• 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.

• 대한기계학회논문집
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• 제15권2호
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• pp.488-496
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• 1991

Dynamic chanracterisitcs and control of a submerged working robot manipulator have been investigated for articulated type robot manipulator with three revoluted joints. A dynamic equation of the manipulator has been derived. The dynamic equation includes not only mass matrix, centrifugal and Coriolis terms and gravity terms but also added mass, buoyant force and drag force terms, which are important terms for underwater motion description. A series of simulations using computed torque method have been performed for the cases of straight and circular trajectory motion controls. The results of this study show that the dynamic characteristics of the submerged working robot manipulator are very different from that of the manipulator which works in air. The influences of added mass, buoyant force and drag force terms to the total required torques have been discussed as distribution ratios to the total required torques.

• 한국터널지하공간학회 논문집
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• 제17권6호
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• pp.623-635
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• 2015

지하수위 아래에 건설되는 복층터널은 비교적 대단면이며 비배수 터널로 건설되는 특징을 가지고 있다. 지하수위 하부에 위치하는 터널은 지하수로 인해 발생하는 부력으로부터 터널의 안정성 확보방안이 필요하다. 일반적으로 터널 라이닝과 지반사이의 경계면에서의 결합력은 부력에 대해 충분한 안정성을 발휘한다. 그러나 장기적인 시간이 경과하면 구조물의 열화로 인하여 결합력이 감소할 수 있다. 본 연구에서는 장기적인 관점에서 부력으로 인한 복층터널의 영향을 조사하였다. 그 결과 부력으로 인해 터널 하단부분에서 변형과 라이닝에 작용하는 응력이 증가하였다. 본 연구로부터 운영중 터널의 라이닝과 지반사이의 결합력을 유지시킬 수 있는 방안이 필요함을 알 수 있다.

• 태양에너지
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• 제9권2호
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• pp.42-50
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• 1989

The Buoyant Jets were analysed experimentally changing flow rate (0.0291/s, 0.0371/s, 0.0451/s), ratio of nozzle tip area to throat area (aspect ratio ${\beta}$=0.4, 1.0, 1.9), and also the temperature difference (${\Delta}T=Ti-T{\infty}$) between the temperature of the inflow water into the storage tank ($1m{\times}1m{\times}3m$) and the mean temperature of the water in the storage tank were changed as $25^{\circ}C,\;35^{\circ}C$ and $45^{\circ}C$. The more aspect ratio decreased, the more the trajectories of Buoyant Jets center-line were decreased and not the more the trajectories of Buoyant Jets centerline were influenced by the increment of the difference of the temperature. The more aspect ratio decreased, the more the half widths and dilution ratio of Buoyant Jets were increased and not the more the half widths and dilution ratio of Buoyant Jets were influenced by the increment of the difference of the temperature. Fr number is the factor that can predict the flow pattern over the whole flow field. And yet for the consideration the near field of Buoyant Jets flow pattern is dominated by magnitude of momentum and buoyancy force.

• 한국시뮬레이션학회논문지
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• 제21권1호
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• pp.35-43
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• 2012

본 연구에서는 수중에서 사출되는 양성부력체와 음성부력체의 수중거동을 사출시험 및 시뮬레이션을 통하여 비교하였다. 다양한 형상을 갖는 음성부력체의 동유체력 계수는 전산유체역학(CFD: Computatioanl Fluid Dynamics) 기법을 이용하여 계산하였으며, CFD에 의해 계산될 수 없는 계수는 기본형과 같은 값을 적용하였다. 종동요각의 시험 값은 시뮬레이션 값보다 훨씬 크게 나타났는데, 이는 추종공기 효과로 추정하였으며, 이 현상을 반영하여 외력 모델링을 수정함으로써 더욱 정확한 시뮬레이션이 가능하였다. 양성부력체와 음성부력체의 수중거동은 같은 사출 조건에서 다소 차이를 보이지만, 운용의 관점에서는 별다른 문제가 없는 것으로 판단하였다.

