Recent work has used an introduced property, termed granular fluidity (defined as the shear rate divided by the stress ratio), to help quantify and model nonlocal behavior within granular flows. A so-called “microscopic” definition was subsequently proposed which links this granular fluidity to the packing fraction, particle diameter, and the granular temperature. This definition provides a physical basis on which the nature of granular fluidity can be understood. Here we have examined the microscopic definition, first replicating the previously demonstrated behavior using DEM simulations of shear cells and then demonstrating that the relationship's coefficients are dependent on the coefficient of friction, the presence of tangential damping, and the presence of rolling resistance. When the geometry is changed from a shear cell to a cylindrical hopper, the relationship shifts away from the expected response, thus demonstrating that there are geometry dependent effects that are not captured by the original formulation. This shows that granular fluidity is more complex than previously thought and that the current microscopic definition is insufficient.

中文翻译：

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检验颗粒流动性的微观定义

最近的工作使用了一种称为颗粒流动性（定义为剪切速率除以应力比）的引入属性，以帮助对颗粒流中的非局部行为进行量化和建模。随后提出了所谓的“微观”定义，该定义将这种颗粒流动性与填充率，粒径和颗粒温度联系起来。该定义提供了可以理解颗粒流动性本质的物理基础。在这里，我们检查了微观定义，首先使用剪切单元的DEM模拟来复制先前演示的行为，然后证明该关系的系数取决于摩擦系数，切向阻尼的存在和滚动阻力的存在。当几何形状从剪切单元更改为圆柱形料斗时，该关系会偏离预期的响应，从而表明原始配方无法捕获某些几何形状相关的影响。这表明颗粒流动性比以前认为的要复杂得多，并且当前的微观定义还不够。