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排序方式: 共有1231条查询结果,搜索用时 171 毫秒
1.
制备了3种不同质量浓度的充填体试件,进行了单轴压缩声发射试验,分析了不同浓度的充填体力学特性,重点研究了试件破坏过程中的声发射振铃计数、声发射累计撞击数与声发射累计能量的比值(r值)、主频及其相对高频信号激增响应系数特征。研究表明:随着浓度的增加,充填体的峰值强度与弹性模量呈增大趋势,充填体中出现的声发射累计振铃计数越多;r值先升高再持续减小到一个较低值,随着外载荷的增加,进入缓慢升高阶段,峰值前均保持在该阶段。充填体破裂前兆信息在声发射信号主频分布中呈现主频段增多现象,表现为由加载初期的1~2个主频段,在临界主破裂时增多到3~5个主频段;且随着浓度的增加,声发射信号主频频段分布越宽,声发射相对高频信号(160~180 kHz)的激增响应系数呈递减趋势。以上特征可为不同浓度的尾砂胶结充填体稳定性监测、预测提供依据。 相似文献
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《Wave Motion》2020
Acoustic properties of an additive-manufactured SiC scaffold with hexagonal symmetry fabricated by the robocasting method are studied both numerically and experimentally. The numerical analysis is based on the finite element method (FEM) using Bloch boundary conditions. The calculations show both angular and frequency dispersion of the acoustic waves with wavelengths comparable to the spacing between the rods, i.e., on a millimeter scale, indicating interesting acoustic properties in the MHz range. The dispersion character leads to focusing of the energy propagation into the directions of the rods of the hexagonal structure. This is illustrated by modal-based calculations of the propagation of longitudinal and out-of-plane shear wave packets with a dominant wavelength. The experimental analysis consists of two steps, the measurement of the resonant spectrum and shear wave propagation character. The measured resonant spectrum is in good agreement with the one calculated using numerically obtained low-frequency properties of the structure, also showing the quality of the overall manufactured structure. The time-domain measurement shows significant changes in the energy propagation between low and high frequencies, as predicted by FEM calculations. 相似文献
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A diagnostic tool for jet noise using a line-source approach and implicit large-eddy simulation data
In this work, we propose a cost-effective approach allowing one to evaluate the acoustic field generated by a turbulent jet. A turbulence-resolving simulation of an incompressible turbulent round jet is performed for a Reynolds number equal to thanks to the massively parallel high-order flow solver Incompact3d. Then a formulation of Lighthill's solution is derived, using an azimuthal Fourier series expansion and a compactness assumption in the radial direction. The formulation then reduces to a line source theory, which is cost-effective to implement and evaluate. The accuracy of the radial compactness assumption, however, depends on the Strouhal number, the Mach number, the observation elevation angle, and the radial extent of the source. Preliminary results are showing that the proposed method approaches the experimental overall sound pressure level by less than 4 dB for aft emission angles below 50°. 相似文献
4.
The interactions of bubbles and coal particles in 600 kHz ultrasonic standing waves (USW) field has been investigated. A high-speed camera was employed to record the phenomena occurred under the USW treatment. The formation and behaviors of cavitation bubbles were analyzed. Under the driving of these cavitation bubbles, whose size is from several microns to dozens of microns, coal particles were aggregated and then attracted by large bubbles due to the acoustic radiation forces. The results of USW-assisted flotation show a significant improvement in recoveries at 600 kHz, which indicates that the interactions of bubbles and particles in the USW field are more efficient than that in the conventional gravitational field. Furthermore, the sound pressure distribution of the USW was measured and predicted by a hydrophone. The analysis of gravity and buoyancy, primary and secondary Bjerknes forces shows that bubble-laden particles can be attracted by the rising bubbles under large acoustic forces. This study highlights the potential for USW technology to achieve efficient bubble-particle interactions in flotation. 相似文献
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《Physics letters. A》2020,384(13):126253
This letter is concerned with acoustic wave propagation and transmission in acoustic waveguides with periodically grafted detuned Helmholtz resonators. The interplay of local resonances and Bragg band gaps in such periodic systems is examined. It is shown that, when the resonant frequencies of the resonators are tuned close to a Bragg band gap, the behavior of the Bragg band gap can be affected dramatically. Particularly, by introducing appropriately tuned resonators, the bandwidth of a Bragg band gap can be reduced to zero, leading to a very narrow pass band with great wave attenuation performance near both band edges. The band formation mechanisms of such periodic waveguides are further examined, providing explicit formulae to locate the band edge frequencies of all the band gaps, as well as the conditions to achieve very narrow pass bands in such periodic waveguides. 相似文献
8.
Peng Wu Qianjin Mu Xiaoxiao Wu Li Wang Xin Li Yuqing Zhou Shuxia Wang Yingzhou Huang Weijia Wen 《Physics letters. A》2019,383(20):2361-2366
The remarkable properties of acoustic metamaterials have attracted massive researches and applications, especially on low-frequency sound absorptions. Currently, most of the acoustic metamaterial absorbers employ resonances in plastic cavities, and their structural strengths are important in many circumstances, especially in harsh environment. However, studies of metamaterials including this point are very scarce. Here, we propose an acoustic metamaterial for low-frequency (<500 Hz) absorptions, composed of three nested square split tubes with inverted opening directions. The efficiency of the absorber is investigated both numerically and experimentally, and absorptions at the peeks are found to exceed 90% and the frequency can be effectively adjusted by tuning its geometric parameters. We further test its yield strength under compression and confirm its buckling behavior happens from the outmost layer. This tunable acoustic metamaterial with a fairly good mechanical strength may lead to broad applications in noise reduction. 相似文献
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