• Ocean Science Journal
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• 제41권3호
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• pp.181-189
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• 2006

Frontal areas between warm and saline waters of the Kuroshio currents and colder and diluted waters of the East China Sea (ECS) influenced by the Changjiang River were identified from the satellite thermal imagery and hydrological data obtained from the Coastal Ocean Process Experiment (COPEX) cruise during the period between March $1^{st}$ and $10^{th}$, 1997. High chlorophyll concentrations appeared in the fronts of the East China Seas with the highest chlorophyll-a concentration in the southwestern area of Jeju Island (${\sim}2.9\;mg/m^3$) and the eastern area of the Changjiang River Mouth (${\sim}2.8\;mg/m^3$). Vertical structures of temperature, salinity and density were similar, showing the fronts between ECS and Kuroshio waters. The water column was well mixed in the shelf waters and was stratified around the fronts. It is inferred that the optimal condition for light utilization and nutrients induced both from the coastal and deep waters enhances the high phytoplankton productivity in the fronts of the ECS. In addition, the high chlorophyll-a in the fronts seems to have been associated with the water column stability as well.

• Advances in environmental research
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• 제4권2호
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• pp.105-117
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• 2015

The groundwater is a very important part of the environment and must be protected for the benefit of the present and future generation. The contamination of soil and groundwater by chemicals has become an increasing concern in the recent past. These chemicals enter the groundwater system by a wide variety of mechanisms, including accidental spills, land disposal of domestic and industrial wastes and application of agricultural fertilizers. Once introduced into an aquifer, these contaminants will be transported by flowing groundwater and may degrade water quality at nearby wells and streams. For improving the management and protection of groundwater resources, it is important to first understand the various processes that control the transport of contaminants in groundwater. Predictions of the fate of groundwater contaminants can be made to assess the effect of these chemicals on local water resources and to evaluate the effectiveness of remedial actions. In this study, an attempt has been made to investigate the behaviour of solute transport through porous media using laboratory experiments. Sodium chloride was used as a conservative chemical in the experiment. During the experiment, pulse boundary condition and continuous boundary conditions were used. Experimental results have been presented for conservative solute transport in the sand. The pattern of the break through curve remains almost same in all the cases of varying flow rate and initial concentration of conservative chemical.

• KIEAE Journal
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• 제8권3호
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• pp.69-76
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• 2008

This is an experimental study on the maximum load value and structural behavior of reinforced concrete columns containing shells as a substitute fine aggregate of concrete, through making reinforced concrete test columns with shells. In this study, the main factors consist of the grain sizes and the percentage of substitution of shells to fine aggregate in two kinds of water cement ratio. The results of the study showed as followed. The maximum load value decreased with increased the rate of substitution about shells and as the grain size of shells became smaller, the load values of them were somewhat changed higher but it is important that we must consider absorption rate of shells sufficiently. If we have a proper water cement ratio in column productions containing the shells, we can meet the requirement of the percentage of substitution until 30%. The deflection and deformation properties of reinforced concrete columns with shells represented typical curves like that of normal reinforced concrete. But as the failture types, they are able to make some change without being out of the fundamental graph forms. After the analyzing structural behaviors and the properties of reinforced concrete test columns containing shells, the most excellent grain size of shells represented 3.0mm and less with taking uniformly, and the percentage of practicable substitution of them to fine aggregate was about 30%.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권4호
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• pp.513-528
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• 2013

A floating Oscillating Water Column (OWC) wave energy converter, a Backward Bent Duct Buoy (BBDB), was simulated using a state-of-the-art, two-dimensional, fully-nonlinear Numerical Wave Tank (NWT) technique. The hydrodynamic performance of the floating OWC device was evaluated in the time domain. The acceleration potential method, with a full-updated kernel matrix calculation associated with a mode decomposition scheme, was implemented to obtain accurate estimates of the hydrodynamic force and displacement of a freely floating BBDB. The developed NWT was based on the potential theory and the boundary element method with constant panels on the boundaries. The mixed Eulerian-Lagrangian (MEL) approach was employed to capture the nonlinear free surfaces inside the chamber that interacted with a pneumatic pressure, induced by the time-varying airflow velocity at the air duct. A special viscous damping was applied to the chamber free surface to represent the viscous energy loss due to the BBDB's shape and motions. The viscous damping coefficient was properly selected using a comparison of the experimental data. The calculated surface elevation, inside and outside the chamber, with a tuned viscous damping correlated reasonably well with the experimental data for various incident wave conditions. The conservation of the total wave energy in the computational domain was confirmed over the entire range of wave frequencies.

• 한국물환경학회지
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• 제25권5호
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• pp.758-763
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• 2009

This study presents the optimal conditions of zero-valent iron (ZVI) pretreatment for color removal from real dye wastewater. Removal of color by ZVI was strongly subject to the acidity of the wastewater buffering the pH increased after ZVI reduction. The real dye wastewater did not contain a sufficient amount of acidity and thus it was necessary to supplement acid to the dye wastewater before treatment. In continuous operation of iron column, the empty bed contact time (EBCT) and initial pH were varied to find the optimal conditions. A non-linear regression model fitted well the experimental result predicting that the optimal EBCT and pH for 80% removal efficiency was present in the range of 57~90 and 5~5.9, respectively. Color of column effluents could be further removed in the following biological oxidation step and the biodegradability of wastewater was also enhanced after iron pretreatment.

