Authors

Abstract

Due to the anisotropy and small size of wheat roots, as well as the neglect of shear process effects on mechanical properties in existing wheat root-soil composite (WRSC) models, the establishment and parameter calibration of WRSC models remain inaccurate, hindering the precise analysis of the microscopic effects of furrow openers on WRSC during no-till sowing. This study aimed to develop an accurate and reliable WRSC model based on the discrete element method (DEM) using rapid particle filling and the Hertz-Mindlin with bonding contact model. Plackett-Burman tests identified particle shear modulus, inter-particle bonding radius, and bonding stiffness as significant factors affecting the ultimate shear force of wheat roots. Steepest ascent tests narrowed the optimal parameter ranges, and Box-Behnken test results were used to establish a quadratic regression model, leading to the optimal parameter combination: particle shear modulus of 7.96 MPa, inter-particle bonding stiffness of 4.13 GN/m³, and bonding radius of 0.32 mm. Actual and simulated shear tests on WRSC were conducted, and key parameters between wheat roots and soil particles were calibrated via steepest ascent tests with the ultimate shear force on the cutter as the target value: static friction coefficient of 0.8, bonding stiffness of 11 MN/m³, and critical stress of 11 MPa. Validation showed a relative error of 7.35% between simulated and actual shear resistance, indicating that the proposed WRSC model and parameters can effectively simulate field operations such as furrowing and rotary tillage.

Abstract in Chinese

针对玉米免耕播种时前茬小麦根系与开沟器相互作用过程分析复杂，且小麦根系的各向异性和直径较小等特点，现有根土复合体模型忽略小麦根系对对剪切过程力学特性的影响导致标定参数不准确的问题，该研究基于离散元法采用颗粒快速填充和 Hertz-Mindlin with bonding 粘结模型建立了一种准确性和可靠性较高的小麦根-土复合体模型。基于Hertz-Mindlin bonding 粘结模型，采用颗粒快速填充的方法，构建小麦根系模型。通过 Plackett-Burrman 试验发现颗粒剪切模量和颗粒间粘结半径、粘结刚度对小麦根系极限剪力有显著影响。通过最陡爬坡试验确定显著性影响参数最优区间的基础上，根据 Box-Behnken 试验结果建立了根系极限剪力与显著性影响参数的二阶回归模型并对其进行优化，得到显著性参数的最佳组合为：颗粒剪切模量 7.96 MPa、颗粒间粘结刚度 4.13 GN/m3、粘结半径 0.32 mm。其次，采用最陡爬坡试验方法，标定了小麦根-土间的关键参数。以切刀受到的极限剪力为目标值，基于小麦根-土复合体进行实际剪切和仿真剪切试验结果，标定得到小麦根系与土壤颗粒间的静摩擦系数为 0.8、粘结刚度为 11 MN/m3、临界应力为 11 MPa。最后，验证标定后的根-土复合体模型，结果显示仿真剪切阻力与实际剪切阻力间相对误差为 7.35%，表明基于离散元法建立的小麦根-土复合体模型可以用于模拟田间实际土壤环境。