• The Journal of Engineering Geology
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• v.6 no.2
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• pp.83-93
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• 1996

A method is proposed to estimate aquifer parameters in a heterogeneous and anisotropic aquifer under steady-state groundwater flow conditions on the basis of maximum likelihood concept. Zonation method is adopted for parameterization, and estimation errors are analyzed by examining the estimation error covariance matrix in the eigenspace. This study demonstrates the ability of the proposed model to estimate parameters and helps to understand the characteristics of the inverse problem. This study also explores various features of the inverse methodology by applying it to a set of field data of the Taegu area. In the field example, transmissivities were estimated under three different zonation patterns. Recharge rates in the Taegu area were also estimated using MODINV which is an inverse model compatible with MODFLOW.The estimation results indicate that anisotropy of aquifer parameters should be considered for the crystalline rock aquifer which is the dominant aquifer system in Korea.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.9 no.3
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• pp.125-131
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• 1997

In order to analyze the feasibility of the drain layer construction method, which is one of the beach protection methods, a hybrid model is constructed by combining the wave model and the seepage flow model. The used wave model is the analytic solution given by Shuto (1972). and the seepage flow model is used by Richards equation which governs the saturated-unsaturated flow in the porous media. It is concluded by the sensitivity analysis of the hybrid model that the most sensitive parameter in the flow field within the beach is the saturated hydraulic conductivity. The developed hybrid model will be efficiently used in the analysis of the parameter when the drain layers are constructed in the beach, if the field datas are obtained more.

• Nuclear Engineering and Technology
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• v.50 no.1
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• pp.97-106
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• 2018

Improved load-following capability is one of the most important technical tasks of a pressurized water reactor. Controlling the nuclear reactor core during load-following operation leads to some difficulties. These difficulties mainly arise from nuclear reactor core limitations in local power peaking: the core is subjected to sharp and large variation of local power density during transients. Axial offset (AO) is the parameter usually used to represent the core power peaking. One of the important local power peaking components in nuclear reactors is axial power peaking, which continuously changes. The main challenge of nuclear reactor control during load-following operation is to maintain the AO within acceptable limits, at a certain reference target value. This article proposes a new robust approach to AO control of pressurized water reactors during load-following operation. This method uses robust feedback-linearization control based on the multipoint kinetics reactor model (neutronic and thermal-hydraulic). In this model, the reactor core is divided into four nodes along the reactor axis. Simulation results show that this method improves the reactor load-following capability in the presence of parameter uncertainty and disturbances and can use optimum control rod groups to maneuver with variable overlapping.

• Proceedings of the Korean Reliability Society Conference
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• 2006.05a
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• pp.93-100
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• 2006

The failure of hydraulic hose assemblies is caused by the impulse pressure and repetitive motions of bending and stretching (flexing) used at high pressure pipe in the form of bursting Since it takes long time to observe the bursting for life analysis, we can reduce test time by the method of applying the Knockdown stress which is equivalent to 70% of initial bursting pressure on rubber hose assemblies with maintaining the failure mode equally In this study, after scale parameter, shape parameter, and acceleration factor by preforming the impulse pressure test until the hose bursts, and finally analyzed the accelerated life.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.2
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• pp.17-25
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• 2013

Performance of DI diesel engine with high fuel injection method is directly related to the emission characteristics and fuel consumption. At present, diesel injection system with piezo element is replacing conventional solenoid type due to their faster electro-mechanical properties. In this study, it was investigated the sensitivity characteristics regarding internal hydraulic modeling based on the AMESim environment of piezo-driven injector The analytic parameter for this study defined such as In/Out orifice, injection hole's diameter and driven voltage on piezo stack. As the results, it was shown that these parameter influence on a fast response characteristics of piezo-driven injector. Also we found fuel pressure recovery time is faster about 0.1 ms due to larger IN orifice diameter. And larger OUT orifice diameter occurs maximum pressure drop with faster its timing of about 0.2 ms.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2821-2835
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• 2020

The phenomenon identification and ranking table (PIRT) is an important basis in the nuclear power plant (NPP) thermal-hydraulic analysis. This study focuses on the importance ranking of the input parameters when lacking the PIRT, and the target scenario is the small break loss of coolant accident (SBLOCA) in a pressurized water reactor (PWR) CPR1000. A total of 54 input parameters which might have influence on the figure of merit (FOM) were identified, and the sensitivity measure of each input on the FOM was calculated through an optimized moment-independent global sensitivity analysis method. The importance ranking orders of the parameters were transformed into the Savage scores, and the parameters were categorized based on the Savage scores. A parameter importance ranking table for the SBLOCA scenario of the CPR1000 reactor was obtained, and the influences of some important parameters at different break sizes and different accident stages were analyzed.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.287-287
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• 2023

