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Design analysis and simulation of an external helical gear
이철희,양진룽,이강희,이철희 사단법인 유공압건설기계학회 2023 드라이브·컨트롤 Vol.20 No.4
This study optimized the parameters of the helical gear based on the original external meshing helical gear pump, combined with the analysis of the stability and flow of the basic parameters of the equipment; herringbone gears were used to eliminate the axial force generated by the helical gears. An optimized helical gear rotor was built with NX. The error between the simulation and calculation results of pump displacement was 3.95% and the simulation results were valid. Analysis of the outlet pressure and lift changes (maximum change rates of 0.38% and 0.25%), pressure analysis of the XY center plane at different times in the same cycle (no pressure surge or drop), and analysis of the axial force of the primary and driven rotors (axis The axial force is close to 0) were performed. The results showed that the flow pulsation of the external gear pump was slight, the operation was smooth, vibration and friction were reduced, the wear of bearings and other components could be diminished, and the service life of the equipment was extended. The simulation results showed that the external gear pump met the design requirements.
Reliable Fault Diagnosis Method Based on An Optimized Deep Belief Network for Gearbox
이철희,Oybek Eraliev,Ozodbek Xakimov,이철희 사단법인 유공압건설기계학회 2023 드라이브·컨트롤 Vol.20 No.4
High and intermittent loading cycles induce fatigue damage to transmission components, resulting in premature gearbox failure. To identify gearbox defects, numerous vibration-based diagnostics techniques, using several artificial intelligence (AI) algorithms, have recently been presented. In this paper, an optimized deep belief network (DBN) model for gearbox problem diagnosis was designed based on time-frequency visual pattern identification. To optimize the hyperparameters of the model, a particle swarm optimization (PSO) approach was integrated into the DBN. The proposed model was tested on two gearbox datasets: a wind turbine gearbox and an experimental gearbox. The optimized DBN model demonstrated strong and robust performance in classification accuracy. In addition, the accuracy of the generated datasets was compared using traditional ML and DL algorithms. Furthermore, the proposed model was evaluated on different partitions of the dataset. The results showed that, even with a small amount of sample data, the optimized DBN model achieved high accuracy in diagnosis
이철희,이종훈,우동식,김강욱 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.10
In this paper, a metamaterial-based zeroth-order (ZOR) mushroom antenna is presented by using a new CRLH TL unit-cell implemented by a U-shaped top plate to extend bandwidth. The ZOR antenna whose resonance frequency is independent of the antenna size can enable the reduction of antenna size. Because the shunt capacitance is determined by the area of a mushroom patch, the U-shaped mushroom having lower shunt capacitance than the Sievenpiper mushroom structure is properly designed to widen small bandwidth of the CRLH TL antenna. The patch of the U-shaped mushroom structure of three unit-cells provides reduced shunt capacitance, and the increased 10 dB bandwidth of 2.5 times at 9.37 GHz can be obtained than the Square-shaped mushroom structure.
Effect of Changing Business Condition on Prenatal Health
이철희 서울대학교 경제연구소 2023 Seoul journal of economics Vol.36 No.3
Previous studies from developed countries suggest that babies conceived during recessions have better birth outcomes. However, the issue of whether the relationship between business condition and infant health differs across countries remains less clear. This paper investigates how the macroeconomic conditions to which mothers are exposed during pregnancy affect the birth outcomes of children. The analyses are based on the universe of birth registration records from 1993 to 2009 that are linked to the unemployment statistics by province and month of birth. Results indicate that prenatal exposure to higher unemployment significantly reduces birth weights and increases the risk of low birth weight. A recession has a stronger negative effect on fetal health during the first and second trimesters than in the final stage of pregnancy. The negative effects of prenatal exposure to higher unemployment rates on birth weight are observed only for the children of non-working mothers. Higher unemployment rates during pregnancy had considerably stronger negative effects on birth outcomes during the period before the financial crises of 1998 and 1999 than in the post-crisis period.
엘리엇의 네 사중주 ―추억과 체험 그리고 언어 표현의 문제와 인간의 삶
이철희 한국T.S.엘리엇학회 2019 T.S. 엘리엇 연구 Vol.29 No.1
엘리엇의 네 사중주는 그의 어느 다른 작품보다도 우리의 깊은 사고를 요구하는 작품이다. 그래서 다양한 별칭이 붙어 있으며 특히 우리가 간과할 수 없는 점은 엘리엇 개인의 추억과 체험에 의존하여 창작된 작품이다. 그래서 엘리엇 역시 자신이 느낀 체험을 문자화(언어화)시키려고 부단히 노력했으며 독자들은 그의 추억과 체험에 의존해서 출현된 언어화를 적절히 이해하는 것이 본 작품에 대한 이해의 최대 관건이다. 그래서 본 연구는 네 사중주의 창작과정에서 ‘추억’과 ‘체험’의 중요성을 간략하게 살펴보았고 이어서 그 ‘추억’과 ‘체험’을 구체화시키려고 노력하는 엘리엇의 모습과 함께 인간의 삶의 바람직한 자세를 시간으로부터의 구원이라는 시각으로 살펴보았다.