• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.154-162
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• 2009

Sonic wave dispersion characteristics are one of the most important targets of study, particularly in estimating shear wave velocity from borehole sonic logging. We have tested dispersion characteristics using monopole and dipole sources. Theoretical dispersion curves were computed for tool-absent and tool-included models having the same physical properties but different diameters (including ${\Phi}520mm$, ${\Phi}150mm$, and ${\Phi}76mm$). Comparisons were made between boreholes of different sizes and between tool-absent and tool-included models. Between the tool-included and the tool-absent boreholes, a close similarity in dispersion curve shape was revealed for the monopole source, and a significant difference was shown for the dipole source. However, for the cut-off frequency, particularly in the engineering boreholes (${\Phi}76mm$ and ${\Phi}50mm$), a significant difference was observed for signals from the monopole source, but approximately the same cut-off frequencies were found with the dipole source. This indicates the need of careful choice of source frequency in monopole-source sonic logging, particularly in an engineering borehole. The results of numerical experiments show that cut-off frequency is exponentially proportional to the inverse of borehole radius, irrespective of the mode type and the presence of a tool, and that the cut-off frequencies for each borehole environment could be expressed as an exponential function, rather than the inversely proportional relationship between the cut-off frequency and the borehole radius that was previously generally recognised. From the direct comparison of dispersion curves, the effects on the dispersion characteristics of borehole size and the presence of the tool can be revealed more clearly than in previous studies, which presented the dispersion curve and/or characteristics for each borehole environment separately.

• The Journal of Engineering Geology
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• v.17 no.3
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• pp.329-337
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• 2007

For seven NX sized borehole models constructed from physical property data for representative geology in Korea, dispersion curves were derived and compared between models having different physical parameters. By comparing and analyzing the dispersion curves obtained from different sources (monopole and dipole) and different borehole sizes (76 mm and 150 mm), dispersion characteristics in sonic log could be understood better, particularly in the case of slim hole sonic log.

• Korean Journal of Soil Science and Fertilizer
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• v.43 no.3
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• pp.275-282
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• 2010

The laboratory column experiments were used to transport of metal elements by infiltration-related dispersion and/or diffusion in mine tailing of the Guryong gold mine. The mine tailing shows the neutral pH (for a pore water) and contains quartz, chlorite, pyrite and calcite. Both a non-reactive solute ($Cl^-$ of 100 mg $L^{-1}$) and a reactive solute (1N HCl), were injected continuously through columns. The breakthrough curve in the non-reactive experiment reached at a maximum under 1.5 pore volumes (PV). The longitudinal dispersion (0.607 cm) and hydrodynamic dispersion coefficient ($1.96{\times}10^{-7}cm^{2}sec^{-1}$) were calculated by the slope. In the reactive experiment, the plateau curve was appeared in the pH values of 5.3, 4.5 and 1.7. The releases of metal elements such as Fe, Mn, Al, Cu, Zn, Pb, and Cd were observed to be related to the pH buffering. High concentrations of Mn, Cd and Zn were observed at the first pH plateau (4 PV and pH 5.3), whereas Fe, Cu, Al and Pb were released as the pH decreased to 4.0 or less. The resulting order of metals mobility, based on the effluent water, is Mn=Cd>Zn>Cu>Fe>Al>Pb.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.2
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• pp.171-175
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• 2014

In this study, we suggest a method to measure the thickness of thin films nondestructively using the dispersion characteristics of a surface acoustic wave propagating along the thin film surface. To measure the thickness of thin films, we deposited thin films with different thicknesses on a Si (100) wafer substrate by controlling the deposit time using the E-beam evaporation method. The thickness of the thin films was measured using a scanning electron microscope. Subsequently, the surface wave velocity of the thin films with different thicknesses was measured using the V(z) curve method of scanning acoustic microscopy. The correlation between the measured thickness and surface acoustic wave velocity was verified. The wave velocity of the film decreased as the film thickness increased. Therefore, thin film thickness can be determined by measuring the dispersion characteristics of the surface acoustic wave velocity.

