• 한국전자파학회논문지
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• 제11권8호
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• pp.1322-1328
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• 2000

본 논문에서는 전자계의 시간 변화 파형을 측정하기 위한 모노폴 안테나의 복소 안테나 인자 및 전달함수의 주파수 응답 특성 등을 논의하고 있다. 안테나에 흐르는 전류분포는 구분적 정현함수를 사용한 Galerkin의 모멘트법으로 계산하고 있으며 저주파수 대역에서는 반사를 줄이기 위해 칩저항을 접속한 경우의 복소 안테나 인자에 대하여 검토하고 있다. 이론 해석의 결과, 칩저항이 접속된 경우는 접속하지 않은 경우보다 복소 안테나 인자의 절대치는 5.6㏈정도 커진다는 것을 확인하였다. 또한, 주파수가 낮은 경우에 유용하게 사용할 수 있는 변형 복소 안테나 인자의 특성에 대해서도 논의하고 있다. 근역장 보정법으로 측정된 복소 안테나 인자와도 비교하여 이론 계산의 타당성을 확인하고 있다.

• Computers and Concrete
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• 제26권1호
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• pp.21-30
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• 2020

Buckling and post-buckling behaviors of geometrically imperfect annular sector plates made from nanoparticle reinforced composites have been investigated. Two types of nanoparticles are considered including graphene oxide powders (GOPs) and silicone oxide (SiO₂). Nanoparticles are considered to have uniform and functionally graded distributions within the matrix and the material properties are derived using Halpin-Tsai procedure. Annular sector plate is formulated based upon thin shell theory considering geometric nonlinearity and imperfectness. After solving the governing equations via Galerkin's technique, it is showed that the post-buckling curves of annular sector plates rely on the geometric imperfection, nanoparticle type, amount of nanoparticles, sector inner/outer radius and sector open angle.

• 한국통신학회논문지
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• 제31권9A호
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• pp.913-919
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• 2006

본 논문에서는 스트립 폭과 격자주기, 비유전율, 유전체 층의 두께, 그리고 TE(transverse electric) 평면파의 입사각에 따른 접지된 다층 유전체위의 저항띠 격자구조에 의한 TE 산란 문제를 수치해석 방법인 FGMM(Fourier-Galerkin Moment Method)을 이용하여 해석하였다. 유도되는 표면전류밀도는 간단한 함수인 지수함수를 사용하여 Fourier 급수로 전개하였다. 전반적으로 다층유전체의 비유전율과 두께가 증가함에 따라 반사전력이 증가하였고, 반사전력의 급변점들은 공진효과에 기인한 것으로 과거에 wood's anomallies$^{[7]}$라고 불리워졌다. 제안된 방법의 검증을 위하여 기존의 완전도체 경우인 균일 저항율 R = 0에 대한 정규화된 반사전력의 수치결과는 기존 논문들과 일치하였다.

• 한국항행학회논문지
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• 제10권3호
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• pp.198-204
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• 2006

본 논문에서는 스트립 폭과 격자주기, 유전체 층의 비유전율과 두께, 그리고 TE(transverse electric) 평면파의 입사각에 따른 접지된 유전체 평면위의 저항띠 격자구조에 의한 TE 산란 문제를 수치해석 방법인 FGMM(Fourier-Galerkin Moment Method)를 이용하여 해석하였다. 유도되는 표면전류밀도는 간단한 함수인 지수 함수를 사용하여 Fourier 급수로 전개하였다. 유전체층의 비유전율과 두께가 증가함에 따라 반사전력이 증가하였고, 반사전력의 급변점들은 공진효과에 기인한 것으로 과거에 wood's anomallies[7]라고 불리워졌다. 제안된 방법의 검증을 위하여 기존의 완전도체 경우인 균일 저항율 R = 0에 대한 정규화된 반사전력의 수치결과는 기존의 논문들과 일치하였다.

