• Water for future
• /
• v.29 no.2
• /
• pp.209-219
• /
• 1996

The existing gate operation rule of Paldang hydroelectric plant has been used since the construction of the dam in 1973 except partial modification due to the construction of Chungju multipurpose dam in 1985. The water level near the downstream of Paldang dam has been lowered about 3 m because of the channel maintenance of Han River development project. Thus, the discharge estimation formula based on the submerged orifice type spillway has to be re-evaluated by considering various patterns of the gate operation rules and lowered channel bed. In this study, three types of gate openings were tested to select the proper gate operation rules through the hydraulic model test for various discharges and opening heights. Also, the numerical analysis has been performed to simulate the flow patterns of downstream. As a result, the gate operation rule, which opens 5 gates each time from the left side, was selected as the proper gate operation rule of Paldang dam.

• Water for future
• /
• v.27 no.1
• /
• pp.123-131
• /
• 1994

A plunge pool is often employed as an energy-dissipating device at the end of a spillway or a pipe culvert. A jet from spillways or pipes frequently generates a scour hole which threatens the stability of the hydraulic structure. Existing scour prediction formulas of plunge pool of spillways or pipe culverts give a wide range of scour depths, and it is, therefore, difficult to accurately predict those scour depths. In this study, a new experimental method and new scour prediction formulas under submerged circular jet for large bed materials with shallow tailwater depths were developed. A major variale, which was not used in previous scour prediction equations, was the ratio of jet size to bed material size. In this study, jet momentum acting on a bed particle and jet diffustion theory were employed to derive scour prediction formulas. Four theoretical formulas were suggested for the two regions of jet diffusion, i.e., the region of flow establishment and the region of established flow. The semi-theoretically developed scour prediction formulas showed close agreement with laboratory experiments performed on a movable bed made of large spherical particles.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2004.05b
• /
• pp.1445-1449
• /
• 2004

Even though there can be a relative long-term or short-term change of their size in natural beaches due to various changes of sea condition such as the location, weather condition (wind and rain) and sea water flow, the budget of deposits in a specific area is generally regarded to be in a condition of equilibrium in terms of technology. However, as coasts are developed by many different kinds of ways (such as construction of sea walls and estuarine, dredging for gathering the aggregate and shore protection construction for establishing a structure) and sources of silt and gravel from rivers are decreased in balanced beaches, the beaches are in a serious danger of lack of sand and sand sources which are one of the maul elements to consist of them. Many swimming beaches in East Sea are directly exposed by waves generated and transmitted from outer seas. On the other hand, the Song-Do sandy beach which is this study's target area has a great condition for beach development because it locates the deepest place that is relatively shallow in Young-Il Man and there is big energy decrease given to waves from outer seas while the waves are reaching the Song-Do beach. Nevertheless, it is considered that artificial condition changes such as dredging for site extension by POSCO, getting straight of Hyoung-San Gang river flow and extension of Po-Hang harbor caused the sand loss of the beach. Therefore, some recovery plans of Song-Do sandy beach will be presented in this study and they will be compared and examined each other by numerical modeling experiment. After that, the best plan will be recommended.

• Ecology and Resilient Infrastructure
• /
• v.2 no.1
• /
• pp.42-53
• /
• 2015

In order to assess the hydraulic effects of flow pattern changes and geomorphological evolution around spur dikes, this study carried out monitoring and numerical simulation on the changes of morphologic characteristics around spur dikes that settled in the bend of the Yeongcheon River. The study site spanned 190 m, and spur dikes were installed in March 2008. Monitoring of the site started in May 2008 and was completed in April 2014. When the water level was higher than the height of the spur dikes, the spur dikes extrude flow from the bank. Therefore, the spur dikes that were built to stabilize the channel have been effectively performing hydraulic functions. With the passing of time, the channel was stabilized and pools formed around the spur dike toes by local scouring. It was confirmed that spur dikes created various physical characteristics in the aspect of channel topography, with sediments deposits occurring between the spur dikes, while riffles and pools formed in the channel.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.9 no.5
• /
• pp.484-491
• /
• 2017

Recent research has shown that quadrupole noise has a significant influence on the overall characteristics of flow-induced noise and on the performance of underwater appendages such as sonar domes. However, advanced research generally uses the Ffowcs Williams-Hawkings analogy without considering the quadrupole source to reduce computational cost. In this study, flow-induced noise is predicted by using an LES turbulence model and a developed formulation, called the formulation Q1As method to properly take into account the quadrupole source. The noise around a circular cylinder in an underwater environment is examined for two cases with different velocities. The results from the method are compared to those obtained from the experiments and the permeable FW-H method. The results are in good agreement with the experimental data, with a difference of less than 1 dB, which indicates that the formulation Q1As method is suitable for use in predicting quadrupole noise around underwater appendages.

• Journal of the Society of Naval Architects of Korea
• /
• v.29 no.3
• /
• pp.21-32
• /
• 1992

Numerical solutions are presented for solving the free surface flow created by a three-dimensional body moving beneath the free surface with constant velocity at an angle of attack. The solution is obtained using a panel method based on the perturbation potential, which employs Havelock sources and normal dipoles distributed on the body surface and Havelock normal dipoles in the wake downstream of the trailing edge. A pressure Kutta condition with an iterative solution procedure is implemented to satisfy equal pressure condition on the upper and lower surfaces at the trailing edge. Numerical calculation examples in the present paper include an ellipsoid at zero angle of attack, a rectangular planform wing at a small angle of attack in the limit of zero Froude number and then free surface flows and hydrodynamic forces acting on the submerged spheroid and parabolic strut are calculated. Discussions are made about the validity of the present method.

