基于离散元法的马铃薯挖掘铲工作阻力仿真与试验研究

发布时间：2019-01-23 16:02

【摘要】：挖掘部件作为马铃薯收获机的核心部件之一,是与马铃薯块茎根系及土壤直接作用的部件,其性能好坏直接影响整机性能。目前,挖掘铲与土壤之间的作用研究只局限于有限元静力学分析及基于连续体理论的动力学分析,但实际上受块茎和根系的影响,块茎、根系周边的土壤离散度相对较大,挖掘过程中土壤颗粒离散度更大。离散元法作为研究非连续介质问题的一种通用方法,更适合研究块茎类收获土壤力学问题。本论文依托国家自然科学基金项目"土壤-马铃薯块茎-根系团聚体动态破裂特性及其与挖掘铲耦合作用机理研究(51505305)",采用田间试验与离散元法仿真模拟相结合的方法,对比研究马铃薯挖掘铲工作过程及受力情况,一方面验证离散元模型的可行性,另一方面为后续挖掘部件的优化设计奠定基础。同时也能为其他块茎类作物的收获土壤动力学分析提供借鉴。主要研究内容为:(1)土壤离散特性的试验验证及参数测定。①在朝阳市建平县种植马铃薯试验田3亩,从结块茎到收获期每隔10天测试一次土壤坚实度,分析块茎膨大对土壤离散程度的影响。②通过试验测定收获期内马铃薯块茎周边土壤的基本物理特性参数,包括土壤质地、含水率、密度以及坚实度,为离散元仿真模型建立提供数据依据。(2)马铃薯挖掘铲工作过程及受力情况离散元仿真模拟。①建立与实际工况相对应的挖掘铲—土壤离散元模型,主要包括接触模型的选择(Hertz-Mindlin粘结接触模型)、马铃薯挖掘铲三维模型的建立(利用SolidWorks软件建立)、土壤颗粒工厂的生成(参数选择通过实验测定及后期反复调试确定)以及仿真边界的建立等。②利用离散元软件EDEM对建立的模型进行挖掘铲运动过程及受力情况的仿真模拟,得出挖掘铲工作过程中的受力情况。(3)田间试验。①田间试验测试系统的搭建,包括测试系统的整体设计与连接以及测力框架、拉力传感器以及角度传感器的选择与标定。②单因素田间试验,保证其他作业参数不变,只改变作业速度大小,得出马铃薯挖掘铲工作阻力的变化情况,分析作业速度对马铃薯收获机工作阻力的影响规律。(4)试验结果与仿真结果对比分析。仿真试验马铃薯挖掘铲所受水平合力与垂直合力随速度增加的变化趋势与田间试验变化趋势基本一致:马铃薯挖掘铲的水平阻力随着速度的增加而增大,在0.25m/s时最小;垂直阻力随着速度的增加先减小后增大,在工作速度为0.38m/s时最小,水平阻力始终大于垂直阻力。研究结果表明采用离散元法进行马铃薯挖掘铲工作阻力仿真模拟是可行的。
[Abstract]:As one of the core parts of potato harvester, excavating part is the component directly acting on potato tuber root system and soil, and its performance directly affects the performance of the whole machine. At present, the research on the interaction between excavating shovel and soil is limited to finite element statics analysis and dynamics analysis based on continuum theory, but in fact, the soil dispersion of tuber and root is relatively large, because of the influence of tuber and root system. The dispersion of soil particles is larger during excavation. As a general method for studying discontinuous media, the discrete element method is more suitable for studying the mechanics of tuber harvesting soil. In this paper, based on the project of National Natural Science Foundation, "dynamic rupture characteristics of soil-potato tuber root aggregates and their coupling mechanism with excavating shovel (51505305)", the field experiment and discrete element method were used to simulate the dynamic rupture characteristics of soil-potato tuber root aggregates. The working process and stress of potato excavating shovel are compared to verify the feasibility of discrete element model on the one hand and lay the foundation for optimization design of subsequent excavated parts on the other hand. At the same time, it can also provide reference for soil dynamics analysis of other tuber crops. The main contents of the study are as follows: (1) Experimental verification of soil dispersion and determination of soil parameters. 1 soil solidity was tested every 10 days from tuber formation to harvest period in potato experimental field in Jianping County, Chaoyang City. The effects of tuber enlargement on soil dispersion were analyzed. 2 basic physical parameters of soil around potato tuber during harvest period were determined, including soil texture, moisture content, density and firmness. It provides data basis for establishing discrete element simulation model. (2) discrete element simulation of potato excavating shovel working process and force. 1 the excavating shovel-soil discrete element model corresponding to actual working condition is established. It mainly includes the selection of contact model (Hertz-Mindlin bond contact model), the establishment of three-dimensional model of potato digging shovel (using SolidWorks software), The generation of soil particle factory (parameter selection is determined by experiment and repeated debugging in the later period) and the establishment of simulation boundary etc. 2 the simulation of the excavating shovel motion process and force condition is carried out by using the discrete element software EDEM. (3) Field experiment. 1 the construction of field test system, including the whole design and connection of test system and the frame of force measurement. The selection and calibration of pull force sensor and angle sensor. 2 single factor field experiment to ensure that the other operation parameters remain unchanged, only change the working speed, and get the change of the resistance of potato digging shovel. The effect of working speed on working resistance of potato harvester was analyzed. (4) the results of test and simulation were compared and analyzed. The variation trend of horizontal force and vertical force along with the speed of potato excavating shovel was basically the same as that of field experiment: the horizontal resistance of potato excavating shovel increased with the increase of speed, and the minimum at 0.25m/s; The vertical resistance decreases first and then increases with the increase of velocity, and the horizontal resistance is always greater than the vertical resistance when the working speed is 0.38m/s. The results show that it is feasible to simulate the resistance of potato excavating shovel by discrete element method.
【学位授予单位】：沈阳农业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S225.71

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