• Journal of Korea Water Resources Association
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• v.50 no.11
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• pp.745-758
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• 2017

The copula-based models have been successfully applied to hydrological modeling including drought frequency analysis and time series modeling. However, uncertainty estimation associated with the parameters of these model is not often properly addressed. In these context, the main purposes of this study are to develop the Bayesian inference scheme for bivariate copula functions. The main applications considered are two-fold: First, this study developed and tested an approach to copula model parameter estimation within a Bayesian framework for drought frequency analysis. The proposed modeling scheme was shown to correctly estimate model parameters and detect the underlying dependence structure of the assumed copula functions in the synthetic dataset. The model was then used to estimate the joint return period of the recent 2013~2015 drought events in the Han River watershed. The joint return period of the drought duration and drought severity was above 100 years for many of stations. The results obtained in the validation process showed that the proposed model could effectively reproduce the underlying distribution of observed extreme rainfalls as well as explicitly account for parameter uncertainty in the bivariate drought frequency analysis.

• Journal of Korea Water Resources Association
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• v.53 no.8
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• pp.569-582
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• 2020

Recently, Korea has faced a change in the pattern of water use due to urbanization, which has caused difficulties in understanding the rainfall-runoff process and optimizing the allocation of available water resources. In this perspective, spatially downscaled analysis of the water balance is required for the efficient operation of water resources in the National Water Management Plan and the River Basin Water Resource Management Plan. However, the existing water balance analysis does not fully consider water circulation and availability in the basin, thus, the obtained results provide limited information in terms of decision making. This study aims at developing a novel water circulation analysis model that is designed to support a quasi-real-time assessment of water availability along the river. The water circulation model proposed in this study improved the problems that appear in the existing water balance analysis. More importantly, the results showed a significant improvement over the existing model, especially in the low flow simulation. The proposed modeling framework is expected to provide primary information for more realistic hydrological drought monitoring and drought countermeasures by providing streamflow information in quasi-real-time through a more accurate natural flow estimation approach with highly complex network.

• Tunnel and Underground Space
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• v.23 no.3
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• pp.219-227
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• 2013

Although Mohr-Coulomb failure criterion has limitations in that it is a linear criterion and the effect of the intermediate principal stress on failure is ignored, this criterion has been widely accepted in rock mechanics design. In order to overcome these shortcomings, the Hoek-Brown failure criterion was introduced and recently a number of 3-D failure criteria incorporating the effect of the intermediate principal stress on failure have been proposed. However, in many rock mechanics designs, the possible failure of rock mass is still evaluated based on Mohr-Coulomb criterion and most of practitioners are accustomed to understanding the strength of rock mass in terms of the internal friction angle and cohesion. Therefore, if the equivalent Mohr-Coulomb strength parameters of the advanced failure criteria are calculated, it is possible to take advantage of the advanced failure criteria in the framework of the Mohr-Coulomb criterion. In this study, a method expressing the tangential Mohr-Coulomb strength parameters in terms of the stress invariant is proposed and it is applied to the generalized Hoek-Brown criterion and the HB-WW criterion. In addition, a new approach describing the geometric meaning of the ${\sigma}_2$-dependency of failure criteria in 3-D principal stress space is proposed. Implementation examples of the proposed method show that the influence of the intermediate principal stress on the tangential friction angle and cohesion of the HB-WW criterion is considerable, which is not the case for the 2-D failure criterion.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.176-176
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• 2019

