• 한국기후변화학회지
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• 제6권2호
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• pp.87-94
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• 2015

To compare changes in winter temperature over South Korea, 30-year average climate data and climate data of recent 10 years (2014~2014) such as mean temperature, daily maximum temperature and daily minimum temperature were analyzed. Also, we set analysis extreme cold waves frequency related to winter such as freezing days, snow days, days with temperature of below -5, and days with temperature of below -10. This process enabled the comparative analysis of winter temperature changes and extreme cold waves frequency related to winter. This study estimated that winter temperature has gradually increased throughout the last five decades, however, the frequency of extreme weather, such as cold waves has also increased.

• 한국기계가공학회지
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• 제18권9호
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• pp.29-35
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• 2019

The structure of the machinery industry due to the 4th industrial revolution is changing from precision and durability to intelligent and smart machinery through sensing and interconnection(IoT). There is a growing need for research on prognostics and health management(PHM) that can prevent abnormalities in processing machines and accurately predict and diagnose conditions. PHM is a technology that monitors the condition of a mechanical system, diagnoses signs of failure, and predicts the remaining life of the object. In this study, the vibration generated during machining is measured and a classification algorithm for normal and fault signals is developed. Arbitrary fault signal is collected by changing the conditions of un stable supply cutting oil and fixing jig. The signal processing is performed to apply the measured signal to the learning model. The sampling rate is changed for high speed operation and performed machine learning using raw signal without FFT. The fault classification algorithm for 1D convolution neural network composed of 2 convolution layers is developed.

• Journal of Electrical Engineering and Technology
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• 제11권5호
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• pp.1093-1099
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• 2016

• 한국기계가공학회지
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• 제9권6호
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• pp.71-77
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• 2010

Although the problems of defects and nonmetallic inclusion in metal fatigue are very complicated, it is particularly important to view these problems from the perspective that defects and inclusions are virtually equivalent to small cracks. This concept will help one to understand various fatigue phenomena caused by Ductile Cast Iron. For different ferrite-pearlite matrix structure, containing more than 90% spheroidal ratio of graphite, GCD 45-3, GCD 50, GCD 60 series and 70%, 80%, 90% spheroidal ratio of graphite, GCD 40, GCD 45-1, GCD 45-2 series, this paper has carried out image analyzer, estimated maximum and mean size of graphite, investigated correlation. It was concluded as follows. (1) A good quality of Ductile cast iron using in this experiment, the graphite was separated well. The effect of the interaction by graphite was verified by microscopic observation and by fracture mechanics investigation in surface, interior of the specimen. (2)${\sqrt{area}}_{max}$ of graphite can be used to predict fatigue limit of Ductile Cast Iron. The Statistical distribution of extreme values of ${\sqrt{area}}$ may be used as a guide line for the control of inclusion size in the steel making processes.

• Wind and Structures
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• 제17권2호
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• pp.227-244
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• 2013

Non-stationary extreme winds such as thunderstorm downbursts are responsible for many structural damages. This research presents a time domain approach for estimating along-wind load effects on tall buildings using multiple wind speed time history samples, which are simulated from evolutionary power spectra density (EPSD) functions of non-stationary wind fluctuations using the method developed by the authors' earlier research. The influence of transient wind loads on various responses including time-varying mean, root-mean-square value and peak factor is also studied. Furthermore, a simplified model is proposed to describe the non-stationary wind fluctuation as a uniformly modulated process with a modulation function following the time-varying mean. Finally, the probabilistic extreme response and peak factor are quantified based on the up-crossing theory of non-stationary process. As compared to the time domain response analysis using limited samples of wind record, usually one sample, the analysis using multiple samples presented in this study will provide more statistical information of responses. The time domain simulation also facilitates consideration of nonlinearities of structural and wind load characteristics over previous frequency domain analysis.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2002년도 금형가공 심포지엄
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• pp.274-284
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• 2002

Deep drawing process for rectangular drawn section is different with that for axisymmetric circular one. Therefore deep drawing process for rectangular drawn section requires several intermediate steps to generate the final configuration without any significant defect. In this study, finite element analysis for multi-stage deep drawing process for high precision rectangular cases is carried out especially for an extreme aspect ratio. The analysis is performed using rigid-plastic finite element method with an explicit time integration scheme of the commercial program, LS-DYNA3D. The sheet blank is modeled using eight-node continuum brick elements. The results of analysis show that the irregular contact condition between blank and die affects the occurrence of failure, and the difference of aspect ratio in the drawn section leads to non-uniform metal flow, which may cause failure. A series of experiments for multi-stage deep drawing process for the rectangular cases are conducted, and the deformation configuration and the thickness distribution of the drawn rectangular cases are investigated by comparing with the results of the numerical analysis. The numerical analysis with an explicit time integration scheme shows good agreement with the experimental observation.

