• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.3
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• pp.139-146
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• 2017

In order to understand the efficacy of submerged breakwater constructed for the beach protection, laboratory experiments were carried out by observing the characteristics of flow around a single shore-parallel submerged breakwater. The velocity field near the shoreline was measured by utilizing the LSPIV (Large-Scale Particle Image Velocimetry) technique, and mean surface and wave height distributions were observed around the submerged breakwater, according to various combinations of incident waves and submerged breakwaters. In this experiment, it was found that the mean flow pattern behind the submerged breakwater was determined by the balance among the gradients of mean water surface and excess wave-momentum flux (i.e., radiation stress tensors) which interact with the wave-induced current developed by the gradients on the rear and the side of the submerged breakwater. The divergent and convergent flow patterns behind the submerged breakwater (i.e., accretion and erosion response) of the numerical study of Ranasinghe et al.(2010) were observed in the measured velocity distributions, and their empirical formula mostly agreed with the experimental results. However, for some cases in this experiment, it was difficult to say that the flow pattern was one of them and was agreed with the empirical formula.

• Journal of Korea Water Resources Association
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• v.49 no.1
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• pp.51-60
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• 2016

The purpose of this study is to examine the control function of discharged flow due to the shape and plane arrangement of permeable submerged breakwater. For the discussion on it in detail, 3-dimensional numerical model based on PBM (Porous Body Model), which is able to simulate directly interaction of Fluid Permeable structure Seabed has been used to simulate water discharge in a NWT (Numerical Water Tank). To verify the applicability, LES-WASS-3D is analyzed comparing to the experimental result about propagation characteristics of dam-break wave through a permeable structure. Using the results obtained from numerical simulation, the effects of the shape and plane arrangement of submerged breakwater on reducing velocity and flow induction have been discussed related to the mean flow distribution and vertical distributions of horizontal velocities around ones.

• Journal of Korea Water Resources Association
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• v.48 no.4
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• pp.291-298
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• 2015

The aim of this study is that a theoretical formula for estimating the one-dimensional longitudinal dispersion coefficient is derived based on a transverse distribution equation for the depth averaged stream-wise velocity in open channel. In "Part I. Theoretical equation for stream-wise velocity" which is the former volume of this article, the velocity distribution equation is derived analytically based on the Shiono-Knight Model (SKM). And then incorporating the velocity distribution equation into a triple integral formula which was proposed by Fischer (1968), the one-dimensional longitudinal dispersion coefficient can be derived theoretically in "Part II. Longitudinal dispersion coefficient" which is the latter volume of this article. SKM has presented an analytical solution to the Navier-Stokes equation to describe the transverse variations, and originally been applied to straight and nearly straight compound channel. In order to use SKM in modeling non-prismatic and meandering channels, the shape of cross-section is regarded as a triangle in this study. The analytical solution for the velocity distribution is verified using Manning's equation and applied to velocity data measured at natural streams. Although the velocity equation developed in this study do not agree well with measured data case by case, the equation has a merit that the velocity distribution can be calculated only using geometric data including Manning's roughness coefficient without any measured velocity data.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.3
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• pp.1439-1443
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• 2011

A theoretical study on the ground water flow adjacent to buried pipe was conducted. Incompressible and irrotational flow were considered in analytical study. Ground water flow were defined by complex potentials. Firstly, uniform flow without buried pipe was analysed and then the effect of buried pipe was considered by superposition via circle theorem. Although two kinds of flow can be added by linearity of complex potentials, investigation of the singularities of the complex potentials should be done in advance. Finally, ground water flow past a buried pipe was analysed via complex potentials and net force exerted on the buried pipe by the ground water flowing past with circulation was derived.

