• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.10
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• pp.49-55
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• 2008

This paper presents a novel evaluation method of life expectancy of power system equipment. The life expectancy means expected remaining lifetime; it can be usefully utilized to maintenance planning, equipment replacement planning, and reliability assessment. The proposed method is composed of three steps. Firstly, a cumulative probability for future years is evaluated for targeted age year. Secondly, the cumulative probability is modeled by well-blown cumulative distribution function(CDF) such as Weibull distribution. Lastly, life expectancy is evaluated as the mean value of the model. Since the model CDF is established in the proposed method, it can also evaluate the probability of equipment retirement within specific years. The developed method is applied to examples of generators of combined cycle power plants to show its effectiveness.

• Journal of Korean Society of Water and Wastewater
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• v.19 no.5
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• pp.647-654
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• 2005

Recently, the economic losses caused by inundation are increasing due to the urbanization and industrialization, i.e., intensive land utilization and concentration of population and properties. It is regarded that the role of the storm sewer systems in urban areas becomes more important as one of the effective countermeasures for reducing the inundation losses. In this study, the effects of rainfall design frequency enhancement on the construction cost of the storm sewer systems were analyzed by increasing the design frequency from the present design frequency of the sewer systems, which is 5~10 years, to 15 years, 20 years and 30 years. The change rate functions of the design discharge and construction cost based on the various design frequencies were derived by regression analysis. According to the analysis, change the rate of design discharge at 15, 20, 30 years rainfall design frequencies were increased by 10%, 17.1%, and 27.2%, respectively, when compared to that at 10 year frequency. Furthermore, it was found that by increasing the design frequency from 10 years to 15 years, 20 years and 30 years, the construction costs were increased by 5.0%, 8.0% and 12.4%, respectively. Finally, their reliabilities need to be tested by applying the rate functions to the real storm sewer districts.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.1007-1015
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• 2013

A stochastic probability model based on the non-homogeneous Poisson process is represented that can correctly analyze the time-dependent linear and nonlinear behaviors of total damage over the occurrence process of loads. Introducing several types of damage intensity functions, the probability of failure and the total damage with respect to mean time to failure has been investigated in detail. Taking particularly the limit state to be the random variables followed with a distribution function, the uncertainty of that would be taken into consideration in this paper. In addition, the stochastic probability model has been straightforwardly applied to the rubble-mound breakwaters with the definition of damage level about the erosion of armor units. The probability of failure and the nonlinear total damage with respect to mean time to failure has been analyzed with the damage intensity functions for armor units estimated by fitting the expected total damage to the experimental datum. Based on the present results from the stochastic probability model, the preventive management for the armor units of the rubble-mound breakwaters would be suggested to make a decision on the repairing time and the minimum amounts repaired quantitatively.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.4
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• pp.336-344
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• 2007

A method is developed to evaluate partial safety factors for armor units, by which uncertainties of random variables in reliability function as well as wave height distribution with service periods could take into account straightforwardly. It is found that partial safety factors for resistance and wave height are correctly increased with improving target levels on failure of coastal structures at the same return and service periods. Therefore, it nay be possible to determine design variables through the same processes as those of deterministic method by using the partial safety factors for resistance and wave height evaluated in this paper, since uncertainties of random variables and the effects of service periods and target probability failure are directly considered in the processes of evaluation of partial safety factors.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1155-1159
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• 2008

본 연구는 강우의 자료년수가 부족하거나 미계측 지점에서의 확률강우량 산정을 위하여 충분한 강우자료가 확보된 지점들의 강우분석을 수행하였다. 30년 이상의 강우기록을 보유한 기상청 산하 57개 강우관측지점에서 12개 지속기간에 대한 연최대치 강우자료를 대상으로 확률분포형 분석을 실시하여 대표확률분포형을 선정한다. 지점별 지속기간의 대표확률분포형 모수를 확인하고 이를 도시하여 국내 전역에 대한 확률분포 모수선도를 작성하였다. 본 연구의 수행으로 인해 얻어진 결과를 요약하면 다음과 같다. 첫째, 전국 57개 지점에 대한 강우분석 결과, 적용한 16개 분포형 중에서 GEV 분포의 적합도가 가장 우수한 것으로 나타났으며, GEV 분포의 모수를 이용한 지속기간별 확률분포 모수선도를 제시하였다. 둘째, 확률분포 모수선도를 이용한 확률강우량과 기존 연구결과의 확률강우량과는 차이는 대부분 기존 연구보다 과다 산정되게 발생하였다. 셋째, 확률분포 모수선도의 활용으로 기존의 연구에서 산정하기 어려웠던 미계측 지점에서의 확률강우량을 보다 편리하게 구할 수 있었으며, 기존의 연구와 비교하였을 때 산정된 확률강우량의 편차가 적어 미계측 지점에서의 확률강우량 산정 시 효율적인 방법이 될 수 있을 것이다.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1541-1545
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• 2010

