• Proceedings of the Korea Water Resources Association Conference
• /
• 2019.05a
• /
• pp.282-287
• /
• 2019

본 연구의 목적은 음파를 이용하는 유속계로부터 관측된 후방산란강도와 실측된 부유사농도의 상관관계를 해석하여, 두 인자 사이의 관련 매개변수를 정량적으로 산정하고 관계식을 도출하는데 있다. 이를 위해 층별 유속계인 Aquadopp Profiler를 사용하여 사질 퇴적물 및 고령토 부유퇴적물 관측센서 검보정 챔버 실험을 수행하였다. 두 인자의 상관관계는 선형회귀분석을 통해 해석하였으며 그 결과로 도출된 접합곡선의 기울기는 각각 안목 A1 이 2.065, 안목 A2가 1.576, 고령토시료일 때 2.588의 값을 갖는데 이러한 차이는 시료 특성으로 설명될 수 있다. 서로 다른 입경을 갖는 시료는 후방산란 민감도에 차이가 있으며 이러한 영향으로 두 시료에서 산정된 계수 값에 차이가 발생한다. 본 연구를 통하여 도출된 측정 결과들은 후방산란강도에 미치는 수층 부유입자들의 영향이 매우 큼을 잘 보여준다. 일반적으로 수층 부유입자는 저면 퇴적물이 부유된 것으로 간주될 수 있으며, 또한 저면 퇴적물은 각 해역별로 site-specific 하다고 할 수 있다.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.29 no.3
• /
• pp.154-161
• /
• 2017

The purpose of this study was to investigate the change of length, opening width, and number of openings effecting on topography change around artificial reefs under erosive wave condition. Hydraulic model test was conducted to see sediment transport around the structures and the relation among the installation condition of the artificial reefs, generated velocity, wave deformation, and topographic change was reviewed. Experimental results show that the sediment transport rate was reduced; however, the scour around the structures was increased under the condition of having a single opening compared to the structures having a plurality of openings which shows inversely proportional to the size of Lr/W.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.7 no.3
• /
• pp.195-202
• /
• 1987

The flow characteristics in the shallow open channel bends are investigated, whose total angles were 30, 60, 90, 120, 150 and 180 in degree, and whose bed frictions were relatively rough(C=30) and smooth(C=60), respectively. The terms analyzed in this study are the water surface profile, the distribution of velocity and the flow direction, relating to the various total angles in the bends. The maximum depth in the bends could be found at the outside section of the location of $15^{\circ}$ local angle from the bend inlet, having no relation to the total angle and bed friction. It is supposed that the path of maximum velocities is especially influenced by the bottom friction when the total angles are bigger than 150 in degree, approximately. The ratio of the superelevation to the velocity head seems to increase as the total angle of the bends increases. The flow direction is skewed to the inner side at the bend inlet, and skewed to the outside at the bend outlet, regardless of their total angles.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2002.11a
• /
• pp.139-145
• /
• 2002

The flow zone through propeller jets are used in evaluating the environmental and constructional effects of navigation on the waterway. It relies on the characteristics of ships and water depth. A numerical model using the momentum theory of the propeller and Shield's diagram was developed in a restricted waterway. Equations for discharge are presented based on thrust coefficients and propeller speed and are the most accurate means of defining discharge. Approximate methods for discharge are developed based on applied ship's power. Equations for discharge are as a function of applied power, propeller diameter, and ship speed. Water depth of the waterway and draft of the shop are also necessary for the calculation of the grain size of the initial motion. The velocity distribution of discharge from the propeller was simulated by the Gaussian normal distribution function. The shear velocity and shear stress were from the Sternberg's formula. Case studies to show the influence of significant factors on sediment movement induced by the ship's propeller at the channel bottom are presented.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
• /
• 1992.08a
• /
• pp.106-113
• /
• 1992

쇄파대에서 파고의 감쇠 및 내부유속장에 대한 이해는 표사문제 및 해안구조물의 설계 등에 있어서 중요하다(Nadaoka and Kondoh, 1982). 특히 해빈변형의 예측문제에 있어서 가장 중요한 문제의 하나는 쇄파대 내ㆍ외에서 저면마찰력과 표사량을 정도 높게 계산하는 것이다.(중략)

• Journal of the Society of Naval Architects of Korea
• /
• v.31 no.3
• /
• pp.100-111
• /
• 1994

This study was carried out for understanding the characteristics of the spray around high speed vessels. Prismatic planing hull made of an acrylate board was used to the tests. The distribution of local spray velocity were estimated from the analysis of the spray visualization. A new test system for measuring the spray thickness is proposed, and was used to estimate the local spray thickness in the model. The pressure distributions on the bottom of the hull are measured and integrated to estimate the pressure drag of the model in the towing tests. Finally. the spray drag/lift component is separated from the total drag/lift on the prismatic hull. These test results show that the spray drag component on high speed vessels is relatively large and important in total drag.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.4 no.4
• /
• pp.208-218
• /
• 1992