• Korean Chemical Engineering Research
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• v.44 no.5
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• pp.505-512
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• 2006

Characteristics of particle holdup and heat transfer were investigated in a liquid-particle swirling fluidized bed whose diameter was 0.102 m and 2.5 m in height. Effects of liquid velocity, particle size and swirling liquid ratio($R_s$) on the particle holdup and immersed heater-to-bed overall heat transfer coefficient were examined. The particle holdup increased with increasing particle size and swirling liquid ratio but decreased with increasing liquid velocity.The local particle holdup was relatively high in the region near the heater when the $R_s$ value was 0.1~0.3, but the radial particle holdup was almost uniform when the $R_s$ value was 0.5, whereas, when the $R_s$ value was 0.7, the local particle holdup was relatively low in the region near the heater. The heat transfer characteristics between the immersed heater and the bed was well analyzed by means of phase space portraits and Kolmogorov entropy(K) of the time series of temperature difference fluctuations. The phase space portraits of temperature difference fluctuations became stable and periodic and the value of Kolmogorov entropy tended to decrease with increasing the value of $R_s$ from 0.1 to 0.5. The Kolmogorov entropy exhibited its maximum value with increasing liquid velocity. The value of overall heat transfer coefficient(h) showed its maximum value with the variation of liquid velocity, bed porosity or swirling liquid ratio, but it increased with increasing particle size. The value of K exhibited its maximum at the liquid velocity at which the h value attained its maximum. The particle holdup and overall heat transfer coefficient were well correlated in terms of dimensionless groups of operating variables.

• Journal of Korea Water Resources Association
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• v.48 no.4
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• pp.299-308
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• 2015

The aim of this study is that a theoretical formula for estimating the one-dimensional longitudinal dispersion coefficient is derived based on a transverse distribution equation for the depth averaged stream-wise velocity in open channel. In "Part I. Theoretical equation for stream-wise velocity" which is the former volume of this article, the velocity distribution equation is derived analytically based on the Shiono-Knight Method (SKM). And then incorporating the velocity distribution equation into a triple integral formula which was proposed by Fischer (1968), the one-dimensional longitudinal dispersion coefficient can be derived theoretically in "Part II. Longitudinal dispersion coefficient" which is the latter volume of this article. The proposed equations for the velocity distribution and the longitudinal dispersion coefficient are verified by using observed data set. As a result, the non-dimensional longitudinal dispersion coefficient is inversely proportional to square of the Manning's roughness coefficient and the non-dimensional transverse dispersion coefficient, and is directly proportional to square of the aspect ratio (channel width to depth).

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.326-326
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• 2017

개수로에서 비에너지(specific energy)는 수로바닥을 기준으로 단위무게의 물이 가지는 에너지로 정의되며 흐름의 위치수두와 속도수두의 합으로 표현된다. 비에너지는 수로단면의 변화에 따른 수심의 변화를 해석하기 위하여 사용되는 중요한 개념이다. 사각형 개수로에서의 비에너지 관계식은 3차방정식의 형태이며, 해석적으로 3개의 해(3개의 수심)를 가지나, 물리적인 의미를 가지는 해는 2개이며 나머지 하나의 해는 음수이므로 물리적인 의미를 가지지 않는다. 물리적인 의미를 가지는 2개의 해는 각각 흐름이 상류(subcritical flow)인 경우와 사류(supercritical flow)인 경우에 대한 수심이다. 즉, 일정한 유량이 흐르는 조건에서 동일한 비에너지를 가지는 수심이 상류와 사류에 각각 존재하는데, 이 2개의 수심을 대응수심(alternate depths)이라 정의한다. 이러한 사각형 개수로에 대한 비에너지 관계식은 3차방정식이므로 그 해석해를 구할 수 있어, 수로단면의 변화에 따른 흐름의 변화를 비교적 쉽게 해석할 수 있다. 사각형 개수로가 아닌 경우의 비에너지 관계식을 이론적으로 고찰하는 연구는 찾아보기 힘들다. 이에 본 연구에서는 포물선형 개수로에 대해서 비에너지 관계식을 유도하였다. 유도된 비에너지 관계식은 비선형 음함수의 형태로 해석적으로 해를 구할 수 없다. 유도된 관계식의 해법으로 2차의 정밀도를 가지는 Newton-Raphson방법을 이용하였으며, 계산의 초기치는 상용화된 Excel에서 쉽게 구할 수 있는 회귀식을 이용하여 구하였다. 적용 예를 통해, 단순 회귀식을 이용하는 경우에는 정해와의 상대오차가 2 - 8% 내외였는데, 본 연구에서 제안하는 방법을 사용하는 경우에는 동일한 조건에서 상대오차가 0.25% 내외를 보였다. 즉 본 연구에서 제시하고 있는 양해법을 이용하면, 포물선형 개수로 흐름의 대응수심을 용이하게 그리고 정확도가 매우 높게 산정할 수 있다.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.287-287
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• 2018

