• Transactions of the Korean hydrogen and new energy society
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• v.35 no.1
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• pp.66-74
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• 2024

This study addresses the escalating issue of worldwide hydrogen gas accidents, which has seen a significant increase in occurrences. To comprehensively evaluate the risks associated with hydrogen, a two approach was employed in this study. Firstly, a qualitative risk assessment was conducted using the bow-tie method. Secondly, a quantitative consequence analysis was carried out utilizing the areal locations of hazardous atmospheres (ALOHA) model. The study applied this method to two incidents, the hydrogen explosion accident occurred at the Muskingum River power plant in Ohio, USA, 2007 and the hydrogen storage tank explosion accident occurred at the K Technopark water electrolysis system in Korea, 2019. The results of the risk assessments revealed critical issues such as deterioration of gas pipe, human errors in incident response and the omission of important gas cleaning facility. By analyzing the cause of accidents and assessing risks quantitatively, the effective accident response plans are proposed and the effectiveness is evaluated by comparing the effective distance obtained by ALOHA simulation. Notably, the implementation of these measures led to a significant 54.5% reduction in the risk degree of potential explosions compared to the existing risk levels.

• Geomechanics and Engineering
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• v.22 no.3
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• pp.207-217
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• 2020

Slope reliability analysis and risk assessment for spatially variable soils under rainfall infiltration are important subjects but they have not been well addressed. This lack of study may in part be due to the multiple and diverse evaluation indexes and the low computational efficiency of Monte-Carlo simulations. To remedy this, this paper proposes a highly efficient computational method for investigating random field problems for slopes. First, the probability density evolution method (PDEM) is introduced. This method has high computational efficiency and does not need the tens of thousands of numerical simulation samples required by other methods. Second, the influence of rainfall on slope reliability is investigated, where the reliability is calculated from based on the safety factor curves during the rainfall. Finally, the uncertainty of the sliding mass for the slope random field problem is analyzed. Slope failure consequences are considered to be directly correlated with the sliding mass. Calculations showed that the mass that slides is smaller than the potential sliding mass (shallow surface sliding in rainfall). Sliding mass-based risk assessment is both needed and feasible for engineered slope design. The efficient PDEM is recommended for problems requiring lengthy calculations such as random field problems coupled with rainfall infiltration.

• Journal of the Korean Institute of Intelligent Systems
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• v.21 no.4
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• pp.475-480
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• 2011

In this paper, we propose a collision risk assesment system. First, using Kalman Filter, we estimate the information of pedestrian, and second, we compute the collision probability using Monte Carlo Simulations(MCS) and neural network(NN). And we update the collision risk using time history which is called belief. Belief update consider not only output of Kalman Filter of only current time step but also output of Kalman Filter up to the first time step to current time step. The computer simulations will be shown the validity of our proposed method.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.05a
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• pp.45-46
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• 2019

Accident rate in domestic construction industry has been increased rapidly in every year. In particular, the rate of death has been shown very high compared with other industries. It means that safety activities performed by government is not effective in reducing the rate of accident. To solve these problems, the risk factors should be predicted in advance, controlled, monitored and managed from start of project to end of project. However, most studies have been conducted by using frequency of occurrence of accident and only listed the importance of risk. Therefore, the objective of this study is to provide basic material to develop risk quantifying model for human accidents on construction site in South Korea. In the future, it is expected to be used as a reference of study on developing safety mangement checklist in construction industry and model for forecasting accident.

• Journal of the Korean Society of Safety
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• v.29 no.4
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• pp.199-207
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• 2014

In this paper, to systematically assess the abandonment risk of main control room (MCR) fire, fire simulations with Fire Dynamics Simulator were performed and abandonment probabilities were estimated for the MCR bench-board fire of domestic reference nuclear power plant. The fire simulation scenarios performed in this study included propagating and non-propagating fires of the MCR bench-board, and the availability and unavailability of heating, ventilation, and air conditioning system (HVACS). The following results were obtained. First, temperature was the major abandonment impact factor for the MCR bench-board fire if the HVACS was available and optical density was that if the HVACS was unavailable. Second, the fire scenario contributing the MCR bench-board fire abandonment risk was identified to be only the propagating fire. Third, it was confirmed that the abandonment probability of the MCR bench-board fire for domestic reference nuclear power plant could be reduced by using the fire modeling.

