• Journal of Mechanical Science and Technology
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• 제16권7호
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• pp.935-941
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• 2002

This work is to investigate the combustion characteristics and flame propagation of the LPG (liquified petroleum gas) and gasoline fuel. In order to characterize the combustion processes of the fuels, the flame propagation and combustion characteristics were investigated by using a constant volume combustion chamber The flame propagation of both LPG and gasoline fuels was investigated by the laser deflection method and the high-speed Schlieren photography. The result of laser deflection method show that the error of measured flame propagation speed by laser method is less than 5% compared with the result of high-speed camera. The flame propagation speed of the fuel is increased with the decrease of initial pressure and the increase of initial temperature in the constant volume chamber. The results also show that the equivalence ratio has a grate effect on the flame speed, combustion pressure and the combustion duration of the fuel-air mixture.

• Journal of electromagnetic engineering and science
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• 제8권3호
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• pp.100-109
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• 2008

The finite volume time domain(FVTD) technique faces serious limitations in simulating electromagnetic scattering at high frequencies due to requirements related to discretization. A modified FVTD method is proposed for electrically large, perfectly conducting scatterers by partially incorporating a time-domain physical optics(PO) approximation for the surface current. Dominant specular returns in the modified FVTD method are modeled using a PO approximation of the surface current allowing for a much coarser discretization at high electrical sizes compared to the original FVTD scheme. This coarse discretization can be based on the minimum surface resolution required for a satisfactory numerical evaluation of the PO integral for the scattered far-field. Non-uniform discretization and spatial accuracy can also be used in the context of the modified FVTD method. The modified FVTD method is aimed at simulating electromagnetic scattering from geometries containing long smooth illuminated sections with respect to the incident wave. The computational efficiency of the modified FVTD method for higher electrical sizes are shown by solving two-dimensional test cases involving electromagnetic scattering from a circular cylinder and a symmetric airfoil.

• Korea-Australia Rheology Journal
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• 제15권3호
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• pp.125-130
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• 2003

The emulsion stability of cosmetic creams based on the water-in-oil (W/O) high internal phase emulsions (HIPEs) containing water, squalane oil and cetyl dimethicone copolyol was investigated with various compositional changes, such as electrolyte concentration, oil polarity and water phase volume fraction. The rheological consistency was mainly destroyed by the coalescence of the deformed water droplets. The slope change of complex modulus versus water phase volume fraction monitored in the linear viscoelastic region could be explained with the resistance to coalescence of the deformed interfacial film of water droplets in concentrated W/O emulsions: the greater the increase of complex modulus was, the more the coalescence occurred and the less consistent the emulsions were. Emulsion stability was dependent on the addition of electrolyte to the water phase. Increasing the electrolyte concentration increased the refractive index of the water phase, and thus decreased the refractive index difference between oil and water phases. This decreased the attractive force between water droplets, which resulted in reducing the coalescence of droplets and increasing the stability of emulsions. Increasing the oil polarity tended to increase emulsion consistency, but did not show clear difference in cream hardness among the emulsions.

• Computers and Concrete
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• 제26권3호
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• pp.275-283
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• 2020

Reinforced concrete (RC) does not provide sufficient resistance against impacts and blast loads, and the brittle structure of RC fails to protect against fractures due to the lack of shock absorption. Investigations on improving its resistance against explosion and impact have been actively conducted on high-performance fiber-reinforced cementitious composites (HPFRCCs), such as fiber-reinforced concrete and ultra-high-performance concrete. For these HPFRCCs, however, tensile strength and toughness are still significantly lower compared to compressive strength due to their limited fiber volume fraction. Therefore, in this study, the tensile behavior of slurry-infiltrated fiber-reinforced cementitious composites (SIFRCCs), which can accommodate a large number of steel fibers, was analyzed under static and dynamic loading to improve the shortcomings of RC and to enhance its explosion and impact resistance. The fiber volume fractions of SIFRCCs were set to 4%, 5%, and 6%, and three strain rate levels (maximum strain rate: 250 s^-1) were applied. As a result, the tensile strength exceeded 15 MPa under static load, and the dynamic tensile strength reached a maximum of 40 MPa. In addition, tensile characteristics, such as tensile strength, deformation capacity, and energy absorption capacity, were improved as the fiber volume fraction and strain rate increased.

• 콘크리트학회논문집
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• 제12권1호
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• pp.113-125
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• 2000

The purpose of this study was to examine the durability characteristics of controlled low strength material(flowable fill) with high volume fly ash content. Flowable fill refer to self-compacted, cementitious material used primarily as a backfill in lieu of compacted fill. The two primary advantages of flowable fill over traditional methods are its ease of placement and the elimination of settlement. Therefore, in difficult compaction areas or areas where settlement is a concern, flowable fill should be considered. The fly ash used in this study met the requirements of KS L 5405 and ASTM C 618 for Class F material. The mix proportions used for flowable fill are selected to obtain low-strength materials in the 10 to 15kgf/$\textrm{cm}^2$ range. The optimized flowable fill was consisted of 60kg f/$\textrm{m}^3$ cement content, 280kgf/$\textrm{m}^3$ fly ash content, 1400kgf/$\textrm{m}^3$ sand content, and 320kgf/$\textrm{m}^3$ water content. Subsequently, durability tests including permeability, warm water immersion, repeated wetting & drying, freezing & thawing for high volume fly ash-flowable fill are conducted. The results indicated that flowable fill has acceptable durability characteristics.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 춘계 학술논문 발표대회
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• pp.146-147
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• 2014

