal time of replacement and find out the methods of its solution. 3. Comparing between the 'Short cut' method and method in this paper, we obtained that our method is more realistic.

• Journal of the Korean Data and Information Science Society
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• 제22권4호
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• pp.775-784
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• 2011

본 논문에서는 비재생무료교체-수리보증이 종료된 이후의 수리가 가능한 시스템에 대한 주기적인 예방보전모형을 고려한다. 이러한 예방보전모형에 대하여 기대순환길이, 총기대비용 그리고 단위시간당 기대비용을 각각 유도하고자 한다. 또한 유도된 단위시간당 기대비용을 최소화하는 최적의 예방 보전주기와 예방보전횟수를 결정하는 방법에 대하여 자세히 설명한다. 끝으로 고장시간이 와이블분포를 따르는 경우에 최적의 주기적 예방보전정책을 결정하여 본다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2021년도 학술발표회
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• pp.145-145
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• 2021

Water distribution networks (WDNs) are designed to satisfy water requirement of an urban community. One of the central issues in human history is providing sufficient quality and quantity of water through WDNs. A WDN consists of a great number of pipelines with different ages, lengths, materials, and sizes in varying degrees of deterioration. The available annual budget for rehabilitation of these infrastructures only covers part of the network; thus it is important to manage the limited budget in the most cost-effective manner. In this study, a novel pipe replacement scheduling approach is proposed in order to smooth the annual investment time series based on a life cycle cost assessment. The proposed approach is applied to a real WDN currently operating in South Korea. The proposed scheduling plan considers both the annual budget limitation and the optimum investment on pipes' useful life. A non-dominated sorting genetic algorithm is used to solve a multi-objective optimization problem. Three decision-making objectives, including the minimum imposed LCC of the network, the minimum standard deviation of annual cost, and the minimum average age of the network, are considered to find optimal pipe replacement planning over long-term time period. The results indicate that the proposed scheduling structure provides efficient and cost-effective rehabilitation management of water network with consistent annual budget.

• Communications for Statistical Applications and Methods
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• 제18권6호
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• pp.697-705
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• 2011

본 논문에서는 수리가 가능한 시스템에 대하여 무료 재생교체-비재생수리보증이 종료된 이후의 최적의 교체정책을 제안한다. 이를 위해서, 무료재생교체-비재생수리보증을 정의하고, 사용자 측면에서 무료재생교체-비재생수리보증이 종료된 이후의 보전모형을 고려한다. 최적의 보전정책을 결정하기 위한 기준으로는 사용자 측면의 단위시간당 기대비용을 사용하는데, 이러한 단위시간당 기대비용을 구하기 위해서 사용자측면의 기대순환길이와 총기대비용을 각각 유도한다. 끝으로 본 논문에서 제안된 무료 재생교체-비재생수리 보증이 종료된 이후의 최적의 교체정책을 설명하기 위해서 수치적 예를 살펴본다.

• 한국경영과학회:학술대회논문집
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• 한국경영과학회 1997년도 추계학술대회발표논문집; 홍익대학교, 서울; 1 Nov. 1997
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• pp.193-196
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• 1997

In this paper we consider a Bayesian theoretic approach to periodic incomplete preventive maintenance with minimal repair at failure. We assume that the system failure rate is increasing as the frequency of PM increases and that the system is replaced at the K-th PM under this maintenance strategy. The optimal policies which minimize the expected cost rates are discussed. We seek the optimal periodic PM interval x and replacement time K under a Weibull failure intensity. Assuming suitable prior distribution for the Weibull parameters, we derive the posterior distribution incorporating failure data and obtain the updated optimal replacement strategies.

• 대한산업공학회지
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• 제33권2호
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• pp.273-281
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• 2007

The decision of how long performing system burn-in must be answered with a probabilistic model of a system lifetime at which infant mortality failures created during assembly processes are quantified. In this paper, we propose such a model which is modified from previous results. Using the system model, we derived system reliability in terms of component and system burn-in times for the two cases of minimal repair at system failure and of component replacement and connection repair at their failure times. The procedure is illustrated with a bridge system and the optimal system burn-in times are obtained for maximizing system reliability. The result suggests that an assumption of minimal repair at system failure may underestimate the optimal burn-in time in practice.

• 대한산업공학회지
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• 제22권4호
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• pp.651-662
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• 1996

This paper concerns with preventive replacement under periodic inspections for an item (system) which is in a state of preparedness. The item is subject to wear. The item fails randomly but the failure rate depends on the accumulated wear. The item is preventively replaced if it survives a certain wear limit at periodic inspections. The foiled item is, however, replaced at periodic inspections. Given the costs for replacements and inspections, and the penalty cost of the time elapsed between failure und its detection, the optimal wear limit according to the long-run expected cost per unit time criterion is derived. It has been proved that the optimal wear limit is unique if an item has increasing weer-dependent failure rate. A numerical example for a stationary gamma wear process with Weibull distributed failure is given to show its applicability.