• ETRI Journal
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• v.36 no.3
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• pp.396-406
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• 2014

We have designed and investigated a new congestion control scheme, called optimal and fully explicit (OFEX) controller. Different from existing relatively explicit controllers, this new scheme can provide not only optimal bandwidth allocation but also a fully explicit congestion signal to sources. It uses the congestion signal from the most congested link instead of the cumulative signal from the flow path. In this way, it overcomes the drawback of relatively explicit controllers exhibiting bias toward multi-bottlenecked users and significantly improves their convergence speed and source throughput performance. Furthermore, our OFEX-controller design considers a dynamic model by proposing a remedial measure against the unpredictable bandwidth changes in contention-based multi-access networks. Compared with former works/controllers, this remedy also effectively reduces the instantaneous queue size in a router and thus significantly improves queuing delay and packet loss performance. We have evaluated the effectiveness of the OFEX controller in OPNET. The experimental comparison with the existing relatively explicit controllers verifies the superiority of our new scheme.

• Proceedings of the Korean System Dynamics Society
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• 2004.08a
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• pp.31-51
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• 2004

본 연구에서는 원자력 발전산업의 효율적인 기술개발 전략 수립을 지원하기 위한 모델을 System Dynamics 방법론을 사용하여 개발하였다. 이를 위하여 우선 원자력 발전산업의 기술경쟁력 평가를 위한 변수 및 평가범위를 선정하고, 선정된 변수들의 인과관계를 정성적으로 평가할수 있도록 인과지도(Casual Loop Diagram)를 개발하였으며, 이를 정량화하여 평가할 수 있도록 흐름도(Stock Flow Diagram)를 개발하였다. 개발된 모델을 사용하여 총 연구비 등의 정책관련 변수들을 변화시키면서 시뮬레이션을 수행해보았다. 본 연구의 한 결과로서 기준 시나리오에 대한 분석 결과 2004년 이후의 원자력발전산업 순편익 누적 결과는 다음과 같다. 또한 시나리오별 비교평가를 실시하여 본 결과, 본 연구에서 정의한 순편익 누적(Cumulative Net Profit) 변수를 적용하면 현재 연구비 추세 대비 30% 까지 연구비를 증가시키는 것이 효율적임을 알 수 있었다.

• Tunnel and Underground Space
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• v.12 no.3
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• pp.198-209
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• 2002

To assess deep geological environment for the research and development of hish-level radioactive waste disposal, six boreholes of 3" in diameter were installed in two granitic areas. An areal extent of the rock block scale in the study sites was estimated by the lineament analysis from satellite images and shaded relief maps. The characterization of fracture system developed in rock block scale was carried out based on the acoustic televiewer logging in deep boreholes. In the Yuseong site, the granite rock mass was divided into the upper and lower zones at around -160m based on the probabilistic distribution characteristics of the geometric parameters such as orientation, fracture frequency, spacing and aperture size. Since the groundwater flow is dependent on the fracture system in a fractured rock mass, the correlation of the fracture frequency and cumulative aperture size to the hydraulic conductivity was also discussed.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.786-789
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• 2002

A recurrent artificial neural network (ANN) model is developed to simulate hydrocarbon recovery process at petroleum-contaminated site. The groundwater extraction rate, vacuum pressure, and saturation hydraulic conductivity are selected as the input variables, while the cumulative hydrocarbon recovery volume is considered as the output variable. The experimental data fer establishing the ANN model are from implementation of a multiphase flow model for dual phase remediation process under different input variable conditions. The complex nonlinear and dynamic relationship between input and output data sets are then identified through the developed ANN model. Reasonable agreements between modeling results and experimental data are observed, which reveals high effectiveness and efficiency of the neural network approach in modeling complex hydrocarbon recovery behavior.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.09a
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• pp.203-206
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• 2004

To analysis the electrokinetic phenomena in the ground dependent on the way of applied electric power, such as constant current and constant voltage, the governing equations are derived considering advection, diffusion, ionmigration, and then they were formulated using by finite difference method. The developed program is verified by comparing the tested and predicted results reported in present papers. The results indicate that the slightly small electrical potential is predicted for constant current and for constant voltage pH near to the cathode was small than the test results. But the other predictions including the final suction, pH of electrolyte and cumulative flow are similar to the test results and predictions.

