Papers by Keyword: Wave Velocity

Abstract: Cement mortar is the most commonly used cement-based material, which widely used in construction materials, filling materials and other fields. The aim of this paper is to study the compressive strength and wave velocity characteristic in different particle sizes and sand/cement ratio. The uniaxial compressive strength test and wave velocity test were carried out in different particle size and sand content of mortar samples, respectively. It was found that the compressive strength and wave velocity decrease with the increase of sand/cement ratio. It is interesting that compressive strength and wave velocity in all specimens gradually increases with the increase of particles sizes. The compressive strength of cement mortar is related to the wave velocity. In detailed, the compressive strength and wave velocity was fit to linear relationship. It could thus be used to predict the compressive strength of cement mortar by wave velocity.

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.

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.

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.

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.

Abstract: Ground penetrating radar (GPR) is a kind of geophysical instruments, which has been widely applied in geology, engineering, resource, environment, military etc. The method mentioned in this paper based on QR decomposition, by solving equations to find the estimated value of the radar wave velocity. This method delivers the features of real-time, accurate, and the accuracy required is not high. It is suitable for real time estimation of GPR detection. By estimating the wave velocity, we can identify the spatial location of underground target. This method provides a convenient way for the detection of underground target.

Abstract: In the quality assessment and classification of engineering rockmass, the elastic wave velocity of rockmass has already become an important parameter. But the valve of the elastic wave velocity has obvious anisotropy which is resulted from the non-uniformity characteristics of the rockmass. Therefore, if the measured elastic wave velocity is directly applied to the quality assessment of engineering rockmass, it will not can reflect the actual engineering properties of the rockmass. In order to solve the above problem, the energy variation of elastic wave propagating in the rockmass is studied. According to the field tests of the rockmasses with different weathering degrees, the dynamic characteristics of the elastic wave such as the attenuation and the dominating vibration frequency are analysed. The relationship between the kinetic parameters and the elastic wave velocities is researched. The results show that there is a good correlation between the kinetic parameters of the wave and the weathered rockmass, which can be applied to the rockmass quality classification and the engineering geology assessment.

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.

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.

Abstract: The wave velocity analysis is a kind of popular geophysical method. These years it is also used in structural damage identification which is discussed in this paper. This method is used to detect the interior damage of structure and is verified to recognize the damage effectively. The expression of the vertical and horizontal velocity is deduced and the wave velocity function curve is drawn according to velocity variety rule. The two dimensional and three dimensional wave field figure is drawn according to the wave velocity analysis and it shows the distinguish between the damaged and integrated structure. We can see the change of the wave shape and velocity and we can identify the damage in terms of the velocity variety rule. So the method introduced in this paper is verified to be a pontential way to identify the structural damage.