基于离散元法的深松作业玉米秸秆运动规律

东北垄作区玉米秸秆还田条件下，针对垄台播种带秸秆残茬易导致深松铲以及后续机具缠草堵塞和阻力增加等问题，建立深松铲-土壤-秸秆-根茬的离散元模型，分析仿真因素秸秆距垄台中心距离、秸秆与机具前进方向夹角、根茬状态（根茬中间切割、根茬一侧切割、根茬挑起和无根茬）和秸秆之间相互影响对深松作业过程中秸秆拨离垄台的影响。进一步探究深松铲作用下垄上秸秆运动规律并分析其扰动比阻（秸秆扰动力矩与深松铲阻力之比）。仿真结果表明：秸秆距垄台中心距离对秸秆位移中的水平侧向运动的影响最大；秸秆水平侧向位移随着秸秆与机具前进方向夹角增大呈减小趋势；根茬状态影响秸秆位移的主次顺序依次为：根茬挑起、根茬一侧切割、无根茬、根茬中间切割；当秸秆距垄台中心距离为60 mm时，秸秆之间相互影响对秸秆位移中的前进方向运动的影响最大；当秸秆距垄台中心距离大于60 mm，秸秆前进方向位移呈增大趋势。秸秆运动的力矩变化趋势为平稳变化，后产生峰值，最后又趋于平稳；影响秸秆力矩的主次顺序依次为：根茬状态、秸秆之间相互影响、秸秆距垄台中心距离、秸秆与机具前进方向夹角。深松过程中，秸秆扰动比阻在切割根茬一侧时达到最大值0.152 mm。田间对比试验结果表明，仿真模型得到的秸秆总位移、水平侧向、前进方向和垂直方向位移与田间试验值的误差分别为0.36%～9.67%、0.16%～12.31%、0.56%～10.11%和0.43%～4.63%，秸秆力矩的误差为0.16%～11.06%。研究结果可为深松铲设计以及优化提供一定的理论依据。

Maize straw motion law in subsoiling operation using discrete element method

Abstract: Sowing stubbles with straw in ridges have seriously caused the entanglement, blockage, and resistance to the subsoiler and subsequent machine tool when returning corn straws to the field in the northeast areas of China. The purpose of this study was to establish a discrete element model of subsoiler-soil-straw-stubble for the motion behavior of straw during subsoiling operation, thereby exploring the movement and mechanical characteristics of straw under different conditions. The soil bin was also built as a common ridge in Northeast China. Among them, the straw was assumed as a rigid body, whereas, the breakable adhesive stubble was an unbreakable rigid body. The simulation and test data were then selected to investigate the motion mechanism of straws. Specifically, the tracking movement of straw was obtained as the simulation data. A high-speed camera was also utilized to record the movement data of straw in the field test. As such, the large variation in the movement of straw was better simulated during subsoiling operation, particularly in the complex field environment. Four influencing factors were achieved to represent the straw plucking away from the ridge in the operation of subsoiling, including the distance between the straw and the center of the ridge, the angle between straw and machine, the state of stubble (cutting in the middle of stubble, cutting on one side of stubble, picking up of stubble and no stubble), and the interaction between straws. Correspondingly, the displacement and torque of straws on ridges were obtained to determine the disturbance-specific resistance (the ratio of straw disturbance moment to subsoiler resistance) under the action of the subsoiler. The simulation results show that the distance between the straw and the center of the ridge presented the greatest influence on the horizontal and lateral movement of straws, where the horizontal-lateral displacement of straw decreased with the increase of the angle between the straw and machine. More importantly, there was the largest displacement in the forward direction of straw, when the angle of straw was 45°. The primary and secondary order of stubble state affecting straw displacement was as follows: stubble pick up > stubble side cutting > no stubble > stubble middle cutting. Especially, there was the greatest influence of the interaction between the straws on the forward direction of straws, when the distance between the straw and the center of the ridge was 60 mm. Once more than 60 mm, the displacement tended to increase in the forward direction of straws. In addition, the torque of straws was calculated to explore the rotation of straw in simulation tests. It was found that the overall trend was as follows: the peak value was generated after the stable operation, and then tended to be stable. Anyway, there was a great influence of stubble on the torque of straw. The errors of the total displacement, horizontal-lateral displacement and forward displacement obtained by the simulation model with the test values were 0.36% -9.67%, 0.16% -12.31%, and 0.56% -10.11%, respectively. The error of straw torque was also 0.16% to 11.06%. The error between the test and simulation value was within the allowable range, indicating a similar changing trend. Consequently, the test verified the rationality and feasibility of discrete element simulation. The finding can greatly contribute to understanding the mechanism of straw during subsoiling, particularly to the reasonable design of subsoil machinery in modern agriculture.