Analytic solutions for the gradient of surface elevation and vertical profiles of velocity driven by the wind stress in the one-dimensional rectangular basin were obtained under the assumption of steady-state. The approach treats the bottom frictional stress $\tau$$_{b}$ as known and includes vertically varying eddy viscosity $textsc{k}$$_{M}$, which is constant, linear and quadratic of water depth. When the $\tau$$_{b}$ is param-terized with surface stress, depth averaged velocity and bottom velocity, the result shows the relation of the no-slip bottom velocity condition and the bottom frictional stress $\tau$$_{b}$. The results of a mode splitted, (x-$\sigma$) coordinate, numerical model were compared with the derived analytic solutions. The comparison was made for the case such that $textsc{k}$$_{M}$ is the constant, linear and quadratic function of water depth. In the case of constant $textsc{k}$$_{M}$, the gradient of surface elevation and vertical profiles of velocity are discussed for a uniform depth, a mild slope and a relatively steep slope. When $textsc{k}$$_{M}$ is a linear and quadratic function of water depth, the vertical structures of velocities are discussed for various $\tau$$_{b}$. The result of the comparison shows that the vertical structure of velocities depends not only on the value of $textsc{k}$$_{M}$ but also on the profile of $textsc{k}$$_{M}$ and bottom stress $\tau$$_{b}$. Model results were in a good agreement with the analytic solutions considered in this study.his study.y.his study.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.6B
• /
• pp.643-651
• /
• 2008

In the present paper, turbulent open-channel flows over longitudinal bedforms are numerically simulated. The Reynolds- averaged Navier-Stokes equations in curvilinear coordinates are solved with the non-linear $k-{\varepsilon}$ model by Speziale( 1987). First, the developed model is applied to rectangular open channel flows for purposes of model validation and parameter sensitivity studies. It is found that the parameters $C_D$ and $C_E$ are important to the intensity of secondary currents and the level of turbulent anisotropy, respectively. It is found that the non-linear $k-{\varepsilon}$ model can hardly reproduce the turbulence anisotropy near the free surface. However, the overall pattern of the secondary currents by the present model is seen to coincide with measured data. Then, numerical simulations of turbulent flows over longitudinal bedforms are performed, and the simulated results are compared with the experimental data in the literature. The simulated secondary currents clearly show upflows and downflows over the ridges and troughs, respectively. The numerical results of secondary currents, streamwise mean velocity, and turbulence structures compare favorably with the measured data. However, it is observed that the secondary currents towards the troughs were significantly weak compared with the measured data.

• Water for future
• /
• v.21 no.4
• /
• pp.399-406
• /
• 1988

Presented in this paper is a brief summary of the basic theory and observation from a laboratory investigation aimed at determining flow characteristics and ice jam topography in a sinuous channel, and in a single-bend channel. The sinuous channel comprised thirteen $90^{\circ}$ bends and was of comparatively small s\aspect ratio. The single-bend channel was a $180^{\circ}$ bend, which was an order of magnitude large in width as well as aspect ratios than the sinuous channel. The simulated ices were polyethylene and polypropylene beads and block. The streamwise velocities near the bottom were larger than that of surface in sinuous channel and forming ice jam in sinuous channel, this phenoumena were found strongly. Jams were generally thicker along the inner bank of bends. The path of maximum-streamwise velocity was displaced towards approachs side of the inner bank of bends. Radial variation of jam thickness was to be regular by increasing size of ice fragments. The rate of jam head progression around outer bank of the single bend was faster than that of inner bank and its velocity was roughly steady. With increasing Froude number, jm thickness became less uniformly distributed; being generally thicker along the inner bank and near the jam's toe. Two-layer model might be adaptable for the computing the streamwise velocity in shallow river bends. Two cells of secondary flow cound be expected in ice covered-river bends.

• 한국해양학회지
• /
• v.19 no.2
• /
• pp.141-152
• /
• 1984

In order to investigate the circulation dynamics of the Keum River estuary, 300velocity fields obtained at six sites over two tidal cycles by using instantaneous profiling technique were analyzed in detail. In this investigation, the variability of shear velocity, bottom shear stress, drag coefficient, and roughness length scale were confirmed. The measured values of the bottom boundary drag coefficient show wide range of variations, i.e., C$\_$100/=6.78${\times}$10$\^$-5/∼1.15${\times}$10$\^$-1/, and the mean of 300 measurements is 1.6${\times}$10$\^$-2/. The relationship between U* and C$\_$100/ also show the scatter in values. However, overall mean values over two tidal cycles at 6 stations show that if U* 1cm/s, C$\_$100/ is unpredictable, if U* 1cm/s, C$\_$100/ increase with U*. The values of Re$\_$100/ and C$\_$100/ have scatter. But the overall mean values over two tidal cycles show that if Re$\_$100/ 3.6${\times}$10$\^$5/, C$\_$100/ is unpredictable, if Re$\_$100/ 3.6${\times}$10$\^$5/, C$\_$100/=1.4${\times}$10$\^$-2/. Finally the flow regime of the Keum River estuary was classified as "subcritical fully turbulent" flow.