• Title/Summary/Keyword: Paper strength

Search Result 9,626, Processing Time 0.04 seconds

Distance Ratio based Probabilistic Broadcasting Mechanism in Mobile Ad Hoc Network (모바일 애드 혹 네트워크에서이격 비율에 근거한 확률적 브로드캐스팅 기법)

  • Kim, Jeong-Hong;Kim, Jae-Soo
    • Journal of the Korea Society of Computer and Information
    • /
    • v.15 no.12
    • /
    • pp.75-84
    • /
    • 2010
  • As broadcasting in Mobile Ad hoc NETwork (MANET) is the process that a node sends a packet to all other nodes in the network. it is used for routing protocols such as Ad hoc On demand Distance Vector (AODV) to disseminate control information for establishing the routes. In this paper, we propose Probabilistic Broadcasting mechanism based on Distance Ratio between sender and receive node in MANETs. The proposed approach is based on the combination of probability and distance based approach. A mobile node receiving broadcast packets determines the probability of rebroadcasting considering distance ratio from sender. The distance ratio of a node is calculated by the distance from sender and the length of radio field strength. As a node with high distance ratio is located far away from sender, rebroadcast probability is set to high value. On contrary, the low rebroadcast probability is set for a node with low distance ratio which is close to sender. So it reduces packets transmission caused by the early die-out of rebroadcast packets. Compared with the simple flooding and fixed probabilistic flooding by simulation, our approach shows better performances results. Proposed algorithm can reduce the rebroadcast packet delivery more than 30% without scanting reachability, where as it shows up to 96% reachability compared with flooding.

A Numerical Study of Tumble Effect on Spray/wall Impingement in the D. I. Engines (직접분사식 엔진내의 분무/벽 충돌 현상에서 텀블 효과에 관한 연구)

  • Chae, Soo;Yang, Hyup;Ryou, Su-Yeal;Ryou, Hong-Sun
    • Transactions of the Korean Society of Automotive Engineers
    • /
    • v.10 no.5
    • /
    • pp.45-57
    • /
    • 2002
  • In this paper, the results gained by applying many impingement models to the cylinder and flat plate were analyzed in comparison with the experimental data to study a spray/wall interaction phenomena. To begin with, the behavior of spray injected normal to the wall was analysed using three different impingement models ; Naber and Reitz model(NR model), Watkins and Wang model(WW model) and Park and Watkins model(PW model) in the present calculation. The results obtained from these models were compared with experimental data of Katsura et. al. The results indicated that PW model was in better agreement with experimental data than the NR and WW model. Also f3r spray injected at 30DEG , the result of three models were compared with experimental data of Fujimoto et. al. The results showed that m model overpredicted the penetration in the radial direction because this model was based on the inviscid jet analogy. WW model did not predicted the radius and height of the wall spray effectively. It might be thought that this discrepancy was due to the lack of consideration of spray film velocity occurred at impingement site. The result of PW model agrees with the experimental data as time goes on. In particular, a height of the spray droplets was predicted more closely to the experimental data than the other two models. The results of PW model in which the spray droplets were distributed densely around the edge of droplet distribution shaped in a circle had an agreement with the experimental data of Fujimoto et. al. Therefore, it was concluded that PW model performed better than M and WW model for prediction of spray behavior. The numerical calculation using PW model performed to the cylinder similar to the real shape of DI engine. The results showed that vortex strength near the wall in the cylinder was stronger than that in the case of flat plate. Contrary to the flat plat, an existence of the side wall in the cylinder caused the tangential velocity component to be reduced and the normal velocity component to be increased. The flow tends to rotate to the inside of cylinder going upward to the right side wall of cylinder gradually as time passes. Also, the results showed that as the spray angle increases, the gas velocity distribution and the tumble flow seemed to be formed widely.

