• 한국사회복지학
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• 제39권
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• pp.5-40
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• 1999

이 연구의 목적은 실업자의 실업기간과 재취업 형태에 영향을 미치는 주된 요인이 무엇인지를 파악하고, 그에 기초하여 보다 바람직한 고용관련정책 마련에 필요한 기초자료를 제공하는 데 있다. 이를 위해 이 연구는 보건사회연구원과 노동연구원이 공동으로 실시한 '1998년도 전국 실업실태 및 복지욕구조사' 자료를 Weibull 모델과 Logistic모델을 이용하여 분석하였다. 분석한 결과, 전체 실업자를 대상으로 할 경우, 연령, 가구 월 평균소득, 가구주 여부, 결혼 여부, 이전 직장의 규모, 실직사유 등의 변수가 실업자의 실업기간에 영향을 미치는 주요 요인으로 파악되었고, 연령, 이전 직장의 직종과 근무형태, 고용보험가입 여부 등의 변수가 실업자의 재취업형태에 영향을 미치는 주요 요인으로 파악되었다. 이러한 실증적 분석의 결과를 바탕으로 이 연구는 불안정한고용상태와 실업, 그리고 실업과 불안정한 재취업의 순환을 반복할 수 있는 취약계층 근로자를 위한 보다 체계적인 실업대책의 필요성을 논하면서 정책적인 제언을 하고자 한다.

• 품질경영학회지
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• 제47권1호
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• pp.87-96
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• 2019

Purpose: The purpose of this paper is to determine an optimal production time for economic production quantity model with preventive maintenance and random defective rate as the function of a machinery deteriorates. Methods: If a machinery shifts from "in-control" state to "out-of-control" state, a proportion of defective items being produced increases. It is assumed that time to state shift is a random variable and follows an arbitrary distribution. The elapsed time until process shift decreases stochastically as a production cycle repeats and quasi-renewal process is used to implement for production facilities to deteriorate. Results: When the exponential parameter for exponential distribution increases, the optimal production time increases. When Weibull distribution is considered, the optimal production time is closely affected by the shape parameter of Weibull distribution. Conclusion: A mathematical model is suggested to find optimal production time and optimal number of production cycles and numerical examples are implemented to validate the patterns for changes of optimal times under different parameters assumptions. The real application is implemented using the proposed approach.

• Communications for Statistical Applications and Methods
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• 제28권1호
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• pp.1-19
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• 2021

Heavy tailed distributions are useful for modeling actuarial and financial risk management problems. Actuaries often search for finding distributions that provide the best fit to heavy tailed data sets. In the present work, we introduce a new class of heavy tailed distributions of a special sub-model of the proposed family, called a new extended alpha power transformed Weibull distribution, useful for modeling heavy tailed data sets. Mathematical properties along with certain characterizations of the proposed distribution are presented. Maximum likelihood estimates of the model parameters are obtained. A simulation study is provided to evaluate the performance of the maximum likelihood estimators. Actuarial measures such as Value at Risk and Tail Value at Risk are also calculated. Further, a simulation study based on the actuarial measures is done. Finally, an application of the proposed model to a heavy tailed data set is presented. The proposed distribution is compared with some well-known (i) two-parameter models, (ii) three-parameter models and (iii) four-parameter models.

• International Journal of Reliability and Applications
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• 제6권1호
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• pp.41-51
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• 2005

The Bayes estimators of the parameters included in the complementary Weibull reliability model are obtained. In the process of deriving Bayes estimators, the scale and shape parameters of the complementary Weibull distribution are considered to be independent random variables having prior exponential distributions. The maximum likelihood estimators of the desired parameters are derived. Further, the least square estimators are obtained in closed forms. Simulation study is made using Monte Carlo method to make a comparison among the obtained estimators. The comparison is made by computing the root mean squared errors associated to each point estimation. Based on the numerical study, the Bayes procedure seems better than the maximum likelihood and least square procedures in the sense of having smaller root mean squared errors.

• Journal of the Korean Data and Information Science Society
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• 제11권2호
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• pp.295-302
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• 2000

생존분석에서 널리 이용되고 있는 모형 중 하나인 와이블 모형에 대해 효율적인 모수 추정에 대해 연구하였다. 공변량을 포함하고 있는 와이블 모형의 모수를 추정하기 위하여 전 치료기간을 여러 단계로 나누어 최대우도법을 적용하는 분할법을 소개하였다. 실제의 자료를 적용하여 분할법과 비분할법으로 모수를 추정하여 비교한 결과 분할법의 효율성을 입증하였다.

