• Journal of Adhesion and Interface
• /
• v.2 no.4
• /
• pp.24-31
• /
• 2001

Polypropylenes(PP) with different melt index values were mixed with ethylene-propylene rubber(EPR) or ethylene-propylene diene monomer rubber(EPDM) and an ethylene copolymer containing carboxylic acid group in a twin screw extruder. Then test specimens were prepared from the pellets of the blends with an injection molding machine. The mechanical properties and morphology of fractured surfaces were measured. Relative peak intensities of carboxylic acid group on the specimen surface were measured with an attennuated total reflection infrared spectrometer (ATR-IR) and compared with each other. The blend specimens were found to have the gradient morphology of rubber domains in PP matrix in the core region and PP skin layer. The blends containing PP of higher melt index showed greater content of ethylene copolymer containing carboxylic acid on the surface when the relative peak intensities of ATR-IR for carboxylic acid were compared. As the melt index values were increased, the decrease tendency in mechanical propeties such as tensile strength and impact strength was more significant for PP/EPR blends than PP/EPDM blends.

• Journal of the Society of Naval Architects of Korea
• /
• v.39 no.4
• /
• pp.17-23
• /
• 2002

The present paper describes the optimum inverse design of 2-D linear cascade airfoil. The pressure coefficient of an airfoil surface is taken as the objective function, and non-orthogonal incompressible Navier-Stokes equation is applied to calculate the pressure coefficient. Both of steepest descent and conjugate gradient method have been used to make the objective function go to zero. The 1st order finite differential method is applied to the searching direction and the golden section method is used to compute the searching distance. As a result of the present work, a good convergence to the target airfoil has been obtained.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.40 no.8
• /
• pp.527-533
• /
• 2016

A new empirical correlation was developed to identify the effect of an inclination angle on pool boiling heat transfer coefficient of a tube submerged in the saturated water at atmospheric pressure. Through the experiments and the survey of published results 431 data points were obtained and the nonlinear least square method was used as a regression technique. The heat flux of the tube($0{\sim}120kW/m^2$), inclination angle($0^{\circ}{\sim}90^{\circ}$), and the length divided by the diameter of a tube(18~42.52) were selected as major parameters. The newly developed correlation well predicts the experimental data within ${\pm}18%$, with some exceptions.

• Korean Journal of Soil Science and Fertilizer
• /
• v.38 no.3
• /
• pp.127-133
• /
• 2005

The measurement technique using laser distometer to estimate soil erosion on sloped upland was assessed for its possibility for application. This technique was practiced in lysimeter installed in Chuncheon and Pyeongchang in 2001. The lysimeter installed at Chuncheon has 12% slope, 10 m slope length, 2 m width, and soil texture was sandy loam, while the lysimeter installed at Pyeongchang showed 23% slope, 15 m slope length, 5 m width, and sandy loam soil. Change of surface soil height was monitored using laser distance meter before and after rainy season on same spots. The Investigated periods in Chuncheon and Pyeongchang were from 22 June to 22 September and from July to October, respectively. Precipitation in Chuncheon and Pyeongchang in this period was 892.2 and 931.9 mm, respectively. Rainfall over 60% of annual precipitation was concentrated on July and August in Chuncheon and September and October in Pyeongchang, respectively. By monitoring the change of surface soil height using laser distance meter before and after rainy season, eroded soil surface in up-down fallow field in Chuncheon was 0.874 cm, while eroded soil surface in slant furrow field in Pyeongchang was 1.127 cm, which correspond to 79.5 and $98.0MT\;ha^{-1}$. Soil erosion increased as furrow length increased. Amounts of estimated soil loss using laser distance meter was 0.98-1.18 times higher compared to the estimated values through Iysimeter experiment, which implies possibility for application to monitor soil loss particularly in up-down and slant furrowed field. However, in the lysimeter with contoured tillage, amount of estimated soil loss using laser distance meter was approximately a half compared to that from lysimeter experiment, which implies inadequacy of distance meter application in contour- tillage field. The great soil loss difference between distance meter and lysimeter might be caused by disruption of some of the contoured furrows in lysimeter. The measurement technique using distometer in this study could be useful to estimate soil loss especially in up-down and slant-tillage fields.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2010.05a
• /
• pp.483-487
• /
• 2010

