• 시스템엔지니어링학술지
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• 제12권2호
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• pp.47-57
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• 2016

As the inventory costs of repairable items in military logistics continue to increase, many studies for optimal inventory level of these items are being carried out in advanced countries, including the US, to reduce these costs. Research on inventory level optimization for repairable items aimed to achieve the availability goal of a system with a MIME(Multi Indenture Multi Echelon) repair policy structure first began with Sherbrooke's METRIC and developed into various types. This research is to analyze and compare recent V-METRIC related studies to search for another variation in this field. This paper mainly looks at how to determine optimum inventory level for each repairable item to achieve a specific availability target within a limited budget, and also how to minimize inventory cost while achieving its availability target by determining optimal inventory level of each repairable item.

• 한국신뢰성학회지:신뢰성응용연구
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• 제4권2호
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• pp.91-104
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• 2004

In this paper we consider the concurrent spare part(CSP) requirements problem of new equipment system. When a part fails, the part is replaced and the repair of failed part is impossible and cannibalization is allowed. We assume that the failure of a part knows a Poisson process. The operational availability concept in CSP is defined, and derive a formula to calculate the operational availability using expected machine operating time during CSP period. A mathematical model is derived for making an CSP requirement determination subject to the constraint of satisfying any given operational availability limitation and an heuristic solution search procedure is derived. An illustrative example is shown to explain the solution procedure.

• 한국정보처리학회논문지
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• 제7권3호
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• pp.745-755
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• 2000

In designing distributed databases, DAP(Data Allocation Problem) is one of the key design issues. Because, however, most of previous researches on DAP have considered only cost aspect, they cannot increase the performance and availability and they are not proper to the system requiring high-availability or real-time processing. Therefore, we need a more formal data allocation model considering multiple aspects. In this paper, we propose the MAPN (Multiple Aspects Petri Net) modeling method for the distributed transaction modeling. The MAPN model, an extended classical petri net, is proposed for the formal modeling considering multiple aspects (cost, performance and availability) concurrently. We demonstrate that we can compose the valid DAP evaluation model considering not only cost but also performance and availability concurrently by using the MAPN structure and MAPN graph.

• 시스템엔지니어링학술지
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• 제12권1호
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• pp.105-112
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• 2016

An aircraft must be designed to minimize system failure rate for obtaining the aircraft safety, because the aircraft system failure causes a fatal accident. The safety of the aircraft system can be predicted by analyzing availability, reliability, and maintainability of the system. In this study, the reliability and the maintainability of the hydraulic system are analysed except the availability, and therefore the reliability and the maintainability analysis process and the results are presented for a helicopter hydraulic system. For prediction of the system reliability, the failure rate model presented in MIL-HDBK-217F is used, and MTBF is calculated by using the Part Stress Analysis Prediction and quality/temperature/environmental factors described in NPRD-95 and MIL-HDBK-338B. The maintainability is predicted by FMECA(Failure Mode, Effect & Criticality Analysis) based on MIL-STD-1629A.

• 한국철도학회논문집
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• 제7권3호
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• pp.271-277
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• 2004

This paper is concerned with the reliability centered maintenance (RCM) of the Automated Guideway Transit (AGT) vehicle system. Korea Railroad Research Institute (KRRI) has developed the AGT vehicle system from 1999 to 2004. The provisions for a specific maintenance system including RAMS (reliability, availability, maintainability & safety) of AGT vehicle system is necessary for maintaining good operation conditions. RCM is a process used to determine what must be done to ensure that any system continues to do whatever its users want it to do in its present operating conditions. Therefore, we introduce RCM in details and describe how RCM should be applied to AGT vehicle system on Gyeong-San test line. Analyses to approach RCM to AGT vehicle system are demonstrated in the seven steps that contain each main task and detailed operating conditions.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 B
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• pp.1288-1290
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• 2003

The maintenance CALS system for car of urban transit is a part of standardization and development of urban transit system, and We have been performed the establishment of maintenance CALS system from 2001 to 2005. The RAMS for management computerization system are utilized in a variety of CALS system for user's convenience and safety in maintenance. Ever since its inception though, the urban transit has searched for ways to improve reliability, availability, maintainability and safety of the railway subsystem. In this paper, This system include RAMS(reliability, availability, maintainability and safety) and expert system of the vehicles shall be enhanced in the future.

