• Structural Engineering and Mechanics
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• 제22권6호
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• pp.719-739
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• 2006

An analytical method for the free vibration of two circular plates coupled with an inviscid and compressible fluid is developed by the Rayleigh-Ritz method. The fluid is bounded by a rigid cylindrical vessel and two circular plates with an unequal thickness and diameter. It was found that the theoretical results could predict well the fluid-coupled natural frequencies with an excellent accuracy when compared with the finite element analysis results. As the fluid thickness increases or the plate thickness difference increases, an abrupt curve veering in the natural frequency loci of the neighboring modes and drastic changes in the corresponding mode shapes are observed. The mode localization frequently appears in the higher modes and in the wide gap between the plates because of a decrease in the fluid coupling owing to the fluid dispersion effect.

• Nuclear Engineering and Technology
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• 제50권7호
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• pp.1106-1111
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• 2018

Electromagnetic waves potentially have been used to heat overdense nuclear fusion plasmas through a double mode conversion from ordinary to slow extraordinary and finally to Electron Bernstein Wave (EBW) modes, OSXB. This scheme is efficient and has not any plasma density limit of electron cyclotron resonance heating due to cut-off layer. The efficiency of conversion depends on the isotropic launching angles of the microwaves with the plasma parameters. In this article, a two-step mode conversions of OSXB power transmission efficiency affected by the fast extraordinary (FX) loses at upper hybrid frequency are studied. In addition, the kinetic (hot) dispersion relation of a overdense plasma in a full wave analysis of a OSXB in Wendelstein 7X (W7-X) stellarator plasma has been numerically simulated. The influence of plasma dependent parameters such as finite Larmor radius, electron thermal velocity and electron cyclotron frequency are represented.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 정기총회 및 창립40주년기념 학술대회 학회본부
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• pp.398-400
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• 1987

Using the transmission line model, we have developed a formalism which is fairly accurate and convenient for analyzing the dispersion characteristics of rectangular dielectric waveguides for integrated optics. The fields in open half space regions are expressed as a Fourier integral form. Including all the TE and TM polarized discrete modes in slab waveguide region, our calculation shows that the discrepancies between the previous vectorial wave analysis using one discrete mode and the brute-force numerical analysis for the rectangular dielectric waveguides can be fully reduced with this method.

• Journal of the Optical Society of Korea
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• 제17권6호
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• pp.538-542
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• 2013

We propose a simple model to elucidate the dispersion behavior of spiraling modes on silver nanowire by finding correspondence parameters and building a simple equivalent relationship with the planar insulator-metal-insulator geometry. The characteristics approximated for the proposed structure are compared with the results from an exact solution obtained by solving Maxwell's equation in cylindrical coordinates. The effective refractive index for our proposed equivalent model is in good agreement with that for the exact solution in the 400-2000 nm wavelength range. In particular, when the radius of the silver nanowire is 100 nm, the calculated index shows typical improvements; the average percentage error for the real part of the effective refractive index is reduced to only 5% for the $0^{th}$ order mode (11.9% in previous results) and 1.5% for the $1^{st}$ order mode (24.8% in previous results) in the 400-800 nm wavelength range. This equivalent model approach is expected to provide further insight into understanding the important behavior of nanowire waveguides.

• 한국해양공학회지
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• 제23권4호
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• pp.6-11
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• 2009

In this study, the internal waves in two-density layered fluids were analyzed using the Numerical Wave Tank (NWT) technique in the frequency domain. The NWT is based on a two-domain Boundary Element Method with the potential fluids using the whole-domain matrix scheme. From the mathematical solution of the two-domain boundary integral equation, two different wave modes could be classified: a surface wave mode and an internal wave mode, and each mode were shown to have a wave number determined by a respective dispersion relation. The magnitudes of the internal waves against surface waves were investigated for various fluid densities and water depths. The calculated results are compared with available theoretical data.

