• Korean Journal of Ecology and Environment
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• v.53 no.4
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• pp.331-335
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• 2020

The red swamp crawfish (Procambarus clarkii) is native to northeastern Mexico and south-central United States. But the species has been introduced to other parts of the world, and cause ecological problems including habitat destruction and competition with indigenous species. In this study, we identified the distribution of P. clarkii in the freshwater system in Korea. P. clarkii were collected in the field sampling and it is assumed that they have settled in major domestic water systems of Korea including six points in the Yeongsangang River, five points in the Mangyeonggang River, two points in the Seomjingang River, and one point in the Geumgang River. In particular, more than 20 individuals were found in Seobongri, Wanjugun and Mosanri, Hampyeonggun, which are believed to form a relatively large population. Considering high mobility and environmental adaptability of the species, the possibility of their dispersal to other water systems is very high. Therefore, continuous monitoring and assessment of their distribution and potential spread are required and effective management to remove them policy is needed to prevent damage in the Korean ecosystem.

• Smart Structures and Systems
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• v.21 no.1
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• pp.27-35
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• 2018

In the water-filling and preloading test, the sensing cables were installed on the surface of steel spiral case and in the surrounding concrete to monitor the strain distribution of several cross-sections by using Brillouin Optical Time Domain Analysis (BOTDA), a kind of distributed optical fiber sensing (DOFS) technology. The average hoop strain of the spiral case was about $330{\mu}{\varepsilon}$ and $590{\mu}{\varepsilon}$ when the water-filling pressure in the spiral case was 2.6 MPa and 4.1 MPa. The difference between the measured and the calculated strain was only about $50{\mu}{\varepsilon}$. It was the first time that the stress adjustment of the spiral case was monitored by the sensing cable when the pressure was increased to 1 MPa and the residual strain of $20{\mu}{\varepsilon}$ was obtained after preloading. Meanwhile, the shrinkage of $70{\sim}100{\mu}{\varepsilon}$ of the surrounding concrete was effectively monitored during the depressurization. It is estimated that the width of the gap between the steel spiral case and the surrounding concrete was 0.51 ~ 0.75 mm. BOTDA based distributed optical fiber sensing technology can obtain continuous strain of the structure and it is more reliable than traditional point sensor. The strain distribution obtained by BOTDA provides strong support for the design and optimization of the spiral case structure.

• Advances in aircraft and spacecraft science
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• v.5 no.4
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• pp.499-513
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• 2018

One of the major problems in glass fiber reinforced epoxy (GFRE) composite pipes is the durability under water absorption. This condition is generally recognized to cause degradations in strength and mechanical properties. Therefore, there is a need for an intelligent system for detecting the absorption rate and computing the mass of water absorption (M%) as a function of absorption time (t). The present work represents a new non-destructive evaluation (NDE) technique for detecting the water absorption rate by evaluating the dielectric properties of glass fiber and epoxy resin composite pipes subjected to internal hydrostatic pressure at room temperature. The variation in the dielectric signatures is employed to design an electrical capacitance sensor (ECS) with high sensitivity to detect such defects. ECS consists of twelve electrodes mounted on the outer surface of the pipe. Radius-electrode ratio is defined as the ratio of inner and outer radius of pipe. A finite element (FE) simulation model is developed to measure the capacitance values and node potential distribution of ECS electrodes on the basis of water absorption rate in the pipe material as a function of absorption time. The arrangements for positioning12-electrode sensor parameters such as capacitance, capacitance change and change rate of capacitance are analyzed by ANSYS and MATLAB to plot the mass of water absorption curve against absorption time (t). An analytical model based on a Fickian diffusion model is conducted to predict the saturation level of water absorption ($M_S$) from the obtained mass of water absorption curve. The FE results are in excellent agreement with the analytical results and experimental results available in the literature, thus, validating the accuracy and reliability of the proposed expert system.

• Journal of ILASS-Korea
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• v.5 no.1
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• pp.5-12
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• 2000

The beneficial aspects of applying emulsion fuels to combustion systems may be due to the changes of fuel properties which lead to the enhanced atomization characteristics. The spray characteristics of water/oil emulsified fuel injected from the pressure-swirl(simplex) atomizer using for oil burner were investigated. Four different water contents from 10 to 40 % by volume at 10% increment were prepared by mixing with the different contents of surfactants. Total amount of surfactant used was varied from 1 to 3 % by volume. This study demonstrates the influence of water and surfactant contents of emulsified fuel, injection pressure on the spray characteristics, i.e. Sauter mean diameter(SMD) and spray angle. The drop size distribution of the emulsified fuel spray was measured with a Malvem particle sizer. In order to measure the spray angle, the digital image processing was employed by capturing multiple images of the spray with 3-CCD digital video camera. It was evident that the addition of water and surfactant changes fuel properties which are the key parameters influencing the atomization of the spray. The increase in surfactant content results in the decrease of SMD and the increase in spray angle. The droplets decease with increase in injection pressure, but the influence of injection pressure in this experimental condition was less important than expected. The more viscous fuel with the increase of water content exhibits the larger droplets in the centerline of the spray, and the less viscous fuel in the outer edges of the spray. The increase in axial position from the nozzle causes the spray angle to decrease. The spray angle decreases with increase in water content. This is due to increase in viscosity with increase in water content.

