• Korean Journal of Optics and Photonics
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• v.14 no.4
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• pp.434-442
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• 2003

Taking advantage of the probability function, we have analyzed the localization phenomenon of the solution of a propagating function under the condition that the propagation constants are randomly distributed. For example, we have investigated the localization phenomenon of the voltage wave for a transmission line in which the characteristic impedance is randomly distributed. We have confirmed that the localized solution is in existence on the random lossless transmission line. Even in the case that the voltage wave is impulsively excited by the current source, the voltage wave is localized. Because the light wave is seriously affected at the localized position in the lossy transmission line, we have determined that the light wave localization phenomena are generated by multi-reflection.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.57-62
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• 2008

Finite difference method using not general SSG(standard staggered grid) but RSG(rotated staggered grid) was applied to simulation of elastic wave propagation. Special free surface boundary condition such as imaging method is needed in finite difference method using SSG in elastic wave propagation but free surface boundary condition in finite difference method using RSG is easily solved with adding air layer. Recently PML(Perfectly Matched layer) is widely used to eliminate artificial reflection waves from finite boundary because of its' greate efficiency. Absorbing ability of CPML(convolutional Perfectly Matched Layer) that is more efficient than that of PML was applied to FDM using RSG in this study. The results of CPML eliminated artificial boundary waves very effectively in FDM using RSG in being compared with that of Cerjan's absorbing method.

• Journal of Navigation and Port Research
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• v.29 no.10 s.106
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• pp.853-858
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• 2005

Recently, various novel numerical models based on Navier-Stokes equation have been developed for calculating wave motions in the sea with coastal or ocean structures. Among those models, Volume Of Fluid (VOF) method might be the most popular one, and it has been used for numerical simulations of wave motions including complicated phenomena of wave breakings. VOF method, however, needs enormous computation time and large computational storage memories in general, thus it is practically difficult to use this method for calculations in the case of random waves because long and stable computation (e.g for more than 100 significant wave periods) is required to obtain statistically meaningful results. On the other hand if the wave motion is potential motion, Boundary Element Method (BEM), which is a much faster and more accurate method than VOF method, can be effectively used. The aim of this study is to develop a new efficient model applicable to calculations of wave motion and/or wave-structure interactions under random waves. To achieve this, a strictly combined BEM-VOF model has been developed by making the best use of both methods' merits; VOF method is used in a restricted fluid domain around a structure where complicated phenomena of wave breakings may exist, and BEM is used in the other domains far from the disturbance where the wave motion may be assumed to be potential. The verification of the model was performed with numerical results for Stokes' 5th order wave propagation and a random wave propagation.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.3
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• pp.269-276
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• 2001

Ultrasonic testing of composite materials is much more difficult than that of isotropic materials, because of the beam skew phenomenon caused by their elastic anisotropy. An established analytical method exists for elastic wave propagation in anisotropic media as a result of previous research efforts. Yet, due to the complexity of the analytical method, solution of real problems must resort to the numerical method. In this work, analytical solutions have first been obtained for the wavefield due to a point source in a unidirectional fiber-reinforced composite, which may be modeled as transversely isotropic. Then, the corresponding numerical solutions have been obtained using the mass-spring lattice model(MSLM). The two solutions have agreed well with each other. Other problems such as reflection from free boundaries and scattering from cracks have also been solved numerically, and the results have been investigated from the viewpoint of wave mechanics. The numerical model whose validity has been confirmed by this work will be of great use in simulating ultrasonic testing of composite materials.

• Journal of Biomedical Engineering Research
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• v.16 no.4
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• pp.525-532
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• 1995

In this paper, a new try to measure nonlinear propagation characteristics of the pulse along blood vessel by using bispectral analysis is introduced, and the possibility of its application to the medical diagnosis is shown. In this method, the waveforms of pulse motion of blood vessel at two separated measuring points on the wall were detected from Doppler frequency modulation of transmitted probing ultrasonic waves. Then the auto- and crossbispectrum of detected waveforms are calculated to estimate the quadratic NTF (nonlinear transfer function) between the two measuring positions. In order to show relationships between the NTF and the nonlinear propagation characteristics, computer simulations have been performed. As the propagation distance increases, harmonic frequency components in NTF increases broadly due to the nonlinear effect in the propagation of blood pulse. In order to represent this phenomena quantitatively, we propose a new parameter, dispersion ratio of WTF. Basic experimental system was constructed by using 3.5MHz probing ultrasonic waves and the preliminary experiments were carried out on ague phantom and human body. Experimental results showed the validity of the measurement system enoughly.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.7-16
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• 2020