최근 이상기후 및 기후변화로 인하여 전 세계의 피해가 증가하고 있다. 하지만 그 피해를 최소화하기 위하여 과도한 비용을 지출 할 수 없기 때문에 적정 설계 빈도에 맞는 치수 정책을 수립한다. 본 연구는 적정 설계 빈도의 설계를 위해 자료기간에 따른 확률강우량의 변화 특성에 대해 분석 하였고, 빈도별 확률강우량을 초과하는 강우사상의 시간적 특성을 분석하기 위해 초과횟수를 산정하여 경향성 분석을 수행하였다. 분석 대상 자료는 기상청에서 관할하고 있는 관측소 중에서 비교적 장기간의 자료를 보유하고 있는 16개 지점을 선정하여 분석하였다. 선정된 지점을 관측년수를 3가지로 나누어 구분하여 빈도해석을 실시하였고, 그 결과 많은 지역에서 확률강우량이 증가하는 것을 확인 할 수 있었다. 또한 빈도해석을 통해 산정된 확률강우량으로 기준을 정하였고, 그 기준을 초과하는 초과횟수를 산정하여 경향성 분석을 수행하였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.309-314
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• 2016

본 연구에서는 확률강우량 산정을 위한 빈도해석 시 보다 타당하고, 신뢰도 높은 강우자료를 선정하여 수공구조물 설계 및 재난방재계획에 합리적인 기준을 제시하고자 이상치 적용에 따른 확률강우량을 산정 비교하였다. 이상치검정의 비교를 위하여 Grubbs and Beck 방법과 미국 수자원평의회 방법을 적용하였으며, 적용결과에 따라 강우자료를 조정하여 확률강우량을 산정 비교하여 타당성을 검토하였다. 본 연구의 수행으로 이상치검정에 따라 강우자료 년수에 변화가 있었으며, 기존의 방법과 확률강우량을 비교하였을 때, 증감이 나타났다.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.304-304
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• 2018

이변량 빈도해석은 일반적으로 고정지속기간 강우량에 대해 빈도해석하는 단변량 빈도해석에 비해 지속기간을 확률변수로 이용하여 강우량과 동시에 확률변수로 사용할 수 있다는 장점이 있다. 하지만 확률분포형의 차원이 증가하기 때문에 기존 단변량 빈도해석에서 요구되던 표본크기보다 더 많은 표본이 필요하다. 우리나라 강우관측소의 경우 오래된 관측소의 경우에도 기록년수가 60년을 넘지 않아 연최대계열로 확률표본을 작성할 경우 이변량 빈도해석을 수행하기에 부족할 수 있다. 따라서 본 연구에서는 Peaks Over Threshold (POT) 방법을 이용하여 적정 확률표본을 선택하는 연구를 진행하였다. 서울 기상청 지점의 강우자료로부터 최소무강우시간을 이용하여 모든 강우사상을 추출하였으며 각 강우사상의 강우량과 지속기간이 확률변수로 사용되었다. 기존에 알려진 POT 방법들과 Anderson-Darling 적합도 검정을 이용한 절단값 산정방법등을 적용하여 확률표본 개수의 변화에 따른 주변분포형의 적합도 검정과 이변량 확률모형의 적합성을 살펴보았다.

• Water for future
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• v.5 no.1
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• pp.27-36
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• 1972

This thesis is the study of the rainfall probability depth in the major areas of Korea, such as Seoul, Pusan and Taegu. The purpose of the paper is to analyze the rainfall in connection with the safe planning of the hydraulic structures and with the project life. The methodology used in this paper is the statistical treatment of the rainfall data in the above three areas. The scheme of the paper is the following. 1. The complementation of the rainfall data We tried to select the maximm values among the values gained by the three methods: Fourier Series Method, Trend Diagram Method and Mean Value Method. By the selection of the maximum values we tried to complement the rainfall data lacking in order to prevent calamities. 2. The statistical treatment of the data The data are ordered by the small numbers, transformed into log, $\sqrt{}, \sqrt[3]{}, \sqrt[4], and$\sqrt[5], and calculated their statistical values through the electronic computer. 3. The examination of the distribution types and the determination of the optimum distibution types By the $x^2-Test$ the distribution types of rainfall data are examined, and rejected some part of the data in order to seek the normal rainfall distribution types. In this way, the optimum distribution types are determined. 4. The computation of rainfall probability depth in the safety project life We tried to study the interrelation between the return period and the safety project life, and to present the rainfall probability depth of the safety project life. In conclusion we set up the optimum distribution types of the rainfall depths, formulated the optimum distributions, and presented the chart of the rainfall probability depth about the factor of safety and the project life.ct life.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.4
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• pp.246-257
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• 2015

The progressive degradation paths of structures have quantitatively been tracked by using stochastic processes, such as Wiener process, gamma process and compound Poisson process, in order to consider both the sampling uncertainty due to the usual lack of damage data and the temporal uncertainty associated with the deterioration evolution. Several important features of stochastic processes which should carefully be considered in application of the stochastic processes to practical problems have been figured out through assessing cumulative damage and lifetime distribution as a function of time. Especially, the Wiener process and the gamma process have straightforwardly been applied to armors of rubble-mound breakwaters by the aid of a sample path method based on Melby's formula which can estimate cumulative damage levels of armors over time. The sample path method have been developed to calibrate the related-parameters required in the stochastic modelling of armors of rubble-mound breakwaters. From the analyses, it is found that cumulative damage levels of armors have surely been saturated with time. Also, the exponent of power law in time, that plays a significant role in predicting the cumulative damage levels over time, can easily be determined, which makes the stochastic models possible to track the cumulative damage levels of armors of rubble-mound breakwaters over time. Finally, failure probabilities with respect to various critical limits have been analyzed throughout its anticipated service life.