• Title/Summary/Keyword: 동하중 계수

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A Study on the Liquefaction Resistance of Anisotropic Sample under Real Earthquake Loading (이방 구속 조건에서 실지진 하중을 이용한 포화사질토의 액상화 저항강도 특성)

  • Lee, Chae-Jin;Kim, Soo-Il;Jeong, Sang-Seom
    • Journal of the Korean Geotechnical Society
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    • v.26 no.2
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    • pp.5-14
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    • 2010
  • In this study, cyclic triaxial tests were performed under anisotropically consolidated condition by using irregular earthquake loading to consider in-situ condition and seismic wave. Jumunjin sand with a relative density 50 percent was used in the tests. The consolidation pressure ratio (K) was changed from 0.5 to 1.0. The Ofunato and Hachinohe wave were applied as irregular earthquake loadings and liquefaction resistance strengths of each specimen were estimated from the excess pore water pressure (EPWP) ratio. As a results of the cyclic triaxial tests, EPWP ratio increased with increased K value. It shows that isotropically consolidated sand is more susceptible to liquefaction than anisotropically consolidated sand under equal confining pressure and dynamic loadings. From the test results, the relationship between K and EPWP ratio normalized by effective confining pressure and deviator stress was proposed. And a new factor which corrects the liquefaction resistance strength for the in-situ stress condition is proposed.

Wheel/Rail Contact Analysis with Consideration of Friction and Torque (마찰과 토크를 고려한 차륜/레일 접촉 해석)

  • Song, Ki-Seok;Han, Seung-Hee;Choi, Yeon-Sun
    • Journal of the Korean Society for Railway
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    • v.17 no.1
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    • pp.14-18
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    • 2014
  • Wheel/rail contact is a significant problem in railway dynamics. In this paper, the wheel/rail contact is examined analytically and numerically as a contact problem between two cylinders where torque and friction have effect. Furthermore, the contact of a real wheel and rail is investigated numerically where the normal and shear force act. This study demonstrates that the wheel/rail contact is a process that generates traction force through creep where rolling and sliding occurs simultaneously depending on the shape of the wheel and rail, and the friction coefficient between them.

Characterization of Thickness and Thermoelastic Properties of Interphase in Polymer Nanocomposites using Multiscale Analysis (멀티스케일 해석을 통한 고분자 나노복합재의 계면 상 두께와 열탄성 물성 도출)

  • Choi, Joonmyung;Cho, Maenghyo
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.29 no.6
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    • pp.577-582
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    • 2016
  • In this study, a multiscale method for solving a thermoelasticity problem for interphase in the polymeric nanocomposites is developed. Molecular dynamics simulation and finite element analysis were numerically combined to describe the geometrical boundaries and the local mechanical response of the interfacial region where the polymer networks were highly interacted with the nanoparticle surface. Also, the micrmechanical thermoelasticity equations were applied to the obtained equivalent continuum unit to compute the growth of interphase thickness according to the size of nanoparticles, as well as the thermal phase transition behavior at a wide range of temperatures. Accordingly, the equivalent continuum model obtained from the multiscale analysis provides a meaningful description of the thermoelastic behavior of interphase as well as its nanoparticle size effect on thermoelasticity at both below and above the glass transition temperature.

An In-silico Simulation Study on Size-dependent Electroelastic Properties of Hexagonal Boron Nitride Nanotubes (인실리코 해석을 통한 단일벽 질화붕소 나노튜브의 크기 변화에 따른 압전탄성 거동 예측연구)

  • Jaewon Lee;Seunghwa Yang
    • Composites Research
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    • v.37 no.2
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    • pp.132-138
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    • 2024
  • In this study, a molecular dynamics simulation study was performed to investigate the size-dependent electroelastic properties of single-walled boron nitride nanotubes(BNNT). To describe the elasticity and polarization of BNNT under mechanical loading, the Tersoff potential model and rigid ion approximation were adopted. For the prediction of piezoelectric constants and Young's modulus of BNNTs, piezoelectric constitutive equations based on the Maxwell's equation were used to calculate the strain-electric displacement and strain-stress relationships. It was found that the piezoelectric constants of BNNTs gradually decreases as the radius of the tubes increases showing a nonnegligible size effect. On the other hand, the elastic constants of the BNNTs showed opposites trends according to the equivalent geometrical assumption of the tubular structures. To establish the structure-property relationships, localized configurational change of the primarily bonded B-N bonded topology was investigated in detail to elucidate the BNNT curvature dependent elasticity.

