• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.738-745
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• 2004

There are a number of ways to reduce the ground vibrations, one of which is by installing underground walls. Model tests for ground vibration have been conducted in recent years, but limited attention has been paid to underground wall which can reduce high vibrations. Up to date, only barriers have been actually installed in dry sand because of many unknown factors subsisting on the behavior of the ground. The characteristics of vibration sources, ground conditions and wall barriers have not been well understood yet, therefore centrifugal modeling was adopted to examine all these characteristics. This paper describes a ball dropping system, which can generate a pulse wave propagation through soil mass, and the test results show the effectiveness of underground wall barrier in reducing mechanical vibration.

• Geomechanics and Engineering
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• 제31권3호
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• pp.305-318
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• 2022

Permeable reactive barriers used for groundwater treatment require proper estimation of the reactive material behavior regarding the emplacement method. This study evaluates the dry emplacement of zeolite (clinoptilolite) to be used as a reactive material in the barrier by carrying out several geotechnical laboratory tests. Dry zeolite samples, exhibited higher wetting-induced compression strains at the higher vertical stresses, up to 12% at 400 kN/m². The swelling potential was observed to be limited with a 3.5 swell index and less than 1% free swelling strain. Direct shear tests revealed that inundation reduces the shear strength of a dry zeolite column by a maximum of 10%. Falling head permeability tests indicate decreasing permeability values with increasing the vertical effective stress. Regarding self-loading and inundation, the porosity along the zeolite column was calculated using a proposed 1D numerical model to predict the permeability with depth considering the laboratory tests. The calculated discharge efficiency was significantly decreased with depth and less than 2% relative to the top for barrier depths deeper than 20 m. Finally, the importance of directional dependence in the permeability of the zeolite medium for calibrating 2D finite element flow analysis was highlighted by bench-scale tests performed under 2D flow conditions.

• 한국재료학회지
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• 제23권8호
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• pp.423-429
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• 2013

Recently, steel structures have increasingly been required to have sufficient deformability because they are subjected to progressive or abrupt displacement arising from structure loading itself, earthquake, and ground movement in their service environment. In this study, high-strength low-carbon bainitic steel specimens with enhanced deformability were fabricated by varying thermo-mechanical control process conditions consisting of controlled rolling and accelerated cooling, and then tensile and Charpy V-notch impact tests were conducted to investigate the correlation between microstructure and mechanical properties such as strength, deformability, and low-temperature toughness. Low-temperature transformation phases, i.e. granular bainite (GB), degenerate upper bainite(DUB), lower bainite(LB) and lath martensite(LM), together with fine polygonal ferrite(PF) were well developed, and the microstructural evolution was more critically affected by start and finish cooling temperatures than by finish rolling temperature. The steel specimens start-cooled at higher temperature had the best combination of strength and deformability because of the appropriate mixture of fine PF and low-temperature transformation phases such as GB, DUB, and LB/LM. On the other hand, the steel specimens start-cooled at lower temperature and finish-cooled at higher temperature exhibited a good low-temperature toughness because the interphase boundaries between the low-temperature transformation phases and/or PF act as beneficial barriers to cleavage crack propagation.

• 한국기계가공학회지
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• 제16권1호
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• pp.134-140
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• 2017

CFRP has many industrial applications due to its low weight and high strength properties. CFRP is a composite material composed of carbon fibers embedded in a polymer matrix; it provides excellent resistance to fatigue wear, corrosion, and breakage due to fatigue. It is increasingly demanded in aircraft, automotive, and medical industries due to its superior properties to aluminum alloys, which were once considered the most suitable for specific applications. The basic machining methods of CFRP are drilling and route milling. However, in the case of drilling, the delamination of each layer, uncut fiber, resin burning, spalling, and exit burrs are barriers to successful application. This paper investigates the occurrence of exit burrs when drilling holes with ultrasonic vibration. Depending on design parameters such as the point angle, the characteristics of hole drilling were identified and appropriate machining conditions were considered.

