• 한국가시화정보학회지
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• 제13권3호
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• pp.20-23
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• 2015

In this experiment, a heterogeneous droplet consisted of de-ionized water and olive oil was made through two 31G injection needles. The injection flow rate was $50{\mu}{\ell}/min$ and the droplet size was 2 mm. The droplet was impinged onto a sapphire plate which was heated up to $300^{\circ}C$ by a heater. Two high speed cameras were used for visualization, and the frame rate was 20,000 fps. A 150W metal halite lamp was used for illumination. The dropping height was fixed to 20 mm and the corresponding Weber number was 10.6 based on water. Due to different boiling points of two liquids, partial boiling features of heterogeneous droplet was observed. At the Leidenfrost condition, micro explosion phenomenon has occurred.

• Steel and Composite Structures
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• 제12권3호
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• pp.207-230
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• 2012

Nowadays CFRP (Carbon Fiber Reinforced Polymer) became widely used materials for the strengthening and retrofitting of structures. Many experimental and analytical studies are encountered at literature about strengthening beams by using this kind of materials against static loads and cyclic loads such as earthquake or wind loading for investigating their behavior. But authors did not found any study about strengthening of RC beams by using CFRP against low velocity impact and investigating their behavior. For these reasons an experimental study is conducted on totally ten strengthened RC beams. Impact loading is applied on to specimens by using an impact loading system that is designed by authors. Investigated parameters were concrete compression strength and drop height. Two different sets of specimens with different concrete compression strength tested under the impact loading that are applied by dropping constant weight hammer from five different heights. The acceleration arises from the impact loading is measured against time. The change of velocity, displacement and energy are calculated for all specimens. The failure modes of the specimens with normal and high concrete compression strength are observed under the loading of constant weight impact hammer that are dropped from different heights. Impact behaviors of beams are positively affected from the strengthening with CFRP. Measured accelerations, the number of drops up to failure and dissipated energy are increased. Finite element analysis that are made by using ABAQUS software is used for the simulation of experiments, and model gave compatible results with experiments.

• 대한토목학회논문집
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• 제34권3호
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• pp.895-906
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• 2014

대수심 부유 구조물의 하부기초 기술 중 하나인 dynamically penetration anchor (DPA 또는 흔히 torpedo anchor로 칭함)의 거동특성을 시험결과 및 수치 해석적 접근을 통해 분석하였다. 기존의 유한요소 해석기법으로는 이러한 대수심 anchor 구조물의 거동 특성을 적절히 모사하기 어렵기 때문에 본 연구에서는 이러한 부분을 해결하기 위해 Coupled Eulerian-Lagrangian (CEL) 법을 통해 지반-구조물 사이에서 발생하는 메쉬(mesh)의 distortion 현상 및 경계조건 등의 문제점을 대변형의 관점에서 해결하고자 하였다. 실측치와의 비교를 통해, CEL 기법의 타당성을 검증하였고, 그 결과 본 연구에서 적용한 CEL 기법이 기존 유한요소 기술로는 구현이 불가능한 대수심 anchoring system의 자유낙하에 의한 전반적인 거동 및 지반의 변형특성을 적절히 예측함을 알 수 있었다. 또한 검증된 기법을 바탕으로 dynamic anchor의 거동에 영향을 주는 여러 요소들에 대한 매개변수 연구를 추가로 수행하였다.

• 셀메드
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• 제1권1호
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• pp.4.1-4.4
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• 2011

Excessive stress is harmful to academic performance in children and may lead to dropping out of school. To meet the demands of a modern life-style which is full of speed, stress and tension, an all-round child health program is crucial. The use of yoga for children has diverse applications in maintaining and developing their physical, mental, intellectual, emotional and spiritual levels. Yoga, through its physical postures (asana), breathing practices (pranayama), cleansing techniques (kriya), meditation therapies (dhyana) and relaxation training (yoga nidra) yields a positive effect in the management of stress in children. Yoga practice benefited children by improving their eye-hand coordination, attention span, levels of concentration, competitive performance and relaxation. Visually impaired children showed a significant decrease in their abnormal anxiety levels when they practiced yoga for three weeks, while a program of physical activity had no such effect. Socially disadvantaged children in a remand home showed significant improvements in sleep, appetite and general well being, as well as a decrease in physiological arousal after yoga. In one study, it is found that a 4-week program of asana and meditation lowers the aggressive behavior of children. Meditation helped to reduce problems related to maladaptive behavior, increase emotional and physical health and psychological well-being in children. Finally, the possible role of yoga in improving the mental state and general well-being of children with cancer is being explored.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.722-729
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• 2004

The horizontal movement of sloping ground due to flow liquefaction has caused many pile foundations to fail, especially those in ports and harbor structures. In this study, a virtual case is assumed in which flow liquefaction is induced by earthquake loads in a fully saturated infinite sand slope with a single pile installation. Under the assumption that the movement of liquefied ground is viscous fluid flow, the influence of ground movement due to flow liquefaction on the pile behavior was analyzed. Since the liquefied soil is assumed as a viscous fluid, its viscosity must be evaluated, and the viscosity was estimated by the dropping ball method ,md the pulling bar method. Finally, the influence of the flow of liquefied soil on a single pile installed in an infinite slope was analyzed by a numerical method.

