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VALIDATION OF NUMERICAL APPROACH FOR THE SEDIMENT OF MULTI-SIZE PARTICLES IN A FLUID CONTAINER
Youngmoo Ji(지영무),Sangmin Choi(최상민) 한국전산유체공학회 2013 한국전산유체공학회지 Vol.18 No.2
In this paper, we reported the verification of numerical simulation approach for sedimentation of the multi-size particles in a container. The comparison between experimentally measured values and numerically evaluated values on settle down process of fully mixed mixture is carried out. In an attempt to represent the natural particle size distribution, various diameters of single particles are simulated and the results are compared with the outcome of the multi-size computation. When the empirical formula for mean particle size estimation is adopted to define the sediment diameter, computation and comparison are conducted.
전기 도금 법으로 제조된 Cu 박막 구조물의 탄성계수와 미세조직과의 연관성 연구
김영무(Youngmoo Kim),한준희(Jun-Hee Hahn),이창승(Chang Seung Lee),박준협(Jun-Hyub Park),홍순형(Soon Hyung Hong) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.8
This paper reports on the manufacturing, surface morphology and Young's modulus of Cu thin films used as MEMS (micro-electro-mechanical systems) devices. Nanoindentation test and microcantilever bending test were performed to evaluate the mechanical properties, especially Young's modulus of these thin films. Cu thin film specimens were produced by MEMS fabrication techniques such as sputtering, electrochemical deposition, lithography and silicon bulk micromachining. Surface morphologies of specimens were measured by atomic force microscopy (AFM). Young's moduli of Cu electrodeposited films were decreased with increasing the thickness of specimens. From these results, it was shown that Young's modulus of Cu thin films had anisotropy with crystal orientations. Elastic moduli were varied with the thickness of thin film due to the texture of Cu thin films. Young's modulus of Cu thin films can be predicted by using two methods. One is to use the elastic modulus of single crystal and the information of distribution of crystal orientation, Voigt model. The other is to calculate it from load-deflection curves computed with ABAQUS. The theoretical estimation of elastic modulus using texture analysis showed good agreement with the results of nanoindentation test. But in computational modeling, Young's moduli were different from the results of bending test with isotropic and anisotropic Cu beams having (001) texture.
Development of Landscaping Techniques of Wall Space by Non-Planting Methods
Lee, Youngmoo Research Institute for Science & Technology HONG-I 2003 Hongik Journal of Science and Technology Vol.7 No.-
Up to this date the landscaping of wall surfaces of a building, a property wall, a retention wall, a sound barrier wall, a river bank, a bridge pier and a hydrolic dam was mostly done by planting climbers like ivy on their surfaces. It is true that ivy covered concrete walls performed much better than the bare concrete in terms of appearance and micro-climatic functions. First of all the green walls look much more beautiful than grey walls. They provide relief and visual delight to the urban dwellers. And also green cover helps to reduce the heating and air conditioning energy. The leaf layer creates insulation blanket between the extreme climate of a city and buildings. It protects the envelope of a building from cold north wind in winter and hot sun's ray in summer. Not only that the green cover absorbs the harmful ultraviolet ray before reaching the building wall but also it soaks up the toxic gases and produces oxygen and phytoncide. This action saves the building from aging and provides fresh air to the urban inhabitants. The green wall also collects dust, prevents reflection of glare and keeps the noise level down by absorption instead of bouncing back. In spite of these obvious benefits excessive and sole use of herbaceous climbers inevitably crated monotonous scenery in terms of aesthetic quality. This thesis proposes alternative ways of landscaping besides planting on the wall surface. The idea is that the introducing non-planting methods such as super graphics. The approach is divided in two ways. The first one is the passive design which is primarily oriented towards viewing. This methods includes the super graphic, graffiti painting, mural, relief, attachment of art objects, tile mosaic, waterfall, night illumination and optical illusion. Installing above elements on the wall surface makes the viewers to appreciate the wall as an art objects on canvas. The second approach is the active design method. The active design involues actual utilizing of the wall face. It is associated with the concept of 'vertical playground'. The approach involues the installment of rock climbing apparatus on the wall face, bungy jumping station, half pipe for the skate board, inline skating and mountain bikes. It also proposes the net climbing, pulley ride and tight rope Other facilities are the viking, wonder wheel, basketball board and movie screen. In general the active design requires a certain amount of space in front of the wall because of the space requirements of play apparatus and safety features. But it should be reminded that above structure are the ones which can be attached to the wall in a flat fashion. In the case of movie screen the most frontal space is needed for the seating of viewers. It fits the square on lawn facing high wall. Introducing hard landscaping on the wall surface can enhance and supplement the planting-only design by providing variety and accent.
