【作者】 张智泓；

【导师】 佟金； 陈东辉；

【作者基本信息】 吉林大学 ， 农业机械化工程， 2014， 博士

【摘要】 通过改变田间微观地貌以实现集雨目的的整地方式称为土壤表面微形貌加工，该整地方式可增加表层土壤的蓄水能力、有效的控制地表径流和土壤流失。在众多实现土壤表面微形貌加工作业的机具中，凸齿镇压器由于在加工地表微坑的同时能对微坑周边土壤起到压实的效果，提高了土壤表面微形貌加工的作业质量，所以被广泛使用。凸齿镇压器作为一种新型的特殊整地机具，在研究该机具与土壤相互作用的过程中，难以直接借鉴现有滚动触土部件与土壤相互作用的研究经验。本研究工作首先从基础理论推导入手，建立了凸齿镇压器工作的运动学及动力学模型；其次将有限元方法与土槽试验相结合，建立了凸齿镇压器与土壤相互作用的三维动态有限元模型，分析了凸齿镇压器与土壤相互作用的机理，并搭建了基于室内土槽的凸齿镇压器牵引试验平台，通过土槽试验对有限元分析结果的有效性进行验证，在验证了有限元模型准确性的基础上，利用有限元方法继续探索不同作业参数对凸齿镇压器作业效果的影响。根据所参加的国家自然科学基金项目(编号：51075185)，针对提高凸齿镇压器的作业效率的需要，为降低凸齿镇压器作业过程中所需的牵引力和提高土壤表面微形貌加工的作业质量，本研究工作将几何结构仿生的技术方法应用于凸齿镇压器的设计。通过向自然界中具有高效掘土能力的不同土壤洞穴动物学习，借鉴其挖掘肢体的几何结构特征，将其提取并抽象为不同的锯齿状结构，用于对凸齿的几何结构进行优化，加工出具有仿生几何结构特征的凸齿镇压器，最后通过土槽牵引试验评价凸齿镇压器的作业效率和质量。自然界中存在一些体型较小且具有较强掘土能力的土壤洞穴动物，其用于土壤挖掘的肢体的几何特征尺寸微小且属于介观尺度(0.1mm-1mm)，在工程仿生领域传统方法难以对其进行量化分析。本研究工作以几何特征为介观尺度的臭蜣螂前足胫节端齿为例，提出了一种量化分析方法，使用计算机视觉技术代替人的视觉鉴别过程，识别了蜣螂前足胫节端齿外缘轮廓二维点云，并量化分析了其几何结构特征，为微小动物肢体的量化分析提供了技术基础。凸齿镇压器为非圆工作轮，在土壤表面滚动的过程中对土壤产生冲击作用，本研究工作采用基础理论推导的方法建立了凸齿镇压器作业过程中的运动学和动力学模型。根据运动学中刚体做平面运动的瞬心定理和牵连运动为平动时质点的加速度合成定理，推导出了凸齿镇压器在不同工作阶段的运动参数计算公式；根据动力学中的动量定理、动能定理和冲量定理，推导出了凸齿镇压器工作状态中所需牵引力、凸齿与地面作用瞬间产生的冲击力和冲击能的计算公式。通过本研究工作，可揭示凸齿镇压器结构参数与运动、动力参数间的相互联系，分析凸齿镇压器作业时冲击土壤的运动规律和特征。使用有限元软件Abaqus建立了凸齿镇压器与土壤相互作用的三维动态模型。为了解决模型运行过程中在土体内部产生的单元畸变而导致模型无法运行的问题，将ALE自适应网格划分方法应用于土体模型运行中的实时网格划分，有效避免了网格单元严重扭曲的情况发生。在模型能顺利运行的基础上，考察了土体模型边界距离、网格密度对有限元分析结果的影响。分析结果表明，只要将网格密度增大到一定程度，有限元分析的结果将趋于稳定并且不依赖于网格尺寸的变化。为了描述凸齿镇压器的运动方式，求解了凸齿镇压器轮缘上一点的旋轮线，结果表明，凸齿镇压器的旋轮线并非光滑曲线，而是呈波动状态，并在接地位置与前进距离方向有一定相反的相对滑动。分析了凸齿镇压器和土壤相互作用的过程中下方土壤的流动变形格式，分析结果表明，在平行于速度方向的纵截面和垂直于速度方向的横截面，凸齿镇压器下方的土壤内部均出现了两个流动方向相反的变形区。所建立的有限元模型为进一步探索不同作业参数对凸齿镇压器作业效果的影响提供了方法基础。为了在室内土槽完成凸齿镇压器的牵引试验，搭建了牵引力测试及数据采集平台，选取牵引力作为有限元预测结果的验证参数，将利用有限元方法所分析出的结果与土槽试验所记录的结果相比较，得出二者牵引力曲线随时间变化的规律基本一致，并且牵引力平均值的相对误差为3.40%，说明有限元求解的结果满足了反映凸齿镇压器实际工作过程中动态特性的要求，同时到了所需要的精度。将有限元方法输出的微坑形貌与土槽实际试验所获得的微坑形貌对比，微坑形貌特征能较好吻合，说明有限元模型能准确反映土壤流动变形特征。在验证了有限元模型有效性和准确性的基础上，利用有限元方法分析不同作业参数对凸齿镇压器作业效果的影响。发现当速度增加到一定程度，凸齿镇压器作业过程中出现了滑移现象，随后计算了凸齿镇压器在不同作业速度下的实时滑移率和总滑移率，结果表明，随着凸齿镇压器作业速度的提高，实时滑移率和总滑移率都明显增加。该项研究工作所得到的结论可以为恰当选择凸齿镇压器的作业参数提供参考。考虑到UHMWPE具有诸多优异性能而逐渐广泛应用于农机具触土部件的制造，为了探索采用UHMWPE材质的凸齿镇压器提高作业效果的潜在优势，使用模态分析的方法对传统铸铁材料和UHMWPE—铸铁组合材料凸齿镇压器前8阶模态的分析，并比较不同模态阶数下最大振幅、固有频率和不同位置点的振幅；设置不同的摩擦因数，分析采用不同材质凸齿镇压器的作业效果。结果表明UHMPWE—铸铁组合材料凸齿镇压器具有更优异的潜在脱土性能，所加工的土壤表面微形貌可具有更高的强度，被牵引时有更好的稳定性。在凸齿镇压器的触土部位使用UHMPWE，只需要较小的载荷就能达到所需的作业深度，另外作业过程中所需牵引力更小。为凸齿镇压器材质的选择提供了设计参考依据。使用几何结构仿生的技术方法对凸齿镇压器进行优化，通过土槽牵引试验评价优化的效果。综合学习了不同土壤洞穴动物挖掘肢体的几何结构特征，将这些几何结构特征提取并简化为不同尺度的仿生锯齿状结构，以应用于仿生凸齿的设计。加工制造出3种不同仿生凸齿镇压器，并在室内土槽完成凸齿镇压器的牵引试验，将仿生凸齿镇压器的试验结果与普通凸齿镇压器相比较，评价不同凸齿镇压器在不同载荷下的作业效率和质量。将不同凸齿镇压器作业过程中的所需牵引力、所加工微坑的深度和所加工微坑的蓄水容积作为考察指标，试验结果表明，仿生凸齿作业过程中所需牵引力比普通凸齿最多可减小6.52%，所加工微坑的深度比普通凸齿最多可增加13.25%，所加工微坑的蓄水容积比普通凸齿最多可增加37.59%。仿生凸齿在作业时充分发挥了类似于土壤洞穴动物掘土时爪趾对土壤的锯切作用，所以能以较小的牵引力加工出深度更深、蓄水容积更大的微坑。上述研究工作为滚动触土工作部件与土壤相互作用的研究，以及通过几何结构仿生的方法对牵引式整地机具关键部件的改进和优化提供了参考。更多还原