• Journal of Korean Society on Water Environment
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• v.21 no.2
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• pp.184-189
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• 2005

Impacts of non-point source pollution on water quality are well known. In this paper, effects of land use, precipitation characteristics, discharge characteristics on non-point source pollutant loadings at urban, agricultural and forestry watersheds were discussed. Rainfall runoffs from fifteen rainfall events were sampled and analysed at two urban watersheds, one rural watershed, and one forestry watershed. EMCs (Event Mean Concentration) were calculated based on monitored flow rates and concentrations. Statistical analysis carried out with runoff loadings and affecting variables indicated that runoff loadings are weakly correlated with the rainfall intensity and the dry days before rainfall events while showed no correlations with rainfall depth nor runoff quantity. By comparing EMCs between study watersheds on log-normal cumulative probability scale, EMCs ranking were in the descending order of urban watershed>agricultural watershed>forestry watershed for SS, TCOD, TN, and TP.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.1
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• pp.111-117
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• 2015

We investigate the influence of spatial rainfall distribution on hillslope soil erosion through laboratory experiments. Two distinct spatial distributions are examined in this study, i.e., rainfall concentrated on central area versus upper area of hillslope. During the entire period of 8 hours for each experiment, direct runoff, subsurface flow, and sediment yield are measured at high temporal resolution (10 minutes). Compared to the case that rainfalll concentrated on central area, upstream concentrated rainfall results in lower peak of the sediment yield curve while greater cumulative sediment yield. Cumulative sediment yield increases over time linearly but its growth rate shows a sudden decrease at around 2 hours. This should be taken into consideration when temporal variability of sediment yield is estimated from observed total amount, and demonstrates the necessity of measuring sediment yield at high temporal resolution.

• Agricultural and Biosystems Engineering
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• v.3 no.2
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• pp.59-64
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• 2002

Odor generated during composting of livestock manure is mainly due to ammonia emission. Biofiltration is a desirable method to control composting odor. This study was conducted to analyze the efficiency of using fresh compost as a biofilter. A mixture of cattle manure and recycled compost was composted in a bin equipped with a suction-type blower. The exhaust gas was filtered through the fresh compost. Residence time was controlled by the flow rate of exhaust gas and the depth of filtering materials. At the aeration rate of 30 L/min(experiment I), ammonia reduction rate varied from 100% to -15% for biofilter A(residence time 56.5 s) and almost 100% for biofilter B(residence time 113 s). At the aeration rate of 30 L/min, the cumulative ammonia reduction rate was 80.5% for biofilter A and 99.9% for biofilter B. At the aeration rate of 50 L/min(experiment II), the lowest reduction rate showed a negative value of -350% on the 8th and 9th day for biofilter A(residence time 33.9 5), and 50% on the loth day for biofilter B(residence time 67.8s). At the aeration rate of 50 L/min, the cumulative ammonia reduction rate was 82.5% fur biofilter A and 97.4% for biofilter B. Filtering efficiency was influenced by residence time. The moisture content(MC) and total nitrogen(T-N) of the filtering material were increased by absorbing moisture and ammonia included in the exhaust gas, while pH was decreased and total carbon(T-C) remained unchanged during the filtering operation.

• Journal of Wetlands Research
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• v.19 no.3
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• pp.287-295
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• 2017

In this study, rainfall runoff characteristics according to peak concentration were analyzed using the water quality and flow data in the Geumho river, and the direction of nonpoint source management such as monitoring and management period by pollution source was derived. Peak Water Quality Concentration is the concept that utilizes the extreme value as the concentration of non-point pollution control standard with the highest water quality in the rainwater runoff. Using this method, the evaluation factors such as cumulative precipitation(total precipitation), peak water quality concentration, cumulative precipitation up to peak water quality concentration, time to peak water quality concentration, and EMC to peak water quality concentration were examined and long- Rainfall runoff characteristics of nonpoint sources were analyzed. The results of the analysis suggested proper monitoring and management method to manage nonpoint source.

• Journal of Korean Society on Water Environment
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• v.33 no.5
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• pp.572-579
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• 2017

Increased impervious surface caused by rapid urbanization serves to produce the discharge of non-point source pollutants such as total suspended solid (TSS). There exist various methods of removing TSS, including a filtration process using granular media (a well-known method to be practically used after the consideration of removal efficiency, clogging, and backwashing efficiency). To determine the TSS removal capability of the filter, we initially performed lab-scale experiments which assessed flow rates, influent concentrations, permeability co-efficients, the particular shapes of suspended solids and potential clogging, and also evaluated TSS removal efficiency when applied to filtration facility in a pilot-scale. In low filtration flux condition, the removal efficiency of suspended solids was more than 95 %, while decreased to 83% in high filtration flux. Regarding the clogging aspect of the experiment, total cumulative solids were loaded up to $19.15kg/m^2$, and TSS removal efficiency was noted to commence to decrease when the loaded solids exceeded $9.0kg/m^2$. It was also noted, however, that superior efficiency was maintained for six hours. In addition, for pilot-scale experiment, the removal efficiency was still high enough (83.4 %) for the solid concentration of 140 ~ 343 mg SS/L and after backwashing, head loss was recovered to 92 ~ 95 % during two hour filtration. With these results, It was confirmed that lifetime of the filter applied to the test was prolonged due to the high treatment efficiency and good backwashing efficiency for the cumulative solids load.