• 소성∙가공
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• 제11권5호
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• pp.430-438
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• 2002

This paper suggests the new technology to control metal flow in orther to change of the cold forging from conventional deep drawing forming. This technology can be summarized the complex forming, which consists of bulk forming and sheet forming, and multi-action forging, which be performed double action press. The proposed technology is applied to hub clutch model which is part of auto-transmission for automobile. The purpose of this study is to investigate the material flow behavior of hub clutch through control the relative velocity ratio and the stroke of mandrel and punch using the flow forming technique. First of all, the finite element simulations are applied to analyse optimal process conditions to prevent flow defect(necking defect etc.) from non-uniform metal flow, then the results are compared with the plasticine model material experiments. The punch load for real material is predict from similarity law. Finally, the model material experiment results are in good agreement with the FE simulation ones.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.350-353
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• 2005

Microstructures according to experimental conditions (pouring temperature, stirring current and stirring time) and hardness according to aging time were investigated for A356 cast aluminum alloy and 7075 wrought aluminum alloy. In pouring temperature control, grains became larger and non-uniform at high temperature, however dendritic shapes were shown at lower temperature. In stirring current control, dendritic grains were not destroyed enough at lower current, however fine grains were agglomerated at higher current. And, in stirring time control, grains were more globular but grew larger and larger with the stirring time increasing.

• 한국위성정보통신학회논문지
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• 제4권1호
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• pp.28-35
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• 2009

본 논문에서는 위성 OFDMA 하향링크에서 PAR을 최소화하기 위한 최적의 사용자 채널 보상기법을 제안한다. 위성 OFDMA 시스템에서는 사용자의 채널 환경에 따른 성능의 저하를 극복하기 위해 사용자의 채널 환경에 따라 전력을 제어하는 PC-OFDMA(Power Control OFDMA) 방식과 변조방식과 코딩방식을 제어하는 AMC-OFDMA(Adaptive Modulation and Coding) 방식을 사용한다. 사용자의 채널 환경에 따라 사용자 부채널(부반송파 그룹)별로 전력을 제어하는, 즉 채널이 좋지 않을 경우 더 큰 출력으로 송신하고 반대의 경우 작은 출력을 송신하는 PCOFDMA와 채널의 상태가 좋지 않은 경우 낮은 변조율과 강한 코딩을 사용하거나 채널이 좋을 경우 데이터율을 높이기 위해 높은 변조율과 약한 코딩을 사용하는 AMC-OFDMA의 PAR 성능을 비교 분석하였다. AMC-OFDMA에서는 변조방식과 부호방식으로 사용자 채널감쇠를 보상하므로 부반송파의 송신전력이 균일하지만 PC-OFDMA의 경우 사용자 부채널별로 전력을 제어하므로 전체 부반송파의 송신전력이 균일하지 않는 특성이 있는데, 부반송파의 불균등 전력은 OFDMA 송신신호의 PAR을 감소시키는 현상을 발견하였다. 또한 PC-OFDMA 방식 중에서 사용자 부채널을 이루는 부반송파의 할당방식에 따라서도 PAR 성능의 차이가 존재함을 보였다.

• Computers and Concrete
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• 제22권1호
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• pp.53-62
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• 2018

Cracking of concrete cover induced by reinforcement corrosion is a critical issue for life-cycle design and maintenance of reinforced concrete structures. However, the critical degree of corrosion, based on when the concrete surface cracks, is usually hard to predict accurately due to the heterogeneity inherent in concrete. To investigate the influence of concrete heterogeneity, a modified rigid-body-spring model, which could generate concrete sections with randomly distributed coarse aggregates, has been developed to study the corrosion-induced cracking process of the concrete cover and the corresponding critical degree of corrosion. In this model, concrete is assumed to be a three-phase composite composed of coarse aggregate, mortar and an interfacial transition zone (ITZ), and the uniform corrosion of a steel bar is simulated by applying uniform radial displacement. Once the relationship between radial displacement and degree of corrosion is derived, the critical degree of corrosion can be obtained. The mesoscale model demonstrated its validity as it predicted the critical degree of corrosion and cracking patterns in good agreement with analytical solutions and experimental results. The model demonstrates how the random distribution of coarse aggregate results in a variation of critical degrees of corrosion, which follows a normal distribution. A parametric study was conducted, which indicates that both the mean and variation of critical degree of corrosion increased with the increase of concrete cover thickness, coarse aggregates volume fraction and decrease of coarse aggregate size. In addition, as tensile strength of concrete increased, the average critical degree of corrosion increased while its variation almost remained unchanged.

