• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회 논문집(I)
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• pp.77-82
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• 1998

It was investigated to evaluate the characteristics of cement-flyash paste affected the replacement level, curing method and chemical admixtures. The strength of cement-flyash paste was lower than that of cement paste only and the differences increased with increasing the replacement level. However, in steam curing, the strength of cement-flyash pastes was improved and specially, the early strength was effectively increased. In order to improve the early strength, the use of $Na_2SO_4$ in cement-flyash paste increased the quality of concrete. In addition, the strength of concrete including 30% of fly ash has improved and obtained the highest strength compared to other concrete mix.

• Journal of Advanced Marine Engineering and Technology
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• 제31권6호
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• pp.797-803
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• 2007

The Industrial Mixers are used in various industrial fields where they are necessary to intimately mix two reactants in a short Period of time. However. despite their widespread use, complex unsteady flow characteristics of industrial mixers are not systematically investigated. The present study aims for clarify unsteady flow characteristics Induced by various impellers in a tank. Impellers are pitched blade turbine(PBT) types, Screw type and Rushton turbine type. In this study choice of the industrial mixer's impeller type using PIV and CFD method. The rotating speed of impellers are fixed by 100RPM.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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• pp.163-166
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• 2006

This paper presents numerical results of fluid flows and mixing in a microfluidic device for AC electroosmotic flow (AC-EOF) with coplanar electrodes on top and bottom walls. Differently from previous EOF a channel which attached a couple of coplanar electrodes can be utilized to mix a target liquid with a reagent. In this study we propose a method of controlling fluid flows and mixing enhancement. To obtain the flow and mixing characteristics, numerical computations are performed by using a commercial code, CFX10. It was found that the flow near the coplanar electrodes is of 3-D complex flows and vortices between the other electrodes, and as a consequence the AC-electroosmotic flow on the electrodes plays an important role in mixing the liquid.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.37-40
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• 2003

The thrust vector control using a fluidic counterflow concept is achieved by applying a vacuum to a slot adjacent to a primary jet which is shrouded by a suction collar. The vacuum produces a secondary reverse flowing stream near the primary. The shear layers between the two counterflowing streams mix and entrain mass from the surrounding fluid. The presence of the collar inhibits mass entrainment and the flow m the collar accelerates causing a drop in pressure on the collar. For the vacuum asymmetrically applied to one side of the nozzle, the jet will vector toward the low-pressure region. The present study is performed to investigate the effectiveness of thrust vector control using the fluidic counterflow concept. A computational work is carried out using the two-dimensional, compressible Navier-Stokes equations, with several kinds of turbulence models. The computational results are compared with the previous experimental ones. It is found that the present fluidic counterflow concept is a viable method to vector the thrust of a propulsion system.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 봄 학술발표회 논문집
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• pp.394-401
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• 1996

This paper persents the crack control of mass concrete in massive machine foundation. The dimension of the machine foundation is 52.6m$\times$14.4m$\times$8.5m. The one distinctive characteristic of mass concrete is thermal behavior. Since the cement-water reaction is exothermic by nature, the temperature rises inside the massive concrete structure. When the heat is not quickly dissipated, it can be quite high. Significant tensile stresses may develop from the volume change associated with the increase of decrease of temperature within the mass concrete structure. To avoid occurrence of harmful cracks due to hydration heat, special attention shall be given to the construction of mass cnocrete structures. The temperature control system of mass concrete is proposed in this paper. This system contains a discussion of materials and concrete mix proportioning, thermal analysis, curing method, temperature control, and measurement of hydration heat. As will be seen throughout the paper, the proposed temperature control system have a great effect on the temperature-related cracks on mass concrete structures.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.1023-1028
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• 2003

The structure of Tower Palace III Sports Center building was designed as concrete Filled Steel Tube(CFT) Column and the filled-in concrete was designed as high compressive strength of 500kgf/$m_2$. The self compacting concrete(SCC, non-vibrating concrete) with 65$\pm$5cm flow must be applied to this case for filling the CFT by injecting the concrete from the column bottom. Laboratory tests and pilot productions of batcher plant were performed for optimum mix design and the full scale Mock-Up test was performed to check the appicability of the construction method. As a result, we observed that good quality SCC and the pressure change of concrete pump normally used domestically. Based on these results, we have constructed 20-40m height CFT columns successfully.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.609-617
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• 2003

The use of Shotcrete(Sprayed concrete) for the support of underground excavations was pioneered by the Civil engineering industry. Permanent shotcrete tunnel linings such as Single-shell, NMT(Norwegian Method of Tunnelling) have been constructed in many countries for reducing construction time and lowering construction costs instead of conventional in-situ concrete linings. Among essential technologies for successful application of Permanent Shotcrete Linings, high performance shotcrete having high strength, high durability, better pumpability has to be developed in advance. This paper presents the ideas and the first field test results of wet-mixed Steel Fiber Reinforced Shotcrete(SFRS) with powder types cement mineral accelerator. From the results, wet-mix SFRS with powdered accelerator exhibited good early strength improvement and less rebound ratio compared to the ordinary accelerator.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.681-686
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• 2003

One of the major degradation processes of reinforced concrete (RC) structure is corrosion of reinforced steel due to chloride attack. Severe environments, such as marine environment and exposure to de-icing salts, could accelerate the steel corrosion of RC structures through the chloride ion intrusion into concrete. In order to delay this degradation process, several kinds of admixtures have been used in concrete mix. In this study, effective diffusion coefficient of chloride ion ($D_{eff}$) and total passed charge of concrete with and without fly ash were measured using electrical method. It is found that fly ash concrete has much less chloride ion coefficient than ordinary concrete at later age. By analyzing the test results, $D_{eff}$ at 28 and 90 days was obtained as a function of water-binder ratio (W/B) and an equation for predicting $D_{eff}$ with age was proposed considering the decreasing rate of $D_{eff}$.

• 전기학회논문지
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• 제61권6호
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• pp.905-909
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• 2012

Recent WTO/TBT agreement was adopted by the IEC domestic. For this reason, low voltage electrical equipment was many Confusion arises. Low voltage circuit was also one of these. The case of low voltage circuit, existing domestic circuit breakers and circuit breakers IEC curve differs from the behavior of each other. If low voltage circuit breaker wrong facility, circuit breaker malfunction may occur due to the large property damage. In this paper, to solve these problems domestic circuit breakers and circuit breaker operation IEC curves were analyzed. And, through experiments suggested compatible breaker way.

• 대한가정학회지
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• 제43권7호
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• pp.159-170
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• 2005

The purpose of this study was to investigate the causes of managerial failure in small apparel retailers by using the qualitative research method. The study was performed by interviews from thirteen owners/managers who experienced failure as small apparel retailers from November 2003 to February 2004. The causes of failure in the small apparel businesses were human related problems, marketing strategy problems, marketing mix, weak managerial ability, and business environment related problems. Of special interest was causes such as incomplete legal documents with franchisers, unexpected tax investigation from the office of National Tax Administration(NTA), sexual discrimination for women owners, and incapable risk management. It is interesting to note that tax investigation by NTA and sexual discrimination in the business custom were shown as the main causes of business failure in Korea.