• 반도체디스플레이기술학회지
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• 제14권3호
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• pp.7-11
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• 2015

In order to protect the patterned mask from contamination during lithography process, pellicle has become a critical component for Extreme Ultraviolet (EUV) lithography technology. According to EUV pellicle requirements, the pellicle should have high EUV transmittance and robust mechanical property. In this study, silicon nitride, which is well-known for its remarkable mechanical property, was used as a pellicle membrane material to achieve high EUV transmittance. Since long silicon wet etching process time aggravates notching effect causing stress concentration on the edge or corner of etched structure, the remaining membrane is prone to fracture at the end of etch process. To overcome this notching effect and attain high transmittance, we began preparing a rather thick (200 nm) $SiN_x$ membrane which can be stably manufactured and was thinned into 43 nm thickness with HF wet etching process. The measured EUV transmittance shows similar values to the simulated result. Therefore, the result shows possibilities of HF thinning processes for $SiN_x$ EUV pellicle fabrication.

• 한국안전학회지
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• 제25권3호
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• pp.112-117
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• 2010

This study presents a methodology to evaluate the driving safety of vehicles against localized high wind on the roads over the valleys or along the coasts. Risk level for vehicle accident is derived from the side slip caused by cross wind, and then safety criteria based on reliability for driving stability are defined. The level of safety is classified according to probability of exceeding against wind speed using the concept of extreme value statistics. To attain the safety level of vehicle on bridges, numerical simulations using Computational Fluid Dynamics(CFD) are performed. Based on this result, risk reduction and quality improvement is expected through analysis for each alternative in bridges design, construction and operation & maintenance stage with proposed process

• 한국지리정보학회지
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• 제13권4호
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• pp.148-156
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• 2010

자원개발 등의 이유로 시베리아나 알래스카와 같은 극한(寒)지 진출이 국내는 물론 세계적으로도 증가 추세에 있다. 이에 따라 본 연구에서는 남극 제2기지 건설사업을 대상으로, 극한지 건설사업 진출을 위한 위성영상 활용방안을 도출하고자 하였다. 남극을 포함한 극한지는 지역적 특성상 원격지이고 접근이 어렵다는 특성에 따라 위성영상의 활용은 필수적이라 할 수 있다. 본 연구에서는 극한지 건설 프로세스 전반에 대한 검토와 극한지 위성영상 활용사례 분석 및 관련 논문 등 문헌리뷰를 통해 건설 단계별 위성영상 활용가능항목 및 활용방안을 제시 하였다.

• 한국수학교육학회지시리즈E:수학교육논문집
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• 제21권3호
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• pp.407-430
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• 2007

수학적 지식의 개인화/배경화, 탈개인화/탈배경화의 과정이 간과되거나 지나치게 강조됨으로써 발생하는 극단적 교수 현상은 항상 우리의 교수 실제에 내재하고 있으며, 사실 교사들을 심리적으로나 교수학적으로 압박하는 현상이라 볼 수 있다. 그러나 학생들이 수학 수업에서 보이는 오류나 오개념, 장애등에 관한 문제는 많은 연구가 이루어져 있지만 교사에 의해 나타나는 극단적 교수 현상에 대한 연구는 거의 이루어지지 않고 있다고 해도 과언은 아니다. 이에 본 연구에서는 네 가지 극단적 교수 현상에 대해 설명하고, 여러 가지 사례연구에서 다양한 예문들을 제시한 후 분석하는 방법으로 이들 극단적 교수 현상에 대한 이해를 도울 것이다. 또한 이러한 분석을 토대로 수학교실에서 나타나는 극단적 교수현상을 극복할 수 있는 방법에 대해서도 논의 할 것이다. 이 연구 논문은 교사들이 자기 자신의 수업을 반성하게 함으로써 극단적으로 진행되는 교수학적 현상의 기준이 될 것이고, 나아가 보다 나은 교수학적 상황을 고려하기 위한 자료를 제공할 것이다.