• 한국안전학회지
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• 제31권4호
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• pp.136-142
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• 2016

The FMEA is a widely used technique to pre-evaluate and avoid risks due to potential failures for developing an improved design. The conventional FMEA does not consider the possible time gap between occurrence and detection of failure cause. When a failure cause is detected and corrected before the failure itself occurs, there will be no other effect except the correction cost. But, if its cause is detected after the failure actually occurs, its effects will become more severe depending on the duration of the uncorrected failure. Taking this situation into account, a risk metric is developed as an alternative to the RPN of the conventional FMEA. The severity of a failure effect is first modeled as linear and quadratic severity functions of undetected failure time duration. Assuming exponential probability distribution for occurrence and detection time of failures and causes, the expected severity is derived for each failure cause. A new risk metric REM is defined as the product of a failure cause occurrence rate and the expected severity of its corresponding failure. A numerical example and some discussions are provided for illustration.

• 한국정보기술응용학회:학술대회논문집
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• 한국정보기술응용학회 2005년도 6th 2005 International Conference on Computers, Communications and System
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• pp.143-146
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• 2005

The software reliability growth depends on the testing time because the failure rate varies whether it is long or not. On the other hand, it might be difficult to reduce failure rate for most of the cases are not available for debugging during operational phase, hence, there are some literatures to study that the failure rate is uniform throughout the operational time. The failure rate reduces and the reliability grows with time regardless of debugging. As a result, the products reliability varies with the time duration of these products in point of customer view. The reason of this is that it accumulates the products experience, studies the exact operational method, and then finds and takes action against the fault circumstances. I propose the simple model to represent this status in this paper.

• Asian Pacific Journal of Cancer Prevention
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• 제16권18호
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• pp.8387-8390
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• 2016

Background: Treatment of biochemical failure after radical prostatectomy for prostate cancer is largely empirically based. The use of PSA kinetics has been used as a guide to determine local or systemic treatment of biochemical failure. We here compared PSA kinetics with detection of bone marrow micrometastasis as methods to determine local or systemic relapse. Materials and Methods: A transversal study was conducted of men with biochemical failure, defined as a serum PSA >0.2ng/ml after radical prostatectomy. Consecutive patients having undergone radical prostatectomy and with biochemical failure were enrolled and clinical and pathological details were recorded. Bone marrow biopsies were obtained from the iliac crest and touch prints made, micrometastasis (mM) being detected using anti-PSA. The clinical parameters of total serum PSA, PSA velocity, PSA doubling time and time to biochemical failure, age, Gleason score and pathological stage were registered. Results: A total of 147 men, mean age $71.6{\pm}8.2years$, with a median time to biochemical failure of 5.5 years (IQR 1.0-6.3 years) participated in the study. Bone marrow samples were positive for micrometastasis in 98/147 (67%) of patients at the time of biochemical failure. The results of bone marrow micrometastasis detected by immunocytochemistry were not concordant with local relapse as defined by PSA velocity, time to biochemical failure or Gleason score. In men with a PSA doubling time of < six months or a total serum PSA of >2,5ng/ml at the time of biochemical failure the detection of bone marrow micrometastasis was significantly higher. Conclusions: The detection of bone marrow micrometastasis could be useful in defining systemic relapse, this minimally invasive procedure warranting further studies with a larger group of patients.

• Structural Monitoring and Maintenance
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• 제2권1호
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• pp.49-64
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• 2015

This paper presents a method for assessing the risk of wave run-up and overtopping of existing coastal defences and for analysing the probability of failure of the structures under future hydraulic conditions. The recent UK climate projections are employed in the investigations of the influence of changing environments on the long-term performance of sea defences. In order to reduce the risk of wave run-up and overtopping caused by rising sea level and to maintain the present-day allowances for wave run-up height and overtopping discharge, the future necessary increase in crest level of existing structures is investigated. Various critical failure mechanisms are considered for reliability analysis, i.e., erosion of crest by wave overtopping, failure of seaside revetment, and internal erosions within earth sea dykes. The time-dependent reliability of sea dykes is analysed to give probability of failure with time. The results for an example earth dyke section show that the necessary increase in crest level is approximately double of sea level rise to maintain the current allowances. The probability of failure for various failure modes of the earth dyke has a significant increase with time under future hydraulic conditions.

