• 대한토목학회논문집
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• 제13권4호
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• pp.123-129
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• 1993

기연구 발표된 수많은 세굴 예측공식들은 여수로나 관암거 하류의 침강지내에서 발생하는 실제 세굴 깊이나 세굴 방지에 필요한 최소 침강지수심을 예측하기가 불가능할 정도로 광범위한 예측치를 나타내고 있다. 이같은 광범위한 예측 세굴 깊이는 대부분 세굴 지배인자에 대한 심도깊은 연구의 부족에 따른 인자들의 지나친 단순화에 기인하고 있다는 것을 문헌조사를 통하여 알수 있었다. 따라서 본 연구는 실험을 통하여 세굴을 지배하는 주요 지배인자들의 영향을 검토하였다. 문헌조사로부터 찾을 수 있었던 세굴 지배인자는 침강지수심, ?의 크기와 폭기정도, 하상입자의 입도분포 및 노출도 등이었으며 본 연구에서는 ?의 수리학적 특성 및 침강지 수면에서의 입사각, 침강지의 기하학적 특성, 그리고 ?의 크기 및 하상입자 크기의 영향을 중점적으로 검토하였다. 그 결과 침강지 수심과 ?의 수리학적 특성 및 기하하적 특성, 그리고 하상입자의 크기 등이 세굴을 지배하는 주요인자임을 알 수 있었다. 특히 기존 실험연구들의 광범위한 세굴 예측치는 ?의 크기와 하상입자의 크기에 대한 기하학적 상사법칙을 무시함에 기인하였음을 발견하였다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2006년도 학술발표회 논문집
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• pp.613-617
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• 2006

개별 하천에 존재하는 하상재료는 상류의 지질특성과 유수에 의한 작용력의 특성을 반영하고 있으며 유수에 의한 작용력은 하상경사와 유량규모에 지배적인 영향을 받는다. 산본 황일(山本 晃一)(1994)에 의하면 자연하천에서 동일한 경사를 가지는 하도 구간은 하상재료, 소류력, 저수로 폭, 수심 등이 대체로 동일한 값을 나타내고 있으며, 하도 특성을 지배하는 주요인자로 각 하천의 평균연최대유량, 하상재료의 대표입경, 하상경사 등을 설정하고 있다. 하상재료는 하도의 물리적, 생태적 특성을 지배하는 대표적인 인자로 의미가 있으나 국내에서는 이와 관련된 연구가 미비한 실정이다. 본 연구에서는 국내 하천의 하도 특성을 분석하는 기초연구로서 대표하천에 대한 하상재료를 채취하여 분석하였으며 이를 분급도와 하상경사와의 관계로 도시하여 하상재료 분포 특성을 분석하였으며 이를 일본 하천의 하상재료 특성과 비교하였다. 분석결과에 의하면 분급도, 무차원 소류력, 하상경사와의 관계 분석을 통해서 자갈과 모래하천은 그 특성이 뚜렷이 구분됨을 확인할 수 있었으며, 하상경사와 대표입경의 관계도 모래와 자갈을 구분하여 접근하여야 함을 확인하였다.

• 한국해양공학회지
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• 제10권3호
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• pp.117-124
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• 1996

A fluidized bed combustion chamber is widely used to incinerate waste material. The most important factor designing the incinerator is the flow characteristics in a fluidized bed, because combustion efficiency is influenced by the flow characteristics. This paper has invesitigated the flow characteristics of bubbles in fluidized bed by means of meassuring a pressure fluctuation in the fluidized bed. A pressure probe system has used to measure the pressure. The data concerned with bubble rising velocity, bubble size, distribution of bubbles and frequency of bubble generation or decay are obtained to find the flow characteristics of bubbles in the fluidized bed. The result obtained from this experimental study can be used to design the fuel feeding system of fluidized bed combustion type incinerator. And it is possible to predict the mixing of waste material and fluidizing material.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2006년도 학술발표회 논문집
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• pp.1576-1580
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• 2006

The destruction of river and damage caused by flood are suddenly increasing due to the abnormal climate. In the investigation result about the damage, approximate 52% of the destruction of embankment are caused by earth work. Moreover, to recover conveyance of relief channel, bed sediment is dredged about 198 millions $m^3$ with 'the project of bed dredging'. So, the concern for bed sediment is the more increasing, the requiring high quality material for banking and the way for application of bed sediment are also the more increasing. In this paper, properties of bed sediment were analyzed through sedimentary mechanism analysis. Moreover, possibility to build embankment with bed sediment in 6 points which is in catchment of the Nak-dong river was also analyzed. At 6 points, which were selected to survey easily, sediment discharge was analyzed with formula. Moreover, size and permeability were analyzed and the feasibility for material of embankment was proposed. If bed sediment wasn't proper, complementary measures were proposed.

• 한국토양비료학회지
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• 제47권1호
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• pp.66-70
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• 2014

Bed-soils can be used to help plants to overcome unfavorable conditions of soils, especially hydraulic properties of soils. This study was conducted to evaluate the effect of organic and inorganic raw materials on saturated hydraulic conductivity ($K_s$) of bed-soils. Perlite and bottom ash, which are inorganic materials, increased more $K_s$ of bed-soils than coco peat, an organic material. However, vermiculite, an inorganic material, increased less than coco peat. Saturated hydraulic conductivity of bed-soil mixed with fine vermiculite ($0.14{\pm}0.02mh^{-1}$) was much lower than one containing coarse vermiculite ($0.85{\pm}0.21mh^{-1}$). Such effect was more apparent when pressure was added on bed-soils containing fine vermiculite ($0.07{\pm}0.01mh^{-1}$), probably reflecting the decrease in pore size with the expansion of vermiculite wetted. Compacting decreased more $K_s$ in the bed-soils containing coco peat or vermiculite than other mixtures. Those results suggest that perlite and bottom ash in bed-soils play an important role in improving saturated hydraulic conductivity but vermiculite in bed-soils may suppress the improvement of saturated hydraulic conductivity with the decrease of its size and with the increase of compacting pressure.

