• Title/Summary/Keyword: Role Equivalence

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The Structural Equivalence and Role Equivalence of Container Ports in Asia-Europe Container Shipping Networks (아시아-유럽 컨테이너 해운 네트워크 구성 항만의 구조적 등위성과 역할 등위성)

  • Lee, Sang-Yoon
    • Journal of Korea Port Economic Association
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    • v.32 no.2
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    • pp.105-122
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    • 2016
  • Numerous studies have evaluated the status of seaports. However, the majority of the research has approached this topic from the view-point of port capabilities, including locational advantage, infrastructure, productivity, and competitiveness. The position and/or role of a port can be understood more precisely and comprehensively by considering the interconnectivity among ports making up enormous global transportation networks. The main objective of this study is to compare the status of 82 container ports on the trunk shipping routes between Asia and Europe by applying the concepts of structural equivalence and role equivalence proposed by the social network analysis method. Network similarities and differences among competing ports in the regions are assessed by analysing their structural equivalence. Furthermore, the hierarchical structures of the ports located on the trunks between Asia and Northwest Europe and between Asia and the Mediterranean are constructed by evaluating their role equivalence. The results of this empirical research shows that Singapore and Rotterdam possess the most significant positions on the ocean corridors between Asia and Northwest Europe. Singapore also holds a leading position on the Asia-Mediterranean shipping route. Lastly, no ports located in the Middle East or Mediterranean regions have an equivalent weight to those of Rotterdam, Hamburg, Antwerp on the Asia-Northwest Europe route.

LES studies on combustion characteristic with equivalence ratios in a model gas turbine combustor (모형 가스터빈 연소기에서 당량비 변화에 따른 연소특성에 관한 LES 연구)

  • Hwang, Cheol-Hong;Lee, Hyun-Yong;Lee, Chang-Eon
    • 한국연소학회:학술대회논문집
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    • 2006.10a
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    • pp.242-250
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    • 2006
  • The impacts of equivalence ratio on the flow structure and flame dynamics in a model gas turbine combustor are investigated using large eddy simulation(LES). Dynamic k-equation model and G-equation flamelet model are employed as LES subgrid model for flow and combustion, respectively. As a result of mean flow field for each equivalence ratio, the increase of equivalence ratio brings about the decrease of swirl intensity through the modification of thermal effect and viscosity, although the same swirl intensity is imposed at inlet. The changes of vortical structure and turbulent intensity etc. near flame surface are occurred consequently. That is, the decrease of equivalence ratio can leads to the increase of heat release fluctuation by the more increased turbulent intensity and fluctuation of recirculation flow. In addition, the effect of inner vortex generated from vortex breakdown on the heat release fluctuation is increased gradually with the decrease of equivalence ratio. Finally, it can be identified that the variations of vortical structure play an important role in combustion instability, even though the small change of equivalence ratio is occurred.

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LES Studies on Flow Structure and Flame Characteristic with Equivalence Ratios in a Swirling Premixed Combustor (선회 예혼합연소기에서 당량비 변화에 따른 유동구조 및 화염특성에 관한 LES 연구)

  • Hwang, Cheol-Hong;Kim, Se-Won;Lee, Chang-Eon
    • Journal of the Korean Society of Combustion
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    • v.11 no.4
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    • pp.27-35
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    • 2006
  • The impacts of equivalence ratio on flow structure and flame dynamic in a model gas turbine combustor are investigated using large eddy simulation(LES). Dynamic k-equation model and G-equation flamelet model are employed as LES subgrid model for flow and combustion, respectively. As a result of mean flow field for each equivalence ratio, the increase of equivalence ratio brings about the decrease of swirl intensity through the modification of thermal effect and viscosity, although the same swirl intensity is imposed at inlet. The changes of vortical structure and turbulent intensity etc. near flame surface are occurred consequently. That is, the decrease of equivalence ratio can leads to the increase of heat release fluctuation by the more increased turbulent intensity and fluctuation of recirculation flow. In addition, the effect of inner vortex generated from vortex breakdown on the heat release fluctuation is increased gradually with the decrease of equivalence ratio. Finally, it can be identified that the variations of vortical structure play an important role in combustion instability, even though the small change of equivalence ratio is occurred.

