• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.3
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• pp.296-307
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• 2010

This paper deals with the energy transmission ratio of the elastic waves transmitting through a solid wall. Based on the displacement of the reflected and transmitted waves relative to the incident waves, the energy transmission ratio of the wave was obtained by multiplying the vibration velocity and stresses. Numerical calculation provided with the transmission ratio and refraction angle corresponding to the incidence angle, and it showed the mode conversion from the incident longitudinal wave to the transmitted transverse wave in particular incidence angle range. The paper established a procedure to find the incidence angle of the maximum energy transmission ratio and confirmed it by experiment.

• Journal of the Korean Society of Safety
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• v.17 no.2
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• pp.58-62
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• 2002

Longitudinal wave tests with finite elastic medium were performed to investigate the difference between measured values and theoretical values of propagation velocity and elasticity modulus. Each accelerometer was attached on finite elastic medium with same phase and different positions to check the particle motion. The results show that measured values of elasticity moduli from both time domain and frequency domain were similiar to theoretical value. Polarity of signal depends entirely on the phase of accelerometer. It proved that the propagation velocity and the particle motion are in the same direction when a compressive stress is applied. And also the propagation velocity and the particle motion depend on the intensity of the stress and material properties respectively.

• Structural Engineering and Mechanics
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• v.58 no.2
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• pp.347-378
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• 2016

Within the scope of the plane-strain state, by utilizing the three-dimensional linearized theory of elastic waves in initially stressed piezoelectric and elastic materials, Lamb wave propagation and the influence of the initial stresses on this propagation in a sandwich plate with pre-stressed piezoelectric face and pre-stressed metal elastic core layers are investigated. Dispersion equations are derived for the extensional and flexural Lamb waves and, as a result of numerical solution to these equations, the corresponding dispersion curves for the first (fundamental) and second modes are constructed. Concrete numerical results are obtained for the cases where the face layers' materials are PZT-2 or PZT-6B, but the material of the middle layer is Steel (St) or Aluminum (Al). Sandwich plates PZT-2/St/PZT-2, PZT-2/Al/PZT-2, PZT-6B/St/PZT-6B and PZT-6B/Al/PZT-6B are examined and the influence of the problem parameters such as piezoelectric and dielectric constants, layer thickness ratios and third order elastic constants of the St and Al on the effects of the initial stresses on the wave propagation velocity is studied.

• The Journal of Engineering Geology
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• v.12 no.3
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• pp.273-284
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• 2002

The purpose of this study is to characterize damage propagation in granite which exists in South Korea. Coarse, medium and fine-grained granite specimens were sampled respectively In order to perform this study, elastic wave velocity test and permeability test were carried out to estimate the physical specificities of specimens before and after damage. Cellulose acetate film duplication method was used to select only cracks from cross section and to make these visible. Using dark-field illumination, approach photographing technique was used to get more distinct photographs of cracks from acetate peel. Computer programs named Photoshop were used to describe cracks. After damage, coarse and medium-grained granite had lower elastic wane velocity, higher permeability, more cracks and more distinct shear fractures than fine-grained granite.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.357-364
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• 1999

In recently site investigations, the need for the determination of dynamic soil properties such as dynamic modules of rigidity, elasticity, dynamic poison's ratio and damping ratio etc. is increasing for the astigmatic designs of the civil structures. To obtain some of the dynamic properties, measurement of elastic waves velocity, both P and S wave, is required. Among various methods to measure elastic wave velocity such and Down Hole, Cross Hole and Refraction etc., Suspension P.S. Logging has an advantage to use for the off-shore investigation where generation of the shock wave and traveling of the wave is difficult. In suspension P.S. logging, specially designed prove equipped with source of shock wave, two 3-channel receivers, departing 1m distance, and other auxiliary facilities is inserted down in a bore hole bottom and raised in predetermined interval, usually 1m or 2m, and measurement is conducted. P.S. logging have been conducted in a off-shore construction project near InChon in the west coast for the first in the country, and form the result, potential of the liquefaction of the subsoil was evaluated and compared with the conventional method.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.301-308
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• 2000

Non-linear behavior of rock under compression can be predicted by a crack model. Crack growth in rock renders rock anisotropic. The degree of anisotropy is explained in terms of elastic moduli as a function of load level. In this study, we calculate the changes of elastic moduli due to crack growth numerically by using a crack model and compare these values with experimental results obtained from the measurement of ultrasonic wave velocities. Image processing technique is used to obtain the initial crack information needed for the numerical calculation of elastic moduli.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.47-55
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• 2000

Non-linear behavior of rock under compression can be predicted by a crack model. Crack growth in rock renders rock anisotropic. The degree of anisotropy is explained in terms of elastic moduli as a function of load level. In this study, we calculate the changes of elastic moduli due to crack growth numerically by using a crack model and compare these values with experimental results obtained from the measurement of ultrasonic wave velocities. Image processing technique is used to obtain the initial crack information needed for the numerical calculation of elastic moduli.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.272-277
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• 2004

The elastic waves in the plate are dispersive waves with the characteristics of Lamb waves. However, $S_0$ symmetric mode is less dispersive in the frequency region less than first cut-off frequency. And, in anisotropic plates such as CFRP plates, the propagation velocities vary with the direction. So, the wave vector direction to be the phase velocity direction is not accord with the energy flow direction to be the group velocity direction. In this work, the group velocities of the $S_0$ symmetric mode less than the first cut-off frequency was analyzed with the group velocity dispersion curves in unidirectional CFRP plate. And, the group velocity curve obtained by the group velocity dispersion curves are compared with the measured velocities as varied the propagation direction of the Lamb wave. The measured velocities are good agreement with the corrected group velocity curve except near the fiber direction which is called the cusp region. When the propagation direction is not accorded with the principal axis, the direction of the group velocities declines to the fiber direction in the unidirectional CFRP plates. This implies that the energy propagates preferentially toward fiber direction.

• Journal of the Korean GEO-environmental Society
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• v.15 no.5
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• pp.57-65
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• 2014

For economic and technical reasons, it is difficult to obtain high quality undisturbed cohesionless samples, hence most researchers rely on preparing remolded and reconstituted representative samples of sandy soils. In this study, moist tamping, air pluviation, and dry deposition methods were applied to make remolded samples at similar relative densities. A series of isotropically consolidated drained tests were conducted with accompanied by measured elastic wave velocities in order to evaluate a difference between sample preparation methods and relative densities. For the elastic wave velocity measurements, piezoelectric elements were installed on the top and bottom cap of the triaxial device. The results showed that soil behavior relies on sample preparation methods, and that the trend of shear wave velocity was the same with volumetric strain behavior.

• Journal of Mechanical Science and Technology
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• v.19 no.5
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• pp.1087-1094
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• 2005

This paper presents the validity and limitation of the thin-shell approach for the analysis of elastic wave propagation in a pipe with nonviscous liquid. The phase velocities calculated by the thin-shell approach were compared with those calculated by the thick-cylinder approach. In contrast to the case of the empty pipe, where only two modes were obtained and the first mode was calculated in a limited frequency range, the results for the liquid-filled pipe exhibits a large number of modes due to the large number of branches of the apparent liquid mass. Several of the lowest modes of the waves in a liquid-filled pipe were calculated for various pipe thicknesses in a low frequency range. The thin-shell approach was valid for a reasonable range of pipe thicknesses.