• 한국자동차공학회논문집
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• 제11권5호
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• pp.89-94
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• 2003

Rolling stock structures such as bogie frame and car body play an important role for the support of vehicle leading. In general, more than 25 years' durability is needed for them. A lot of study has been carried out for the prediction of the fatigue life of the bogie frame and car body in experimental and theoretical domains. One of the new methods is a probabilistic fatigue lift evaluation. The objective of this paper is to estimate the fatigue lift of the bogie frame of an electric car, which was developed by the Korea Railroad Research Institute (KRRI). We used two approaches. In the first approach probabilistic distribution of S-N curve and limit state function of the equivalent stress of the measured stress spectra are used. In the second approach, limit state function is also used. And load spectra measured by strain gauges are approximated by the two-parameter Weibull distribution. Other probabilistic variables are represented by log-normal and normal distributions. Finally, reliability index and structural integrity of the bogie frame are estimated.

• 한국태양에너지학회 논문집
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• 제31권6호
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• pp.23-31
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• 2011

The wind energy is one of the most prospective resources in renewable energy. However, the WTGS shouldn't be installed indiscriminately because the power system can be negatively influenced by a variable and uncertain nature of the wind energy. It is the reason why it has to be limited to install the WTGS thoughtlessly mentioned above that support the importance of the maximum penetration limit of wind power. It may required that power system operators suggests a new way of power system operation as percentage of the WTGS increase in the existing power system. The wind power is fixed in a limited area, so using rate of the wind power will be increased by installing additional WTGS. In this paper, we have studied on economic evaluation of the wind capacity increased by restricting the output of the WTGS as the way to increase the wind capacity.

• 산업기술연구
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• 제15권
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• pp.5-13
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• 1995

Natural gas, which is getting more important as a fuel, should be liquefied and shipped in a special tank. During transportation, a spill of liquefied natural gas(LNG) could occur by a collision or even an accident. As a result, violent explosion called the superheat-limit explosion(SLE) can take place in some cases, unexpectedly. Such explosion may result from the formation of a superheated liquid which has attained the superheat-limit temperature when hot(water) and cold(LNG) liquids come into contact. Natural gas mixtures can be considered as discrete light components plus continuous heavy fractions where several continuous distribution function can be adopted. This work is aiming at prediction of the superheat-limit explosion condition by suing continuous thermodynamics development of algorithm to predict.

• 대한수학교육학회지:학교수학
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• 제12권3호
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• pp.273-299
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• 2010

본 논문의 목적은 고등학교 수준의 학생들이 표집분포의 개념을 학습할 수 있도록 '표집분포 시뮬레이션 (Sampling Distributions Simulation)'을 설계하고 구현하는 것이다. '표집분포 시뮬레이션'은 다음과 같이 4차시로 구성되어 있다. 1차시-신뢰도와 신뢰구간의 의미 학습하기 2차시-표집분포의 의미 학습하기 3차시-중심극한정리의 의미 학습하기 4차시-이항분포의 정규근사 학습하기 본 연구를 통하여 표집분포의 중요성에 대한 학생들이 인식이 달라지고 이해가 증진되기를 기대한다. 또 본 연구의 결과로 제공되는 프로그램 '표집분포의 시뮬레이션' 수업을 통해 통계적 추론 능력이 향상되고, 아울러 통계적 추론 속에서 표집 분포의 역할이 충분히 이해되기를 기대한다.

• 산업경영시스템학회지
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• 제22권52호
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• pp.347-354
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• 1999

Statistical Process Control(SPC) which uses control charts is widely used to inspect and improve manufacturing process as a effective method. A parametric method is the most common in statistical process control. Shewhart chart was made under the assumption that measurements are independent and normal distribution. In practice, this assumption is often excluded, for example, in case of (equation omitted) chart, when the subgroup sample is small or correlation, it happens that measured data have bias or rejection of the normality test. A bootstrap method can be used in such a situation, which is calculated by resampling procedure without pre-distribution assumption. In this study, applying bootstrap percentile method to (equation omitted) chart, it is compared and evaluated standard process control limit with bootstrap percentile control limit. Also, under the normal and non-normal distributions, where parameter is 0.5, using computer simulation, it is compared standard parametric with bootstrap method which is used to decide process control limits in process quality.

• 한국수자원학회논문집
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• 제43권11호
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• pp.967-976
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• 2010

