• Progress in Superconductivity
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• v.3 no.1
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• pp.28-30
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• 2001

We studied the flux-flow current-voltage characteristics of microwave-generated fluxons formed in serially stacked intrinsic Josephson junctions fabricated on$ HgI_2$-intercalated $Bi_2$$Sr_2$$CaCu_2$O/8+x/(Bi2212) single crystals. With increasing the irradiation power of 73$\square$76 GHz microwave, the supercurrent branch became resistive and split into multiple sub -branches. Each sub-branch represented a specific mode of collective motion of Josephson fluxons. We also observed similar branch splitting In a mesa prepared on an underdoped Bi2212 single crystal in a static magnetic field.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.114-117
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• 2006

The air filter in engine intake system has a function of filtrating the dirt in the scavenging air as well as attenuating the noise. The noise attenuation within the air cleaner filter, however, has been regarded as negligible by the field engineers. In this paper, for the analysis of the acoustical performance of air filter, an acoustical model was suggested and the characteristics of air filter system were investigated. Fibrous structure of the filter element was modeled as a micro-perforated panel using the flow resistivity and porosity. The pleated geometry of the filter element was modeled as two coupled ducts that have permeable walls, in which each duct area was assumed being constant. Using such simplified geometry, a mathematical model was developed for the sound propagation within a narrow duct system. Visco-thermal effect was considered in modeling the sound propagation through such tubes; the filter box was modeled as a rigid rectangular box. By combining two models, a four-pole transfer matrix was derived. For the validation purpose, transmission loss was measured for a plastic rectangular box containing an air filter. A noticeable effect of the air filter element was observed by including the filter into the box. Comparing the predicted and measured data, we found that the predicted TL agrees well with experimental results, in particular, in magnitude and frequency at TL troughs.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.3
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• pp.137-146
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• 1997

Spray characteristics of high pressure injectors for diesel engines have been experimentally studied with special emphasis on the effect of swirl. A constant volume chamber was rotated in order to generate a continuous swirl having the flow field of a solid body rotation, resulting in the linear dependance of the swirl number on the rotating speed of the chamber. Emulsified fuel is injected into the chamber and the developing process of fuel sprays is visualized. The fuel spray developing process in D.I. diesel engine was investigated by this liquid injection technique. The effect of swirl on the spray tip penetration is quantified through modelling. Results show that the spray tip penetration is qualitatively different for low and high pressure injections. For high pressure injection case, a good agreement is achieved between the experimental results and the modeling accounting the effect of swirl. For low pressure injection, a reasonable agreement is obtained. It is found that excessive swirl may cause adverse effect on spray dispersion during the initial combustion period since the spray can not be impinged on chamber wall.

• Journal of Environmental Impact Assessment
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• v.14 no.2
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• pp.63-73
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• 2005

This study was performed to characterize stormwater runoff of pollution material from nonpoint sources during rainfall in drainage basins of Hongjechun watershed, and to suggest management methods to control the first flush of nonpoint sources. We conducted 4 times of field surveys including 3 times of wet period and 1 times of dry period for 5 stations, which consist of 3 stations in main stream of Hongjechun and 1 station in tributaries of Sinyoungchun and Gukichun, respectively. The variation of pollutant concentrations in terms of BOD, COD, SS and TP was large depending on the flow rate of stormwater, while a little change of TN concentration was investigated. Depending on the rainfall event, the difference of flowrates, and runoff loadings was large, while the difference of those for dry wether period was not noticeable for various sub-basins. In the results of unit load calculation, the range of 153-277 kg/ha/yr for BOD, 222-422 kg/ha/yr for COD, 264-432 kg/ha/yr for SS, 40-70kg/ha/yr for TN, and 13-25 kg/ha/yr for TP was obtained for Hongjechun, Sinyoungchun, and Gukichun sub-basins. Compared with the previous studies, the result of this study was founded to be acceptable.

• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.318-321
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• 2000

Most compressive strengths commonly used in the construction field are in a range of 240 to 300 kgf/$\textrm{cm}^2$ at 28 days. To get this rage of strengths, however, high-flowing concrete requires cementitious binders more than 400 to 450 kg/$\textrm{cm}^2$ for preventing segregation and sedimentation of aggregates. This amount of cementitious binder generates a large emission of excessive hydration heat, which may consequently induce harmful cracks in concrete structure. In order to reduce excessive hydration heat, thus, this paper aims at fabricating a high-flowing concrete under the condition that cement content is kept as low as 350kg/$\textrm{cm}^3$ by using viscose agents. In a parametric study, effects of cement types such as a ternary blended cement and Type V on he physical characteristics of high-flowing concrete were evaluated. In addition, the influence of viscosity was also investigated by applying two different viscose agents, one in a range of 6,000 to 10,000 cps and the others of 10,000 to 14,000 cps. In terms of chemical admixtures used in concrete mixture, the superplasticizer was Sulfonated Melamine-Formaldehyde Condensate with about 30,000 of molecular weight, and main component of viscose agent was HPMC (Hydroxy Propyl Methyl Cellulose). Slump flow was fixed at 50cm with different dosages of superplasticizer in weight.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.11
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• pp.914-922
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• 2002

