Yang H, Li R, Kong P, Sun Q C, Biggs M J, Zivkovic V
School of Optical-Electrical and Computer Engineering, Shanghai Key Lab of Modern Optical System, and Engineering Research Center of Optical Instrument and System, Ministry of Education, University of Shanghai for Science and Technology, Shanghai 200093, China.
School of Chemical Engineering, The University of Adelaide, SA, 5005, Australia.
Phys Rev E Stat Nonlin Soft Matter Phys. 2015 Apr;91(4):042206. doi: 10.1103/PhysRevE.91.042206. Epub 2015 Apr 30.
We used speckle visibility spectroscopy to measure the time-resolved dynamcis of avalanching down the inclined surface of a granular material in a half-full rotating drum operating in the slumping regime. The distribution of the avalanche period, t(d), rest time between them, t(r), and peak particle velocity fluctuation, δv(p)(2), are all normally distributed. While the distributions of the two times at the top and bottom of the free surface are very similar, the particle velocity fluctuation is greater at the bottom of the free surface than at the top. The rest time is observed to be inversely related to the drum speed. Combining this with the relation of t(r) and the difference of the upper and lower angle of repose for the granular material, Δθ, we find that the latter decreases linearly with increasing rotational speed. We also observe that t(d) increases in a linear fashion with the drum speed. Using the relation of t(r) and the distance that particles have to move during an avalanche, we further find that a new scaling relation of the mean number of avalanches required to traverse the free surface with drum speed. We find that the slumping frequency increases with the rotating speed before becoming constant in the slumping-to-rolling transition region. Finally, we find that the average peak of the fluctuation speed of the avalanche, δv(p)(2), increases linearly with the drum speed.
我们使用散斑可见度光谱法来测量在处于坍塌状态的半满旋转鼓中，颗粒材料沿倾斜表面崩塌的时间分辨动力学。雪崩周期t(d)、雪崩之间的静止时间t(r)以及峰值颗粒速度波动δv(p)(2)的分布均呈正态分布。虽然自由表面顶部和底部这两个时间的分布非常相似，但自由表面底部的颗粒速度波动比顶部更大。观察到静止时间与鼓速成反比。将此与t(r)以及颗粒材料上下休止角之差Δθ的关系相结合，我们发现后者随转速增加呈线性下降。我们还观察到t(d)随鼓速呈线性增加。利用t(r)与颗粒在一次雪崩期间必须移动的距离之间的关系，我们进一步发现了穿越自由表面所需的平均雪崩次数与鼓速之间的新标度关系。我们发现，在从坍塌到滚动的过渡区域，坍塌频率在变得恒定之前随转速增加。最后，我们发现雪崩波动速度的平均峰值δv(p)(2)随鼓速呈线性增加。
