• Journal of the Korean Society for Precision Engineering
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• v.16 no.2 s.95
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• pp.138-144
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• 1999

Longitudinal wave and shear wave velocity changes of PMMA Polymer meterial under the the unidirection load were measured. The Third-order elastic modulus and acousto-elastic modulus of PMMA are obtained. The theoretical and experemental values of the velocity change of each wave by stress are compared each other and the validity of theoretical expression is examinated.

• Journal of the Korean Wood Science and Technology
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• v.32 no.3
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• pp.33-41
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• 2004

In ancient wooden structures, the mechanical properties of the structural members have been reduced by time-dependent degradations such as fatigue or creep. Also, the external and internal deterioration was caused by environmental condition, fungi, bacteria, or insect, and then reduced the quality of structural members. However, the previous methods for evaluating the deterioration have been mainly depended on the visual inspection. In this study, therefore, ultrasonic stress wave test, accelerometer stress wave test were used to evaluate the deterioration of structural wood members in ancient wooden structures. Based on the results, the quantitative criteria of stress wave transmitted velocity were proposed to evaluate the deterioration of structural member. The proposed criteria were related to the degree of deterioration. In accelerometer stress wave, the criteria of deterioration of wave reciprocal velocity was below 1800 ㎲/m at incipient deterioration (below 12% ratio of deterioration), between 1800 and 2200 ㎲/m at moderate deterioration (12~17%) and above 2200 ㎲/m at severe deterioration (above 17%). The ultrasonic stress wave, the criteria of deterioration were 800 and 950 ㎲/m at below 8% and above 15% of the degree of deterioration respectively.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.10 s.115
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• pp.1057-1066
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• 2006

Acoustic streaming Induced by longitudinal vibration at 30 kHz is visualized for a test fluid flow between the stationary glass plate and ultrasonic vibrating surface with particle imaging velocimetry (PIV) To measure an increase in the velocity of air flow due to acoustic streaming, the velocity of air flow in a gap between the heat source and ultrasonic vibrator is obtained quantitatively using PIV. The ultrasonic wave propagating into air in the gap generates steady-state secondary vortex called acoustic streaming which enhances convective cooling of the stationary heat source. Heat transfer through air in the gap is represented by experimental convective heat transfer coefficient with respect to the gap. Theoretical analysis shows that gaps for maximum heat transfer enhancement are the multiple of half wavelength. Optimal gaps for the actual design are experimentally found to be half wavelength and one wavelength. A drastic temperature variation exists for the local axial direction of the vibrator according to the measurement of the temperature distribution in the gap. The acoustic streaming velocity of the test fluid in the gap is at maximum when the gap agrees with the multiples of half wavelength of the ultrasonic wave, which are specifically 6 mm and 12 mm.

• Geophysics and Geophysical Exploration
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• v.16 no.4
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• pp.250-256
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• 2013

Using shear wave velocity is more reasonable to estimate strength and integrity of rock compared with using compressional wave. It is often ambiguous to pick the dominant frequency caused by torsional wave when evaluating $V_S$ of rock specimen from FFRC method. It is also sometimes ambiguous to pick the first arrival point of S wave compared with P wave in the signals acquired from ultrasonic velocity method. Otherwise, the procedure of evaluating $V_P$ using ultrasonic velocity method and $V_L$ using FFRC method is relatively stable. Through the relationship between elastic modulus, poisson's ratio and $V_S$ can be obtained from $V_P$, $V_L$. Applicability was checked using model specimens having different material property and length and rock specimens sampled in mine area, and usefulness of proposed procedure was verified.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.544-550
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• 1997

In this study, the advanced on-sided stress wave velocity measurement method was applied to investigate the effects of composition, age and moisture content in concrete. Two concrete specimens that have different composition were used to figure out the change of the Longitudinal and Surface wave velocity due to different composition. The other concrete specimen was cast and the Longitudinal and Surface wave velocity was monitored during curing process. After 28-day old, the effect of moisture content in the concrete specimen to the stress wave velocity is presented in this paper during the time period 43-74 days after casting. For drying process. an aggregate drying oven was used. A conventional ultrasonic through transmission method was used to compare with the results determined by the one-sided method.

