基于离散元法的沙土与螺旋式挖坑机钻头作用机理研究

Soil dynamics is always one of the most popular problems. Because of the complicated non-linear constitutive model of soil, the investigation on this topic is slow. Discrete element method is good at simulating the dynamic behaviour of dis-continuum, and glued-particle-agglomerate can simulate the soil physical constitutive model adding the adhesive force between particles. In this study, the process of digging a hole in sandy soil with an earth auger will be simulated with DEM. Firstly, the soil direct shear tests and the simulations with DEM will be carried out, for calibrating the model parameters of DEM and establishing the mathematical relationships between the sandy soil and its DEM model. Secondly, the hole-digging experiments and 3D DEM simulations will be investigated, taking a real auger drill as one of the typical soil-cutting tools. By means of the comprehensive analysis of the results of the experiments and DEM simulations, it will be studied that the mechanism of sandy soil dynamic action on the drill and the influence to the wear and vibration of the drill. This study will provide a new numerical method for simulating the soil dynamics, and the conclusions will give some theoretical advice to the optimal design of auger drills and energy saving and emission reduction.

土壤动力学问题一直是学术界研究的热点问题之一，因其复杂的物理本构非线性而使得许多与此相关的实验与数值研究进展缓慢。离散元法可以解决松散介质的动态问题，可通过粘连力将颗粒单元粘结为固化颗粒群来仿真土壤的本构。本项目将离散元法应用于沙地挖坑问题的研究中，首先通过土力学直剪试验与离散元三维模拟的对比性分析，标定离散元模型参数，将沙土宏观物性参数与颗粒微观参数建立数学联系；然后将挖坑机钻头作为一种典型的土壤作业机械，通过挖坑试验与DEM三维数值模拟，综合分析土壤在螺旋式钻头的作用下的动力学行为，及其与钻头磨损和振动问题之间的关系。本项目不仅可为土壤动力学的数值研究提供一种新的思路和数值方法，具有方法和理论的创新性，而且，还可以为挖坑机的优化设计和节能减排提供理论依据。

该项目利用直剪试验初步分析了沙土的宏观参数与离散元模型微观颗粒参数间的标定关系；将螺旋式钻头挖坑和螺旋输送机作为两个典型例子来分析颗粒介质与螺旋叶片相互作用的运动特征及与主要影响因素的关系。通过对螺旋输送机输送颗粒物料的实验及离散元模拟对比研究，初步分析了输送角度、转速和颗粒尺寸等对输送效率的影响规律；而对挖坑实验的研究，得到了扭矩阻力和铅垂阻力与土壤物性、钻头转速和直线进给速度等参数之间的关系。本课题还研究了颗粒料床受大颗粒冲击的动态行为，初步学习的非球形颗粒的离散单元算法会对今后的科研工作提供新思路。