【Abstract】 Micro-topographical preparation is an operation that numerous geometrically orderedsurface depressions are formed by modifying soil surface micro-topography to collect andhold water during rainfall. Consequently, water runoff is reduced, erosion is mitigated andwater infiltration is increased. Compared with other working tool for micro-topographicalpreparation, toothed wheel not only can prepare micro-topographical structure surface, butalso consolidate soil, improving soil preparation quality, hence it was widely employed.Predicting and investigating the interaction behavior between soil and toothed wheel isone of prime import factors in enhancing the workability and efficiency ofmicro-topographical preparation. However, toothed wheel is a novel apparatus in landpreparation and has special shape, so research experience from other rolling soil-engagingcomponent can hardly be referenced directly for it. In this study, starting from the basictheoretical derivation, toothed wheel kinematic and dynamic operating models wereestablished. The finite element method (FEM) and soil bin test were applied and integrated.The FEM was used to provide a three-dimensional (3-D) finite element model to simulatesoil and toothed wheel interaction dynamically, and predict the interaction behavior betweensoil and toothed wheel. Indoor soil bin based toothed wheel traction test platform was built.Through soil bin test, the FEM model was calibrated. Based on the verified FEM model,effects of different operating parameters on the toothed wheel operating results wereexplored.Involved in the project sponsored by the National Natural Science Foundation of China(No:51075185), which aims at the requirement of improving working efficiency of thetoothed wheel, and the necessity of reducing draft force of the toothed wheel as well asimproving the quality of micro-topographical preparation, this study applied bionic approach,specifically bionic geometry, to optimize the design of toothed wheel. Through learningfrom diverse burrowing animals with highly efficient ability of soil digging, their variousgeometric structures of digging organs were used for reference. The essences and principlesof those geometric structures were captured and extracted, then simplified them with serratedstructures. The bionic serrated structure was used to optimize the design of toothed wheel. Finally, the working efficiency and quality of both bionic and normal toothed wheel wereevaluated through soil bin test.Some soil burrowing animals existing in nature with strong burrowing ability haverelatively small body shape. The geometrical feature size of their organs used for digging aretiny and in the meso-scale. In the research area of bionic engineering, it was difficult andinefficient to analyze those geometrical structures quantitatively by using traditional methods.In this study, the end tooth of dung beetle foreleg was taken as a case study, proposed anovel method of quantitative analysis. Using computer vision technology to take place of thehuman visual identification process, recognize the outer contour of two-dimensional pointcloud of the end tooth of dung beetle foreleg, and quantitatively analyze its geometricalstructure. This study provides the technological base for quantitative analysis of structuralcharacteristics of meso-scale animal organs.Toothed wheel is a non-circular working wheel, having impact effect on soil whenrolling over the soil surface. In this study, adopted basic theoretical derivation approach,established kinematics and dynamics model of operating toothed wheel. At different workingphases of toothed wheel, formulas of toothed wheel motion parameters