• 한국터널지하공간학회 논문집
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• 제15권3호
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• pp.301-310
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• 2013

현재 도로터널에는 화재시 임계풍속을 유지할 수 있도록 제트팬을 설치하고 있으며, 제트팬 댓수는 임계풍속을 유지하기 위한 유동저항, 자연풍에 의한 환기저항, 열부력에 의한 환기저항을 고려하여 산정한다. 그러나, 국내의 경우, 제트팬 댓수 산정시 열부력은 고려하지 않고 있는 실정이다. 이에 본 연구에서는 열부력이 제트팬 댓수에 미치는 영향을 검토하기 위해서 터널연장(500, 750, 1000, 1500, 2000, 3500 m) 및 경사도(-1.0, -1.5, -2.0%)를 변수로 하여 화재성장곡선에 따른 비정상상태의 수치 시뮬레이션을 수행하였으며, 열기류의 평균온도 및 열부력에 의한 압력손실을 검토하여 열부력이 제트팬 댓수에 미치는 영향을 검토하였다. 이에 본 연구에서는 화재로 인한 열부력을 고려하는 경우에 제트팬 댓수의 증가가 필요하며, 특히, 설계화재강도를 100 MW로 하는 경우에는 본 해석조건의 모든 범위에서 열부력에 의한 압력손실이 차량저항에 의한 압력손실의 최대치보다 증가하며, 현행설계기준을 적용하는 경우보다. 최소 2~11대의 제트팬 대수의 증가가 필요한 것으로 분석되었다. 따라서 제연용 제트팬 용량 산정시 열부력에 대한 고려가 반드시 필요한 것으로 나타났다.

• 한국구조물진단유지관리공학회 논문집
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• 제8권4호
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• pp.165-174
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• 2004

본 연구에서는 고속철도 ${\bigcirc}{\bigcirc}$역사 공사구간 중 굴착구간에 인접하여 하천이 위치하고 공사구간 좌측에는 항상 만수위 상태의 저수지가 있어 지반 굴착시 지하 5m 깊이에서 지하수위가 존재하는 구간에 설치된 부력앵커의 수평재하시험에 관한 연구이다. 따라서 본 연구에서는 지하수위 면이 발생하는 구간에 설치된 부력앵커의 현장 수평재하시험을 통해 영구적으로 지하수위에 의해 부력을 받는 구조물의 장기적인 안정성을 평가하고자 한다. 이를 위해 고강도 강봉이나 강연선을 사용, 지반과의 마찰력을 이용하여 부력에 저항하는 방법으로 충분한 인발력을 확보할 수 있는 Bar Type 앵커를 사용하였다. 고속철도의 제동과 가속에 의해 수평력을 받는 지하구조물 바닥 슬래브에 부력방지용 앵커를 설치하였다. 이로 인해 Bar Type 부력앵커에 발생되는 거동특성을 파악하기 위해 수평재하시험을 실시하여 고속철도의 주, 정차시 열차의 급제동및 출발에 의해 발생되는 수평력에 대한 부력앵커의 거동특성을 파악하고자 하였다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.437-440
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• 2006

Particle suspension is frequently observed in many natural flows such as in the atmosphere and the ocean as well as in various engineering flows. Recently, airborne micro or nano-scale particles in atmosphere attract much attention from environmental society since small particle cause serious environmental problems in the industrialized areas. Also, the characteristics of such heavy particles' behavior is quite different from its fluid particles because the inertia force and buoyance force acting on the heavy particles are different than those acting on fluid particles. Therefore, our studies is to investigate the characteristics of the behavior of heavy particles considering the inertia effect with or without gravity effect, but do not consider modification of turbulence by the particles, that is one-way interaction. We carried out direct numerical simulation of isotropic turbulence with particles under the Stokes drag assumption for a spherical particle. These results can be used in the development of a stochastic model for predicting particle's behavior.

• 한국환경과학회지
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• 제10권5호
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• pp.323-327
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• 2001

A new method is developed to estimate the evaporation of water from a surface with high accuracy and resolution. The principle of new method is to detect a weight change of buoyant weight according to a change in water level of Class A Pan mesured by the use of a strain-gauge load cell. Field test of evaporation recording new instrument was carried out at Suwon for 10 days July 1999. It is possible in field observation to measure hourly evaporation amount by newly developed evaporation recording instrument in Class A Pan against strong solar radiation. Present study provide a possibility of domestic high accuracy instrument development below than 0.1mm water level measurement accuracy. If there is low humidity and high wind speed conditions which is possible to evaporate from water surface during night time. And it needs continuous study to understand between meteorological elements and latent heat effect at ground level by field observation study using high accuracy evaporation recording instrument.

• 한국농림기상학회지
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• 제4권4호
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• pp.197-202
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• 2002

A new method is used to estimate the amount of water evaporation from Class A Pan with higher precision and accuracy. The principle of method is to detect the weight change of a buoyant sinker resulting from a change in water level of Class A Pan. A strain-gauge load cell is used to measure the weight change. Field observation of evaporation was done at Pohang Meteorological Station from June 24 to August 4, 2002. By using this new method, it is possible to measure hourly evaporation accurately even under a strong solar radiation and wind disturbance, enabling a direct comparison of evaporation with other meteorological elements. At night, under low humidity and high wind speed conditions, more evaporation was recorded than during daytime. Maximum evaporation rates observed during this period exceed 1.0 mm/hour under the sunny and windy conditions with low humidity. To understand relationships between meteorological elements and latent heat flux at ground level, we suggest intensive held experiments using high accuracy evaporation recording instruments with hourly time interval.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.83-88
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• 2013

The purpose of this study is to develop the algorithm for dynamic interaction analysis of submerged floating tunnel and vehicles. The dynamic behavior characteristic of submerged floating tunnel is certainly different with general structures, because the submerged floating tunnel is floating in the middle of water, and subjected to constant buoyance. Therefore the analyses in various aspects should be carried out to secure structural stability and practicality of structures. To conduct the dynamic interaction analysis, the structure is modeled by commercial FEM program ABAQUS to investigate modal characteristic. Also the added mass concept is applied to represent the inertial force by a fluid, and then dynamic interaction analyses are conducted with superposition method when the KTX is moving along the submerged floating tunnel. And the time histories are presented for vertical and lateral displacement at the center of the tunnel.