Railway Governance and Power Structure in China

  • Lee, Jinjing
    • International Journal of Railway
    • /
    • v.1 no.4
    • /
    • pp.129-133
    • /
    • 2008
  • Over the last $15{\sim}20$years, many countries have adopted policies of railway privatization to keep up with increasing competition from road and air transport. Although each country and case has its own history, market characteristics, political context as well as administrative process, railway privatizations (including railway restructure, concession etc.) in the west usually are accompanied with the establishment of new regulatory regimes. Therefore, railway governance has been innovating towards an interaction of government, regulator, industry bodies, user groups, trade unions and other interested groups within the regulatory framework. However, it is not the case in China. Although China had seen a partial privatization in some branch lines and is experiencing a much larger-scale privatization by establishing joint-ventures to build and operate high-speed passenger lines and implementing an asset-based securitization program, administrative control still occupies absolutely dominant position in the railway governance in China. Ministry of Railway (MOR) acts as the administrator, operator as well as regulator. There is no national policy that clearly positions railway in the transportation network and clarifies the role of government in railway development. There is also little participation from interested groups in the railway policy making, pricing, service standard or safety matter. Railway in China is solely governed by the mere executive agency. Efficiency-focused economic perspective explanation is far from satisfaction. A wider research perspective from political and social regime is of great potential to better explain and solve the problem. In the west, separation and constrains of power had long been established as a fundamental rule. In addition to internal separation of political power(legislation, execution and jurisdiction), rise of corporation in the 19th century and association revolution in the 20th century greatly fostered the growth of economic and social power. Therefore, political, social and economic organizations cooperate and compete with each other, which leads to a balanced and resonable power structure. While in China, political power, mainly party-controlled administrative power has been keeping a dominated position since the time of plan economy. Although the economic reform promoted the growth of economic power of enterprises, it is still not strong enough to compete with political power. Furthermore, under rigid political control, social organizations usually are affiliated to government, independent social power is still too weak to function. So, duo to the limited and slow reform in political and social regime in China, there is an unbalanced power structure within which political power is dominant, economic power expanding while social power still absent. Totally different power structure in China determines the fundamental institutional environment of her railway privatization and governance. It is expected that the exploration of who act behind railway governance and their acting strength (a power theory) will present us a better picture of railway governance as a relevant transportation mode. The paper first examines the railway governance in China and preliminarily establishes a linkage between railway governance and its fundamental institutional environment, i.e. power structure in a specific country. Secondly, the reason why there is no national policy in China is explored in the view of political power. In China, legislative power is more symbolic while party-controlled administrative power dominates political process and plays a fundamental role in Chinese railway governance. And then, in the part three railway finance reform is analyzed in the view of economic power, esp. the relationship of political power and economic power.

  • PDF

An Experimental Study on the Mechanical Properties of HPFRCCs Reinforced with the Micro and Macro Fibers (마이크로 및 매크로 섬유에 의해 보강된 고인성 시멘트 복합재료의 역학적 특성에 관한 실험적 연구)

  • Kim Moo-Han;Kim Jae-Hwan;Kim Yong-Ro;Kim Young-Duck
    • Journal of the Korea Concrete Institute
    • /
    • v.17 no.2 s.86
    • /
    • pp.263-271
    • /
    • 2005
  • HPFRCC(High Performance Fiber Reinforced Cementitious Composite) is a class of FRCCs(Fiber Reinforced Cementitious Composites) that exhibit multiple cracking. Multiple cracking leads to improvement in properties such as ductility, toughness, fracture energy, strain hardening, strain capacity, and deformation capacity under tension, compression, and bending. These improved properties of HPFRCCs have triggered unique and versatile structural applications, including damage reduction, damage tolerance, energy absorption, crack distribution, deformation compatibility, and delamination resistance. These mechanical properties of HPFRCCs become different from the kinds and shapes of used fiber, and it is known that the effective size of fiber in macro crack is different from that in micro crack. This paper reports an experimental findings on the mechanical properties of HPFRCCs reinforced with the micro fiber(PP50, PVA100 and PVA200) and macro fiber(PVA660, SF500). Uniaxial compressive tests and three point bending tests are carried out in order to compare with the mechanical properties of HPFRCCs reinforced with micro fibers or hybrid fibers such as compressive strength, ultimate bending stress, toughness, deformation capacity and crack pattern under bending, etc.,

A Seismatic Performance Analysis of Circular RC Bridge Piers I. Evaluation of Influence Parameters of Confinement Steel Ratio (원형 철근콘크리트 교각의 내진성능 I. 심부구속철근비 영향 변수 평가)

