Department of Chemical and Process Engineering, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand.
ABQMR Incorporated, Albuquerque, NM, United States of America; Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge University West Site, Philippa Fawcett Dr, Cambridge CB3 0AS, United Kingdom.
J Magn Reson. 2019 Oct;307:106569. doi: 10.1016/j.jmr.2019.106569. Epub 2019 Aug 10.
Continuum dynamics of granular materials are known to be influenced by rotational, as well as translational, motion. Few experimental techniques exist that are sensitive to rotational motion. Here we demonstrate that MRI is sensitive to the rotation of granules and that we can quantify its effect on the MRI signal. In order to demonstrate the importance of rotational motion, we perform discrete element method (DEM) simulations of spherical particles inside a Couette shear cell. The variance of the velocity distribution was determined from DEM data using two approaches. (1) Direct averaging of the individual particle velocities. (2) Numerical simulation of the pulsed field gradient (PFG) MRI signal acquisition based on the DEM data. Rotational motion is found to be a significant effect, typically contributing up to 50% of the signal attenuation, thus amplifying the calculated velocity variance. A theoretical model was derived to relate an MRI signal to the angular velocity distribution. This model for the signal was compared to previously published experimental data as well as simulated MRI results and found to be consistent.
颗粒物质的连续体动力学已知会受到旋转和平移运动的影响。很少有实验技术对旋转运动敏感。在这里，我们证明 MRI 对颗粒的旋转敏感，并且我们可以定量地确定其对 MRI 信号的影响。为了证明旋转运动的重要性，我们在 Couette 剪切室中对球形颗粒进行了离散元法 (DEM) 模拟。使用两种方法从 DEM 数据确定速度分布的方差。(1) 直接平均单个颗粒的速度。(2) 根据 DEM 数据数值模拟脉冲场梯度 (PFG) MRI 信号采集。发现旋转运动是一个显著的影响，通常贡献高达信号衰减的 50%，从而放大了计算出的速度方差。推导出一个将 MRI 信号与角速度分布相关联的理论模型。将该信号模型与先前发表的实验数据以及模拟的 MRI 结果进行了比较，发现它们是一致的。
