• International Journal of Reliability and Applications
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• 제17권1호
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• pp.85-105
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• 2016

In this paper accelerated life testing is incorporated in quality control technique of acceptance sampling plan to induce early failures in high reliability products.Stress under accelerated condition can be applied in constant-stress, step-stress and progressive-stress or combination of such loadings. A ramp-stress results when stress is increased linearly (from zero) with time. In this paper optimum failure-censored ramp-stress accelerated life test sampling plan for log-logistic distribution has been formulated with cost considerations. The log-logistic distribution has been found appropriate for insulating materials. The optimal plans consist in finding optimum sample size, sample proportion allocated to each stress, and stress rate factor such that producer's and consumer's interests are safeguarded. Variance optimality criterion is used when expected cost per lot is not taken into consideration, and bilevel programming approach is used in cost optimization problems. The methods developed have been illustrated using some numerical examples, and sensitivity analyses carried out in the context of ramp-stress ALTSP based on variable SSP for proportion nonconforming.

• 품질경영학회지
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• 제24권3호
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• pp.37-49
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• 1996

For highly reliable devices it is often defined to "fail" when its performance degrades below a specified value. In this paper we consider a method for optimally designing accelerated degradation tests(ADTs) in which the performance over exposure time and stress has Weibull distribution. For the product whose performance has Weibull distribution, the optimum plan - low stress level and sample proportions allocated to each test condition - is obtained, which minimize the asymptotic variance of maximum likelihood estimator of a stated quantile at design stress. We also present compromise ADTs plan that can be used for the practical purpose.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.34.2-34.2
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• 2011

Wind guide can be installed on the top of buildings to collect wind. In this study, optimum shape of wind guide is developed, and proposed to combinate with the vertical wind turbine. Impact of parameters for wind guide is analyzed with several cases planned by Taguchi test plan. Front angle, rear angle, and roof angle are selected as key variables and changed into four different levels. By the experimental plan, totally, 64 cases are reduced to 16 cases of analysis. With optimum design of wind guide, the installed vertical axis wind turbines can be operated with maximum power output.

• International Journal of Reliability and Applications
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• 제18권2호
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• pp.45-63
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• 2017

In this paper, we have formulated optimum Accelerated Life Test (ALT) plan for a parallel system with two independent components using masked data with ramp-stress loading scheme and Type-I censoring. Consider a system of two independent and non-identical components connected in parallel. Such a system fails whenever all of its components has failed. The exact component that causes the system to fail is often unknown due to cost and time constraint. For each parallel system at test, we observe its system's failure time and a set of component that includes the component actually causing the system to fail. The stress-life relationship is modelled using inverse power law, and cumulative exposure model is assumed to model the effect of changing stress. The optimal plan consists in finding out the optimum stress rate using D-optimality criterion. The method developed has been explained using a numerical example and sensitivity analysis carried out.

• International Journal of Reliability and Applications
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• 제15권2호
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• pp.85-98
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• 2014

Accelerated life testing (ALT) is a well famous technique in life testing and reliability studies, this is particularly used to induce so high stress leading to failure of the highly reliable units quickly under stipulated duration of time. The step-stress ALT is one of the systematic experimental strategy of ALT applied to fail the units in steps. In this article we focus on two important issues (i) necessity of life tests at higher steps with relevant causes (ii) to develop a new optimum test plan for 3-step SSALT under the modified cumulative exposure model proposed by Khamis and Higgins (1998). It is assumed that the lifetime of test units follows Rayleigh distribution and its scale parameter at constant stress level is assumed to be a log-linear function of the stress. The maximum likelihood estimates of the parameters involved in the step-stress ALT model are obtained. A simulation study is performed for numerical investigation of the proposed new optimum plan 3-step, step-stress ALT. The necessity of the life test units at 3-step step-stress is also numerically examined in comparison to simple step-stress setup.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.189-192
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• 2006

고유가 시대에 정보시스템의 발달과 더불어 안전하고 경제적인 항해계획의 수립을 지원하는 시스템에 대한 요구가 증대되고 있다. 이에 저자들이 개발한 최적항로평가시스템에 대하여 그 개발 내용 및 적용 사례를 소개한다. 기상예보데이터를 이용하여 소요시간 및 연료소모량 관점에서 최적화된 항해 계획을 생성하며, Parametric roll 을 포함한 각종 내항성능 지표를 정량적으로 평가하여, 항해자로 하여금 항해의 안전성 및 경제성 관점에서 최적화된 항해 계획을 수립하도록 지원하는 시스템을 개발하였다. 개발된 시스템의 유효성은 실 항해중 적용한 사례 및 시뮬레이션 결과를 통해서 검증하였다.

