密集颗粒流绕变速物体的流变动力学模型

The significance of rheological dynamics of dense granular flow around an object is comparable with the classic "flow around a circular cylinder" problem in fluid physics. However, the contact mechanism and scale correlation between particles are endowed with high nonlinearity and strong dissipation, making the rheological characteristics of dense granular medium difficult to describe. Therefore, solving the rheological dynamics of dense granular flowing around objects is conductive to understand the mechanical properties and guide the establishment of the constitutive relation of dense granular medium. Based on the local and non-local feature, this project is to establish rheology dynamics model for dense granular flow around objects with variable speed. This project focuses on the unified characterization of the dynamic characteristics of dense particle flow around a project under different inertia numbers. Meanwhile, the resistance applied on the object is calculated by the proposed method. Then, a resistance model for the objects is to be developed by considering the influence of relative velocity, objects' dimension, shape and the embedded depth etc. Finally, the theory models will be validated and improved through experimental study.The implementation of this project will provide a basis for the unification of dense granular flow constitutive relations, as well as a new way and a new perspective for solving major engineering problems related to granular media.

密集颗粒流绕物体运动的流变动力学研究在颗粒介质力学的地位就如流体物理中经典的“圆柱绕流”问题，由于颗粒介质本身的高非线性和强耗散的接触机制及内在尺度关联，使得密集颗粒介质的流变特征难以描述，而“绕流问题”的解决能够深入了解介质本身的力学特性并指导密集颗粒介质本构关系的建立。因此，本项目基于颗粒流的非局部特征和体积分数对密集颗粒流本构关系影响的考虑，建立密集颗粒流绕变速物体运动的流变动力学模型，着重研究不同惯性数下密集颗粒流绕物体运动时动力特性的统一表征。同时，提出物体在密集颗粒流中运动所受阻力的统计方法。然后考虑物体与颗粒流相对速度、物体的大小、形态及放置深度等对阻力的影响，建立物体在颗粒流中的阻力模型。最后，完成密集颗粒流绕物体运动的实验平台搭建及测量，对理论模型进行验证。该项目的开展为密集颗粒流本构关系的统一提供基础，为解决重大工程问题提供新途径和新视角。

密集颗粒介质发生流变后的流动与经典流体的异同性是深入理解颗粒介质特性的关键问题。本项目基于实验、数值仿真和理论的方法，以密集颗粒流绕柱体以及物体冲击颗粒介质为构型，考虑了颗粒流的局部和非局部特征，研究不同惯性数下密集颗粒流绕物体运动时动力特性的表征。然后考虑物体与颗粒流相对速度、物体的大小、形态及放置深度等对阻力的影响，建立物体在颗粒流中的阻力模型。同时，通过开展杨氏模量在3个量级（100Pa~10000Pa）上变化的弹性球冲击颗粒介质的实验研究，揭示出冲击坑直径的幂律在上述两种情形之间连续变化的特征，表明刚球和液滴冲击所获得的冲击坑尺度关系是弹性球模量变化结果的上下限。理论上建立了冲击物与颗粒之间的能量分配机制，对星球表面冲击坑形态及尺度关系的形成机理给出物理解释，并为物体与颗粒介质相互作用后的变形建立归一化标度率。