颗粒系统堆积的休止角是颗粒学中一个基础性的科学问题,深入认识其影响因素和变化规律对于土木、化工等工程优化具有重要意义.目前基于实验测量的研究受限于可用的颗粒种类和测量手段,难以完备地揭示各种物理参数对休止角的影响规律.离散元(Discrete element method,DEM)是一种可直接对复杂的大型颗粒系统的运动进行仿真的数值方法.本文借助DEM方法对颗粒系统的休止角问题开展了高精度数值研究,揭示了影响颗粒堆积休止角的重要颗粒物性参数.在DEM建模方面,为了表征非球形度对仿真的影响,本研究采用了滚动摩擦系数,并利用既有的实验数据进行了模型验证.同时,本文利用堆积体在垂直平面内投影的二值化图像来合理计算休止角.仿真结果表明,滑动和滚动摩擦系数均与休止角的大小呈正相关,滑动摩擦系数的增加可将休止角提升一倍,而滚动摩擦系数对休止角的影响存在一个上限阈值,达到该阈值后将不能继续增加休止角的大小;颗粒的杨氏模量、回弹系数对休止角的影响不显著.此外,本文利用DEM方法研究了堆积体的传热特性,发现在加热过程中,堆积体内部具有最高热流率的区域从堆积体的底部迁移到上部.
Numerical Analysis of the Angle of Repose in Particle Systems Using the Discrete Element Method
The angle of repose in particle systems is a fundamental scientific problem in particle sci-ence.A deep understanding of its influencing factors and patterns of variation is of great significance for optimization in fields such as civil and chemical engineering.However,existing research based on experi-ments is limited by available types of particles and measurement methods,making it difficult to compre-hensively reveal the impact regulations of various physical parameters on the angle of repose.This paper conducts a high-precision numerical study on the angle of repose in particle systems using the discrete ele-ment method(DEM),uncovering the most important particle property parameters that affect the angle of repose.DEM is a numerical method that directly simulates the motion of complex particle systems.Specif-ically,this study adopts a rolling friction coefficient to characterize the influence of non-sphericity on the simulation and validates the established model with existing experimental data.In addition,binary images of the heap projection in the vertical plane are utilized to calculate the angle of repose reasonably.Simula-tion results show that both sliding and rolling friction coefficients are positively correlated with the angle of repose.Increasing the sliding friction coefficient can double the angle of repose,while increasing the angle of repose caused by the rolling friction coefficient will reach an upper threshold.Once reaching this value,the angle of repose cannot be further increased.The particle's Young's modulus and restitution coefficient have a relatively small impact on the angle of repose.At the same time,this study employs the DEM to in-vestigate the heat transfer characteristics of granular heaps.It is observed that during heating,the region with the highest heat flux within granular heaps migrates from the bottom to the top.These results reveal the most important factors affecting the angle of repose and can guide engineering optimization.
discrete element methodangle of reposecontrol variable methodgranular heaps
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