• Journal of the Korean Society of Manufacturing Process Engineers
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• v.5 no.2
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• pp.56-64
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• 2006

Rapid progress in many branches of technology has led to a demand on new materials such as high strength light weight alloys, powdered alloys and composite materials. The hydrostatic extrusion is essentially a method of extruding a clad rod through a die. In order to investigate the effect of the process conditions such as friction heat, deformation and clad thickness on the clad extrusion process, viscoplastic finite element simulations were conducted. A specific model for theoretical analysis used in this study is The single scalar variable version of Hart's model. An experiment also has been carried out using 1.5MN hydrostatic extruder with variable speed ram, LVDT and load cell for comparison. It is found that the hydrostatic extrusion pressure considering the effect of heat dissipation in this theoretical work was closer to the experimental pressure than the isothermal hydrostatic extrusion pressure.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.4
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• pp.115-120
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• 2011

A ribbed tube consumes more power to transport the fluid by comparing with flat one. After the tangential velocity component occurs, its contact area with the ribbed tube becomes large and it enables the effective energy transportation. The flow characteristics vary according to the geometry of tube rib. This study aims to investigate the flow characteristics of fluids working at Reynolds numbers of 20,000, 40,000, 60,000 and 80,000 with the air at $15^{\circ}C$ in the ribbed test tube high 1mm and wide 8.48mm. As the flow characteristics are included with the states of fully developed hydrodynamical region, axial velocity vector distribution and non-dimensional velocity distribution, they are shown with the physical validity.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.2
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• pp.33-39
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• 2010

The thickness of original hinge model is changed for structural stability in this study. The front end with the largest deformation of 9.8813 mm or the rear middle part with the largest equivalent stress of 6082.6 MPa is respectively shown at door hinge. The lower part of joint pin head with the largest deformation of 0.17499 mm and the largest equivalent stress of 1540.2 MPa are shown. The advanced model with more thickness and stability is shown to have smaller displacement in half and smaller equivalent stress by 3 times by comparing with the original model.

• Transactions of Materials Processing
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• v.14 no.1 s.73
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• pp.14-20
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• 2005

To carry out perfectly the forming analysis of the extruding products, it is necessary that the friction boundary condition between dies and blanks should be worked out the accurate numerical friction models. But, the existing numerical models of the extrusion may be large different from the actual conditions. In this study, accurate analysis of the extrusion forming for the variation of pressure and velocity should be subjected. It is to develop the accuracy of the numerical friction models and potentialize to apply for the high speed forming work in the extrusion. Therefore, the results should improve the accuracy, cause the energy saving for the extrusion and finally expand the applying areas of the results.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.24-27
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• 2001

Friction between the sheet and tools is one of the important factors affecting the sheet metal forming. Therefore, the clarification of the friction is essential to improve the formability of the sheet. In order to find the effect of material property and lubricant viscosity on the frictional characteristics, tensile test, surface roughness test and friction test are performed. The results showed that friction characteristics are mainly influenced by the surface roughness and lubricant viscosity. A mathematical model of the friction is developed for calculating friction coefficient in terms of surface roughness and lubricant viscosity. The validity and accuracy of the mathematical model of the friction are verified through the experiment and FEM analysis.

• Transactions of Materials Processing
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• v.13 no.3
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• pp.248-252
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• 2004

The mechanical properties of polycrystalline thin-films, critical for Micro-Electro-Mechanical Systems (MEMS) components, are known to have the size effect and the scatter in the length scale of microns by the numbers of intensive investigation by experiments and simulations. So, the consideration of the microstructure is essential to cover these length scale effects. The lattice based stochastic model for the microstructure evolution is used to simulate the actual microstructure, and the fast and reliable algorithm is described in this paper. The kinetics parameters, which are the key parameters for the microstructure evolution based on the nucleation and growth mechanism, are extracted from the given micrograph of a polycrystalline material by an inverse method. And the method is verified by the comparison of the quantitative measures, the number of grains and the grain size distribution, for the actual and simulated microstructures. Finite element mesh is then generated on this lattice based microstructure by the developed code. And the statistical finite element analysis is accomplished for selected microstructure.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.615-617
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• 2005

