• 대한안전경영과학회지
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• 제17권1호
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• pp.93-101
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• 2015

The demand from customers on better products and systems seems to be ever increasing. To meet the demand, the systems are becoming more and more complicated in terms of both scale and functionality, thereby requiring enormous effort in the development. One bright spot of this trend is that such effort has been the driving forces of the remarkable advancement in modern systems development. On the other hand, safety issues appear to be critical in many large-scale systems such as transportation and weapon systems including high-speed trains, airplanes, ships, missiles/rockets launchers, and so on. Such systems turn out to be prone to a variety of faults and thus the resultant failure can cause disastrous accidents. For the reason, they can be referred to as safety-critical systems. The systems failure can be attributed to either random or systemic factors (or sometimes both). The objective of this paper is on how to reduce potential systemic failure in safety critical systems. To do so, a proper system design is pursued to minimize the risk of systemic failure. A focus is placed on the fact that complex systems have a lot of complicated interfaces among the system elements. To effectively handle the sources of hazards at the complicated interfaces and resultant failure, a method is developed by utilizing a design structure matrix. As a case study, the developed method is applied in the design of train control systems.

• 대한토목학회논문집
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• 제11권3호
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• pp.59-65
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• 1991

본 연구에서는 국내 고속도로의 표준단면들을 포함한 포장구조 해석모델을 사용하여 아스팔트 콘크리트 포장체의 피로파괴 기준식을 개발하였다. 해석 대상 모델은 쇄석 및 아스팔트 안정처리 기층을 갖는 2430개의 4충 포장구조로 하였으며, 각 모델의 물성을 공용성 한계를 PSI=2.5로 한 AASHTO 설계식과 다층 탄성해석 프로그램인 SINELA에 적용, 포장체의 통과예상 교통량과 아스팔트 콘크리트층 하단에서의 최대 인장 변형률과의 관계를 회귀분석하였다. 분석 결과로부터, 신뢰도 50%와 95% 수준의 파괴기준식을 제안하였다. 타 연구결과와 비교한 결과 신뢰도 95% 수준의 파괴기준식은 균열의 발생을 공용성 한계로 보는 기존의 피로 파괴기준식과 같은 정도의 교통량을 추정하고 있음을 알 수 있었다. 또한 신뢰도 수준에 따른 파괴기준식을 신뢰도 50%, 수준의 파괴기준식으로부터 간접 추정할 수 있는 관계식을 제안하였다.

• 한국군사과학기술학회지
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• 제14권5호
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• pp.859-870
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• 2011

The purpose of this paper is to develop reliability analysis procedures for repairable systems with interval failure time data and apply the procedures for assessing the storage reliability of a subsystem of a certain type of guided missile. In the procedures, the interval failure time data are converted to pseudo failure times using the uniform random generation method, mid-point method or equispaced intervals method. Then, such analytic trend tests as Laplace, Lewis-Robinson, Pair-wise Comparison Nonparametric tests are used to determine whether the failure process follows a renewal or non-renewal process. Monte Carlo simulation experiments are conducted to compare the three conversion methods in terms of the statistical performance for each trend test when the underlying process is homogeneous Poisson, renewal, or non-homogeneous Poisson. The simulation results show that the uniform random generation method is best among the three. These results are applied to actual field data collected for a subsystem of a certain type of guided missile to identify its failure process and to estimate its mean time to failure and annual mean repair cost.

• 한국안전학회지
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• 제26권4호
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• pp.7-13
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• 2011

A study on reliability estimation of sequential-ordered multiple failure modes, which are sequentially ordered between failure modes in a considering system, was performed. Especially, an approach to estimate the probabilities of failure modes has been proposed under an assumption that failure modes are mutually exclusive and sequentially ordered by only a critical variable. A feasibility of the proposed approach were studied by a practical example, which is a reliability estimation of passive safety systems for a probabilistic safety assessment(PSA) of a very high temperature reactor(VHTR) that is under development as a future nuclear system with enhanced safety features. It is difficult to define a robust failure state of this nuclear system because of its enhanced radiation release characteristics, so the new approach is a useful concept to estimate not only its safety but also a PSA. A feasibility study applied two failure modes(e.g., small and large release of radioactive materials) with considering the integrated behavior of this nuclear system. It is expected that the multiple release states for a practical estimation can be easily extended to the aforementioned example. It was found out that the proposed approach was a useful technique to cover the unfavorable features of this nuclear system as to performing a VHTR PSA.

