• The Journal of the Acoustical Society of Korea
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• v.17 no.5
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• pp.79-84
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• 1998

본 논문은 길이방향으로 조화함수 형태로 변화하는 단면적을 가진 원형단면의 탄성 막대에서 전파하는 비틂 탄성파의 전파속도에 대한 이론적 및 실험적 결과를 제시한다. 주 기적인 미소한 반경 변화를 섭동법에 의해 다루어 전파속도의 이론적 근사해를 구하였다. 그결과 전파속도는 반경 변화 폭의 제곱에 비례하는 양 만큼 감소하는 경향이 나타났다. 이 론적 경향을 검증하기 위한 실험은 자왜현상으로 비틂파를 전파시키고 나사면을 가진 탄성 도파관에서 전파속도를 측정하는 방법으로 행하였다.

• Journal of the KSME
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• v.34 no.7
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• pp.510-516
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• 1994

탄성파의 속도는 파동 전파 매질의 밀도와 탄선계수에 달려 있으므로, 박막이 입혀진 기판에서 전파하는 표면파에 대해서 기판과 박막의 밀도와 탄성계수 및 박막의 두께 등을 알면 전파 속 도를 계산할 수 있다. 박막의 탄성계수를 모르는 경우에는 표면파 속도를 측정하여 역으로 탄 성계수를 산출할 수 있다. 이러한 역산과정에는 일반적인 비선형 방정식의 curve-fitting에 이용될 수 있는 simplex법이 효율적으로 활용된다. 이 글에서는 표면파 속도를 측정하고 그 데이터로 부터 역산하여 박막의 탄성계수를 구하는 원리와 과정을 설명한다.

• Journal of the Korean earth science society
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• v.27 no.5
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• pp.539-547
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• 2006

The activity of the seismic wave propagation around the cavity is investigated for the exact inversion of the crosshole tomography data, in order to understand the possibility of the existence inside the underground cavity. It is found that the adequate frequency range for the tunnel investigation is about 2 kHz to 5 kHz, and the grid space should be set up to 1/10 of the wavelength. The propagation of the seismic wave near the cavity may go through or detour the cavity according to the seismic velocity inside the cavity. The detouring wave propagates with the seismic velocity of mother rock in spite of the velocity of inside of the cavity. The smaller the velocity difference is between the mother rock and cavity, the more frequent penetration of the seismic wave through the cavity appears.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.291-296
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• 2006

The aspect of wave propagation around cavity was investigated for the exact inversion of crosshole tomography data in order to understand the possibility of the existence of underground cavity. We found that the adequate frequency range for the tunnel investigation was about 2kHz to 5kHz, and the grid space was set up to 1/10 length of wavelength. The propagation of the seismic wave near the cavity may go through or detour the cavity according to the seismic velocity of inside of cavity. The detouring wave propagates with the seismic velocity of mother rock in spite of the velocity of inside of cavity. The smaller the velocity difference between the mother rock and cavity, the more frequent penetration of the seismic wave through the cavity was appeared.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.4
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• pp.227-236
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• 1997

Quantitative analysis and imaging of elastic wave propagation are very important for the materials evaluation as well as flaw detection. The elastic wave propagation in an anisotropic media is more complex, and analysis and imaging become essential for flaw detection and materials evaluation. In the anisotropic media, the wave velocity is dependent on the propagation direction. In addition, the direction of group velocity is different from that of phase velocity, the direction of energy flow is not same as the propagation direction of wavefront (beam skewing effect). Especially, this effect becomes critical for the large anisotropic media such as fiber composite materials, and the results using elastic waves for those materials have to be analyzed considering the wave propagation mechanism. Since the analytical approach for the wave propagation in the anisotropic materials is limited, the numerical analysis such as finite difference method (FDM) have been used for these case. Therefore, 2-dimensional FDM program for the elastic wave propagation is developed, and wave propagation in anisotropic media are simulated.

• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.393-398
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• 2007

Seismic traveltime tomography technique was conducted at a site composed of black shale. It is well known that black shale has strong anisotropic property. Therefore, the anisotropic property of black shale has to be considered to obtain the appropriate subsurface velocity model by an inversion process. To estimate the anisotropic constant of the velocity of the black shale in the survey area, the relation between the velocity, which is calculated by the straight ray path and the first arrival time, and the angle of the ray propagation was examined. The elliptically shaped relation was found and it reveals that the black shale contains the anisotropic property of velocity. It was also noticed that the horizontal velocity is faster than the vertical velocity. When the estimated anisotropic constant was applied in the process of the velocity inversion for three sets of field data, we could obtain the appropriate velocity structures of the site that is consistent with the result of the geological survey.

• The Journal of the Acoustical Society of Korea
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• v.18 no.8
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• pp.54-60
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• 1999

The paper describes a theoretical study on the speed of the torsional elastic waves propagating in a circular cylinder whose outer radius varies periodically as a harmonic function of the axial coordinate. The approximate solution for the phase speed has been obtained using the perturbation technique for sinusoidal modulation of small amplitude. It is shown that the wave speed in the cylinder with a corrugated outer surface is less than that in a smooth cylinder by the square of the amplitude of the surface perturbation. This theoretical prediction agrees reasonably with an experimental observation reported earlier. It is also shown that the wave speed reduction due to the surface corrugation becomes larger for a thinner cylinder and for a bigger density of corrugation.

• Tunnel and Underground Space
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• v.11 no.2
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• pp.120-121
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• 2001

The purpose of this study is to investigate concrete flaw using seismic first arrival and various inversion method. Seismic wave propagation was calculated using finite element method in theoretical modelling and tomogram was made using various inversion methods in theoretical and experimental modelling. Five steps of seismic first arrival were selected from FEM results and these data were used to calculate seismic velocity section. According to the results, exact seismic first arrival picking method was proposed and experimental modelling was conducted.

• The Journal of Engineering Geology
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• v.4 no.3
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• pp.269-281
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• 1994

Microscopic study and X-ray diffraction analysis were carried out to find out rock type, tock forming minerals; and weathering characteristics of rocks at the constructing site of the churyong Tunnel, Kyongju-Gun, Kyongbuk. Seismic velocity and compressional strength were measured to evaluate mechanical properties of rock. The rock of the study area is Jurassic tuff consisting of clay minerals, crystals of quartz and feldspar, fragments of volcanic rocks and shale. Fresh tuff has compressional strength of about $443kg/\textrm{cm}^2$ and seismic velocity of about 3680m/sec in average. It is classified as soft rock. Rock fragment within tuff is andesite and it has compressional strength of about $2500kg/\textrm{cm}^2$ and seismic velocity of about 4340m/sec in average. It is classified as hard rock. A good linear relationship is found between compressional streangth and seismic velocity in both laboratory sample and in-situ rocks. Laboratory samples has seismic velocities faster about 1.5km/sec than those in-situ rocks. It is interpreted that joints, fractures, and water content in the in-situ rocks result in decreas of seismic velocity. As Tuff has more than 50% of clay minerals in matrix and shale fragments, it absorbs water easily in atmospheric condition. Therefore, though the rock in the study area is medium hard rock before weathering, it is weathered very easily in the case of exposure to natural environment, comparing with other rock.

• The Journal of the Acoustical Society of Korea
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• v.18 no.5
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• pp.28-34
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• 1999

The effects of the viscosity of an adjacent viscous fluid on the characteristics of the elastic waves have been studied theoretically and experimentally. Expressions for the wave speed and attenuation of the elastic waves of transverse motion, such as the torsional wave propagating in a circular cylinder and the Love wave in a layered half-space solid, have been obtained as functions of the viscosity and mass density of the fluid by exact and asymptotic analyses. The theoretical results have been compared with experimental observations, and it has been demonstrated that a device described herein can be used as a sensor for measuring the viscosity of a fluid with a known mass density.