An analysis of horizontal deformation of a pile in soil using a continuum soil model for the prediction of the natural frequency of offshore wind turbines (해상풍력터빈의 고유진동수 예측을 위한 지반에 인입된 파일의 연속체 지반 모델 기반 수평 거동 해석)

  • Ryue, Jungsoo;Baik, Kyungmin;Lee, Jong-Hwa
    • The Journal of the Acoustical Society of Korea
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    • v.35 no.6
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    • pp.480-490
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    • 2016
  • As wind turbines become larger and lighter, they are likely to respond sensitively by dynamic loads applied on them. Since the responses at resonances are particularly interested, it is required to be able to predict natural frequencies of wind turbines reliably at early design stage. To achieve this, the foundation-soil analysis is needed to be carried out and a finite element approach is adopted in general. However, the finite element approach would not be appropriate in early design stage because it demands heavy efforts in pile-soil modelling and computing facilities. On the contrary, theoretical approaches adopting linear approximations for soils are relatively simple and easy to handle. Therefore, they would be a useful tool in predicting a pile-soil interaction, particularly in early design stage. In this study an analysis for a pile inserted in soil is performed. The pile and soil are modelled as a beam and continuum medium, respectively, within an elastic range. In this analysis, influence factors at the pile head for lateral loads are predicted by means of this continuum approach for various length-diameter ratios of the pile. The influence factors predicted are validated with those reported in literature, proposed from a finite element analysis.

An Experimental Study on the Dynamic Increase Factor and Strain Rate Dependency of the Tensile Strength of Rock Materials (암석재료 인장강도의 동적 증가계수 및 변형률 속도 의존성에 대한 실험적 연구)

  • Oh, Se-Wook;Choi, Byung-Hee;Min, Gyeong-Jo;Jung, Yong-Bok;Cho, Sang-Ho
    • Explosives and Blasting
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    • v.39 no.1
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    • pp.10-21
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    • 2021
  • Brittle materials such as rocks and concretes exhibit large strain-rate dependency under dynamic loading conditions. This means that the mechanical properties of such materials can significantly be varied according to load velocity. Thus, the strain-rate dependency is recognized as one of the most important considerations in solving problems of blast engineering or rock dynamics. Unfortunately, however, studies for characterizing the dynamic properties of domestic rocks and other brittle materials are still insufficient in the country. In this study, dynamic tensile tests were conducted using the Hopkinson pressure bar apparatus to characterize the dynamic properties of Geochang granite and high-strength concrete specimens. The dynamic Brazilian disc test, which is suggested by ISRM, and the spalling method were applied. In general, the latter is believed to have some advantages in experiments under high-strain rate deformation. It was found from the tests that there were no significant difference between the dynamic tensile strengths obtained from the two different test methods for the two materials given. However, this was not the expected result before the tests. Actually, authors expected that there be some differences between them. Hence, it is thought that further investigations are needed to clarify this results.

Stiffness Characterization of Subgrade using Crosshole-Type Dynamic Cone Penetrometer (크로스홀 형태의 동적 콘 관입기를 이용한 노반의 강성특성 평가)

  • Hong, Won-Taek;Choi, Chan Yong;Lim, Yujin;Lee, Jong-Sub
    • Journal of the Korean Geotechnical Society
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    • v.34 no.2
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    • pp.55-63
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    • 2018
  • In order to support the load of the train with enough stiffness, a study on an effective method for the characterization of the stiffness of the compacted subgrade is required. In this study, the crosshole-type dynamic cone penetrometer (CDCP) is used for the stiffness characterization of the subgrade along the depth. For the application of the CDCP test, three points of compacted subgrades are selected as the study sites. For the study sites, CDCP test, in-situ density test, and light falling weight deflectometer (LFWD) test are conducted. As the results of CDCP tests, shear wave velocity profiles are obtained by using the travel times and the travel distances of the shear waves along the depth. In addition, maximum shear modulus ($G_{max}$) profiles are estimated by using the density of the subgrades and the shear wave velocity profiles. The averaged maximum shear moduli at each testing point are highly correlated with the dynamic deflection moduli ($E_{vd}$) determined by LFWD tests. Therefore, a reliable stiffness characterization of the subgrade can be conducted by using CDCP tests. In addition, because CDCP characterizes the stiffness of the subgrade along the depth rather than a representative value, CDCP test may be effectively used for the stiffness characterization of the subgrade.

