• Korean Journal of Materials Research
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• v.4 no.1
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• pp.31-36
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• 1994

The bonding behavior of $SiO_{2}$ thin film and glass during VCR head fabrication was investigated, varying the surface roughness of substrate and the sputtering parameter. Insufficient fillings of grooves In the $SiO_{2}$ film with glass was postulated to give rise to the generation of bubble in the glass. The surface roughness of $SiO_{2}$ film was found to depend on that of substrate. The lower the deposition rate, the smoother the surface of film. The bubble free glass after bonding could be obtained using substrate polished with 0.05$\mu\textrm{m}$ $Al_2O_3$ powder under the sputtering condition of 10% oxygen pressure.

• The KSFM Journal of Fluid Machinery
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• v.4 no.3 s.12
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• pp.7-13
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• 2001

The present study investigates convective heat/mass transfer and flow characteristics inside a cooling passage of rotating gas-turbine blades. The rotating duct has staggered ribs with $70^{\circ}$ attack angle, which are attached on leading and trailing surfaces. Naphthalene sublimation technique is employed to determine detailed local heat transfer coefficients using the heat and mass transfer analogy. Additional numerical calculations are conducted to analyze the flow patterns in the cooling passage. The present experiments employ two-surface heating conditions in the rotating duct because the exposed surfaces to hot gas stream are pressure and suction side surfaces in the middle passages of an actual gas-turbine blade. Secondary flows are generated by Coriolis and centrifugal forces in the spanwise and streamwise directions. The ribs attached on the walls disturb the mainflow resulting in recirculation and secondary flows near the ribbed wall. The local heat transfer and flow patterns in the passage are changed significantly according to rib configurations and duct rotation speeds. Therefore, the geometry and arrangement of the ribs are important for the advantageous cooling performance. The experimental results show that the ribs enhance the heat transfer more than $70\%$ from that of the smooth duct. The duct rotation generates the heat transfer discrepancy between the leading and trailing walls due to the secondary flows induced by the Coriolis force. The overal heat transfer pattern on the leading and trailing walls for the first and second passes are depended on the rotating speed, but the local heat transfer trend is affected mainly by the rib arrangements.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.325-333
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• 2001

The present study investigates convective heat/mass transfer and flow characteristics inside the cooling passage of the gas-turbine blades. It is important to increase not only the heat transfer rates but also the uniformity of heat transfer in the cooling passage. The square duct has compound-angled ribs with $60^{\circ},\;70^{\circ}$ and $90^{\circ}$ attack angles, which are installed on the test plate surfaces. a naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy. The ribs disturb the main flow resulting in the recirculation and secondary flows near the ribbed wall and the vertices near the side-wall. The local heat transfer and the secondary flow in the duct are changed largely according to the rib orientation. Therefore, geometry and arrangement of the ribs are important fur the advantageous cooling performance. The angled ribs increase the heat transfer discrepancy between the wall and center regions because of the interaction of the secondary flows. The average heat/mass transfer coefficient and pressure drop of the ribs with the $60^{\circ}$ $-90^{\circ}$ compound-angle are higher than those with the $60^{\circ}$ attack angle. Also, the thermal efficiency of the compound-angled rib is higher than that with the $60^{\circ}$ attack angle. The uniformity of heat/mass transfer coefficient on the cross ribs may is higher than that on the parallel ribs array.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.22-29
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• 2001

The present study investigates the effects of various rib arrangements and rotating on heat/mass transfer in the cooling passage of gas turbine blades. The cooling passage has very complex flow structure, because of the rib turbulator and rotating effect. Experiments and numerical calculation are conducted to investigate the complex flow structures and heat transfer characteristics; the numerical computation is performed using a commercial code, FLUENT ver.5, to calculate the flow structures and the experiments are conducted to measure heat/mass transfer coefficients using a naphthalene sublimation technique. For the rotating duct tests, the test duct, which is the cross section of is $20mm\times40mm$ (the hydraulic diameter, $D_h$, of 26.7 mm, has two-pass with $180^{\circ}$ turning and the rectangular ribs on the wall. The rib angle of attack is $70^{\circ}$ and the maximum radius of rotation is $21.63D_h$. The partition wall has 10 mm thickness, which is 0.5 times to the channel width, and the distance between the tip of the partition wall and the outer wall of the turning region is 26.7 mm $(1D_h)$. The turning effect of duct flow makes the very complex flow structure including Dean type vortex and high turbulence, so that the heat/mass transfer increases in the turning region and at the entrance of the second pass. The Coriolis effect deflects the flow to the trailing surface, resulting in enhancement of the heat/mass transfer on the trailing surface and reduction on the leading surface in the first pass. However, the opposite phenomena are observed in the second pass. The each rib arrangement makes different secondary flow patterns. The complex heat/mass transfer characteristics are observed by the combined effects of the rib arrangements, duct rotation and flow turning.

