• 한국전자파학회논문지
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• 제22권2호
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• pp.191-198
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• 2011

본 논문에서는 1차원 모드 방정식의 FDTD 해석 결과와 분수 함수 근사법을 이용하여 다층 구조의 Green 함수를 근사화 하는 방법을 제안한다. 파수 값에 따른 FDTD 해석 결과를 Fourier 변환 과정을 거쳐 spectral domain 상에서 Green 함수를 계산한다. FDTD 수치 해석 결과로 얻은 Green 함수에 분수 함수 근사법을 적용하여 pole과 residue를 계산하여 Green 함수를 분수 함수로 근사화 한다. 제안된 방법은 path-loss 계산 방법 중 하나인 정상 모드(normal mode)에 사용할 수 있다. 단일 주파수 해석에 유효한 기존의 정상 모드 방법과는 달리 본 논문에서 제안하는 FDTD 기반 방법은 광대역 해석을 할 수 있다. 제안된 방법의 유용성을 입증하기 위해 정상 모드 해석기반의 Kraken 시뮬레이터 결과와 공진 모드의 pole 값을 비교한다. 또 알려진 해석해를 갖는 문제에 제안된방법을 적용하여 정확도를 검증하였다.

• 대한전자공학회논문지TC
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• 제41권6호
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• pp.79-86
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• 2004

정확한 closed-form 근린함수 계산방법은 공간영역 그린함수에 포함된 Sommerfeld 적분의 계산시간을 줄이기 위해 기존에 이용되어온 복소 영상법(Complex image method)과 2단계 근사화법(Two-level approach)에 비해 훨씬 적은 오차를 갖는다. 본 논문에서는 정확한 closed-form 그린함수 계산방법을 일반적인 전원을 포함하는 평판구조에 적용하는 방법을 제안하였다.

• Journal of Magnetics
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• 제12권2호
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• pp.72-76
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• 2007

We investigate the spin transfer torque in metallic multilayer system by employing Keldysh non-equilibrium Green function method. We study the dependences of the spin transfer torque on the detailed energy configuration of ferromagnetic, spacer, and lead layers. With Keldysh non-equilibrium Green function method applied to a single band model, we explore spin transfer torque effect in various layer structures and for various material parameters.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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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.

• Ocean Systems Engineering
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• 제7권4호
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• pp.399-412
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• 2017

The Gauss-Legendre integral method is applied to numerically evaluate the Green function and its derivatives in finite water depth. In this method, the singular point of the function in the traditional integral equation can be avoided. Moreover, based on the improved Gauss-Laguerre integral method proposed in the previous research, a new methodology is developed through the Gauss-Legendre integral. Using this new methodology, the Green function with the field and source points near the water surface can be obtained, which is less mentioned in the previous research. The accuracy and efficiency of this new method is investigated. The numerical results using a Gauss-Legendre integral method show good agreements with other numerical results of direct calculations and series form in the far field. Furthermore, the cases with the field and source points near the water surface are also considered. Considering the computational efficiency, the method using the Gauss-Legendre integral proposed in this paper could obtain the accurate numerical results of the Green function and its derivatives in finite water depth and can be adopted in the near field.

• Kyungpook Mathematical Journal
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• 제59권1호
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• pp.13-22
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• 2019

This paper presents a symbolic method for solving a boundary value problem with inhomogeneous Stieltjes boundary conditions over integro-differential algebras. The proposed symbolic method includes computing the Green's operator as well as the Green's function of the given problem. Examples are presented to illustrate the proposed symbolic method.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.256-258
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• 2011

Using the axial Green's function method for Steady Stokes flows, we introduce a new pressure correction formula to satisfy the incompressibility condition, in which the pressure is related to the integral of the second order derivatives of the velocity. Based on this formula, we propose the iterative method for solving the Stokes flows in complicated domains. Even if the domain is complex, this method maintains the second order of convergence for the velocity.

• 한국해양공학회지
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• 제11권2호
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• pp.91-99
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• 1997

This paper presents theoretical formulations and numerical computations for predicting first-and second-order hydrodynamic force on a ship advvancing in waves. The theoretical formulation leads to linearized radiation and diffration problems solving the three-dimensional Green function integral equations over the mean wetted body surface. Green function representing a translating and pulsating source potantial for infinite water depth is used. In order to solve integral equations for three dimentional flows using Green function efficiently, the Hoff's method is adopted for numerical calculation of the Green function. Based on the first-order solution, the mean seconder-order forces and moments are obtained by directly integrating second-order pressure over the mean wetted body surface. The calculated items are carried out for analyzing the seakeeping characteristics of Series 60. The calculated items are hydrodynamic coefficients, wave exciting forces, frequency response functions and addd resistance in waves.

• 한국정보통신학회논문지
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• 제5권5호
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• pp.1001-1010
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• 2001

TLM 법에서 이산 그린함수 흡수경계는 광대역에서 정밀한 수치해석에 사용되어왔다. 그러나 이산 그린함수 흡수경계는 이산 그린함수를 얻는 수치해석이 부가적으로 요구되기 때문에 흡수경계를 적용하는 과정이 복잡하다. 그러므로 흡수경계를 적용하는 과정의 간소화를 위해서 본 논문에서는 새로운 그린 흡수층을 제안한다. 제안된 그린 흡수층은 이산 그린함수의 손실처리 방법을 응용하여 구현하였으며 최적의 흡수 상태를 그린 흡수층의 길이에 대응하는 손실 증가율과 감쇠상수리 관계로 얻을 수 있었다. 또한 최적의 흡수상태가 되는 그린 흡수층을 적용하여 도파관 대역통과필터를 해석하였다. 그 결과, 기존의 그린함수 흡수경계와 제안된 그린 흡수층을 적용한 해석 결과가 정확히 일치하였다.

• 한국지진공학회논문집
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• 제24권2호
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• pp.59-65
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• 2020

The empirical Green's function method is applied to the foreshock and the mainshock of the 2016 Gyeongju earthquake to simulate strong ground motions of the mainshock and scenario earthquake at seismic stations of seven metropolises in South Korea, respectively. To identify the applicability of the method in advance, the mainshock is simulated, assuming the foreshock as the empirical Green's function. As a result of the simulation, the overall shape, the amplitude of PGA, and the duration and response spectra of the simulated seismic waveforms are similar with those of the observed seismic waveforms. Based on this result, a scenario earthquake on the causative fault of Gyeongju earthquake with a moment magnitude 6.5 is simulated, assuming that the mainshock serves as the empirical Green's function. As a result, the amplitude of PGA and the duration of simulated seismic waveforms are significantly increased and extended, and the spectral amplitude of the low frequency band is relatively increased compared with that of the high frequency band. If the empirical Green's function method is applied to several recent well-recorded moderate earthquakes, the simulated seismic waveforms can be used as not only input data for developing ground motion prediction equations, but also input data for creating the design response spectra of major facilities in South Korea.