基于离散元法的旋耕过程土壤运动行为分析

土壤与耕作部件间的相互作用规律是设计和选用土壤耕作部件的基础。研究土壤和耕作部件间的相互作用规律就是要研究耕作部件对土壤产生的作用和它们之间的作用力,首先必须探讨耕作部件工作时土壤运动规律和施加于土壤的作用力。为此本文建立基于离散元方法的旋耕工作模型;对比分析实验与仿真的土壤位移:在土槽实验中采用示踪块方法测量土壤位移,仿真中通过追踪表层土壤颗粒的运动获得仿真位移;利用实验和仿真数据对土壤位移和运动机理进行分析。结果表明:土壤水平和侧向位移都随着转速增加呈现增加的趋势;土壤的水平运动位移总是大于同转速下的侧向位移。浅层土壤颗粒的运动位移最大,中层土壤次之,深层土壤最小。较深位置的土壤,距离旋转中心越近的土壤颗粒水平位移和侧向位移越大。在旋耕刀切土范围内的土壤,有向相反方向运动趋势的浅、中、深层颗粒比例分别为26.2%、72.1%、48.4%。在水平力作用下,大部分土壤颗粒随着旋耕刀切土有向后运动的行为;土壤在开始时刻的侧向受力和侧向运动方向,由颗粒的侧向位置是否偏离侧切刃轴线决定,位于侧切刃轴线左侧的颗粒,则其侧向力向左,反之亦然;土壤在垂直方向先随着刀具入土向下运动,然后滑出刀刃边界被抛起。本文建立的仿真模型得到的土壤水平位移和侧向位移与相应实验值的误差为24.9%和15.3%。本文运用离散元法进行旋耕过程中土壤宏观和细观运动行为的分析,有助于理解旋耕刀与土壤的相互作用机理,为旋耕机械的设计与优化提供理论依据。

Analysis of Soil Dynamic Behavior during Rotary Tillage Based on Distinct Element Method

The interaction of soil tillage tool plays a pivotal role in analysis and optimization of the tillage process. The dynamic behavior of soil needs to be developed primarily when studying the soil tillage tool interaction. The simulation of soil rotary blade interaction using distinct element method (DEM) and indoor soil bin experiment were conducted to provide a better understanding of the soil movement. Firstly, DEM model of soil rotary blade interaction was established. Secondly, comparison of experimental results and simulation results were done, positions before and after tillage of surface soil particle were used as soil displacement in simulation, and tracer method was employed to measure soil displacement in experiment. Then, the movement of soil which belongs to different positions was analyzed. The results showed that soil forward and side displacement in experiment increased with increasing rotational speed of blade, the forward displacement was larger than the side displacement. The displacement of shallow soil was the largest, and then middle soil and deep soil had the minimum displacement. The closer the soil to the rotational point was, the larger the forward and side displacement of soil were. For the particles in tillage scope, the percent of particles which moved to the opposite direction were 26.2%, 72.1% and 48.4% for shallow soil, middle soil and deep soil, respectively. Most soil particles moved backward in horizontal direction during tillage process. The direction of side force and side displacement depended on the situation that the soil particle lay in the left or right side of the lengthwise edge axis. If the soil lay in the left side of the lengthwise edge axis, the side displacement was towards the left and vice versa. The soil particle moved downward with the rotary blade at the beginning of soil cutting, and later it slipped from the border of blade and being tossed up. The average error of soil displacement between simulation results and experimental results was 24.9% for soil forward displacement while 15.3% for soil side displacement. The paper studied the macro and meso movement of soil particles during rotary tillage, which is helpful to understand the interaction between rotary blade and soil and develop the mechanism of rotavator design and optimization.