离散元模拟中沙土参数标定方法研究

农业机械与土壤相互作用仿真时,选用颗粒相互作用参数的准确度将直接影响仿真结果。本文提出一种通过试验与模拟相结合系统地标定沙土颗粒相互作用参数的方法。通过堆积角测试装置、三轴剪切试验仪、图像颗粒分析系统等设备测量计算沙土的堆积角、剪切模量、粒径分布和外观形貌等参数,为颗粒或工厂建模提供参考。使用标准球和非标准球对沙土颗粒的碰撞恢复因数、静摩擦因数、滚动摩擦因数进行标定。研究不同质量和不同标定方法(抽板法和漏斗法)是否对堆积角产生影响。模拟结果表明,选用标准球标定时,碰撞恢复因数是0.15,静摩擦因数是0.8,滚动摩擦因数是0.2,抽板法得到的堆积角是33.99°,相对误差是4.74%;漏斗法得到的堆积角是33.59°,相对误差是3.51%。同时,选用非标准球进行标定时,碰撞恢复因数是0.15,静摩擦因数是0.2,滚动摩擦因数是0.3,抽板法得到的堆积角是32.06°,相对误差是1.20%。由此看出,颗粒外观形貌对颗粒间静摩擦因数影响相对较大。

Calibration Methods of Sandy Soil Parameters in Simulation of Discrete Element Method

When the interaction between agricultural machinery and soil is simulated, the accuracy of the chosen particle parameters will directly have an effect on the simulation results. A systematic method for calibrating the interaction parameters of sand particles was proposed based on the combination of experiment and simulation. By the repose angle test apparatus, the triaxial shearing test instrument and the particle image analysis system equipment, the repose angle of the sandy soil, the shear modulus, the particle size distributions and morphology were obtained, which provided reference for particles or factory modeling. The standard ball and non-standard ball were used to calibrate the coefficient of restitution, coefficient of static friction and coefficient of dynamic friction between particles. The effect of different qualities and different calibration methods (drawing plate method and funnel method) on the repose angle were studied. The effect of different qualities of the soil on repose angle was small, and it can be ignored. Meanwhile, there was no significant difference between the two calibration methods. When the standard ball was used for calibration, the repose angle obtained from the simulation was closest to that of the test (coefficient of restitution was 0.15. coefficient of static friction was 0.8, and coefficient of dynamic friction was 0.2). The repose angle of drawing plate method was 33.99°, and the relative error was 4.74%. The repose angle of the funnel method was 33.59°, and the relative error was 3.51%. When the non-standard ball was used for calibration, the repose angle of the drawing plate method was 32.06°, and the relative error was 1.20% (coefficient of restitution was 0.15, coefficient of static friction was 0.2, and coefficient of dynamic friction was 0.3.). It can be seen that the effect of particle appearance on the coefficient of static friction was relatively large. The result provides a new idea and method for the calibration of particle parameters.