• Korean Journal of Ecology and Environment
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• v.43 no.2
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• pp.199-211
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• 2010

The objectives for this study were to evaluate spatial and temporal characteristics of water quality, based on long-term water quality monitoring data during 1993~2008. We found that physico-chemical and ecological conditions in the Daecheong Reservoir (DR) were modified by the construction of upper dam (i.e., Yongdam Reservoir). total phosphorus (TP), Secchi depth (SD), and chlorophyll-a (CHL) in the DR showed significant longitudinal decreases along the headwater-to-the downlake, indicating a large spatial variation, and this gradient was more intensified during the high-flow season (monsoon). Nutrient-rich water containing high nitrogen and phosphorus in the monsoon season (July~August) passed through the reservoir as a density current in the metalimnetic depth, and also high suspended solids increased in the metalimnetic depth, especially during the monsoon. According to the deviation analysis of Trophic State Index (TSI), >50% of TSI (CHL)-TSI (SD) and TSI (CHL)-TSI (TP) values were negatives, so that inorganic suspended solids (non-votatile solids) influenced the underwater light regime against phytoplankton growth. Also, ratios of CHL:TP after the dam construction evidently increased, compared to the values before the upper dam constructions, indicating a greater yield of phytoplankton in the unit phosphorus. Overall data showed that ecological and functional changes in Daecheong Reservoir occurred after the construction of upper dam (Yongdam Reservoir).

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1365-1369
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• 2010

본 연구에서는 자연하안 조성을 위한 공법 설계시 공법의 적용 위치, 규모, 제원 등을 선정하기 위한 수문학적 정보 및 하천의 수문학적 특성에 적합한 식생을 선정하기 위한 수심, 침수기간 정보를 제공하기 위한 기법을 제시하였다. 이를 위해 장기 유출모형인 SWAT 모형을 적용하였으며, 자연하안 조성 공법 중 하나인 방틀이 시험 적용된 평창강을 대상으로 수문학적 특성을 분석하기 위한 유황 분석을 실시하였다. 평창강의 상안미 수위관측소 상류부에 위치한 방틀 시험지점의 유황을 분석하기 위해 상안미 수위관측소 상류유역을 대상유역으로 하여 상안미 수위관측소의 관측유량과 비교를 통해 신뢰성 있는 검보정을 마친 모형을 이용, 1989년부터 2008년까지 20년간의 유출분석을 실시하였다. 모의된 20년간의 일유출자료를 토대로 방틀 시공 단면의 유황곡선을 도시하여 유량특성을 분석하였으며, 유량을 수심으로 환산하여 대상 단면의 침수기간별 수심분포를 산정하였다. 또한 대상 단면의 하안을 침수기간별로 구분하여 하안의 높이에 따라 적정한 식생의 종류를 선정할 수 있는 자료를 생성하였다. 이와 같은 정보의 제공은 공법 설계에 필수적으로서 본 해석기술의 주요한 성과 및 활용성이라고 판단된다.

• Korean Chemical Engineering Research
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• v.57 no.5
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• pp.735-742
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• 2019

In this work, the electrokinetic interactions between the undulated structure of an ion-selective membrane and electroconvective instability has been studied using numerical analysis. Using finite element method, electric field-ionic species transport-flow field were analyzed by fully-coupled manner. Through the numerical study, the Dukhin's mode as the mechanism of undulated surface for the electroconvective instability were proven. The Dukhin's mode which competes with Rubinstein's mode has roles of (i) decreasing transition voltage to overlimiting regime and (ii) non-linearly increasing of overlimiting current. Also, (iii) the mixing efficiency is enhanced by removal mechanism of high-frequency Fourier mode of the electroconvective instability. Conclusively, the undulated ion-selective surface would provide energy-efficient mechanism for ion-selective transport systems such as electrodialysis, electrochemical battery, etc.

