• Journal of the Korean Society of Safety
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• v.39 no.2
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• pp.75-86
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• 2024

Hydrogen has been selected as one of the key technologies for reducing CO₂ emissions to achieve carbon neutrality by 2050. However, hydrogen safety issues should be fully guaranteed before the commercial and widespread utilization of hydrogen. Here, a bow-tie risk assessment is conducted for the hydrogen fuel supply system in a gas turbine power plant, which can be a mass consumption application of hydrogen. The bow-tie program is utilized for a qualitative risk assessment, allowing the analysis of the causes and consequences according to the stages of accidents. This study proposed an advanced bow-tie method, which includes the barrier criticality matrix and visualized maps of quantitative risk reduction. It is based on evaluating the importance of numerous barriers for the extent of their impact. In addition, it emphasizes the prioritization and concentrated management of high-importance barriers. The radar chart of a bow tie allows the visual comparison of risk levels before/after the application of barriers (safety measures). The risk reduction methods are semi-quantitatively analyzed utilizing the criticality matrix and radar chart, and risk factors from multiple aspects are derived. For establishing a secure hydrogen fuel storage system, the improvements suggested by the bow-tie risk assessment results, such as 'Ergonomic equipment design to prevent human error' and 'Emergency shutdown system,' will enhance the safety level. It attempts to contribute to the development and enhancement of an efficient safety management system by suggesting a method of calculating the importance of barriers based on the bow-tie risk assessment.

• Aerospace Engineering and Technology
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• v.4 no.2
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• pp.71-78
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• 2005

The purpose of FMECA is to identify parts and design whose damage can effect the mission performance and to improve the spacecraft design using these data. In consequence of this analysis, each failure mode which can be happened during operation and manufacturing period is identified, and their effects on mission performance are reviewed. In this technical report, the FMECA procedures and results for the satellite which is now under development are showed.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1991.10a
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• pp.29-32
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• 1991

It is well known that the fatigue damage process in composite materials is very complicated due to complex failure mechanisms that comprise debounding, matrix cracking, delamination and fiber splitting of laminates. Therefore, the residual strength, instead of a single dominant crack length, is chosen to describe the criticality of the damage accumulated in the sublaminate. In this study, two models for residual strength degradation established by Yang-Liu and Tanimoto-Ishikawa that are capable of predicting the statistical distribution of both fatigue life and residual strength have been investigated and compared. Statistical methodologies for fatigue life prediction of composite materials have frequently been adopted. However, these are usually based on a simplified probabilistic approach considering only the variation of fatigue test data. The main object of this work is to propose a fatigue reliability analysis model which accounts for the effect of all sources of variation such as fabrication and workmanship, error in the fatigue model, load itself, etc. The proposed model is examined using the previous experimental data of GFRP and it is shown that it can be practically applied for fatigue problems in composite materials.

• Journal of the Korean Society of Systems Engineering
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• v.12 no.1
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• pp.41-58
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• 2016

Reliability Centered Maintenance (RCM) introduces a systematic method and decision logic tree for utilizing previous operating experience focused on reliability and optimization of maintenance activities. In this paper RCM methodology is applied on safety injection system for APR-1400. Functional Failure Mode Effects and Criticality Analysis (FME&CA) are applied to evaluate the failure modes and the effect on the component, system and plant. Logic Tree Analysis (LTA) is used to determine the optimum maintenance tasks. The results show that increasing the condition based maintenance will reduce component failure and improve reliability and availability of the system. Also the extension of the surveillance test interval of Safety Injection Pumps (SIPs) would lead to an improved pump's availability, eliminate the unnecessary maintenance tasks and this will optimize maintenance activities.

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1464-1478
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• 2021

Selective Production of Exotic Species is an innovative plant for advanced nuclear physic studies. A radioactive beam, generated by using an UCx target-ion source system, is ionized, selected and accelerated for experimental objects. Very high vacuum conditions and appropriate safety systems to storage exhaust gases are required to avoid radiological risk for operators and people. In this paper, Failure Mode, Effects, and Criticality Analysis of a preliminary design of high activity gas recovery system is performed by using a modified Fuzzy Risk Priority Number to rank the most critical components in terms of failures and human errors. Comparisons between fuzzy approach and classic application allow to show that Fuzzy Risk Priority Number is able to enhance the focus of risk assessments and to improve the safety of complex and innovative systems such as those under consideration.

• Journal of the Korean Society for Railway
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• v.9 no.6 s.37
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• pp.739-745
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• 2006

The role of maintenance in railway is going to be extended to improve the reliability of railway system in the aspect of Asset management gradually. In this paper, the meaning of reliability and safety in RCM which has been applied in order to improve the efficiency of maintenance is deduced. And the analysis task of reliability and safely which has been recommended in railway standards such as EN50126 and IEC62278 is reviewed in the aspect of RCM. Finally, the several ways are proposed to apply RCM to railway system through the comparison between the RCM procedure and the analysis procedure for the reliability and safety in railway standards. Hereafter, if the analysis of reliability and safety is performed with the concept of RCM in the beginning of railway business, it will be more efficient to improve the reliability and manage the railway asset.

