• 대한기계학회논문집A
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• 제37권10호
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• pp.1269-1278
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• 2013

엔드밀링 공정은 형상창성기구의 특성 상, 절삭면적의 주기적인 변화를 피할 수 없다. 그러므로, 본 연구에서는, 가공 중 절삭날과 공작물 사이의 간섭영역에 해당하는 절삭면적의 모델을 확립하여, 가공면 형상 특성과 절삭면적의 관계를 규명하고자 한다. 대상 가공면은 측벽을 선정하였으며, 형상 특성은 축 방향 진직도를 선택하였다. 절삭면적 및 축방향 진직도에 영향을 미치는 특이점 추정 모델의 타당성은 반경 방향 및 축 방향 절삭깊이를 변화시키며 엔드밀링 가공을 수행하여 검증하였다. 연구 결과, 배분력이 음의 값을 갖지 않는 안정적인 엔드밀링 가공의 경우, 상향절삭은 절삭면적이 증가했다. 일정해지는 영역에서, 하향절삭은 절삭면적이 일정했다 감소하는 영역에서 가공면을 창성하며, 영역이 변화될 때 가공면에 특이점이 발생하는 것이 확인되었다.

• Journal of Welding and Joining
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• 제17권1호
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• pp.97-103
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• 1999

Ships, structures on the ocean, bridges, and other structures tend to be large by the development of industry. These ultra thick plate were welded with large heat input, which causes welding stresses, deformation and buckling, so it has to be considered the weld design, safety, reliability. The welded residual stresses were produced and redistributed due to the effect of large heat input. The mechanical phenomenon has not been surely identified yet. In spite of the lack of the study on the box column, there are various types of steel frame such as I type, H type, + type and $\bigcirc$ type, used in high story building. In this study, we performed computer simulation with two dimensional heat conduction and plane deformation thermal elasto-plastic finite element computer program as changing the plate thickness to 100mm, 150mm and groove angle to $60^{\circ}C$, $45^{\circ}C$, $30^{\circ}C$ of corner joint in box column. And then, to identify mechanical phenomenon such as the phenomenon of thermal distribution, welding residual stresses and deformation and to decide optimum groove angle and welding condition. The main conclusion can be summarized as follows: 1) Since the groove angle has became cooling down rapidly due to its smaller value, the temperature slope was steeped somewhat. 2) The tensile stress within the welding direction stresses was somewhat decreased at the weld metal and HAZ, increasing of the groove angle. 3) The local stress concentration of the groove angle $60^{\circ}C$ was appeared smaller than groove angle $30^{\circ}$.

• 한국재료학회지
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• 제13권6호
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• pp.369-373
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• 2003

Magneto-optic Kerr Effect(MOKE), AFM and magnetoresistance measurements have been carried out on as-deposited and annealed Magnetic Tunnel Junctions(MTJs) with junction sizes 180, 250, 320 and 380 $\mu\textrm{m}$ in order to investigate the correlation among interlayer exchange coupling, surface roughness and junction size. Relatively irregular variations of coercivity $H_{c}$ (∼17.5 Oe) and interlayer exchange coupling $H_{E}$ (∼17.5 Oe) are observed over the junction in as-deposited sample prepared by DC magnetron sputtering. After annealing at $200^{\circ}C$, $H_{c}$ decreases to 15 Oe, while $H_{ E}$ increases to 20 Oe with smooth local variation. $H_{E}$ shows very good correlation with surface roughness across the junction in agreement with Neel's orange peel coupling. The increasing slope per $\mu\textrm{m}$ of normalized $H_{c}$ and $H_{E}$ are same near junction edge along free-layer direction irrespective of junction size, giving relatively uniform $H_{c}$ and $H_{ E}$ for wider junction size. Thickness profiles of the junctions measured with $\alpha$-step show increasingly flat top surface for larger junctions, indicating better uniformity for large. junctions in agreement with the normalized$ H_{c}$ and H$/_{E}$ curves. TMR ratios also increase with increasing junction size, indicating improvement for larger uniform junctions.

