• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.764-771
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• 2010

The stability analysis method of an unsaturated slope considering the suction stress was performed on the infinite sand slope. During drying and wetting processes, the Soil-Water Characteristics Curve (SWCC) of the sand with the relative density of 75% was measured using the automated SWCC apparatus. Also, the Suction Stress Characteristics Curve (SSCC) was estimated. Based on these results, the stability analysis of an unsaturated infinite slope was carried out considering the slope angle, the weathering zone and the relative change in friction angle as a soil depth. According to the result of slope stability analysis, the safety factors of slope were less than 1 when the slope angles were more than $50^{\circ}$. The safety factors of slope tend to increase with increasing the depth from the ground surface. Especially, the safety factors have a tendency to increase and decrease above near the ground water level due to the suction stress. The maximum safety factor of slope in this analysis was occurred at the Air Entry Value (AEV) of drying process. The influence range of suction stress above the ground water level can be found out and can be defined as the funicular zone which means the metric suction range from the air entry point to the point of residual volumetric water content.

• Nuclear Engineering and Technology
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• v.48 no.6
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• pp.1321-1329
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• 2016

To get an insight into the operating characteristics of the passive residual heat removal system of molten salt reactors, a two-phase natural circulation test facility was constructed. The system consists of a boiling loop absorbing the heat from the drain tank, a condensing loop consuming the heat, and a steam drum. A steady-state experiment was carried out, in which the thimble temperature ranged from $450^{\circ}C$ to $700^{\circ}C$ and the system pressure was controlled at levels below 150 kPa. When reaching a steady state, the system was operated under saturated conditions. Some important parameters, including heat power, system resistance, and water level in the steam drum and water tank were investigated. The experimental results showed that the natural circulation system is feasible in removing the decay heat, even though some fluctuations may occur in the operation. The uneven temperature distribution in the water tank may be inevitable because convection occurs on the outside of the condensing tube besides boiling with decreasing the decay power. The instabilities in the natural circulation loop are sensitive to heat flux and system resistance rather than the water level in the steam drum and water tank. RELAP5 code shows reasonable results compared with experimental data.

• Korean Journal of Soil Science and Fertilizer
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• v.40 no.2
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• pp.164-171
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• 2007

This experiment was conducted to investigate heavy metal speciation and bioavailability from soil to the edible parts of water dropwort near industrial complex. The soils and water dropwort were collected from the paddies cultivating water dropwort(10 sites), stream sediments(5 sites), and background soils(3 sites) near industrial complex. The total concentrations of Cd Cu, and Ni were higher than those of permissible level for soil contamination(Cd 3, Cu 100, Ni $50mg\;kg^{-1}$ in soil) suggested by Kloke(1979). Dominant chemical forms of Cd in paddies cultivating water dropwort and stream sediments were exchangeable form(49.1-56.3%), and those of Cu, Zn, and Ni were Fe and Mn oxide bound and residual forms. The mobility factor of heavy metals in paddies cultivating water dropwort and stream sediments was in the order Cd>Zn>Ni>Cu>Pb, specially, the mobility factor of Cd (62-72%) were relatively higher than that of other metals in soils. The total concentrations of Cd in soils showed significant positive correlation with the ratios of exchangeable and Fe and Mn oxide bound forms, while correlated negatively with residual form. Heavy metal contents in root parts were higher than those in top parts of water dropwort. The bioavailability of water dropwort varied considerably between the different parts and heavy metals. Cd, Cu and Ni contents in water dropwort were correlated with each fractions in soils. Specially, the exchangeable form of Cd and Ni in soils showed significant positive correlation with the those contents of water dropwort.