• The Journal of Korean Physical Therapy
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• v.32 no.6
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• pp.383-387
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• 2020

Purpose: The purpose of the present study was to investigate the effects of a simultaneous dual-task and horse-riding simulator (HRS) training regime on pulmonary function and flexibility. Methods: Sixteen subjects were recruited and randomly allocated to two groups: a dual-task (DT) (n=8) or a single-task (ST) (n=8) training group. Flexibility and pulmonary function were assessed before and after HRS training. Both groups underwent HRS training for 4 weeks, 3 times/week in 15-minute training sessions. The ST group underwent HRS training and the DT group underwent dual-task HRS training, which consisted of throwing and catching a ball and ring catching while HRS training. Results: Training significantly increased flexibility and FVC (forced vital capacity) and FEV1 (forced expiratory volume in 1 second) in both groups (p<0.05), but FEV1/FVC and PEF (peak expiratory flow) were not significantly different after training in both groups (p>0.05). After the training, flexibility and FVC in the DT group were significantly greater than in the ST group (p<0.05), but FEV1, FEV1/FVC, and PEF were not significantly different (p>0.05). Conclusion: Simultaneous dual-task and HRS motor training improved flexibility, FVC, and FEV1, and our comparative analysis suggests that dual-task HRS training improved flexibility and FVC more than single-task training.

• Advances in aircraft and spacecraft science
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• v.10 no.5
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• pp.419-437
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• 2023

This paper presents the study of the effects of rigid-body motion simultaneously with the presence of the effects of temporal variation due to the existence of morphing speed on the aeroelastic stability of the two-stage telescopic wings, and hence this is the main novelty of this study. To this aim, Euler-Bernoulli beam theory is used to model the bending-torsional dynamics of the wing. The aerodynamic loads on the wing in an incompressible flow regime are determined by using Peters' unsteady aerodynamic model. The governing aeroelastic equations are discretized employing a finite element method based on the beam-rod model. The effects of rigid-body motion on the length-based stability of the wing are determined by checking the eigenvalues of system. The obtained results are compared with those available in the literature, and a good agreement is observed. Furthermore, the effects of different parameters of rigid-body such as the mass, radius of gyration, fuselage center of gravity distance from wing elastic axis on the aeroelastic stability are discussed. It is found that some parameters can cause unpredictable changes in the critical length and frequency. Also, paying attention to the fuselage parameters and how they affect stability is very important and will play a significant role in the design.

• Nuclear Engineering and Technology
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• v.35 no.5
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• pp.426-441
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• 2003

A reactor inlet header break experiment, B9401, performed in the RD-14M multi channel test facility was analyzed using RELAP5/MOD3.2 and RELAP5/CANDU[1]. The RELAP5 has been developed for the use in the analysis of the transient behavior of the pressurized water reactor. A recent study showed that the RELAP5 could be feasible even for the simulation of the thermal hydraulic behavior of CANDU reactors. However, some deficiencies in the prediction of fuel sheath temperature and transient behavior in athe headers were identified in the RELAP5 assessments. The RELAP5/CANDU has been developing to resolve the deficiencies in the RELAP5 and to improve the predictability of the thermal-hydraulic behaviors of the CANDU reactors. In the RELAP5/CANDU, critical heat flux model, horizontal flow regime map, heat transfer model in horizontal channel, etc. were modified or added to the RELAP5/MOD3.2. This study aims to identify the applicability of both codes, in particular, in the multi-channel simulation of the CANDU reactors. The RELAP5/MOD3.2 and the RELAP5/CANDU analyses demonstrate the code's capability to predict reasonably the major phenomena occurred during the transient. The thermal-hydraulic behaviors of both codes are almost identical, however, the RELAP5/CANDU predicts better the heater sheath temperature than the RELAP5/MOD3.2. Pressure differences between headers govern the flow characteristics through the heated sections, particularly after the ECI. In determining header pressure, there are many uncertainties arisen from the complicated effects including steady state pressure distribution. Therefore, it would be concluded that further works are required to reduce these uncertainties, and consequently predict appropriately thermal-hydraulic behaviors in the reactor coolant system during LOCA analyses.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.6
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• pp.399-406
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• 2013

In the present study, the flat plate model test method is developed to evaluate the skin friction of the marine coating in the cavitation tunnel. Six-component force balance is used to measure the profile drag of the flat plate and strut. LDV(laser Doppler velocimetry) technique is also employed to evaluate the drag and to figure out the reason of the drag reduction. The flow velocities above the surface can be used to assess the skin friction, combined with direct force measurement. Since the vortical structure in the coherent turbulence structure influences on the skin friction in the high Reynolds number regime, the interaction between the turbulence structure and the surface wall is paying more attention. This sort of thing is important in the passive control of the turbulent boundary layer because the skin friction can't be determined only by wall condition. As complicated flow phenomena exist around a paint film, systematic measurement and analysis are necessary to evaluate the skin friction appropriately.