• Journal of Wetlands Research
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• v.6 no.1
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• pp.149-166
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• 2004

Water quality and ecological environment in the Han River estuary was analyzed using the longterm water quality monitoring data from National Fisheries Research and Development Institute (NFRDI) and the existing data collected in this area. Based on the salinity distribution and changes of current direction in the lower Han River and its estuary, boundaries of the estuary were identified and also, distribution patterns of the phyto- and zooplankton, benthos, ichthyoplankton and fish were discussed related with the salinity changes in the macrotidal subestuary of Han River. Seasonal and spatial distribution of salinity suggested that the direct impact of freshwater be limited to the Incheon North Harbour all the year round and even extended to the southern area of Gyunggi Bay near Palmi island during limited time, usually in summer. Upper limit of salt water intrusion through the Han River is likely to be Singok underwater dam located Gimpo, Gyunggi Province, and normally limited to much lower part of the river, Jeonryuri, Gimpo. Biological boundaries of the Han River estuary exceeded the physical boundaries based on the salinity distribution. Many estuarine species in plankton and fish were found at the totally freshwater or saltwater depending on the seasons and tidal cycles. Some estuarine ichthyoplanktons showed extremely limited distributions in the estuary whereas adult fish revealed wide ranges of salinity adaptation. Critical environmental issues in the Han River estuary and its drainage basin are likely to be 1) pressure on development-promoted district for new town in the drainage area of the estuary, 2) reduction of tidal flat by reclamation, 3) pollutant input through river from municipal sewages and industrial wastes, and 4) ecological barrier between river and terrestrial systems by the military wire fence and riverside road.

• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.11-21
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• 2001

The focus of this paper is on the numerical investigation of obliquely incident wav interactions with a system composed of fully submerged and floating dual buoy/vertical-flexible-membrane breakwaters placed in parallel with spacing between two systems. The fully submerged two systems allow surface and bottom gaps to enable wave transmission over and under the system. The problem is formulated based on the two-dimensional multi-domain hydro-elastic linear wave-body interaction theory. The hydrodynamic interaction of oblique incident waves with the combination of the rigid and flexible bodies was solved by the distribution of the simple sources (modified Bessel function of the second kind) that satisfy the Helmholz governing equation in fluid domains. A boundary element program for three fluid domains based on a discrete membrane dynamic model and simple source distribution method is developed. Using this developed computer program, the performance of various dual systems varying buoy radiuses and drafts, membrane lengths, gaps, spacing, mooring-lines stiffness, mooring types, water depth, and wave characteristics is thoroughly examined. It is found that the fully submerged and floating dual buoy/membrane breakwaters can, if it is properly tuned to the coming waves, have good performances in reflecting the obliquely incident waves over a wide range of wave frequency and headings.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2818-2827
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• 2015

The spatial patterns and characteristics of these sequential earthquakes and ground motions induced by the earthquakes are examined by contours of peak ground velocity (PGV) and geometric mean peak ground velocity (GMPGV) using both ordinary kriging in geographical information system (GIS) and data, the records obtained from strong motion stations, acquired after recent sequential earthquakes in Canterbury, New Zealand (NZ). The performance of underground water pipeline system is examined by using data acquired after earthquakes. The spatial distribution of GMPGV is superimposed on water pipeline repairs throughout the water distribution system in areas affected principally by transient ground motion using GIS and then water pipeline repair rates, expressed as repairs/km, for different types of pipe are evaluated relative to the estimated GMPGV outside liquefaction areas. The earthquake performance of underground water pipeline systems is summarized in this study.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.449-455
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• 1998

A header' is the device that makes uniform flow distribution in all branches from header of heat exchangers, pipe burner or chemical equipments. In this study, experimental tests have been performed in order to investigate the flow distribution characteristics in a straight header and tapered header which have 6 and 11 glass pipe branches. The experimental equipment consists of a water circulation system where the fluid velocity in each glass pipe is measured by Ar-ion LDV system. From the experiments and the theoretical equation, it could be recommended that tapered header should be determined so that its internal velocities inside the header become uniform according to taper of the header and number of attached branches for uniform flow distribution in energy systems.

• Journal of Korean Society on Water Environment
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• v.28 no.1
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• pp.26-37
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• 2012

Multi-dimensional hydrodynamic and water quality models are widely used to simulate the physical and biogeochemical processes in the surface water systems such as reservoirs and estuaries. Most of the models have adopted the Eulerian grid modeling framework, mainly because it can reasonably simulate physical dynamics and chemical species concentrations throughout the entire model domain. Determining the optimum grid cell size is important when using the Eulerian grid-based three-dimensional water quality models because the characteristics of species are assumed uniform in each of the grid cells and chemical species are represented by concentration (mass per volume). The objective of this study was to examine the effect of grid-size of a three dimensional hydrodynamic and water quality model (EFDC) on hydrodynamics and mass transport in the Saemangeum Reservoir. Three grid resolutions, respectively representing coarse (CG), medium (MG), and fine (FG) grid cell sizes, were used for a sensitivity analysis. The simulation results of numerical tracer showed that the grid resolution affects on the flow path, mass transport, and mixing zone of upstream inflow, and results in a bias of temporal and spatial distribution of the tracer. With the CG, in particular, the model overestimates diffusion in the mixing zone, and fails to identify the gradient of concentrations between the inflow and the ambient water.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.5
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• pp.583-598
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• 2009

From the engineering standpoint, this study puts a special emphasis on application of adaptive management. To do this, we analyze the recent issue about water scarcity of the Gwangdong dam. Using the system dynamics model, we defined the system including water balance in the dam, dam manager's operation rules, regional water supply and local water distribution, and customer damage. It was expected that the model is useful to explain the real case, and also water scarcity of Gwangdong led to total damage of about 2.56 billion won, mainly to customers in the Taebaeck city. Two adaptive management options (i.e., optimal allocation of limited water resources, and early control of dam storage) were applied to the model in order to examine whether adaptive management is effective to mitigate the damage, it is concluded that the case study could largely reduce or entirely avoid the damage with adaptive engineering options.