• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.586-591
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• 2009

권 등(2008)은 수면보다 높은 정방형 다열기둥의 수리실험을 수행하여 바닥마찰과 구조물에 의한 흐름저항을 포함하고 항력상호작용계수가 적용된 Manning계수 형태의 상당저항계수 이론식을 제안하였으나 저항체의 횡방향 간격에 대해서는 충분한 연구가 수행되지 못하였다. 따라서 본 연구에서는 오리피스의 에너지 손실계수를 적용하여 횡방향 간격에 따른 항력상호작용계수식을 제안하였다. 또한 정방형 다열기둥의 다양한 횡방향 간격에 따른 흐름양상을 FLOW-3D를 이용한 수치실험을 수행하여 상당저항계수 n을 측정하였으며 수치실험 결과를 본 연구에서 제안한 횡방향 항력상호작용계수식이 적용된 이론식과 비교하였다. 이론식과 수치실험 결과는 잘 일치하였으며 이 결과로부터 본 논문에서 제안한 횡방향 항력상호작용계수식이 유효함을 확인하였다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.1
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• pp.6-10
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• 1987

The authors carried out an experiment to measure the hydrodynamic resistance of the gear and the efficiency of otter board of the midwater trawl, which is the same used in the former experiment in this series of studies. The whole resistance of the gear was measured by a 10 ton scale recording tension meter, and they were analyzed into the shearing force and the drag with relevant factors determined in the former experiments. The results obtained can be summarized as follows: 1. The whole drag of gear T(kg) and the drag of net R sub(N) (kg) can be expressed as T=2.15 v super(1.12). R sub(N)=1.96 v super(1.01) (v: towing speed in m/sec) 2. The formula of estimating the drag of net deduced by Koyama's method can be expressed as R sub(N)=4.3$\times$d/l$\times$abv 3. The shearing force and the drag of otter board is about 19 to 22% and 5 to 7% of the drag of net, respectively. Whereas, the shearing coefficient and the drag coefficient calculated by the resistance and the opening of gear are 1.5 and 0.42, respectively.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.6
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• pp.38-46
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• 2011

In order to simulate the ignition-gas injection in the interior ballistics, a two-dimensional analytic code for two-phase flows has been developed. The Eulerian-Lagrangian approach and the low-dissipation simple high-resolution upwind scheme(LSHUS) have been adopted in the numerical code for the propellant combustion of the gun propelling charges. The ghost-cell extrapolation method has been used for the moving boundary in the chamber with the projectile movement. The calculation results of the developed code have been compared and verified through those of the dimensionless IBHVG2 code and the previous one-dimensional code. In comparison with the two-phase flows according to the drag models, the numerical analysis of the muzzle velocity has been affected by the drag model.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.408-412
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• 2007

본 연구는 자갈하상하천에서 하상에 분포하는 입자에 작용하는 전단력을 이용하여 등가조도를 산정할 수 있는 모형을 개발하였다. 등가조도는 기존의 연구들처럼 경험적으로 특정입도에 의해 산정하지 않고 하상에 분포하는 각 입자에 작용하는 입자 전단력을 산정하고, 하상 평균전단력과의 관계로서 산정하였다. 입자 전단력은 항력을 통해 산정하였으며, 이때 항력계수는 입자의 돌출 높이를 고려할 수 있도록 하였다. 또한 입자에 부딪히는 평균유속은 수치적분을 통해 입자의 돌출 높이에 따라 가변성을 고려할 수 있도록 식으로 제시하였다. 단위면적당 입자 전단력과 하상 평균 전단력과의 관계를 통해 등가조도의 함수로서 식을 제시한 후 수치해석방법의 하나인 증분 탐색법을 통해 등가조도를 산정할 수 있도록 하였다. 그리고 산정된 등가조도를 이용하여 수위-유량관계 및 흐름저항매개변수를 산정하여 적정성을 검토하였다.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.435-441
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• 2006

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1998.09a
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• pp.100-105
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• 1998