• 한국해안해양공학회지
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• 제12권4호
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• pp.168-180
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• 2000

In the Part I, the three dimensional model testing with NNW deep water wave direction gave the results such that the occurrence of breaking waves over the peak of Ear-Do caused very small wave height at the structure position. But the measured wave forces were rather greater than the calculated forces based on deep water wave height. Furthermore, It was also perceived that the time series of the forces looked like corresponding to the case that waves were superimposed by an unidirectional current. In the present Part II, the current is presumed to be a flow secondly induced by breaking waves, and an extensive study to clarify the current in a quantitative sense is performed through numerical analysis and hydraulic experiment. The results showed that a strong circulation can surely occur in the vicinity of the structure due to radiation stress differentials given by the breaking waves. It was also recognized that the velocity of the induced current varied with the magnitude of energy dissipation rate introduced in the numerical analysis. The numerical analysis was tuned adjusting the dissipation rate so that the calculated wave field could closely match with the experimental results of Part I. The fluid force (in prototype) for the optimal match showed approximately 2.2% increased over the calculated value based on the deep water wave height (24.6m) whereas the force corresponding to the average of the experimental values showed the increase of about 13.0%.

• 한국해안해양공학회지
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• 제18권2호
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• pp.154-165
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• 2006

본 연구에서는 수중 천퇴부에서 쇄파가 발생할 시 주변 파랑과 파랑류의 평형계를 직접 해석할 수 있는 Boussinesq 방정식 모델을 수립하고 이 결과를 수리실험 결과와 비교하였다. 사용된 쇄파모델은 쇄파 감쇠항을 모멘텀 방정식에 포함시키는 일종의 와점성 계수 모델이며, 관련된 쇄파 매개변수의 적정 값들을 Vincent and Briggs (1989)의 규칙파 실험자료를 이용한 민감도 분석을 통하여 결정하였다. 구해진 적정 매개변수 값들을 가지고 수치해석을 수행하여 이 결과를 불규칙파 실험결과와 이어도 천연암초의 수리모형실험 결과와 비교하였다. 그 결과, 천퇴부 하류 쪽에 파 진행방향으로 향하는 강한 쇄파유도류가 발생함에 따라 저파고대가 형성되며 전반적으로 계측파고의 분포와 유사함을 확인하였다.

• 공업화학
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• 제5권2호
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• pp.255-262
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• 1994

아크용융방법으로 준비한 Ti-5Bi 합금을 산화시켜 제조한 산화티타늄의 에너지변환효율(${\eta}_e$)을 광학농도, 광에너지에 따라서 측정하였다. 그리고 광학농도 및 전해액의 pH변화에 따른 플랫-밴드전압변화를 측정하였다. 광학농도와 광에너지가 증가하면 에너지변환효율은 증가하였으며 광학농도 $0.2W/cm^2$, 조사되는 빛의 에너지가 4.0eV에서 최대 에너지변환효율은 각각 3.2%, 13%로 나타났다. 에너지변환효율은 인가전압 의존성을 보여주었으며 0.5V의 전압을 인가하였을 경우 최대값을 보여주었다. 한편 전체 광전류의 발생은 산화티타늄 공핍층 내의 전자-정공쌍의 생성반응에 의해 율속되었다. 광학농도가 증가하면 플랫-밴드전압은 -0.065V/decade의 기울기를 나타내었으며 전해액의 pH가 감소하면 플랫-밴드전압은 양의 방향으로 이동하였으며 그 기울기값은 0.059V/pH로 Nernst 식의 기울기값과 일치하였다.

• 대한공간정보학회지
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• 제17권1호
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• pp.53-59
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• 2009

일반도시계획은 보편적이고 획일적인 건축행위를 제한하는 평면계획인 반면 지구단위계획은 필지, 가구, 획지단위 별로 차등을 두어 다양한 건축행위를 유도할 수 있는 입체적인 계획이다. 그러므로 단지계획을 위해서는 토지이용계획 등 2차원적인 토지정보뿐만 아니라 채광, 배수, 향 등의 분석을 위해 3차원적인 지형정보의 이용이 필요하다. 이러한 필요성을 충족시키기 위해 GIS 및 사진측량 기법을 이용하여 정보를 구축한다면 보다 합리적이고 효율적으로 단지계획을 수립할 수 있다. 본 연구에서는 테스트지역에 대해 GIS기법을 이용하여 단지계획을 위한 정보를 구축하였으며 위성영상과 DEM으로 대상지역의 3차원 모델을 구축하여 분석하였다. 연구결과 토지이용분석, 배향 분석, 수계분석, 경사분석을 실시하여 지구단위계획 수립에 효율적으로 활용할 수 있었다. 또한 분석결과를 반영하여 실제 대상지역에 대해 지구단위계획을 수립한 결과 적절하며 효율적임을 알 수 있었다.

