Papers by Keyword: Surface Wave

Abstract: This study reports the unique phenomenon of the coalescence of oil droplets floating over the water surface. For the first time, the coalescence has been initiated through the creation of externally generated low-amplitude surface waves. We used a simple and cost-effective method to manifest the surface waves over the free surface of water to study the merging dynamics. The time-lapse images depict the entire stage of parent droplets merging. The study reveals that the coalescence time required for the complete transformation of parent droplets into the resultant droplet increases as the number of parent droplets over the free surface of water increases. We studied the time-dependent variation in the velocity of two non-identical parent droplets. The experiment reveals that the smaller droplet propagates faster than the larger droplet over a free surface of water. The peak velocities of the two droplets are 2.0 cm/s and 1.07 cm/s, respectively. The point of deposition of droplets does not influence the coalescence phenomenon; whether the droplets are deposited at the center of the petri dish or the wall, they still show coalescence. However, the droplets that are deposited near the center of the petridish propagate faster compared to those deposited near the wall due to the higher intensity of vibration at the center.

Abstract: Existing non-destructive test methods are usually ineffective in detection of surface breaking cracks with large depths in concrete structure. This paper introduces a method suitable for detection of deep cracks based on surface wave time reversal theory. A numerical simulation based on the finite element model is performed to investigate surface cracks detection. A damage index was defined based on the correlation coefficient between the actuated and the reconstructed wave signals. The results demonstrated that the presence of crack had a significant influence on the propagation characteristics of surface waves along concrete. Cracks in different sizes were introduced and correlated with the damage index. Enlarging the crack depth resulted in an increase in the distortion of reconstructed signals, and a higher damage index was obtained. The results illustrated the effectiveness of the surface wave time-reversal process in identifying cracks in concrete structures.

Abstract: This research explores the use of the seismic surface wave technique which is called as a spectral analysis of surface wave (SASW) for investigating the shallow soil profile. The testing was conducted on soft ground located at Universiti Tun Hussein Onn Malaysia (UTHM). The testing was conducted using a new developed in-house seismic surface wave testing system. An impact source using 5 kg hammer is used to generate seismic energy and four differencesarrangement of the source to receiver distances to produce soil profile. The profile of phase velocity was obtained at a depth of 0.15 m to 1.8 m were between 68 m/s and 95 m/s. The results were calibrated with the hand vane shear test which is used to obtain the undrained shear strength and thus converted empirically to seismic velocity at 45 m/s and 95 m/s. The result shows good agreement between velocity obtained from the surface wave testing system and hand vane shear test. Therefore, the new developed in-house seismic surface wave system has been proven can be used to determine the seismic velocity at shallow depth.

Abstract: Seismic data acquisition needed a relatively fast data logger and multi channels input capability. For this purpose, we construct a measuring instruments based on low cost voltage data logger DI710ULS from DATAQ. The sensors (geophones) have 4.5 [Hz] natural frequency, produce an alternating electric voltage at rate 28 [V/m/s]. The ground shaking / velocity rate of active seismic surface-wave measurement from 5 kg hammer, at 3m distances, is less than 2 [mm/s]. This will produce an alternating voltage at less than 100 [mV].The active seismic surface wave measurements need around 1 ms time sampling for every channels and this instruments can record 7200 data for 8 differential channels, which is sufficient for this purpose. The DI710ULS has a standalone capability and all digital data were recorded in SDcard, whose very light and compact for field acquisition. By only 14[bit] DAC, the data shows reliable and seems good enough by 12.2 [μV] sampling. The data collected by using this data logger were successfully processed for surface wave analysis, and giving a reasonable result.

Abstract: The paper is devoted to a theoretical study of nonlinear wave on a free-surface thin film down an inclined uneven plane. The problem is quite different from that of a viscous films flow along a smooth surface. Thus nondimensional variables are introduced in two ways according to the different relationship of the shallow water parameter and the topography parameter. Further, the zero-order and first-order stream function are derivated on the basis of perturbation method. Finally, the equations which govern the surface height of surface wave on a viscous fluid film down an inclined uneven wall are obtained.

Abstract: Surface-wave dispersion analysis is widely used in civil engineering to infer a shear wave velocity model of the subsoil for a wide variety of applications. Combining with a example, multi-channel analysis of surface waves method (MASW) was discussed in this paper. The entire MASW's procedure of three steps: acquiring ground roll data in the field, processing the data to determine dispersion curve, and back calculation of the geologic parameters for different depths. Based upon all the research results by far, MASW method is an efficient methods because of its high accuracy that is achieved by both special field technique and data processing technique.

Abstract: Seismic response of the Weihe basin generated by 5.12 Wenchuan earthquake is simulated by using the spectral-element method and parallel computing technique, considering 3D basin model incorporated with real topography. The wave propagation and the comparison of the synthetic and observed records are studied in detail in this paper. The result shows that appropriate source and detailed basin model and accurate numerical technique can simulate the wavefield and large basin ground motion well.

Abstract: Seismic response of the Shidian basin to moderate scenario earthquake is investigated considering 3D basin model incorporated with real topography by using the spectral-element method and parallel computing technique. The wave propagation process, the generation of surface wave, and the impact of soil deposits velocity to the basin-induced surface wave are studied in this paper. The results show that the amplification behavior of the basin is the interactions of basin geometry and low velocity soil deposits. First, locally small hollows in the basin are apt to trap seismic waves and produce much stronger ground motion, basin edge and areas with deep sediments are also characterized with large amplification. Then, basin with softer soil deposits produces stronger surface waves with lower propagation velocity and higher mode.

Abstract: Based on the shallow water wave potential flow theory and slender ship assumption, the mathematical model is established for calculating wave caused by ship moving at supercritical speed. The wave pattern caused by ship moving at supercritical speed in shallow water was calculated by using the finite difference method. The effects of channel wall were analyzed. The computed results were compared with the ones calculated by Fourier integral transform method and experiment. A good agreement exists between the calculated with experimental results. The mathematical model and the calculation method were validated.

Abstract: Liquid jets in cross air flows are widely used and play an important role in propulsion systems, such as ramjet combustors. Surface waves on the liquid jets in gaseous crossflows have been observed in numerous experiments. Especially for lower gas Webber number, liquid jets breaks up due to the surface waves. However compared with injecting into gas coaxial flow, liquid jet will be deformed in crossflow due to the transverse aerodynamic force. Deformation of jet is investigated by analyzing stress force equilibrium of the cross-section. Though linear instability analysis, dispersion relation and growth rate of surface waves of liquid jet with deformation were derived. According to the present theoretical analysis, the cross-section shape can be deformed to stable ellipse only if the gas velocity was lower than 9m/s for 1mm diameter jet. The maximum growth rate of disturbances takes place at wave number 0.7 approximately, and it will decrease with increasing the jet diameter. The range of instable wave number will expand and the most instable wave number will grow for the deformed jets.