• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.376-379
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• 2010

Bubble rising phenomenon is widely founded in many industrial applications such as a stream generator in power plant. Many experimental and numerical researches have been already performed to predict dynamic behavior of the bubble rising process. Recently numerical approaches are getting popular since it can offer much detailed information which is almost impossible to obtain from the experiments. Rising bubble could penetrate through the top free surface which makes the problem much more complicate in addition to the phase changing effect even with latest numerical techniques. In this paper, the top free surface effect on rising bubble has been investigated. The gas-liquid interface was explicitly tracked using high-order Level Contour Reconstruction Method(LCRM) which is a hybridization of Front-Tracking and Level-Set method. Break-up behavior of rising bubble at free surface showed different characteristics with initial diameter of bubble.

• Journal of Advanced Marine Engineering and Technology
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• 제26권1호
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• pp.116-124
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• 2002

The bubble model by Keller and Prosperetti is adapted to solve the nonlinear oscillation of a gas bubble. This formulation leads to accurate results since it introduces the energy equation instead of the polytropic assumption for the bubble interior. The numerical method used in this study is stable enough to handle large amplitude of bubble oscillation. The numerical results show some interesting nonlinear phenomena fur the bubble oscillator. The excitation changes the natural frequency of the bubble and makes some harmonic resonances at $f/f_0=1/2, 1/3$ and so on. The natural frequency of a bubble oscillator decreases compared with the linear case result, which means that the nonlinear bubble oscillation system is a "softening"system. In addition, the frequency response curve jumps up or down at a certain frequency. It is also found that there exist multi-valued regions in the frequency response curve depending on the initial conditions of bubble. The dependency of the bubble motion on the initial condition can generate extremely large pressure and temperature which might be the cause of the acoustic cavitation and the sonoluminescence.inescence.

• 복식
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• 제53권2호
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• pp.71-85
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• 2003

In the turn of the century, fashion designers have not just drawn upon one or two subcultural styles but have extracted elements from many subcultures to use in a single collection. In true postmodern style these are freely combined with historical, cross-cultural and futuristic influences to create new fashions. The process could be explained by bubble-up phenomenon, retroism. pastiche and pursuit of pleasure. In the course of illustrating subcultural styles transformed into mainstream fashion, the case of Punk was studied as a turning point of modernist and postmodern period which have been introduced by high fashion designers since the birth in 1976. The following cases have continued to appear entering upon the third millennium and the aesthetic value of those can be summarized as ambiguity, eclecticism, and deconstruction. In other words. the energy and authenticity of Punk has been considered to be desirable in high fashion, however designers focus on clothing and adornment rather than ideology and lifestyle. The aesthetic property of subcultural style defeats the established notion of standardized fashion and stimulates new consciousness. which allows a room to be diversified and subdivided.

• 한국컴퓨터정보학회논문지
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• 제22권12호
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• pp.117-123
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• 2017

The personalized search algorithm is a search system that analyzes the user's IP, cookies, log data, and search history to recommend the desired information. As a result, users are isolated in the information frame recommended by the algorithm. This is called 'Filter bubble' phenomenon. Most of the personalized data can be deleted or changed by the user, but data stored in the service provider's server is difficult to access. This study suggests a way to neutralize personalization by keeping on sending random query words. This is to confuse the data accumulated in the server while performing search activities with words that are not related to the user. We have analyzed the rank change of the URL while conducting the search activity with 500 random query words once using the personalized account as the experimental group. To prove the effect, we set up a new account and set it as a control. We then searched the same set of queries with these two accounts, stored the URL data, and scored the rank variation. The URLs ranked on the upper page are weighted more than the lower-ranked URLs. At the beginning of the experiment, the difference between the scores of the two accounts was insignificant. As experiments continue, the number of random query words accumulated in the server increases and results show meaningful difference.

• 부동산연구
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• 제27권1호
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• pp.33-44
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• 2017

최근 중국은 부동산 가격이 급격히 상승하고 있으며, 인플레이션이 부동산 가격의 상승을 유발시킨다는 주장이 제기되고 있다. 따라서 본 연구에서는 2006-2014년의 중국 성별 패널 자료를 이용하여 인플레이션이 중국 부동산시장의 버블에 미치는 영향을 분석하였다. 분석방법은 정태 및 동태(static and dynamic) 패널 데이터 모델을 사용하였다. 본 연구의 분석결과, 인플레이션이 중국 부동산 버블형성의 주요 원인이며 중국 동부지역에서 그 영향이 더욱 뚜렷하게 나타남을 확인할 수 있었다. 우리는 더불어 중국부동산거품이 일정 정도 시장자체조정기제의 영향을 받았다는 흥미로운 현상을 발견했다.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.269-270
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• 2006

A finite difference lattice Boltzmann model which allows us to simulate gas-liquid two-phase flows with large density difference, for instance, 800 times for air and water is considered. Two-particle model is used and the density difference is introduced by changing the acceleration according to the fluid density. Numerical measurement of surface tension agrees well with theoretical predictions. Simulations of two-phase phenomenon for phase-transition is carried out, showing applicability of the model for two-phase flows. The two-dimensional cavitating flow around a board set up in the fluid way is also simulated. As a result, it was confirmed that the FDLB method with two-particle model was effective in numerical simulation of cavitating flow and the bubble periodically grew up at the low pressure area behind the board, in which the fluid condition was influenced by the cavitation number.