Thermo-acoustic waves can be thermally generated in a compressible flow field by rapid heating and cooling, and chemical reaction near the boundary walls. This mechanism is very important in the space environment in which natural convection does not exist. Also this may be a significant factor for heat transfer when the fluids are close to the thermodynamic critical point. In this study, the generation and transmission characteristics of thermo-acoustic waves in an air-filled confined domain with two-step pulsed heating are studied numerically. The governing equations are discretized using control volume method, and are solved using PISO algorithm and second-order upwind scheme. For the purpose of stable solution, time step was set to the order of $1\times10_-9s,\;and\;grids\;are\;50\times2000$. Results show that temperature and pressure distributions of fluid near the boundary wall subjected to a rapid heating are increased abruptly, and the induced thermo-acoustic wave propagates through the fluid until it decays due to viscous and heat dissipation. Pressure waves have sharp front shape and decay with a long tail in the case of step heating, but these waves have sharp pin shape in the case of pulsed heating.

• International Journal of Railway
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• v.7 no.4
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• pp.100-108
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• 2014

A numerical analysis method for predicting aerodynamic noise at inter-coach space of high-speed trains, validated by wind-tunnel experiments for limited speed range, is proposed. The wind-tunnel testing measurements of the train aerodynamic sound pressure level for the new generation Korean high-speed train have suggested that the inter-coach space aerodynamic noise varies approximately to the 7.7th power of the train speed. The observed high sensitivity serves as a motivation for the present investigation on elucidating the characteristics of noise emission at inter-coach space. As train speed increases, the effect of turbulent flows and vortex shedding is amplified, with concomitant increase in the aerodynamic noise. The turbulent flow field analysis demonstrates that vortex formation indeed causes generation of aerodynamic sound. For validation, numerical simulation and wind tunnel measurements are performed under identical conditions. The results show close correlation between the numerically derived and measured values, and with some adjustment, the results are found to be in good agreement. Thus validated, the numerical analysis procedure is applied to predict the aerodynamic noise level at inter-coach space. As the train gains speed, numerical simulation predicts increase in the overall aerodynamic sound emission level accompanied by an upward shift in the main frequency components of the sound. A contour mapping of the aerodynamic sound for the region enclosing the inter-coach space is presented.

• Journal of the Korean Society of Costume
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• v.61 no.7
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• pp.80-100
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• 2011

The purpose of this research is to classify that fashion and art in the twentieth century broadened the creative field by individually applying each other's ideas or through collaboration. This paper analyses the work of individual artists and fashion designers who created work on the boundaries of fashion and art. These samples are selected to extract features related to specific periods as it is proposed that contemporary creation has been developed from a combination of fashion and art, sharing their distinct concerns. Accordingly, this research will focus on the collaboration between fashion and art in the twentieth century from the aspect of 'fashion into art'/'art into fashion' in order to analyse the historical flow, and thereby examine the relationship between fashion and art. The cross-fertilization between fashion and art was initiated as an imitation of form in the early twentieth century, and led to a 'new cross-disciplinary form' which exists on the boundary of fashion and art. This paper considers the relationship between fashion and art from the perspective of sharing intrinsic concepts and the creation of a new creative sphere. It analyses the characteristics of the works of fashion designers and artists whose works lie on the boundary between fashion and art.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1915-1920
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• 2004

An edge tone is the discrete tone or narrow-band sound produced by an oscillating free shear layer impinging on a rigid surface. In this paper we present a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method. We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing a conventional FDLB model, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of ${\alpha}=23^{\circ}$ . At a stand-off distance ${\omega}$ , the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and to propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips.

• Aerospace Engineering and Technology
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• v.12 no.1
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• pp.144-151
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• 2013

The KOrea Multi-Purpose SATellite-2 (KOMPSAT-2) is to provide 1.0 m Ground Sample Distance (GSD) panchromatic image and 4.0 m GSD multi-spectral image data for various applications. The KOMPSAT-2 system performs mission applications in the field of earth observations, covering land, sea, coastal zones, and Geographic Information Systems (GIS). The purpose of this document is to compute ground coordinate using satellite position, velocity and attitude data in KOMPSAT-2 and document for work-flow of location accuracy correction in KOMPSAT-2.