• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.1
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• pp.40-50
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• 1994

For an accurate prediction of the temperature field induced by heated water discharged into a shallow crossflow, a two-dimensional near-field numerical model is developed. It is based on a 4-equation turbulence model in which the transport equations for mean of the temperature fluctuation squared and its dissipation rate are added to those of a 2-equation turbulence model which cannot give the information of the thermal time scale ratio. Vertical diffusion is also considered by including buoyancy production and turbulence heat flux terms. The developed model is applied to a steady flow in an open channel with simple geometry and the results are compared with existing experimental data and those of the already established 2-equation turbulence model. Numerical results of the model agree with the experimental data better than those of the 2-equation model. The present model also simulates quite adequately the physical characteristics of thermal discharge in the jet entrainment and stable regions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.7
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• pp.619-625
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• 2015

Swirl injectors are widely used for Liquid Rocket Engine(LRE) as fuel injection system and following researches are also being carried out throughout the world. Especially, solving combustion instability problem is essential for every type of LREs. In this study, cold test was carried out for open type swirl injector as a fundamental research to solve combustion instability problem. Pressure fluctuation was applied to the inlet flow coming into the injector and the following response characteristics were observed. The effect of swirl chamber geometry was also studied by changing both swirl chamber length and diameter.

• Journal of Korea Water Resources Association
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• v.45 no.5
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• pp.465-472
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• 2012

Recently, as the development of water front and natural type river is gradually increasing, it is mostly the case in that the flow analysis is implemented by only the flood level of the starting point without the tidal effect when the flood water level of the starting point is highly estimated than the high tidal water level in the design of river adjacent to an estuary. This research has analyzed the variation of tidal current for Oncheon river in Busan using Delft-3D program, considering that the tidal effect can cause the change of the flood water level of the starting point although the flood water level is higher than the flood tide level. As a result, considering the tidal effect at downstream boundary condition, water level indicates a periodicity of tide in particular region and the fluctuation range of water level is extended to upstream.

• Journal of Environmental Science International
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• v.27 no.8
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• pp.689-699
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• 2018

The changes on community structures of benthic macroinvertebrates, relevance to the environment and interrelationship between benthos were studied over two years in stream with large environmental disturbance, which caused by localized heavy rain during Typhoon Chaba in October 2016. As a result, the number of species and individuals were increased after localized heavy rain, especially numbers of individuals of Ephemeroptera and Plecoptera were greatly increased. On the contrary, those of Semisulcospira libertina and Semisulcospira forticosta of Mesogastropoda were greatly decreased. Dominant species was Baetis fuscatus of Ephemeroptera, numbers of species and individuals of Ephemeroptera, Plecoptera and Trichoptera(EPT group) were dramatically increased from 26 species, 110 individuals to 32 species, 365 individuals respectively. This suggests that the change of river bed and flow velocity due to heavy rain provided a suitable environment for the EPT group that preferred the rift of a stream. In the functional feeding group, only gathering collectors and filtering collectors were identified in autumn of 2017 because some functional groups preferentially adapted to the changed environment. The interspecific competition and environmental condition were the worst in autumn after heavy rain due to the increase individuals of some species. The ecological score of benthic macroinvertebrate community(ESB) was higher after the heavy rain than before. Results of the Group Pollution Index(GPI), Korean Saprobic Index(KSI) and Benthic Macroinvertebrate Index(BMI) were similar to those before and after heavy rainfall. Therefore, ESB was the most discriminating method for estimating the biological water quality in this study. Some species that are sensitive to water quality changes still appear or increase individuals in the area under investigation after the heavy rain. On the other hand, the individuals of some pollutant species decreased. This is thought to be because the habitat fluctuation caused by heavy rainfall has improved the water environment.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.4
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• pp.812-818
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• 2003

This paper presents a developed outside rotor type induction motor for the fan. Nearly all of the induction motors consist of two parts, rotor and stator, and the position of rotor is generally inside of stator. However, the rotor of the developed induction motor is located outside of stator. It is believed that the outside rotor type induction motor is suitable for the fan due to its large inertia, that is, it is considered that the change of air flow rate resulting from input power or load fluctuation is reduced. In this paper, the two tests which are suitable to obtain the electrical parameters of the outside rotor type induction motor were described, then various parameters of outside rotor type induction motor were measured. These are the locked rotor test and no load test. By using these tests, it was possible to determine the parameters which are presented in the steady-state equivalent-circuit of the outside rotor type induction motor. Load test of induction motor was carried out using a dynamometer and the torque-speed curve was obtained. It is believed that the results of this paper can be used for the development of the outside rotor type induction motor.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.10
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• pp.859-864
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• 2014

This experimental study investigates the effects of a downstream cylinder in the wake change on upstream object's diameter. A V-shaped object is placed in the upstream of the test section and a circular cylinder containing a load-cell is placed in the downstream. The velocity distribution of the wake generated from the upstream object with a change in its diameter is investigated. Further, the fluctuation in the lift coefficient and Karman-vortex emission frequency with a change in the position of the downstream cylinder is examined. The study results reveal the following. i) The flow velocity in the wake is smaller than that in the main stream. ii) The lock-in phenomenon occurs when the diameter of the upstream object is larger than that of the downstream cylinder. iii) To generate maximum fluctuating lift force of the downstream cylinder in the wake, the position of the downstream cylinder must be moved with changing diameter of the upstream object together.

