• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1616-1621
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• 2006

하천 지형은 흐름과 유사거동에 의한 세굴 또는 퇴적에 의하여 끊임없이 변한다. 이 연구에서는 최근 하천지형의 변화가 크게 일어나고 있는 한강 신곡수중보 직하류 우안의 고수부지 형성 이력에 대한 조사 및 분석을 실시하였다. 조사결과, 1981년 이전까지 하중도(제주초도)가 안정된 형태로 존재하였으나, 1980년대 중반을 거치면서 하중도는 소멸되었고 1990년대 중반 이후부터 우안에 비슷한 규모의 고수부지가 생성되었음을 알 수 있었다. 이 고수부지의 형성과정을 평가하면 다음과 같다. 1) 초기단계(흐름 변화에 따른 이동사주의 정지): 1995년 이전까지는 하천 내 자연적/인위적 교란에도 불구하고 이열사주 형태의 이동상이 유지되다가 1995년 이후 1988년 준공된 신곡수중보의 직.간접적인 영향을 받는다. 이로 인한 하중도의 소멸이 가중되면서부터 신곡수중보 직하류 우안의 이동사주가 정지하기에 이른다. 2) 성장단계(조석에 따른 부유사 반복 퇴적): 이동상 사주가 정지된 뒤 매일 2회씩 반복되는 조석의 영향을 받은 고농도의 부유사가 정지된 사주 위에 반복되어 퇴적되는 양상이 일어난다. 3) 정착단계(정지사주의 고수부지화): 정지사주에서 부유사가 퇴적하고 갈대와 같은 초본류 식생이 활착하게 되면서 부유사 퇴적은 가중되어 간다. 이러한 과정에서 1999년과 같은 대홍수 때 부유사의 고수부지 내 퇴적이 결정적이었을 것이다. 4) 확장단계(고수부지 확장단계): 대홍수 때 고수부지의 퇴적과 아울러 산재하던 버드나무가 교란을 받아 고수부지에서 새로운 버드나무 군락의 터전을 이루어 밀생하게 된다. 향후 고수부지가 잠기는 규모의 홍수가 빈발할 경우 퇴적층의 유실보다는 부유사 퇴적이 많아져 고수부지는 확장단계에 접어들게 된다.70{\sim}90$ 시간 동안 실험을 수행하였다. 세굴의 측정은 투명한 아크릴로 제작된 수제 내부에 CC카메라를 수제 전 후면 및 측면에 설치하여 월류수제의 세굴 발생을 실시간으로 측정하며 동시에 수제의 각 면에 각각 3개의 압력센서를 설치하여 압력분포를 측정함으로써, 월류수제 주변의 압력변화에 따른 세굴심의 실시간 변화를 비교할 수 있도록 하였다. 수심이 연중 $25{\sim}35m$를 유지하는 H호의 경우 간헐식 폭기장치를 가동하는 기간은 물론 그 외 기간에도 취수구의 심도를 표층 10m 이하로 유지 할 경우 전체 조류 유입량을 60% 이상 저감할 수 있을 것으로 조사되었다.심볼 및 색채 디자인 등의 작업이 수반되어야 하며, 이들을 고려한 인터넷용 GIS기본도를 신규 제작한다. 상습침수지구와 관련된 각종 GIS데이타와 각 기관이 보유하고 있는 공공정보 가운데 공간정보와 연계되어야 하는 자료를 인터넷 GIS를 이용하여 효율적으로 관리하기 위해서는 단계별 구축전략이 필요하다. 따라서 본 논문에서는 인터넷 GIS를 이용하여 상습침수구역관련 정보를 검색, 처리 및 분석할 수 있는 상습침수 구역 종합정보화 시스템을 구축토록 하였다.N, 항목에서 보 상류가 높게 나타났으나, 철거되지 않은 검전보나 안양대교보에 비해 그 차이가 크지 않은 것으로 나타났다.의 기상변화가 자발성 기흉 발생에 영향을 미친다고 추론할 수 있었다. 향후 본 연구에서 추론된 기상변화와 기흉 발생과의 인과관계를 확인하고 좀 더 구체화하기 위한 연구가 필요할 것이다.게 이루어질 수 있을 것으로 기대된다.는 초과수익률이 상승하지만, 이후로는 감소하므로, 반전거래전략을 활용하는 경우 주식투자기간은 24개월이하의 중단기가 적합함을

