• Journal of Korean Port Research
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• 제14권1호
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• pp.47-55
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• 2000

In order to cope with the changes of container terminal situation in these days, many simulation studies for container terminal have been accomplished. But previous simulation studies using simulation language have limitations in model representation and difficulties in modeling of large scaled container terminal system. To make these problems better, this paper addresses an object-oriented simulation of container terminal system using a DEVS formalism. The DEVS(Discrete Event System Specification) formalism, developed by Zeigler, supports specification of discrete event system in a hierarchical and modular manner. The formalism provides a mathematical basis for studying discrete event systems with better understood and sounder semantics. In a step of system modeling, a DEVS formalism aims at the exact system modeling that has a basis of semantics and utilizing the object-oriented manner can flexibly cope with the changes of system environment. In this study a model is developed and verified through the simulation of some alternatives.

• Journal of the Korea Society for Simulation
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• 제2권1호
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• pp.107-124
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• 1993

This paper presents an object -oriented simulation approach. AgvTalk, to design and analze AGV system configuration and control. Smalltalk-80 is used as an implementation language in AgvTalk. AgvTalk includes 25 object classes and more than 300 object methods in its library. Compared to general purpose simulation languages. AgvTalk provides several important benefits. First, the hierarchical features and modularity create possibilities for the extension and reuse of simulation object components. This extensibility and reusability provide more flexible modeling capabilities for simulation of many alternative AGV systems. Second, detailed behavior of each object in the AGV system can be modeled easily and exactly in AgvTalk because there are no limiting modeling constructs. Third, AgvTalk provides a user -friendly simulation modeling environment through the MVC -triad of Smalltalk-80.

• Journal of Cadastre & Land InformatiX
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• 제47권1호
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• pp.53-79
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• 2017

The main purpose of this study was to detect and classify public perceptions toward smog disasters on Twitter using topic modeling. To help achieve these objectives and to identify gaps in the literature, this research carried out a literature review on public opinions toward smog disasters and topic modeling. The literature review indicated that there are huge gaps in the related literature. In this research, this author formed five research questions to fill the gaps in the literature. And then this study performed research steps such as data extraction, word cloud analysis on the cleaned data, building the network of terms, correlation analysis, hierarchical cluster analysis, topic modeling with the LDA, and stream graphs to answer those research questions. The results of this research revealed that there exist huge differences in the most frequent terms, the shapes of terms network, types of correlation, and smog-related topics changing patterns between New York and London. Therefore, this author could find positive answers to the four of the five research questions and a partially positive answer to Research question 4. Finally, on the basis of the results, this author suggested policy implications and recommendations for future study.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권8호
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• pp.3602-3620
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• 2016

Dynamic topology is one of the main influence factors on network performability. However, it was always ignored by the traditional network performability assessment methods when analyzing large-scale mobile ad hoc networks (MANETs) because of the state explosion problem. In this paper, we address this problem from the perspective of complex network. A two-layer hierarchical modeling approach is proposed for MANETs performability assessment, which can take both the dynamic topology and multi-state nodes into consideration. The lower level is described by Markov reward chains (MRC) to capture the multiple states of the nodes. The upper level is modeled as a small-world network to capture the characteristic path length based on different mobility and propagation models. The hierarchical model can promote the MRC of nodes into a state matrix of the whole network, which can avoid the state explosion in large-scale networks assessment from the perspective of complex network. Through the contrast experiments with OPNET simulation based on specific cases, the method proposed in this paper shows satisfactory performance on accuracy and efficiency.

• Proceedings of the KIEE Conference
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• 대한전기학회 2006년 학술대회 논문집 정보 및 제어부문
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• pp.120-122
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• 2006

The paper concerns the hybrid optimization of fuzzy inference systems that is based on Hierarchical Fair Competition-based Parallel Genetic Algorithms (HFCGA) and information data granulation. The granulation is realized with the aid of the Hard C-means clustering and HFCGA is a kind of multi-populations of Parallel Genetic Algorithms (PGA), and it is used for structure optimization and parameter identification of fuzzy model. It concerns the fuzzy model-related parameters such as the number of input variables to be used, a collection of specific subset of input variables, the number of membership functions, the order of polynomial, and the apexes of the membership function. In the hybrid optimization process, two general optimization mechanisms are explored. Thestructural optimization is realized via HFCGA and HCM method whereas in case of the parametric optimization we proceed with a standard least square method as well as HFCGA method as well. A comparative analysis demonstrates that the proposed algorithm is superior to the conventional methods.

