• Journal of the Korean Society of Visualization
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• v.20 no.1
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• pp.29-37
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• 2022

We carried out a laboratory experiment about the thermo-fluidic characteristics of natural convection boundary layer over a vertical heated plate under constant heat flux condition. Particle image velocimetry has been applied to observe the surface convection velocity close to the vertical plate submerged in the water chamber with the condition of Ra = 7 × 10⁹ and Pr = 8.1. The velocity distributions indicate that the distinct stripe-like structures appears in the upstream (earlier transition region) and the distinct negative-positive and Λ(λ)-shaped flow structures in the downstream (mid-transition region). In addition, the temporal variation of spanwise and streamwise velocity is also presented.

• Korean Journal of Environmental Agriculture
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• v.11 no.1
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• pp.1-8
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• 1992

New formulation of diazinon as granule preparing with piperonyl butoxide(PBO) and triphenyl phosphate(TPP) known as the inhibitor of monooxygenase(mo) and esterase was tested with the mortality of rice leaf hopper. Also, the mixed formulation of diazinon with tricyclazole, carbofuran and EPN were investigated about the residual pattern of diazinon in submerged soil condition at $30{\pm}2^{\circ}C$. Although the mortality about rice leaf hopper was higher only 10% on new formulation of diazinon than commercial at recommended dose but was 30-60% at half dose. Half life of diazinon in the formulation with 0.1% of PBO+TPP was 4.53 days in sterilized soil and 2.33 days in non-sterilized soil, and it was delayed about 0.74 and 0.45 respectively in contrast with the commercial granule. Also, half life of the new formulation with 1% PBO and PBO+TPP was delayed 0.44(PBO) and 0.65day(PBO+TPP) in non-sterilized soil condition, respectively. Half life of mixed formulation with tricyclazole, carbofuran, EPN or EPN+Carbofuran was delayed 2.61, 1.04, 0.43 or 2.7 days, respectively. As a result, the persistence rate of new formulation and mixed formulation was increased by inhibition of two enzymes affecting to the dgradation of diazinon in submerged soil.

• Journal of Wetlands Research
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• v.11 no.1
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• pp.39-48
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• 2009

Wetland plants are an important component for wetland design and construction because they determine functions of wetlands through interactions with the abiotic environment such as wetland soil and hydrology as well as with other wetland organisms. In this study, germination experiments with soils from a natural wetland that contain seeds of wetland plants were conducted in wetland mesocosms to investigate the applicability of natural wetland soils for introducing and establishing wetland plants into constructed wetlands. Seven species were germinated in the experiment, with two new species that were not found in the field survey of wetland plants in the West Nakdong River area, Korea. The number of plant individuals germinated in submerged conditions (15 individuals) was much greater than that in waterlogged conditions (2 individuals). In experiments in which soils from a natural wetland and a wetland construction site were mixed at different ratios, the largest number of plant individuals was observed in the condition with 100% natural wetland soil. The highest growth was observed at 50% natural wetland soil for Hydrilla verticillata and 100% for Ceratophyllum demersum. These results suggest that 1:1 mixture of soils from natural wetland wetlands and wetland construction sites would provide an appropriate condition for secure establishment of submerged plants in constructed wetlands.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.1
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• pp.95-104
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• 2022