• Journal of the Korean Society for Marine Environment & Energy
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• v.3 no.4
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• pp.56-64
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• 2000

Behavior of trace metals in Masan Bay, Korea was studied in August 1998 when the oxygen deficient condition occurred. Dissolved Cd and Zn concentration in the surface waters decreased with increasing distance from Masan Harbor. Dissolved concentrations of Cd, Cu Pb and Zn in the surface waters were higher than bottom waters. Particulate(acid-teachable fraction) concentrations of Cu, Cd and Pb in the surface waters of Masan Bay decreased with increasing distance from Masan Harbor. Bottom waters contained higher concentrations of particulate Cd, Cu, Pb and Zn than surface waters. Distribution coefficients between dissolved and particulate phase (K/sub d/) of Cu and Cd decreased with the increasing distance from the Harbor, possibly due to reaction of these elements with sewage-derived particulate matter Al, Zn, Cu, Cd, and Pb in the surface sediment showed relatively high concentration in the inner Masan Bay.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.6
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• pp.757-764
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• 2019

Depressurization occurs around underwater objects moving at high speeds. This causes cavitation nuclei to expand, resulting in cavitation. Cavitation is accompanied by an increase in noise and vibration at the site, particularly in the case of thrusters, and this has a detrimental ef ect on propulsion performance. Therefore, predicting cavitation is necessary. In this study, an analytical method for cavitation noise is developed and applied to an elliptic wing. First, computational fluid dynamics are performed to obtain information about the flow fields around the wing. Then, through the cavitation nuclei density function, number of cavitation nuclei is calculated using the initial radius of the nuclei and nuclei are randomly placed in the upstream with large pressure drop around the wing tip. Bubble dynamics are then applied to each nucleus using a Lagrangian approach for noise analysis and to determine cavitation behavior. Cavitation noise is identified as having the characteristics of broadband noise. Verification of analytical method is performed by comparing experimental results derived from the large cavitation tunnel at the Korea Research Institute of Ships & Ocean Engineering.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.3
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• pp.1778-1785
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• 2014

In order to construct offshore structures safely, geotechnical investigation should be carried out with high accuracy. Up to now, onshore geotechnical investigation equipments installed on the barge are used for offshore geotechnical investigation. In this case, many limitations can be confronted such as deep water depth, high wave, strong current, severe wind and so on. For the safe and economic offshore geotechnical investigation with high precision, a seabed type unmanned automated site investigation equipment is developed. It can be operated remotely underwater conditions with 100m water depth and can explore the ground depth of 50m. Also, the standard penetration test (SPT), soil boring, soil sampling and rock coring can be possible using the equipment. Numerical analysis was conducted to secure the stability of the equipment against current of 4 knot. Energy efficiency of SPT apparatus which is attached to the equipment shows 78% in average.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.9
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• pp.917-922
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• 2015

The goal of this study is to consider the application of alternative blended fuel to diesel engine. In this study, as the test fuels, we use a blended fuel mix of diesel and hydrogen peroxide. As the primary variable, we vary the mixing ratio of diesel and hydrogen peroxide in the experimental and numerical analysis. We perform an evaporative behavior characteristics analysis of the emulsified fuel using the Schlieren method. The numerical analysis was carried out based on results obtained from the experimental analysis using the commercial code(ANSYS CFX). Consequently, we found that the micro-explosion depends on the fraction of hydrogen peroxide, and we propose a numerical method for the quantitative evaporation analysis of emulsified fuel droplets using the calculation of the volume fraction in the oil domain.

• Applied Chemistry for Engineering
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• v.19 no.1
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• pp.122-128
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• 2008

We evaluated the relationship between the multiplication of heterotrophic microorganisms and physicochemical factors in the final discharged sewage water from J municipal waste water treatment plants. Dissolved organic carbon (DOC) was the most crucial factor influencing multiplication of heterotrophic plate counts (HPC) among the water quality variables selected. Degrading bacteria, such as proteolytic bacteria, lipholytic bacteria, starch degrading bacteria, cellulolytic bacteria, and pectinolytic bacteria, were monitored to understand the condition of nutrients in finished sewage effluent. The percentages of lipid and protein combined occupied 81% in finished sewage water. The multiplication of HPC showed the highest value in August. The formation of trihalomethane (THM) was low in the finished discharge water during chlorine disinfection, which was $71{\mu}/L$ (which was less than $100{\mu}/L$- the standard of drinking water quality) with 10 mg/L of chlorine during 15 min.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.1
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• pp.1-7
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• 2017

