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Discrete Optimum Design of Ship Structures by Genetic Algorithm (유전적 알고리즘에 의한 선체 구조물의 이산적 최적설계)

  • Y.S. Yang;G.H. Kim;W.S. Ruy
    • Journal of the Society of Naval Architects of Korea
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    • v.31 no.4
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    • pp.147-156
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    • 1994
  • Though optimization method had been used for long time for the optimal design of ship structure, design variables in the most cases were assumed to be continuous real values or it was not easy to solve the mixed integer optimum design problems using the conventional optimization methods. Thus, it was often tried to use various initial starting points to locate the best optimum paint and to use special method such as branch and bound method to handle the discrete design variables in the optimization problems. Sometimes it had succeed, but the essential problems for dealing with the local optimum and discrete design variables was left unsolved. Hence, in this paper, Genetic Algorithms adopting the biological evolution process is applied to the ship structural design problem where the integer values for the number of stiffen design variables or the discrete values for the plate thickness variables would be more preferable in order to find out their effects on the final optimum design. Through the numerical result comparisons, it was found that Genetic Algorithm could always yield the global optimum for the discrete and mixed integer structural optimization problem cases even though it takes more time than other methods.

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Carbonation Assessment for Superstructure of Bridge Used in Urban Area for 46-Years by Core Specimens Extracted from the Structure (도심지에서 46년 사용된 교량 상부구조물에서 채취한 코어를 통한 탄산화 실태조사)

  • Kwon, Seung-Hee;Kwon, Seung-Jun
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.7 no.2
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    • pp.151-157
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    • 2019
  • Concrete bridge constructed in metropolitan cities has different superstructure members like slabs and girders, and their carbonation depths vary with different design strengths and local environmental conditions. In this paper, 54 concrete cores were obtained from prestressed concrete girders and the related tests were performed for compressive strength and carbonation depth measurement. Referred to the specified compressive strength of 24MPa for slab and 35MPa for I-type girder, the strengths from cores were evaluated to 82% and 73% of design grade, respectively. For carbonation depth, the slab member showed 30.6mm of average with 32.9% of COV(Coefficient of Variation) and I-type girder showed 16.7~17.0mm with 22.8~33.6 of COV. The I-type girder has much lower carbonation depth and COV compared to slab member, however it has higher COV than column structures.

Analysis on Flexural Behavior of Spiral Steel Pipe Considering Residual Stress Developed by Pipe Manufacturing (조관에 의한 잔류 응력을 고려한 스파이럴 강관의 휨 거동 분석)

  • Kim, Kyuwon;Kim, Jeongsoo;Kang, Dongyoon;Kim, Moon Kyum
    • Journal of the Korean Institute of Gas
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    • v.23 no.4
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    • pp.65-73
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    • 2019
  • A spiral steel pipe has been more used widely as a structural member as well as transport pipeline because the pipe can be manufactured continuously, consequently more economical than the conventional UOE pipe. As improved pipe manufacture technology makes spiral pipes to have high strength and to have larger diameters, the spiral pipes have been recently used as long distance transport pipeline with a large diameter and strain-based design is thus required to keep structural integrity and cost effectiveness of the spiral pipe. However, design codes of spiral pipe have not been completely established yet, and structural behaviors of a spiral pipe are not clearly understood for strain-based design. In this paper, the effects of residual stresses due to the spiral pipe manufacture process are investigated on the flexural behavior of the spiral pipe. Finite element analyses were conducted to estimate residual stresses due to the manufacturing process for the pipes which have different forming angle, thickness, and strength, respectively. After that, the results were used as initial conditions for flexural analysis of the pipe to numerically investigate its flexural behaviors.

Design Enhancement to Avoid Radar Mast Resonance in Large Ship using Design of Experiments (실험계획법을 이용한 대형 선박용 레이더 마스트의 공진회피 설계)