• Journal of Biosystems Engineering
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• 제13권2호
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• pp.38-45
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• 1988

This study was intended to develop the system automatically controlling travel direction of combine by means of sensing paddy rows. The control system was composed of three detecting levers having different length, micro-switch, microcomputer and electro-hydraulic control system. Sensor and control system developed was tested to estimate optimum design values and its actual performance as installed in combine. The computer simulation and performance test at simulated and actual field were conducted to test for possibility of practical use. The results of the study arc summarized. as follows: 1. The travel traces of combine hiving the conventional sensor with 2 levers and the new sensor detecting the slope of paddy rows were compared through computer simulation. Turning frequency of combine having new sensor was fewer than that of conventional sensor, but the rate of turning for the combine with new sensor was much greater than that of conventional sensor. 2. As sensor was established behind the tip of divider, the sensor itself well followed paddy rows but the tip of divider did not, resulting in divider being deviated from paddy rows. It was analyzed that the sensor should be attached closer to the tip of divider to have a better performance of the control system. 3. The greater the length of sensor lever for given location of sensor attachment and combine forward speed, the higher sensitivity of turning in control system. Moreover, increasing combine speed resulted in a worse performance of control system following paddy rows. Consequently, it was necessary that an optimum length of sensor attachment and for the range of combine operational speed. 4. Field test of combine installed with the sensor and electro-hydraulic system developed in this study showed that it may be operated smoothly and well behaved to paddy rows to 4th gear of combine speed which was 59cm/s. Consequently. it was concluded that the combine with the guidance control system developed in this study may be successfully used for paddy combining.

• 한국자원식물학회지
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• 제22권5호
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• pp.389-393
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• 2009

수요증가가 예상되는 겨우살이의 인공번식을 위한 기초자료로 활용하고자 겨우살이의 분포지역의 기주수종과 서식지 환경을 조사하여 분석하였다. 겨우살이의 자생지는 전국에 분포하고 있었으며, 기주식물로는 졸참나무와 같은 참나무류가 대부분이였고 밤나무, 벚나무, 오리나무, 돌배나무 등에서 볼 수 있었다. 군락지의 같이 자생하는 침엽수인 소나무, 잣나무와 활엽수인 느티나무, 감나무, 고로쇠나무, 단풍나무, 뽕나무, 은행나무에서는 관찰되지 않았다. 자생지의 고도는 해발 $0{\sim}1200\;m$까지 잘 생육되고 방향과 지형을 가리지 않고 기주식물이 잘 생육 할 수 있는 곳이면 전국에서 재배가 가능할 것으로 판단되었으며, 종자 전파는 조류에 의함이 확인할 수 있었다. 겨우살이의 기생은 흡기 발생부터 기주식물의 표피 또는 조직성분에 따라 영향이 있을 것으로 생각되며 인공재배 연구의 좋은 성과를 위해 겨우살이가 잘 기생하는 기주식물의 기주 특이성에 대한 연구가 이루어져야 할 것으로 사료된다.

• 한국농공학회논문집
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• 제60권1호
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• pp.1-10
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• 2018

This study analyzed pore water pressure, seepage and leakage quantity, height of seepage and critical hydraulic gradient in order to suggest the seepage characteristics of agricultural reservoir embankment considering filter interval. The seepage characteristics of a deteriorated reservoir embankments were conducted according to the horizontal filter intervals range using three- dimensional finite element analysis. The wider the horizontal filter interval, the higher the pore water pressure increased, and the pore water pressure ratio in the center of the core has a greater effect than the base part. The seepage and leakage quantity appeared largely in the two-dimensional analysis conditions (case 1), where the filter was constructed totally in the longitudinal direction of the embankment, the wider the horizontal filter interval was gradually reduced. The reasonable filter intervals to yield efficient seepage characteristics were within 30 m for the pore water pressure of the core and the height of the seepage line. The stability of the filter installation was able to evaluate the stability of the piping by the critical hydraulic gradient method. The deteriorated reservoir with no filters or decreased functionality can significantly reduce the possibility of piping by simply installing a filter on the downstream slope. In the future, the deteriorated reservoir embankment should be checked for the reservoir remodeling because the core and filter functions have been lost or decreased significantly. In the case of a new installation, the seepage characteristic behavior due to the core and filter changes should be applied to the field after obtaining a reasonable horizontal filter interval that satisfies the safety factor by a three-dimensional analysis.