• The Journal of the Acoustical Society of Korea
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• v.23 no.4E
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• pp.140-145
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• 2004

A laboratory study was carried out to investigate the change of ultrasonic velocity as a function of temperature for fluid mud (i.e., suspension). Pulse transmission technique with ultrasonic wave was used for ultrasonic velocity measurement. The five samples for fluid mud were prepared for concentration range of $30.6{\%}\;(1.24\;g/cm^{3}\;in\;density),\;23.3{\%}\;(1.19\;g/cm^{3}),\;11.5{\%}(1.10\;g/cm^{3}),\;7.8{\%}\;(1.08\;g/cm^{3}),\;and\;3.8{\%}\;(1.05\;g/cm^{3})$ by weight. The ultrasonic velocity in fluid mud was investigated to increase $(approximately\;2.83\;to\;4.95\;m/s/^{\circ}C)$ with increasing temperature, due to the effect of viscosity and compressibility of water with changing temperature. But the increasing rate tends to decrease at temperature higher than $30^{\circ}C,$ caused by the effect of viscosity. The concentration of fluid mud more affect to the ultrasonic velocity at higher temperature range than that at lower temperature. Overall the temperature effect on the ultrasonic velocity in fluid mud was a similar rate as for distilled water and seawater, suggesting fluid mud significantly depends on the behavior of water.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1998.10a
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• pp.150-160
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• 1998

Measuring temperature with ultrasonic wave apparatus is desirable in the case of both below 300$0^{\circ}C$ and ideal gas because of the fact that the temperature of gas is the function of only sound velocity. In this study, being used a heatable wind channel and a blower, the variation of temperature is observed in accordance with diverse flow rate(air velocity). The frequency modulation method is used to measure the temperature which is varying in hot air flow till 10$0^{\circ}C$. The length changed in the position of ultrasonic sensors is considered. Also, the effects of air velocity at the same temperature and various facing angles of ultrasonic sensors are considered. As a result of this study, it has been found that the temperature in gas flow is correctly measured regardless of both the distance of ultrasonic sensors and the variation of air velocity, and that there is just a little influence of facing angles.

• Smart Structures and Systems
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• v.17 no.1
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• pp.73-89
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• 2016

The stress dependence of ultrasonic wave velocity is known as the acoustoelastic effect. This effect is useful for stress monitoring if the acoustoelastic coefficient of a subject medium is known. The acoustoelastic coefficients of metallic materials such as steel have been studied widely. However, the acoustoelastic coefficient of concrete has not been well understood yet. Basic constituents of concrete are water, cement, and aggregates. The mix proportion of those constituents greatly affects many mechanical and physical properties of concrete and so does the acoustoelastic coefficient of concrete. In this study, influence of the water-cement ratio (w/c ratio) and the fine-coarse aggregates ratio (fa/ta ratio) on the acoustoelastic coefficient of concrete was investigated. The w/c and the fa/ta ratios are important parameters in mix design and affect wave behaviors in concrete. Load-controlled uni-axial compression tests were performed on concrete specimens. Ultrasonic wave measurements were also performed during the compression tests. The stretching coda wave interferometry method was used to obtain the relative velocity change of ultrasonic waves with respect to the stress level of the specimens. From the experimental results, it was found that the w/c ratio greatly affects the acoustoelastic coefficient while the fa/ta ratio does not. The acoustoelastic coefficient increased from $0.003073MPa^{-1}$ to $0.005553MPa^{-1}$ when the w/c ratio was increased from 0.4 to 0.5. On the other hand, the acoustoelastic coefficient changed in small from $0.003606MPa^{-1}$ to $0.003801MPa^{-1}$ when the fa/ta ratio was increased from 0.3 to 0.5. Finally, it was also found that the relative velocity change has a linear relationship with the stress level of concrete.

• Journal of Powder Materials
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• v.19 no.3
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• pp.215-219
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• 2012

An attempt was made to evaluate creep reliability of two commercial Ni-based superalloys by using ultrasonic wave. The materials include fine-grained PM alloy fabricated by mechanical alloying and subsequent hot isostatic pressing, and IN738LC cast alloy with a grain size of a few cm. Microstructural parameters (fraction of creep cavity and size of ${\gamma}^{\prime}$ precipitates) and ultrasonic parameters (velocity, attenuation) were measured to try to find relationships between them. Ultrasonic velocity decreased with creep cavity formation in PM alloy. On the other hand, no distinct changing trend of ultrasonic velocity was observed for IN738LC alloy. Ultrasonic attenuation was found to have a linear correlation with the size of ${\gamma}^{\prime}$ precipitates and was suggested as a potential parameter for monitoring creep reliability of IN738LC alloy.

• Journal of the Korean Wood Science and Technology
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• v.32 no.4
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• pp.74-81
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• 2004

The ultrasonic non-destructive method was used for wood decay test. The temperature change and moisture contents of wood were estimated how the ultrasonic wave velocity changes. The relationship between weight loss of wood decayed by T. palustris and ultrasonic wave velocity was investigated. The non-destructive methods of different condition of logwood were estimated. Decay map of old wood was made by non destructive methods. Through these tests, we can accumulate the data to judge the degree of wood decay. The decay map of wood could be used for the analysis of old wood.