• Nuclear Engineering and Technology
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• v.22 no.1
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• pp.12-19
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• 1990

The Loss of Offsite Power Transient at 77.5% power which occurred on June 9, 1981 at the Kori Unit 1 PWR (Pressurized Water Reactor) is simulated using the RELAP5/MOD2 system thermal-hydraulics computer code. Major thermal-hydraulic parameters are compared with the available plant data. The comparison of the analysis results with the plant data demonstrates that the RELAP5/MOD2 code has the capability to simulate the thermal-hydraulic behaviour of PWRs under accident conditions of this type with accuracy, except the pressurizer pressure and level. The pressurizer pressure increase is sensitive to the in surge now it is believed that the interracial heat transfer in a horizontal stratified flow regime may be estimated low and the compression effect due to insurge flow may be high. In the nodalization sensitivity study it is found that S/G noding with junctions between bypass plenum and steam dome is preferred to simulate the S/G water level decreasing and avoid the spurious level peak at trubine trip.

• Journal of Korea Water Resources Association
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• v.42 no.10
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• pp.773-783
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• 2009

The effects of rainfall input uncertainty on predictions of stream flow are studied based extended GLUE (Generalized Likelihood Uncertainty Estimation) approach. The uncertainty in the rainfall data is implemented by systematic/non-systematic rainfall measurement analysis in Weida catchment, Germany. PDM (Probability Distribution Model) rainfall runoff model is selected for hydrological representation of the catchment. Using general correction procedure and DUE(Data Uncertainty Engine), feasible rainfall time series are generated. These series are applied to PDM in MC(Monte Carlo) and GLUE method; Posterior distributions of the model parameters are examined and behavioural model parameters are selected for simplified GLUE prediction of stream flow. All predictions are combined to develop ensemble prediction and 90 percentile of ensemble prediction, which are used to show the effects of uncertainty sources of input data and model parameters. The results show acceptable performances in all flow regime, except underestimation of the peak flows. These results are not definite proof of the effects of rainfall uncertainty on parameter estimation; however, extended GLUE approach in this study is a potential method which can include major uncertainty in the rainfall-runoff modelling.

• Journal of the Korean Society of Safety
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• v.32 no.4
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• pp.34-39
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• 2017

Typical flow regime of overflow at barrier or weir constructed in mid and small streams becomes as the submerged flow during most flood events. One of major causes of barrier failure has been reported as the levee-scour near the conjuction node between barrier and levee. However, most related design guidelines in Korea have not mentioned about the protection of levee around barrier or weir in detail. Furthermore, most previous researches have focused on the flow characteristics of overflow around several types of weirs but they did not have considered the material properties of levee itself. In this study, local scour near barrier was investigated with different material properties of levee under the submerged overflow condition which is assumed to reenact a flood event. Based on results from Fritz et al. and Mavis et al., a theoretical formula was also proposed in initial stage of laboratory experiments. And hydraulic experiments were carried out for the verification of the proposed formula. Levee was installed in the prismetic trapezoidal open channel and most parts were made of concrete except for movable section in which scour was expected to occur for the efficiency of experimental procedure. Each compaction of movable section in levee was followed by the basis of the KS F 2312. Further, after performing the experiments to find the optimum water content for each sediment, the specific amount of water was injected before flowing water. The difference between the proposed theoretical formula and experiment results was not much but considerable, which might be caused by the effect of compaction. For theoretical approach, it seemed that the formula did not take into account the compaction of levee, thus the correction coefficient for levee compaction determined in the literature was considered. Finally, the formula for the length of scour around barrier or weir was proposed, which can be useful to predict a levee in the reference design of revetment in mid and small streams. As shortly future study, scour length of levee around barrier or weir under different flow conditions such as perfect overflow condition will be studied and it will be able to contribute to suggest the design formula or criteria under all overflow conditions near barrier or weir.