| 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. |
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