Micro hydropower is a readily available renewable energy source that can be harvested utilizing hydrokinetic turbines from shallow water canals, irrigation and industrial channel flows, and run-off river stream flows. These sources generally have low head (<1 m) and low velocity which makes it difficult to harvest energy using conventional turbines. A horizontal-axis screw turbine was designed and numerically tested to extract power from such low-head water sources. The 3-bladed screw-type turbine is placed horizontally perpendicular to the incoming flow, partially submerged in a narrow water channel at no-head condition. The turbine hydraulic performances were studied using Computational Fluid Dynamics models. Turbine design parameters such as the shroud diameter, the hub-to-shroud ratios, and the submerged depths were obtained through a steady-state parametric study. The resulting turbine configuration was then tested by solving the unsteady multiphase free-surface equations mimicking an actual open channel flow scenario. The turbine performance in the shallow channel were studied for various Tip Speed Ratios (TSR). The highest power coefficient was obtained at a TSR of 0.3. The turbine was then scaled-up to test its performance on a real site condition at a head of 0.3 m. The highest power coefficient obtained was 0.18. Several losses were observed in the 3-bladed turbine design and to minimize losses, the number of blades were increased to five. The power coefficient improved by 236% for a 5-bladed screw turbine. The fluid losses were minimized by increasing the blade surface area submerged in water. The turbine performance was increased by 74.4% after dipping the turbine to a bottom wall clearance of 30 cm from 60 cm. The final output of the novel horizontal-axis screw turbine showed a 2.83 kW power output at a power coefficient of 0.63. The turbine is expected to produce 18,744 kWh/year of electricity. The design feasibility test of the turbine showed promising results to harvest energy from small hydropower sources.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.3
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• pp.132-145
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• 2016

In case of the seabed around and under gravity structures such as submerged breakwater is exposed to a large wave action long period, the excess pore pressure will be generated significantly due to pore volume change associated with rearrangement soil grains. This effect will lead a seabed liquefaction around and under structures as a result from decrease in the effective stress. Under the seabed liquefaction occurred and developed, the possibility of structure failure will be increased eventually. In this study, to evaluate the liquefaction potential on the seabed quantitatively, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank model and the finite element elasto-plastic model. Under the condition of the regular wave field, the time and spatial series of the deformation of submerged breakwater, the pore water pressure (oscillatory and residual components) and pore water pressure ratio in the seabed were estimated.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.1
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• pp.54-65
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• 2012

While fishery has been continuously suffering from deteriorating economic feasibility, the amount of the deposited marine litter has been increasing due to an increased number of marine leisure tourists which are caused by an improved quality of life and five-day work week. In addition, the fishery area has been reduced by the reclamation projects and it is being destroyed by marine pollution with a variety of contaminants coming from land and sea. To protect and improve fisheries in these poor conditions, Korean governments have implemented the submerged marine litter collection projects. However, previous research results on the marine environment and resources indicate that it requires a lot of time investment to achieve tangible results of such improvement. The 300 billion won marine environment and resource investigation project has been executed since July 2004 by Korean governments, which demands strategic approaches to obtain more effective and satisfactory results before the project expires in 2013. Ocean environment research institutes and governments need to cooperate each other to gain efficient and reasonable achievement by identifying and linking related projects. This study suggests that the marine environment and resources investigation projects should run parallel with the submerged marine litter collection projects on mutually agreed research items in the identical area of the ocean to obtain cost-effective improvement of marine environment and fishery conditions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.6
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• pp.332-349
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• 2016

OLAFOAM is the powerful CFD code and is an expanded version of $OpenFOAM^{(R)}$, for wave mechanics simulation. The $OpenFOAM^{(R)}$ does provide many solvers to correspond to each object of the numerical calculation in a variety of fields. OLAFOAM's governing equation bases on VARANS (Volume-Averaged Reynolds-Averaged Navier-Stokes) equation, and the finite volume method is applied to numerical techniques. The program is coded in C++ and run on the Linux operating system. First of all, in this study, OLAFOAM was validated for 1) wave transformation inside porous structure under bore and regular wave conditions, 2) wave transformation by submerged breakwater under regular wave condition, and 3) regular wave transformation and resultant vertical velocity distribution under current by comparison with existing laboratory measurements. Hereafter, this study, which is almost no examination carried out until now, analyzed closely variation characteristics of water surface level, wave height, frequency spectrum, breaking waves, averaged velocity and turbulent kinetic energy around porous submerged breakwater in the wave and current coexisting field for the case of permeable or impermeable rear beach. It was revealed that the wave height fluctuation according to current direction(following or opposing) was closely related to the turbulent kinetic energy, and others.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.4
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• pp.629-637
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• 2000