  • Lee Dae-Hyoung;Park Chang-Kyu;Kim Hyun-Jun;Chung Young-Soo
    • Journal of the Korea Concrete Institute
    • /
    • v.17 no.4 s.88
    • /
    • pp.603-611
    • /
    • 2005
  • For the establishment of rational seismic design code for RC (reinforced concrete) bridge pier, this paper has analyzed the seismic code of RC bridge pier specified in )veil-known codes such as KHBDS (Korea Highway Bridge Design Specification), AASHTO Standard, ATC-32, Eurocode 8, NZS 3101, etc. So as to secure aseismic ductility of RC pier, transverse confinement steel ratios of those codes have been examined together with other design parameters such as strength of concrete and reinforcing steel, axial force ratio, aspect ratio, longitudinal steel ratio, etc. However, there has been arisen a doubt for the validity of those parameters. Thus, the objective of this study is to quantitatively evaluate the validity of design parameter of each code on the experimental seismic ductility for about 80 test specimens. It was concluded from this study that the axial force ratio is a dominant factor for the seismic displacement ductility. Therefore, it Is desirable that the axial force ratio be further taken into account in the corresponding seismic design formula of RC bridge pier in current KHBDS.

Flexural Experiment of PSC-Steel Mixed Girders and Evaluation for Analyses on Tangentional Stiffness of Connection (프리스트레스트 콘크리트-강 혼합거더의 휨 실험 및 경계면 수평계수 분석)

  • Kim, Kwang-Soo;Jung, Kwang-Hoe;Sim, Chung-Wook;Yoo, Sung-Won
    • Journal of the Korea Concrete Institute
    • /
    • v.20 no.2
    • /
    • pp.231-237
    • /
    • 2008
  • This study was performed to evaluate joint behavior of prestressed concrete(PSC)-steel mixed girders through the flexural test of 14 beams according to embedded length, amount of reinforcing steel, stud arrangement, and prestressing force. All test beams were failed by turns of desertion of reinforcing steel, stud, and steel plate. From test results, prestressing force was more effective on performance of connection than stud arrangement and reinforcing steel. And the spacing of stud is also more effective than embedding length. This paper also presented 3D nonlinear analysis considering the slip of composite section as well as the static load tests of PSC-steel mixed girders. According to the slip modulus, the nonlinear analysis showed that the behavior of hybrid girders could be divided into three parts as full-composite, partial-composite and non-composite. However, the experimental results showed that the PSC-steel hybrid girders with shear connectors took the part of partial composite action in ultimate load stage. In addition, it was founded that stud shear connectors and welded reinforcements were contributed to improve the ultimate strength of hybrid girders for about 20%.

An Experimental Study and Value Analysis for Performance Assessment of the Embo-thane Membrane Waterproofing Method (엘보탄도막방수공법의 성능평가를 위한실험적 연구 및 VE분석)

  • Yoon, Cha-Woong;Lee, Seung-Soo;Kim, Sang-Rok;Seo, Jong-Won
    • Korean Journal of Construction Engineering and Management
    • /
    • v.10 no.5
    • /
    • pp.123-134
    • /
    • 2009
  • Since 1970s, urethane waterproofing method is broadly used in rooftops, underground spaces, and sports stadium for its outstanding ultraviolet blockage, watertightness, and elasticity. However, development of slippage-resistance and endurance, improvement of function considering convenience and visually pleasing of users, urethane waterproofing method is necessary, since rooftops and underground spaces have slippage and external force risks. Therefore, many improved waterproofing methods are being developed and, recently, embo-thane waterproofing method, which applies embo-spray coating system, has been developed. This paper explains exposure, nonexposure, and floor-material of embo-thane waterproofing method, and then perform experimental study for comparison with urethane waterproofing method about tensile strength, coefficient of expansion, performance of bond, anti-abrasion, and slippage-resistance. In addition, the performance index was presented for the superiority of embo-thane waterproofing method compared to urethane by setting up evaluation criteria considering not only physical performance but also design side of embo-thane waterproofing method, and Value Analysis applying AHP. Also for an assessment considering uncertain result, Monte Carlo Simulation Method was used to operate reliability analysis through statistic approach method.