하천에서 물이 비교적 빠른 속도로 흘러가면 압력 변동, 하상의 조도, 하천내 구조물 등의 영향에 의해 수면이 끊임없이 변형을 일으키며 수면에 작은 물결(수면 파문)이 생긴다. 이러한 수면 파문은 유수에 의해 유수의 평균 유속으로 이류되며, 이 때문에 인간이 유수의 흐름을 시각적으로 인식할 수 있다. 이러한 표면 파문은 적절한 영상 분석을 하면 표면 유속 측정의 추적자로 이용할 수 있다. 본 연구는 유수 표면을 연속된 영상을 촬영하고, 일련의 영상을 시공간 영상(space-time image)으로 만든 뒤, 휘도 경사법(graylevel gradient method)으로 유속 벡터를 추출하는 새로운 방법을 제시하였다. 이 분석 과정은 기존의 입자 영상 유속계(PIV, Particle Image Velocimetry) 기법을 이용하는 방법보다 훨씬 간단하고 분석 시간도 크게 절약할 수 있다. 또한, 수면 파문의 전파에 따른 중력파의 영향을 시공간 영상의 처리 과정에서 잡음으로 간주하여 처리할 수 있다는 장점을 가지고 있다. 개발된 루틴을 표면 영상 유속계(SIV, Surface Image Velocimtery)에 구현하여 새로운 영상 유속계를 개발하였다. 시공간 영상 분속을 이용하는 새로운 영상 유속계를 실험실 수로의 영상 자료에 적용하여 그 정확도, 적용성, 장단점 등을 분석하였다. 제안된 방법에 의한 평균류 산정 결과는 물리적으로 타당하며, 저속 또는 저휘도에서의 분석 성능이 뛰어난 것으로 밝혀졌다. 다만, 이방향 흐름의 분석에서는 문제가 있는 것이 밝혀졌다.

• Journal of the Korean institute of surface engineering
• /
• v.24 no.1
• /
• pp.16-16
• /
• 1991

Generally brittle eta phase produced during TiC deposition has a effect on the TRS (transverse rupture strength ; thoughness). Therefore it is necessary to reduce eta(η), phase for the improvement of tool life. At this experiment some properties (TRS, bonding strength, tool life, eta phase)have been investigated by inserting TiN or TiCN underlayer between TiC layer and substrate. The results obtained were as follows; 1. by inserting underlayer eta phase were decreased and TRS was increased, but the bonding strength was decreased. 2. the diffusion of W, Co from the substrate was hindered by the underlayer. 3. TiC layer with TiCN underlayer had the finsest grain size. 4. by inserting underlayer (TiCN or TiN) the tool life was improved and especially notch and crater wear resistance was greatly improved.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.17 no.4
• /
• pp.35-41
• /
• 2008

R/In order to satisfy the customer's variant needs for a product quality in recent years, a demand for developing higher precision machining technologies in a lot of application areas such as automobile, cellular phone and semiconductor has been increased more and more. Magnetic abrasive polishing(MAP) process is one of these precision technologies. In this study, to verify the parameters' effect of the MAP process on the surface roughness improvement of the plane and the inclined workpiece, well planned experiments which was called the design of experiments were carried out. Considered polishing factors were spindle speed, supplied current, abrasive type and working gap between the workpiece and the solid tool. As a result, it was seen that the supplied current and the working gap greatly affected the surface roughness improvement.

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

• Journal of the Korean Ceramic Society
• /
• v.34 no.1
• /
• pp.70-78
• /
• 1997

3Y-TZP/SUS316 Functionally Graded Material (FGM) was fabricated by slip casting method. Alumina mold was used to overcome problems of gypsum mold in slip casting process, and the optimal dispersion con-ditions of 3Y-TZP/SUS316 binary slurries was determined using electrokinetic sonic amplitude and a viscometer, and observing sedimentation behavior. The properties of the specimens casted by gypsum mold and alumina mold were compared in terms of changes in shrinkage rate, drying and sintering conditions, and microstructure. It was found that the specimens obtaine from the alumina mold showed a clean surface, easier thickness control of each layer, and higher productivity. Especially, no degradation was observed in the SUS316 prepared using alumina mold. Thus it is desirable to use porous alumina mold rather than gyp-sum mold for the slip casting of 3Y-TZP/SUS316-FGM.

• Investigative Magnetic Resonance Imaging
• /
• v.12 no.1
• /
• pp.27-32
• /
• 2008

Purpose : We developed a 3D CSI (chemical shift imaging) sequence that uses the PRESS (point resolved spectroscopy) excitation scheme and spiral-based readout gradients. Materials and Methods : We implemented constant-density spirals ($32{\times}32$ matrix, $24{\times}24\;cm$ FOV) which use analytic equations to enable real-time prescription on the scanner. In-vivo data from the brain were collected and reconstructed using the gridding algorithm. Results : Data illustrate that with our imaging sequence, the benefits of the PRESS technique, which include elimination of lipid artifacts, remain intact while flexible scan time versus resolution tradeoffs can be achieved using the constant-density spirals. Volumetric high resolution 3D CSI covering 5760 cm3 could be obtained in 12.5 minutes. Conclusion : Spiral-based readout gradients offer a flexible tradeoff between scan time versus resolution. By combining this feature with PRESS based excitation, efficient methods of volumetric spectroscopic imaging can be accomplished by obtaining whole brain coverage while eliminating lipid contamination.