• Journal of the Korean Geotechnical Society
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• v.24 no.4
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• pp.115-123
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• 2008

The dispersive phase velocity of a wave propagating through multilayered systems such as a soil site is an important parameter and carries valuable information in non-destructive site characterization tests. The dispersive phase velocity of a wave can be determined using the phase spectrum, which is easily evaluated through the cross power spectrum. However, the phase spectrum determined using the cross power spectrum is easily distorted by background noise which always exists in the field. This causes distortion of measured signal and difficulties in the determination of the dispersive phase velocities. In this paper, a new method to evaluate the phase spectrum using the harmonic wavelet transform is proposed and the phase spectrum by the proposed method is applied to the determination of dispersion curve. The proposed method can successfully remove background noise effects. To evaluate the validity of the proposed method, numerical simulations of multi-layered systems were performed. Phase spectrums and dispersion curves determined by the proposed method were found to be in good agreement with the actual phase spectrums and dispersion curves biased by heavy background noise. The comparison manifests the proposed method to be a very useful tool to overcome noise effects.

• The Journal of the Acoustical Society of Korea
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• v.25 no.3
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• pp.107-112
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• 2006

The elastic waves in a plate are dispersive waves due to the characteristics of Lamb waves. However, S0 symmetric mode is less dispersive in the frequency region below the first cut-off frequency. The wave Propagation velocities vary with the direction in anisotropic plates such as Carbon Fiber Reinforced Plastic (CFRP) Plates. The wave vector direction and energy flow vector direction are same in isotropic plates. However, the wave vector direction same as the phase velocity direction is not in accordance with the energy flow direction same as the group velocity direction in anisotropic plates. In this study. the dispersion curves or the phase velocity from anti-symmetric and symmetric Lamb wave dispersion equation are calculated for unidirectional laminated composite plate. Slowness surface is sketched using phase velocity under the first cut-off frequency. The direction and magnitude of group velocity are corrected with this slowness surface. The measured group velocities are in good agreement with the corrected group velocity curve except near the fiber direction zone which is called the cusp region.

• Geomechanics and Engineering
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• v.13 no.5
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• pp.775-791
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• 2017

Surface wave techniques are widely used as non-invasive method for geotechnical site characterization. Field surface wave data are collected and analyzed using different processing techniques to generate the dispersion curves, which are further used to extract the shear wave velocity profile by inverse problem solution. Characteristics of a dispersion curve depend on the subsurface layering information of a vertically heterogeneous medium. Sometimes soft layer can be found between two stiff layers in the vertically heterogeneous media, and it can affect the wave propagation dramatically. Now most of the surface wave techniques use the fundamental mode Rayleigh wave propagation during the inversion, but this may not be the actual scenario when a soft layer is present in a vertically layered medium. This paper presents a detailed and comprehensive study using finite element method to examine the effect of soft layers which sometimes get trapped between two high velocity layers. Determination of the presence of a soft layer is quite important for proper mechanical characterization of a soil deposit. Present analysis shows that the thickness and position of the trapped soft layer highly influence the dispersion of Rayleigh waves while the higher modes also contribute in the resulting wave propagation.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.258-263
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• 2004

An efficient technique for the calculation of guided wave dispersion curves in composite pipes is presented. The technique uses a forward-calculating variational calculus approach rather than the guess and iterate process required when using the more traditional partial wave superposition technique The formulation of each method is outlined and compared. The forward-calculating formulation is used to develop finite element software for dispersion curve calculation. Finally, the technique is used to calculate dispersion curves for several structures, including an isotropic bar, two multi-layer composite bars, and a composite pipe.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.04a
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• pp.61-65
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• 2001

A new flaw detection technique using by SH angle beam method has been discussed. The SH-wave is horizontally polarized shear wave and the surface SH wave has a characteristic of traveling along near surface layer. The surface SH wave technique is valuable for the detection of fatigue cracks at fillet weld heels which cannot be detected by other ultrasonic technique such as angle beam technique and The dispersion curves of it has simple characterization. In this work, using these beneficial chraterization, quality evaluation of spot weld with ultrasonic sound intensity of SH-wave passing through nugget area of spot weld are verified experimentally.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.33 no.3
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• pp.248-258
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• 1997

The analytical solutions of the Fraunhofer Diffraction(FD) theory and the principle for measurement of the dispersion relation of plasma wave is presented. Especially, the method for measurement of low-frequency wave is discussed. The wavenumbers of the density fluctuations are obtained from the curve fitting between the expremental FD profile and theoretical one for each frequency component. In measurement of the wavenumber of the low -frequency region, the information of the wavenumber is easily obtained from the ratio of the intensity at = 0 to the intensity at =0.5. The millimeter wave FD apparatus was designed to measure low-frequency density fluctuations. The determined wavenumbers are in the range of =0.1~ 1.0cm. Thus, the millimeter wave FD method was shown to be useful for the measurement of low-frequency density fluctuations, which are impossible to be measured by using a convention. Thomson scattering. The obtained dispersion relations will be useful information for plasma waves.