【作者】 颜辉；

【导师】 于建群；

【作者基本信息】 吉林大学 ， 农业机械化工程， 2012， 博士

【摘要】 本文以一种新型玉米精密排种器——组合内窝孔玉米精密排种器和三种玉米种子为研究对象，对非规则形状颗粒——玉米种子的建模方法、复杂结构机械部件——排种器的建模方法和非规则形状颗粒的离散元法计算方法等进行了深入研究，在此基础上采用课题组研发的基于离散元法的三维CAE软件，对组合内窝孔玉米精密排种器进行了设计和工作过程仿真分析，并与排种器的台架试验结果进行了对比，以期建立一种玉米精密排器优化设计的新方法，本文的主要研究工作和结果如下。1）按照玉米排种器工作过程仿真分析的需要，选择平安18、吉峰218和长单228三种玉米种子作为实验样本，对三种玉米种子的物理力学性质进行了测试，包括三轴尺寸、千粒重、颗粒密度、刚度系数、碰撞恢复系数、动静摩擦系数等。在此基础上，对于种子品种、种子含水率等相关因素对碰撞恢复、刚度、摩擦系数等产生的影响进行了分析，为排种器工作过程仿真分析提供参数依据。2）对颗粒建模方法进行了综述，总结了非规则形状颗粒的五种球充填建模方法。对以玉米种子为代表的非规则形状颗粒的建模方法进行了深入研究。以三种玉米种子——平安18、吉峰218和长单228为研究对象，提出基于形状特征和基于扫描数据的玉米种子颗粒建模方法。建立了基于点云和基于三角形网格面的球颗粒自动填充建模算法；在Pro/ENGINEER软件环境下，建立了球颗粒手动充填建模方法。分别采用两种建模方法，建立了较为精细的玉米种子颗粒模型，并对其性质进行了分析，建立了求解颗粒质心、惯性主轴及其转动惯量的方法。最后通过一些简单实例验证了所建立模型的可行性和有效性，为后续仿真实验奠定基础。3）提出由边界的三维Pro/ENGINEER模型，建立其三维离散元法分析模型的方法。在对Pro/ENGINEER软件进行二次开发的基础上，深入研究了边界Pro/ENGINEER实体模型中与颗粒材料接触的规则曲面的识别及读取、运动及材料属性的绑定和数据存储等问题；初步建立了平面、球面、圆柱面、圆锥面、球冠面、圆台面和球台面等十余种规则曲面的离散元法分析模型；在此基础上，实现了由组合内窝孔玉米精密排种器的三维Pro/ENGINEER实体模型建立其三维离散元法分析模型，为该排种器工作过程和性能的仿真分析奠定基础。4）研究了采用球颗粒组合方法，建立非规则形状颗粒——玉米种子分析模型时，非规则形状颗粒的离散元法计算方法，包括非规则形状颗粒的邻居搜索方法、接触判断方法、接触叠合量求解方法、接触作用力计算方法和颗粒运动计算方法等，初步建立了非规则形状颗粒的离散元法计算方法。5）进行了组合内窝孔玉米精密排种器工作过程的台架试验。采用透明有机玻璃研制出组合内窝孔精密排种器试验样机，选择三种玉米种子（平安18、吉峰218、长单228）和三种排种轮转速（26.82r/min、39.33r/min、51.96r/min），在PSJ排种器性能试验台上，进行了该排种器的台架试验，并采用高速摄像系统和爆破分析软件，对排种器的工作过程及其性能进行了深入分析。得到了三种转速下,三种玉米种子的单粒率、双粒率和空穴率；对三种转速下,三种玉米种子的清种开始角、清种终止角、种子面倾斜角进行了分析；对种子的运动轨迹、合速度等进行了分析。6）利用Pro/ENGINEER软件，设计了组合内窝孔玉米精密排种器的三维实体模型；采用课题组自主研发的边界建模模块，通过读取排种器的三维实体模型数据，建立了该排种器的三维离散元法分析模型；采用课题组自主研发的离散元法仿真模块，仿真分析了组合内窝孔玉米精密排种器的工作过程及性能，包括排种性能指标、清种角、投种角、种子面倾斜角、种子的运动轨迹、合速度等，同时将仿真分析结果和排种器的台架试验结果进行了对比，可知：①三种转速下，仿真与试验的单粒率、双粒率和空穴率相对误差最大值为9.89%；②清种开始角和清种终止角的仿真值均比试验值小，其绝对误差最大值分别为8.49°、19.8°，相对误差最大值为12.38%；③投种角的仿真值与试验值相差不大，其绝对误差最大值为2.78°，相对误差最大值为14.11%；④充种轨迹和投种轨迹的仿真与试验结果均比较接近，且相对误差较小；⑤种子运动合速度的仿真值与试验值绝对误差很小（均在0.1单位以内），相对误差除个别位置外均在10%以内，仿真值与试验值的变化趋势基本一致；⑥以长单228种子为例，分析了不同刚度系数（300、3000、30898N/m）、不同摩擦系数及不同颗粒建模方法对仿真结果的影响。综上所述，虽然仿真结果与试验结果有误差，但两者比较接近、变化趋势一致；由此验证了采用离散元法和自主研制的CAE软件分析玉米排种器的可行性和有效性，为组合内窝孔玉米精密排种器的优化设计建立了一种新方法。更多还原