• 한국정밀공학회지
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• 제13권10호
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• pp.36-45
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• 1996

The precise estimation of the reliability and life of the Ravigneaux planetary gear train used in an automatic transmission is necessary in order to enable accurate material and geometric properties to reliability distrobution and the number of load cycles at failure. These are critical for the proba- bilistic design of complex planetary gear system as Ravigneaux type particularly during various gear ratios. The Ravigneaux planetary gear train has five gears, such as a forward and a reverse sun gear, a short and a long pinion, and an annulus gear. In this paper, the Ravigneaux gear system is analyzed to figure out the reliablity distribution. i.e. the probability of survival in the system without its overhaul. First, the reliablity method based on the Weibull distribution is used in conjuction with the Palmgren's model to predict both the individual reliabilities of its components and the nimber of load cycles when the system failed. Then using the presented method, the life of the Ravigneaux gear system can be determined. Alwo the different design parameters such as tooth face width, material property, and Weibull exponent are applied and reached to optimal ones. Thus, the precise evaluation of the reliability and life of the Ravigneaux planetary gear train used in an automatic transmission can be effectively carried out.

• 한국항공우주학회지
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• 제47권1호
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• pp.35-40
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• 2019

본 연구의 목적은 항공기 구조개발에 널리 적용되고 있는 탄소섬유 복합재의 피로특성을 확인하고, 실기체 피로시험에 활용되고 있는 자료를 획득하는 것이다. 복합재 구조의 내구성 및 손상허용성의 평가는 주로 피로시험을 통하여 이루어지며, 실기체 피로시험에 적용되고 있는 파라미터에는 피로수명계수와 하중증대계수가 있다. 탄소섬유/에폭시 일방향 및 직물형 복합재로 시편을 제작하였으며, 응력비와 적층패턴을 달리하여 피로시험을 수행하였다. Sendeckyj 모델을 적용한 와이블 분포와 개별적인 피로수명에 대한 와이블 분포를 이용하여 형상 파라미터를 분석하였다. 또한 신뢰도를 고려한 피로수명계수와 하중증대계수를 평가하였다.

• 한국전기전자재료학회논문지
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• 제30권9호
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• pp.551-557
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• 2017

It is extremely important to improve methodologies for the lifetime assessment of porcelain insulators. While there has been a considerable amount of work regarding the phenomena of lifetime distributions, most of the studies assume that aging distributions follow the Weibull distribution. However, the true underlying distribution is unknown, giving rise to unrealistic inferences, such as parameter estimations. In this article, we review several distributions that are commonly used in reliability and survival analysis, such as the exponential, Weibull, log-normal, and gamma distributions. Some properties, including the characteristics of failure rates of these distributions, are presented. We use a Bayesian approach for model selection and parameter estimation procedures. A well-known measure, called the Bayes factor, is used to find the most plausible model among several contending models. The posterior mean can be used as a parameter estimate for unknown parameters, once a model with the highest posterior probability is selected. Extensive simulation studies are performed to demonstrate our methodologies.

• Computers and Concrete
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• 제15권4호
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• pp.485-501
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• 2015

Cooling by the flow of water through an embedded cooling pipe has become a common and effective artificial thermal control measure for massive concrete structures. However, an extreme thermal gradient induces significant thermal stress, resulting in thermal cracking. Using a mesoscopic finite-element (FE) mesh, three-phase composites of concrete namely aggregate, mortar matrix and interfacial transition zone (ITZ) are modeled. An equivalent probabilistic model is presented for failure study of concrete by assuming that the material properties conform to the Weibull distribution law. Meanwhile, the correlation coefficient introduced by the statistical method is incorporated into the Weibull distribution formula. Subsequently, a series of numerical analyses are used for investigating the influence of the correlation coefficient on tensile strength and the failure process of concrete based on the equivalent probabilistic model. Finally, as an engineering application, damage and failure behavior of concrete cracks induced by a water-cooling pipe are analyzed in-depth by the presented model. Results show that the random distribution of concrete mechanical parameters and the temperature gradient near water-cooling pipe have a significant influence on the pattern and failure progress of temperature-induced micro-cracking in concrete.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.88-91
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• 2001

The reliability data analysis for components of CNC machining center is studied in this paper. The failure data of mechanical part is analyzed by Exponetial, Weibull, and Log-normal distributions. And then, the optimum failure distribution model is selected by goodness of fit test. The reliability data analysis program is developed using ASP language. The failure rate, MTBF, life, and failure mode of mechanical parts are estimated and searched by this program. The failure data and analysis results are stored in the database.