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Finite-Element Analysis of Radial Extrusion for a Thin Disk with Severe-Plastic Deformation
박종진 대한금속·재료학회 2012 METALS AND MATERIALS International Vol.18 No.3
Severe plastic deformation is an effective method to obtain fine or ultrafine grains in metallic materials. In the present study, a radial extrusion of a round bar was investigated for the capability of producing a thin disk by severe plastic deformation by the rigid-plastic finite-element method. Similar to the deformation mechanism in the ECAP, the shear deformation was observed to develop at the corner of the container; its magnitude increases as the radius of the corner decreases. Additional plastic deformation was obtained as the material flowed in the radial direction. However, waviness of the sheet in the radial direction and occurrence of cracking were observed at the periphery of the disk. To resolve these problems, the bottom surface of the container was conically designed in order to provide an inclination angle along the radial direction. This process was further modified to a radial extrusion of a pipe for a hollow disk or thin ring with severe-plastic deformation.
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Finite-Element Analysis of a Vertical Twin-Roll Casting
박종진 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.2
Metallic strips can be produced by twin-roll casting, in which the melt is cooled, solidified, and rolled to aspecific thickness. In the present study, the rigid-thermoviscoplastic finite-element method was applied tothe analysis of complex phenomena including melt flow, heat transfer, solidification, and plastic deformationoccurring in a vertical twin-roll casting of magnesium alloy AZ31. The melt was found to be confined in rotationalmotions of two symmetric vortexes developed at the roll entrance, and thus only the melt near the nozzlewall became solidified and rolled to a sheet. As the nozzle thickness increased, the vortex increased in sizeresulting in more bifurcation and instability, which are definitely adverse to material properties of the strip. The maximum cooling rate of 600 °C/s was found at the centerline as solidification took place at the rollexit. Other findings are also discussed including roll force, roll torque, and pressure distribution, which weregreatly dependent upon the plastic deformation after solidification.
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박종진,김동규 한국체육철학회 2012 움직임의철학 : 한국체육철학회지 Vol.20 No.3
마라톤경기는 우리 민족의 역사와 특별한 관련성이 있다. 한국민족이 올림픽이라는 국제대회에 참가하여 첫 금메달과 함께 올림픽 신기록을 세운 종목이 바로 마라톤이다. 이후 일장기말소사건을 거치면서 마라톤은 일제강점기에 독립정신을 일깨우고, 민족적 자부심을 가지게 한 촉매제로 작용하였다. 해방 직후 미군정 시기에는 태극기를 가슴에 달고, 연속적인 우승과 함께 대회신기록을 갱신함으로써 ‘마라톤왕국 코리아’라는 별칭이 붙었다. 이는 당시 신생독립국인 대한민국의 유일한 국위선양 방법이었으며, 한국 스포츠史에서 ‘민족정신의 고취’와 ‘국가알림’의 통로가 되었다. 세계화, 국제화 시대에 있어서도 그 기초가 되는 세포구조는 민족이며, 스포츠야 말로 이의 동류의식과 결속의 지름길이 될 수 있다. 그러한 의미에서 한국의 마라톤은 국제사회에서 한국의 기호이자 국가 이미지였다. 정치의도와의 밀접한 연관성에 의해 ‘강요된 충성’을 수단으로 낙착된 국가주의와는 달리, 한국 마라톤은 ‘자발적 애국’을 통한 민족정신의 고양을 상징하는 민족주의의 발현이었던 것이다. Marathon has a special relationship with the history of Korean people. The first gold medal and new record in the Olympics by a Korean were achieve in the marathon game. Afterwards, the Japanese flag erasure incident awakened the spirit for independence during the Japanese colonization era and served as a catalyst for ethnic pride. Right after the liberation, during the U.S. military government era, Koreans competed with the Korean flag on their chests, and with a series of wins and new Olympic records, earned the nickname of‘Kingdom of Marathon, Korea.’ This was the only way of boosting the national prestige for Korea which was a new independent country at the time, and it became the route of‘letting the world know of Korea’and‘inspiration of ethnic spirit’in the history of sports in Korea. Even in the globalization era, the cell structure at the base is the ethnicity, and sports can be the shortcut to such consciousness of kind and unity. In such respect, marathon of Korea was the symbol and national image of Korea in the global society. Unlike nationalism settled with a means of‘forced loyalty’by the close relationship with political intent, marathon of Korea was a manifestation of nationalism symbolizing the uplifting of ethnic spirit through‘voluntary patriotism.’
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박종진,최규석,박인규,강정진 한국인터넷방송통신학회 2012 한국인터넷방송통신학회 논문지 Vol.12 No.1
Control Theory for continuous-time system has been well developed. Due to the development of computer technology, digital control scheme are employed in many areas. When delays are in control systems, it is hard to control the system efficiently. Delays by controller-to-actuator and sensor-to-controller deteriorate control performance and could possibly destabilize the overall system. In this paper, a new approximated discretization method and digital design for control systems with multiple state, input and output delays and a generalized bilinear transformation method with a tunable parameter are also provided, which can re-transform the integer time-delayed discrete-time model to its continuous-time model. Illustrative example is given to demonstrate the effectiveness of the developed method. 연속시간 시스템의 제어 이론은 잘 개발되어 왔다. 컴퓨터 기술의 발달로 인해 디지털 제어 기법이 여러 분야에 적용되어 왔다. 제어 시스템에 시간 지연이 있는 경우는 시스템을 효율적으로 제어하는 것이 어렵다. 제어기와 액츄에이터 그리고 센서와 제어기 간에 있는 지연은 제어 성능을 떨어뜨리고 전체 시스템을 불안정하게 할 수 있다. 본 논문에서는 다중의 상태, 입력 그리고 출력 지연을 가지는 제어 시스템을 위한 새로운 근사 이산화 방법과 디지털 설계 그리고 조정가능한 계수를 가지는 일반화된 쌍선형 변환 방법을 제안한다. 이 방법은 정수의 시간 지연을 가지는 이산 시간 모델을 동일한 연속 시간 모델로 다시 변환할 수 있다. 실제적인 예제를 통해 제안된 방법의 효율성을 증명한다.
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