• Wind and Structures
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• 제7권2호
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• pp.107-130
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• 2004

This paper presents a time-domain approach for analyzing nonlinear random vibrations of long-span suspended cables under transversal wind. A consistent continuous model of the cable, fully accounting for geometrical nonlinearities inherent in cable behavior, is adopted. The effects of spatial correlation are properly included by modeling wind velocity fluctuation as a random function of time and of a single spatial variable ranging over cable span, namely as a one-variate bi-dimensional (1V-2D) random field. Within the context of a Galerkin's discretization of the equations governing cable motion, a very efficient Monte Carlo-based technique for second-order analysis of the response is proposed. This procedure starts by generating sample functions of the generalized aerodynamic loads by using the spectral decomposition of the cross-power spectral density function of wind turbulence field. Relying on the physical meaning of both the spectral properties of wind velocity fluctuation and the mode shapes of the vibrating cable, the computational efficiency is greatly enhanced by applying a truncation procedure according to which just the first few significant loading and structural modal contributions are retained.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.51-59
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• 2000

The Interactions of shock wave with turbulent boundary layers in high-speed flows cause complex flowfields which result in increased adverse pressure gradients, skin friction and temperature. Accurate and reliable prediction of such phenomena is needed in designing high-speed propulsion systems. Such analyses of the complex flowfields require sophisticated numerical scheme that can resolve interactions between shock wave and boundary layers accurately. Therefore the purpose of the present. article is to introduce an accurate and efficient mixed explicit-implicit generalized Galerkin finite element method. To demonstrate the validity of the theory and numerical procedure, several benchmark cases are investigated.

• 대한기계학회논문집A
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• 제20권5호
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• pp.1436-1444
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• 1996

The problem ofinstability of laminated circular cylindrical shell under the action of torsio or lateral pressure is investigated. The analysis is based on the Sander's theory for finite deformations of thin shell. The buckling is elastic for thin compoisite shell nad the geometry is assumed to be free of initial imperfections. The equilibrium equations are obrained by usitn the p[erturbation technique. Solution procedure is based on the Galerkin mehtod. The computer program for numerical results is made for several stacking sequence, length-to-radius ratio, and radius-to-thickness ratio. The numerical results of buckling load are present.

• Interaction and multiscale mechanics
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• 제2권3호
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• pp.263-276
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• 2009

This paper is intended to investigate interaction response of a train running over a suspension bridge undergoing support settlements. The suspension bridge is modeled as a single-span suspended beam with hinged ends and the train as successive moving oscillators with identical properties. To conduct this dynamic problem with non-homogeneous boundary conditions, this study first divides the total response of the suspended beam into two parts: the static and dynamic responses. Then, the coupled equations of motion for the suspended beam carrying multiple moving oscillators are transformed into a set of nonlinearly coupled generalized equations by Galerkin's method, and solved using the Newmark method with an incremental-iterative procedure including the three phases: predictor, corrector, and equilibrium-checking. Numerical investigations demonstrate that the present iterative technique is available in dealing with the dynamic interaction problem of vehicle/bridge coupling system and that the differential movements of bridge supports will significantly affect the dynamic response of the running vehicles but insignificant influence on the bridge response.

• Smart Structures and Systems
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• 제26권3호
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• pp.361-371
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• 2020

Exact solution for nonlinear behavior of clamped-clamped functionally graded (FG) buckled beams is presented. The effective material properties are considered to vary along the thickness direction according to exponential-law form. The in-plane inertia and damping are neglected, and hence the governing equations are reduced to a single nonlinear fourth-order partial-integral-differential equation. The von Kármán geometric nonlinearity has been considered in the formulation. Galerkin procedure is used to obtain a second order nonlinear ordinary equation with quadratic and cubic nonlinear terms. Based on the mode of the corresponding linear problem, which readily satisfy the boundary conditions, the frequencies for the nonlinear problem are obtained using the Jacobi elliptic functions. The effects of various parameters such as the Young's modulus ratio, the beam slenderness ratio, the vibration amplitude and the magnitude of axial load on the nonlinear behavior are examined.

• Structural Engineering and Mechanics
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• 제57권4호
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• pp.617-639
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• 2016

In this work, an analytical formulation based on both hyperbolic shear deformation theory and stress function, is presented to study the nonlinear post-buckling response of symmetric functionally graded plates supported by elastic foundations and subjected to in-plane compressive, thermal and thermo-mechanical loads. Elastic properties of material are based on sigmoid power law and varying across the thickness of the plate (S-FGM). In the present formulation, Von Karman nonlinearity and initial geometrical imperfection of plate are also taken into account. By utilizing Galerkin procedure, closed-form expressions of buckling loads and post-buckling equilibrium paths for simply supported plates are obtained. The effects of different parameters such as material and geometrical characteristics, temperature, boundary conditions, foundation stiffness and imperfection on the mechanical and thermal buckling and post-buckling loading capacity of the S-FGM plates are investigated.