• Smart Structures and Systems
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• 제9권1호
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• pp.71-104
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• 2012

In this research, a typical tension-leg type of floating platform incorporated with an innovative concept of underwater tuned liquid column damper system (UWTLCD) is studied. The purpose of this study is to improve the structural safety by means of mitigating the wave induced vibrations and stresses on the offshore floating Tension Leg Platform (TLP) system. Based on some encouraging results from a previous study, where a Tuned Liquid Column Damper (TLCD) system was employed in a floating platform system to reduce the vibration of the main structure, in this study, the traditional TLCD system was modified and tested. Firstly, the orifice-tube was replaced with a smaller horizontal tube and secondly, the TLCD system was combined into the pontoon system under the platform. The modification creates a multipurpose pontoon system associated with vibration mitigation function. On the other hand, the UWTLCD that is installed underwater instead would not occupy any additional space on the platform and yet provide buoyancy to the system. Experimental tests were performed for the mitigation effect and parameters besides the wave conditions, such as pontoon draught and liquid-length in the TLCD were taken into account in the test. It is found that the accurately tuned UWTLCD system could effectively reduce the dynamic response of the offshore platform system in terms of both the vibration amplitude and tensile forces measured in the mooring tethers.

• 대한화학회지
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• 제42권1호
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• pp.51-56
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• 1998

남조류 독성물질인 Microcystins은 자연계에 매우 미량 존재하기 때문에 이를 분리 및 정제하기가 쉽지 않다. 본 연구에서는 자연계에 존재하는 남조류 동결건조시료로부터 Microcystin RR과 LR을 분리 및 정제하는 새로운 방법을 개발하였다. 약 7.5g의 실리카겔을 정지상으로 사용하고 혼합용액인 ethyl acetate: iso-propanol:water(30: 45: 25)을 이동상으로 사용하는 open column system으로 시료를 전개한후 용액을 3mL간격으로 받아냈다. 받아낸 용액중의 Microcystin RR과 LR은 TLC와 HPLC(high performance Liquid Chromatography)를 이용하여 확인한 후 농축, 정제하였다.

• 한국전산구조공학회논문집
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• 제22권5호
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• pp.429-437
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• 2009

본 연구에서는 수평관과 수직관의 단면이 다른 액체기둥흡진기(LCVA)의 제진효과를 극대화하기 위한 최적형상을 수치 해석에 의한 변수연구를 통해 찾았다. 특정 진동수에 동조되고, 동일한 총질량을 가지면서 치수 및 수위와 관련된 구속조건을 만족하는 다양한 형상의 LCVA를 설계하고, 이 가운데 가장 큰 등가감쇠비를 획득하는 형상을 찾았다. 그 결과 LCVA 형상의 설계에서 수위변동폭이 최적형상을 결정하는 중요한 구속조건 역할을 한다는 것을 확인하였다. 유체가 운동하는 평면과 직교하는 방향의 LCVA 수평폭을 증가시킬수록 등가감쇠비가 증가하였으며, 증가율은 점차 둔화되는 것으로 나타나 적정 수평폭의 결정이 중요한 것으로 나타났다.

• 한국해양공학회지
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• 제24권2호
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• pp.1-9
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• 2010

Oscillating Water Column is one of the most widely used converting systems all over the world. The operating performance is influenced by the efficiencies of the two converting stages in the OWC chamber-turbine integrated system. In order to study the effects of the pressure drop induced by the air turbine, the experiments using the impulse turbine and the orifice device are carried out in the wave simulator test rig. The numerical simulation utilizing the orifice and porous media modules is calculated and validated by the corresponding experimental data. The numerical wave tank based on the two-phase VOF model embedded with the above modules is employed to investigate the wave elevation, pressure variation inside the chamber and the air flow velocity in the duct. The effects of the air turbine on the integrated system and interaction among the wave elevation, pressure and air flow velocities variations are investigated, which demonstrates that the present numerical model are more accurate to be employed.

• 한국항해항만학회지
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• 제36권9호
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• pp.729-735
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• 2012

The primary wave energy conversion by a three-dimensional bottom-mounted oscillating water column (OWC) wave power device in regular waves has been studied. The linear potential boundary value problem has been solved following the boundary matching method. The optimum shape parameters such as the chamber length and the depth of the front skirt of the OWC chamber obtained through two-dimensional numerical tests in the frequency domain have been applied in the design of the present OWC chamber. Time-mean wave power converted by the OWC device and the time-mean second-order wave forces on the OWC chamber structure have been presented for different wave incidence angles in the frequency-domain. It has been shown that the peak period of $P_m$ for the optimum damping parameter coincides with the peak period of the time.mean wave drift force when ${\gamma}=0$.