• Journal of Navigation and Port Research
• /
• v.34 no.5
• /
• pp.325-330
• /
• 2010

An open water rudder test was carried out to figure out the flow characteristics around a twin rudder at $Re=1.5{\times}10^4$. In the analysis, the unique characteristics of a twin rudder, which affects rudder forces, were explained. The analysis includes varying angles of attack from 10 to 30 degrees. In this paper, the measured results have been compared with each other to predict the performance characteristics of a twin rudder's 2-dimensional section by 2-frame grey level cross correlation PIV method. The length L=0.75C between upper and lower rudders could be defined as the critical length.

• Journal of Korean Society of Water and Wastewater
• /
• v.33 no.4
• /
• pp.243-250
• /
• 2019

This objective of this study was to investigate the degradation characteristics of phenol, a refractory substance, by using a submerged dielectric barrier discharge (DBD) plasma reactor. To indirectly determine the concentration of active species produced in the DBD plasma, the dissolved ozone was measured. To investigate the phenol degradation characteristics, the phenol and chemical oxygen demand (COD) concentrations were evaluated based on pH and the discharge power. The dissolved ozone was measured based on the air flow rate and power discharged. The highest dissolved ozone concentration was recorded when the injected air flow rate was 5 L/min. At a discharge power of 40W as compared to 70W, the dissolved ozone was approximately 2.7 - 6.5 times higher. In regards to phenol degradation, the final degradation rate was highest at about 74.06%, when the initial pH was 10. At a discharged power of 40W, the rate of phenol decomposition was observed to be approximately 1.25 times higher compared to when the discharged power was 70W. It was established that the phenol degradation reaction was a primary reaction, and when the discharge power was 40W as opposed to 70W, the reaction rate constant(k) was approximately 1.72 times higher.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2020.06a
• /
• pp.310-310
• /
• 2020

자연하천에서 식생의 성장은 유속 및 수위 변화에 중요한 영향을 미치며, 따라서 식생으로 인한 흐름저항은 흐름과 유사이송 모델링을 위한 중요 매개 변수가 된다. 즉, 수치 모델을 활용함에 있어 식생의 흐름 저항을 정확하게 추정하는 것이 매우 중요하며, 보다 정확한 추정을 위해 실험 혹은 현장 데이터를 활용한 보정과정이 필수적으로 요구된다. 본 연구에서는 식생 패치를 포함한 인공 수로의 흐름 모의를 위해 실규모 실험 수로에서 측정된 유속 및 수위 데이터를 활용하여 모델보정을 수행하고자 한다. 이를 위해 공간 분포 별로 각기 다른 흐름 저항식의 적용이 가능하며, 식생 저항 공식을 포함하고 있는 Delft3D 모델을 활용하였다. 또한 실규모 수로에서의 유속 및 수위 데이터 수집을 위해 한국건설기술연구원 하천연구센터에서 실험을 수행하였다. 실험 구간의 길이는 약 120 m이고 하폭은 11 m이며, 국내 하천에서 보이는 식생패치의 유사한 형태를 재현하기 위해 하천 내 가장 많이 활착되어있는 버드나무와 유사한 형태의 인공식생을 제작하였다. 인공 식생은 지그재그로 배치되었으며, 식생의 전체 높이는 1.1 m이고, 각 패치 당 23그루의 인공 식생이 총 8개 패치에 식재되었다. 모의 조건은 상류단 유입 유량 2.805 ㎥/s, 하류단수위 98.764 m의 정류 조건을 적용하였다. 또한 식생 패치 구간에서의 흐름 저항 추정을 위해 Delft3D 모델 내에서 선택가능 한 Baptist의 비침수(Non-submerged)식을 적용하였으며, 항력계수 결정을 위해 1과 1.5를 적용하여 측정 수위와 비교하였다. Delft3D의 흐름 모의 결과, 항력계수 1.5를 적용했을 때, 측정 수위와 거의 일치하는 것으로 나타났으며, 항력계수 1.0을 적용했을 경우, 측정 수위에 비해 다소 낮게 모의되는 것으로 나타났다. 또한 항력계수 1.5인 경우 식생 패치 구간에서 평균 0.65 m/s의 유속이 발생하였다.

• Journal of Korean Society of Environmental Engineers
• /
• v.30 no.9
• /
• pp.948-954
• /
• 2008

Membrane bioreactor(MBR) processes have been widely applied to wastewater treatment for last decades due to its excellent capability of solid-liquid separation. However, membrane fouling was considered as a limiting factor in wide application of the MBR process. Excess aeration into membrane surface is a common way to control membrane fouling in most MBR. However, the excessively supplied air is easily dissipated in the reactor, which results in consuming energy and thus, it should be modified for effective control of membrane fouling. In this study, cylindrical tube was introduced to MBR in order to use the supplied air effectively. Membrane fibers were immersed into the cylindrical tube. This makes the supplied air non-dissipated in the reactor so that membrane fouling could be controlled economically. Two different air supplying method was employed and compared each other; nozzle and porous diffuser which were located just beneath the membrane module. Transmembrane pressure(TMP) was monitored as a function of airflow rate, flux, and ratio of the tube area and cross-sectioned area of membrane fibers(A$_m$/A$_t$). Flow rate of air and liquid was regulated to obtain slug flow in the cylindrical tube. With the same flow of air supply, nozzle was more effective for controlling membrane fouling than porous diffuser. Accumulation of sludge was observed in the tube with the nozzle, if the air was not suppled sufficiently. Reduction of membrane fouling was dependent upon the ratio, A$_m$/A$_t$. For diffuser, membrane fouling was minimized when A$_m$/A$_t$ was 0.27, but 0.55 for nozzle.