• Title, Summary, Keyword: Inhomogeneous

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Theoretical and numerical analysis of the influence of initial stress gradient on wave propagations

  • Tao, Ming;Chen, Zhenghong;Li, Xibing;Zhao, Huatao;Yin, TuBing
    • Geomechanics and Engineering
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    • v.10 no.3
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    • pp.285-296
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    • 2016
  • The investigation of stress wave propagation in a medium with initial stress has very important application in the field of engineering. However, the previous research less consider the influence of initial stress gradient on wave propagation. In the present paper, the governing equation of wave propagation in elastic continuum material with inhomogeneous initial stress is derived, which indicated that the inhomogeneous initial stress changed the governing equation of wave propagation. Additionally, the definite problem of wave propagation in material with initial stress gradient is verified by using mathematical physics method. Based on the definite problem, the elastic displacement-time relationship of wave propagation is explored, which indicated that the inhomogeneous initial stress changed waveform and relationship of displacement-time histories. Furthermore, the spall process of blasting wave propagation from underground to earth surface is simulated by using LS-DYNA.

Torsional wave in an inhomogeneous prestressed elastic layer overlying an inhomogeneous elastic half-space under the effect of rigid boundary

  • Kakar, Rajneesh
    • Earthquakes and Structures
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    • v.9 no.4
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    • pp.753-766
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    • 2015
  • An investigation has been carried out for the propagation of torsional surface waves in an inhomogeneous prestressed layer over an inhomogeneous half space when the upper boundary plane is assumed to be rigid. The inhomogeneity in density, initial stress (tensile and compressional) and rigidity are taken as an arbitrary function of depth, where as for the elastic half space, the inhomogeneity in density and rigidity is hyperbolic function of depth. In the absence of heterogeneities of medium, the results obtained are in agreement with the same results obtained by other relevant researchers. Numerically, it is observed that the velocity of torsional wave changes remarkably with the presence of inhomogeneity parameter of the layer. Curves are compared with the corresponding curve of standard classical elastic case. The results may be useful to understand the nature of seismic wave propagation in geophysical applications.

Plasticity of Amorphous Alloys: 2. Inhomogeneous Deformation (비정질 합금의 소성 2: 불균일변형)

  • Park, Kyoung-Won;Lee, Chang-Myeon;Lee, Jae-Chul
    • Korean Journal of Metals and Materials
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    • v.47 no.11
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    • pp.773-785
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    • 2009
  • Studies of a number of Cu-Zr amorphous alloys have demonstrated that those exhibiting greater plastic strain during homogeneous deformation at room temperature show lower global plasticity associated with inhomogeneous deformation in a typical compression test. Using a combination of experiments and molecular dynamics simulations, we clarify this seeming paradox between the homogeneous and inhomogeneous deformation by exploring the microstructural aspects in view of the structural disordering, disorder-induced softening, and shear localization and relate these findings to the global plasticity of bulk amorphous alloys. Additional analyses were conducted to derive a simple structural parameter that allows the prediction of the global plasticity of bulk amorphous alloys.

A laboratory experiment on estimation of homogeneity of subsurface media by Polarimetric Ground Penetrating Radar

  • Kobayashi, Takao
    • 한국지구물리탐사학회:학술대회논문집
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    • pp.31-34
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    • 2006
  • Laboratory experiment of polarimetric GPR measurement was conducted for the purpose of estimating subsurface inhomogeneity. Tow realization of inhomogeneous subsurface media were made by burying stone objects of different dimensions in homogeneous dry sand. Polarization ratio of cross polarization to co polarization data were examined to find their obviously distinguishable behavior.

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Characteristic Changes in Ground-Penetrating Radar Responses from Dielectric-Filled Nonmetallic Pipes Buried in Inhomogeneous Ground (비균일 지하에 묻혀있는 유전체 충진 비금속관에 의한 지표투과레이다 응답의 특성 변화)

  • Hyun, Seung-Yeup
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.30 no.5
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    • pp.399-406
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    • 2019
  • The variation of ground-penetrating radar(GPR) signal characteristics from dielectric-filled nonmetallic pipes buried in inhomogeneous ground are compared through a numerical simulation. The relative permittivity distribution of the ground is generated by using the continuous random media(CRM) technique. As a function of the relative permittivity of the material filling the nonmetallic pipe buried in the ground media, GPR signals are simulated by using the finite-difference time-domain(FDTD) method. We show that, unlike the case for homogeneous ground, the distortion characteristics of the reflected waves caused by the front convex surface and the rear concave surface of the pipe buried in inhomogeneous ground are different depending on the permittivity contrast between the inside and outside of the pipe.

Modified SDIE MLFMM Method for Inhomogeneous Impedance Material Containing PEC or PMC Region (PEC 또는 PMC 영역을 포함하는 불균일 임피던스 매질의 산란 해석을 위한 수정된 SDIE MLFMM 방법)

  • Lee, Hyunsoo;Koh, Il-Suek;Yoo, Ji Hee
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.29 no.10
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    • pp.805-810
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    • 2018
  • A coated perfect electric conductor(PEC) interface to reduce scattered fields can be efficiently modeled by using the impedance boundary condition. The self-dual integral equation(SDIE) proposed by Yan et al. may be an efficient multi-level fast multipole method (MLFMM) formulation for the impedance object. This equation can be applied to an inhomogeneous impedance material, but its accuracy can be degenerated when the material contains a PEC or perfect magnetic conductor(PMC) region. In this paper, we modify the original SDIE formulation for an inhomogeneous object containing a PEC or PMC region and numerically verify its accuracy.

