• 한국수자원학회논문집
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• 제31권3호
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• pp.291-301
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• 1998

본 연구에서는 치수 및 이수에 있어서 항상 어려움을 겪고 있는 개수로 만곡구간에서 하상재료의 변화에 따른 흐름 및 하상변동 특성을 분석하기 위하여 중심각 180'인 만곡수로를 제작하고, 모래(D50 = 0.26 MM, S = 1.54)와 안트라싸이트(D50 = 0.26 mm, S = 1.54)를 하상재료로 선택하여 실험을 실시하였다. 실험결과, 최대세굴심은 만곡각 30'-60' 외측제방부근에서 평균수심의 약 2배까지 실측되었으며, 최대세굴심의 발생위치는 안트라싸이트인 경우에 모래에서보다 5'-15' 정도 상류부에서 관측되었다. 종단면 최대유속선은 하상재료와 관계없이 내측에서 외측으로 편의되고 있으며, 하상이 거칠수록 하류로 이동하였다. 하상이 매끄러울수록 흐름의 최대 편의각은 만곡수로 상류부에서 발생하고 있으며, 그 크기도 증가하였다. 안트라싸이트의 경우가 모래의 경우보다 2차흐름이 크게 발생하는 것으로 실측되었으며, 두개의 핵이 존재하는 현상이 관측되었다.

• Ecology and Resilient Infrastructure
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• 제6권4호
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• pp.243-249
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• 2019

본 연구는 드론 기반의 초분광 센서를 활용하여 수위변화에 대한 하상재료의 분광정보 차이를 분석하는 것이 목적이다. 하상재료는 흙, 자갈, 호박돌, 갈대, 식생을 대상으로 하였으며 5개 하상재료에 대한 초분광 영상촬영을 실시하고 각 재료의 분광정보를 비교 분석하였다. 수위 변화를 위해 유량조절이 가능한 실험수로를 제작하고 수로 내 하상재료를 설치하였다. 수위 조건은 0.0 m, 0.3 m, 0.6 m이며 수위에 따라 CASE를 구분하였다. 영상촬영 후 각 하상재료별 10개 포인트를 평균한 값을 분석 자료로 사용하였다. 분석 결과 흙, 자갈, 호박돌, 갈대의 파장별 반사율은 비슷한 유형을 보이지만 각 재료별 가시광선과 근적외선 영역에서는 분광정보의 고유특징이 나타났다. 또한 수위가 깊어질수록 가시광선과 근적외선 영역에서 반사율은 감소하고 있으며 감소 비율은 하상재료에 따라 차이가 발생하였다. 하상재료에 대한 고유정보는 향후 하천환경평가를 위한 기초연구 자료로 활용될 것으로 기대된다.

• 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.

• 한국지반공학회논문집
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• 제24권10호
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• pp.113-120
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• 2008

하천제방 축조를 위한 많은 양질의 성토재료는 시공헌장에서 쉽게 구하기 어려우며, 하천제방의 경제성 및 안정성에 있어서 가장 중요한 요인이라 할 수 있다. 따라서 경제적이고 안정적인 하천제방을 축조하기 위해서는 하상재료를 이용한 제방축조기술의 연구가 필수적이며 이를 위해서는 하상재료에 대하여 현장시험을 통한 설계 및 시공방법, 공학적 특성 분석이 요구되어진다. 본 연구에서는 대구 현풍천의 하상토(SP)를 대상으로 원재료 및 양질토인 화강풍화토(SW)와의 혼합에 따른 현장 다짐에 따른 공학적 특성을 평가하고 현장 혼합방법을 제시하였다.

• 한국세라믹학회지
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• 제56권2호
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• pp.153-159
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• 2019

In this study, fly ash of a fluidized bed boiler produced in a power plant was stabilized by hydration and carbonation reaction. Then, each raw material was pulverized by two kinds of grinding equipment (Planetary mills and pot mills); the degree of grinding and the agglomeration behavior were observed. It was found that there were changes of specific surface area and particle size distribution according to grinding time. The surface of the raw material was observed using an optical microscope. As a result, agglomerates of about 75 ㎛ or more due to electrostatic phenomenon were formed as the grinding time became longer; it was confirmed that the crushing efficiency slightly increased with use of antistatic agent.

• 한국정밀공학회지
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• 제11권1호
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• pp.89-96
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• 1994

This study is to develop a new composite material, a mixture of epoxy resin and granite aggergates which is called Expoxy-Granite, to overcome the inherent disadvantages of conventional materials commonly used as a bed structure material of long-term dimensional/ thermal stability. Under the various manufacturing conditions which could be formulated through experimental investigation, we have constructed 6 kinds of Epoxy-Granite structure models having one fifth the size of the ultra-precision machine tool bed structure. They are compared with cast iron and pure granite models through the dynamic test and the thermal deformation test. Both in the steel ball dropping test and in the forced vibration test, three types of epoxy-granite models made in this study have shown much better dynamic characteristics than the cast iron model and almost the same characteristics as compared with the pure granite model. In the thermal deformation test the above composite materials have also represented lower thermal displacements in the vertical direction of each model as compared with other specimens. It is therefore seen that the epoxy-granite complsite material can be applied to the construction of high-precision machine tool bed, instead of cast iron or pure granite.

• Tribology and Lubricants
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• 제33권5호
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• pp.214-219
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• 2017

Abrasive fluidized bed machining (AFBM) is similar to general abrasive fluidized machining (AFM) in that it can perform polishing of the outer and inner surfaces of a 3-dimensional shape by the flow of particles. However, in the case of AFM, the shear force generated by the flow of the particles causes material removal, while in AFBM, the abrasive particles are suspended in the chamber to form a bed. AFBM can be used for deburring, polishing, edge contouring, shot peening, and cleaning of mechanical parts. Most studies on AFBM are limited to metals, and research on application of AFBM to plastic materials has not been performed yet. Therefore, in this study, we investigate the effect of rotating speed of the specimen and the air flow rate on the material removal characteristics during AFBM of polyacetal with a horizontal AFBM machine. The material removal rate (MRR) increases linearly with increase of the rotating speed of the main shaft because of the shear force between the particles of the fluidized bed and the rotation of the workpiece. The reduction in surface roughness tends to increase as the rotating speed of the main shaft increases. As the air flow rate increases, the MRR tends to decrease. At a flow rate of 70 L/min or more, the MRR remains almost constant. The reduction of the surface roughness of the specimen is found to decrease with increasing air flow rate.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2002년도 제24회 KOSCO SYMPOSIUM 논문집
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• pp.171-178
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• 2002

Numerical simulations of the condition in the iron ore sintering bed are performed for various parameters. The sintering bed is modelled as an unsteady one-dimensional progress of solid material, containing cokes and iron ore. Bed temperature, solid mass and gas species distributions are predicted for various parameters of moisture contents, cokes contents and air suction rates, along with the various particle diameters of the solid for sensitivity analysis. Calculation results show that influences of these parameters on the bed condition should be carefully evaluated for achievement of the self-sustaining combustion without the high temperature section, which can cause the excessive melting in the bed. It suggests that the model should be extended to consider the bed structural change and multiple solid phase, which can treat the inerts and fuel particles separately.

• 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.

• 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.