In this study, as the resistance of the carbonation for high volume admixture incorporating concrete, coating effect of using refined cooking oil in the surface of high volume admixture incorporating concrete has been tested. The following results could be made as the conclusion. For the fresh concrete, the slump and air content has been identified as satisfying the target range. For the hardened concrete, comparing with specimen of Plain, specimen with coating showed better long age compressive strength. For the carbonation speed, the specimen of FA30 showed highest speed and the specimen of BS60 showed higher speed than specimen of Plain. For all the specimens coated with RCO, as the decrease of capillary pores inside the concrete, the carbonation speed has been obviously decreased and with even better effect than using PEP coating. It could be identified that specimens with coating by RCO showed good effect on refrain the speed of carbonation.

• KSBB Journal
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• 제4권2호
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• pp.177-184
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• 1989

항생물질 발효액의 균사체 분리에 있어서 Modified regenerated cellulose 막을 이용한 Cross-flow filtration으로 높은 Flux를 얻을 수 있었다. 막분리시 가급적 높은 유속, 높은 온도, 특정 균사체농도(약 20% PMV)에서 높은 Flux를 보여주었으며 Fouling 정도는 균사체 농도가 높을수록 또한 유속이 낮을수록 심각한 것으로 나타났다. 발효액을 농축 분리할 때의 Flux profile은 1단계 Sublayer형성에 의한 급속감소, 2단계 평형, 3단계 Fouling에 의한 급속감소의 세 구간으로 나눌 수 있었으며 Diafiltration의 적용으로 3단계의 Flux 감소 현상을 현저히 완화시킬 수 있었다. 한편 Diafiltration에 의한 항생물질 회수시 초기부터Diafiltration하는 것보다는 특정 PMV까지 농축시킨 후 Diafiltration하는 경우에 작업시간과 여액의 Volume을 최소화 할 수 있었으며 본 실험에서는 98%의 회수율을 얻기 위해서 Di-afiltration을 시작하는 Optimum PMV는 20%였다.

• 한국표면공학회지
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• 제51권1호
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• pp.47-53
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• 2018

Sn-based lithium-ion batteries have low cost and high theoretical specific capacity. However, one of major problem is the capacity fading caused by volume expansion during lithiation/delithiation. In this study, 3-dimensional foam structure of Cu-Sn alloy is prepared by co-electrodeposition including large free space to accommodate the volume expansion of Sn. The Cu-Sn foam structure exhibits highly porous and numerous small grains. The result of EDX mapping and XPS spectrum analysis confirm that Cu-Sn foam consists of $SnO_2$ with a small quantity of CuO. The Cu-Sn foam structure electrode shows high reversible redox peaks in cyclic voltammograms. The galvanostatic cell cycling performances show that Cu-Sn foam electrode has high specific capacity of 687 mAh/g at a current rate of 50 mA/g. Through SEM observation after the charge/discharge processes, the morphology of Cu-Sn foam structure is mostly maintained despite large volume expansion during the repeated lithiation/delithiation reactions.

• 한국광학회지
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• 제9권6호
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• pp.385-389
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• 1998

본 논문에서는 공간정합필터의 데이터 베이스로써 체적 홀로그램을 이용한 광상관기를 구성하였다. 광상관 시스템은 광학의 고속 및 병렬처리 특징을 지니며, 공간정합필터가 기록된 체적홀로그램은 방대한 저장 능력과 실시간 랜덤 엑세스의 장점을 갖는다. 데이터 베이스로 사용되는 영상들은 각가 공간광변조기에 디스플레이 되어 퓨리에 변환 렌즈를 통과한 후 퓨리에 변환된 공간정합필터의 형태로 광굴절 매질에 기록된다. 대용량의 데이터 베이스를 구성하기 위한 다중화 방법으로 스텝 모터를 이용하여 광굴절 매질을 회전하는 각다중화 기술을 사용하였다. 체적홀로그래픽 광상관 실험을 통하여 지문인식에의 응용 가능성을 제시하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.172-175
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• 2001

The high temperature deformation behavior of two-phase gamma TiAl alloy has been investigated with the variation of temperature and ${\gamma}/{\alpha}_2$ volume fraction. For this purpose, a series of load relaxation tests and tensile tests have been conducted at temperature ranging from 800 to $1050^{\circ}C$. In the early stage of the deformation as in the load relaxation test experimental flow curves of the fine-grained TiAl alloy are well fitted with the combined curves of two processes (grain matrix deformation and dislocation climb) in the inelastic deformation theory. The evidence of grain boundary sliding has not been observed at this stage. However, when the amount of deformation is large (${\epsilon}{\approx}$ 0.8), flow curves significantly changes its shape indicating that grain boundary sliding also operates at this stage, which has been attributed to the occurrence of dynamic recrystallization during the deformation. With the increase in the volume fraction of ${\alpha}_2$-phase, the flow stress for grain matrix deformation increases since ${\alpha}_2$-Phase is considered as hard phase acting as barrier for dislocation movement. It is considered that cavity initiation is more probable to occur at ${\alpha}_2/{\gamma}$ interface rather than at ${\gamma}/{\gamma}$ interface.