• Journal of the Korea Concrete Institute
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• v.18 no.2 s.92
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• pp.189-198
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• 2006

The composition of most engineering materials is heterogeneous at some degree. It is simply a question of scale at which the level of heterogeneity becomes apparent. In the case of cementitious granular materials such as concrete the heterogeneity appears at the mesoscale where it is comprised of aggregate particles, a hardened cement paste and voids. Since it is difficult to consider each separate particle in the topological description explicitly, numerical models of the meso-structure are normally confined to two-phase matrix particle composites in which only the larger inclusions are accounted for. 2-D and 3-D concrete blocks(Representative Volume Element, RVE) are used to simulating heterogeneous concrete meso-structures in the form of aggregates in the hardened mortar with nearly zero-thickness linear or planar interfaces. The numerical sensitivity of these meso-structures are Investigated with respect to the different morphologies of heterogeneity and the different level of coupling constant among fracture mode I, II and III. In addition, a numerically homogenized concrete block in 3-D using Hashin-Shtrikman variational bounds provides an evidence of the effective cracking paths which are quite different with those of heterogenous concrete block. However, their average force-displacement relationship show a pretty close match each other.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.707-715
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• 2007

The vulnerability of concrete to its environment is significantly dependent on the fact that concrete is a porous material. For well-consolidated and well-cured concrete, its service life is a very long and an entrance of aggressive substance might be only pores. However, for cracked concrete, cracks should be preferential channel for the penetration of aggressive substance such as chloride ions. The effect of crack on chloride penetration depends on its size for example, crack width and crack depth. The purpose of this study is examining the effect of crack width and crack depth on chloride penetration. In order to visualize chloride penetration via cracks, RCM (rapid chloride migration) testing is accomplished. Crack width is examined using an optical microscope and CMOD value is used to estimate average crack width. From the examination on the trend of chloride diffusion coefficients of concrete specimens with various crack widths, a critical crack width and a critical crack depth are found out.

• Journal of the Korea Concrete Institute
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• v.22 no.4
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• pp.559-566
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• 2010

Fifteen lightweight concrete mixes were tested to evaluate the effect of maximum size of coarse aggregate and the replacement level of natural sand on the various properties of fresh lightweight concrete. The different properties, such as water absorption against the elapsed time, pore size distribution and micro-structure of lightweight aggregates used, influencing on the workability of fresh concrete were also measured. Test results showed that the initial slump of lightweight concrete decreased with the increase of the replacement level of natural sand. The slump of all-lightweight concrete sharply decreased by around 80% of the initial slump after 30~60 minutes. The air content and bleeding rate of lightweight concrete were significantly affected by the replacement level of natural sand as well as the maximum size of coarse aggregates. Empirical equations recommended in ACI 211 and Korea concrete standard specifications underestimated the air content of the lightweight concrete, indicating that the underestimation increases with the decrease of the replacement level of natural sand. In addition, equations to predict the air content and bleeding rate of lightweight concrete were proposed based on the test results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.7
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• pp.726-733
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• 2017

A magnetic shutter gear is a device that transfers mechanical power by synchronizing the magnetic field between permanent magnet layers facing circumferentially through a harmonic modulator. However, magnetic gears uses many rare-earth permanent magnets to guarantee comparable torque density to that of mechanical reducer. Hence, we propose a novel axial magnetic gear with a dramatically reduced number of permanent magnets and a closed magnetic path. The torque of the system was compared to that of an existing shutter gear through a harmonic analysis of the air-gap magnetic field. The modulator thickness and open ratio were considered as the primary design parameters, and the cogging effect was analyzed for variation of the reduction ratio. A dynamic model between the high-speed side and low-speed side was derived, and position control was performed for a constructed hardware implementation.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1639-1643
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• 2008

국내에서의 범람홍수 및 범람으로 인한 제방붕괴 특성은 그 해석상의 어려움으로 인해 주로 과거 범람상황 및 지형도를 통한 경험적 추정 등에 의존해 오고 있는 실정으로 정교한 물리학적 이론에 근거하지 못하였으므로 범람홍수량, 제방의 붕괴폭 등을 정확하게 예측하기에는 미흡한 점이 많았다. 도시하천과 같이 제방 인접한 곳에 주거, 산업시설 등이 밀집하고 있는 지역에서의 제방붕괴로 인한 홍수류의 범람은 막대한 인명 및 재산피해를 발생시키는 큰 재해가 될 수 있다. 본 연구를 통해서 홍수시 제방월류로 인한 제방붕괴 양상을 예측하고 이를 통해 범람유량의 정확한 예측을 통하여 도시하천 제방 계획시 홍수피해와 투자액을 감안한 경제적인 하천 제방단면 결정을 위한 기본자료로 활용될 수 있고, 도시 중요시설물의 입지 선정시 홍수피해에 대한 판단자료로 이용될 수 있을 것이다. 본 연구에서 개발된 모형을 이용하여 Teton 댐, Mantaro landslide 댐, Spirit Lake 장애물 댐 등에 적용하여 개발된 모형의 정확성을 입증하였다. 적용결과 개발된 모형은 기존의 모형과 같은 결과를 나타내어 국내 계산환경에 적용가능함을 보여 앞으로 이용가능성이 큰것을 알 수 있었다. 적용결과 파이핑의 발생위치의 영향은 대체로 파이핑의 위치가 제체의 윗부분에 위치할수록 최대 유출량은 커지는 것으로 나타났으나 Lawn Lake 댐의 경우에는 사면의 식생의 영향으로 다른 결과를 나타내었다. 점착력은 경우에는 점착력이 클수록 유출량의 크기는 감소하는 것으로 나타났으며 마찰각은 최대 붕괴폭의 크기 및 발생시간, 댐의 높이와 폭, 저수용량 등과 유출량이 연관있어 좀 더 많은 계산결과를 이용하여 심도있는 고찰이 요구되었다. 입자의 중간크기, 공극률, 균일성의 경우 적용된 댐들 모두 유사한 결과를 나타내었고 변수들이 커질수록 유출량도 증가하였다. 댐 사면 경사의 경우에는 상,하류 사면 모두 경사가 완만할수록 유출량이 감소하였다. 위의 결과를 통해 개발된 제방붕괴 해석모형은 좀 더 많은 연구와 적용을 통해 개선과 검증이 이루어진다면 국내 제방붕괴해석에 필요한 해석모형이 될 수 있다고 판단되었다.