• 한국환경교육학회지:환경교육
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• 제15권2호
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• pp.1-13
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• 2002

The progress of environmental science and technology in the developed countries has been rapid in recent years. Particularly remarkable has been the advancement of various pollutant control measures, which have brought the pollution of inorganic factors such as air and water under control. In contrast, diversity of the ecosphere, of which man is a part, is being steadily impoverished and the biological community is getting unvaryingly uniform. These phenomena were brought about by the expansion of artificial environment such as new industrial complexes, transportation facilities and urban development. Man has constructed uniform and artificial environment, believing in the premise of confrontation with nature, to such a scale that the natural environment and biological community have lost their balance. This will increasingly endanger the soundness of the biotic environment of nature, which constitutes the potential foundation both for the survival environment of man as biological entity and for the development of human civilization. In order to guarantee the soundness of man's body, intelligence and sensitivity as wholesome gene pool on the earth and for the future of man, primarily important environmental education is the understanding of how man can everlasting exist in and with the survival environment. In view of this reality, it is vitally important to create ecologically diverse and well-balanced environment with living materials, i.e., vegetation in order to secure lasting survival environment for man. This task is urgently required in highly artificial environment where non-biological materials have forced the impoverishment of the biological community. Therefore, environmental education for the future should not be totally oriented to technology as that in the past nor it is limited to the medical aspect where well-being of human is the sole object of concern. That is to say, environmental education for the future should be one that provides knowledge that human can understand his place based on the ecological concept and thereby make him to have ethical consciousness that he can control his behavior within the reasonable level for ecological niche who he is located.

• 한국정밀공학회지
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• 제29권3호
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• pp.289-294
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• 2012

There are several indicators to represent characteristics of chemical mechanical planarization (CMP) such as material removal rate (MRR), surface quality and removal uniformity on a wafer surface. Especially, the removal uniformity on the wafer edge is one of the most important issues since it gives a significant impact on the yield of chip production on a wafer. Non-uniform removal rate at the wafer edge (edge effect) is mainly induced by a non-uniform pressure from nonuniform pad curvature during CMP process, resulting in edge exclusion which means the region that cannot be made to a chip. For this reason, authors tried to minimize the edge exclusion by using an edge profile control (EPC) ring. The EPC ring is equipped on the polishing head with the wafer to protect a wafer from the edge effect. Experimental results showed that the EPC ring could dramatically minimize the edge exclusion of the wafer. This study shows a possibility to improve the yield of chip production without special design changes of the CMP equipment.

• 한국환경교육학회지:환경교육
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• 제15권1호
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• pp.137-147
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• 2002

The progress of environmental science and technology in the developed countries has been rapid in recent years. Particularly remarkable has been the advancement of various pollutant control measures, which have brought the pollution of inorganic factors such as air and water under control. In contrast, diversity of the ecosphere, of which man is a part, is being steadily Impoverished and the biological community is getting unvaryingly uniform. These phenomena were brought about by the expansion of artificial environment such as new industrial complexes, transportation facilities and urban development. Man has constructed uniform and artificial environment, believing in the premise of confrontation with nature, to such a scale that the natural environment and biological community have lost their balance. This will increasingly endanger the soundness of the biotic environment of nature, which constitutes the potential foundation both for the survival environment of man as biological entity and for the development of human civilization. In order to guarantee the soundness of man's body, intelligence and sensitivity as wholesome gene Pool on the earth and for the future of man, primarily important environmental education is the understanding of how man can everlasting exist in and with the survival environment. In view of this reality, it is vitally important to create ecologically diverse and well-balanced environment with living materials, i.e., vegetation in order to secure lasting survival environment for man. This task is urgently required in highly artificial environment where non-biological materials have forced the impoverishment of the biological community. Therefore, environmental education for the future should not be totally oriented to technology as that in the past nor it is limited to the medical aspect where well-being of human is the sole object of concern. That is to say, environmental education for the future should be one that provides knowledge that human can understand his place based on the ecological concept and thereby make him to have ethical consciousness that he can control his behavior within the reasonable level for ecological niche who he is located.

