• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.169-179
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• 2003

Undrained shear strength of clay deposit is one of the most important properties in the design of geotechnical structures. The use of piezocone test is rapidly growing due to its merit that can measure the in-situ undrained shear strength continuously with less error. The reliability of the shear strength from piezocone test depends upon the cone factor applied. Many researchers have suggested different ranges of values for the factors. This study performs to find out the validity of the suggested values in Korea and their charateristics related to the mechanical properties of clay. Piezocone tests were performed at the site of pilot project of ground improvement at Yangsan-Mulgeum Gyeongnam to investigate the charateristics of piezocone factors. The piezocone fators$(N_{kt}, N_{ke}, N_{\Delta u})$ based on the undrained shear strength from quick triaxial compression test are generally within the suggested range. And there appears considerable relations between undrained shear strength and $(N_{kt}, N_{ke}, N_{\Delta u})$ and between preconsolidation pressure and $(N_{kt}, N_{ke})$, while plasticity index, rigidity index and friction ratio do not show any relations with cone factors. The results also reveal that factor $(N_{\Delta u})$ shows higher reliability than factors $(N_{kt} and N_{ke})$, which show smaller standard deviation, breadth of change and scattering.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.291-298
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• 2008

Cracks in concrete generally interconnect flow paths and increase concrete permeability. The increase in concrete permeability due to the progression of cracks allows more water or aggressive chemical ions to penetrate into concrete, facilitating deterioration. The goal of this research is to study the relationship between crack width and water permeability of cracked concrete. Tests have been carried out as a function of hydraulic pressure (0.1 $\sim$ 2 bar) and crack width (30 $\sim$ 100 ${\mu}m$). Splitting and reuniting method was used to manufacture cracked concrete specimens with controlled crack width. Crack widths are checked by using a microscope($\times$100). The results show a considerable increase of water transport with crack width and hydraulic pressure. When the crack width is smaller than 50${\mu}m$, the crack width has little effect on concrete permeability. Due to the autogenous healing, the water flow through the crack gradually reduces with time. When crack width is 100 ${\mu}m$ and hydraulic pressure increase from 0.1 bar to 0.25 bar, concrete permeability increases rapidly about 190 times according to the test results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1991.11a
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• pp.110-115
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• 1991

일반적으로 거의 모든 재료의 기계적인 물성치들이 여러가지 하중조건에 의해 변화하는데 그 중 탄성계수는 하중속도, 온도, 재료의 특성에 따라 변화한다. 지금까지 국내에서의 연구동향을 보면 하중속도가 탄성계수에 미치는 영향에 대한 연구보고는 미약한 실정이다.(중략)

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.1
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• pp.25-30
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• 2014

The flow characteristics of two types of overhung compressor volutes for automobile turbochargers were analyzed numerically using commercial software. For obtaining high performance from a volute, it is necessary that the volute have a high pressure recovery coefficient and a low loss coefficient. We investigated the flow characteristics of two types of overhung compressor volutes with a fixed diffuser inlet angle of $24^{\circ}$ and a mass flow rate of 0.055 kg/s. The first type is a volute with one-arc cross section (type 1) and the second type is with three-arc cross section (type 2). Our results showed that between the two types of volutes, type 2 had the higher pressure recovery coefficient and the lower loss coefficient along the entire angular position.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.1
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• pp.19-26
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• 1996

An experimental and computational study of the pressure fluctuation induced by a propeller on a hull surface was carried out with three ship models and seven model propellers. The fluctuation of pressure on a flat plate was measured at KRISO cavitation tunnel and calculated by a panel and lifting surface method(XForShip code). To extend the measurement data on the flat plate into that on complex hull forms, the correction factor was determined as a ratio of the solid boundary factor(SBF). The computation of pressure fluctuation around complex hull forms was also performed to make the full scale prediction and compared with the corrected experimental data. The calculated values agreed well with the compensated experimental data and it was found that the correction factor was about 0.65-0.7.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.2
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• pp.51-57
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• 2012

Base pressure at the base of high-speed jet has long been one of the important issues from both the view points of fluid dynamics as well as practical engineering applications. The base pressure characteristics of incompressible flows have been well known to date. However, the base pressure at transonic or supersonic speeds would be different due to the compressibility effects and shock waves. In the present paper, a CFD study has been performed to understand the base pressure characteristics at transonic and supersonic speeds, prior to experimental work. An emphasis is placed on the control of the base pressure using a simple orifice. A variety of supersonic jet plumes have been explored to investigate the flow variables influencing the base pressure. The results obtained were validated with existing experimental data and discussed in terms of the base pressure and discharge coefficient of the orifice.

• Journal of the Korea Institute of Building Construction
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• v.15 no.3
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• pp.291-297
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• 2015

In this study, the evaluation and the analysis of the correlation between rheological properties and pumpability of high performance concrete, C80A which was applied to the height of from 200 m to 350 m in a super tall building, was carried out by measuring pumping pressure and flow rate, testing concrete properties at before and after pumping. As the results, C80A had satisfactory properties of fresh and hardened concrete to the requirements even after pumping and the maximum pumping pressure showed increase of 10~15% at every 50m higher pumping and the average flow rate showed the above $25m^3$ per hour which means proper productivity. Additionally it was verified that pumping pressure and friction factor in pipeline are inversely proportional to slump flow and showed a tendency to increase according to the higher T-500 value.

• Journal of Energy Engineering
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• v.16 no.4
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• pp.181-186
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• 2007

In order to investigate the heat transfer coefficient and pressure drop during evaporation of $CO_2$, basic experiment on the evaporation heat transfer characteristics in a horizontal smooth tube was performed. The experimental apparatus consisted of a test section, a DC power supply, a heater, a chiller, a mass flow meter, a pump and a measurement system. Experiment was conducted for various mass fluxes ($200{\sim}1200\;kg/m^2s$), heat fluxes ($10{\sim}80\;kW/m^2$) and saturation temperatures ($-5{\sim}5^{\circ}C$). With the increase of quality, the evaporation heat transfer coefficient decreased. With the increase of heat flux, the evaporation heat transfer coefficient increased. Significantly change of the heat transfer coefficient was observed at any heat flux and mass flux. With the increase of saturation temperature, the heat transfer coefficient increased. Pressure drop increased with the increase of mass flux and the decrease of saturation temperature.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.69-78
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• 2003

In order to investigate the dynamic behavior of weathered granite soils before and after freezing-thawing, cyclic triaxial tests were conducted for the specimens not only with the variation of silt contents within 20% but with plasticity index within 20%. As the results, the dynamic shear modulus of weathered granite soils decreased with increasing silt contents. However, the change in damping ratio was negligible. The influence of freezing-thawing on shear modulus and damping ratio was minimal for the granite soils with variation of silt contents. For the case of the weathered soils with variation of plasticity index, the shear modulus increased with plasticity index within 20%, while the modulus decreased remarkably after freezing-thawing.

• Journal of Korean Society of Steel Construction
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• v.12 no.2 s.45
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• pp.143-150
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• 2000

Depending upon the combination of tolerances specified in the standards on bolt, nut and washer for high tension bolt sets, there arises center-to-center deviation between bolt and washer. This deviation nay cause loss of effective contact area between nut- and washer-faces, which leads to some dispersion of the torque coefficient K. By adapting circular arc surface instead of flat surface for the nut, it is shown through numerical analyses that the dispersion of the torque coefficient can be minimized. In this way, optimum radius of curvature of the nut bearing surface is proposed.