• International Journal of Reliability and Applications
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• 제13권1호
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• pp.19-35
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• 2012

This paper presents an optimum design of step-stress partially accelerated life test (PALT) plan which allows the test condition to be changed from use to accelerated condition on the occurrence of fixed number of failures. Various life distribution models such as exponential, Weibull, log-logistic, Burr type-Xii, etc have been used in the literature to analyze the PALT data. The need of different life distribution models is necessitated as in the presence of a limited source of data as typically occurs with modern devices having high reliability, the use of correct life distribution model helps in preventing the choice of unnecessary and expensive planned replacements. Truncated distributions arise when sample selection is not possible in some sub-region of sample space. In this paper it is assumed that the lifetimes of the items follow Truncated Logistic distribution truncated at point zero since time to failure of an item cannot be negative. Optimum step-stress PALT plan that finds the optimal proportion of units failed at normal use condition is determined by using the D-optimality criterion. The method developed has been explained using a numerical example. Sensitivity analysis and comparative study have also been carried out.

• 한국방재학회 논문집
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• 제9권3호
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• pp.117-126
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• 2009

유역종합치수계획 수립 시 유역 내 적용이 가능한 구조물적 비구조물적 치수계획은 매우 광범위하고, 특히 그 중에서도 구조물적 홍수방어 시설들의 특성은 매우 다양하다. 이들을 조합하여 유역의 홍수 저감능력을 최대화 하는 최적대안을 선정하는 것은 쉬운 일이 아니며, 현재 구조물적 홍수방어 후보대안에 대한 적절한 평가 기준이나 다양한 홍수방어 후보대안들 중 최적대안의 선정에 관한 지침 또한 미흡한 실정이다. 본 연구에서는 유역종합치수계획의 구조물적 홍수방어 후보대안들에 대한 치수경제성 및 정책성 평가 결과를 바탕으로 최적대안을 선정하는 과정에서, 의사결정기법 중의 하나인 계층화분석기법을 도입하여 적용함으로써 평가항목들 간의 가중치 결정 및 최적대안을 도출하는 과정을 예시하였다. 후보대안들 각각의 하위 세부 평가항목들의 가중치 결정에는 계층화분석기법 전용 프로그램인 Expert Choice 11.5를 활용하였으며, 연구 결과를 바탕으로 유역종합치수계획의 구조물적 홍수방어 최적대안 선정에 있어 보다 표준화된 절차를 제시하였다.

• 보건행정학회지
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• 제28권3호
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• pp.233-239
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• 2018

A rapid decrease of total fertility rate to 1.08 in 2005 prompted the Korean government to plan and implement a '5-year plan for ageing society and population policy' starting from 2006. The 1st and 2nd 5-year plans had not shown any discernible impact on the fertility and the 3rd 5-year plan was launched in 2016. However, the fertility rate is going down further. The author reviewed the contents and assessment reports of the fertility promotion plan to suggest ideas for complementing the shortcomings of it. Author defined the major determinants of marriage and child birth as philosophy, politics, sense of value, social norm, culture, healthcare, and education. The plan was examined in view of these determinants. Transformation of Korea from an agricultural society to an industrialized society in a short period of time had brought about changes in most of the determinants of marriage and child birth; in particular philosophy and sense of value. These aspects were not put into consideration in the plan. Author suggested to launch a social education program for the general public to establish a sound philosophy of life, reform the sense of value on family, child birth and education, and cultivate the skill to draw a consensus through discussions on the social issues. A special program to promote marriage of women at the optimum age for child birth was proposed. The government should implement well balanced policy for economic development and labor. Multidisciplinary approach was recommended for these tasks.

• Journal of the Korean Data and Information Science Society
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• 제5권2호
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• pp.87-94
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• 1994

In this paper, we consider optimum plan to determine stress change times under the three-step stress PALTs, assuming that each test units follows an exponential distribution. The tampered random variable(TRV) model for the three-step stress PALTs setup are introduced, and maximum likelihood estimators(MLEs) of the failure rate and the acceleration factors are obtained. The change times to minimize the generalized asymptotic variance(GAVR) of MLEs of the failure rate and the acceleration factors are proposed for the three-step stress PALTs.