Mechanical Properties of High Performance Concrete with Material for Lateral Confinement (횡구속재 변화에 따른 고성능 콘크리트의 역학적 특성)

  • Han, Cheon-Goo;Jung, Duk-Woo;Jin, En-Hao
    • Journal of the Korea Concrete Institute
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    • v.15 no.1
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    • pp.110-116
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    • 2003
  • Recently, as concrete structure becomes high rise and large scaled tendency, demands for high performance concrete such as high strength, high fluidity and high durability has been increased. Even though high performance concrete performs high strength, workability and durability, compared to with those of normal concrete, it is more brittle than normal concrete. Accordingly, this paper is intended to improve toughness and compressive strength through investigating the mechanical properties of the high performance concrete confined with metal lath, glass fiber and carbon fiber laterally in the case of 30% and 40% of W/B. According to the results, the compressive strength increases in order of metal lath, carbon fiber and glass fiber. Considering strain-stress curve with the kinds of material for lateral confinement, while brittleness failure occurs in plain concrete just after maximum load, it is improved in some degree in confined concrete due to increase of the strain by increase of toughness. Elastic modulus increases slightly in case of confined concrete, like the compressing strength.

Wear Properties of Nuclear Graphite IG-110 at Elevated Temperature (원자력용 흑연 IG-110 에 대한 고온 마모 특성 평가)

  • Wei, Dunkun;Kim, Jaehoon;Kim, Yeonwook
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.5
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    • pp.469-474
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    • 2014
  • The high temperature gas-cooled reactor (HTR-10) is designed to produce electricity and hydrogen. Graphite is used as reflector, support structures, and a moderator in reactor core; it has good resistance to neutron and is a suitable material at high temperatures. Friction is generated in the graphite structures for the core reflector, support structures, and moderator because of vibration from the HTR-10 fuel cycle flow. In this study, the wear characteristics of the isotropic graphite IG-110 used in HTR-10 were evaluated. The reciprocating wear test was carried out for graphite against graphite. The effects of changes in the contact load and sliding speeds at room temperature and $400^{\circ}C$ on the coefficient of friction and specific wear rate were evaluated. The wear behavior of graphite IG-110 was evaluated based on the wear surfaces.

Design of Mach-Scale Blade for LCH Main Rotor Wind Tunnel Test (소형민수헬기 주로터 풍동시험을 위한 마하 스케일 블레이드 설계)

  • Kee, YoungJung;Park, JoongYong
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.46 no.2
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    • pp.159-166
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    • 2018
  • In this study, the internal structural design, dynamic characteristics and load analyses of the small scaled rotor blade required for LCH(Light Civil Helicopter) main rotor wind tunnel test were carried out. The test is performed to evaluate the aerodynamic performance and noise characteristics of the LCH main rotor system. Therefore, the Mach-scale technique was appled to design the small scaled blade to simulate the equivalent aerodynamic characteristics as the full scale rotor system. It is necessary to increase the rotor speed to maintain the same blade tip speed as the full scale blade. In addition, the blade weight, section stiffness, and natural frequency were scaled according to the Mach-type scaling factor(${\lambda}$). For the design of skin, spar, torsion box, which are the main components of the blade, carbon and glass fiber composite materials were adopted, and composite materials are prepreg types that can be supplied domestically. The KSec2D program was used to evaluate the section stiffness of the blade. Also, structural loads and dynamic characteristics of the Mach scale blade were investigated through the comprehensive rotorcraft analysis program CAMRADII.