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Study of the Radiation Effect by Equivalence ratio change on the 3-D Turbulent Combustion (당량비 변화에 따른 복사 특성이 3차원 난류 연소에 미치는 영향 연구)

  • Kim, Tea-Kuk;Yoon, Kyung-Beom;Min, Dong-Ho;Chang, Hee-Chul;Kim, Jin-Soo
    • 한국연소학회:학술대회논문집
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    • 2006.10a
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    • pp.79-85
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    • 2006
  • Radiative heat transfer is very important in many combustion systems since they are operated in high temperature. Fluid flows in most of the combustion systems are turbulent to promote fast mixing of the hydrocarbon fuel and oxidant. Major combustion products are $CO_2$ and $H_2O$. The turbulent flow is modeled by using the standard ${\kappa}-{\epsilon}$ model and the radiation transfer is modeled by using the discrete ordinates method where the radiative gas properties are calculated by using the weighted sum of gray gases model with a gray gas regrouping(WSGGM-RG). Effect of the radiation on the combustion characteristics in a three-dimensional rectangular enclosure is studied by changing the equivalence ratio. Results show that the radiation plays a significant role on the heat transfer in the combustion systems by resulting in a temperature drop of 16% as compared to that obtained without radiation. The equivalence ratio also affects the combustion by different contribution of the radiative transfer with different gas compositions.

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Improved Computation of L-Classes for Efficient Computation of J Relations (효율적인 J 관계 계산을 위한 L 클래스 계산의 개선)

  • Han, Jae-Il;Kim, Young-Man
    • Journal of Information Technology Services
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    • v.9 no.4
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    • pp.219-229
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    • 2010
  • The Green's equivalence relations have played a fundamental role in the development of semigroup theory. They are concerned with mutual divisibility of various kinds, and all of them reduce to the universal equivalence in a group. Boolean matrices have been successfully used in various areas, and many researches have been performed on them. Studying Green's relations on a monoid of boolean matrices will reveal important characteristics about boolean matrices, which may be useful in diverse applications. Although there are known algorithms that can compute Green relations, most of them are concerned with finding one equivalence class in a specific Green's relation and only a few algorithms have been appeared quite recently to deal with the problem of finding the whole D or J equivalence relations on the monoid of all $n{\times}n$ Boolean matrices. However, their results are far from satisfaction since their computational complexity is exponential-their computation requires multiplication of three Boolean matrices for each of all possible triples of $n{\times}n$ Boolean matrices and the size of the monoid of all $n{\times}n$ Boolean matrices grows exponentially as n increases. As an effort to reduce the execution time, this paper shows an isomorphism between the R relation and L relation on the monoid of all $n{\times}n$ Boolean matrices in terms of transposition. introduces theorems based on it discusses an improved algorithm for the J relation computation whose design reflects those theorems and gives its execution results.

Stability Characteristics of Syngas($H_2$/CO)/Air Premixed Flames using an Impinging Jet Burner (충돌제트 버너에서 합성가스($H_2$/CO)/공기 예혼합화염의 안정화 특성)

  • Park, Ju-Yong;Lee, Kee-Man;Hwang, Cheol-Hong
    • Journal of the Korean Society of Combustion
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    • v.16 no.1
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    • pp.15-21
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    • 2011
  • An experimental study was conducted to investigate the flame stability of the synthetic gas (syngas) using an impinging premixed jet burner. Since the syngas mainly consisted of $H_2$ and CO, the $H_2$/CO mixture was simulated as the syngas. $H_2$/CO mixture ratios, fuel/air mixture velocities and equivalence ratios were used as major parameters on the flame stabilitym The role of the impinging plate on the flame stability was also examined. In addition, laminar burning velocities of the $H_2$/CO mixture were predicted numerically to understand the characteristics of the flame stability for the syngas. The increase in the H2 concentration into the syngas brings about the extension of the blowout limit and the reduction in the flashback limit in terms of the stable flame region. The impinging jet plate broadened the blowout limit but does not play important role in changing of the flashback limit. Finally, it was found that the stability region of the flame using the syngas, which is expressed in terms of the mixture velocity and the equivalence ratio in this study, significantly differed from that of $CH_4$.

