麦-玉耕作秸秆混土还田模式下离散元参数标定

Calibration of discrete element parameters in wheat-corn farming straw mixed soil returning mode

麦-玉一年两熟的江淮、黄淮地区秸秆混土还田保护性耕作模式,麦秸秆-土壤混合的种床缺乏准确的物料相互接触参数,阻碍了机械化玉米精密播种过程中关键部件、种粒、肥料与混合种床相互作用研究,进而制约了机具优化与改进。采用物理与EDEM离散元方法结合研究非连续体麦秸秆-土壤混合物之间相互作用,选用Bonding V2黏结模型搭建柔性麦秸秆段“元颗粒”,选取Hertz-Mindlin with JKR模型对一定湿度的土壤进行参数标定。首先,以圆桶提升麦秸秆和土壤种床混合物堆积角为响应值,采用Plackett-Burman筛选试验和最陡爬坡试验分别对显著影响因素从大到小排序和缩近最佳取值范围。利用Box-Behnken试验构建了显著影响因素与堆积角二阶回归模型,对显著因素交互项进行响应曲面分析,利用Design-Expert软件优化模型并以实测堆积角39.94°为目标响应值,计算得土壤JKR表面能0.500、土壤-秸秆动摩擦系数0.065 8、土壤-秸秆JKR表面能0.262及土壤-土壤动摩擦系数0.155,仿真验证误差1.08%,表明标定的接触模型参数可靠。该研究可为麦-玉保护性耕作模型下混合种床与机具精密播种相互作用研究提供参考和理论依据。

In response to protective tillage model of straw mixed soil returning to the fields in the Jianghuai and Huanghuai regions,where wheat-corn are harvested twice a year,lack of accurate material contact parameters in wheat straw-soil mixed seedbed hinders research on interaction between key components,seeds,fertilizers,and mixed seedbeds in the precision sowing process of mechanized corn,thereby restricting optimization and improvement of machinery.A combination of physics and EDEM discrete element method was adopted to study interaction between non continuous wheat straw and soil mixture.Bonding V2 bonding model was used to build flexible wheat straw segments "elemental particles",and the Hertz-Mindlin with JKR model was selected to calibrate parameters of soil with certain humidity.Firstly,stacking angle of wheat straw and soil seedbed mixture was taken as response value by using a circular bucket to lift.Plackett-Burman screening test and steepest climbing test were used to sort and shorten optimal range of significant influencing factors from large to small,respectively.A second-order regression model for significant influencing factors and stacking angle was constructed using Box-Behnken experiments.Response surface analysis was performed on interaction terms of significant factors.Design-Expert software was used to optimize model and measured stacking angle was 39.94° as the target response value.Results showed that surface energy of soil JKR was 0.500,dynamic friction coefficient of soil-straw was 0.065 8,surface energy of soilstraw JKR was 0.262,and dynamic friction coefficient of soil-soil was 0.155,simulation validation error was 1.08%,indicating reliability of calibrated contact model parameters.This study could provide a reference and theoretical basis for study of interaction between mixed seedbeds and precision seeding equipment under wheat jade conservation tillage model.