• Environmental Analysis Health and Toxicology
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• v.12 no.3_4
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• pp.23-29
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• 1997

The main reason of applying chlorination is to sterilize microbes existing in the drinking water treatment. But chlorination could lead to the formation of disinfection by-products (DBPs) by the reaction of free chlorine with humic substance in the water. Especially the DBPs including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and haloketones (HKs) exist in the tap water. The US environmental protection agency (US EPA) defines that trihalomethanes, dichloroacetic acid, trichloroacetic acid, and dichloroacetonitrile among DBPs are probable/possible human carcinogens. US EPA suggests maximum contaminant levels (MCLs) for THMs (80$\mu$g/L) and HAAs (60$\mu$g/L) in drinking water. In Korea, THMs in drinking water has been surveyed but DBPs in general has not been studied in drinking water practically. Therefore only THMs have been regulating as criteria compounds since 1990 but neither HAAs nor HANs. Researches on HAAs are yet to be found. HAA formation potentials(HAAFPs) have not been practiced. HAAs depends on the characteristics of water sources by chlorination. In this study, HAAFPs from three distinct sources were investigated by laboratory chlorination experiments. This study was performed to measure the level of HAAs in drinking water in Seoul area. At April 1996, after collecting the raw waters from the three sites with the different properties, the water samples were chlorinated at various conditions(pH 5.5, pH 7.0 and without pH adjustment) in the state of raw water to have 0. 5mg/L of residual chlorine concentration. And the raw water, treated water, and tap water of water treatment were collected to measure the HAAs concentration. The quantitative analysis of HAAs was conducted by US EPA methods.

• Journal of Communications and Networks
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• v.18 no.6
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• pp.902-912
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• 2016

Recent advances in energy harvesting (EH) technology have motivated the adoption of rechargeable mobile devices for communications. In this paper, we consider a point-to-point (P2P) wireless communication system in which an EH transmitter with a non-ideal rechargeable battery is required to send a given fixed number of bits to the receiver before they expire according to a preset delay constraint. Due to the possible energy loss in the storage process, the harvest-use-and-store (HUS) architecture is adopted. We characterize the properties of the optimal solutions, for additive white Gaussian channels (AWGNs) and then block-fading channels, that maximize the energy efficiency (i.e., battery residual) subject to a given rate requirement. Interestingly, it is shown that the optimal solution has a water-filling interpretation with double thresholds and that both thresholds are monotonic. Based on this, we investigate the optimal double-threshold based allocation policy and devise an algorithm to achieve the solution. Numerical results are provided to validate the theoretical analysis and to compare the optimal solutions with existing schemes.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.2
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• pp.107-113
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• 2011

To evaluate the performance of the hydrodynamic model, we introduced 10 skill assessments that are assorted by two groups: quantitative skill assessments (Absolute Average Error or AAE, Root Mean Squared Error or RMSE, Relative Absolute Average Error or RAAE, Percentage Model Error or PME) and qualitative skill assessments (Correlation Coefficient or CC, Reliability Index or RI, Index of Agreement or IA, Modeling Efficiency or MEF, Cost Function or CF, Coefficient of Residual Mass or CRM). These skill assessments were applied and calculated to evaluate the hydrodynamic modeling at one of Florida estuaries for water level, current, and salinity as comparing measured and simulated values. We found that AAE, RMSE, RAAE, CC, IA, MEF, CF, and CRM are suitable for the error assessment of water level and current, and AAE, RMSE, RAAE, PME, CC, RI, IA, CF, and CRM are good at the salinity error assessment. Quantitative and qualitative skill assessments showed the similar trend in terms of the classification for good and bad performance of model. Furthermore, this paper suggested the criteria of the "good" model performance for water level, current, and salinity. The criteria are RAAE < 10%, CC > 0.95, IA > 0.98, MEF > 0.93, CF < 0.21 for water level, RAAE < 20%, CC > 0.7, IA > 0.8, MEF > 0.5, CF < 0.5 for current, and RAAE < 10%, PME < 10%, CC > 0.9, RI < 1.15, CF < 0.1 for salinity.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.12
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• pp.1305-1310
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• 2005

As a way to the optimum design of the collector well lateral in riverbed filtration, experiments were performed using sand tanks which were connected to form a model lateral system. Measured were the residual hydraulic heads along the laterals, the discharge rates at each sand tank and the production rates at the collector well while the model laterals were operated with various scenarios of changing parameters including water level of the collector well, the lateral diameter and length, and the hydraulic conductivity of the sand. Results showed that riverbed filtration could be more efficient when the resistance in the lateral was weak compared with the resistance in the sand, which was indicated by the more flattened distribution of the residual hydraulic heads along the lateral. Results also showed that the discharge rate increased exponentially with the approach to the collector well, and that the exponent increased as the lateral diameter decreased and/or the hydraulic conductivity of the sand increased. It was also seen that the well production increased with the increase in the lateral length and diameter although the marginal productivity decreased. It could be concluded that the axial flow velocity in the lateral was an important factor governing the efficiency of a lateral in riverbed filtration and that the maximum entrance velocity to the collector well, over which the efficiency decreased drastically, was about 1 m/sec under the conditions of this study.

