• 한국CDE학회논문집
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• 제14권5호
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• pp.306-313
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• 2009

This paper presents the unique formation process of a volumetric space with the digital algorithm developed for Voronoi diagram in order to generate an effective parametric architectural form. By applying systematic parameters of architectural conditions within digital parametric tools, the interactions among sub-spaces developed by Voronoi diagram are enhanced by manipulating the spatial structures. In this paper, we discuss how the parametric distributing and zoning geometrical system can support designers in developing a free-formed space, and research on how this system creates a 3D volumetric space. With the in-depth research on the system and structure of Voronoi diagram, the approaches to the application of Voronoi diagram into architectural form generation are clarified to be an effective, creative and successful digital tool. The result of the application of the Voronoi diagram improves the design quality with systematic language in the sense that the sub-regions are created and controlled under the systematic and balanced hierarchy having dynamic relationships among each others with the restoration of the equilibrium of forces and tensions. This 3-dimensional Voronoi diagram provides another means for designers to solve architectural issues and to reinforce their design concepts.

• 한국표면공학회지
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• 제29권5호
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• pp.545-548
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• 1996

$CrN_x$ films were deposited on SKD61 and S45C by cathodic arc ion plating process. In this study, the microstructure, microhardness, a hesion, wear and corrosion properties of the CrNx films were studied for various nitrogen partial pressures and the results were compared with those from the electroplated hard Cr. The crystal structure of the films was characterized by X-ray diffraction. Wear tests were performed under no lubricant condition at atmosphere by ball-on-disc type tribotester. Corrosion resistance of the films were studied by electrochemical corrosion test, measuring current demsity-potential curves. The results indicated that the $CrN_x$ films formed using ion plation method showed higer hardness and lower current density, friction coefficient than electroplated hard Cr. Consequently, the application of the CrNx coationgs by ion plating which is free of environmental pollution, is expected to improve lifetime of components in industrial practice.

• 대한기계학회논문집B
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• 제21권5호
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• pp.700-712
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• 1997

The flowfield generated by a 2-D rotating cylinder on a plane moving at freestream velocity was experimentally investigated in a wind tunnel to simulate aerodynamic characteristics of rotating wheels of an automobile. In the flowfield around a rotating cylinder at 3*10$^{3}$ < Re$_{d}$<8*10$^{3}$, unique mean flow and turbulence characteristics were confirmed by hot-wire measurements as well as frequency analysis, which was supported by flow visualization. In the vicinity of a rotating cylinder, a unique turbulence structure on .root.over bar u'$^{2}$ profiles was formed in hump-like shape at 1 < y/d < 3. A peak frequency which characterized the effect of a rotating cylinder had the same value of the rotation rate of a cylinder. In case of cylinder rotation, the depths of mean velocity -defect and turbulent-shear regions were thickened by 20-40% at 0 < x/d < 10 compared with the case of cylinder stationary. Far downstream beyond x/d > 10, the flowfield generated by a rotating cylinder showed self-similarity in the profiles of mean velocity and turbulence quantities. The effect of a rotating cylinder was independent of its rotation rate and Reynolds number in the measurement range.

• 한국콘텐츠학회논문지
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• 제10권5호
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• pp.427-435
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• 2010

교과서에 쓰인 과학 용어 네트워크를 구축하여, 네트워크의 구조, 관련 정보 및 연관 관계를 분석하기 위하여 핵심용어를 도출하였다. 본 연구에서는 과학, 생물1 및 생물2 교과서 각 과목별로 출판사 세 곳을 선정하고 각각의 교과서에서 추출한 용어들을 노드로, 한 문장 안에 있는 과학 용어를 링크로 연결하여 네트워크를 구축하였다. 모든 교과서의 과학 용어 네트워크는 척도 없는(scale-free) 네트워크의 특성을 보여주었다. 복잡한 (complex) 네트워크에서 가중치가 낮은 것부터 제거하는 방법인 k-core 알고리즘을 적용하여 핵심 (core) 네트워크를 구축하였는데, 몇 개의 모듈이 연결되는 형태를 보여주었다. 과학교과서의 경우에는 물리, 화학, 생물, 지구과학 분야별로 크게 네 개의 모듈을 형성하였고, 생물1과 생물2 교과서는 각단원별로 용어들이 모여 있는 특성을 지닌 네트워크를 나타냈다. 본 연구에서 복잡한 네트워크에서 핵심네트워크를 구축하여 유용한 정보를 도출할 수 있는 가능성을 제시하였다.