• 한국정밀공학회지
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• 제18권4호
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• pp.97-103
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• 2001

Accuracy of a machined part is determined by the relative motion between the cutting tool and the workpiece. One of the important factors which affects the relative motion is the geometric errors of a machine tool. In this study, firstly, geometric errors are measured by laser interferometer, and the positioning error of each control point selected uniformly on the control surface CAD model can be estimated from th oirm shaping model and geometric error data base. Where a form shaping function is derived from the link of homogeneous transformation matrix. Secondly, control points are shifted to the estimated amount of positioning errors. A new control surface is modeled with NURBS(Non Uniform Rational B-Spline) surface approximation to the shifted control points. By generating tool paths to the redesigned control surface, we reduce the machining error quite.

• Journal of Electrical Engineering and Technology
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• 제13권4호
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• pp.1740-1751
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• 2018

This paper proposes a novel fault tolerant tracking control (FTTC) scheme for a class of nonlinear systems with actuator failures based on the policy iteration (PI) algorithm and the adaptive fault observer. The estimated actuator failure from an adaptive fault observer is utilized to construct an improved performance index function that reflects the failure, regulation and control simultaneously. With the help of the proper performance index function, the FTTC problem can be transformed into an optimal control problem. The fault tolerant tracking controller is composed of the desired controller and the approximated optimal feedback one. The desired controller is developed to maintain the desired tracking performance at the steady-state, and the approximated optimal feedback controller is designed to stabilize the tracking error dynamics in an optimal manner. By establishing a critic neural network, the PI algorithm is utilized to solve the Hamilton-Jacobi-Bellman equation, and then the approximated optimal feedback controller can be derived. Based on Lyapunov technique, the uniform ultimate boundedness of the closed-loop system is proven. The proposed FTTC scheme is applied to reconfigurable manipulators with two degree of freedoms in order to test the effectiveness via numerical simulation.

• 융합신호처리학회논문지
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• 제24권1호
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• pp.27-33
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• 2023

최근 기후변화로 인한 물 부족 현상이 발생하고 있으며 저수지의 녹조 발생으로 농업용수의 물 관리 필요성이 증대되고 있다. 기존의 녹조 방지는 많은 사람이 현장에 투입돼 운영되고 보트를 통한 이동으로 최적의 살포 시간을 놓치고 있다. 이를 해결하기 위해서는 오염을 사전에 차단하고 시간 내 이동하여 균일하게 복합 미생물을 균일하게 살포하는 기술이 필요하다. 방제 드론은 농약 살포에 활용되고 있으며 방제 드론을 활용하여 녹조 방지 업무에 적용이 가능하다. 본 논문에서는 해양 방제 시스템 구축을 위한 기초연구로 저수지 환경 적용을 위해 수행되었으며, 그 결과물의 하나로 방제 드론에 사용 가능한 핵심기술인 드론 전용 노즐의 특성을 산출하였다. 특히, 기존의 농업용 방제 드론이 제시된 살포 간격 내에서 농도가 불균일하다는 단점이 있음을 파악하였고, 이를 보완하기 위해 노즐 위치선정 및 노즐 살포 균일도를 산출하였다. 실험 결과를 바탕으로 저수지 환경의 녹조 감시 시스템 구축의 핵심 알고리즘을 개발하고 추후 해양 방제 업무 적용에 활용이 가능하도록 정밀 방제 기술을 제안한다.