Surface water-groundwater interaction (SWGI) is an important hydrological process that influences both the quantity and quality of water resources. However, regional scale SWGI model calibration and uncertainty analysis have been a challenge because integrated models inherently carry a vast number of parameters, modeling assumptions, and inputs, potentially leaving little time and budget to explore questions related to model performance and forecasting. In this study, we have proposed the application of iterative ensemble smoother (IES) for uncertainty analysis and calibration of the widely used integrated surface-subsurface model, SWAT-MODFLOW. SWAT-MODFLOW integrates Soil and Water Assessment Tool (SWAT) and a three-dimensional finite difference model (MODFLOW). The model was calibrated using a parameter estimation tool (PEST). The major advantage of the employed IES is that the number of model runs required for the calibration of an ensemble is independent of the number of adjustable parameters. The pilot point approach was followed to calibrate the aquifer parameters, namely hydraulic conductivity, specific storage, and specific yield. The parameter estimation process for the SWAT model focused primarily on surface-related parameters. The uncertainties both in the streamflow and groundwater level were assessed. The work presented provides valuable insights for future endeavors in coupled surface-subsurface modeling, data collection, model development, and informed decision-making.

• Journal of Korean Society on Water Environment
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• v.21 no.5
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• pp.511-515
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• 2005

CBOD(carbonaceous BOD) decay rate was investigated for the execution of water quality model in Nakdong-Rive basin. Estimation of laboratory-derived CBOD decay rate, $k_l$ and CBOD decay rate in natural waters, $k_d$ were carried out. Hydraulic factors were applied for the calculation of $k_d$. Values of biochemical oxygen demand were investigated in Weagwan, Koreong, Jeokpo, Namgi and Mulgeom sites for the four times. The ranges of $k_l$ value were $0.04{\pm}0.01{\sim}0.14{\pm}0.03$. The values of $k_l$ in upstream sites were much larger than those in the downstream sites. The values of $k_d$ were 0.025, 0.036, 0.005 and 0.001 at Weagwan, Jeokpo, Namgi and Mulgeom, respectively, indicating that values of $k_d$ were generally larger than those of $k_l$.

• Journal of the Korean Society of Groundwater Environment
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• v.2 no.2
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• pp.78-84
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• 1995

In 1983, 83 Wenner vertical electrical sounding(VES)s and 22 pumping tests had been carried out by Korea Agricultural Development Corporation(KADC) in Guam Myun, Yeoju Gun, Kyounggi Province. Also, 10 boreholes had been constructed in the area. Using these data electrical and hydraulic properties of aquifer in the Ganam area are investigated in this study. Assuming that the underground is 1-D, VES data are analyzed. Data analysis shows that the subsurface of study area can be interpreted as 4-layer structure and the 3rd layer which is regarded as aquifer has mean thickness of 10 m and mean resistivity of 506 ohm-m and rests on resistive bedrock. Under the circumstances, as most part of electric current flows parallel to the bedding, longitudinal unit conductance is an important parameter controlling VES curves and very closely correlates with transmissivity of aquifer in the study area. Thus, relation between longitudinal unit conductance and transmissivity is investigated in this study. Since resistivity and thickness of each layer are obtained from interpretation of VES data, the relations between transmissivity and resistivity, and between hydraulic conductivity and resistivity are also studied. Studies of such relations show that longitudinal conductance is proportional to transmissivity, and resistivity is inversely proportional to transmissivity and hydraulic conductivity.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.12 no.4
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• pp.315-334
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• 2014

Wolsong Low- and Intermediate-level radioactive waste (LILW) disposal center has two different types of disposal facilities and interacts with the neighboring Wolsong nuclear power plant. These situations impose a high level of complexity which requires in-depth understanding of phenomena in the safety assessment of the disposal facility. In this context, multidimensional radionuclide transport model and hydraulic performance assessment model should be developed to identify more realistic performance of the complex system and reduce unnecessary conservatism in the conventional performance assessment models developed for the $1^{st}$ stage underground disposal. In addition, the advanced performance assessment model is required to calculate many cases to treat uncertainties or study parameter importance. To fulfill the requirements, this study introduces the development of two-dimensional integrated near-field performance assessment model combining near-field hydraulic performance assessment model and radionuclide transport model for the $2^{nd}$ stage near-surface disposal. The hydraulic and radionuclide transport behaviors were evaluated by PORFLOW and GoldSim. GoldSim radionuclide transport model was verified through benchmark calculations with PORFLOW radionuclide transport model. GoldSim model was shown to be computationally efficient and provided the better understanding of the radionuclide transport behavior than conventional model.