This study presents an acoustic technique to estimate the hydraulic conductivity of soils. Acoustic attenuation and propagation velocity spectra were measured for dry and saturated sandy specimens to confirm that the relationship between Biot's characteristic frequency and its associated hydraulic conductivity exists only for saturated soils. From the experiments presented in this paper, both attenuation-based and propagation-velocity-based techniques resulted in almost identical characteristic frequencies for saturated soils. The propagation velocity based measurements, however, show a a a slightly clearer trend compared to the attenuation based measurements. The results also show that the acoustically estimated hydraulic conductivities of soils agree well with constant head laboratory test results, demonstrating that this acoustic technique can be a useful nondestructive tool to estimate the hydraulic conductivity of sandy or silty soils.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.101-110
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• 2006

In general, environment-induced vibration propagates from the center of source to the destination through ground. In fact, the mechanism of wave propagation is highly dependent on the ground conditions, and various methods to protect structures from such a ground vibration have been proposed. The method of wall barrier has been frequently used to cut off ground vibration effectively. However, the capability of wall barrier may be affected by various factors like constituent material of it. Therefore, it is important to figure out appropriate material for the wall barrier. This study is focused on the effect of EPS on the vibration protection. Centrifuge model tests were performed. Two types of models such as a cylindrical and a rectangular wall were used. For the cylindrical type of wall, installation depth was changed, while the length of the wall varied fur the rectangular type to figure out the capability of vibration protection.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.3
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• pp.167-174
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• 2021

Recent investigation into the integrity of nuclear containment buildings has highlighted the importance of developing an elaborate diagnostic method to evaluate the distribution and size of cavities inside concrete walls. As part of developing such a method, this paper presents a finite element approach to modeling elastic waves propagating in the containment building walls of a nuclear power plant. We introduce a perfectly matched layer (PML) wave-absorbing boundary to limit the large-scale nuclear containment wall to the region of interest. The formulation results in a semi-discrete form with symmetric damping and stiffness matrices. The transient elastic wave equations for a mixed unsplit-field PML were solved for displacement and stresses in the time domain. Numerical results show that the sensitivity of displacement, velocity, acceleration, and stresses is large depending on the size and location of the cavity. The dynamic response of the wall slightly differs depending on the existence of the containment liner plate. The results of this study can be applied to a full-waveform inversion approach for characterizing cavities inside a containment wall.

• The Journal of the Acoustical Society of Korea
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• v.11 no.4
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• pp.22-30
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• 1992

The propagation of coherent time-harmonic elastic SH waves in a medium with random distribution of cylindrical inclusions is studied for characterizing the dynamic elastic modulus and the attenuation property of fiber-reinforced composite materials. A multiple scattering theory using the single scattering coefficients in conjunction with the Lax's quasicrystalline approximation is derived and from which the dispersion relation for such medium is obtained. The pair-correlation functions between the cylinders which are needed to formulate the multiple scattering interaction between the cylinders are obtained by Monte Carlo simulation method.From the numerically calculated complex wavenumbers, the propagation speed of the average wave, the coherent attenuation coefficient and the effective shear modulus are presented as functions of frequency and area density.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.5
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• pp.614-620
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• 1998

In this paper, we analyze theoritically the propagation and radiation characteristics for elliptical corrugated waveguides. The solutions of wave equations in an elliptic cylinder system are obtained in terms of Mathieu functions of 1st and 2nd kind. The electromagnetic fields in the elliptical corrugated waveguide can be represented by series and products of angular and radial Mathieu functions. By using impedence matching at the boundary between the inner region and the slot region, characteristic equations are derived. Then the characteristic equation is solved for $HE_{11}$ mode which is dominant mode in the elliptical corrugated waveguide and the fields in the aperture is calculated. And the propagation pattern for the elliptical corrugated waveguides is calculated through the field equivalence principle.