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In this study, the vortex-induced vibrations of a cylinder near a rigid plane boundary in a steady flow are studied experimentally. The phenomenon of vortex-induced vibrations of the cylinder near the rigid plane boundary is reproduced in the flume. The vortex shedding frequency and mode are also measured by the methods of hot film velocimeter and hydrogen bubbles. A parametric study is carded out to investigate the influences of reduced velocity, gap-to-diameter ratio, stability parameter and mass ratio on the amplitude and frequency responses of the cylinder. Experimental results indicate: (1) the Strouhal number (St) is around 0.2 for the stationary cylinder near a plane boundary in the sub-criti- cal flow regime; (2) with increasing gap-to-diameter ratio (eo/D), the amplitude ratio (A/D) gets larger but frequency ratio (f/fn) has a slight variation for the case of larger values of eo/D(eo/D 〉 0.66 in this study); (3) there is a clear difference of amplitude and frequency responses of the cylin- derbetween the larger gap-to-diameter ratios (e0/D 〉 0.66) and the smaller ones (e0/D 〈 0.3); (4) the vibration of the cylinder is easier to occur and the range of vibration in terms of Vr number becomes more extensive with decrease of the stability parameter, but the frequency response is affected slightly by the stability parameter; (5) with decreasing mass ratio, the width of the lock-in ranges in terms of Vr and the frequency ratio (f/fn) become larger.  相似文献
2.
An analytical solution to the three-dimensional scattering and diffraction of plane SV-waves by a saturated hemispherical alluvial valley in elastic half-space is obtained by using Fourier–Bessel series expansion technique. The hemispherical alluvial valley with saturated soil deposits is simulated with Biot’s dynamic theory for saturated porous media. The following conclusions based on numerical results can be drawn: (1) there are a significant differences in the seismic response simulation between the previous single-phase models and the present two-phase model; (2) the normalized displacements on the free surface of the alluvial valley depend mainly on the incident wave angles, the dimensionless frequency of the incident SV waves and the porosity of sediments; (3) with the increase of the incident angle, the displacement distributions become more complicated; and the displacements on the free surface of the alluvial valley increase as the porosity of sediments increases.The project was supported by the National Natural Science Foundation of China (50478062 and 10532070) and Open Fund at the Key Laboratory of Urban Security and Disaster Engineering (Beijing University of Technology), Chinese Ministry of Education. The English text was polished by Keren Wang.  相似文献
3.
The liquefaction of loess under dynamic loading is studied experimentally with a dynamic triaxial test system. The effects of over-consolidation ratio (OCR), saturation degree and the frequency of dynamic loading upon loess liquefaction are investigated. The development of pore pressure within loess samples is also discussed. Based on the experimental results, the empirical relationship between pore pressure ratio and loading cycle number ratio is established for normal consolidated saturated loess.The project supported by the National Natural Science Foundation of China (50178005)  相似文献
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