双剪类流动模型的非圆形颗粒离散元数值验证

Evaluation of double-shearing type kinematic models for granular flows by use of distinct element methods for non-circular particles

双滑移自由转动模型、双剪模型和双滑移转动率(DSR2)模型这3种双剪类模型均是基于运动理论的塑性模型,其关键区别在于转动率参量的选取。采用改进后的NS2D离散元程序,对长短轴比例分别为1.4和1.7的椭圆颗粒试样进行不排水单剪试验以验证上述双剪类模型中转动率参量选取的合理性。数值试验结果表明:①双滑移自由转动模型中的限定条件因未考虑能量消散过程中颗粒转动的影响而过于严格;②双剪模型中转动率参量为主应力方向变化率的假定与数值试验结果差距显著;③DSR2模型中采用平均纯转动率(APR)可很好地预测转动率参量的变化,且该模型可用于砂土非共轴微观机制的研究;④参量APR能考虑剪切过程中颗粒转动对能量耗散的影响,可将离散介质力学和连续介质力学有机结合起来,是运动模型中合理且重要的参量。

The double-sliding free-rotating model, double-shearing model and double-slip and rotation rate model （DSR^2 model） are three types of double-shearing kinematic models, which formulate the plastic flows of granular materials. These modelsincorporate different physical interpretations of angular velocity. A developed distinct element method program NS2D is used to generate assemblages which are composed of elliptical particles with aspect ratios of 1.4 and 1.7, respectively. Theassemblages are then subjected to undrained simple shear tests to validate the above-mentioned models. The results show that： （1） the postulation in the double-sliding free-rotating model seems to be unduly restrictive for not considering the effect ofparticle rotation on energy dissipation; （2） a quantitative and qualitative difference between the observed rotation rate of the major principal stress axes and the theoretic angular velocity does not support the double-shearing model; （3） the DSR^2 modelpresents a successful prediction of the angular velocity by means of the averaged micro-pure rotation rate （APR）, and it can be used to study the non-coaxiality of granular materials; and （4） the APR is a rational and important variable which considers theeffect of particle rotation in the energy dissipation process, and bridges discrete and continuum granular mechanics.