• Membrane Journal
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• v.24 no.1
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• pp.50-62
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• 2014

An asymmetric microfiltration membranes were prepared with polysulfone by an immersion precipitation phase inversion method. Microfiltration membranes were prepared by polysulfone/N-methyl-2-pyrrolidone/polyvinylpyrrolidone/phosphoric acid casting solution and water coagulant. The vapor induced phase inversion method was used to prepare the membranes. The pore size and the morphology were changed by the phosphoric acid additive, the temperature of casting plate and the exposure time at the relative humidity of 74%. The morphology of membranes was investigated by scanning electron microscopy and microflow permporometer. By the addition of the phosphoric acid additive in the casting solution, the morphology of the prepared membranes were changed from a dense sponge structure to a loose asymmetric sponge structure. Due to the addition of catalytic amount of phosphoric acid to NMP casting solution, the mean pore size increased almost $0.2{\mu}m$ and the water flux increased about 3,000 LMH. The temperature of casting plate and exposure time had a apparent effect on the skin layer structure and the pore size and the porosity of the membrane.

• Journal of Sensor Science and Technology
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• v.11 no.3
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• pp.171-182
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• 2002

The differential electromagnetic transducer for IME(implantable middle ear) system, which have two small permanent magnets glued with the same pole facing each other in the coil, has high vibration efficiency and does not influenced by external magnetic field. In this paper, using finite element method, highly efficient structure of the transducer was proposed and vibration force of the transducer was calculated by electromagnetic theory. And the necessary vibration force of transducer to transmit the sound signal to inner ear when the transducer is attached at stapes was calculated and the design parameters of the transducer were investigated. Using the parameters, the differential electromagnetic transducer was manufactured in small size to implant in confined human middle ear. And it was examined by unloaded and loaded vibration experiment using temporal bone sampled from cadaver.

• Journal of Plant Biology
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• v.38 no.1
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• pp.79-86
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• 1995

Visible injury symptoms such as necrosis, chlorosis and premature senscence in the leaves of Ginkgo bloba and Pinus thunbergii treated with acid rain of pH 3.2 or below were observed. The epicuticular wax erosions were observed by SEM after exposure to acid rain of pH 2.4 and 3.2 in G. biloba and pH 4.0 below in P. thunbergii. The adaxial epidennal cells and sponge parenchyma cells were compressed, and those were distorted in the leaves of G. biloba treated with simulated acid rain of pH 3.2 or below. However, vascular tissue was intact. With increase of acidity, mesophyll cells were smaller than those of control while intercellular space in mesophyU was increased. In P. thunbergii, sponge parenchyma cells and vascular tissue except epidennis were distorted after exposure to acid rain of pH 2.4. The size change of stomata in foliar injury was not observed, but the stomatal index and size of stomatal aperture in leaves treated with acid rain increased. The stomata of injured leaf were opened in both species examined.amined.

• The Journal of Engineering Geology
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• v.21 no.4
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• pp.381-391
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• 2011

Weathering can reduce rock strength and eventually affect the structural stability of a rock mass, which is important in the field of engineering geology. Several methods have been developed to evaluate the degree of weathering, including the chemical weathering index. In this study, we analyzed the weathering degree and characteristics of microtextures and pores in crystalline rocks (gneiss and granites) based on petrographic observations, the chemical weathering index, mineralogy by XRD, microtextural analysis by SEM/EDS, measurements of pore size and surface area by the BET method, and microporosity by X-ray CT. The formation of secondary minerals and microtexture in gneiss and granitic rocks are assumed to be affected by complex processes such as dissolution, precipitation, and fracturing. Hence, it is clear that some chemical weathering indices that are based solely on whole-rock chemistry (e.g., CIA and CWI) are unable to provide reliable assessments of the degree of weathering. Great care is needed to evaluate the degree of chemical weathering, including an understanding of the mineralogy and microtexture of the rock mass, as well as the characteristics of micropores.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.4
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• pp.18-25
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• 2020

The purpose of this study is to investigate the mechanical and carbon-capture properties of foam concrete containing stainless steel argon oxygen decarbonization(AOD) slag. AOD slag was used as a binder, and foam concrete having a foaming ratio of 69 ± 0.5 % and a slurry density of 573.2 to 578.6 kg / ㎥ was produced. In order to examine the effect of carbonation, blended specimen was cured by two types : normal curing and CO₂ curing. As a result of the experiment, the specimens incorporating AOD slag showed higher compressive strength than Plain after CO₂ curing. According to the analysis of the image of foam concrete, it was confirmed that the ST30 has a lower total pore volume and average pore size than plain, resulting in high compressive strength. The SEM analysis confirmed the formation of calcite by carbonation of AOD slag. Through the thermogravimetric analysis, the increase of CO₂ uptake was confirmed by the incorporation of AOD slag. Foam concrete has a higher porosity than normal concrete, so it is expected that carbon-capture performance can be improved by using a AOD slag.