• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.262-263
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• 2006

The free sintering of metallic powders blended with non sintering inclusions is investigated by the Discrete Element Method (DEM). Each particle, whatever its nature (metallic or inclusion) is modeled as a sphere that interacts with its neighbors. We investigate the retarding effect of the inclusions on the sintering kinetics. Also, we present a simple coarsening model for the metallic particles, which allows large particles to grow at the expense of the smallest.

• Korean Chemical Engineering Research
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• 제46권3호
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• pp.567-570
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• 2008

내경 0.109 m의 유동층에서 다입자경 모래에 대한 압력요동의 표준편차와 유속간의 선형회귀분석을 이용한 최소유동화속도 측정법의 적용성을 조사하였다. 다입자경 모래를 평균입자크기가 같은 Gaussian 분포에서 입자분포의 표준편차에 따른 최소유동화속도를 측정하고, 측정치를 타 연구자들의 식과 비교 검토하였다. 압력요동의 표준편차 값 선형회귀분석법과 층내 압력강하로부터 구한 최소유동화속도를 구하였다. 최소유동화속도 결정에서 유속 범위는 혼합도가 낮은 유속범위와 free bubbling 영역 이상을 제외한 범위값 이어야 하며, 이 유속범위에서 측정위치는 혼합이 양호한 층 중앙이 가장 적절하다.

• 폴리머
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• 제35권5호
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• pp.451-457
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• 2011

라텍스 기법으로 제조한 폴리스티렌(PS)/다중벽 탄소나노튜브(MWCNT) 나노복합재료의 라텍스 입자 크기에 따른 유변학적, 전기적 물성을 고찰하였다. 나노복합재료는 무유화제 유화중합과 분산중합으로 합성한 단분산 PS 입자에 MWCNT를 초음파 분산시킨 다음 동결건조 과정을 거쳐 제조하였다. PS/MWCNT 나노복합재료는 MWCNT 함량이 증가할수록 점차 네트워크 구조를 형성하여 저장 탄성률, 복소 점도 및 전기 전도도가 급격하게 증가하였다. MWCNT 함량에 따른 저장 탄성률 및 복소 점도 증가 효과는 라텍스 입자 크기가 큰 경우 더욱 뚜렷하였다. 입자 크기에 따른 전기적 물성은 MWCNT 함량에 따라 상이한 경향을 보여 주었는데, 함량이 적은 경우 작은 입자로 제조한 나노복합재료가 높은 전기 전도도를 보여 주었으나 함량이 증가할수록 큰 입자의 경우가 높은 값을 보여 주었다.

• 대한기계학회논문집B
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• 제26권2호
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• pp.227-237
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• 2002

A numerical technique for simulating the aggregation of charged particles was presented with a Brownian dynamic simulation in the free molecular regime. The Langevin equation was used for tracking each particle making up an aggregate. A periodic boundary condition was used for calculation of the aggregation process in each cell with 500 primary particles of 16 nm in diameter. We considered the thermal force and the electrostatic force for the calculation of the particle motion. The electrostatic force on a particle in the simulation cell was considered as a sum of electrostatic forces from other particles in the original cell and its replicate cells. We assumed that the electric charges accumulated on an aggregate were located on its center of mass, and aggregates were only charged with pre-charged primary particles. The morphological shape of aggregates was described in terms of the fractal dimension. In the simulation, the fractal dimension for the uncharged aggregate was D$\_$f/ = 1.761. The fractal dimension changed slightly for the various amounts of bipolar charge. However, in case of unipolar charge, the fractal dimension decreased from 1.641 to 1.537 with the increase of the average number of charges on the particles from 0.2 to 0.3 in initial states. In the bipolar charge state, the average sizes of aggregates were larger than that of the uncharged state in the early and middle stages of aggregation process, but were almost the same as the case of the uncharged state in the final stage. On the other hand, in the unipolar charge state, the average size of aggregates and the dispersion of particle volume decreased with the increasing of the charge quantities.

• 한국건축시공학회지
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• 제19권1호
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• pp.39-46
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• 2019

본 연구에서는 비압축성 Navier-Stokes 방정식을 적용한 ISPH 기법을 이용하여 3차원 유동 수치해석 모델을 개발하였다. 수치해석을 위해 MATLAB을 사용하여 ISPH 프로그램을 구현하였다. ISPH의 커널 함수로 piecewise cubic spline 함수를 사용하였다. 벽 경계조건으로 고정 가상 입자를 사용하였으며, 가상 밀도를 적용하여 자유 표면 경계 부근의 입자들을 결정하였다. 수치해석 모델과 코드의 정도를 확인하기 위해 $T_{500}$ 시험, 슬럼프 플로우 시험, L-box 시험의 수치해석 결과와 실험 결과를 비교하였다. 수치해석 결과 고유동 콘크리트의 점성계수 및 항복응력 변화에 따른 유동 현상의 특성을 잘 묘사하였으며, 기존의 실험값과 비교적 잘 일치함을 확인할 수 있었다.