Flame Characteristics on Wall Recess Type Ceramic Combustor for Low Pollutants (Wall Recess형 저공해 세라믹 연소기의 화염특성)

  • 전영남;채재우
    • Journal of Korean Society for Atmospheric Environment
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    • v.12 no.2
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    • pp.131-139
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    • 1996
  • The developent of ceramic combustor is being increased beca- use of the excellent physical properties of ceramic material, that is, high-resistant strength, high emissivity power and high corrosin-resistance. Ceramic combustor has been interested in the application of ultra-lean combustion for low NO$_{x}$ emission and gaseuos waste incineration with good combustion. This experimental study was conducted to investigate the combustion and emission characteristics of wall recess type ceramic combustor with equivalence ratio, mixture flow velocity and wall recess depth as parameters. The results in this study are as follows: 1. Wall recess played a important role to extend flame stability region. 2. The peak temperature of gas was peoportional to equivalence ratio, mixture flow velocity and wall recess depth. 3. The static pressure of mixing chamber and inlet temperature depended on the position of flame zone. 4. NO reduction was achieved by lean mixture without lower combustibility.y.

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Continuous Flames and Countably Approximating Frames

  • 이승온
    • Journal for History of Mathematics
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    • v.13 no.2
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    • pp.95-104
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    • 2000
  • This paper is a sequel to [24]. It is well known that the order structure plays the important role in the study of various mathematical structures. In 1972, Scott has introduced a concept of continuous lattices and has shown the equivalence between continuous lattices and injective $T_0-spaces$. There have been many efforts made to generalize continuous lattices and extend corresponding properties to them. We introduce another class of frames, namely countably approximating frames, generalizing continuous frames and study its basic properties.

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REMARKS ON SIMPLY k-CONNECTIVITY AND k-DEFORMATION RETRACT IN DIGITAL TOPOLOGY

  • Han, Sang-Eon
    • Honam Mathematical Journal
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    • v.36 no.3
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    • pp.519-530
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    • 2014
  • To study a deformation of a digital space from the viewpoint of digital homotopy theory, we have often used the notions of a weak k-deformation retract [20] and a strong k-deformation retract [10, 12, 13]. Thus the papers [10, 12, 13, 16] firstly developed the notion of a strong k-deformation retract which can play an important role in studying a homotopic thinning of a digital space. Besides, the paper [3] deals with a k-deformation retract and its homotopic property related to a digital fundamental group. Thus, as a survey article, comparing among a k-deformation retract in [3], a strong k-deformation retract in [10, 12, 13], a weak deformation k-retract in [20] and a digital k-homotopy equivalence [5, 24], we observe some relationships among them from the viewpoint of digital homotopy theory. Furthermore, the present paper deals with some parts of the preprint [10] which were not published in a journal (see Proposition 3.1). Finally, the present paper corrects Boxer's paper [3] as follows: even though the paper [3] referred to the notion of a digital homotopy equivalence (or a same k-homotopy type) which is a special kind of a k-deformation retract, we need to point out that the notion was already developed in [5] instead of [3] and further corrects the proof of Theorem 4.5 of Boxer's paper [3] (see the proof of Theorem 4.1 in the present paper). While the paper [4] refers some properties of a deck transformation group (or an automorphism group) of digital covering space without any citation, the study was early done by Han in his paper (see the paper [14]).

Numerical Study on the Stabilization of Turbulent Swirling Lifted Premixed Syngas Flames (석탄가스 난류선회유동 예혼합부상화염의 안정성 해석)

  • Kang, Sung-Mo;Lee, Jeong-Won;Kim, Yong-Mo
    • 한국신재생에너지학회:학술대회논문집
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    • 2008.05a
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    • pp.349-352
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    • 2008
  • This study has numerically modeled the combustion processes of the turbulent swirling premixed lifted syngas flames in the low-swirl burner (LSB). In these turbulent swirling premixed flames, the four tangentially-injected air jets induce the turbulent swirling flow which plays the crucial role of stabilizing the turbulent lifted flames. In the present approach, the turbulence-chemistry interaction is represented by the level-set based flamelet model. Numerical results indicate clearly that the present level-set based flamelet approach has realistically simulated the structure and stabilization mechanism of the turbulent swirling premixed lifted flames in the low-swirl burner. Computations are made for the wide range of the syngas chemical composition and the dilution level at two pressure conditions (1.0, 5.0 bar). Numerical results indicate that the lifted height in the LSB is increased by decreasing the H2 percentage and increasing the dilution level at the given equivalence ratio. It is also found that the flashback is occurred for the hydrogen composition higher than 80% at the equivalence ratio, 0.8. However, at the syngas composition range in the IGCC system, the stable lean-premixed lifted flames are formed at the low-swirl burner.

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