• Nuclear Engineering and Technology
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• 제33권1호
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• pp.93-101
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• 2001

The spacer grid is one of the main structural components in the fuel assembly, which supports the fuel rods, guides cooling water, and protects the system from an external impact load, such as earthquakes. Therefore, the mechanical and structural properties of the spacer grids must be extensively examined while designing them. In this paper, a numerical method for predicting the buckling strength of spacer grids is presented. Numerical analyses on the buckling behavior of the spacer grids are performed for a various array of sizes of the grids considering that the spacer grid is an assembled structure with thin-walled plates and imposing proper boundary conditions by nonlinear dynamic finite element method using ABAQUS/Explicit. Buckling tests on several numbers of specimens of the spacer grid were also carried out in order to compare the results between the test and the simulation result. The drop test is accomplished by dropping a carriage on the specimen at a pre-determined position. From this test, the specimens are buckled only at the uppermost and the lowermost layer among the multi-cells, which is similar to the local buckling at the weakest point of the grid structure. The simulated results also similarly predicted the local buckling phenomena and were found to give good correspondence with the experimental values for the thin-walled grid structures.

• Journal of Electrochemical Science and Technology
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• 제4권1호
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• pp.1-18
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• 2013

Gallium is an important element in the production of a variety of compound semiconductors for optoelectronic devices. Gallium has a low melting point and is easily oxidized to give oxides of different compositions that depend on the conditions of solutions containing Ga. Gallium electrode reaction is highly irreversible in acidic media at the dropping mercury electrode. The passive film on a gallium surface is formed during anodic oxidation of gallium metal in alkaline media. Besides, some results in published reports have not been consistent and reproducible. An increase in the demand of intermetallic compounds and semiconductors containing gallium gives rise to studies on electrosynthesis of them and an increase of gallium concentration in the environment with various application of gallium causes the development of electroanalysis tools of Ga. It is required to understand the electrochemistry of Ga and to predict the electrochemical behavior of Ga to meet these needs. Any review papers related to the electrochemistry of gallium have not been published since 1978, when the review on the subject was published by Popova et al. In this study, the redox behavior, anodic oxidation, and electrodeposition of gallium, and trace determination of gallium by stripping voltammetries will be reviewed.

• 한국콘텐츠학회논문지
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• 제6권6호
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• pp.9-15
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• 2006

무선 통신 시스템에서는 무선 채널의 속성상 채널 고장과 복구를 고려한 성능분석을 수행해야 한다. 본 논문에서는 고정 혼합 모델과 근사 모델 기법에 대하여 논의하고 이들에 대한 SRN 모델을 개발한다. 고정 혼합 모델은 채널 고장 및 복구와 채널 할당 및 서비스를 혼합한 모델로 상태 크기의 문제점이 발생할 수 있어 이를 해결할 수 있는 계층 모델을 개발한다. 계층 모델은 고장과 복구를 고려한 가용도를 상위 모델로 채널 할당 및 서비스를 하위레벨로 갖는 근사 모델이다. 하위모델은 핸드오프 호를 위한 가드채널과 음성 호의 선점 핸드오프 방식을 모델링한다. 성능지표인 신규 호 차단 확률과 핸드오프 호 분실 확률의 수치결과가 주어진다.

• 한국재료학회지
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• 제29권10호
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• pp.592-602
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• 2019

Feasibility is investigated for reduction of chromium ore by Si sludge with mixed silicothermic and carbothermic reaction. The reduction behavior of chromium ore using Si sludge is investigated precisely to determine the effects of carbon addition, reaction time, and reaction temperature. The pellets are dropped into the furnace after temperature stabilized. As the amount of C addition increases, the amounts of CO and $CO_2$ gas generation increase. After the dropping of the pellets, the pellets are heated and the reaction starts at about 1,573 K or higher. The pellets maintain their shape until 10 min after the drop, and then melted. As the holding time increased, the size of the reduced metal particles increased. The chromium ore is rapidly reduced by the Si sludge, and the slag penetrated into the chromium ore and reduction progressed inside. As the reduction temperature increased, the reaction initiation time is shortened and the reaction fraction of the reduction reaction increased. As the reaction temperature increased, agglomeration of reduced ferrochrome metal is promoted.

• Geomechanics and Engineering
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• 제30권4호
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• pp.363-372
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• 2022

One of the most frequent issues in tunnel excavation is the collapse of rock blocks and the dropping of rock fragments from the tunnel face. The tunnel face can be reinforced using a number of techniques. One of the most popular and affordable solutions is the use of face longitudinal dowels, which has benefits including high strength, flexibility, and ease of cutting. In order to examine the reinforced face, this work shows the longitudinal deformation profile and ground response curve for a tunnel face. This approach is based on assumptions made during the analysis phase of problem solving. By knowing the tunnel face response and dowel behavior, the interaction of two elements can be solved. The rock element equation derived from the rock bolt method is combined with the dowel differential equation to solve the reinforced ground response curve (GRC). With a straightforward and accurate analytical equation, the new differential equation produces the reinforced displacement of the tunnel face at each stage of excavation. With simple equations and a less involved computational process, this approach offers quick and accurate solutions. The FLAC3D simulation has been compared with the suggested analytical approach. A logical error is apparent from the discrepancies between the two solutions. Each component of the equation's effect has also been described.