• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.1359-1370
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• 2008

In the track geometry such as rails, sleepers, ballasts and fastener, track deterioration occurs by repetitive train weight and the high-speed railway takes a trend faster than normal. Track deterioration of over threshold value harms ride comfort and furthermore affect in trains safety seriously. An organic and systematic track maintenance system is very important because a trend of the track deterioration effects on track life-cycle and running safety. Also costs of the railway track permanent way and its maintenance are extremely large, forming a significant part of the total infrastructure expenditure. Therefor reasonable and efficient track maintenance has to be planed on a budget. It is required to carry out not only corrective maintenance but preventive maintenance for the track maintenance. In order to perform maintenance jobs in the boundary of the machines and resources given regarding the type and amount jobs, it is necessary to determine feasible or optimal scheduling considering the priority. In this study, the system organization and required functions for the development of track maintenance system supported track deterioration prediction and optimal scheduling are proposed.

• International Journal of Precision Engineering and Manufacturing
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• 제9권4호
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• pp.74-78
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• 2008

High-speed tool steels are extensively used in tooling industries for manufacturing cutting tools, forming tools, and rolls. Electrical discharge machining (EDM) has been found to be an effective process for machining these extremely hard and difficult-to-cut materials. Extensive research has been conducted to identify the optimum machining parameters for EDM with different tool steels. This paper presents a fundamental study of the surface characteristics of SKH-51 tool steel machined by micro-EDM, with particular focus on obtaining a better surface finish. An RC pulse generator was used to obtain a better surface finish as it produces fine discharge craters. The main operating parameters studied were the gap voltage and the capacitance while the resistance and other gap control parameters were kept constant. A negative tungsten electrode was used in this study. The micro-EDM performance was analyzed by atomic force microscopy to determine the average surface roughness and the distance between the highest peak and lowest valley. The topography of the machined surface was observed using a scanning electron microscope and a digital optical microscope.

• 한국군사과학기술학회지
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• 제25권2호
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• pp.151-159
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• 2022

In this paper, we implement a digital multi-beamformer using FPGA(Field Programmable Gate Array) which has advantages in parallel and real-time data processing. This is accomplished through the use of not only high-speed data communication but also multiple beam forming, which is currently required by MFR(Multi Function Radar). As a result, the beamformer can process 24 Gbps throughput in real-time and form 5 digital beams at the same time. It is also compared to the results of Matlab simulations. We demonstrate how an implemented beamformer can be used in an MFR system by using a digital array antenna.

• 한국기계가공학회지
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• 제16권2호
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• pp.28-33
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• 2017

Recently, the operation of precision pocket machining has been studied for the high speed and accuracy in industry to increase production and quality. Moreover, the demand for products with complex 3D free-curved surface shapes has increasing rapidly in the development of computer systems, CNC machining, and CAM software in various manufacturing fields, especially in automotive engineering. The type of aluminum (Al6061) that is widely used in aerospace fields was used in this study, and end-mill down cutting was conducted in fillet cutting at a corner with end-mill tools for various process conditions. The experimental results may demonstrate that the end mill cutter with four blades is more advantageous than that of the two blades on shape forming in the same condition precise machining conditions. It was also found that cutting forces and tool deformation increased as the cutting speed increased. When the tool was located at $45^{\circ}$ (four locations), the corner was found to conduct the maximum cutting force rather than the start point of the workpiece. The experimental research is expected to increase efficiency when the economical precision machining methods are required for various cutting conditions in industry.

• 한국화재소방학회논문지
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• 제25권3호
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• pp.85-90
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• 2011

본 연구는 국내 고층건물 특별피난계단의 부속실에 설치되는 급기가압 제연시스템에서 화재 발생 시 피난을 위하여 출입문이 개방되었을 경우 형성되는 방연풍속의 특성을 FDS를 이용하여 해석하였고, 해석 결과를 분산분석으로 기류의 특성에 따른 측정 방안을 분석하고자 한다. 부속실과 같은 구획공간의 설계 조건에서 급기댐퍼에서 토출되는 보충량은 심한 와류를 형성하고 형성된 와류의 범위 안에 출입문이 존재할 경우 비정상적인 기체의 유동이 출입문지점에 발생한다는 것을 선행연구를 통하여 확인할 수 있었다. 국가화재안전기준 NFSC 501A에서 방연풍속을 측정할 때에는 출입문의 개방에 따른 개구부를 대칭적으로 균등 분할하는 10 이상의 지점에서 측정하는 풍속의 평균치로 할 것으로 정하고 있으나 이러한 조건에서는 출입구 상부 지점에 기류의 유입 현상을 파악하기 어렵고 풍속의 편차가 심하기 때문에 측정점을 공기조화설비의 시험조정 평가 기술기준에서 제시하는 64점 이상으로 세분화하여 측정하여야 할 것이다.

