• 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.

• Industrial Engineering and Management Systems
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• 제3권2호
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• pp.134-139
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• 2004

During the last three decades, a few attentions have been paid for investigating the cost distribution for the optimal maintenance problems. In this article, we derive the moment of the discounted cost distribution over an infinite time horizon for the basic age replacement problem. With first two moments of the discounted cost distribution, we approximate the underlying distribution function by three theoretical distributions. Through a Monte Carlo simulation, we conclude that the log-normal distribution is the best fitted one to approximate the discounted cost distribution.

• 산업경영시스템학회지
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• 제29권3호
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• pp.135-142
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• 2006

Engineers are always concerned with life cycle costs for making important economic decisions through engineering action like reliability of products. Decisions during the reliability growth development of products involve trade-offs between invested costs and its returns. In order to find minimal LCC containing the reliability improvement cost, production cost, repair and replacement costs, and holding cost of spare parts for failure items we suggest in this paper relationship between development cost and sustaining cost in values of growth parameter $\beta$ of AMSAA model. This model is applied to the reliability growth program based on AMSAA model during R&D phase, the warranty activities of items and the block replacement policy for maintenance of items in avionic equipment.

• 한국국방경영분석학회지
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• 제33권1호
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• pp.19-29
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• 2007

본 연구는 최적의 정비주기 산정을 위해 공군의 항공기 정비정보체계(AMMIS, Aircraft Maintenance Management Information System) 및 상태검사의 데이터 분석을 통하여 항공기 부품 신뢰도 분석평가체계를 개발하기 위한 개념설정 및 운영방안에 대한 내용이다. 항공기부품의 고장자료를 선별하여 추출한 후 신뢰도 소프트웨어를 활용해 정비주기를 개선하고 상태검사시 측정한 고장 추세를 통계 소프트웨어로 분석하여 검사 주기를 재설정하는 방법을 통해 항공기 부품 신뢰도 분석평가체계의 운영 모델을 제시한다.

• 한국안전학회지
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• 제14권2호
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• pp.155-162
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• 1999

reliability from components reliability. In this case, it assumes that components failure is mutually independent, but it may not true in real systems. In this study, the mean cost per unit time is computed as the ratio of mean life to the mean cost. The mean life is obtained by the reliability function under power rule model. The mean cost is obtained by the mathematical model based on the inspection interval. A heuristic method is proposed to determine the optimal number of redundant units and the optimal inspection interval to minimize the mean cost per unit time. The assumptions of this study are as following : First, in the load-sharing k-out-of-n:G system, total loads are applied to the system and shared by the operating components. Secondly, the number of failed components affects the failure rate of surviving components as a function of the total load applied. Finally, the relation between the load and the failure rate of surviving components is set by the power rule model. For the practical application of the above methods, numerical examples are presented.

• 한국품질경영학회:학술대회논문집
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• 한국품질경영학회 1998년도 The 12th Asia Quality Management Symposium* Total Quality Management for Restoring Competitiveness
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• pp.269-276
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• 1998

This paper proposes an opportunistic age replacement policy. The system has two types of failures. Type I failures (minor failures) are removed by minimal repairs, whereas type II failures are removed by replacements. Type I and type II failures are age-dependent. A system is replaced at type II failure (catastrophic failure) or at the opportunity after age T, whichever occurs first. The cost of the minimal repair of the system at age z depends on the random part C(z) and the deterministic part c(z). The opportunity arises according to a Poisson process, independent of failures of the component. The expected cost rate is obtained. The optimal $T^{\ast}$ which would minimize the cost rate is discussed. Various special cases are considered. Finally, a numerical example is given.

• Nuclear Engineering and Technology
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• 제56권4호
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• pp.1472-1479
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• 2024

Cyber-Physical Energy Systems (CPESs) integrate cyber and hardware components to ensure a reliable and safe physical power production and supply. Renewable Energy Sources (RESs) add uncertainty to energy demand that can be dealt with flexible operation (e.g., load-following) of CPES; at the same time, scenarios that could result in severe consequences due to both component stochastic failures and aging of the cyber system of CPES (commonly overlooked) must be accounted for Operation & Maintenance (O&M) planning. In this paper, we make use of Deep Reinforcement Learning (DRL) to search for the optimal O&M strategy that, not only considers the actual system hardware components health conditions and their Remaining Useful Life (RUL), but also the possible accident scenarios caused by the failures and the aging of the hardware and the cyber components, respectively. The novelty of the work lies in embedding the cyber aging model into the CPES model of production planning and failure process; this model is used to help the RL agent, trained with Proximal Policy Optimization (PPO) and Imitation Learning (IL), finding the proper rejuvenation timing for the cyber system accounting for the uncertainty of the cyber system aging process. An application is provided, with regards to the Advanced Lead-cooled Fast Reactor European Demonstrator (ALFRED).