우수관거 시설에서 맨홀은 관거의 접합을 위해 반드시 설치되어야 하는 중요한 요소이다. 이러한 맨홀 접합부에서는 유입관으로 유입되는 유량의 급격한 확대와 유출관으로 배수되는 유량의 급격한 축소 등 흐름의 복잡한 변화가 발생한다. 맨홀에서의 복잡한 흐름은 설계강우를 초과하지 않는 강우량에서 과부하 조건을 형성하며 도심지 침수의 심각한 영향을 미친다. 특히 여러 관이 접합되어 있는 합류맨홀의 경우 유출관거로의 원활한 배수가 유도되지 않을 뿐 아니라 다양한 방향의 흐름이 서로 상충하며 급격한 에너지 손실을 유발한다. 도심지 중 하류부에서 주로 발생하는 침수피해는 복잡한 우수관거 시설의 구성에 따른 합류맨홀의 증가로 인해 그 규모가 늘어나는 추세이다. 바닥이 평평한 기본형태의 맨홀에서 발생되는 과부하 흐름과 여러 유량 조건에서의 에너지 손실에 관한 연구는 지속적으로 수행되어왔다. 최근 맨홀 내부에 흐름을 유도시켜주는 인버트를 설치하여 에너지 손실을 저감하려는 연구가 활발히 이루어지고 있지만 이를 실제 도시지역에 적용하여 침수해석이나 관거 배수능력 평가를 수행하기 위한 필요한 기초자료는 미비한 실정이다. 본 연구에서는 인버트가 설치된 개선형 4방향 합류맨홀의 유량 조건을 다양하게 변화시키며 유입유량 조건에 따른 개선형 맨홀의 손실계수를 분석하였다. 유량 조건은 세 개의 유입관에서 각각 설계유량 $1{\ell}/s$의 유량이 유입되는 총 유입유량 $3{\ell}/s$를 기준으로 각 유입관의 유입유량을 10%씩 변화시킨 40case의 유량 조건을 선정하였다. 이렇게 선정된 유량 조건은 경우에 따라 중간 맨홀, 3방향 합류맨홀 또는 4방향 합류맨홀의 흐름을 다양하게 나타내었으며, 40case의 손실계수를 분석하여 모든 맨홀 접합 조건에서의 손실계수를 파악할 수 있었다. 합류맨홀에서의 개선형 인버트 적용성을 확인하기 위하여 인버트가 설치된 개선형 맨홀에서 산정된 손실계수를 기초로 모든 유입유량 조건에서 적용이 가능한 손실계수 범위도를 작도하였다. 손실계수 범위도는 통계분석에 활용되어 개선형 맨홀의 유입유량 조건에 따른 손실계수 산정식을 도출하는 기초자료로 활용되었다. 이와 같이 도출된 산정식을 적용하면 실제 도심지에 개선형 맨홀을 적용하였을 경우에도 정확한 침수 해석이나 관거 배수능력 평가가 가능할 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 1983.07a
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• pp.3-21
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• 1983

• Water for future
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• v.24 no.1
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• pp.109-117
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• 1991

The governing equation of flow in porous media is developed on the bases of the continuity equation of fluid for transient flow through a saturated-unsaturated zone, and substitution of Darcy's law. The numerical solutions are obtained by finite element method based on the Galerkin principles weighted residuals. The analysis are carried out by using the unsteady storm data observed and rainfall intensities which are obtained by using the rainfall excess model in considering of the initial losses. The functional relationships between the hydraulic conductivity, capillary pressure head and volumetric water content are applied to the flow of water through unsaturated soil varied with changes of water content.