An Analysis on BitTorrent Performance Based on the Number of Unchoked Peers (Unchoked Peer 개수에 따른 BitTorrent 성능 분석)

  • Chung, Tae-Joong;Han, Jin-Young;Kim, Hyun-Chul;Kwon, Tae-Kyoung;Choi, Yang-Hee
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.35 no.8B
    • /
    • pp.1197-1203
    • /
    • 2010
  • A strength of BitTorrent, which is widely used for file sharing today, is due to its peer selection mechanism which is designed to encourage peers to contribute data. In the peer selection phase in BitTorrent, peers to upload the file in a swarm are selected by determining which peers upload the most to themselves. However, the number of peers to upload (i.e., number of unchoked peers) is fixed to four in its peer selection mechanism of BitTorrent, which yields inefficiency because the situation of the swarm may vary frequently (e.g., number of peers in the swarm, download rates, and upload rates). In this paper, we analyze the swarming system performance when the number of unchoked in BitTorrents is not static, but dynamic. For empirical investigation, we established a testbed in Seoul National University by modifying an open-source BitTorrent client, which is popular. Through our experiments, we show that an adaptive mechanism to adjust the number of unchoked peers considering the situation of the swarm is needed to improve the performance of BitTorrent.

Horizontal Behavior Characteristics of Umbrella-Type Micropile Applied in Sandy Soil Subjected to Seismic Motion (사질토 지반에 설치된 우산형 마이크로파일의 지진 시 수평거동 특성)

  • Kim, Soo-Bong;Son, Su Won;Kim, Jin Man
    • Journal of the Korean GEO-environmental Society
    • /
    • v.21 no.7
    • /
    • pp.5-16
    • /
    • 2020
  • Currently, the seismic design standards have been strengthened due to the occurrence of the Gyeongju and Pohang earthquake, and seismic performance evaluation of existing facilities is being conducted. It aims to secure a seismic performance effect during earthquakes by improving the micro-pile method, which can be constructed in limited confined places while minimizing damage to existing facilities. The improvement method is to construct all the piles in the square-tray-type plate on the top of the pile by constructing the slope pile in the form of an umbrella around the vertical pile, the main pillar. In this paper, the numerical analysis was performed to analyze the horizontal displacement behavior of an umbrella-type micropile for various real-measurement seismic waves in sandy soil. As a result of numerical analysis, the softer the ground, the better the effect of horizontal resistance of umbrella-type micropile. The horizontal displacement reduction effect was pronounced when the embedded depth was 15 m or more at the same ground strength, and it was found to be effective in earthquakes if it was settled on the ground with an N value of 30 or more. The embedded depth and horizontal displacement suppression effect of the micropile was proportional. Generally, the weaker the ground, the greater the displacement suppression effect. Umbrella-type micropile had a composite resistance effect in which the vertical pile resists the moment and inclined pile resists the axial force.

Safety of Ductility Demand Based Seismic Design for Circular RC Bridge Columns (원형 철근콘크리트 교각에 대한 연성도 내진설계법의 안전성)

  • Lee, Jae-Hoon;Hwang, Jung-Kil;Choi, Jin-Ho
    • Journal of the Korea Concrete Institute
    • /
    • v.20 no.2
    • /
    • pp.193-202
    • /
    • 2008
  • Seismic design for bridge columns of the current Korea Highway Bridge Design Specifications which adopt full ductility design concept results in reinforcement congestion problems in construction site. It is due to large amount of confining steel is required even for small ductility demand which is a normal case in low and moderate seismicity regions like Korean peninsular. Therefore a new seismic design method based on limited ductility concept was proposed, which is called ductility demand based design method. It uses the new confining steel design equation considering ductility demand and aspect ratio of the column as well as material strength. The purpose of this study is to verify safety of the ductility demand based design method by the confining steel design equation. Eighty nine circular column test results are selected and investigated in terms of ductility factor and its safety. The safety factor for the circular column test results ranges between 1.11 and 3.98, and the average is 1.90. In this paper, the basic concept and detailed design procedure of the ductility demand based design method are also introduced as well as the investigation of the safety with respect to the major variables in confining steel design.