• Title, Summary, Keyword: Green's function

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Approximate Method of Multi-Layer Green's Function Using FDTD Scheme and Rational Function Approximation (FDTD 방법과 분수 함수 근사법을 이용한 다층 구조에서의 Green 함수 근사화)

  • Kim, Yong-June;Koh, Il-Suek;Lee, Yong-Shik
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.22 no.2
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    • pp.191-198
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    • 2011
  • In this paper, a method to approximate a multi-layer Green's function is proposed based on a FDTD scheme and a rational function approximation. For a given horizontal propagation wavenumber, time domain response is calculated and then Fourier transformed to the spectral domain Green's function. Using the rational function approximation, the pole and residue of the Green's function can be estimated, which are crucial for a calculation of a path loss. The proposed method can provide a wideband Green's function, while the conventional normal mode method can be applied to a single frequency problem. To validate the proposed method, We consider two problems, one of which has a analytical solution. The other is about multi-layer case, for which the proposed method is compared with the known normal mode solution, Kraken.

Prediction of Sound Field Inside Duct with Moving Medium by using one Dimensional Green's function (평균 유동을 고려한 1차원 그린 함수를 이용한 덕트 내부의 음장 예측 방법)

  • Jeon, Jong-Hoon;Kim, Yang-Hann
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.915-918
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    • 2005
  • Acoustic holography uses Kirchhoff·Helmholtz integral equation and Green's function which satisfies Dirichlet boundary condition Applications of acoustic holography have been taken to the sound field neglecting the effect of flow. The uniform flow, however, changes sound field and the governing equation, Green's function and so on. Thus the conventional method of acoustic holography should be changed. In this research, one possibility to apply acoustic holography to the sound field with uniform flow is introduced through checking for the plane wave in a duct. Change of Green's function due to uniform flow and one method to derive modified form of Kirchhoff·Heimholtz integral is suggested for 1-dimensional sound field. Derivation results show that using Green's function satisfying Dirichlet boundary condition, we can predict sound pressure in a duct using boundary value.

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BOUNDARY BEHAVIOR OF GREEN'S POTENTIALS WITHIN TANGENTIAL APPROACH REGION

  • Choi, Ki Seong
    • Journal of the Chungcheong Mathematical Society
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    • v.11 no.1
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    • pp.163-172
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    • 1998
  • In this paper, we will study properties of the Green's potential for the Green's function of B which is defined in [8]. In particular, we will investigate boundary behavior of some functions related with Green's function within tangential approach regions that were used in [4].

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An Accurate Closed-form Green's Function for the Planar Structure with General Sources (일반적인 전원을 포함하는 평판구조에 대한 정확한 Closed-form 그린함수)

  • Kang Yeon-Duk;Lee Taek-Kyung
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.41 no.6
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    • pp.79-86
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    • 2004
  • In the integration of Sommerfeld type for space domain Green's function, a accurate closed-from Green's function method provides more exact solution than the typical complex image method and two-level method. The accurate closed-form Green's function method is applied to obtain the space domain Green's functions of planar structures with general sources. Please put the abstract of paper here.

Analysis of Waveguid Filter Using Green′s Absorbing Layer in three Dimension TLM Method (3차원 TLM 법에서 그린 흡수층을 이용한 도파관 필터의 해석)

  • 김병수;전계석
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.5 no.5
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    • pp.1001-1010
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    • 2001
  • In TLM method, Discrete Green's function ABC have been used when improved the exactness of analyzing in wide frequency band. But this technology has a complicated process to apply absorbing boundary, which means it needs additional numerical analyzing process to obtain discrete Green's function data. so, In this paper, we propose new Green's absorbing layer for simple process to apply absorbing boundary. newly proposed Green's absorbing layer is produced by applying of loss operation, loading discrete Green's function with attenuation. A state of optimum absorbing would be obtained by relation between increasing rate of loss, attenuation constant and length of green's absorbing layer. and then Analysts of waveguide BPF is carried out using Green's absorbing layer within state of optimum absorbing, then this result is in corrective agreement with the result applying traditional discrete Green's function ABC.

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Thermal Stress Calculations Using Enhanced Green's Function Considering Temperature-dependent Material Properties (온도 의존적 재료물성치를 고려한 개선된 그린함수 기반 열응력 계산)

  • Han, Tae-Song;Huh, Nam-Su;Jeon, Hyun-Ik;Ha, Seung-Woo;Cho, Sun-Young
    • Journal of The Korean Society of Manufacturing Technology Engineers
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    • v.24 no.5
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    • pp.535-540
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    • 2015
  • We propose an enhanced Green's function approach to predict thermal stresses by considering temperature-dependent material properties. We introduce three correction factors for the maximum stress, the time taken to reach maximum stress, and the time required to attain steady state based on the Green's function results for each temperature. The proposed approach considers temperature-dependent material properties using correction factors, which are defined as polynomial expressions with respect to temperatures based on Green's functions, that we obtain from finite-element (FE) analyses at each temperature. We verify the proposed approach by performing detailed FE analyses on thermal transients. The Green's functions predicted by the proposed approach are in good agreement with those obtained from FE analyses for all temperatures. Moreover, the thermal stresses predicted using the proposed approach are also in good agreement with the FE results, and the proposed approach provides better predictions than the conventional Green's function approach using constant, time-independent material properties.

