• Title/Summary/Keyword: Cross-anisotropy

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Elastic-plastic Micromechanics Modeling of Cross-anisotropic Granular Soils: I. Formulation (직교 이방적 사질토의 미시역학적 탄소성 모델링: I. 정식화)

  • Jung, Young-Hoon;Chung, Choong-Ki
    • Journal of the Korean Geotechnical Society
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    • v.23 no.3
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    • pp.77-88
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    • 2007
  • A micromechanics-based model to simulate the elastic and elastic-plastic behavior of granular soils is developed. The model accounts for the fabric anisotropy represented by the statistical parameter of the spatial distribution of contact normals, the evolution of fabric anisotropy as a function of stress ratio, the continuous change of the co-ordination number relating to the void ratio, and the elastic and elastic-plastic microscopic contact stiffness. Using the experimental data for metallic materials, the elastic-plastic contact stiffness is derived as a power function of the normal contact force as well as the contact force initiating the yielding of contact bodies. To quantitatively assess microscopic model parameters, approximate solutions of cross-anisotropic elastic moduli are derived in terms of the micromechanical parameters.

Dynamic Response Analysis of Composite H-type Cross-section Beams (복합재료 H-형 단면 보의 동적응답 해석)

  • Kim, Sung-Kyun;Song, Oh-Seop
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.20 no.6
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    • pp.583-592
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    • 2010
  • Equations of motion of thin-walled composite H-type cross-section beams exposed to concentrated harmonic and non-harmonic time-dependent external excitations, incorporating a number of nonclassical effects of transverse shear, primary and secondary warping, and anisotropy of constituent materials are derived. The forced vibration response characteristics of a composite H-type cross-section beam exhibiting the circumferentially asymmetric stiffness(CAS) configuration are exploited in connection with the structural bending-torsion coupling resulting from directional properties of fiber reinforced composite materials.

Preparation and Swelling Behavior of Cross-Linked Films of Hydroxypropyl Chitosan Possessing Cholesteric Liquid-Crystalline Order (Cholesteric 액정질서를 지닌 Hydroxypropyl Chitosan 가교필름의 제조와 팽윤거동)

  • 마영대;김경희
    • Polymer(Korea)
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    • v.24 no.3
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    • pp.418-430
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    • 2000
  • A new hydroxylpropyl chitosan (HPCTO) capable of forming both thermotropic and lyotropic liquid crystalline phases was synthesized by reaction of alkali chitosan with propylene oxide and its solid films cross-linked with glyoxal were prepared by casting the liquid crystalline solution in methanol. The thermal and swelling properties of the cross-linked films were investigated. The films displayed fingerprint patterns characteristic of cholesteric liquid-crystalline phase, and their pitches increased with increasing temperature and cross-linker concentration. The cross-linked samples exhibited an anisotropic swelling in both water and methanol, suggesting that the two-dimensional cross-linking preferentially performs between HPCTO molecules. The degree of anisotropy highly depended on the solvent, but hardly on the cross-linker concentration investigated.

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The Influence of Deformation Modes on the Coefficient of Consolidation in the Normally Consolidated Clay (변형형상에 따른 정규압밀 점성토의 압밀계수 변화)

  • Park, Jae-Hyeon;Jeong, Young-Hoon;Chung, Choong-Ki
    • Proceedings of the Korean Geotechical Society Conference
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    • 2004.03b
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    • pp.823-830
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    • 2004
  • Consolidation tests under various deformation modes were performed to investigate the effect of deformation modes on the coefficient of consolidation in the normally consolidated clay in remolded and undisturbed clay. The degree of soil anisotropy was evaluated using cross-anisotropic elasticity theory suggested by Graham et al.(1983). Experimental results showed that the vertical compressibility was larger than the horizontal compressibility by $12{\sim}21%$ for the remolded clay and by $23{\sim}60%$ for the undisturbed clay, respectively. The results of a series of consolidation tests under the specific deformation modes showed that the coefficient of consolidation under 1 dimensional vertical strain condition was larger than that under 3 dimensional strain condition due to different deformation mode. Furthermore, the coefficient of consolidation under 1 dimensional vertical strain condition was larger than that under 1 dimensional horizontal strain condition by $40{\sim}60%$ in undisturbed clay, which clearly emphasized the significant effect of soil anisotropy on the rate of consolidation. Consequently, it can be concluded that the anisotropic deformation modes of soils, especially naturally deposited clays, should be taken into account for more accurate evaluation of the coefficient of consolidation.

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Free Vibration Analysis of Composite H-Type Cross-section Beams (복합재료 H형 단면 보의 자유진동 해석)

  • Kim, Sung-Kyun;Song, Oh-Seop
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.20 no.5
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    • pp.492-501
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    • 2010
  • Equations of motion of thin-walled composite H-type cross-section beams incorporating a number of nonclassical effects of transverse shear and primary and secondary warping, and anisotropy of constituent materials are derived. The vibrational characteristics of a composite thin-walled beam exhibiting the circumferentially asymmetric stiffness system(CAS) and the circumferentially uniform stiffness system(CUS) are exploited in connection with the bending-transverse shear coupling and the bending-twist coupling resulting from directional properties of fiber reinforced composite materials.

