Papers by Keyword: Dispersion Curve

Abstract: Several techniques based on ultrasound have been proposed for non-destructive evaluation (NDE). It has been widely applied in many fields such as medicine, mechanical, and construction, especially for the detection of cracks and flaws in structures and for the identification of material properties, which is capable of performing tasks to provide quick measurements while guaranteeing great accuracy. In this paper, we have developed the technique of ultrasonic transmission by water immersion as an alternative technique to study the propagation of ultrasonic waves in two structural materials: wood and wood protected by liquid paint (cement). Overall, the application of the transmission technique by change of the angle of incidence enables the demonstration of the experimental dispersion curves for the ultrasonic modes within the plates and allows the investigation and characterization of the function of the paint system (cement) in the wood plate.

Abstract: Dispersion curves present fundamental information on guided waves such as wavelength and dispersivity as well as phase and group velocities at a certain frequency, which is essential for the application of guide wave technology. A numerical method based on modal analysis using ANSYS software was presented to calculate the dispersion curves of guided waves in rod. The mode shapes of different modes of guided waves were obtained and discriminated, and the dispersion curves of rod were extracted. The numerical result and the analytical ones matched very well, which verified the effectiveness of this method. This numerical method can be applied to arbitrary waveguide which can be considered as a periodic structure with constant cross-section.

Abstract: Surface wave dispersion imaging approach is crucial for multi-channel analysis of surface wave (MASW). Because the resolution of inversed S-wave velocity and thickness of a layer are directly subjected to the resolution of imaged dispersion curve. The τ-p transform approach is an efficient and commonly used approach for Rayleigh wave dispersion curve imaging. However, the conventional τ-p transform approach was severely affected by waves amplitude. So, the energy peaks of f-v spectrum were mainly gathered in a narrow frequency range. In order to remedy this shortage, an improved τ-p transform approach was proposed by this paper. Comparison has been made between phase shift and improved τ-p transform approaches using both synthetic and in situ tested data. Result shows that the dispersion image transformed from proposed approach is superior to that either from conventionally τ-p transform or from phase shift approaches.

Abstract: In the paper the shear wave velocity profile is studied using the MASW test. The experimental dispersion curves were obtained from the signal process proposed by Ryden. Theoretical dispersion curve can be constructed by thin layer stiffness matrix method. A real-parameter genetic algorithm is required to minimize the error between the theoretical and experimental dispersion curves. To reduce the error of experimental and theoretical dispersion curve using real-parameter genetic algorithm is feasible. The results show that the soil layers of the study area can be modeled as a sandy fill overlaid on an underlying half space. Test results also show that the asymptotes at high frequencies of the fundamental mode approach the phase velocities for the fill of 190 m/s. The depths of weathered bedrock estimating from dispersion curves match well with that of borehole data.

Abstract: In the paper the shear wave velocity and Poisson’s ratio profile are studied using the MASW test. Slant stacking was adopted in experimental dispersion curve constructing. Theoretical dispersion curve can be constructed by thin layer stiffness matrix method. A real-parameter genetic algorithm is required to minimize the error between the theoretical and experimental dispersion curves. Test results show that spectrum using slant stacking shows the fundamental mode of Rayleigh wave in the frequency range from 15 Hz to 50Hz. To reduce the error of experimental and theoretical dispersion curve using real-parameter genetic algorithm is feasible. The results also show that the strata of Lu-Liao-His Earth Dam can be modeled as 3 soil layers with an underlying half space.

Abstract: To understand more about Lamb waves on composite laminates damage detection features, the Lamb wave group velocity dispersion curves are calculated and plotted by using dichotomy method in MATLAB. The signal parameters are chosen according to Group velocity dispersion curves. The dynamic response signals of the composite plate are obtained by finite element method. Damage location is calculated by the actual group velocity of Lamb wave and time of flight of the difference signal before and after damage.

Abstract: The Rayleigh dispersion curves of multilayered soil are calculated by means of thin-layer method and rapid scalar method, respectively, in which two-layered and three-layered soil model are adopted. In addition, the disperse properties of multilayered soil are analyzed, and it is found that thin layer method is superior to rapid scalar method in low frequency domain, while in the high frequency domain it has little difference between each other.

Abstract: SH wave propagation behavior in functionally graded materials plates with variant material components was studied by positive series method. The dispersion curves of phase velocity and group velocity of functionally graded materials plates with stress-free surfaces are obtained and compared with those of homogeneous plate. The conclusions show that variant material components have a great influence to the disperse curves of phase velocity and group velocity. There is great significance of these results for ultrasonic nondestructive testing technique and inversion method of material parameters.

Abstract: Based on linear magneto-electro-elasticity, the circumferential SH wave equation of transversely isotropy piezoelectricity-piezomagnetic functionally graded cylindrical curved plate is obtained. The Legendre orthogonal polynomial series expansion approach is employed to derive its asymptotic solution. The dispersion curves, electric potential and magnetic potential distributions are calculated. The influence of the piezoelectricity and piezomagnetism on the circumferential SH wave is investigated and the influential factors are analyzed. Finally, the influence of the gradient field and the ratio of the radius to thickness on the piezoelectric effect and piezomagnetic effect are illustrated.

Abstract: The finite element model with artificial boundary was used to simulate dynamic response of an underground circular structure (tunnel, cavern) and displacement of the ground surface under incidence of Rayleigh wave, and to quantitatively analyze the effects of incident wavelength, diameter of structure, and liner stiffness on ground surface displacement amplification. The numerical results show that, the surface displacement amplitude with a tunnel can be 1.3 times of that for the case of without the tunnel. It is suggested that the effects of a tunnel on ground motion should be considered when the tunnel is planned and designed.