• 한국항해항만학회지
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• 제30권6호
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• pp.525-531
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• 2006

항만에 있어서 하역장비는 매우 중요하다. 컨테이너 크레인이나 트랜스퍼 크레인 같은 장비가 고장이 나면 수리나 예비품의 재주문에 걸리는 시간동안 작업이 이루어지지 못하므로 엄청난 비용손실을 초래한다. 그러나 가격이 고가이므로 예비품을 많이 보유할 수도 없는 형편이다. 대체적으로 부피가 크고 고가인 항만 장비의 특성상 효율적인 예방정비와 고장 분석을 통해 장비의 신뢰성을 확보하는 것이 무엇보다 필요하다. 본 연구는 항만 장비 중 주요 장비인 트랜스퍼 크레인을 선정하여 시스템 및 기능, 고장 메카니즘을 분석하였으며, 고장/정비 이력 데이터의 수집 및 정리를 통하여 고장과 정비 작업의 내용을 표준화하였다. 장비의 운영 및 정비 작업을 전산화하기 위한 기초 작업인 본 연구는 다음 세대 장비의 최적 설계와 장비의 최적 운영 정책을 설계하는 새로운 시도가 될 것이다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 춘계학술대회 및 창립 30주년 심포지엄(논문집)
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• pp.363-366
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• 2006

항만에 있어서 하역장비는 매우 중요하다. 컨테이너 크레인이나 트랜스퍼 크레인 같은 장비가 고장이 나면 수리나 재주문에 걸리는 시간동안 작업이 이루어지지 못하므로 엄청난 비용손실을 초래한다. 그러나 가격이 고가이므로 예비품을 많이 보유할 수도 없는 형편이다. 대체적으로 부피가 크고 고가인 항만 장비의 특성상 효율적인 예방정비와 고장 분석을 통해 장비의 신뢰성을 확보하는 것이 무엇보다 필요하다. 본 연구는 항만 장비 중 주요 장비인 트랜스퍼 크레인을 선정하여 시스템 및 기능, 고장 메카니즘을 분석하였으며, 고장/정비 이력 데이터의 수집 및 정리를 통하여 고장과 정비 작업의 내용을 표준화하였다. 장비의 운영 및 정비 작업을 전산화하기 위한 기초 작업인 본 연구는 다음 세대 장비의 최적 설계와 장비의 최적 운영 정책을 설계하는 새로운 시도가 될 것이다.

• The Korean journal of internal medicine
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• 제39권3호
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• pp.469-476
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• 2024

Background/Aims: The reimbursement policy for cryptogenic stroke (CS) was expanded in November 2018 from recurrent strokes to the first stroke episode. No reports have demonstrated whether this policy change has affected trends in implantable loop recorder (ILR) utilization. Methods: We identified patients who received an ILR implant using the Korea Health Insurance Review and Assessment Service database between July 2016 and October 2021. Patients meeting all the following criteria were considered to have CS indication: 1) prior stroke history, 2) no previous history of atrial fibrillation or flutter (AF/AFL), and 3) no maintenance of oral anticoagulant for ≥4 weeks within a year before ILR implant. AF/AFL diagnosed within 3 years after ILR implant or before ILR removal was considered ILR-driven. Results: Among 3,056 patients, 1,001 (32.8%) had CS indications. The total ILR implant number gradually increased for both CS and non-CS indications and the number of CS indication significantly increased after implementing the expanded reimbursement policy. The detection rate for AF/AFL was 26.3% in CS patients over 3 years, which was significantly higher in patients implanted with an ILR within 2 months after stroke than those implanted later. Conclusions: The expanded coverage policy for CS had a significant impact on the number of ILR implantation for CS indication. The diagnostic yield of ILR for AF/AFL detection seems better when ILR is implanted within 2 months than later. Further investigation is needed to demonstrate other clinical benefits and the optimal ILR implantation timing.