Thailand had issued a national strategic development master plan with issues related to water resources and water security in the entire water management. Water resources are an important factor of living and development of the country's socio-economy to be stable, prosperous and sustainable. Therefore, water management in both multidimensional and multi-sectoral systems is important and will supports socio-economic and environmental development. The direction of national development in accordance with the national strategic framework for 20 years that requires the country to level up security level in terms of water, energy and food. To response to the proposed goals, there is a subplan to increase water productivity of the entire water system for economical development use by evaluating use value and to create more value added from water use to meet international standard level. This study aims to evaluate the water productivity of Thailand in each basin and all sectors such as agricultural sector, service and industrial sectors by using the water use data from water account analysis and GDP data from NESDB during the past 10 years (1996-2015). The comparison of water productivity with other countries will also be conducted and in addition, the measures to improve water productivity in next 20 years will be explored to response to the National Strategic Master Plan goals. Water productivity is defined as output per unit of water depleted. The simplest way to compare water productivity across different enterprises is in monetary terms. World Bank presents water productivity as an indication of the efficiency by which each country uses its water resources. There are two data sets used for water productivity analyses, i.e., the first is water use data at end users and the second is Gross Domestic Product. The water use at end users are estimated by water account method based on the System of Environmental-Economic Accounting for Water (SEEA-Water) concept of United Nations. The water account shows the analyses of the water balance between the use and supply of each water resource in physical terms. The water supply and use linkage in the water account analyses separated into each phases, i.e., water sources, water managers, water service providers, water user at end user under water regulators of all kinds of water use activities such as household, industrial, agricultural, tourism, hydropower, and ecological conservation uses. The Gross Domestic Product (GDP), a well- known measuring method of the national economic growth is not actually a comprehensive approach to describe all aspects of national economic status, since GDP does not take into account the costs of the negative impacts to natural resources that result from the overexploitation of development projects, however, at present, integrating the environment with the economy of a country to measure its economic growth with GDP is acceptable worldwide. The study results will show the water use at each basin, use types at end users, water productivity in each sector from 1996-2015 compared with other countries, Besides the productivity improvement measures will be explored and proposed for the National Strategic Master Plan.

• Journal of Aerospace System Engineering
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• v.15 no.5
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• pp.24-32
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• 2021

Personal Air Vehicle (PAV), Cargo UAS (Cargo UAS), and existing manned and unmanned aircraft are key vehicles for urban air mobility (UAM), and should demonstrate compatibility for the design of aircraft systems. The safety assessment required by for certification to ensure safety and reliability should be systematically performed throughout the entire cycle from the beginning of the aircraft development process. However, with the increasing complexity of safety critical aviation systems and the application of state-of-the-art systems, conventional experience-based and procedural-based safety evaluation methods make ir difficult to objectively assess safety requirements and system safety. Therefore, Model-Based Safety Assessment (MBSA) using modeling and simulation techniques is actively being studied at domestic and foreign countries to address these problems. In this paper, we propose a Model-Based Safety Evaluation framework utilizing modeling and simulation-based integrated flight simulators. Our case studies on the Traffic Collision Availability System (TCAS) and Wheel Brake System (WBS) confirmed that they are practical for future safety assessments.

• Journal of Korea Water Resources Association
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• v.54 no.5
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• pp.321-334
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• 2021

A fixed reflectivity-rainfall relationship approach, such as the Marshall-Palmer relationship, for an entire year and different seasons, can be problematic in cases where the relationship varies spatially and temporally throughout a region. From this perspective, this study explores the use of long-term radar reflectivity for South Korea to obtain a nationwide calibrated Z-R relationship and the associated uncertainties within a Bayesian inference framework. A calibrated spatially structured pattern in the parameters exists, particularly for the wet season and parameter for the dry season. A pronounced region of high values during the wet and dry seasons may be partially associated with storm movements in that season. Overall, the radar rainfall fields based on the proposed modeling procedure are similar to the observed rainfall fields. In contrast, the radar rainfall fields obtained from the existing Marshall-Palmer relationship show a systematic underestimation. In the event of high impact weather, it is expected that the value of national radar resources can be improved by establishing an active watershed-level hydrological analysis system.

• Journal of Korea Water Resources Association
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• v.51 no.12
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• pp.1207-1216
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• 2018

Discharge or water level predictions at tidally affected river reaches are currently still a great challenge in hydrological practices. This research aims to predict water level of the tide dominated site, Jamsu bridge in the Han River downstream. Physics-based hydrodynamic approaches are sometimes not applicable for water level prediction in such a tidal river due to uncertainty sources like rainfall forecasting data. In this study, TensorFlow deep learning framework was used to build a deep neural network based LSTM model and its applications. The LSTM model was trained based on 3 data sets having 10-min temporal resolution: Paldang dam release, Jamsu bridge water level, predicted tidal level for 6 years (2011~2016) and then predict the water level time series given the six lead times: 1, 3, 6, 9, 12, 24 hours. The optimal hyper-parameters of LSTM model were set up as follows: 6 hidden layers number, 0.01 learning rate, 3000 iterations. In addition, we changed the key parameter of LSTM model, sequence length, ranging from 1 to 6 hours to test its affect to prediction results. The LSTM model with the 1 hr sequence length led to the best performing prediction results for the all cases. In particular, it resulted in very accurate prediction: RMSE (0.065 cm) and NSE (0.99) for the 1 hr lead time prediction case. However, as the lead time became longer, the RMSE increased from 0.08 m (1 hr lead time) to 0.28 m (24 hrs lead time) and the NSE decreased from 0.99 (1 hr lead time) to 0.74 (24 hrs lead time), respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.479-488
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• 2019