• Journal of Biosystems Engineering
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• 제20권1호
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• pp.95-103
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• 1995

A series of study has been conducted to develop a multi-purpose fruit grader using a black ＆ white image processing system equipped with a 550 nm interference filter. A device and high performance algorithms were developed for sizing and color grading of Fuji apple in the previous study. In this study an emphasis was put on finding correlations between weights of several kinds of fruits and their area fractions(AF), and on compensating the blurring effect upon sizing and color grading by conveying speed of fruit. Also, the effect of orientation and direction of fruit on conveyor during image forming was analyzed to identify any difficulty (or utilizing an automatic fruit feeder. The results are summarized as follows. 1. The correlation coefficients(r) between the weights of fruits and their image sizes were 0.984~0.996 for apples, 0.983~0.990 for peachs, 0.995 for tomato, 0.986 for sweet persimmon and 0.970~0.993 for pears. 2. It was possible to grade fruits by color with the area weighted mean gray values(AWMGV) based on the mean gray valves of direct image and the compensated values of reflected image of a fruit, and also possible to sort fruits by size with AF. Accuracies in sizing and color grading ranged over 81.0% ~95.0% and 82.0% ~89.7% respectively as compared with results from sizing by electronic weight scale and grading by expert. 3. The blurring effect on the sizing and color grading depending on conveying speed was identified and regression equations were derived. 4. It was found that errors in sizing and coloring grading due to the change in direction and orientation of Fuji apple on the conveyor were not significant as far as the stem end of apple keeping upward.

• 소성∙가공
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• 제28권1호
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• pp.21-26
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• 2019

Direct Laser Melting (DLM) of $Ti-xTiH_2$ (mixing ratio x = 2, 5, 10 wt.%) blended powder is characterized by producing porous titanium parts. When a high energy laser is irradiated on a $Ti-TiH_2$ blended powder, hydrogen gas ($H_2$) is produced by the accompanying decomposition of the $TiH_2$ powder, and acts as a pore-forming and activator. The hydrogen gas trapped in a rapidly solidified molten pool, which generates porosity in the deposited layer. In this study, the effects of a $TiH_2$ mixing ratio and the associated processing parameters on the development of a porous titanium were investigated. It was determined that as the content of $TiH_2$ increases, the resulting porosity density also increases, due to the increase of $H_2$ produced by $TiH_2$. Also, porosity increases as the scan speed increases. As fast solidified melting pools do not provide enough time for $H_2$ to escape, the faster the scan speed, the more the resulting $H_2$ is captured by the process. The results of this study show that the mixing ratio (x) and laser machining parameters can be adjusted to actively generate and control the porosity of the DLM parts.

• 한국환경과학회지
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• 제24권12호
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• pp.1657-1671
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• 2015

In this study, the wind direction and the wind speed of the nearest temperature observations point of the National Weather Service was analyzed in order to investigate the rapid rise and drop of water temperature in the East Coast appeared after passing of the 2015 typhoon No. 9 and 11. Then the figures were simulated and analyzed using the WRF(weather research and forecast) model to investigate in more detailed path of the typhoon as well as the changes in the wind field. The results were as follows. A sudden drop of water temperature was confirmed due to upwelling on the East coast when ninth typhoon Chanhom is transformed from tropical cyclones into extra tropical cyclone, then kept moving eastwards from Pyongyang forming a strong southerly wind after 13th and this phenomenon lasted for two days. The high SST(sea surface temperature) is confirmed due to a strong northerly wind by 11th typhoon Nangka. This strong wind directly affected the east coast for three days causing the Ekman effect which transported high offshore surface waters to the coast. The downwelling occurred causing an accumulation of high temperature surface water. As a results, the SST of 15m and 25m rose to that of 5m.

• 한국전기전자재료학회논문지
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• 제22권7호
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• pp.595-601
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• 2009

For the silicon oxide $(SiO_x)$ films prepared by using the facing target sputtering (FTS) apparatus that was manufactured to enhance the preciseness of the fabricated thin-film and sputtering yield rate by forming a higher-density plasma in the electrical discharge space for using it as a thin-film passivation system for flexible organic light emitting devices (FOLEDs). The deposition characteristics were investigated under various process conditions, such as array of the cathode magnets, oxygen concentration$(O_2/Ar+O_2)$ introduced during deposition, and variations of distance between two targets and working pressure. We report that the optimum conditions for our FTS apparatus for the deposition of the $SiO_x$ films are as follows: $d_{TS}\;and\;d_{TT}$ are 90mm and 120mm, respectively and the maximum deposition rate is obtained under a gas pressure of 2 mTorr with an oxygen concentration of 3.3%. Under this optimum conditions, it was found that the $SiO_x$ film was grown with a very high deposition rate of $250{\AA}$/min by rf-power of $4.4W/cm^2$, which was significantly enhanced as compared with a deposition rate (${\sim}55{\AA})$/min) of the conventional sputtering system. We also reported that the FTS system is a suitable method for the high speed and the low temperature deposition, the plasma free deposition, and the mass-production.

• 대한기계학회논문집A
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• 제38권12호
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• pp.1373-1377
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• 2014

핫스탬핑 공정은 고강도의 강을 얻을 수 있는 방법으로써, 일반적으로 보론강을 오스테나이트 온도까지 가열한 후, 성형과 냉각을 통해 제품을 생산한다. 열처리된 보론강은 1500MPa 이상의 강도를 가지기 때문에 경량화와 안전성을 동시에 향상시킬수 있는 특징이 있다. 뿐만아니라 우수한 성형성으로 인한 치수정밀도가 기존 강판대비 90 % 이상 향상되어 우수한 성형품질을 확보할 수 있는 장점도 있다. 따라서 본 연구에서는 디스크 레이저를 사용하여 핫스탬핑 강판의 맞대기 및 겹치기 용접을 실시하여 용접특성을 파악하였다. 실험결과, 맞대기 용접에서는 맞댄면의 갭에 영향으로 인해 겹치기 용접과 비교하여 더 빠른 속도에서도 완전 용입을 얻을 수 있었으며, 모든 용접부에서 열영향부에서 화이트밴드가 관찰되었다.