  • Park, Jun Hyeong;Lee, Daeyong;Yang, Jung-Wook;Song, Chang Yong
    • Journal of Ocean Engineering and Technology
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    • v.33 no.1
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    • pp.50-60
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    • 2019
  • Recently, problems with excessive vibration of the radar masts of large bulk carriers and crude oil tankers have frequently been reported. This paper explores a design method to avoid the resonance of a radar mast installed on a large ship using various design of experiment (DOE) methods. A local vibration test was performed during an actual sea trial to determine the excitation sources of the vibration related to the resonant frequency of the radar mast. DOE methods such as the orthogonal array (OA) and Latin hypercube design (LHD) methods were used to analyze the Pareto effects on the radar mast vibration. In these DOE methods, the main vibration performances such as the natural frequency and weight of the radar mast were set as responses, while the shape and thickness of the main structural members of the radar mast were set as design factors. From the DOE-based Pareto effect results, we selected the significant structural members with the greatest influence on the vibration characteristics of the radar mast. Full factorial design (FFD) was applied to verify the Pareto effect results of the OA and LHD methods. The design of the main structural members of the radar mast to avoid resonance was reviewed, and a normal mode analysis was performed for each design using the finite element method. Based on the results of this normal mode analysis, we selected a design case that could avoid the resonance from the major excitation sources. In addition, a modal test was performed on the determined design to verify the normal mode analysis results.

Progressive Collapse of Steel High-Rise Buildings Exposed to Fire: Current State of Research

  • Jiang, Jian;Li, Guo-Qiang
    • International Journal of High-Rise Buildings
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    • v.7 no.4
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    • pp.375-387
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    • 2018
  • This paper presents a review on progressive collapse mechanism of steel framed buildings exposed to fire. The influence of load ratios, strength of structural members (beam, column, slab, connection), fire scenarios, bracing systems, fire protections on the collapse mode and collapse time of structures is comprehensively reviewed. It is found that the key influencing factors include load ratio, fire scenario, bracing layout and fire protection. The application of strong beams, high load ratios, multi-compartment fires will lead to global downward collapse which is undesirable. The catenary action in beams and tensile membrane action in slabs contribute to the enhancement of structural collapse resistance, leading to a ductile collapse mechanism. It is recommended to increase the reinforcement ratio in the sagging and hogging region of slabs to not only enhance the tensile membrane action in the slab, but to prevent the failure of beam-to-column connections. It is also found that a frame may collapse in the cooling phase of compartment fires or under travelling fires. This is because that the steel members may experience maximum temperatures and maximum displacements under these two fire scenarios. An edge bay fire is more prone to induce the collapse of structures than a central bay fire. The progressive collapse of buildings can be effectively prevented by using bracing systems and fire protections. A combination of horizontal and vertical bracing systems as well as increasing the strength and stiffness of bracing members is recommended to enhance the collapse resistance. A protected frame dose not collapse immediately after the local failure but experiences a relatively long withstanding period of at least 60 mins. It is suggested to use three-dimensional models for accurate predictions of whether, when and how a structure collapses under various fire scenarios.

Content and Value Analysis of the Records of Green Party Korea's Election Activities (녹색당 선거활동 기록의 의미 분석 연구)

  • Ju, Hyun Mi;Yim, Jin Hee
    • The Korean Journal of Archival Studies
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    • no.49
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    • pp.121-173
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    • 2016
  • An election is a major event in a country that elects the people's representatives. Currently, Korea's electoral system has a structure that limits the exclusion of the minority's opinion. Also, it has strengthened the monopoly of major political parties. Despite the harsh conditions, Green Party Korea has proposed an alternative to prevent even the minority from being excluded by practicing direct democracy and expanding proportional representation through the institutionalization of the democratic process within the party. Election campaigns should thus reflect this orientation of Green Party Korea. The local elections and the national elections reflect Korea's political and social status and show the course over two minority parties beyond such limits. Moreover, they provide evidence of the activities of Green Party Korea. The paper analyzes how the election archives of the party hold the values of democracy, how minor parties jump to another because of the unfavorable election system, and how the archives of Green Party Korea reflect its values on the political history of Korea.

Beam-Column Connection with 1200mm Deep Multi-Reduced Taper Beam for Intermediate Moment Frame (깊이 1200mm급 변단면보의 중간모멘트골조용 내진접합부 개발)

