• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.12
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• pp.805-814
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• 2011

In the present study, the detailed flow structure and heat transfer characteristics in the newly-designed heat transfer surface geometry were investigated. The surface geometry proposed in the present study is a traditional dimple structure combining with a protrusion inside the dimple, which is named a protrusion-in-dimple in this study. The basic idea underlying the present surface geometry is to enhance the flow mixing and the corresponding heat transfer in the flow re-circulating region generated by a conventional dimple cavity. The present study was performed by the direct numerical simulation at a Reynolds number of 2800 based on mean velocity and channel height and Prandtl number of 0.71. Three different protrusion heights for protrusion-in-dimples were considered as the main design parameter of the present study. The calculated pressure drop and heat transfer capacity were assessed in terms of the Fanning friction factor and Colburn j factor. The overall performances estimated in terms of the volume and area goodness factor for protrusion-in-dimple cases were higher than the conventional dimple case.

• Journal of the Korea Society for Simulation
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• v.27 no.3
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• pp.117-129
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• 2018

In this paper we will discuss two different layout concepts which can be applied to rail-vehicle assembly factory. The existing system is based on the traditional flow line, and the suggested system is based on the fixed position layout. The main factors which affect on the system performances are the variation of process time, shortage rate of part and the shortage period. Simulation experiments indicate that the fixed position layout is better with respect to the throughput, mean flow time per vehicle and the mean flow time per fleet. Furthermore, the fixed position layout is more robust than the flow line because performance measures are insensitive to the variations of factors.

• Journal of KIISE
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• v.43 no.7
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• pp.744-750
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• 2016

Recent cloud infrastructures provide competitive performances and operation costs for many internet services through pay-per-use model. Particularly, object storages are highlighted, as they have unlimited file holding capacity and allow users to access the stored files anytime and anywhere. Several lines of research are based on cloud-backed file systems, which support traditional POSIX interface rather than RESTful APIs via HTTP. However, these existing file systems handle all files with uniform size backing objects. Consequently, the accesses to cloud object storages are likely to be inefficient. In our research, files are profiled according to characteristics, and appropriate backing unit sizes are determined. We experimentally verify that different backing unit sizes for the object storage improve the performance of cloud-backed file systems. In our comparative experiments with S3QL, our prototype cloud-backed file system shows faster performance by 18.6% on average.

• Wind and Structures
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• v.19 no.4
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• pp.443-465
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• 2014

Hyperbolic thin-shell cooling towers have complicated vibration modes, and are very sensitive to the effects of group towers and wind-induced vibrations. Traditional aero-elastic models of cooling towers are usually designed based on the method of stiffness simulation by continuous medium thin shell materials. However, the method has some shortages in actual engineering applications, so the so-called "equivalent beam-net design method" of aero-elastic models of cooling towers is proposed in the paper and an aero-elastic model with a proportion of 1: 200 based on the method above with integrated pressure measurements and vibration measurements has been designed and carried out in TJ-3 wind tunnel of Tongji university. According to the wind tunnel test, this paper discusses the impacts of self-excited force effect on the surface wind pressure of a large-scale cooling tower and the results show that the impact of self-excited force on the distribution characteristics of average surface wind pressure is very small, but the impact on the form of distribution and numerical value of fluctuating wind pressure is relatively large. Combing with the Complete Quadratic Combination method (hereafter referred to as CQC method), the paper further studies the numerical sizes and distribution characteristics of background components, resonant components, cross-term components and total fluctuating wind-induced vibration responses of some typical nodes which indicate that the resonance response is dominant in the fluctuating wind-induced vibration response and cross-term components are not negligible for wind-induced vibration responses of super-large cooling towers.

• Journal of Power Electronics
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• v.19 no.5
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• pp.1303-1314
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• 2019

This paper studies the harmonic characteristics of ship electric propulsion systems and their treatment methods. It also adopts effective measures to suppress and prevent ship power systems from affecting ship operation due to the serious damage caused by harmonics. Firstly, the harmonic characteristics of a ship electric propulsion system are reviewed and discussed. Secondly, aiming at problems such as resonant frequency and filter characteristics variations, resonance point migration, and unstable filtering performances in conventional passive filters, a method for fully tuning of a passive dynamic tunable filter (PDTF) is proposed to realize harmonic suppression. Thirdly, to address the problems of the uncontrollable inductance L of traditional air gap iron core reactors and the harmonics of power electronic impedance converters (PEICs), this paper proposes an electromagnetic coupling reactor with impedance transformation and harmonic suppression characteristics (ECRITHS), with the internal filter (IF) designed to suppress the harmonics generated by PEICs. The ECRITHS is characterized by both harmonic suppression and impedance change. Fourthly, the ECRITHS is investigated. This investigation includes the harmonic suppression characteristics and impedance transformation characteristics of the ECRITHS at the fundamental frequency, which shows the good performance of the ECRITHS. Simulation and experimental evaluations of the PDTF are carried out. Multiple PDTFs can be configured to realize multi-order simultaneous dynamic filtering, and can effectively eliminate the current harmonics of ship electric propulsion systems. This is done to reduce the total harmonic distortion (THD) of the supply currents to well below the 5% limit imposed by the IEEE-519 standard. The PDTF also can eliminate harmonic currents in different geographic places by using a low voltage distribution system. Finally, a detailed discussion is presented, with challenges and future implications discussed. The research results are intended to effectively eliminate the harmonics of ship electric power propulsion systems and to improve the power quality of ship power systems. This is of theoretical and practical significance for improving the power quality and power savings of ship power systems.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.4
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• pp.8-14
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• 2019