• 대한기계학회논문집B
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• 제20권6호
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• pp.2046-2056
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• 1996

The constrained melting inside an isothermally heated horizontal cylinder has been repeatedly investigated in many studies only for the moderate Rayleigh numbers. This study extends the range of Rayleigh numbers to systematically investigate the transition during melting processes, especially focusing on the complex multi-cellular flow pattern and thermal instability. The enthalpy-porosity formulation, with appropriate source terms to account for the phase change, is employed. For low Rayleigh numbers, initially developed single-cell base flow keeps the flow stable. For moderate Rayleigh numbers, even small disturbances in balance between thermal buoyance force and viscous force result in branched flow structure. For high Rayleight numbers, Benard type convection is found to develop within a narrow gap between thee wall and the unmelted solid. The marginal Rayleigh number and the corresponding wave number are in excellent agreement with those from linear stability theory.

• 한국초등과학교육학회지:초등과학교육
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• 제19권1호
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• pp.131-143
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• 2000

The unit of a buoyant force included in the 7th national science curriculum for 6th grade students. On the contrary, it seldom that students' conception about buoyant phenomena is studied, even though there has been many studies of students' conceptions of basic science contents. The purpose of this study was to survey the elementary school students' conceptions of a buoyant force, to analyze their cognitive levels, and to explore the relationships between them. Sixth grade students (total numbers is 192) were selected .from 5 .lasses in two elementary schools in a local city of Kyungsangdo. They were asked to respond two kinds of test, which are the Logical Thinking Ability (GALT) to investigate students' cognitive levels and the Buoyant Force Questionnaire (BFQ). We developed BFQ test, based on the 7th national science curriculum for 6th grade and the previous researches of a buoyant force. We, qualitatively, analysed students' frequency of responses about a buoyant force and their types of explanation, and, quantitatively, analysed the relationships between cognitive levels and conceptions of a buoyant force with SPSS/ PC 7.0 programmes. The results of cognitive level showed that half of 6th grade students were in the concrete operational stage, 43.2% in the transitional stage, 6.8% in the formal stage. However, their sub-logical thinking abilities in a combinational, conservational, controlling variables, proportional, probability and correlational logic were very fluctuated from 91% to 8%. The results that only 4.8% of elementary students had correct conceptions of a buoyant force suggest that 6th grade students had great difficulties in understanding of that concept. Their difficulties would originated from the frequent common-sense explanations of a buoyant phenomena in terms of the weight or the unique properties or the contact area of an object or with/without air. Furthermore students' explanations, frequently, changed with context of problems of a buoyant force. Scheffe test of quantitative results that elementary students in the concrete level had 50.6% of concept formation in a buoyant force, the transitional level 54.5%, and in the formal operational level 62.8% showed significant differences of conceptions of a buoyant force with cognitive levels. Therefore the concrete operational elementary students had more difficulties of understanding of a buoyant force than the transitional and formal level, which is required to higher cognitive levels. This conclusion have implications that the unit of a buoyant force have to be presented with concrete activities for majority of students who are in concrete and transitional levels.

• 한국수소및신에너지학회논문집
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• 제23권5호
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• pp.538-544
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• 2012

The bubbles made of hydrogen and oxygen gases producted by electrolysis disturb the electrolysis, but the behavior of these bubbles in the electrolysis stack isn't clearly defined. In order to study on the behavior of bubbles in the flow pattern of the meshes type separator, the flow visualization experiment was performed by using of a visible alkaline electrolysis stack and a stereoscopic microscope. As the results, a fine size bubbles adhered to the separator's surface in the electrolyte solution have grown large sized bubbles until each bubble's buoyance is lager than the sum of surface adhesion force and weight. And then the large bubbles flow into the upper area of the separator. Also, as wide area of the separator have been occupied by various sized bubbles, the electrolysis efficiency is declined.

• 한국수소및신에너지학회논문집
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• 제24권1호
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• pp.84-90
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• 2013

The hydrogen or oxygen gas producted by electrolysis become many bubbles in the electrolyte, but exact data on the behavior of these bubbles in the separator of an electrolysis stack didn't become known. In this study, the flow visualization experiment on the behavior of bubbles in the flow pattern of the array type separator is performed by using of a visible alkaline electrolysis stack and a stereoscopic microscope. As the results, a fine size bubbles adhered to the surface of the flow pattern grow to large sized bubbles until each bubble's buoyance is lager than the sum of external force and weight. And then the large bubbles flow into the upper area of the separator. Bubbles adhered to the surface of the vertical flow pattern grow quickly than them adhered to the surface of the horizontal flow pattern. Also, he electrolysis efficiency is declined because many multi-size bubbles occupied the wide volume in the flow pattern.