• Journal of the Geological Society of Korea
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• v.54 no.5
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• pp.529-544
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• 2018

Dongrae hot spring belongs to the residual magma type and has a long history of bathing since the Silla dynasty in Korea. Due to long development of hot spring water, it is expected that the amount of hot spring water in Dongrae hot spring has been changed. In this study, long-trem water level data of Dongrae hot spring were examined for recognizing the change of the hot spring. By the fluctuation analysis of the hot spring water level from January 1992 to July 2018, the maximum and minimum annual drawdowns of no. 27 well were 137.70 and 71.60 meters, respectively, with an average drawdown of 103.39 m. On the other hand, the maximum and minimum annual drawdowns of no. 29 well were 137.80 and 71.70 meters, with an average drawdown of 103.49 m. Besides, drawdown rate became bigger in recent years. As a result of analyzing autocorrelation of the two wells, the correlation coefficient ranged from 0.919 to 0.991, showing seasonal groundwater level fluctuation. The cross correlation analysis between water level and precipitation as well as water level and hot spring discharge resulted in the correlation coefficients of -0.280 ~ 0.256 and 0.428 ~ 0.553, respectively. Therefore, using Dongnae hot-spring water level data from 1992 to 2018, the Mann-Kendall test and Sen's test showed that the continuous decline of water level was mainly caused by the pumping of the hot spring water among various reasons.

• Journal of Environmental Health Sciences
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• v.20 no.1
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• pp.54-61
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• 1994

This study was carried out to investigate the degree of contamination in private-drinking water supply (PDWS) and simple-piped water supply (SPWS), and to compare of water quality between them for 3 years from 1990 to 1992. The results of the study were as follows: 1. Private-drinking water supply (PDWS) (1) Field-Site (ㄱ) The items which were very significantly over the criteria (p<0.01), were temp., pH, NO-N, standard plate count (S.P.C.) and Coliform. (ㄴ) No. of households which were over the criteria, were 11.2~51.7% in temp., pH, NH$_3$-N and NO$_2$-N, and 83.1~93.3% in NO-N, S.P.C. and Coliform. (2) Moutain-Site (ㄱ) The items which were over the criteria, were NO$_2$-N (p<0.05), S.P.C. (p<0.01) and Coliform (p<0.01). (ㄴ) No. of households which were over the criteria, were 33.6 ~ 75.6% in NO$_2$-N, S.P.C. and Coliform. (3) No. of households which were fit to the criteria of all items, were 9.0% in field-site and 14.1% in mountain-site. 2. Simple-piped water supply (SPWS) (1) The items which were very significantly over the critera (p<0.01), were standard plate count (S.P.C.) and Coliform. (2) The water qualities of adjacent and remote samples were better than those of source samples. (3) Residual chloride was not detected in any sample. In conclusion, rural community requires to be continually performed the policy of safety drinking water supply, and to be devised an epoch-making counterplan for the level-up of simple-piped water supply (SPWS), espically on the method of disinfection.

• Journal of the Korean GEO-environmental Society
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• v.2 no.1
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• pp.81-89
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• 2001

Soil-bentonite mixture is often used for barrier wall to prevent seawater intrusion. In this study, the effect of seawater on the permeability of soil-bentonite mixture is examined, and the effect of permeability change on the seawater intrusion is investigated. Seawater intrusion in coastal areas was modeled using a finite element method. Seawater intrusion in the seawater-contaminated zone was determined by considering the hydraulic conductivity changes using the residual flow procedure (RFP) in the simulation model. Steady state and unsteady state conditions with variations in ground water levels in an inland area were investigated. The interface between fresh water and seawater, found by the proposed method, was located lower at the seawater side and the level at the fresh water side is higher than those by conventional methods.