• 한국해양공학회지
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• 제23권6호
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• pp.12-16
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• 2009

In this study, the wave profiles and kinematics of highly nonlinear waves at various water depths were calculated using a 2D fully nonlinear Numerical Wave Tank (NWT). The NWT was developed based on the Boundary Element Method (BEM) with the potential theory and the mixed Eulerian-Lagrangian (MEL) time marching scheme by 4th-order Runge-Kutta time integration. The spatial variation of intermediate-depth waves along the direction of wave propagation was caused by the unintended generation of 2nd-order free waves, which were originally investigated both theoretically and experimentally by Goda (1998). These free waves were induced by the mismatch between the linear motion of wave maker and nonlinear displacement of water particles adjacent to the maker. When the 2nd-order wave maker motion was applied, the spatial modulation of the waves caused by the free waves was not observed. The respective magnitudes of the nonlinear wave components for various water depths were compared. It was found that the high-order wave components greatly increase as the water depth decreases. The wave kinematics at various locations were calculated and compared with the linear and the Stokes 2nd-order theories.

• 열처리공학회지
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• 제19권4호
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• pp.219-224
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• 2006

Silver paste with low sintered temperature has been developed in order to apply electronic parts, such as bus electrode, address electrode in PDP (Plasma Display Panel) with large screen area. In this study, nano-sized silver particles with 10-30 nm were synthesized from silver nitrate ($AgNO_3$) solution by chemical reduction method and silver paste with low sintered temperature was prepared by mixing silver nanoparticles, conventional silver powder with the particle size 1.6 um and Pb-free frit. Conductive thick film from silver paste was fabricated by screen printing on alumina substrate. After firing at $540^{\circ}C$, the cross section and surface morphology of the thick films were analyzed by FE-SEM. Also, the sheet resistivity of the fired thick films was measured using the four-point technique.

• Earthquakes and Structures
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• 제14권2호
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• pp.117-128
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• 2018

In this research work, free vibrations of simply supported functionally graded plate resting on a Winkler-Pasternak elastic foundation are investigated by a new shear deformation theory. The influence of alternative micromechanical models on the macroscopic behavior of a functionally graded plate based on shear-deformation plate theories is examined. Several micromechanical models are tested to obtain the effective material properties of a two-phase particle composite as a function of the volume fraction of particles which continuously varies through the thickness of a functionally graded plate. Present theory exactly satisfies stress boundary conditions on the top and the bottom of the plate. The energy functional of the system is obtained using Hamilton's principle. The closed form solutions are obtained by using Navier technique, and then fundamental frequencies are found by solving the results of eigenvalue problems. Finally, the numerical results are provided to reveal the effect of explicit micromechanical models on natural fundamental frequencies.

• Journal of Pharmaceutical Investigation
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• 제40권6호
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• pp.373-378
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• 2010

In order to develop a topical preparation which has a high occlusive property with skin moisturization, nano-structured lipid carrier (NLC) systems along with solid lipid nanoparticle (SLN) were designed. Various NLC dispersions were successfully formulated with Compritol 888 ATO as a solid lipid, Labrafil M 1944 CS as an oil, and Tween 80 as a surfactant. The increase of oil content (5 to 50%) led to the decrease in the occlusion factor in the order of SLN > NLC-5 > NLC-15 = NLC-30 > NLC-50. Particle size of lipid particulates was in the range of 100 to 160 nm. NLC-based carbogels were prepared by the employment of humectants such as urea, glycerin, and Tinocare GL to carbomer gel. NLC-30 gel formulations containing 4 or 8 % of lipid particles showed improved occlusive effect in vitro, compared to NLC-free gel base. Even though NLC-free gel base revealed comparable occlusion effect by itself, the occlusion factor of 4 % NLC-30 gel was about 2-fold higher than that of NLC-free gel base.

• 한국재료학회지
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• 제18권3호
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• pp.128-136
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• 2008

Evaluation of the solid surface properties by an analysis of the liquid penetration rate into powder beds is very important in applications of powder products. The penetration rate is related the surface property in powder beds. In order to analyze the surface property of powders, the contact angle values of several powders were obtained using the Washbun equation and the Wicking method. The surface free energy value ${\gamma}S$ was divided into a polar component ${\gamma}S^p$ and a dispersion component ${\gamma}S^d$. Inorganic powders such as calcite were used as test samples. The effects of the particle size and the type of experimental liquid on the penetration rate were measured. It was confirmed that the surface free energy of the grinding sample is smaller than that of the classification sample.