The flight test operational procedure artifact includes mission planning, execution methods, and safety measures for each step of test progress. As the development of guided missiles has become more advanced and strategic, flight test has become increasingly complex and broadened. Therefore, increased reliability of the flight test operation procedures was required to ensure test safety. Particularly, the design of the flight test operational procedures required verification through M&S to predict and prepare for the uncertainty in a new test. The relevant studies have published the optimal framework development for flight tests and the model-based improvements of flight test processes, but they lacked the specificity to be applied directly to the flight test operational procedures. In addition, the flight test operational procedures, which consist of document bases, have caused problems such as limitations of analysis capabilities, insensitive expressions, and lack of scalability for the behavior and performance analysis of test resources. To improve these problems, this paper proposes how to design operational procedure of guided missile flight test system by applying MBSE(Model-based Systems Engineering). This research has improved reliability by increasing the ability to analyze the behavior and performance of test resources, and increased efficiency with the scalability applicable to multiple flight tests. That can be also used continuously for the guided missile flight tests that will be developed in the future.

• Journal of Korean Society of Disaster and Security
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• v.13 no.4
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• pp.25-36
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• 2020

An increasing frequency and intensity of natural disasters have been observed due to climate change. To better prepare for these, the MOIS (ministry of the interior and safety) announced a comprehensive plan for minimizing damages associated with natural disasters, including drought and heavy snowfall. The spatial-temporal pattern of snowfall is greatly influenced by temperature and geographical features. Heavy snowfalls are often observed in Gangwon-do, surrounded by mountains, whereas less snowfall is dominant in the southern part of the country due to relatively high temperatures. Thus, snow depth data often contains zeros that can lead to difficulties in the selection of probability distribution and estimation of the parameters. A generalized mixture distribution approach to a maximum snow depth series over the southern part of Korea (i.e., Changwon, Tongyeoung, Jinju weather stations) are located is proposed to better estimate a threshold (𝛿) classifying discrete and continuous distribution parts. The model parameters, including the threshold in the mixture model, are effectively estimated within a Bayesian modeling framework, and the uncertainty associated with the parameters is also provided. Comparing to the Daegwallyeong weather station, It was found that the proposed model is more effective for the regions in which less snow depth is observed.

• Membrane Journal
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• v.30 no.6
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• pp.409-419
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• 2020

In this study, PEBAX/ZIF-8 and PEBAX/amineZIF-8 composite membranes were prepared according to the content of zeolitic imidazolate framework-8 (ZIF-8), amine-modified ZIF-8 (amineZIF-8), the gas permeability properties of N2 and CO2 were investigated for each composite membrane. In the case of the PEBAX/ZIF-8 composite membrane, the permeability of N2 and CO2 increased as the ZIF-8 content increased, and in the case of the PEBAX/amineZIF-8 composite membrane, the permeability of N2 and CO2 increased up to 20 wt% of amineZIF-8, but decreased at the higher content. CO2/N2 ideal selectivity increased up to 20 wt% of ZIF-8 and amineZIF-8 contents in both PEBAX/ZIF-8 and PEBAX/ amineZIF-8 composite membranes, and then decreased thereafter, in the case of PEBAX/amineZIF-8 composite membrane was less decreased. The reason for the highest CO2/N2 ideal selectivity at 20 wt% of amineZIF-8 is that amine modification improved the compatibility between PEBAX and amineZIF-8, and thus amineZIF-8 was evenly dispersed in PEBAX, resulting in the greatest effect of the porous ZIF-8 with a 3.4 Å pore size and the amine with affinity for CO2.