Jeon, Youngmoo,Lee, Jeongyeon,Kim, Myungjin,Oh, Jiseop,Hwang, Taejin,Piao, Yuanzhe The Royal Society of Chemistry 2019 Nanoscale Vol.11 No.11
<P>Molybdenum disulfide (MoS2) is a promising anode material for lithium-ion batteries owing to its high theoretical capacity and low cost. However, it exhibits low electrical conductivity and volume expansion, resulting in poor electrochemical performance. In this work, three-dimensional porous carbon/MoS2 composites with Fe3O4 nanoparticles (C-MF) are synthesized <I>via</I> a mix-bake-wash method. The few-layered MoS2 in the porous carbon matrix provides improved electrical conductivity and facilitates lithium ion diffusion, so the composites exhibit a high specific capacity of 939.6 mA h g<SUP>−1</SUP> on average at 0.1 A g<SUP>−1</SUP> and a high rate capability (515.9 mA h g<SUP>−1</SUP> at 5 A g<SUP>−1</SUP>). Moreover, the Fe3O4 nanoparticles in C-MF, which are anchored on the composites, improve the specific capacity and effectively mitigate diffusion of lithium polysulfides during cycling, resulting in remarkable cycling stability (590.1 mA h g<SUP>−1</SUP> after 500 cycles at 2 A g<SUP>−1</SUP>). This work suggests that not only C-MF but also C@MoS2 with other metal oxides synthesized using this facile strategy have potential for energy-related applications.</P>
Kim, Youngmoo,Lee, Dongju,Hwang, Jaewon,Ryu, Ho Jin,Hong, Soon Hyung Elsevier 2016 Materials characterization Vol.114 No.-
<P><B>Abstract</B></P> <P>The present study has investigated the consolidation behaviors of tantalum powders during compaction and sintering, and the characteristics of sintered components. For die compaction, the densification behaviors of the powders are simulated by finite element analyses based on the yield function proposed by Shima and Oyane. Accordingly, the green density distribution for coarser particles is predicted to be more uniform because they exhibits higher initial relative tap density owing to lower interparticle friction. It is also found that cold isostatic pressing is capable of producing higher dense compacts compared to the die pressing. However, unlike the compaction behavior, the sintered density of smaller particles is found to be higher than those of coarser ones owing to their higher specific surface area. The maximum sintered density was found to be 0.96 of theoretical density where smaller particles were pressed isostatically at 400MPa followed by sintering at 2000°C. Moreover, the effects of processing conditions on grain size and texture were also investigated. The average grain size of the sintered specimen is 30.29μm and its texture is less than 2 times random intensity. Consequently, it is concluded that the higher pressure compaction technique is beneficial to produce high dense and texture-free tantalum components compared to hot pressing and spark plasma sintering.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Higher Ta density is obtained from higher pressure and sintering temperature. </LI> <LI> High compaction method enables P/M Ta to achieve the density of 16.00g·cm<SUP>−3</SUP>. </LI> <LI> A P/M Ta component with fine microstructure and random orientation is developed. </LI> </UL> </P>
Solid-state sintering mechanism of blended elemental Ti-6Al-4V powders
Kim, Youngmoo,Song, Young-Beom,Lee, Sung Ho The Korean Powder Metallurgy Institute 2018 한국분말재료학회지 (KPMI) Vol.25 No.2
The objective of this study is to reveal the sintering mechanism of mixed Ti-6Al-4V powders considering the densification and the homogenization between Ti and Al/V particles. It is found that the addition of master alloy particles into Ti enhances densification by the migration of Al into the Ti matrix prior to the self-diffusion of Ti. However, as Ti particles become coarser, sintering of the powders appears to be retarded due to slower inter-diffusion of the particles due to the reduced surface energies of Ti. Such phenomena are confirmed by a series of dilatometry tests and microstructural analyses in respect to the sintering temperature. Furthermore, the results are also consistent with the predicted activation energies for sintering. The energies are found to have decreased from 299.35 to $135.48kJ{\cdot}mol^{-1}$ by adding the Al/V particles because the activation energy for the diffusion of Al in ${\alpha}-Ti$ ($77kJ{\cdot}mol^{-1}$) is much lower than that of the self-diffusion of ${\alpha}-Ti$. The coarser Ti powders increase the energies from 135.48 to $181.16kJ{\cdot}mol^{-1}$ because the specific surface areas of Ti decrease.