• Journal of Ocean Engineering and Technology
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• 제13권3B호
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• pp.106-115
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• 1999

Modeling a discrete event system such as a sequential control system is difficult compared with a continuous system. Petri nets have been introduced as an analyzing and design tool for the discrete systems. One of the problems in its applications is that the model can not be analyzed easily in the case of large scale or complicated systems because of increase of the number of components of the system. To overcome this problem, some methods for dividing or reducing Petri nets have been suggested. In this paper, an approach for a hierarchical expression of Petri nets based on Sequential Function Chart(SFC) is proposed. A measuring tank system will be described as a typical kind of discrete systems. The system is modeled by sub Petri nets based on SFC in order to analyze and visualize efficiently about the dynamic behaviors of the system. Some numerical simulations using state equations are performed to prove the validity of the proposed method.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권12호
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• pp.6017-6037
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• 2017

In a multi-resolution image encoding system, the image is encoded into a single file as a layer of bit streams, and then it is transmitted layer by layer progressively to reduce the transmission time across a low bandwidth connection. This encoding scheme is also suitable for multiple decoders, each with different capabilities ranging from a handheld device to a PC. In our previous work, we proposed an edge adaptive hierarchical interpolation algorithm for multi-resolution image coding system. In this paper, we enhanced its compression efficiency by adding three major components. First, its prediction accuracy is improved using context adaptive error modeling as a feedback. Second, the conditional probability of prediction errors is sharpened by removing the sign redundancy among local prediction errors by applying sign flipping. Third, the conditional probability is sharpened further by reducing the number of distinct error symbols using error remapping function. Experimental results on benchmark data sets reveal that the enhanced algorithm achieves a better compression bit rate than our previous algorithm and other algorithms. It is shown that compression bit rate is much better for images that are rich in directional edges and textures. The enhanced algorithm also shows better rate-distortion performance and visual quality at the intermediate stages of progressive image transmission.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제12권3호
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• pp.493-499
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• 2008

Cellular Automata(CA) has been used as modeling and computing paradigm for a long time. And CA has been used to model many physical systems. While studying the models of such systems, it is seen that as the complexity of the physical system increase, the CA based model becomes very complex and becomes to difficult to track analytically. Also such models fail to recognize the presence of inherent hierarchical nature of a physical system. In this paper we give the characterization of Hierarchical Cellular Automata(HCA). Especially we analyze transition rules, characteristic polynomials and cyclic structures of HCA.

• Communications for Statistical Applications and Methods
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• 제28권1호
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• pp.59-79
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• 2021

Value at Risk (VaR) is one of the most common risk management tools in finance. Since a portfolio of several assets, rather than one asset portfolio, is advantageous in the risk diversification for investment, VaR for a portfolio of two or more assets is often used. In such cases, multivariate distributions of asset returns are considered to calculate VaR of the corresponding portfolio. Copulas are one way of generating a multivariate distribution by identifying the dependence structure of asset returns while allowing many different marginal distributions. However, they are used mainly for bivariate distributions and are not widely used in modeling joint distributions for many variables in finance. In this study, we would like to examine the performance of various copulas for high dimensional data and several different dependence structures. This paper compares copulas such as elliptical, vine, and hierarchical copulas in computing the VaR of portfolios to find appropriate copula functions in various dependence structures among asset return distributions. In the simulation studies under various dependence structures and real data analysis, the hierarchical Clayton copula shows the best performance in the VaR calculation using four assets. For marginal distributions of single asset returns, normal inverse Gaussian distribution was used to model asset return distributions, which are generally high-peaked and heavy-tailed.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제10권4호
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• pp.43-52
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• 1990

Theoretical foundation and algorithms are presented of a new surface modeling and pre-processing system for the three-dimensional structures. The modeling method is based on the boundary representation scheme and composed of two hierarchical model structures: curve-network and surface models. The concept of modeling curve as a union of links is introduced to facilitate surface modeling via various transfinite mapping techniques or Coons Patches. Efficiency and novel aspects of the present method are discussed. Finite element mesh genceration and application procedures will be reported in a later paper.