水稻秸秆离散元柔性模型参数标定与试验验证

Calibration and Verification of Flexible Rice Straw Model by Discrete Element Method

摘要:

针对秸秆还田机具关键部件设计优化过程中秸秆-刀具互作关系分析缺乏准确秸秆离散元模型的问题，本文以水稻秸秆为研究对象，基于Hertz-Mindlin with Bonding接触模型，采用颗粒替换方式构建水稻秸秆离散元柔性模型，开展了离散元接触模型参数标定与多工况试验验证。通过物理试验测定了水稻秸秆摩擦因数，以秸秆弯曲试验测得最大载荷作为参数标定试验指标，通过Plackett-Burman试验和最陡爬坡试验筛选柔性模型显著性因素及其最优值范围，并由Central-Composite试验确定了显著性因素的最优值组合为：法向接触刚度3.040×1010 N/m3、切向接触刚度2.296×1010 N/m3，该标定参数值所得最大载荷仿真值与实测值相对误差为1.82%，表明标定参数有效。通过刀具弯曲试验和旋耕刀旋转切割试验验证上述标定方法在不同工况下的有效性，刀具弯曲试验中仿真所得最大载荷与实测最大载荷相对误差不大于4.55%，旋耕刀旋转切割试验中仿真所得最大扭矩与实测最大扭矩相对误差不大于7.95%，研究结果表明，以弯曲试验参数标定法构建的水稻秸秆柔性模型在秸秆弯曲试验和旋耕刀旋转切割过程仿真中均准确有效，适用于旋耕作业条件下仿真分析，可为秸秆还田机具旋耕部件优化设计提供参考。

Abstract:

Rice straw in the fields of the middle and lower reaches of the Yangtze River exhibits high stubble retention and a substantial straw volume. The interaction between straw and tools are complicated and have a significant impact on the performance of straw incorporation implement. The lack of accurate rice straw model by discrete element method (DEM) limits the analysis of the interaction between straw and tools during the design and optimization of key components of straw incorporation implement. A flexible rice straw model was established by the particle replacement method based on the Hertz-Mindlin with Bonding contact model in DEM. Calibration of the discrete element model and multi-condition experimental verification were conducted. The friction coefficients of rice straw were determined through physical experiments, and the maximum load was measured in the straw bending test as the calibration index. The Plackett-Burman experiment and the steepest ascent experiment were used to select significant factors and their optimal value ranges for the flexible model, and the optimal parameter combinations for significant factors of the straw bonding model were determined by Central-Composite tests. The result was the normal contact stiffness was 3.040×1010 N/m3, and the tangential contact stiffness was 2.296×1010 N/m3. The relative error between the maximum load obtained from the simulation with the calibrated parameters and the actual maximum load with the experiment was 1.82%. It indicated the effectiveness of the calibration method. To verify the effectiveness of the above calibration method under different working conditions, the bending test of blades and the rotating cutting test of the rotary blade were conducted. The relative error between the maximum load obtained with the simulation and experiment in the bending test of blades was not more than 4.55%, while the relative error of the maximum torque between the simulation and experiment in the rotating cutting test of the rotary blade was not more than 7.95%. It indicated that the flexible rice straw model by DEM calibrated using the bending test was accurate and effective in simulating straw bending test and rotating cutting of the rotary blade processes and applicable to simulation analysis under the rotary tillage operating conditions. The research provided an effective model and method to analysis of the interaction between straw and tools for the optimization design of key components of straw incorporation implement.