• Journal of Coastal Disaster Prevention
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• v.6 no.3
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• pp.111-120
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• 2019

In coastal morphological modelling, there are a number of input factors: wave height, water depth, sand particle size, bed friction coefficients, coastal structures and so forth. Measurements or estimates of these input data may include uncertainties due to errors by the measurement or hind-casting methods. Therefore, it is necessary to consider the uncertainty of each input data and the range of the uncertainty during the evaluation of numerical results. In this study, three uncertainty factors are considered with regard to the prediction of coastal erosion in Ilsan beach located in Ilsan-dong, Ulsan metropolitan city. Those are wave diffraction effect of XBeach model, wave input scenario and the specification of the coastal structure. For this purpose, the values of mean wave direction, significant wave height and the height of the submerged breakwater were adjusted respectively and the followed numerical results of morphological changes are analyzed. There were erosion dominant patterns as the wave direction is perpendicular to Ilsan beach, the higher significant wave height, and the lower height of the submerged breakwater. Furthermore, the rate of uncertainty impacts among mean wave direction, significant wave height and the height of the submerged breakwater are compared. In the study area, the uncertainty influence by the wave input scenario was the largest, followed by the height of the submerged breakwater and the mean wave direction.

• Journal of Aerospace System Engineering
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• v.18 no.2
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• pp.1-11
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• 2024

This paper applies a relative impact angle control guidance law to a communication-based multi-missile network system with uncertainties and disturbances. The multi-missile network system is represented as a transitive reduction directed acyclic graph. Furthermore, this paper introduces both centralized and decentralized guidance laws based on the graph's structure. The relationship between these guidance laws is analyzed by comparing them based on the communication structure and the presence of system noise. To analyze the effects of decentralized optimal cooperative guidance law, this paper assumes uncertainty in missile dynamics and predicted impact point information for the relative impact angle control mission. Monte Carlo simulations are conducted for various mission environments to analyze the impact of communication and its structure on the system.

• The Korean Journal of Applied Statistics
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• v.37 no.1
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• pp.13-38
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• 2024

As economic uncertainties have increased recently due to COVID-19, there is a growing need to quickly grasp private consumption trends that directly reflect the economic situation of private economic entities. This study proposes a method of estimating private consumption in real-time by comprehensively utilizing big data as well as existing macroeconomic indicators. In particular, it is intended to improve the accuracy of private consumption estimation by comparing and analyzing various machine learning methods that are capable of fitting ultra-high-dimensional big data. As a result of the empirical analysis, it has been demonstrated that when the number of covariates including big data is large, variables can be selected in advance and used for model fit to improve private consumption prediction performance. In addition, as the inclusion of big data greatly improves the predictive performance of private consumption after COVID-19, the benefit of big data that reflects new information in a timely manner has been shown to increase when economic uncertainty is high.

• Journal of Navigation and Port Research
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• v.48 no.3
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• pp.206-213
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• 2024

This paper aims to investigate the causal relationship between geopolitical risk and stock price volatility in the shipping industry. Given its international nature and dependence on global trade, this industry is exposed to various uncertainties and risk factors. This study specifically focuses on the impact of geopolitical risk, which has gained significant attention in recent years due to events such as the Russia-Ukraine War and the Israel-Hamas War. To analyze this relationship, the study utilizes vector autoregressive model-based causality tests. The research estimates the causal relationship between geopolitical risk indicators and the stock price volatility of five shipping companies listed on the Korea Exchange. The study covers the period from 2000 to 2023. The results indicate the following: Firstly, an increase in geopolitical risk leads to a rise in stock price volatility for shipping companies. Moreover, the impact of actual geopolitical events, rather than just diplomatic disputes, is statistically significant. Lastly, the impact of geopolitical risk is particularly significant in the bulk shipping sector.

• Journal of the Korea Society of Computer and Information
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• v.29 no.5
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• pp.11-20
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• 2024

This study presents TabNet, a novel deep learning method, to enhance corporate credit rating accuracy amidst growing financial market uncertainties due to technological advancements. By analyzing data from major Korean stock markets, the research constructs a credit rating prediction model using TabNet. Comparing it with traditional machine learning, TabNet proves superior, achieving a Precision of 0.884 and an F1 score of 0.895. It notably reduces misclassification of high-risk companies as low-risk, emphasizing its potential as a vital tool for financial institutions in credit risk management and decision-making.

• Journal of The Korean Society of Agricultural Engineers
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• v.66 no.2
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• pp.35-52
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• 2024

This study conducted an assessment of potential impacts on the drought in agricultural reservoirs using the recently proposed SSP (Shared Socioeconomic Pathways) scenarios by IPCC (Intergovernmental Panel on Climate Change). This study assesses the potential impact of climate change on agricultural water resources and infrastructure vulnerability within Gyeongsangnam-do, focusing on 15 agricultural reservoirs. The assessment was based on the KRC (Korea Rural Community Corporation) 1^st vulnerability assessment methodology using RCP scenarios for 2021. However, there are limitations due to the necessity for climate impact assessments based on the latest climate information and the uncertainties associated with using a single scenario from national standard scenarios. Therefore, we applied the 13 GCM (General Circulation Model) outputs based on the newly introduced SSP scenarios. Furthermore, due to difficulties in data acquisiton, we reassessed potential impacts by redistributing weights for proxy variables. As a main result, with lower future potential impacts observed in areas with higher precipitation along the southern coast. Overall, the potential impacts increased for all reservoirs as we moved into the future, maintaining their relative rankings, yet showing no significant variability in the far future. Although the overall pattern of potential impacts aligns with previous evaluations, reevaluation under similar conditions with different spatial resolutions emphasizes the critical role of meteorological data spatial resolution in assessments. The results of this study are expected to improve the credibility and accuracy formulation of vulnerability employing more scientific predictions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.4
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• pp.195-202
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• 2008

