• 비파괴검사학회지
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• 제37권1호
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• pp.29-36
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• 2017

최근 KTX (Korean Train Express) 열차의 사고의 대부분은 기기의 오작동, 차량 부품의 노후와에 따른 고장 및 장애발생, 신호장치에 대한 인적오류 등이 주된 원인이였다. 특히, 차량부품 중 제동 디스크의 파손은 하부 차축 및 차륜에 충격을 가해 탈선의 우려와 고속 충돌 등 대형 인명 피해를 낳을 수 있다. 따라서 본 연구에서 KTX의 제동 디스크(Solid Type, Ventilation Type)를 형상화하고, 이를 동작시켜 균열을 측정하여 DB화 할 수 있는 균열검측시스템을 구축하였다. 제동 디스크의 표면균열을 검사하기 위하여 Rayleigh wave를 이용하였으며 수침기법으로는 제동디스크 장착상태에서 탐상의 어려움이 인하여 국부수침 탐상기법을 활용하여 제동디스크의 초음파 검사모듈을 개발하였다. 또한 제동디스크의 회전에 따라 측정된 균열을 저장할 수 있는 균열검측 자동화장치와 제동 디스크의 초음파 검사모듈을 이용하여 제동 디스크의 표면결함을 평가하였다.

• Journal of Biosystems Engineering
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• 제17권3호
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• pp.229-236
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• 1992

In an effort to localize the spray-dryer which is markedly used for drying food materials, a experiment was carried out with a wheel type atomizer locally designed and manufactured to evaluate the effect of rotational speed, feed rate and physical properties of liquid food material on the droplet size, and to develop a model to predict the droplet size sprayed at various operational conditions. The result are summarized as follows. 1. The frequency of droplet size sprayed from the atomizer at every treatment were similar to normal distributions. 2. Under the test conditions adopted in this study, that is, rotational speed of the atomizer ranging from 15,000 to 20,000 rpm (55.0 m/sec - 73.3 m/sec), feed rate from 14 to 37 kg/hr and viscosity of the material from 1.14 to 350 cP, the mean volume-surface dia. of droplets was decreased as increase in rotational speed and was not affected significantly by the feed rate and viscosity. 3. Through the dimensional analysis, a prediction model was developed as follows : $$\frac{Dvs}{r}=K[\frac{Q}{{\mu}r}]^a[\frac{rN^2}{g}]^b[\frac{{\rho}^2r^3g}{{\mu}^2}]^c[\frac{L}{r}]^d$$ and it was proved that the above model was better in degree of fitness than other models reported. 4. A prediction equation for the droplet size sprayed from the atomizer under the test was expressed as follows : $$\frac{Dvs}{r}=0.0215[\frac{Q}{{\mu}r}]^{0.06}[\frac{rN^2}{g}]^{0.3314}[\frac{{\mu}^2}{{\rho}^2r^3g}]^{0.0158}$$.

• 한국기계가공학회지
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• 제13권1호
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• pp.92-99
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• 2014

An aspherical lens, which resolves several problems with a spherical lens,typically serves asa key part of an optical system. Generally, an aspherical lens is fabricated using a diamond turning machine or by mean of injection molding. However, residual stress and/or tool marks can arise when using a commercial fabricating method such as DTM or injection molding. A polishing process, thus, is commonly used to obtain a high-precision aspherical lens. In this study, a polishing method using MR fluid was applied to minimize several problems, in this case residual stress and the creation of tool marks, during the cutting process. The MR polishing system was developed to polish aspherical lenses. A series of experiments were performed to obtain a very fine surface roughness. PMMA (the lens material for molding) was used as a workpiece, and the gap size, magnetic field intensity, wheel speed and feed rate were selected as the parameters in this study. Finally, a very fine surface roughness of Ra=2.12nm was obtained after MR polishing.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.1248-1253
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• 2011

It is increasing construction of long span railway bridge with concrete track system for speed up of railway and efficient maintenance of track. As the sleeper of the concrete track system layed on a bridge is fixed on deck of the bridge, the displacement of the sleeper and deck is same. Therefore, the spacing between two sleeper installed at the end of the adjacent deck near the expansion joint of bridge becomes vary according to the longitudinal expansion of a deck by temperature change. By the way, if the spacing of sleepers become increase excessively, it causes large bending stress of in a rail, and it can leads failure or reduction of fatigue life of the rail. Further more, the excessive displacement of the rail may induce decrease ride comfort as well as corrugation of rail surface. Therefore, it is required to determine the allowable maximum sleeper spacing to prevent such problems. For the purpose, investigation on the influence factor on sleeper spacing for straight track was carried out. Variation of bending moment in a rail, wheel force, and the ratio of primary and secondary deflection of the rail according to sleeper spacing was investigated, and, as a result, the maximum allowable sleeper spacing at the bridge expansion joint was suggested.