• Journal of Applied Reliability
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• v.10 no.2
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• pp.93-105
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• 2010

The following thesis provides an explanation for the definition of the MIL-HDBK-2155 : Failure Reporting, Analysis and Corrective Action System (FRACAS), which systemizes the collection and analysis of failure data and the feedback process of the results. It also presents a plan based on MIL-HDBK-2155 for the collection and analysis of operating specifications on weapon systems. The collection and analysis of failure data and the feedback process utilizing FRACAS contributes to identifying improvement requirements during equipment operation as well as finding and eliminating the root cause of the failures. The objective of applying FRACAS to weapon systems is to receive source data feedback for reliability enhancements and performance improvements during operation. This is done by recognizing weaknesses in the design or operation by identifying the type of failures that might occur, and by performing Failure Modes, Effects and Criticality Analysis(FMECA) and Failure Tree Analysis(FTA).

• Sleep Medicine and Psychophysiology
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• v.14 no.1
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• pp.42-48
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• 2007

Introduction: Detrended fluctuation analysis (DFA) is used as a way of studying nonlinearity of EEG. In this study, DFA is applied on sleep EEG of normal subjects to look into its nonlinearity in terms of EEG channels and sleep stages. Method: Twelve healthy young subjects (age：$23.8{\pm}2.5$ years old, male：female=7：5) have undergone nocturnal polysomnography (nPSG). EEG from nPSG was classified in terms of its channels and sleep stages and was analyzed by DFA. Scaling exponents (SEs) yielded by DFA were compared using linear mixed model analysis. Results: Scaling exponents (SEs) of sleep EEG were distributed around 1 showing long term temporal correlation and self-similarity. SE of C3 channel was bigger than that of O1 channel. As sleep stage progressed from stage 1 to slow wave sleep, SE increased accordingly. SE of stage REM sleep did not show significant difference when compared with that of stage 1 sleep. Conclusion: SEs of Normal sleep EEG showed nonlinear characteristic with scale-free fluctuation, long-range temporal correlation, self-similarity and self-organized criticality. SE from DFA differentiated sleep stages and EEG channels. It can be a useful tool in the research with sleep EEG.

• Journal of the Korea Safety Management & Science
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• v.2 no.4
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• pp.91-102
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• 2000

Nowadays, every kind of system is changed so complex and enormous, it is necessary to assure system reliability, product liability and safety. Fault tree analysis(FTA) is a reliability/safety design analysis technique which starts from consideration of system failure effect, referred to as “top event”, and proceeds by determining how these can be caused by single or combined lower level failures or events. So in fault tree analysis, it is important to find the combination of events which affect system failure. Minimal cut sets(MCS) and minimal path sets(MPS) are used in this process. FTA-I computer program is developed which calculates MCS and MPS in terms of Gw-Basic computer language considering Fussell's algorithm. FTA-II computer program which analyzes importance and function cost of VE consists. of five programs as follows : (l) Structural importance of basic event, (2) Structural probability importance of basic event, (3) Structural criticality importance of basic event, (4) Cost-Failure importance of basic event, (5) VE function cost analysis for importance of basic event. In this study, a method of initiation such as failure, function and cost in FTA is suggested, and especially the priority rank which is calculated by computer-aided decision analysis program developed in this study can be used in decision making determining the most important basic event under various conditions. Also the priority rank can be available for the case which selects system component in FMEA analysis.

• Journal of Korean Society of Rural Planning
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• v.25 no.2
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• pp.35-45
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• 2019

This study revises current feasibility evaluation guideline for agricultural infrastructure improvement project considering recent changes in social and economic environment in rural area. We use an AHP(Analytic Hierarchy Process) approach to consider qualitative evaluation items in policy enforcement and balanced regional development as well as quantitative items in current economic analysis in the process of feasibility evaluation and decision making. The criteria system is composed of three level hierarchy. In the first level which consists of economic analysis, policy analysis, and regional development analysis, economic analysis was ranked top with relative weight of 0.45 and regional development analysis the lowest with 0.22. In the second level which consists of three evaluation items under policy analysis, consistency in policy enforcement, risk factors, and special evaluation factors, consistency in policy enforcement was ranked top. Finally, 13 detailed evaluation items in the third level were surveyed and ranked by using a comprehensive criticality vector. The result shows that the three most important evaluation items are 'degree of underdevelopment', 'spill-over effect of regional economy' and 'consistency with related planning and policy direction'.