Ocean reverberation is an important issue in underwater acoustics, which usually influences the working performance of the active sonars significantly. The deep-water reverberation data are collected from the South China Sea experiment including the reverberation signals at large receiving depths near the bottom, showing that the wave intensity increases obviously at some moments with time increasing. To analyze in depth the data, a uniform bottom-reverberation model is proposed based on the ray theory, which can calculate monostatic and bistatic reverberation intensity and explain the generation process of deep-water reverberation. The mesh method is first used in this model by dividing bottom scatterers into a number of grids. Then reverberation is calculated based on the exact time of generating the scattering signal from each grid. Due to the exact arrival time, the presented model can provide more accurate result than classical models, in which scatterers are usually treated as circular rings or elliptical rings. Numerical results are compared with experimental reverberations at different receiving distances and depths. The simulated and experimental results agree well overall for large receiving depths, whereas agreement extent decreases for the case of receiving depth close to the sea surface. The analytical results indicate that the applied scattering coefficient is suitable for this experimental sea area, and meanwhile verify that this scattering model is more accurate for low-angle bottom backscatters corresponding to the reverberation at large receiving depths.
Aiming at the fracture of the bracket of sanding nozzle of CRH5 EMU bogie, the fatigue strength analysis and modal analysis of the bracket were conducted according to En13749 and BS7608 standards, and the track excitation during the vehicle running was thoroughly analyzed. The cause leading to the fracture of the bracket was found and the bracket was redesigned.
Abstract:In light of complex topography in southern mountain area, a small chained deep-ploughing machine with crawler was developed. Its key part was a chained deep-ploughing device, whose service life could be impacted by vibration frequency as well as strength and rigidity of the material used. This paper presented the design of the chained deep-ploughing device and related kinematics and mechanical analyses. With the help of finite unit method and Ansys Workbench, simulation analysis of modal and harmonic response was conducted. Modal and vibration mode of the first six orders concluded verified the fact that the deep ploughing device was able to avoid resonance and meet requirements for deep ploughing. This also provided basis for other dynamic response.
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