• Restorative Dentistry and Endodontics
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• 제2권1호
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• pp.15-19
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• 1976

The author studied on the transfer of radioactive fluorine ($^{18}F$) to dental hard tissue through animal experiments which was divided into two groups. First group of rats were sacrified 1, 2, 5, 10 and 20 minutes after intraperitoneal injection. Second group were sacrified 1 and 3 minutes after topical application on anterior teeth. The teeth were removed and sectioned by means of abrasive wheel and polished on india stone as thick as about 50 microns. Autoradiograph picture was made by close contact of high-speed dental X-ray film on prepared specimen for 2 hours. The results of this study were as follows; 1) There was no evidence of transfer of $^{18}F$ on dental hard tissue on the cases of 1, 2 and 5 minutes survival after intraperitoneal injection. 2) Radioactive sodium fluorine incorporated to dental hard tissue was slight and diffuse at 10 minutes cases and significant incorporated picture was noticed at 20 minutes cases in intraperitoneal injection. 3) On topical application groups incorporated $^{18}F$ to enamel was traced clearly only on enamel surface at 1 minute cases and significant transfer into whole enamel was found at 3 minutes cases.

• 한국식품과학회지
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• 제25권6호
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• pp.769-774
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• 1993

Fluidized bed opposed jet mill을 사용하여 초미세분쇄한 후 Turboplex classifier로 공기분급한 탈지미강분말의 입도는 air classifying wheel speed (ACWS)가 낮아짐에 따라 입자의 크기와 표준편차는 증가하고 단위부피당 표면적은 감소하였다. ACWS 21,000rpm에서 분급한 미강분말의 형태는 구형이었으며 입도 median이 $3.7{\mu}m$이었다. ACWS별로 회수된 시료의 단백질, 지방, 회분은 ACWS에 따라 전반적으로 증가하는 경향이었다. Mg, Zn, Fe 및 Mn 함량은 ACWS가 증가할수록 비교적 증가하는 경향을 보였으며, phytic acid함량은 중간 ACWS에서 약간 높은 값을 보였다. 식이섬유함량은 $25.2{\sim}31.5%$의 값을 보였고, ACWS 15,000rpm에서 최대값을 나타내었다. ACWS에 따른 시료의 색도는 ACWS가 높을수록 백색도(L)가 증가하였고, 적색도(a)와 황색도(B)는 감소하는 경향을 나타내었다. 보수력(WHC)은 12,000rpm에서 2.88g/g solid로 가장 높았고 ACWS가 높아짐에 따라 감소하는 추세를 보였으나, 보유력은 반대로 ACWS에 따라 약간 증가하는 경향을 보였다. 분급된 미강분말 현탁액의 유동특성은 Bingham body에 속하였으며 농도와 ACWS가 증가함에 따라 항복응력 및 점도가 상승하였다. 분급된 미강분말을 5% 수준으로 대체하여 케이크를 제조한 경우 대조구보다 케이크의 높이와 부피가 증가하였다.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 2017년도 춘계공동학술대회
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• pp.17-17
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• 2017

In electric agricultural machine the gearhead is needed to convert the high speed low torque rotation motion generated by DC motor to lower speed high torque motion used by the vehicle. The gearhead consist of several spur gears works as reduction gears. Spur gear have straight tooth and are parallel to the axis of the wheel. Spur gears are the most easily visualized gears that transmit motion between two parallel shafts and easy to produce. The modeling and simulation of spur gears in DC motor gearhead is important to predict the actual motion behavior. A pair of spur gear tooth in action is generally subjected to two types of cyclic stress: contact stress and bending stress including bending fatigue. The stress may not attain their maximum values at the same point of contact fatigue. These types of failure can be minimized by analysis of the problem during the design stage and creating proper tooth surface profile with proper manufacturing methods. To improve its life expectation in this study modal and stress analysis of gearhead is simulated using ansys work bench software based on finite element method (FEM). The modal analysis was done to understand gearhead deformation behaviour when vibration occurs. FEM static stress analysis is also simulated on gearhead to simulate the gear teeth bending stress and contact stress behavior. This methodology serves as an approach for gearhead design evaluation, and the study of gear stress behavior in DC motor gearhead which is needed in the small workshop scale industries.