• 한국주조공학회지
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• 제33권5호
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• pp.215-225
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• 2013

The alloys required for fossil power plants are altered from stainless steel that has been used below $600^{\circ}C$ to Ni-based alloys that can operate at $700^{\circ}C$ for Hyper Super Critical (HSC) steam turbine. The IN740 alloy (Special Metals Co. USA) is proposed for improved rupture strength and corrosion resistance at high temperature. However, previous studies with experiments and simulations on stable phases at about $700^{\circ}C$ indicated the formation of the eta phase with the wasting of a gamma prime phase, which is the most important reinforced phase in precipitation hardened Ni alloys, and this resulted in the formation of precipitation free zones to decrease the strength. On the basis of thermodynamic calculation, the new Ni-based superalloy named LESS 1 (Low Eta Sigma Superalloy) was designed in this study to improve the strengthening effect and structure stability by depressing the formation of topologically close packed phases, especially sigma and eta phases at high temperature. A thermal exposure test was carried out to determine the microstructure stability of LESS 1 in comparison with IN740 at $800^{\circ}C$ for 300 hrs. The experimental results show that a needle-shaped eta phase was formed in the grin boundary and it grew to intragrain, and a precipitation free zone was also observed in IN740, but these defects were entirely controlled in LESS 1.

• 한국해안해양공학회지
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• 제14권2호
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• pp.171-181
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• 2002

최근, 구조물에 의한 쇄파를 수반한 다양한 파랑변형 해석법중에 자유수면의 추적기법인 VOF법을 이용한 수치해석기법이 각광을 받고 있다. 본 연구는 수중투과성구조물(잠제)에 의한 파랑변형 및 유속장의 해석을 위해 조파를 위한 line-source와 파의 재반사를 방지하기 위한 부가감쇠영역이 설치된 2차원수치파동수조에 잠제를 설치하고 구조물에 의한 파랑변형의 자유수면 추적을 위해 VOF법을 적용하였다. 2차원수치파동수조를 이용한 본 연구의 수치해석수법의 타당성 검증을 위해 수리실험을 실시하였으며 그 결과 본 수치해석결과와 잘 일치하였다. 일열잠제와 이열잠제에 대한 수치해석을 통해 잠제 주변 유속장 해석으로부터 일열잠제의 경우 배후에서 와가 발생하고 이열잠제의 경우 잠제사이와 잠제배후에서 와가 발생함을 확인하였으며 잠제의 천단상에서는 강한 비선형성분파가 발생하고 투과층내의 유속방향은 자유수면의 형상에 의해 좌우됨을 확인하였다

• 한국표면공학회지
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• 제44권3호
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• pp.82-88
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• 2011

A uniform chromium-free conversion coating treated with an alkaline phosphate- permanganate solution was formed on the AZ 31 magnesium alloy. The effect of acid pickling on the morphology and on the corrosion resistance of the alkaline phosphate-permanganate conversion coating was investigated. The chemical composition and phase structure of conversion coating layer were determined via optical microscopy, SEM, EDS, XPS and XRD. Results show that the conversion coatings are relatively uniform and continuous, with thickness 1.8 to $2.4\;{\mu}m$. The alkaline phosphate-permanganate conversion coating was mainly composed of elements Mg, O, P, Al and Mn. The conversion-coated layers were stable compounds of magnesium oxide and spinel ($MgAl_2O_4$). These compounds were excellent inhibitors to corrosion. The electrochemical corrosion behaviors of coatings in 3.5 wt.% NaCl solutions were evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization technique. EIS results showed a polarization resistance of $0.1\;k{\Omega}$ for the untreated Mg and $16\;k{\Omega}$ for the alkaline phosphate-permanganate conversion treatment sample, giving an improvement of about 160 times. The results of the electrochemical measurements demonstrated that the corrosion resistance of the AZ 31 magnesium alloy was improved by the alkaline phosphate-permanganate conversion treatment.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2016년도 학술발표회
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• pp.65-65
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• 2016