• Journal of Chest Surgery
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• 제27권2호
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• pp.122-127
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• 1994

A retrospective study of 737 consecutive patients surviving the first 24 hours who underwent valve replacement surgery from July 1980 to June 1993 was undertaken to determine the prevalence, variables that could be used to predict outcome and results of therapy for postoperative acute renal failure[ARF]. Twenty-one patients[2.8 %] developed acute renal failure. Positive risk factors noted in the development of postoperative renal failure included age, New York Heart Association class III & IV, endocarditis and elevated preoperative concentration of serum creatinine. The duration of cardiopulmonary bypass, aortic cross-clamping and the total duration of the operation also closely correlated with the incidence of ARF. The mortality rate for established ARF was 38.1% and ARF was associated with a significant increase in the length of hospitalization, ventilator support and intensive care unit stay. The incidence and mortality rate of oliguric renal failure was 38.1% and 85.7%. The highest mortality rate was associated with two or more postoperative complications and serum creatinine value exceeded 5 mg/dl. We concluded that therapy should be aimed at prevention of oliguric renal failure, or at least its conversion to nonoliguric renal failure, and early institution of renal replacement therapy with intensive support probably gives the best chance for survival.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1988년도 학술세미나 강연집
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• pp.3-67
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• 1988

Model studies on the response of homgeneous earth embankment dams subjected to strike-slip fault movement have been penomed via centrifuge and finite element analysis. The centrifuge model tests have shown that crack development in earth embankment experiences two major patters: shear failure deep inside the embankment and tension failure near the surface. The shear rupture zone develops from the base level and propagates upward continuously in the transverse direction but allows no open leakage chnnel. The open tensile cracks develop near the surface of the embankment, but they disappear deep in the embankment. The functional relationship has been developed based on the results of the centrifuge model tests incorporating tile variables of amount of fault movement, embankment geometry, and crack propagation extent in earth des. This set of information can be used as a guide line to evaluate a "transient" safety of the duaged embankment subjected to strike-slip fault movement. The finite element analysis has supplemented the additional expluations on crack development behavior identified from the results of the centrifuge model tests. The bounding surface time-independent plasticity soil model was employed in the numerical analysis. Due to the assumption of continuum in the current version of the 3-D FEM code, the prediction of the soil structure response beyond the failure condition was not quantitatively accurate. However, the fundamental mechanism of crack development was qualitatively evaluated based on the stress analysis for the deformed soil elements of the damaged earth embankment. The tensile failure zone is identified when the minor principal stress of the deformed soil elements less than zero. The shear failure zone is identified when the stress state of the deformed soil elements is at the point where the critical state line intersects the bounding surface.g surface.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.649-658
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• 2009

The Aim of this development is the safety management network of embankment facilities using forecasting analysis algorism. Using this algorithm it is possible to predict a failure of embankment facilities in advance. therefore, it is necessary for making plans of a safety countermove. In this development we have researched the analysis method which could operate effectively the embankment facilities using real-time monitoring data from a remote sensing system and the safety managerial program using the algorithm from the analysis method developed.

• 산업공학
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• 제19권1호
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• pp.19-25
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• 2006

In the development process, the objective of a reliability growth program is to track the increase in system reliability, and determine as early as possible whether or not the system reliability is growing at a sufficient rate to meet the required goal and allocate available resources accordingly. Implementation of this kind of program will provide very useful information on concept selection, product/process reliability, and cost effectiveness without too much time, money and engineering effort being spent on the development of failure suspect parts. The purpose of this research is to present a practical method for efficiently monitoring a reliability growth test process using AMSAA(Army Materiel Systems Analysis Activity) reliability growth model. The presented growth management is a viable method for identifying failure modes, incorporating design changes and monitoring reliability progress on an on-going basis during the early stages of a product development program.

• Communications for Statistical Applications and Methods
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• 제16권5호
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• pp.871-880
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• 2009

Recently, there has been much development on burn-in models in reliability area. Especially, the previous burn-in models have been extended to more general cases. For example, (i) burn-in procedures for repairable systems have been developed (ii) an extended assumption on the failure rate of the system has been proposed and (iii) a stochastic model for burn-in procedure in accelerated environment has been developed. In this paper, recent extensions and advances in burn-in models are introduced and some issues to be considered in the future study are discussed.

• 대한방사선기술학회지:방사선기술과학
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• 제9권1호
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• pp.131-135
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• 1986

The reciprocity law failure of the blue sensitive screen-film system was treasured, by authors. As a result, it has been found that reciprocity law failure is mote likely to occur at lower exposure, lower density and higher development temperature.