Dynamic Response Analysis of Composite H-Type Cross-Section Beams to Random Loads (랜덤하중이 가해진 복합재료 H-형 보의 동적 응답 해석)

  • Kim, Sung-Kyun;Song, Pong-Gun;Song, Oh-Seop
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2011.10a
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    • pp.130-135
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    • 2011
  • A study of the bending-extension-transverse shear coupled random response of the composite beams with thin-walled open sections subjected to various types of concentrated and distributed random excitations is dealt with in this paper. First of all, equations of motion of thin-walled composite H-type cross-section beams incorporating a number of nonclassical effects of transverse shear and primary and secondary warping, and anisotropy of constituent materials are derived. On the basis of derived equations of motion, analytical expressions for the displacement response of the composite beams are derived by using normal mode method combined with frequency response function method.

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Wind Data Simulation Using Digital Generation of Non-Gaussian Turbulence Multiple Time Series with Specified Sample Cross Correlations (임의의 표본상호상관함수와 비정규확률분포를 갖는 다중 난류시계열의 디지털 합성방법을 이용한 풍속데이터 시뮬레이션)

  • Seong, Seung-Hak;Kim, Wook;Kim, Kyung-Chun;Boo, Jung-Sook
    • Journal of Korean Society for Atmospheric Environment
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    • v.19 no.5
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    • pp.569-581
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    • 2003
  • A method of synthetic time series generation was developed and applied to the simulation of homogeneous turbulence in a periodic 3 - D box and the hourly wind data simulation. The method can simulate almost exact sample auto and cross correlations of multiple time series and control non-Gaussian distribution. Using the turbulence simulation, influence of correlations, non-Gaussian distribution, and one-direction anisotropy on homogeneous structure were studied by investigating the spatial distribution of turbulence kinetic energy and enstrophy. An hourly wind data of Typhoon Robin was used to illustrate a capability of the method to simulate sample cross correlations of multiple time series. The simulated typhoon data shows a similar shape of fluctuations and almost exactly the same sample auto and cross correlations of the Robin.

Operation Characteristic Analysis of a Comb Actuator due to a Anisotropy Variation in RIE Etching (RIE 식각시 발생하는 비등방도 변화에 따른 머리빗형 액튜에이터의 동작 특성 분석)

  • Kim, Bong-Soo;Park, Ho-Jun;Pak, Jung-Ho
    • Journal of Sensor Science and Technology
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    • v.8 no.5
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    • pp.368-376
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    • 1999
  • This paper predicts the changes in the spring constant, the resonant frequency, the electrostatic force, and the displacement of a resonant structure due to non-ideal anisotropic RIE etching process. First, a $6\;{\mu}m$ thick polysilicon was etched by RIE and the anisotropy of the etched structure was measured as a function of a RF power, a $Cl_2$ flow rate and a chamber pressure. In the experimental results, an anisotropy was decreased as the RF power, the $Cl_2$ flow rate, or the chamber pressure was increased. A comb actuator's operation characteristic was predicted depending on the anisotropy variations in RIE etching. Comb actuators with three different support beam structures were investigated : fixed-fixed, crab-leg, and double crab-leg. As the RIE etch anisotropy becomes non-ideal, i.e. the cross section becomes rather a trapezoidal than a rectangular shape, it decreases spring constant, resonant frequency and electrostatic force of a comb actuator but it increases the displacement of the mass. Among the three structures, the comb actuator with double crab-leg support beams is more influenced by anisotropy variation in RIE etch than other two.

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Evaluation of Bending Characteristics for Carbon FRP Structure having Circle Cross-section (원통 CFRP 구조재의 굽힘 특성 평가)

  • Kim, Jung-Ho;Kim, Ji-Hoon
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.20 no.2
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    • pp.202-206
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    • 2011
  • Works on the strength and stiffness in the structural members are carried out widely with various material and cross-sections with ever increasing safety concerns, they are presently applied in various fields including railroad trains, air crafts and automobiles. In addition to this, problem of lighting structural members became important subject by control of exhaust gas emission, fuel economy and energy efficiency. So, Light weight of member structures is necessary for the high performance and various functions. In this study, the CFRP flat and circular member was manufactured by CFRP prepreg sheet in autoclave. Carbon FRP is an anisotropy material whose mechanical properties change with its fiber orientation angle, so this study apply to the effects of the fiber orientation angle on the bending characteristics of the member. Each CFRP flat and circle are compared by strength and stiffness.

Identification of linearly unstable modes in the near-Earth current disruption

  • Mok, Chin-Ook;Ryu, Chang-Mo
    • Bulletin of the Korean Space Science Society
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    • 2009.10a
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    • pp.44.1-44.1
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    • 2009
  • Identification of wave characteristics during current disruption events in the near-Earth geomagnetic tail region (~ 10 RE) is important to understand the substorm onset mechanism. In this paper, linear stability analysis in the ion-cyclotron grequency range, considering temperature anisotropy and cross-field flow is presented. It is found that the ion-cyclotron drift waves propagating in a quasi-perpendicular direction with respect to the ambient magnetic field are characterized by low frequencies ($\omega$ < $0.5{\Omega}ci$), while quasi-parallel waves have frequencies close to the ion-cyclotron frequency ($\omega{\sim}{\Omega}ci$). This finding is consistent with the observation by THEMIS spacecraft of a current disruption event in which a similar high- and low-frequency band structure is also present [A. T. Y. Lui, et al., J. Geophys. Res. 113, A00C06 (2008)]. It is also found that the quasi-perpendicular mode is excited by the ion cross-field flow.

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