Concrete behavior in early-age is changing due to hydration reaction with time, and a resistance to chloride attack and strength development are different characterized. In the present work, changing strength and resistance to chloride attack are evaluated with ages from 28 days to 6 months. For the purpose, strength, diffusion coefficient, and passed charge are evaluated for normal concrete with 3 different mix proportions considering 28-day and 6-month curing conditions. With increasing concrete age, the changing ratio of strength falls on the level of 135.3~138.3%, while diffusion coefficient and passed charge shows 41.8%~51.1% and 53.6%~70.0%, respectively. The results of chloride diffusion coefficient and passed charge show relatively similar changing ratios since they are much dependent on the chloride migration velocity in electrical field. The changing ratios in chloride behaviors are evaluated to be much larger than those in compressive strength since the ion transport mechanism is proportional to not porosity but square of porosity.

• Journal of Radiation Protection and Research
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• v.11 no.2
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• pp.139-145
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• 1986

An improved mothod of assessing fuel status by analyzsis of the fission product in the reactor coolant system is proposed. The release mechanism of specific fission products is established for determination of the coefficients in the equations which relate the radioactivities with the amount of defected fuel. Knock-out and migration models are employed in the formulation of the release mechanism. The influence of the tramp uranium is quantified. Sample calculations were made for KNU 1 reactor system using the I-131 and I-133 concentrations in the primary coolant. The estimated number of defected fuel pins in the third and sixth cycles appeared to be $9.34{\pm}1.13\;and\;0.294{\pm}0.092$, respectively.

• Journal of Korean Society of Water and Wastewater
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• v.14 no.1
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• pp.84-98
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• 2000

Control of Trihalomethanes(THMs) is a major concern of many water treatment plants. A number of researchers have studied the effectiveness of activated carbon adsorption process in removing THMs or organic halogen compounds. Recently, attention has been paid to the biological activated carbon (BAC) treatment of THM precursors as an alternative to the carbon adsorption treatment because of its effectiveness as well as its low running cost. In this study, changes of THM formation potential(THMFP) and removal of substrates in the SBR effluent were investigated in an attempt to clarify the mechanisms of the decrease/increase of THMFP in the BAC treatment. The increase and decrease of THMFP concentrations were observed in effluents during prolonged operation. When PCP or DBS was feeded as substrate contained in SBR effluent, the THMFPs were easyly removed with TOCs removal. But the case of SBR effluent containing SDS or glycine was introduced, and when microbial growth came to its near steady state, the THMFPs of treated effluents were increased more or less in comparison to those in the influents. Such increases of THMFP coincided with the increase in microbial growth within the activated carbon fiber(ACF) column. In the case of only sucrose was feeded as substrate on ACF colume, THMFP concentrations of effluent were higher than those of influent. The THMFP concentration was significantly increased on inlet part of ACF column, which biomass inhabits abundantly, then they were decreased gradually. These increases mean production of the secondary THM precursors by biological activities, which can be removed by adsorption and biological degradation on ACF column.

• Journal of computational fluids engineering
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• v.21 no.3
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• pp.15-23
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• 2016

In the present study, two phase flows around a projectile vertically launched from an underwater platform have been numerically investigated by using a three dimensional multi-phase RANS flow solver based on pseudo-compressibility and a homogeneous mixture model on unstructured meshes. The relative motion between the platform and projectile was described by six degrees of freedom equations of motion with Euler angles and a chimera technique. The propulsive power of the projectile was modeled as the fluid force acting on the lower surface of the body by the compressed air emitted from the underwater platform. Various flow conditions were considered to analyze the fluid-dynamics motion parameters of the projectile. The water level of platform and the current speed around the projectile were the main parametric variables. The numerical calculations were conducted up to 0.75sec in physical time scale. The dynamics tendency of the projectile was almost identical with respect to the water level variation due to the constant buoyancy term. The moving speed of the projectile along the vertical axis inside the platform decreased when the current speed increased. This is because the inflow from outside of the platform impeded development of the compressed air emitted from the floor surface of the launch platform. As a result, the fluid force acting on the lower surface of the projectile decreased, and injection time of the projectile from the platform was delayed.