were derivedaccording to rigid body plane motion’s instantaneous velocity center theorem in kinematics,along with acceleration composition theorem of translational motion. According to thetheorem of impulse and theorem of kinetic momentum in dynamics, along with the kineticenergy theorem, deduced the equation of toothed wheel required operational draft force,instaneous impact force and impact energy. Through this study, the relation betweenstructural parameters and motion parameters of toothed wheel can be revealed. Moreover,the behavior of toothed wheel movement and dynamics of impact operation characteristicscan be investigated.Using commercial finite code ABAQUS, a3-D finite element analysis (FEA) of soiland toothed wheel interaction was carried out to investigate the behavior of the soil andtoothed wheel interface. In order to mitigate solution convergence problems caused byelement distortion, an Arbitrary Langrangian–Eulerian (ALE) scheme was adopted topreserve the quality of mesh throughout the numerical simulation. The results reveal that theALE technique prevents convergence problems cause by mesh over distortion and allows thesimulation to run continuously. The effects of boundary distance and mesh density of soilbin model on FEA results were evaluated. The results show that as the mesh density increaseto a certain degree, FEA results will tend to stabilize and do not depend on the mesh sizevariances. To describe the movement pattern of toothed wheel, the cycloid of outer edgepoint of toothed wheel was calculated. Results show that, the cycloid of toothed wheel fluctuates along coordinates rather than a smooth curve. In addition, at the ground contactposition, the cycloid show certain backward sliding relative to the ground. Furthermore, itwas found that both longitudinal and cross section in soil under toothed wheel showed twodeformed zone that had opposite flow direction. In this study, finite element model wasestablished and provided a methodological base for further exploration of the effects ofdifferent operating parameters on the toothed wheel workability.In order to perform toothed wheel traction test, test rig and force measurement systemwere designed and developed based on indoor soil bin. In order to calibrate FEM model,draft force recorded by FEM model and soil bin test were compared. The results show bothof the draft force versus time had the same variation pattern, and the mean relative error ofaveraged draft force of FEA compared to soil bin test was3.40%. This indicate the results ofthe FEA solution can meet the requirement of reflecting the dynamic behavior in toothedwheel working process and achieve the desired accuracy. Comparing the topographiccharacteristics of micro-basin, results show micro-basin topographic characteristics from theFEA solution were in good agreement with that form soil bin test result. This indicate theFEM model can effectively reflect soil flow and deform characteristics.Based on the calibrated FEM model, the effects of different working parameters ontoothed operating results were predicted and analyzed by reusing FEM. It was found that asthe toothed wheel operating speed increased to a certain value, slip phenomenon wasobserved. Real