• International Journal of Automotive Technology
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• 제8권1호
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• pp.9-18
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• 2007

Phase separation and low cetane number are the main barriers to the large-scale use of ethanol-diesel blend fuel on small diesel engines. In this paper, an additive package is designed on the basis of the blended fuel properties to overcome these limitations. The experiments show that the solubility of ethanol in diesel is evidently increased by adding $1{\sim}2%$ (in volume) of the additive package and the flammability of ethanol-diesel blend fuel with the additive has reached the neat diesel level under the cold start conditions. Effects of the ethanol content in diesel on fuel economy, combustion characteristics, and emission characteristics are also investigated with the ethanol blend ratios of 10%, 20% and 30%. The increase in ethanol content shows that the specific fuel consumption and the brake thermal efficiency are both gradually increased compared to neat diesel. The soot concentrations of the three blended fuels are all greatly lower than that of neat diesel. $NO_x$ emission is increased with an increase in the engine load and is reduced with the increase in the ethanol blend ratio under a high load.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 추계학술대회 논문집
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• pp.755-761
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• 2009

The major advantage of transparent materials over traditional materials in noise barriers is aesthetics. The transparent panel materials such as clear plastic or glass are an ideal way of reducing or virtually eliminating the visual impact of a noise barrier. With the use of transparent materials, the drivers' view of the roadside and the sunlight penetration to the highway would not be blocked. With the use of transparent materials, the highway and barrier appear less imposing. Korean Industrial Standards for soundproof panels have been established. But, transparent soundproof panels are not included in this standards. And, some specifications provide only a few basic characteristics for transparent soundproof panels. To develop guidelines on quality criteria for transparent soundproof panel, their mechanical properties such as wind load resistance, safety under impact, and abrasion resistance were experimentally investigated.

• 한국진공학회지
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• 제6권S1호
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• pp.80-88
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• 1997

The attempt to enhance the strength of materials has been an important subject for materials engineering and scientists. The strength of materials is termed as the ability to support high load without excessive deformation and without breaking catastrophically. The control of dislocation densities and barriers to the movement of dislocations have been considered to be the important methods for the strengthening materials. One of the approaches is mechanical blocking of dislocations by alternately depositing material layers. The typical structure of materials is multilayered and laminated composites. The thickness of each layer is typically in the range of nanometer. Ton avoid confusion with other terminology they may be defined as microlaminate composite materials. The manufacturing process of multilayered laminate structure will be introduced. And the current theoretical theories will be reviewed in view of strengthening of microlaminte composite materials.

• 한국가시화정보학회지
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• 제16권1호
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• pp.42-47
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• 2018

A needle-free injector is one of the new non-invasive players in impregnating the biological barriers. It is considered as the next phase in drug delivery and therapeutic applications. One of the major fields of application is in skin remodeling procedures. Although many studies were carried out in understanding the principle in the needle-free injection procedure, fewer studies were done with the aim of therapeutic applications. In the present study, we tried to identify key parameters that affect the jet divergence and peak stagnation pressure on the skin surface in a conventional needle-free injector for skin treatment. A summary of the working principle and effect of the key parameters are presented.

• International Journal of Fluid Machinery and Systems
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• 제9권4호
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• pp.325-331
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• 2016

A bathtub vortex above the outlet of a rotating barrel is simulated. By analyzing the Ekman layer theory, it can be found that the main flow circulation is inversely proportional to the thickness of Ekman layer. The thicker the Ekman boundary layer, the weaker the rotational strength and the shorter of the length of gas core is. According to this law, models of barriers with rods of different heights are established. The reduction of air-core length in this air entrainment vortex and weakening the strength of rotation field were achieved.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.86-93
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• 2005

In this paper, we discuss the merits of mechanical machining to generate micro features on large surfaces. An overseas technology trend related to the micro machining and dedicated machinery is also presented. We provide an overview of what characteristics the machinery is required to have to generate micro features on large surfaces and what kind of technical barriers need to be overcome to put the technology to practical use.