• 한국농림기상학회지
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• 제1권1호
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• pp.36-40
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• 1999

A new method was developed to measure underground water level with high reliability. The principle of new method was to detect a change of a buoyant force according to change in water level of underground water measured by the use of a straingage load cell. Field test of the instrument was carried out in Cheju Island. The results were as follows; 1) The present study provided a possibility to develop a new underground water level meter. 2) This new instrument accomplished high reliability at field test in Cheju Island. 3) There is possibility of development of water level meter which measure various range of water level to detect a weight change of a buoyant forcd.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2001년도 제22회 KOSCI SYMPOSIUM 논문집
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• pp.9-16
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• 2001

When large size nozzle with low jet velocity is used, the buoyancy effect arises from the density difference among propane, air, and burnt gas. Flame characteristics in such buoyant jets have been investigated numerically to elucidate the effect of buoyancy on lifted flames. It has been demonstrated that the cold jet has circular cone shape since upwardly injected propane jet decelerates and forms stagnation region. In contrast to the cold flow, the reacting flow with a lifted flame has no stagnation region by the buoyancy force induced from the burnt gas. To further illustrate the buoyancy effect on lifted flames, the reacting flow with buoyancy is compared with non-buoyant reacting flow. Non-buoyant flame is stabilized at much lower height than the buoyant flame. At a certain range of fuel jet velocities and fuel dilutions. an oscillating flame is demonstrated numerically showing that the height of flame base and tip vary during one cycle of oscillation. Under the same condition. non-buoyant flame exhibits only steady lifted flames. This confirms the buoyancy effect on the mechanism of lifted flame oscillation.

• 한국운동역학회지
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• 제12권2호
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• pp.393-405
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• 2002

When our body is immersed in water, we experience weightlessness. The degree of weightlessness that we experience varies depending on the proportion of the body immersed in water, being governed by the relationship between the weight of body and the buoyant force acting on the body. Human body during the performance of swimming in no exception to these influences. Swimmers body is subject to a time and position dependent force system. Even the magnitude of the buoyant force acting on the swimmers body at every given instant and the corresponding position of the CB change continuously. The findings of this study support the following conclusions. The buoyancy torque was the primary source of bodyroll exhibited by front crawl swimmers performing at distance pace, accounting for 88 % of the bodyroll. Faster swimmers used buoyancy more effectively to generate bodyroll, partially supporting the postulation that an effective use of buoyancy for bodyroll may reduce the generated hydrodynamic forces to be wasted in non-propulsive directions and maximize forward propulsion.

• 한국컴퓨터정보학회논문지
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• 제23권9호
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• pp.21-26
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• 2018

A variety of game algorithms have been proposed in recent years. Racing games using these new algorithms have greatly improved compared to those in the past. According to the analysis of racing games done by wheelgamer.com, a website that specializes in racing games, cars are the most common subject in mainstream racing games. These results show there are very few racing games using special subjects such as boats. This paper proposes a method to develop a realistic boat racing game using the Buoyont Force, beyond the limitation of typical racing games that are restricted to cars. A Material Editor based on Unreal Engine 4.12 is used to manifest the Dynamic Material of realistic ocean water. Blueprint, a visual scripting function, is used to materialize buoyancy which allows the boat to move freely along the waves.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제32회 KOSCO SYMPOSIUM 논문집
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• pp.26-31
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• 2006

Flickering behaviors of lean premixed flame of propane/air and methane/air flame anchored by a pilot flame in a tube were investigated. Unsteady behaviors of the flame were monitored by a high speed ICCD camera and the flickering frequency was defined as the number of flame curvatures passing a fixed spatial point in a second. Unlike previous studies in which flames are in open condition so that the flickering mechanism is an unstable interaction of hot buoyant products with the ambient air, flames in this study are surrounded by a tube which means they are not open to ambient air, so that there is no interaction between hot buoyant products and ambient air. Despite the fact, there exists flickering phenomena and the flickering frequency ranges from 10 Hz to 50 Hz which is wider compared to previous studies. We relate the flickering mechanism to flame-generated vorticity and analytic solution for locally approximated flow is used. As a result, the relationship between flickering wavelength and dimensionless vorticity is acquired and the cause of higher range of flickering frequency is explained.