Underestimation of the capacity can have serious economic consequences, as deficient bridges must be posted, repaired or replaced. Accurate prediction of bridge behavior may allow for more bridges to remain in service with or without minor repairs. The presented research is focused on the reliability evaluation of the actual load carrying capacity of existing bridges based on the field testing. Reliability analysis is performed on 17 previously tested bridges. Bridges are first evaluated based on the code specified values and design resistance. However, after the field testing program, it is possible to apply the experimental results into the bridge reliability evaluation procedures. The girder distribution factors obtained from the tests are also applied in the reliability calculation. The results indicate that the reliability indices of selected bridges can be significantly increased due to the reduction of uncertainties without sacrificing the safety of structures, by including the result of field measurement data into calculation.

• Journal of Radiation Protection and Research
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• v.41 no.1
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• pp.31-39
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• 2016

Background: It is necessary to consider the overall countermeasure for analysis of nuclear activities according to the increase of the nuclear facilities like nuclear power and reprocessing plants in the neighboring countries including China, Taiwan, North Korea, Japan and South Korea. South Korea and comprehensive nuclear-test-ban treaty organization (CTBTO) are now operating the monitoring instruments to detect radionuclides released into the air. It is important to estimate the origin of radionuclides measured using the detection technology as well as the monitoring analysis in aspects of investigation and security of the nuclear activities in neighboring countries. Materials and methods: A three-dimensional forward/backward trajectory model has been developed to estimate the origin of radionuclides for a covert nuclear activity. The developed trajectory model was composed of forward and backward modules to track the particle positions using finite difference method. Results and discussion: A three-dimensional trajectory model was validated using the measured data at Chernobyl accident. The calculated results showed a good agreement by using the high concentration measurements and the locations where was near a release point. The three-dimensional trajectory model had some uncertainty according to the release time, release height and time interval of the trajectory at each release points. An atmospheric dispersion model called long-range accident dose assessment system (LADAS), based on the fields of regards (FOR) technique, was applied to reduce the uncertainties of the trajectory model and to improve the detective technology for estimating the radioisotopes emission area. Conclusion: The detective technology developed in this study can evaluate in release area and origin for covert nuclear activities based on measured radioisotopes at monitoring stations, and it might play critical tool to improve the ability of the nuclear safety field.

• Korean Journal of Agricultural and Forest Meteorology
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• v.12 no.1
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• pp.1-10
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• 2010

A regional climate model (RCM) can be a powerful tool to enhance spatial resolution of climate and weather information (IPCC, 2001). In this study we conducted dynamical downscaling using Weather Research and Forecasting Model (WRF) as a RCM in order to obtain high resolution regional agroclimate indices over the Korean Peninsula. For the purpose of obtaining detailed high resolution agroclimate indices, we first reproduced regional weather for the period of March to June, 2002-2008 with dynamic downscaling method under given lateral boundary conditions from NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data. Normally, numerical model results have shown biases against observational results due to the uncertainties in the modelis initial conditions, physical parameterizations and our physical understanding on nature. Hence in this study, by employing a statistical method, the systematic bias in the modelis results was estimated and corrected for better reproduction of climate on high resolution. As a result of the correction, the systematic bias of the model was properly corrected and the overall spatial patterns in the simulation were well reproduced, resulting in more fine-resolution climatic structures. Based on these results, the fine-resolution agro-climate indices were estimated and presented. Compared with the indices derived from observation, the simulated indices reproduced the major and detailed spatial distributions. Our research shows a possibility to simulate regional climate on high resolution and agro-climate indices by using a proper downscaling method with a dynamical weather forecast model and a statistical correction method to minimize the model bias.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.2
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• pp.37-45
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• 2022

A simplified model using the lifetime distribution has been presented to estimate the Mean Residual Life (MRL) of rubble-mound breakwaters, which is not like a stochastic process model based on time-dependent history data to the cumulative damage progress of rubble-mound breakwaters. The parameters involved in the lifetime distribution can be easily estimated by using the upper and lower limits of lifetime and their likelihood that made a judgement by several experts taking account of the initial design lifetime, the past sequences of loads, and others. The simplified model presented in this paper has been applied to the rubble-mound breakwater with TTP armor layer. Wiener Process (WP)-based stochastic model also has been applied together with Monte-Carlo Simulation (MCS) technique to the breakwater of the same condition having time-dependent cumulative damage to TTP armor layer. From the comparison of lifetime distribution obtained from each models including Mean Time To Failure (MTTF), it has found that the lifetime distributions of rubble-mound breakwater can be very satisfactorily fitted by log-normal distribution for all types of cumulative damage progresses, such as exponential, linear, and logarithmic deterioration which are feasible in the real situations. Finally, the MRL of rubble-mound breakwaters estimated by the simplified model presented in this paper have been compared with those by WP stochastic process. It can be shown that results of the presented simplified model have been identical with those of WP stochastic process until any ages in the range of MTT F regardless of the deterioration types. However, a little of differences have been seen at the ages in the neighborhood of MTTF, specially, for the linear and logarithmic deterioration of cumulative damages. For the accurate estimation of MRL of harbor structures, it may be desirable that the stochastic processes should be used to consider properly time-dependent uncertainties of damage deterioration. Nevertheless, the simplified model presented in this paper can be useful in the building of the MRL-based preventive maintenance planning for several kinds of harbor structures, because of which is not needed time-dependent history data about the damage deterioration of structures as mentioned above.