• Journal of the Korean Society for Railway
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• v.18 no.5
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• pp.466-470
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• 2015

In this study, Fenton oxidation was applied to railroad track ballasts contaminated with small amounts of oil. In order to perform the experiment on Fenton oxidation, petroleum contaminated ballast was collected from the railroad track and experiments on major factors of the remediation process were implemented in the laboratory. Then, the feasibility of insitu Fenton oxidation was investigated for the railroad track that was partially contaminated with oil. As a result, the residual TPH concentration of ballast was reduced to about 1,000 mg/kg-ballast in laboratory experiments using 0.1 mol Fe/L $H_2O_2$. Due to the drainage structure of the track bed, a considerable amount of $H_2O_2$ was released below the ballast without the sufficient reaction with the contaminated ballast; therefore, additional studies are necessary for the effective field application of Fenton oxidation.

• Applied Chemistry for Engineering
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• v.30 no.1
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• pp.95-101
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• 2019

The cremation rate of Korea in 2016 was 82.7% which is four times greater than 20.5% in 1994. As increasing the cremation rate gradually, it cause a shortage of cremation facilities resulting in building more cremation facilities to meet the increasing inquiries on cremation or a large amount of fuels for the longer operation of the crematory. In this study, the crematory system optimizing its thermal efficiency characteristics and also responding to increasing inquiries on cremation was proposed in order for solving such problems, In particular, the heat flow characteristics including a heat transfer coefficient by performing a simulation using computational fluid dynamics (CFD) was investigated. The CFD model was validated with on-site experiments for a cremation facility. As a result of the simulation, the fuel consumption decreased nearly 25% and residence time increased in the main combustor. Also, the improved crematory was constructed with an expanded combustor, heat exchanger, second combustion air system, refractory and insulation material. From on-site experiments, the energy consumption was saved to approximately 54.4%, while the burning time reduced nearly 20 minutes.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.1
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• pp.123-136
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• 2018

The objective of this study is to propose a new methodology to fabricate a reliable engineering-scale buffer block, which shows homogeneous and uniform distribution in buffer block density, for in-situ experiments. In this study, for the first time in Korea, floating die press and CIP (Cold Isostatic Press) are applied for the manufacture of an engineering-scale bentonite buffer. The optimized condition and field applicability are also evaluated with respect to the method of manufacturing the buffer blocks. It is found that the standard deviation of the densities obtained decreases noticeably and that the average dry density increases slightly. In addition, buffer size is reduced by about 5% at the same time. Through the test production, it is indicated that the stress release phenomenon decreases after the application of the CIP method, which leads to a reduction in crack generation on the surface of the buffer blocks over time. Therefore, it is confirmed that the production of homogeneous buffer blocks on industrial scale is possible using the method suggested in this study, and that the produced blocks also meet the design conditions for dry density of buffer blocks in the AKRS (Advanced Korea Reference Disposal System of HLW).

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.143-148
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• 2005

The main purpose of this study is to suggest and evaluate an operational method for assessing the potential impact of climate change on hydrologic components and water resources of regional scale river basins. The method, which uses large scale climate change information provided by a state of the art general circulation model(GCM) comprises a statistical downscaling approach and a spatially distributed hydrological model applied to a river basin located in Korea. First, we construct global climate change scenarios using the YONU GCM control run and transient experiments, then transform the YONU GCM grid-box predictions with coarse resolution of climate change into the site-specific values by statistical downscaling techniques. The values are used to modify the parameters of the stochastic weather generator model for the simulation of the site-specific daily weather time series. The weather series fed into a semi-distributed hydrological model called SLURP to simulate the streamflows associated with other water resources for the condition of $2CO_2$. This approach is applied to the Yongdam dam basin in southern part of Korea. The results show that under the condition of $2CO_2$, about $7.6\% of annual mean streamflow is reduced when it is compared with the observed one. And while Seasonal streamflows in the winter and autumn are increased, a streamflow in the summer is decreased. However, the seasonality of the simulated series is similar to the observed pattern and the analysis of the duration cure shows the mean of averaged low flow is increased while the averaged wet and normal flow are decreased for the climate change.

• Journal of the Korean earth science society
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• v.34 no.1
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• pp.51-58
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• 2013

An appropriate determination of time step is one of the important problems in atmospheric modeling. In this study, we investigate the sensitivity of numerical solutions to time step in a nonlinear atmospheric model. For this purpose, a simple nondimensional dynamical model is employed, and numerical experiments are performed with various time steps and nonlinearity factors. Results show that numerical solutions are not sensitive to time step when the nonlinearity factor is not influentially large and truncation error is negligible. On the other hand, when the nonlinearity factor is large (i.e., in a highly nonlinear regime), numerical solutions are found to be sensitive to time step. In this situation, smaller time step increases the intensity of the spatial filter, which makes small-scale phenomena weaken. This conflicts with the fact that smaller time step generally results in more accurate numerical solutions owing to reduced truncation error. This conflict is inevitable because the spatial filter is necessary to stabilize the numerical solutions of the nonlinear model.