• 한국항공우주학회지
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• 제36권8호
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• pp.761-766
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• 2008

본 논문에서는 사용자 위치결정에 널리 사용되는 GPS를 일본의 QZSS (Quasi-Zenith Satellite System)과 결합하여 서울 도심지역에서의 위성항법시스템의 가용도 및 DOP (Dilution Of Precision)성능을 분석하였다. QZSS 궤도 파라메터를 이용한 궤도 시뮬레이터를 구현하였다. 3D GIS 수치지도를 기반으로 서울 도심의 3차원 모델을 생성하고, 위성 관측 알고리즘을 이용하여 구성한 가시위성 시뮬레이션 시스템에 대해 기술하였다. 서울 도심지에서 GPS와 QZSS의 결합을 통한 가용도와 DOP 성능 향상을 보였다.

• 시스템엔지니어링학술지
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• 제10권1호
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• pp.33-41
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• 2014

New design concept of Reactor Coolant System (RCS) including a reactor assembly for the SMR is introduced in this work. An exploration of new type of reactor that is advanced from proposed SMRs is performed by using systems engineering approach. In this point of view project structured on three main phases; needs analysis (NA), concept exploration (CE), and concept definition (CD). Main objectives as an output of the CE stage are a small size, low cost, shortening the schedule, and enhancing safety. The SMRs usually have a small size requirement. In order to meet the size requirement and to achieve a productivity, in other words, easiness to manufacture, this paper suggests an integrated PWR design concept through researching predecessors. Although the integrated PWR concept provides many advantages, it has disadvantages that composite of maintenance and a low availability problem. Therefore, this paper comes up with a run-to-fail design concept based on modular design to address the maintenance problem and to maximize the availability of SMRs as well as to be compatible with the overall-SMRs including Barge Mounted(BM)type.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 춘계학술대회 논문집
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• pp.515-520
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• 1998

In this paper, we propose a new fault tolerant architecture for high availability systems, where for module internal operations both processor modules perform the same tasks at the same time independently of each other while for module external operations both processor modules act actively. That is, operations of synchronization between dual processor modules except clock synchronization are requested only when module external operations are executed. The architecture can not only improve system availability by reducing system reintegration time but also reduce performance degradation problem due to frequent synchronization between dual processor modules. The clock unit consists of a clock generator and a clock synchronization circuit. This supplies a stable clock signal under clock unit disorder of any processor module or rapid clock signal variation. And this architecture achieves system availability and data credibility by designing as symmetrical form.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권5호
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• pp.2396-2413
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• 2018

Trust management is one of the most challenging issues for the highly heterogeneous Internet of Things (IoT). In the context of the IoT, it is difficult to evaluate the node's trustworthiness in the same trust model when a node provides different services. Guaranteeing the availability of the trust management service is another significant challenge because of the dynamic nature of IoT environments. With these issues in mind, this paper propose a robust and adaptive trust management system for the IoT that is able to measure the trustworthiness of nodes based on feedbacks collected from participants in a specific context and ensure the availability of trust management services. The main contributions of our system are: 1) Proposing a partly decentralized trust management framework, which improves the resiliency of the trust mechanism; 2) Proposing an adaptive trust evaluation scheme and a three-dimensional context representation makes trust evaluation more accurate and specific; 3) Enhancing the adaptive trust evaluation scheme by incorporating a bad behavior factor in trust estimation, which efficiently distinguishes misleading feedbacks from On-Off attacks. Simulation results show the good performance of the proposed system and especially show effectiveness against On-Off attacks compared to other trust mechanisms.