Development of Elliptic Relaxation Model With The Inhomogeneous Correction (비균질 수정을 사용한 타원완화모형 개발)

  • Chun Kun Ho;Choi Young Don;Shin Jong Keun
    • Proceedings of the KSME Conference
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    • pp.815-818
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    • 2002
  • The elliptic relaxation model(ERM) with the inhomogeneous correction intermediate between near wall with and far from the wall. The source of the ERM usually was appled quasi-homogeneous pressure-strain correlation in homogeneous situations. This formulation was easily applied to the linear model or non-linear pressure-strain model. It is observed that the boundary conditions of the relaxation operator dominate the homogeneous pressure-strain model in the near wall region. While looking at high-Reynolds number flows, it was found necessary to modify the effect of the relaxation operator throughout the log region by accounting for gradients of the flatness variable and turbulent length scales. These effects are kinematic blocking of the wall normal velocity fluctuation and pressure reflections from the surface. This model is wall distances and unit vectors which make the model applicable to flows boundary by a complex geometry. Inhomogeneous correction model is computed inertial and non-inertial channel flow These are compared DNS(Kim et at., Kristofffrsen & Andersson) for channel flow. The present model could be predicted well for rotating flows.

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Coupling of Electromagnetic and Electrostatic Waves in Inhomogeneous Plasmas

  • Kim, Kyung-Sub;Kim, Eun-Hwa;Lee, Dong-Hun
    • Bulletin of the Korean Space Science Society
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    • pp.82-82
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    • 2003
  • It is well known that electromagnetic (EM) waves are mode converted to electrostatic (ES) waves in inhomogeneous plasmas. We examine this issue in a three-dimensional multi-fluid numerical model. First, we derive a set of coupled linear wave equations when a one-dimensional inhomogeneous density profile is assumed in a cold and collisionless plasma. The massive ions are considered as fixed because we are interested in high frequency waves in plasmas. It is shown that the EM mode satisfies the 0th order modified Bessel equation near the resonant region where the frequency matches the local electron plasma frequency. It is expected that the EM waves are coupled and damped to the ES waves owing to the logarithmic singular behavior at such resonances. Second, we numerically test the same case in a 3-D multi-fluid model. An impulsive input is assumed to excite EM waves in the inhomogeneous 3-D box model. The wave spectra of electric and magnetic fields are presented and compared with the analytical results. Our results suggest that the EM energy is irreversibly converted into the ES energy wherever the resonant condition is satisfied. Finally we discuss how the mode conversion appears in both electric and magnetic fields by analyzing time histories of each component. We also compare our results with MHD wave coupling. It is numerically confirmed in this study that the coupling of EM and ES waves is similar to that of compressional and transverse MHD waves.

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Inhomogeneous amplitude modulation effects on the MTF of binocular objective (비균일 진폭변조가 쌍안경 대물경의 MTF에 미치는 영향)

  • 홍경희
    • Korean Journal of Optics and Photonics
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    • v.10 no.2
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    • pp.102-106
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    • 1999
  • In this study, inhomogeneous amplitude modulation effects on the imaging performance a lens system are expermentally investigated by measuring the diffraction OTF. The lens under the test is a binocular objective made in Korea. Inhomogeneous amplitude modulation is carried out by positioning the modulator cross contacted to the lens under test which is illuminated by collimated light beam. The aberration characteristics of the lens under test are examined by caculating the ray-fan through finite ray tracing. The MTFs of the lens illuminated by the homogeneous and inhomogeneous light beam are measured on the Gaussian image plane and compared with one another.

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Analysis of Three-Dimensional Cracks in Inhomogeneous Materials Using Fuzzy Theory

  • Lee, Yang-Chang;Lee, Joon-Seong
    • International Journal of Fuzzy Logic and Intelligent Systems
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    • v.5 no.2
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    • pp.119-123
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    • 2005
  • This paper describes a fuzzy-based system for analyzing the stress intensity factors (SIFs) of three-dimensional (3D) cracks. 3D finite element method(FEM) was used to obtain the SIF for subsurface cracks and surface cracks existing in inhomogeneous materials. A geometry model, i.e. a solid containing one or several 3D cracks is defined. Several distributions of local node density are chosen, and then automatically superposed on one another over the geometry model by using the fuzzy theory. Nodes are generated by the bucketing method, and ten-noded quadratic tetrahedral solid elements are generated by the Delaunay triangulation techniques. The singular elements such that the mid-point nodes near crack front are shifted at the quarter-points, and these are automatically placed along the 3D crack front. The complete FE model is generated, and a stress analysis is performed. The SIFs are calculated using the displacement extrapolation method. The results were compared with those surface cracks in homogeneous materials. Also, this system is applied to analyze cladding effect of surface cracks in inhomogeneous materials.