• 대한토목학회논문집
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• 제26권5D호
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• pp.831-838
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• 2006

본 연구에서는 차량의 주행속도, 차축하중 그리고 타이어 압력변화에 따른 아스팔트 포장의 주요 응답 특성을 분석하고자 하였다. 시험도로 아스팔트 포장 중 기층의 두께가 서로 다른 A5(180mm)와 A8(280mm)단면을 선정하여 표준 3축 덤프트럭에 의한 아스팔트의 변형률과 수직응력의 변화를 계측하였다. 모든 주행시험은 각 포장 단면의 주행차로에서 진행되었으며 실제 주행속도와 이동경로는 레이저 원더링 시스템을 적용하여 실시간으로 관찰, 기록하였다. 아스팔트 포장의 변형률은 차량의 주행속도가 증가할수록 그 크기가 감소하는 일반적인 점탄성 거동을 보였다. 특히 수직응력은 차축하중 뿐만 아니라 주행속도에도 영향을 받는 것으로 보아 속도별 차량의 운동특성이 각 차축으로 전달되는 연직하중의 크기에 많은 영향을 주고 있음을 알 수 있었다. 일반적으로 타이어 공기압이 증가하고 차축하중이 증가할수록 아스팔트 하부의 최대 인장변형률은 증가하였다. 두 아스팔트 포장 단면에서 다층탄성해석을 수행한 결과 변형률은 계측된 결과보다 크게 예측되었으며 수직응력은 수치해석결과가 계측결과보다 작게 평가되었다.

• 한국토양비료학회지
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• 제47권6호
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• pp.425-431
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• 2014

Most fields in highland areas are covered with rye or hairy vetch for conservation during a fallow. However, using cover crops needs an effort to sow, and this makes top soil more vulnerable to loss due to surface disturbances. The aims of this study were to develop an automatic seeding-regulator device using a low-price, extensive-use GPS sensors and a DC motors and to evaluate a working efficiency of it after adaptation to partial tillage machine for reducing seeding effort. The amount of runoff water and soil loss was evaluated with partial tillage and simultaneous-seeding after harvesting soybean, in 17% slope lysimeters. In results, the seeding amount with the machine speed was stable between $0.5{\sim}0.8m\;s^{-1}$ of working sections. The automatic control device of seeding-rate could be enough to solve the slip problems of power selecting supply system or five four-wheel drive device. In partial tillage and simultaneous seeding, runoff water was 11.6% ($1.8m^3ha^{-1}$) of the scatter-seeding control ($15.5m^3ha^{-1}$) and soil loss was 13.2% ($7kg\;ha^{-1}$) of the scatter-seeding control ($53kg\;ha^{-1}$). These results suggest that partial tillage and simultaneous-seeding methods are very effective in decreasing work effort and soil loss of sloped land.

• Journal of Astronomy and Space Sciences
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• 제21권2호
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• pp.141-152
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• 2004

우주망원경용 비구면 반사경 가공 공정은 고정입자 연삭, 자유입자 래핑, 연마의 순서를 따른다. 숙련공에 의한 경험적 공정조절에 의해 목표 비구면을 가공하는 전통적 연삭 공정에서는 수 ${mu}m$ 높이의 표면 밑 손상을 남기며 뒤이은 자유입자 래핑 및 연마 공정에서 이를 제거하며 가공한다. 본 연구는 컴퓨터 수치 제어 연삭 공정진화 모델을 개발하여, 연삭가공을 통해 반사경 표면조도 최소 40nm이하, 가공 예측정확도 20nm급을 이루었다. 구체적인 방법론으로 초정밀가공기의 연삭모듈을 이용하여 연삭 휠 입자의 크기, 이송속도, 공작물 회전선속도 등 연삭 변수를 변화시키며 직경 20, 100mm Zerodur 소재를 초기 연삭하였다. 초기 연삭 변수와 측정된 표면조도와의 관계를 경험적 해석과 다 변수 회귀분석 해석 방법을 통하여 공정조절용 수치 연삭 모델을 구성하였다. 정량적 공정제어는 입력된 연삭변수들로부터 가공 후 표면조도를 예측하고, 측정된 표면조도를 이용하여 수치연삭 모델을 개량한 후 다음 가공에서 측정될 표면조도를 예측하는 순으로 만복 진행되었다. 본 연구에서는 CNC 연삭공정조절로부터 최소 평균 표면조도 36nm, 예측정확도 ${pm}20nm$를 얻었다. 이 연구결과는 정량적 연삭공정제어 모델을 사용하여 자유입자 래핑 공정을 수행할 필요 없이 연삭에서 직접 연마 공정으로 진행할 수 있는 획기적인 공정 효율 향상을 의미한다.