대기중에 위치한 뇌운안에 전하가 떠다니는 상태에서는 구름안과 주변에 높은 전계의 전위가 발생한다. 이 전하가 축적되면 대지 방전이 발생하고 송전선로 등에 뇌격이 침입하게 된다. 뇌 방전은 수 km에 달하는 대기중에 발생하는 거대한 전기현상이지만 이 낙뢰가 전기의 흐름이라는 것은 벤자민 프랭클린의 현장 시험에 대해 최초로 증명되었다. 이러한 대기중에 발생하는 거대한 전기현상인 낙뢰가 송전선로에 침입하여 송선선로 애자련을 섬락시키는 과정은 대단히 복잡한 전자기적인 현상이다. 그것은 가스 방전 현상, 감속에 중요한 역할을 하는 전자계의 빠른 변화, 도체와 철탑에 나타나는 코로 나와 관련된 비선형 효과 및 주파수 및 전류와 관련된 대지의 임피던스 통 다양한 현상이 종합적으로 관련된다. 따라서 가공 송전선로의 낙뢰에 대한 동작특성의 평가시 낙뢰 현상의 불규칙한 특성 및 신뢰할만한 데이터의 부족에 따른 많은 불확실성이 존재한다. 이 때문에 가공 송전선로에서 낙뢰에 의한 트립(Trip) 사고수의 계산을 위해 단순화된 방법이 아주 유용하며 효과적일 수 있다. 본 논문에서는 EGM (Electrogeometric Model) 모델을 사용하여 대지경사자의 크기에 따른 차폐실패 트립 사고율의 영향을 검토하였다.

• Proceedings of the KIEE Conference
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• 2006.05a
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• pp.44-47
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• 2006

송전철탑의 접지저항은 승선선로의 내뢰성능 평가에 중요한 파라메타 중 하나이다. 송전선로가 일단 가압된 이후에는 가공지선에 의해 모든 철탑이 병렬 연결되어 철탑 단독의 접지저항 측정은 현실적으로 어려운 문제가 있다. 본 논문에서는 리비아전력청의 협조 하에 가공지선 분리 전후의 220 KV 송전철탑의 접지저항측정을 위하여 수행한 전위강하시험과 컴퓨터 시뮬레이션에 의한 분석결과를 제시함으로써 컴퓨터 모델을 이용한 철탈 접지저항 추정방법의 신뢰성을 검증하고자 한다.

• Annual Conference on Human and Language Technology
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• 2018.10a
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• pp.373-377
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• 2018

판례는 재판에 대한 선례로, 법적 결정에 대한 근거가 되는 핵심 단서 중 하나이다. 본 연구에서는 채권회수를 예측하는 서비스 구축을 위한 단서를 추출하기 위해 채권 회수 판례를 수집하여 이를 분석한다. 먼저 채권 회수 판례에 대한 기초 분석을 위하여, 채권 회수 사례와 비회수 사례를 각 20건씩 수집하여 분석하였으며, 이후 대법원 및 법률 지식베이스의 채권 관련 판례 12,457건을 수집하고 채권 회수 여부에 따라 가공하였다. 채권 회수 사례와 비회수 사례를 분류하기 위한 판례 내의 패턴을 분석하여 레이블링하고, 이를 자동 분류할 수 있는 Bidirectional LSTM 기반 심층학습 모델을 구성하여 학습하였다. 채권 관련 판례 가공 기준에 따라 네 가지의 데이터 셋을 구성하였으며, 각 데이터셋을 8:2의 비율로 나누어 실험한 결과, 검증 데이터에 대하여 F1 점수 89.82%의 우수한 성능을 보였다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.47-52
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• 2004

Springback comes from the release of residual stress after forming. The control of phenomenon is especially important in the sheet metal forming since there are no other practical methods available to correct the dimensional inaccuracy from springback. Therefore the accurate predication before the die machining has been a long goal in the Held of sheet metal forming. The aim of the present study is to enhance the prediction capability of finite element(FE) analysis for the springback phenomenon. For this purpose FE analysis for V-bending has been carried out with the commercial programs, LS-DYNA. The FE analysis results have been validated through the comparison of experimental. The experimental results measured directly by the strain gauge have given the confidence to FEA.