• Journal of the Korean Institute of Navigation
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• v.18 no.4
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• pp.33-47
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• 1994

On developing port system, the performance tests of system in relation to ship maneuver generally consists of the three parts: the channel transit, the manoeuvring in a turning basin and the docking/undocking. The quantifications of risk of an accident has priviously been difficult due to the low occurrence of accidents relative to the number of transits. Additionally, accident statistics could not be related port system because of the large number of factors contributing to the accident. such as human error, equipment failure, visibility, light, traffic. etc. In case of the channel transit, "Relative Risk Factor(RRF)" or "Relative Risk Factor for Meeting Traffic" was proposed as the as the measures derived to quantify the relative risk of accident by M.W.Smith. This factor measure the tracking performance, the turning performance and the passing performance at meeting traffic. On the other hand, the safety of berthing maneuver is not measured with a few evaluating factors as controlled due to complex controllabilites such as steering, engine, side thrusters or tugs. This work, therefore, aims to propose the evaluating measure by the Analytic Hierarchy Process(AHP). Six experimental scenarios were establised under the various environmental conditions as independent variables. In every simulation, the difficulty of maneuver was scored by captain and compared with AHP scores. The results show almost same and from which the weights of eight evaluating factors could be fixed. Additionally, the limit value of relative factor in berthing safety to six scenarios could be estimated to 0.11.e estimated to 0.11.

• The Korean Journal of Applied Statistics
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• v.34 no.6
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• pp.875-887
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• 2021

Value at Risk (VaR) is the most popular measure for market risk. In this paper, we consider the VaR estimation of portfolio consisting of a variety of assets based on multivariate copula model known as vine copula. In particular, sparse vine copula which penalizes too many parameters is considered. We show in the simulation study that sparsity indeed improves out-of-sample forecasting of VaR. Empirical analysis on 60 KOSPI stocks during the last 5 years also demonstrates that sparse vine copula outperforms regular copula model.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.19 no.6
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• pp.175-184
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• 2009

There have been two methods of estimating computer related security risk such as qualitative and quantitative methods which have distinctive advantages or disadvantages. The former is too narrative and somehow abstract to implement and the latter produces concrete result but needs lots of data, so that it is needed to develop a method overcoming such difficulties. It is advised to mix such two methods in a proper way depending on the conditions of a computer system. In this article, a concept of fuzzy number is employed on the way of mixing the two methods and provide a simple example using fuzzy numbers. Simulation was conducted for an assumed model system and it is demonstrated how to calculated expected and unexpected risk.

• The Journal of Industrial Distribution & Business
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• v.13 no.10
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• pp.1-8
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• 2022

Purpose: Support vector machines (SVMs) ensemble has been proposed to improve classification performance of Credit risk recently. However, currently used fusion strategies do not evaluate the importance degree of the output of individual component SVM classifier when combining the component predictions to the final decision. To deal with this problem, this paper designs a support vector machines (SVMs) ensemble method based on fuzzy integral, which aggregates the outputs of separate component SVMs with importance of each component SVM. Research design, data, and methodology: This paper designs a personal credit risk evaluation index system including 16 indicators and discusses a support vector machines (SVMs) ensemble method based on fuzzy integral for designing a credit risk assessment system to discriminate good creditors from bad ones. This paper randomly selects 1500 sample data of personal loan customers of a commercial bank in China 2015-2020 for simulation experiments. Results: By comparing the experimental result SVMs ensemble with the single SVM, the neural network ensemble, the proposed method outperforms the single SVM, and neural network ensemble in terms of classification accuracy. Conclusions: The results show that the method proposed in this paper has higher classification accuracy than other classification methods, which confirms the feasibility and effectiveness of this method.

• Korean Chemical Engineering Research
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• v.52 no.4
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• pp.467-474
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• 2014

Preliminary design in chemical process furnishes economic feasibility through calculation of both mass balance and energy balance and makes it possible to produce a desired product under the given conditions. Through this design stage, the process possesses unchangeable characteristics, since the materials, reactions, unit configuration, and operating conditions were determined. Unique characteristics could be very economic, but it also implies various potential risk factors as well. Therefore, it becomes extremely important to design process considering both economics and safety by integrating process simulation and quantitative risk analysis during preliminary design stage. The target of this study is LNG liquefaction process. By the simulation using Aspen HYSYS and quantitative risk analysis, the design variables of the process were determined in the way to minimize the inherent explosion risks and operating cost. Instead of the optimization tool of Aspen HYSYS, the optimization was performed by using stochastic optimization algorithm (Covariance Matrix Adaptation-Evolution Strategy, CMA-ES) which was implemented through automation between Aspen HYSYS and Matlab. The research obtained that the important variable to enhance inherent safety was the operation pressure of mixed refrigerant. The inherent risk was able to be reduced about 4~18% by increasing the operating cost about 0.5~10%. As the operating cost increases, the absolute value of risk was decreased as expected, but cost-effectiveness of risk reduction had decreased. Integration of process simulation and quantitative risk analysis made it possible to design inherently safe process, and it is expected to be useful in designing the less risky process since risk factors in the process can be numerically monitored during preliminary process design stage.