해양구조물의 연직 원형파일에 작용하는 파력은 주로 항력과 관성력의 합으로 표시되는 Morison 식을 이용하여 결정하여 왔다. 그러나 Morison 식은 대칭형상을 유지하며 비교적 완만히 변화하는 파에 대해서 적용이 가능하다. 구조물 부재에 쇄파가 작용할 경우, 쇄파파력은 항력과 관성력에 추가하여 강한 충격쇄파력을 포함하게 된다. 본 연구는 임의 이차원 경사해빈에서 경계요소법을 적용하여 쇄파 내부점들의 수립자 속도 및 가속도를 계산하고, 이들을 이용하여 쇄파에 의한 쇄파파력을 계산하기 위한 모델기법을 수립한다.(중략)

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.3
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• pp.171-181
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• 2017

Two-phase cross flow exists in many shell-and-tube heat exchangers such as condensers, evaporators, and nuclear steam generators. The drag force acting on a tube bundle subjected to air/water flow is evaluated experimentally. The cylinders subjected to two-phase flow are arranged in a normal square array. The ratio of pitch to diameter is 1.35, and the diameter of the cylinder is 18 mm. The drag force along the flow direction on the tube bundles is measured to calculate the drag coefficient and the two-phase damping ratio. The two-phase damping ratios, given by the analytical model for a homogeneous two-phase flow, are compared with experimental results. The correlation factor between the frictional pressure drop and the hydraulic drag coefficient is determined from the experimental results. The factor is used to calculate the drag force analytically. It is found that with an increase in the mass flux, the drag force, and the drag coefficients are close to the results given by the homogeneous model. The result shows that the damping ratio can be calculated using the homogeneous model for bubbly flow of sufficiently large mass flux.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.2
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• pp.107-115
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• 1999

In order to develop a convenient method for the estimation of transport distance of settling stones in quiescent water or flowing water, introduced was the simple but relatively accurate equation of drag coefficient. The equation of drag coefficient introduced was confirmed to give relatively accurate evaluation for the drag force of smooth-surface sphere, and the effects of surface roughness and shape can be considered by adjusting empirical parameters. A theoretical equation has been developed for the settling velocity or settling distance of smooth-surface sphere in quiescent fluid, and the computation results have been obtained by adjusting the empirical parameter for the settling distance of stone in quiescent water. The 2nd order ordinary differential equation has been developed for the case of settling stones in flowing fluid, and a numerical model has been developed by using Runge-Kutta method for its solution. A number of cases have been tested by adjusting the empirical parameter.

• Korean Chemical Engineering Research
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• v.48 no.4
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• pp.462-469
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• 2010

Gas-liquid 2 phase processes are usually used in chemical, biochemical, environmental engineering and food process. For optimizing these processes, understanding bubble's precise movement and shape are needed. Bubble's movement and shape are effected by liquid's properties-viscosity, surface tension and bubble's properties-size, velocity. This paper deals with experimental data of bubble's movement and shape in high viscous silicone oil. Also, drag coefficient and deformation factor given by other researcher's papers and books are used to predicting and comparing bubble's terminal velocity, drag coefficient, deformation factor and shape with experimental value. Experimental data show that bubble moves faster when it moves in lower viscous silicone oil and it's drag coefficient is bigger when it moves in high viscous silicone oil. Bubble's shape is close to sphere when moving in high viscous silicone. Formulas proposed by Batchelor expect most accurate prediction for bubble's velocity and drag coefficient. Bubble's 2D shape predicted by Batchelor's energy balance, drag coefficient and deformation factor show excellent agreement with experimental bubble's 2D shape.

• The KSFM Journal of Fluid Machinery
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• v.9 no.2 s.35
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• pp.7-12
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• 2006

This study is to develop a system of electric power generation utilizing the wind resources available in the domestic wind environment. We tested drag-type vortical wind turbine models, which have two different types of blades: a flat plate and circular arc shape. Through a performance test, conditions of maximum rotational speed were found by measuring the rpm of wind turbine. The rotational speed was measured by a tachometer in a wind tunnel and the tunnel wind speed was by using a pilot-static tube and a micro manometer. The performance test for a prototype was accomplished by calculating power, power coefficient, torque coefficient from the measurement of torque and rpm by a dynamometer controller From the measurements for miniature turbine models with two different blades, the circular arc shape was found to Produce a maximum rotational speed for the same wind velocity condition. Based on this result, the prototype with the circular arc blade was made and tested. We found that it produces 500W at the wind velocity of 10.8 m/s and the power coefficient was 20%.