Papers by Keyword: Wave Velocity

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Authors: Muhamad Bunnori Norazura, Rhys Pullin, Karen M. Holford, R.J. Lark
Abstract: Acoustic Emission (AE) testing in concrete structures shows great potential for monitoring and assessing the health condition of structures. Source location is normally based on the arrival times of transient signals, the simplest method is known as the Time of Arrival (TOA) method, where the location of the damage can be determined from the arrival time of the event at two or more sensors. When using this method, the wave velocity of the signals that propagate through the material needs to be determined. Homogenous materials, such as steel, have welldefined velocities, but in non-homogeneous materials such as concrete the wave velocity is more difficult to predict. This makes the use of a single wave velocity as required in the TOA method very difficult due to the variety of wave velocities obtained, especially for large structures. This paper explores wave propagation in concrete structures over a variety of source to sensor distances. Experiments were performed on a reinforced concrete beam and a reinforced concrete slab, using an Hsu-Nelsen (H-N) Source. It is found that, in general, as the source to sensor distance increases, the wave velocity decreases. The presence of longitudinal and transverse waves is demonstrated and the influence of the part of the waveform used for temporal measurement is explored. In order to provide a practical approach to velocity determination, different thresholds are investigated and the results are discussed in relation to the wave modes present.
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Authors: Jong Ho Park, Joon Hyun Lee, Gyeong Chul Seo, Sang Woo Choi
Abstract: In carbon steel pipes of nuclear power plants, local wall thinning may result from erosion-corrosion or flow-accelerated corrosion(FAC) damage. Local wall thinning is one of the major causes for the structural fracture of these pipes. Therefore, assessment of local wall thinning due to corrosion is an important issue in nondestructive evaluation for the integrity of nuclear power plants. In this study, laser-generated ultrasound technique was employed to evaluate local wall thinning due to corrosion. Guided waves were generated in the thermoelastic regime using a Q-switched pulsed Nd:YAG laser with a linear slit array. . In this paper, time-frequency analysis of ultrasonic waveforms using wavelet transform allowed the identification of generated guided wave modes by comparison with the theoretical dispersion curves. Modes conversion and group velocity were employed to detect thickness reduction.
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Authors: Shinnosuke Takeda, Kinya Ogawa, Kenichi Tanigaki, Keitaro Horikawa, Hidetoshi Kobayashi
Abstract: Dynamic elastic Finite Element Method (FEM) and Discrete element method (DEM) simulations are carried out to investigate dynamic penetration of a projectile into a target of granular medium. It was found that the highly densified region of granular medium was generated just ahead of the projectile and began to propagate spherically with much higher velocity than that of projectile which leaves relatively rarefied medium region. This propagation phenomenon was probably the result of a collision and momentum transfer between particles in target granular medium. The propagation velocity of the densified region decreased during penetration as depending not only on the packing ratio of target medium but also on the projectile velocity. The resistance force of projectile was also investigated in the case of penetration of projectiles with various body lengths. The resistance force increased rapidly and reached to the peak. The peak value was expressed in terms of momentum change of target particles. The resistance force decreased periodically after the peak value. The period clearly depended on the length of projectile. It is obvious that this was caused by the stress wave reverberations in the projectiles with various body lengths.
167
Authors: Andriyanto Setyawan, Indarto, Deendarlianto, Apip Badarudin
Abstract: An investigation on the liquid holdup, wave velocity, and wave frequency in horizontal annular flow has been experimentally conducted through the measurement of liquid holdup using constant electric current method (CECM) sensors. To investigate the effect of viscosity, water and glycerin were used as working liquid, using superficial liquid velocity and superficial gas velocity of 0.05 to 0.2 m/s and 12 to 40 m/s, respectively. Liquids with higher viscosity give the higher liquid holdup, lower wave velocity, and lower wave frequency. Correlations for liquid holdup and mean film thickness, wave velocity, and wave frequency have been developed with mean average errors (MAE) of 13.5%, 9.2%, and 8.6%, respectively.
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Authors: Andriyanto Setyawan, Indarto, Deendarlianto, Prasetyo
Abstract: The wave characteristics of horizontal annular two-phase flow in 16 mm diameter pipe were experimentally investigated using flush-mounted constant electric current method (CECM) sensors and visual observations. To examine the effect of surface tension on the wave velocity and frequency, air and three kinds of liquids with different surface tension were used, i.e., water, 2%-butanol solution, and 5%-butanol solution. The gas and liquid superficial velocities were varied from 12 to 40 m/s and 0.05 to 0.2 m/s, respectively. The liquid holdup was measured directly using CECM, while the wave velocity and frequency were determined using cross correlation and power spectral density functions of liquid holdup signals. Generally, combination of air and liquid with the highest surface tension gives the highest liquid holdup and wave frequency. Simple correlations for wave velocity and wave frequency were also developed.
248
Authors: Xu Qiao, Hao Zhang, Tong Liu, Yuan Yuan Zhang, Yun Hai Xia, Feng Yang
Abstract: According to the need of ground penetrating radar (GPR) measurement of underground targets, we proposed a new method for the prediction of wave velocity. This method based on radar image curves and K-means clustering algorithm, and we can predict the wave velocity accurately. Proved by the experiment, the calculation precision of this method is higher. Although there are some errors in measurement results, it has good robustness to get it corrected.
242
Authors: Jun Wei Liu, Feng Yu, Kun Qi
Abstract: The increase in pile bearing capacity with time after installation is known as soil/pile set-up. A mechanism of pile set-up is discussed in detail and a three-phase model is suggested. A serious of low-strain dynamic tests on full scale pile was carried out in mixed soil for monitoring the increase of wave velocity and stiffness. Wave velocity and stiffness have similar increase trend, but the stiffness shows a larger increase rate. An optimized design procedure to incorporate the pile set-up effects is proposed.
418
Authors: Yong Huang, Peng Liu, Xiao Ming Li, Peng Yin, Xiu Yu Zheng
Abstract: One-terminal fault location provides many advantages including its simple principle, high relative reliability, low cost and high precision. But there still be some problems in practice, such as detection of wave front, calculation of wave velocity and identification of source of reflected wave. In order to settle the problems above, decoupling methods, acquisition of traveling wave signals, calculation of wave velocity, key factors influencing precision of fault location and so on are discussed. This paper will be of importance in the research of one-terminal fault location method and further improvement of reliability and precision.
3419
Authors: Li Gang Zhang, Hong Zhu, Hong Biao Xie, Jian Wang
Abstract: This work addresses the dispersion of Love wave in an isotropic homogeneous elastic half-space covered with a functionally graded layer. First, the general dispersion equations are given. Then, the approximation analytical solutions of displacement, stress and the general dispersion relations of Love wave in both media are derived by the WKBJ approximation method. The solutions are checked against numerical calculations taking an example of functionally graded layer with exponentially varying shear modulus and density along the thickness direction. The dispersion curves obtained show that a cut-off frequency arises in the lowest order vibration model.
252
Authors: Li Gang Zhang, Hong Zhu, Hong Biao Xie, Lin Yuan
Abstract: The P wave propagation in the functionally graded materials (FGM) is studied. The differential equation with varied-coefficient of wave motion in the FGM is established. By using of the WKBJ approximation method, the differential equation with varied-coefficient is solved, and the closed-analytical solutions of displacement in the FGM are obtained. The properties of the FGM whose shear modulus and mass density are gradually varying in exponential form are calculated; the curves of P wave velocity and amplitude, and the general properties of the P wave in the FGM are analyzed.
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