• Journal of Mechanical Science and Technology
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• 제14권5호
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• pp.562-568
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• 2000

The pressure in a water-entry induced cavity, is analyzed up to the closed cavity (bubble). Water-entry is a highly transient phenomenon, and the evolution of the water-entry cavity must be explained by considering the entry speed, shape of the solid body, atmosphere pressure, and cavity pressure as the primary variables. This work is an extension of the cavity dynamics model recently reported by Lee (l997a). To extend the model for a wide range of entry speeds the cavity pressure is calculated from a one-dimensional quasi-steady flow model. The estimation of the cavity pressure allows us to explain the experimentally observed surface closure phenomena at low entry speeds. Predictions for the time of surface closure are compared with the published experimental data.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 1995년도 춘계학술발표회 초록집
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• pp.185-198
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• 1995

This is an experimental study conducted to visualize the nucleate boiling phenomena and flow regimes occurring inside the liquid pool in a closed two-phase thermosyphon. To meet this purpose, an annular-type thermosyphon was designed and manufactured using a glass tube and a stainless steel tube, being assembled axisymmetrically. The heat to be supplied to the working fluid is generated within a very thin layer of stainless steel tube wall by applying a high frequency electromagnetic field through the induction coil, axisymmetrically set around the evaporator zone. Some important results were as follows ; 1) Considering the structural complexity of the tested thermosyphon, it showed good performance for the range of heat flux 2＜ q" ＜25kW/$m^2$ and saturation vapor pressure, 0.1＜Pv＜1.1bar 2) different type of nucleating boiling regimes were observed as described below, -Pulse boiling regime : Flow pattern changed cyclically with time during 1 cycle of pulse boiling process. The onset of Nucleation was followed by expulsive growing of vapor bubble, resulting in the so called blow-up phenomenon, massive expulsion of large amount of liquid around the bubble. -Transient : Some spherical vapor bobbles were observed growing out from 2~3 nucleating sites, that was dispersed at the lower part of the heated tube wall in the liquid pool. But the rest upper region above the nucleating sites were filled with churns or bubbles of vapor. -Continuous nucleate boiling regime : The whole zone of evaporator was filled with lots of spherical vapor bubbles, and the bubbles showed tendency to decrease in diameter as the heat flux increased.ased.

• 복식
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• 제53권3호
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• pp.13-31
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• 2003

The purpose of this study is to analyze the formative style and aesthetic value of contemporary subcultural style with the understanding of characteristics of subcultural style in the sociocultural context. As for the research methodology, literary survey has been performed to study the concept and the history of subcultural styles from 1940s to 1980s. In addition, demonstrative studies on aesthetic images have been carried out through the analysis of pictures and photographs in order to categorize the subcultural styles since 1990s. In this study, subcultural styles since 1990s have been illustrated through the socio-cultural grounds. which are diversity of street culture, diffusion of moss culture or bubble-up phenomenon, pursuit of anti-social ideology among intellectual heads, club Cultures in the form of kitsch and pastiche and communal thinking as collective harmony. With the socio-cultural context examined above, subcultural styles in the contemporary fashion are categorized and deduced following aesthetic values ; Drag and Club style as the tendency of surrealists or artificial hedonists, Urban military style and Cyberpunks as pursuit of Bionic being, Sports casual style based upon, the pursuit of comfort and freedom, Vintage style and Retro dressing represented by the spirit of DIY (no It Yourself), Ecology style of New conservatives, and Mysticism style as the fusion of technology and shamanism (Technoshamanism).

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
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• pp.81-89
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• 1999

The major source of noise in the process of transporting liquids is related to the cavitation phenomenon. The control valve noise is mostly dominated by bubble dynamics under cavitating conditions. In this investigation, an orifice configuration is set-up to correlate its flow-field and acoustic signatures with those from a control valve device. The performance and noise characteristics form the orifice configuration in anechoic surroundings were measured to reveal the noise sources depending on pressure differences across the orifice configuration. The sound powers from the orifice configuration are effectively normalized using proposed scaling parameters. Flow-excited dynamic systems for which there is no strong coupling between the flow and the system response can be described using a linear source-filter model. On this assumption, the normalized sound powers can be decomposed of noise source function and a response function. To find noise sources, pressure spectra measured over a range of pressure differences are transformed into the product of two non-dimensional frequency function : $P_{ss}(He,f_{ca},x/D) = F(f_{ca})\;G(He,x/D)$. This scheme of finding noise sources is shown to be applicable to the cavitation noise from the control valve effectively Two kinds of cavitating modes based on our experimental data are found and discussed.