위어나 낙차공 같은 수공구조물 직하류부에서는 다양한 형태의 흐름조건이 발생한다. 낙차공 하류에서 발생하는 독특한 흐름형태 중 하나는 정상파형도수를 갖는 파형흐름이다. 이 연구에서는강 등(2010)이 수리실험을 수행한 바 있는 계단형 위어 하류부에서의 형성되는 파형흐름을 3차원 수치해석을 수행한다. 위어 구조물 위를 통과하는 난류흐름을 해석하기 위해서 Spalart-Allamaras 1방정식 모형을 이용한 URANS 수치모의와 DES (detached eddy simulation)을 실시하였다. 위어 주변에서의 자유수면 변동, 파상도수, 자유수면에서의 와류 그리고 바닥부근에서의 재순환 영역의 형상과 크기, 선정된 종방향 위치들에서의 흐름방향유속분포 등의 항으로 수치해석결과를 실험값과 비교하여 수치모의의 적절성과 난류모델들의 성능을 평가한다.

• 마이크로전자및패키징학회지
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• 제11권3호
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• pp.1-7
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• 2004

주석 도금은 특정 환경하에서 위스커를 발생시키며, 이는 전자부품의 불량을 초래한다. 최근 세계곳곳에서는 환경보호를 위해 "무연"의 사용을 권고하고 있다. 본 논문에서는 두 종류 무연 도금 재료에서 도금 온도와 신뢰성시험 하에서 성장하는 위스커를 평가하였다. 도금 온도가 높아질수록 표면에 형성되는 도금 입자의 크기는 커지고, 위스커의 성장은 작아진다. 또한 온도 순환시험에서 성장한 위스커는 무광택 Sn 도금은 굽은 모양을, 무광택 Sn-Bi에서는 줄무의 모양이 관찰되었고, Sn 도금에 비해 Sn-Bi에서 위스커가 작게 성장하였다. 무광택 Sn 도금된 FeNi42 리드프레임은 TC 300 사이클에서 직경이 $7.0{\~}10.0{\mu}m$이고, 길이가 $25.0{\~}45.0{\mu}m$인 위스커가 성장하였다. 또한 Cu는 300 사이클에서는 표면에 노듈(핵 상태)만이 관찰되었고, 600 사이클에서 길이가 $3.0{\~}4.0{\mu}m$의 위스커로 성장하였다. TC 600 사이클 후 FeNi42는 계면에서 ${\~}0.34{\mu}m$의 얇은 $Ni_3Sn_4$가, Cu에서는 두께가 $0.76{\~}l.14{\mu}m$인 $Cu_6Sn_5$와 ${\~}0.27{\mu}m$의 $Cu_3Sn$ 화합물들이 두껍게 성장하였다. 따라서 FeNi42 리드프레임은 열팽창계수의 차이, Cu에서는 금속간 화합물의 형성이 위스커의 성장에 영향을 미치는 주요 인자이다.

• The Korean Journal of Ceramics
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• 제2권1호
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• pp.19-24
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• 1996

The phase distribution and interface chemistry by the solid-state reaction between SiC and nickel were studied at temperatures between $550 \;and\; 1250^{\circ}C$ for 0.5-100 h. The reaction with the formation of silicides and carbon was first observed above $650^{\circ}C$. At $750^{\circ}C$, as the reaction proceeded, the initially, formed $Ni_3Si_2$ layer was converted to $Ni_2$Si. The thin nickel film reacted completely with SiC after annealing at $950^{\circ}C$ for 2 h. The thermodynamically stable $Ni_2$Si is the only obsrved silicide in the reaction zone up to $1050^{\circ}C$. The formation of $Ni_2$Si layers with carbon precipitates alternated periodically with the carbon free layers. At temperatures between $950^{\circ}C$ and $1050^{\circ}C$, the typical layer sequences in the reaction zone is determined by quantitative microanalysis to be $SiC/Ni_2$$Si+C/Ni_2$$Si/Ni_2$$Si+C/…Ni_2$Si/Ni(Si)/Ni. The mechanism of the periodic band structure formation with the carbon precipitation behaviour was discussed in terms of reaction kinetics and thermodynamic considerations. The reaction kinetics is proposed to estimate the effective reaction constant from the parabolic growth of the reaction zone.