A two-phase anaerobic reactor with a submerged microfiltration system was tested for its ability to produce methane energy from organic wastewater. A membrane separation system with periodic backwashing with compressed air was submerged in the acidogenic reactor. The cartridge type of microfiltration (MF) membrane with pore size of $0.5{\mu}m$ (mixed esters of cellulose) was tested. An AUBF (Anaerobic Upflow Sludge Bed Filter: 1/2 packed with plastic media) was used for the methanogenic reactor. Soluble starch was used as a substrate. The COD removal was investigated for various organic loading with synthetic wastewater of 5,000 mg starch/L. When the hydraulic retention time (HRT) of the acidogenic reactor was changed from 10 to 4.5 days, the organic loading rate (OLR) varied from 0.5 to $1.0kg\;COD/m^3-day$. When the HRT of the methanogenic reactor was changed from 2.8 to 0.5 days, the OLR varied from 0.8 to $5.8kg\;COD/m^3-day$. The acid conversion rate of the acidogenic reactor was over 80% in the 4~5 days of HRT. The overall COD removal efficiency of the methanogenic reactor showed over 95% (effluent COD was below 300 mg/L) under the highly fluctuating organic loading condition. A two-phase anaerobic reactor showed an excellent acid conversion rate from organic wastewater due to the higher biomass concentration than the conventional system. A methanogenic reactor combined with sludge bed and filter, showed an efficient COD and SS removal.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.5
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• pp.215-226
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• 2018

In this paper, to estimate the dynamic behavior of a submerged floating tunnel(SFT) by underwater explosion(UE), the SFT is modeled and analyzed by the explicit structural analysis package LS-DYNA. The section of SFT near to explosion point is modeled to shell and solid elements using elasto-plasticity material model for concrete tubular section and steel lining. And the other parts of the SFT are modeled to elastic beam elements. Also, mooring lines are modeled as tension-only cable elements. Total mass of SFT is including an added mass by hydrodynamic effect. The buoyancy on the SFT is considered in its initial condition using a dynamic relaxation method. The accuracy and the feasibility of the analysis model aree verified by the results of series of free field analysis for UE. And buoyancy ratio(B/W) of SFT, the distance between SFT and an explosion point and the arrangement of mooring line aree considered as main parameters of the explosion analysis. As results of the explosion analysis, the dynamic responses such as the dent deformation by the shock pressure are responded less as more distance between SFT and an explosion point. However, the mooring angle of the diagonal mooring system can not affect the responses such as the horizontal displacement of SFT by the shock pressure.

• KSBB Journal
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• v.20 no.1 s.90
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• pp.60-65
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• 2005

The objective of this work was to evaluate a solid-state fermentation process for the practical production of arachidonic acid(AA) by Mortierella alpina ATCC 32222. In the present investigation, batch culture kinetics for both submerged- and solid-state fermentations was carried out at $25^{\circ}C$ to identify the relationship between growth and arachidonic acid (AA) production. Glucose and yeast extract were used in submerged fermentations by using flasks, while rice bran was used as a sole raw material in the other type of fermentations by using a series of Petri dishes. It was evident that a mixed-growth associated pattern existed between the two variables, irrespective of modes of fermentations. The effect of carbon to nitrogen (CfN) ratio on AA production in solid-state fermentation was studied in the range of 6.5 - 20. As a result, an optimum condition was found to be 6.5. Supplementary carbon source was not necessary to meet the optimum C/N ratio. Unlike the Previous results obtained by other researchers, a supplement of sodium glutamate up to $4\%$ (w/w) to the rice bran medium did not have a positive effect on the AA productivity. However, an increase in AA productivity was obtained with the rice bran medium supplemented with sesame oil.