In Korean traditional wooden architecture, joint performance varies with the material characteristics of timber, the form of joint, the precision of timber-trimming and the like. Case studies prove that the beam-to-column joint type has large influence on the degrees of deformation and spacing. This is not only true of single-story buildings, but also of large-scale multi-story buildings more apparently. Therefore, this study followed the process of examining to joint types, producing their specimens and testing their structural performance. As a consequence of structural test, the dovetail joint specimen showed the best outcomes of the maximum load and rigidity. Synthesizing the structural performances by respective forms of joints, the Doraegeoji dovetail joint specimen showed the higher performance, followed in order by the Doraegeoji mortise joint specimen and the Tongneoko dovetail joint specimen. The structural performance of a building varies with the characteristics by the shouldering forms of penetrating beams and with the joint types within the columns. This should be considered for the new construction or restoration of multi-story buildings, and be continuously researched henceforth.

• Steel and Composite Structures
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• v.31 no.1
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• pp.99-112
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• 2019

Semi-rigid joints have been widely studied in literature in recent decades because they affect greatly the structural response of frames. In literature, the behavior of semi-rigid joints is commonly assumed to be identical under positive and negative moments which are obviously incorrect in many cases where joint details such as bolt arrangement or placement of haunch are vertically asymmetrical. This paper evaluates two common types of steel frames with asymmetrical beam-to-column joints by Direct Analysis allowing for plasticity. A refined design method of steel frames using a proposed simple forth order curved-quartic element with an integrated joint model allowing for asymmetrical geometric joint properties is presented. Furthermore, the ultimate behavior of six types of asymmetrical end-plate connections under positive and negative moment is examined by the Finite Element Method (FEM). The FEM results are further applied to the proposed design method with the curved-quartic element for Direct Analysis of two types of steel frames under dominant gravity or wind load. The ultimate frame behavior under the two different scenarios are examined with respect to their failure modes and considerably different structural performances of the frames were observed when compared with the identical frames designed with the traditional method where symmetrical joints characteristics were assumed. The finding of this research contributes to the design of steel frames as their asymmetrical beam-to-column joints lead to different frame behavior when under positive and negative moment and this aspect should be incorporated in the design and analysis of steel frames. This consideration of asymmetrical joint behavior is recommended to be highlighted in future design codes.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.3
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• pp.93-98
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• 2022

Recently, fast storage media such as Optane have emerged, and memory system configurations designed for disk storage should be reconsidered. In this paper, we analyze the effect of the page size on the memory system performances when fast storage is adopted. Based on this, we design a page size model that can guide an appropriate page size for given workloads in virtualized environments. Configuring different page sizes for various workloads is not an easy matter in traditional systems, but due to the widespread adoption of cloud systems, page sizing performed in our model is feasible for virtual machines, which are generated for executing specific workloads. Simulation experiments under various virtual machine scenarios show that the proposed model improves the memory access time significantly by configuring page sizes for given workloads.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.6 no.11
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• pp.585-594
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• 2016

Information system development projects are increasingly enlarging in size and are becoming more complex in the development environment. The traditional approaches for the development of information system, however, haven't shown the expected performances in the management for them and many researchers have been trying to find a new approach for overcoming this challenges. And one of the new approaches is the PMO and it is introduced to solve the problems of project management and the related organizational, technical, and administrative problems. This study attempted to find the efficient information system establishment plan. In particular, this study wants to research the practicality of PMO and the detailed utilization plans. As a result, this study proposes the structure of project implementation, the requirements, the direction of the basic system design, the scope of system development, and the budgeting for the systems. It is expected to contribute the successful implementation of the project.

• 한국체육학회지인문사회과학편
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• v.54 no.4
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• pp.257-269
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• 2015

The purpose of this study was to conduct content analysis on expression activity section in the physical education textbooks of 2009 curriculum revision and provide a basis for future middle school physical education. in order to accomplish the purpose of this study, 5 different kinds of physical education textbook. The physical education textbooks were examined through the comparative analysis and previous studies conducted for selections of the analysis bases. The results were as follows. First, textbooks devoted the space from 14.1 to 17.3%. In deployment and configuration of the section, each textbooks were used variety of methods, photographs and illustrations for motivations and advanced learning. Second, the instructional objectives were presented 4-6 each text book including expression activity concepts, understanding expression methods, personal competence reinforcement through creative activity, and watching performances. Learning contents were to focus on the concepts of aesthetic component in the esthetical expression, to highlight creative component in the modern expression, to express characteristic dances through understanding of the culture in the traditional expression. lastly, the middle assessments hight the understanding of each contents but small assessments focus on attitudes of character education.