• Journal of the Korean Society for Railway
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• v.13 no.4
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• pp.447-454
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• 2010

The defects of rail head induced by fatigue and deterioration are mainly classified by two types ; one occurred on the surface of rail head the another occurred on the inner rail head. This study performed the surface irregularity measurement of rail head according to the passing tonnage in the urban railway. Also, we carried out microscopic structure test, chemical component test and micro-hardness test for the specimen which is the used rail on metro line by accumulated passing tonnage. As a result of this study, for new rail, it should be performed initial grinding in order to remove 0.3mm of de-carbonized layer. The preventive-cyclic grinding for preventing RCF defects is proposed two options : grinding by the whole line and grinding by specified sections.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.64-71
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• 2010

It is suggested that the service life of the continuous welded rail(CWR) is estimated by the relationship between the rail surface irregularity according to the accumulated passing tonnage and bending fatigue of welded part in CWR. In this study, based on the results of bending fatigue tests of rail and results of measuring tests in situ of rail bending stress, this study estimated the bending fatigue life of welded rail in concrete track, adopting a Haibach's rule. The bending fatigue life of CWR considered the rail surface irregularity, train speed and the S-N curve by types of rail welding. In addition, this study estimated it for the fracture probability 1%, 0.1%, 0.01%. Therefore, this study proposed bending fatigue life of CWR in concrete track.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.8
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• pp.5327-5332
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• 2014

In Korea, the quantitative growth rate of artificial reef construction is supposed to reach the peak point. Therefore, new approach is needed to the point of artificial reefs business. Functional reefs, such as shellfish reefs, recreational reefs, seaweed reefs, and fish reefs, are beneficial alternatives. This study conducted hydraulic testing to assess the stability of corrugated artificial reefs (ARs) that were constructed to promote the growth of shellfish and seaweed. The results of this study showed that some dimensionless design parameters affected the stability of corrugated artificial reefs under a range of wave and water depth conditions in a fixed bed condition. The findings also highlight the importance of hydraulic experiments in solving the problems that have emerged in the design and construction of artificial reefs.

• Journal of IKEEE
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• v.5 no.1 s.8
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• pp.75-84
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• 2001

The reliable data relating to the condition of road surface is of increasing importance to deliver the road condition to driver and road management authority. This paper describes the development of a new high-speed. automatic, road data collection system, which collects the longitudinal road data with ${\sim}30cm$ interval covering full width of the road at 100km/h speed. The system calculates the international roughness index (IRI) from the collected data and displays the IRI and road profile data on the screen. To develope the system, we implement an optical range finder, advanced distance and motion detectors, and signal processing and display modules. The measurement accuracy of the system at 70km/h operation speed shows ${\pm}0.1m/km$ in the IRI for the standard road. To confirm the performance of the developed system, we also measure the IRI of a deployed highway road and compare the results with a conventional system and human eye measurement results.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.215-215
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• 2019

우리나라 뿐만 아니라 세계 각지에서 태풍이나 집중호우로 인한 침수피해가 증가하고 있다. 그 원인으로는 수공구조물의 설계빈도를 초과하는 강우, 도시지역 확장으로 인한 불투수지역의 확대, 배수시설의 용량부족 등이 있다. 본 연구에서는 수치지형도, 토양도, 토지이용도 등 누구나 쉽게 구할 수 있는 자료를 이용하여 홍수로 인한 피해가 발생하기 쉬운 지역을 선별하고자 하였다. 우선 강우가 지표면에 도달하게 되면 지표면의 경사, 토양의 특성, 토지이용 등에 영향을 받아 침투되지 못하고 표면에 고이게 되는데 이를 유출생성지도로 표현하였다. 그리고 이렇게 생성된 표면유출수가 지표면의 경사, 지표면의 요철(凹凸), 도로나 철도 등의 인공선형축 등에 영향을 받아 흐르기 쉬우며 이를 유출이동지도로 표현하였다. 또한, 이동된 유출수가 고이기 쉬운 저지대, 지표면의 요철 등으로 인해 누적되는 유출누적지도로 표현하였다. 유출생성지도는 이동, 누적지도의 입력자료가 되어 상류의 유출생성의 정도가 하류지역에 영향을 주도록 하였으며, 최종적으로 유출이 동지도와 누적지도가 실제 침수흔적도와 얼마나 일치하는지 확인하기 위해 서울시 침수흔적도와 비교하였다. 기존의 재해 지도를 얻기 위해서는 강우량을 조사하여 수치모형에 입력함으로써 1차원 또는 2차원의 침수예상도를 작성하는 반면에 본 연구에서는 지형 정보만을 가지고 취약지구를 선정하기 때문에 유역전체 또는 시, 도 단위로 광범위한 연구 영역에 적용이 가능하다. 또한, Spatial MCDM 등을 통해 여러 Raster 자료를 하나의 지표로 나타내기보다 유출수가 생성(또는 이동, 누적)되기 쉬운 지역을 1, 그렇지 않은 지역은 0으로 표현하는 이분법적 분석을 통해 가중치설정과 모호한 경계의 처리 때문에 사용자 및 자료에 따라 취약한 지역이 달라지는 것을 방지하고자 하였다. 이를 통해 표면 유출수로 인해 침수피해가 발생하기 쉬운 지역을 홍수취약지구로 선정하여 침수재해 중점관리 우선순위가 될 수 있도록 하였다.

• Plant Journal
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• v.15 no.1
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• pp.25-30
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• 2019

In this study, by varying flow patterns, which is one of the hydraulic factors of FAC, a strategy to reduce pipe wall thinning by mass transfer has been investigated. A similarity between heat transfer and mass transfer was verified via theoretical analysis, and local convective heat transfer coefficients were analyzed using a commercial numerical analysis program. When ribs were installed inside and outside of the internal surface in the straight section of the pipe, the maximum local heat transfer coefficient was shown to decrease substantially by up to 24.9% compared to the basic flow depending on the position and shape of ribs. If a guide vein was inserted in the pipe elbow, the maximum local heat transfer coefficient decreased by up to 26.7% compared to the basic flow depending on the internal surface area of the pipe by the guide vein.