  • Jung, Si-Hwa;Alemayehe, Robel Wondimu;Park, Man-Woo;Ju, Young-Kyu
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.35 no.4
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    • pp.135-146
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    • 2019
  • Deep beam has high section modules compared with shallow beam of the same weight. However, deep beam has low rotational capacity and high possibility of brittle failure so it is not possible to apply deep beams with a long span to intermediate moment frames, which should exhibit a ductility of 0.02rad of a story drift angle of steel moment frames. Accordingly, KBC and AISC limit the beam depth for intermediate and special moment frame to 750mm and 920mm respectively. The purpose of this paper is to improve the seismic performance of intermediate moment frame with 1200mm depth beam. In order to enhance vulnerability of plastic deformation capacity of deeper beam, Multi-Reduced Taper Beam(MRTB) shape that thickness of beam flange is reinforced and at the same time some part of the beam flange width is weakened are proposed. Based on concept of multiple plastic hinge, MRTB is intended to satisfy the rotation requirement for intermediate moment frame by dividing total story drift into each hinge and to prevent the collapse of the main members by inducing local buckling and fracture at the plastic hinge location far away from connection. The seismic performance of MRTB is evaluated by cyclic load test with conventional connections type WUF-W, RBS and Haunch. Some of the proposed MRTB connection satisfies connection requirements for intermediate moment frame and shows improved the seismic performance compared to conventional connections.

An Analysis of the Migration of the Public Institutes workers on Resettlement to Local cities (혁신도시 이전공공기관 종사자의 거주이전 결정요인 분석)

  • ROH, Yong Sik;LEE, Young Hwan
    • Journal of the Korea Convergence Society
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    • v.12 no.2
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    • pp.221-231
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    • 2021
  • This paper identify factors of migration of employees' household who work for relocated public institutions. As a factors of migration, we consider individual and household characteristics, the gravity model of distance and population and so on. Considering discrete dependant variable and structure of data, we employ the logistic multilevel model and random intercept model. The result indicates employees' who are female, 30s and 40s, higher education level(PhD) and whose spouse are unemployed tend to transfer their residential registration to new city near relocated public institution. Regarding regional variable, the distance from employee's previous residential location and number of migration of prior year are statistically significant. Also the model indicate regional economy, educational and residential environment of new city influence employee's decision for transferring residential registration.

Partial Offloading System of Multi-branch Structures in Fog/Edge Computing Environment (FEC 환경에서 다중 분기구조의 부분 오프로딩 시스템)

  • Lee, YonSik;Ding, Wei;Nam, KwangWoo;Jang, MinSeok
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.26 no.10
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    • pp.1551-1558
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    • 2022
  • We propose a two-tier cooperative computing system comprised of a mobile device and an edge server for partial offloading of multi-branch structures in Fog/Edge Computing environments in this paper. The proposed system includes an algorithm for splitting up application service processing by using reconstructive linearization techniques for multi-branch structures, as well as an optimal collaboration algorithm based on partial offloading between mobile device and edge server. Furthermore, we formulate computation offloading and CNN layer scheduling as latency minimization problems and simulate the effectiveness of the proposed system. As a result of the experiment, the proposed algorithm is suitable for both DAG and chain topology, adapts well to different network conditions, and provides efficient task processing strategies and processing time when compared to local or edge-only executions. Furthermore, the proposed system can be used to conduct research on the optimization of the model for the optimal execution of application services on mobile devices and the efficient distribution of edge resource workloads.

Effectiveness study of a cement mortar coating based on dune sand on the carbonation of concrete

  • Korichi, Youssef;Merah, Ahmed;Khenfer, Med Mouldi;Krobba, Benharzallah
    • Advances in concrete construction
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    • v.13 no.4
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    • pp.315-325
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    • 2022
  • Reinforced concrete structures are exposed throughout their lifetime to the phenomenon of carbonation, which considerably influences their durability by causing corrosion of the reinforcements. The fight against this phenomenon is usually ensured by anti-carbonation coatings which have the possibility of limiting the permeability to carbon dioxide or with coatings which absorb the CO2 present in the air. A coating with good crack-bridging (sealing) capacity will prevent water from entering through existing cracks in concrete. Despite the beneficial effect of these coatings, their durability decreases considerably over time with temperature and humidity. In order to use coatings made from local materials, not presenting any danger, available in abundance in our country, very economical and easy to operate is the main objective of this work. This paper aim is to contribute to the formulation of a corrected dune sand-based mortar as an anti-carbonation coating for concrete. The results obtained show that the cement mortar based on dune sand formulated has a very satisfactory compressive strength, a very low water porosity compared to ordinary cement mortar and that this mortar allows an improvement in the protection of the concrete against the carbonation of 60% compared to ordinary cement mortar based on alluvial sand. Moreover, the formulated cement mortars based on dune sand have good adhesion to the concrete support, their adhesion strengths are greater than 1.5MPa recommended by the standards.