Some properties of the Green's function of simplified elastodynamic problems

  • Sanchez-Sesma, Francisco J.;Rodriguez-Castellanos, Alejandro;Perez-Gavilan, Juan J.;Marengo-Mogollon, Humberto;Perez-Rocha, Luis E.;Luzon, Francisco
    • Earthquakes and Structures
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    • v.3 no.3_4
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    • pp.507-518
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    • 2012
  • It is now widely accepted that the resulting displacement field within elastic, inhomogeneous, anisotropic solids subjected to equipartitioned, uniform illumination from uncorrelated sources, has intensities that follow diffusion-like equations. Typically, coda waves are invoked to illustrate this concept. These waves arrive later as a consequence of multiple scattering and appear at "the tail" (coda, in Latin) of seismograms and are usually considered an example of diffuse field. It has been demonstrated that the average correlations of motions within a diffuse field, in frequency domain, is proportional to the imaginary part of Green's function tensor. If only one station is available, the average autocorrelation is equal to the average squared amplitudes or the average power spectrum and this gives the Green's function at the source itself. Several works address this point from theoretical and experimental point of view. However, a complete and explicit analytical description is lacking. In this work we study analytically some properties of the Green's function, specifically the imaginary part of Green's function for 2D antiplane problems. This choice is guided by the fact that these scalar problems have a closed analytical solution (Kausel 2006). We assume the diffusiveness of the field and explore its analytical consequences.

Dyadic Green`s Function for an Unbounded Anisotropic Medium in Cylindrical Coordinates

  • Kai Li;Park, Seong-Ook;Pan, Wei-Yan
    • Journal of electromagnetic engineering and science
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    • v.1 no.1
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    • pp.54-59
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    • 2001
  • The dyadic Green`s function for an unbounded anisotropic medium is treated analytically in the Fourier domain. The Green`s function, which is expressed as a triple Fourier integral, can be next reduced to a double integral by performing the integral, by performing the integration over the longitudinal Fourier variable or the transverse Fourier variable. The singular behavior of Green`s is discussed for the general anisotropic case.

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A Solution for Green's Function of Orthotropic Plate (직교이방성 평판의 Green 함수에 대한 새로운 해)

  • Yang, Kyeong-Jin;Kang, Ki-Ju
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.3
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    • pp.365-372
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    • 2007
  • Revisited in this paper are Green's functions for unit concentrated forces in an infinite orthotropic Kirchhoff plate. Instead of obtaining Green's functions expressed in explicit forms in terms of Barnett-Lothe tensors and their associated tensors in cylindrical or dual coordinates systems, presented here are Green's functions expressed in two quasi-harmonic functions in a Cartesian coordinates system. These functions could be applied to thin plate problems regardless of whether the plate is homogeneous or inhomogeneous in the thickness direction. With a composite variable defined as $z=x_1+ipx_2$ which is adopted under the necessity of expressing the Green's functions in terms of two quasi-harmonic functions in a Cartesian coordinates system Stroh-like formalism for orthotropic Kirchhoffplates is evolved. Using some identities of logarithmic and arctangent functions given in this paper, the Green's functions are presented in terms of two quasi-harmonic functions. These forms of Green's functions are favorable to obtain the Newtonian potentials associated with defect problems. Thus, the defects in the orthotropic plate may be easily analyzed by way of the Green's function method.

Error Analysis Caused by Using the Dftin Numerical Evaluation of Rayleigh's Integral (레일리 인테그랄의 수치해석상 오차에 대한 이론적 고찰)

  • Kim, Sun-I.
    • Journal of Biomedical Engineering Research
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    • v.10 no.3
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    • pp.323-330
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    • 1989
  • Large bias errors which occur during a numerical evaluation of the Rayleigh's integral is not due to the replicated source problem but due to the coincidence of singularities of the Green's function and the sampling points in Fourier domain. We found that there is no replicated source problem in evaluating the Rayleigh's integral numerically by the reason of the periodic assumption of the input sequence in Dn or by the periodic sampling of the Green's function in the Fourier domain. The wrap around error is not due to an overlap of the individual adjacent sources but berallse of the undersampling of the Green's function in the frequency domain. The replicated and overlApped one is inverse Fourier transformed Green's function rather than the source function.

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