• 한국가시화정보학회:학술대회논문집
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• 2007.11a
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• pp.134-137
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• 2007

The temporal evolution of wake behind a circular cylinder oscillating rotationally with a relatively high forcing frequency has been investigated experimentally using a dynamic PIV technique. Experiments were carried out with varying the frequency ratio $F_R\;(=f_f/f_n)$ in the range from 0.0 (stationary) to 1.6 at oscillation amplitude of ${\theta}_A=30^{\circ}$ and Reynolds number of $Re=4.14{\times}10^3$. Depending on the forcing condition ($F_R$), the flow was divided into three regimes; non-lock-on ($F_R=0.4$), transition ($F_R=0.8$, 1.6) and lock-on regimes ($F_R=1.0$) with markedly different flow structure in the near-wake region behind the cylinder. When the frequency ratio was less than 1.0 ($F_R{\le}1.0$), the rotational oscillatory motion of the cylinder decreased the length of the vortex formation region and enhanced the mutual interaction between large-scale vortices across the wake centerline. The entrainment of ambient fluid seemed to play an important role in controlling the near-wake flow and shear-layer instability. However, the flow characteristics changed markedly beyond the lock-on flow regime ($F_R=1.0$) due to high-frequency forcing. At $F_R=1.6$, the mutual interactions between the vortices shed from both sides of the cylinder were not so strong. Thereby, the flow entrainment and momentum transfer into the wake center region were reduced. In addition, the size of the large-scale vortices decreased since the lateral extent of the wake was suppressed.

• Journal of Soil and Groundwater Environment
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• v.21 no.3
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• pp.35-48
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• 2016

A micromodel was applied to estimate the effects of geological conditions and injection methods on displacement of resident porewater by injecting scCO₂ in the pore scale. Binary images from image analysis were used to distinguish scCO₂-filled-pores from other pore structure. CO₂ flooding followed by porewater displacement, fingering migration, preferential flow and bypassing were observed during scCO₂ injection experiments. Effects of pressure, temperature, salinity, flow rate, and injection methods on storage efficiency in micromodels were represented and examined in terms of areal displacement efficiency. The measurements revealed that the areal displacement efficiency at equilibrium decreases as the salinity increases, whereas it increases as the pressure and temperature increases. It may result from that the overburden pressure and porewater salinity can affect the CO₂ solubility in water and the hydrophilicity of silica surfaces, while the neighboring temperature has a significant effect on viscosity of scCO₂. Increased flow rate could create more preferential flow paths and decrease the areal displacement efficiency. Compared to the continuous injection of scCO₂, the pulse-type injection reduced the probability for occurrence of fingering, subsequently preferential flow paths, and recorded higher areal displacement efficiency. More detailed explanation may need further studies based on closer experimental observations.

• The Journal of the Acoustical Society of Korea
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• v.24 no.3
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• pp.171-177
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• 2005

The effect of diffusers on Early Stage Support (ST1) in a concert hall was investigated at 8 positions in a 1:25 stage scale model. Experiments were carried out when the stage floor was covered with and without absorption cloth to investigate the effect of stage floor reflection (absorption coefficient - 0.6 at 500Hz). To find out the effect of stage wall. three types of wall diffusers were used. As a result. absorption cloth on stage floor reduced the ST1 values at high frequency. but the average value of ST1 was not changed. Three types of stage wall diffusers were revealed as unaffecting. but it was observed that the ST1 values varied to positions of stage. The ST1 values were evenly distributed when hemisphere diffusers were used. Therefore. the use of floor absorption did not have much effect on the ST1 values, and the diffusers had some effect on the distribution of the ST1 values.

• Resources Recycling
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• v.14 no.2
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• pp.28-32
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• 2005

By using thermal decomposition method, the preliminary experiments for recovery of metallic Ga from GaAs scraps produced in the manufacturing of compound semiconductors were carried out in laboratory(200 g/batch) scales. From these results, decomposition appratus with packed tower was constructed in commercial scale(30 kg/batch). The decomposition rate of GaAs increased with raising decomposition temperature, but the yield of Ga decreased over 1000$^{\circ}C. As a result, the optimum decomposition temperature was 1000~1050$^{\circ}C when the pressure of decomposition reactor was 2~2.5${\times}10^{-2} mmHg, and the yield of Ga was about 89 wt.%. The commercial decomposition apparatus was designed with packed tower because the partial pressure of As in vapor state was not reduced even if the temperature of As vapor was decreased. The recovery yield of Ga from GaAs scraps in large scale experiment showed 99%.

• Fire Science and Engineering
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• v.20 no.4 s.64
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• pp.58-64
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• 2006

Smoke extraction in tunnel fire is investigated experimently with thermal model. The object is a immersed tunnel, of which the partial extraction system exists between the tubes. The model tunnel is measured 12 m long, 0.5 m wide and 0.35 m high. The fire is simulated to pool fire and the size corresponds to full scale fire of 5 MW based on Froude modeling. The performance of partial extraction system is determined under two ventilations, natural and longitudinal ones. The results show that compared with longitudinal ventilation, the smoke extraction efficiency of natural ventilation is increased about 30% because of smoke stratification in tunnel. Also the efficiency is identical to the iso-thermal model. The results will be help for activation of the ventilation system in emergency such as in the event of tunnel fires.