• 대한기계학회논문집
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• 제19권9호
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• pp.2365-2372
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• 1995

The objective of this study is to get the basic data for the development of fluidized bed combustor. For this purpose, various rake angles(.theta.=20.deg., 25.deg., 30.deg., 35.deg.) of finned tubes and a smooth tube were installed horizontally in the fluidized bed combustor of 410*250mm. The effect of fluidized bed temperature, superficial velocity in bed, size of bed materials, rake angle of finned tubes on the heat transfer coefficient was experimentally investigated. The following results were obtained. (1) Under the fluidized bed temperature(750.deg. C-900.deg. C), and the gas velocity in bed(1.1-2.8m/sec), The highest heat transfer coefficient was measured with the rake angle of finned tubes was .theta.=25.deg. and .theta.=35.deg. for the average fluidized material particle size of 1.22mm and 1.54mm, respectively. Generally, the heat transfer coefficient of finned tubes is 1.4 to 2.4 times larger than that of smooth tubes. (2) The size of bed materials influences the rake angle of finned tubes which can have the highest heat transfer coefficient. As the temperature in bed gets higher, the effect of the rake angle of finned tubes on the heat transfer coefficient becomes greater.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2004년도 학술발표회
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• pp.429-433
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• 2004

According to researchers, the influential factors of scouring are generally divided into three factors: the flow conditions, the type and position of structures, and the characteristics of bed materials. In addition, scouring is affected by the 3-dimensional turbulent boundaries, the unsteady flow, the movement of sediment in the scour-hole area, the approach flow velocity and depth, the width of bridge foundation/pier, and the particle size of bed materials. However, it is difficult to estimate the scour depth near bridge piers when all conditions are factored in at once. Therefore, for reasonably accurate estimates of scour depth, it is essential to consider sufficiently the flow force and resisting force for scour. That is, to determine the shear stress concerning the bed material distribution is needed. In this study, the experiments were performed under the condition of a steady state of flow. As a result, scouring occurred at velocity ratios of 0.476,$(V/V_c=0.476)$, and the scour depth was increased linearly as the velocity ratio increased. in addition, the average values of shear stress ratio at zero scouring depth in both rectangular and circular piers were approximately 7$(\tau_c/\tau_{approach})$ and in the case for same size bed particle material. The results of this study can be used for the fundamental material for estimating the scour depth of bed materials.

• Journal of the Korean Wood Science and Technology
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• 제34권2호
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• pp.30-36
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• 2006

Wood fuel must be dried before combustion to minimize the energy loss. Sawdust of Japanese red pine was dried in a batch type fluidized-bed to investigate the drying characteristics of sawdust as a raw material for bio-fuel. The minimum fluidization air velocity was increased as particle size was increased. It took about 21 minutes and 8 minutes to dry 0.08 m-deep bed of particles with average particle size of 1.3 mm from 100% to 10% moisture content at air temperature of $20^{\circ}C$ and $50^{\circ}C$, respectively.

• 한국연소학회지
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• 제1권1호
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• pp.19-29
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• 1996

This study is to investigate the characteristics of heat transfer of a horizontal tube, with radial fins of various configuration, immersed in a high temperature fluidized bed. The experimental heat transfer variation is compared with that of a smooth tube. The finned tubes and smooth tube, with outside and inside diameter of 48.6mm and 30.6mm, are made of steel tubes. The depth of the fin is 5mm, the rake angles of fin are $25^{\circ},\;35^{\circ},\;45^{\circ}$ and the widthes of fin for each rake angle are 0mm, 1mm, 2mm and 3mm. A bed temperature is fixed at $880\;{\pm}\;10^{\circ}C$. A granular refractory(silica sand) is used as a bed material with mean particle diameters of 1.22mm and 1.54mm. The maximum heat transfer coefficient is achieved with the rake angle of $25^{\circ}$ and the width of 0mm for the mean particle size 1.22mm. The coefficient is 2.14 times larger than that for a smooth tube. The rake angle for the maximum heat transfer coefficient depends on the particle size of bed material. Also the transfer coefficient decreases as the width of fin increases.

• 한국수자원학회논문집
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• 제37권5호
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• pp.387-395
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• 2004

본 논문에서는 하상변동 및 유사입자의 시간적 공간적 분포를 동시에 모의할 수 있는 2차원 수치모형을 제시하였다. 사행수로의 하상변동은 만곡부의 외측에서는 하상이 세굴되고 훨씬 더 거친 입경의 재료로 구성되며, 만곡부의 내측에서는 하상이 상승하고, 세립토로 구성되었다. 또한 사행하천에서 흐름의 방향에 대한 입자분포 과정은 상류의 변곡점에서 시작하여, 하류 변곡점에서 마치게 되는 것을 보여주었다. 하천의 경계가 불규칙하고 복잡한 하천에서는 혼합사호 형성된 하천에서보다 균일사로 이루어진 하천에서 하상이 깊게 세굴되는 현상을 보여준다. 혼합사로 이루어진 하천에서의 공간적 입도 분포는 사행하천에서와 마찬가지로 하상이 퇴적되는 사행의 내측에서는 세립토로 구성되고 하상이 세굴되는 외측에서는 굵은 입자로 구성되는 것을 보여주었으며, 하천 폭이 좁은 부분에서는 하상의 세출 및 하상재료가 굵게 변화되는 것을 보여주었다.