우수관의 성능이 한계상태(performance limit state)에 도달할 확률을 정량적으로 산정할 수 있는 FORM(First-Order Reliability Model)의 AFDA(Approximate Full Distribution Approach) 신뢰성 모형을 개발하였다. 우수관망에서 각각의 관으로 유입하는 유량이 그 관의 허용 가능 배출량을 초과하여 성능한계상태에 도달할 때 이를 파괴상태(failure state)라 정의하여 신뢰함수를 수립하였다. 우수관거로의 유입량은 합리식, 유출량은 Manning의 공식을 적용하였다. 또한 신뢰성 해석을 위한 관련 확률변수들에 대한 통계적 특성과 분포함수에 대한 해석이 수행되었다. 강우자료의 불확실성 해석에서 우리나라 여러 중소도시에 대한 연 최대강우강도의 확률분포가 Gumbel 극치분포함수와 일치함을 확인하였다. 개발된 신뢰성 모형을 Y자형 우수관망에 적용하여 성능한계상태가 발생할 확률, 즉 파괴확률(probability of failure)을 정량적으로 산정하였다. Manning의 공식을 이용하여 우수관의 직경 변화에 따른 파괴확률의 거동특성을 분석하였다. 특히 문경과 대전의 50년 재현기간을 갖는 설계 강우강도에 대한 우수관의 파괴확률을 산정한 결과에 의하면, 관의 직경이 특정수치 이하일 경우 파괴확률이 급격히 커지는 것을 확인할 수 있었다. 이는 실제 우수관의 유효직경이 설계직경에 가깝도록 항상 관내 불순물을 제거하는 것이 파괴확률을 줄이는 최선의 방법임을 의미하는 것이다. 또한 우수관 시스템의 경우 여러 개의 관이 모여 하나의 관으로 흘러 들어가는 경우가 많으며 이 경우 다중파괴유형(multiple failure mode)을 적용하여 시스템이 파괴상태에 도달할 확률을 정량적으로 산정하였다. 본 연구에서 개발된 신뢰성 모형은 우수관의 운용, 관리, 감독은 물론 설계에 활용이 가능 할 것이다.

• 한국공작기계학회논문집
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• 제10권6호
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• pp.42-47
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• 2001

In this study, fatigue limit of ductile cast iron is evaluated based on phenomena of the microscopic observation, such as matrix structure, spheroidal ratio, size of graphite and distribution. Three different ferrite-pearlite matrix structure, GCD 45-), GCD 50, GCD 60 series, all of which contain more than 70% spheroidal ratio of graphite, were used to obtain the correlation between maximum size of graphite and fatigue strength. It was concluded as fellows. (1) In Ductile cast iron of ferrite-pearlite matrix, the fatigue limit of GCD 60 series with 73% pearlite structure was the highest. (2) From observation of the starting point of crack of all specimens, it is noted that the crack initiates, in graphite, goes through ferrite and propagates into pearlite. (3) A good quality of Ductile cast iron used in this experiment can be checked from uniformly distributed graphite. The negligible interaction effect between graphites was verified by microscopic observation and fracture mechanics investigation in surface and interior of the specimen.

• 한국자동차공학회논문집
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• 제11권3호
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• pp.7-12
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• 2003

Mixture formation in the cylinder of a lean bum engine has been observed by Laser Induced Fluorescence technique. XeCl laser (308nm) was used to produce a laser sheet. 3-pentanone has been added to iso-octane fuel to produce fluorescence, the intensity of which is proportional to the concentration of the fuel. The laser sheet was introduced through the piston window and the fuel distribution in the vertical plane was observed through a side window. Comparison has been made for the cases of selected fuel injection timing as 0, 360, 405, and 450 CA. For the case of 0 and 360 CA injection, uniform fuel distribution in the combustion chamber has been obtained at the ignition time which is favorable for the high load mode. And the late injection cases, 405 and 450 CA, revealed the stratified formation of rich mixture around the spark plug. That extends the lean misfire limit and reduces cyclic variation in the low load mode.

• 품질경영학회지
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• 제35권3호
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• pp.107-117
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• 2007

The fatigue has been considered the most failure mode of metal, ceramic, and composite materials. In this paper, numerical experiments to asses the usefulness of two Dixon's methods(small and large samples) and 14 S-N methods on assumptions of lognormal fatigue limit distribution under RFL(Random Fatigue Limit) model are conducted for staircase(or up-and-down) test and compared by MSE(Mean Squared Error) and bias for estimates of mean log-fatigue limit. Also, guidelines for staircase test plans to choose initial stress level and step size are recommended from numerical experiments including sensitivity analyses. In addition, the parametric bootstrap method to construct a confidence interval for the mean of log-fatigue limit by the percentile method using a transition probability matrix of Markov chain is presented and illustrated with an example.

• 한국산업보건학회지
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• 제24권4호
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• pp.556-565
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• 2014

Objectives: This study is aimed at inquiring into the grasp of real condition of working environment and improvements by calculating the hypertension distribution consequent on job stress risk and exposure level of alleviating factors. In addition, this study is intending to estimate the hypertension distribution through socio-demographic factors and level of stressors occurring at working environment, such as high workload, low control, low support, job insecurity, long working hours, low income. Methods: This study estimated the hypertension distribution using the tertiary Korean Working Conditions Survey data, and conducted comparative analysis according to the category of individual questionnaire items using odds ratio. Result: As a result of study, it was found that in the event that working environment satisfaction is low and business & an immediate superior's attitudes are negative, the hypertension distribution was high. Particularly, it was found that physical risk factor musculoskeletal risk factor, and mental risk factor in a workplace were all increasing the hypertension distribution. Conclusions: With the aged workers' labor market participation ratio increasing, hypertension could be a major issue in the field of Occupational Safety and Health. Thus, it's necessary that the relevant employer should lower the hypertension distribution through creation of pleasant working environment and inducement of workers to improve in the relations with their superiors. As for the uppermost limit of this study, there is a limit to clarifying the mechanism of hypertension through multivariate statistics analysis because it's difficult to establish causal relationship by individual questionnaire item as the working conditions survey is made by cross-sectional study. In the follow-up research, this study is going to do research on the mechanism of hypertension through questionnaire supplementation and in-depth analysis.