• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5B
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• pp.295-300
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• 2012

Reflection coefficients of wave due to the types of a submerged breakwater on the inclined incident wave are numerically computed by using boundary element method. The analysis method is based on the wave pressure function with the continuity in the analytical region including fluid and structures. When compared with the existing results on the inclined incident wave, the results of this study show good agreement. It is found that both maximum and minimum values of the reflection coefficient are appeared frequently, as the width of a submerged breakwater becomes wider, and the reflection coefficient increase, as the wave period is longer. In addition, the effect on the reflection coefficient due to the change of submerged breakwater hight is lager than that due to the change of submerged breakwater width. The results indicate that dissipating characteristics of wave due to the types of a submerged breakwater own high dependability regarding the change of inclined incident waves. Therefore, the results of this study is estimated to be applied as an accurate numerical analysis referring to inclined incident waves in real sea.

• Economic and Environmental Geology
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• v.36 no.6
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• pp.491-499
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• 2003

The Okinawa Trough is a rift basin formed by extension. Analysis of multichannel seismic reflection profiles from the northwestern margin of the northern Okinawa Trough reveal that the trough is characterized by a series of tilted fault blocks bounded by listric normal faults and half-grabens developed between blocks, showing typical rifted structures. The trough display three kinds of sedimentary sequences with different seismic reflection characteristics: prerift, synrift and postrift sediments. The prerift sequence develops parallel to the dip direction of tilted fault blocks. The synrift sediments, mostly deposited in the half-grabens between tilted fault blocks, are generally well characterized by divergence of the reflectors towards the blocks indicating contemporaneous deposition during tilting. The postrift sediments are featured by continuous and parallel reflectors. The width of the half-graben and the throw-displacement rate of the basin bounding fault are closely connected. The throw-displacement rate is the maximum when the rifting event is the most active and the width of the half-graben is proportional to the rate.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.5
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• pp.997-1003
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• 2000

When finite length signal is the input of QMF banks which are composed of the M-band orthogonal wavelet filter, the boundaries of reconstructed signal are not reconstructed perfectly. For boundary signals to be reconstructed perfectly, different type filters or methods are applied to them. In this paper, the design method of boundary filters which can be reconstructed the boundary signal perfectly was proposed, in case the dimension of M-band decomposed signal is the same as that of input signal. The boundary filters were designed using the perfect reconstruction condition of paraunitary matrix. In an application of subband coding of still image, the proposed boundary filters achieve better PSNR about 5% in reconstructed image than reflected method at the same bit rate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.8A
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• pp.829-835
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• 2002

When finite length image signal is decomposed into M-band synthesized using M-band orthogonal wavelet transform, the boundary signal of image are not reconstructed perfectly. for boundary signals to be reconstructed perfectly, different type filter bank or technique is applied to them when the dimension of analysed is proposed. It can be designed using the singular value decomposition of boundary perfect reconstruction matrix which is obtained from paraunitary matrix which is obtained from paraunitary matrix. And it is also discussed to design the boundary filter bank for improving the coding performance when it is applied to subband coder. The proposed boundary filter bank shows 7% gains in PSNR compared with reflected method.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.240-241
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• 2003

경계면 근처에서의 에바네슨트파의 상호작용은 입사, 반사 및 굴절된 평면파의 삼중모드로 설명한다. 경계에서 굴절률이 낮은 영역에 위치한 DCM 색소분자에 의한 자발방출은 굴절률이 높은 영역에서 입사된 삼중모드와 굴절률이 낮은 영역에서 입사한 삼중모드와 상호작용을 하며, 광 측정기에서는 이 두 모드의 선형결합을 보게된다. 자발방출에 대한 실험결과는 이러한 이론을 뒷받침 해준다. (중략)

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.10 no.2
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• pp.93-99
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• 1998

Parabolic approximation and sponge layer are applied as open boundary condition for elliptic finite difference wave model. Generalized conjugate gradient method is used as a solution procedure. Using parabolic approximation a large part of spurious reflection is removed at the spherical shoal experiment and sponge layer boundary condition needs more than 2 wave lengths of sponge layer to give similar results. Simulating the propagation of waves on a rectangular harbor, it is identified that iterative scheme can be applied easily for the non-rectangular computational region.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.2
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• pp.203-209
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• 2018

To correctly predict the neutron behavior based on diffusion calculations, it is necessary to adopt well-specified boundary conditions using suitable diffusion approximations to transport boundary conditions. Boundary conditions such as the zero net-current, the Marshak, the Mark, the zero scalar flux, and the Albedo condition have been used extensively in diffusion theory to approximate the reflective and vacuum conditions in transport theory. In this paper, we derive and analyze these conditions to prove their mathematical validity and to understand their physical implications, as well as their relationships with one another. To show the validity of these diffusion boundary conditions, we solve a sample problem. The results show that solutions of the diffusion equation with these well-formulated boundary conditions are very close to the solution of the transport equation with transport boundary conditions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.1
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• pp.89-103
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• 2009

This study investigates the applicability of the time reversal concept in modem acoustics to the Lamb waves, which have been widely studied for defect detection in plate-like structures. According to conventional time reversal acoustics, an input signal can be reconstructed at an excitation point if an output signal recorded at another point is reversed in the time domain and emitted back to the original source point. However, the application of a time reversal process(TRP) to Lamb wave propagations is complicated due to velocity and amplitude dispersion characteristics of Lamb waves and reflections from the boundaries of a structure. In this study, theoretical investigations are presented to better understand the time reversibility of Lamb waves. In particular, the effects of within-mode dispersion, multimode dispersion, amplitude dispersion, and reflections from boundaries on the TRP are theoretically formulated. Simple numerical case studies are conducted to validate the theoretical findings of this study.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.1
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• pp.49-54
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• 2021

In this paper, n this paper, E-polarized electromagnetic scattering problems by a resistive strip grating between a double dielectric layer are analyzed by applying the PMM(Point Matching Method) known as a numerical method of electromagnetic fileld. The boundary conditions are applied to obtain the unknown field coefficients, and the resistive boundary condition is applied to analysis of the resistive strip. The numerical results for the normalized reflected and transmitted power are analyzed by according as the relative permittivity and thickness of the double dielectric layers, and the resistivity of resistive strip. Overall, when the resistivity of the resistive strip decreased or the relative permittivity of the dielectric layer increased, the reflected power increased, and as the reflected power increased, the transmitted power decreased relatively. Especially, as the relative permittivity of double dielectric layer increases, the minimum value of the variation curve of the reflected power shifted in the direction that the grating period decreased. The numerical results for the presented structure of this paper are shown in good agreement compared to those of the existing papers.

• Journal of the Korean Society for Railway
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• v.18 no.4
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• pp.289-300
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• 2015

An important source of noise from railways is rolling noise caused by wheel and rail vibrations induced by acoustic roughness at the wheel-rail contact. In conventional approaches to predicting rail noise, the rail is regarded as placed in a free space so that the reflection from the ground is not included. However, in order to predict rail noise close to the rail, the effect of the ground should be contained in the analysis. In this study the rail noise reflected from the ground is investigated using the wavenumber domain finite element and boundary element methods. First, two rail models, one using rail attached to the rigid ground and one using rail located above rigid ground, are considered and examined to determine the rigid ground effect in terms of the radiation efficiency. From this analysis, it was found that the two models give considerably different results, so that the distance between the rail and the ground is an important factor. Second, an impedance condition was set for the ground and the effect of the ground impedance on the rail noise was evaluated for the two rail models.