• Journal of Korean Society of Steel Construction
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• v.9 no.2 s.31
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• pp.181-191
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• 1997

Before cables are constructed, tower of suspension bridge is behaved as a cantilever type. Buffeting occured by unsteady loading of the tower due to velocity fluctuation in the oncoming flow has a wind velocity consistent with fundamental frequency of the tower and may give rise to large response by the tower resonance. To reduce the dynamic response by buffeting, the behavior of tower with TMD(Tuned Mass Damper) has studied using finite element method in time domain. The buffeting was obtained by transforming the velocity spectrum in frequency domain to random variable in certain time domain. The most probable maximum displacement which can be occured during the time interval was obtained using peak factor. The optimum location for TMD installation and TMD specification were decided by parametric study. Also, the effect of vibration control about various wind velocity was studied by the TMD which has optimum specification and location.

• Journal of Soil and Groundwater Environment
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• v.21 no.6
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• pp.22-35
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• 2016

Global climate change could have an impact on hydrological process of a watershed and result in problems with future water supply by influencing the recharge process into the aquifer. This study aims to assess the change of groundwater recharge rate by climate change and to predict the sustainability of groundwater resource in Pyoseon watershed, Jeju Island. For the prediction, the groundwater recharge rate of the study area was estimated based on two future climate scenarios (RCP 4.5, RCP 8.5) by using the Soil Water Balance (SWB) computer code. The calculated groundwater recharge rate was used for groundwater flow simulation and the change of groundwater level according to the climate change was predicted using a numerical simulation program (FEFLOW 6.1). The average recharge rate from 2020 to 2100 was predicted to decrease by 10~12% compared to the current situation (1990~2015) while the evapotranspiration and the direct runoff rate would increase at both climate scenarios. The decrease in groundwater recharge rate due to the climate change results in the decline of groundwater level. In some monitoring wells, the predicted mean groundwater level at the year of the lowest water level was estimated to be lower by 60~70 m than the current situation. The model also predicted that temporal fluctuation of groundwater recharge, runoff and evapotranspiration would become more severe as a result of climate change, making the sustainable management of water resource more challenging in the future. Our study results demonstrate that the future availability of water resources highly depends on climate change. Thus, intensive studies on climate changes and water resources should be performed based on the sufficient data, advanced climate change scenarios, and improved modeling methodology.

• Korean Journal of Environmental Biology
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• v.37 no.3
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• pp.317-334
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• 2019

The present study was conducted to investigate the differences in managed farming practices, including low-intensive farming, duck farming, and golden apple snail farming, in a rice ecosystem by comparing terrestrial arthropod communities. A total of 75 species from 70 genera belonging to 43 families in 11 orders were identified from 9,622 collected arthropods. Araneae, Hemiptera, and Coleoptera were the richest taxa. Collembola was the most abundant, followed by Diptera, Hemiptera, and Araneae. Bray-Curtis similarity among the farming practices was very high (76.7%). The biodiversity of each farming practice showed a similar seasonality pattern. The richest species group was the predators, followed by the herbivores. The species richness and diversity of ecologically functional groups among the farming practices were not statistically significant, except for the abundance of predators in golden apple snail farming. The biodiversity seasonality of ecological functional groups in each farming practice showed similar patterns. The biomass of Araneae, Hemiptera, Coleoptera, and Diptera was greater than the other taxa, in general. The biomass of each ecological functional group showed little difference and the biomass fluctuation patterns in each farming practice were almost the same. Collectively, the community structures and biodiversity of terrestrial arthropods among the farming practices in the present study were not different. The present study may contribute to sustain rich biodiversity in irrigated rice fields and to advanced studies of food webs or energy flow structures in rice fields for ecological and sustainable agriculture.

• Journal of Soil and Groundwater Environment
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• v.16 no.2
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• pp.61-76
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• 2011

This study was objected to provide suggestions for best management practices to restore the cultural and historical values of the wells in Palaces as well as their water qualities. Water resources in the five Palaces in Seoul Metropolitan, including Gyeongbokgung, Changdeokgung, Changgyeonggung, Jongmyo Shrine, and Deoksugung, were surveyed for their physical flows and chemical compositions from April to July in 2010. Ground waters in most wells were found at depths within 5 m from the ground surface, showing typical water-table aquifer systems. Hydraulic gradients indicate water resources in Gyeongbokgung, Changdeokgung, and Changgyeonggung flowing toward south, and toward east in Deoksugung area. Especially, water-level fluctuation data at S-10 in Deoksugung implied the influence of groundwater discharge facility. In Jongmyo Shrine, water was not detected in wells, indicating the water level was lower than the well depth. Based on the water chemistry and stable isotope analyses, water resources and their qualities appeared to be formed by the water-rock interaction along the groundwater paths. S-10 (Deoksugung) and S-14 (Changgyeonggung) samples were contaminated with nitrate ($NO_3$) in levels of higher than Korean drinking water standard, 10 mg/L as $NO_3$-N, but once in four sampling campaigns. In the situation that water resources in Palaces still maintain natural characteristics, the materials that will be used for the restoration and improvement of the Palace water supplies should be carefully selected not to disturb the natural integrity. In addition, because the wells are located in the center of metropolitan area, a systematic monitoring should be applied to detect and to manage the potential impacts of underground construction and various pollution sources.