• 한국항만경제학회:학술대회논문집
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• 한국항만경제학회 2006년도 국제학술대회
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• pp.103-124
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• 2006

This paper is concerned with a comparative study on the economic effects upon the Korean economy by transport mode, ie road, rail, air, and coastal and inland water transportation between 1990 and 2000, using input-output analysis. The economic effects consist of backward and forward linkage effects, production inducing and import-inducing effects. The data employed for this study come from the Bank of Korea database for Input-Output structure of the Korean economy. The major findings in this study are, among others:(1) the power of dispersion(=backward linkage effect) of coastal and inland water transportation sector is the highest among the four transport sectors, while road cargo transport mode showed the highest the degree of sensitivity (=forward linkage effect); (2) rail cargo transport recorded the highest production inducing effects; and (3) air transport mode achieved the highest ranking in the import-inducing effects.

• Computers and Concrete
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• 제20권3호
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• pp.257-262
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• 2017

This study aims to develop a signal processing scheme to accurately predict the thickness of concrete slab using air-coupled impact-echo. Air-coupled impact-echo has been applied to concrete non-destructive tests (NDT); however, it is often difficult to obtain thickness mode frequency due to noise components. Furthermore, apparent velocity in concrete is a usually unknown parameter in the field and the thickness of the concrete slab often cannot be accurately measured. This study proposes a signal processing scheme using guided wave analysis, wherein dispersion curves are drawn in both frequency-wave number (f-k) and phase velocity-frequency ($V_{cp}-f$) domains. The theoretical and experimental results demonstrate that thickness mode frequency and apparent velocity in concrete are clearly obtained from the f-k and $V_{cp}-f$ domains, respectively. The proposed method has great potential with regard to the application of air-coupled impact-echo in the field.

• 한국정보통신학회논문지
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• 제15권1호
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• pp.188-194
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• 2011

광결정 광섬유를 포함한 WDM-ROF (wavelength division multiplexing - radio over fiber) 시스템의 고주파신호 전송특성을 분석하였다. 기존의 단일모드 광섬유를 사용한 WDM-ROF 시스템에 있어, 각 WDM 채널의 파장에 따른 고주파신호 전송특성을 분석하였다. 이 경우, 원격노드(remote node)에서의 고주파 신호 특성은 단일모드 광섬유의 분산 특성으로 인해 각 WDM 채널의 파장에 따라 고주파신호 수신 파워의 편차를 나타내게 되며, 이는 전체 시스템 설계시 제한 요소로 작용하게 된다. 광결정 광섬유를 단일모드 광섬유와 함께 사용함으로써 광결정 광섬유의 분산 보상 특성을 이용하여 WDM 채널에 따른 고주파 전송특성을 개선할 수 있음을 확인하였다.

• Journal of the Optical Society of Korea
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• 제15권3호
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• pp.232-236
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• 2011

We analyze the linear equalizers used in optically amplified on-off-keyed (OOK) systems to combat chromatic dispersion (CD) and polarization mode dispersion (PMD), and we derive the mathematical minimum mean squared error (MMSE) performance of these equalizers. Currently, the MMSE linear equalizer for optical OOK systems is obtained by simulations using adaptive approaches such as least mean squared (LMS) or constant modulus algorithm (CMA), but no theoretical studies on the optimal solutions for these equalizers have been performed. We model the optical OOK systems as square-law nonlinear channels and compute the MMSE equalizer coefficients directly from the estimated optical channel, signal power, and optical noise variance. The accuracy of the calculated MMSE equalizer coefficients and MMSE performance has been verified by simulations using adaptive algorithms.

• 비파괴검사학회지
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• 제27권6호
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• pp.582-590
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• 2007

Imperfectly jointed interface serves as mechanical waveguide for elastic waves and gives rise to two distinct kinds of guided wave propagating along the interface. Contact acoustic nonlinearity (CAN) is known to plays major role in the generation of these interface waves called generalized Rayleigh waves in non-welded interface. Closed crack is modeled as non-welded interface that has nonlinear discontinuity condition in displacement across its boundary. Mathematical analysis of boundary conditions and wave equation is conducted to investigate the dispersive characteristics of the interface waves. Existence of the generalized Rayleigh wave(interface wave) in nonlinear contact interface is verified in theory where the dispersion equation for the interface wave is formulated and analyzed. It reveals that the interface waves have two distinct modes and that the phase velocity of anti-symmetric wave mode is highly dependent on contact conditions represented by linear and nonlinear dimensionless specific stiffness.