• 한국국방경영분석학회지
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• 제25권2호
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• pp.144-157
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• 1999

In this paper, we consider a new preventive replacement policy for the system which deteriorates while it is in operation with an increasing failure rate. The system is subject to two types of failure. A type 1 failure is repairable while a type 2 failure is not repairable. In the new policy, a system is replaced at the age of $t_p$ or at the instant the$\textsc{k}^{th}$ type 1 failure occurs, whichever comes first. However, if a type 2 failure occurs before a preventive replacement is performed, a failure replacement should be made. We assume that a type 1 failure can be rectified with a minimal repair. We also assume that a replacement takes a non-negligible amount of time while a minimal repair takes a negligible amount of time. Under a cost structure which includes a preventive replacement cost, a failure replacement cost and a minimal repair cost, we develop a model to find the optimal ($\textsc{k},t_p$) policy which minimizes the expected cost per unit time in the long run while satisfying a system availability constraint.

• 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.

• 품질경영학회지
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• 제47권3호
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• pp.571-582
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• 2019

Purpose: To develop a risk metric for failure cause that can help determine the action priority of each failure cause in FMEA considering time sequence of cause- failure- detection. Methods: Assuming a quadratic loss function the unfulfilled mission period, a risk metric is obtained by deriving the failure time distribution. Results: The proposed risk metric has some reasonable properties for evaluating risk accompanied with a failure cause. Conclusion: The study may be applied to determining action priorities among all the failure causes in the FMEA sheet, requiring further studies for general situation of failure process.

• 품질경영학회지
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• 제18권2호
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• pp.33-42
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• 1990

This paper proposes the maintenance model of multi-component system when the failure characteristics and types of components are considered. In this model, it is assumed that a system is composed of a critical component, a major component and a minor component. Also, failure types is classified into major failure and minor failure. If major failure occurs to critical component before system age replacement time, the system is renewed. If major failure does not occur until its age replacement time, preventive maintenance is performed at age replacement time T. Minimal repairs are carried out after each minor failure. Major component is minimal-repaired if any failure is discovered during operation. Minor component should be replaced as soon as any failure is found. This paper determines the optimal replacement time of the system which minimizes total maintenance cost. Numerical example illustrates these results.

• 한국환경과학회지
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• 제17권11호
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• pp.1295-1305
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• 2008

This study aims at the analyze of unsteady downstream flow due to dam failure along dam failure scenario and applied to Yeoncheon Dam which was collapsed August 1st 1999, using HEC-RAS simulation model. The boundary conditions of this unsteady flow simulation are that dam failure arrival time could be at 02:45 a.m. August 1st 1999 and failure duration time could be also 30 minutes. Downstream 19.5 km from dam site was simulated for unsteady flow analysis in terms of dam failure and non-failure cases. For the parameter calibration, observed data of Jeonkok station were used and roughness coefficient was applied to simulation model. The result of the peak discharge difference was 2,696 to $1,745\;m^3/sec$ along the downstream between dam failure and non-failure and also peak elevation of water level showed meanly 0.6m difference. Those results of these studies show that dam failure scenarios for the unknown failure time and duration were rational because most results were coincident with observed records. And also those results and procedure could suggest how and when dam failure occurs and downstream unsteady flow analyzes.

• 터널과지하공간
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• 제20권2호
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• pp.97-104
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• 2010

가속 크리프 거동을 보이는 재료의 파괴를 설명하기 위하여 재료 파괴식($\ddot{\Omega}=A{(\dot{\Omega})}^\alpha$, $\Omega$는 변위와 같은 측정가능한 양을 나타낸다)이 사용된다. 상수 A와 $\alpha$는 주어진 측정 자료를 곡선적합하여 얻는다. 본 연구에서는 재료 파괴식을 이용하여 터널의 파괴시간을 예측하였고, 재료 파괴식을 적용하기 위하여 4가지 곡선적합기법이 사용되었다. 4가지 곡선적합기법 중 로그속도-로그가속도기법, 로그시간-로그속도기법, 역속도법은 선형최소자승법을 이용하고 비선형최소자승기법은 Levenberg-Marquardt 알고리즘을 이용한다. 로그속도-로그가속도기법은 재료 파괴식을 대수형태로 만들어 해석을 하기 때문에 터널의 파괴시간 예측에 재료 파괴식을 적용하는 것이 타당한지에 대한 근거를 제시한다. 로그속도-로그가속도기법에 따른 자료의 상관계수가 0.84로 비교적 높게 나타났기 때문에 재료 파괴식을 터널의 파괴시간 예측에 적용하는 것이 타당하다고 판단된다. 실제 파괴시간과 4가지 곡선적합기법으로부터 얻은 예측 파괴시간을 비교한 결과 로그시간-로그속도기법이 가장 우수한 결과를 보여주는 것으로 나타났다.