time slip ratio and total slip ratio under different operational speeds werecalculated. Results show that both real time slip ratio and total slip ratio increases with theincrease of the increase of the operational speed. This study can provide reference for theselection of toothed wheel working parameters.Considering that UHMWPE has many excellent material properties and has beenwidely used in soil-engaging tools to improve tillage effectiveness, UHMWPE was selectedin to evaluate its potential advantages as manufacturing material of the toothed wheel. Modalanalysis was performed to compare vibration characteristics of toothed wheel both madefrom cast iron material and UHMWPE-cast iron combinatorial material. Using the anterior8ranks of modals, the natural frequency and maximum amplitude of the two types of toothedwheel were compared. The results show that compared with cast iron material toothed wheel,UHMWPE-cast iron combinatorial material toothed wheel can acquire better adhesionreduction ability on the convex teeth, which ensure the structural strength of themicro-basins on soil surface and have enhanced the stability at the center of the wheel disk.With different friction factors, the effects of different materials on toothed wheel operationalresults were analyzed. It was found UHMWPE toothed wheel can prepare micro-basin to the desired depth at lower vertical load and require less draft force. This study providesreference for toothed wheel material selection.The technical approach of bionic geometrical structure was used to optimize toothedwheel. Subsequently, the working quality and efficiency of different toothed wheels wereevaluated through soil bin test. Unique characteristics of geometrical structure existing insoil burrowing animals’ digging organs were comprehensively studied, and their essence andcommonality were abstracted. These characteristics were extracted, simplified, and thenrepresented by bionic serrated structure. The bionic serrated structures were used for thedesign to optimize toothed wheel. Three types of bionic toothed wheel were manufacturedand traction tests in soil bin were conducted. Taking required draft force, depth, and volumeof prepared micro-basin as the indexes, different toothed wheel working efficiency andquality were evaluated. Results show that compared with traditionally used toothed wheel,bionic toothed wheel can reduce required draft force up to6.52%, increase depth of preparedmicro-basin up to13.25%, and expand volume of prepared micro-basin up to37.59%. It wasfound that the cutting mechanism of bionic toothed wheel behaved as saw cutting thatsimilar to the digging action of soil burrowing animals when performingmicro-topographical preparation. Thus, bionic toothed wheel required less draft force foroperating compared with normal toothed wheel, and prepared micro-basin with increaseddepth and water harvesting volume.This study provides reference for investigating the interaction between soil and rollingcomponent. Appling the approach of bionic geometrical structure for further innovativedesign of geometrically optimized land preparing implement of agricultural machinery,energy consumption can be reduced and working quality can be improved.更多还原