【Abstract】 This paper forces on Combination Inner-Cell Corn Precision Seed Metering Device, anew type of corn precision seed metering device, In-depth research of irregular shapeparticles, corn seeds modeling method, the complex structure of mechanical parts, meteringdevice modeling method, DEM calculation of the irregular shape of the particles, simulationanalysis on the design and working process are conducted on the working platformintegrated by CAE software base on DEM developed independently by the research groupand Pro/ENGINEER software. After that, the results acquired by experiments of seedmetering device are analyzed contrastively in order to establish a new kind of method for theoptimization design of corn precision seed metering device based on the discrete elementmethod. The main research works and results are as follows.1) Test analysis is conducted on the physico-mechanical properties of corn seed.Ping’an18, Jifeng218and Changdan228corn seeds are selected as the experiment samplesand then test is made on physico-mechanical parameters of these samples including size ofthree axes, rigidity coefficient, thousand grain weights, collision coefficient of restitution,coefficient of kinetic and static friction and density of pellet. Besides, analysis is also madethe influences of seed varieties, seed moisture content and other relevant factors on collisionrestitution, rigidity, friction and other coefficients, which offers parameter basis for thesimulation analysis of the working process of seed metering device.2) The general particle modeling methods are reviewed in this part, and then, five kindsof ball filling modeling method for irregular shape particle are summarized. Research isconducted on the modeling approach of irregular particles represented by corn seed. Basedon Ping’an18, Jifeng218and Changdan228corn seeds, a modeling method of corn seedparticles is proposed according to the shape features by three-dimensional scanner. In Pro/ENGINEER software environment, modeling method of manually filling spheres isestablished; based on the point cloud and triangle mesh surface, automatic ball particlesfilling algorithm is realized. A more refined corn seed particle model is completed.Furthermore, the model character is analyzed so that the method of the particle centroidcalculating and axes of inertia calculating are acquired. At the end of this part, the reliabilityof the model is verified by some simple cases, laying the foundation for follow-upsimulation of this paper.3) The boundary3D Pro/ENGINEER models is proposed, its3D discrete elementanalytical model is posed. On the basis of the further development on Pro/ENGINEERsoftware, in-depth research is done on identification and reading, eliminating redundancy,setting virtual boundary, motion, binding of material property, data storage and other problems of regular surface（applying graphic method) that contact with particle material inboundary Pro/ENGINEER physical model, more than ten kinds of regular surfaces model ofdiscrete element method including Plane, spherical, cylindrical surface, conical surface,surface of the spherical cap, round table and ball countertops are established, in the end, thegeneration of3D discrete element analytical model from3D Pro/ENGINEER physicalmodel of combination inner-cell corn precision seed metering device is realized.4) Research is made on that ball combination method of irregular particles is utilized tobuild the analytical model of the irregular particle of corn seed, including irregular particleneighbor searching method, contact judgment method, contact overlapping solving method,contact force computing method and particle motion computing method, and also thediscrete element computing method of irregular particles is established basically.5) Bench test of working process of combination inner-cell corn precision seedmetering device is conducted. Transparency organic glass is utilized to develop theexperimental prototype of combination inner-cell precision seed metering device and thenthree kinds of corn seeds (Ping’an18, Jifeng218and Changdan228corn seeds)and differentseed metering wheel rotate speeds(26.82r/min、39.33r/min、51.96r/min) are selected toconduct bench test of combination inner-cell corn precision seed metering device on theperformance test bench of PSJ seed metering device. Besides, high speed video system andblasting analysis software are applied to analyze the working process and performance ofseed metering device deeply. Three corn seeds’ single grain rate, double grain rate and holerate are acquired at three kinds of wheel rotate speed; three corn seeds’ clear seeds startingangle, clear seeds ending angle and seed surface tilt angle are analyzed at three kinds ofwheel rotate speed; furthermore, the trajectory of the seed and resultant velocity areanalyzed.6) Pro/ENGINEER software is used to design the3D physical model of combinationinner-cell corn precision seed metering device. Boundary modeling module developedindependently by the research group is applied to establish the3D discrete element analyticalmodel through reading the data of3D physical model of seed metering device. Simulationanalysis is conducted on the working process and performance of combination inner-cellcorn precision seed metering device through the discrete element simulation moduledeveloped independently by the research group and then the result of simulation analysisincluding the seeding performance indicators, clear seed angle, cast seed angle, the seedsurface tilt angle, the trajectory of seed, and the resultant velocity, with the data of bench testof seed metering device are contrasted. The results show that:①Under three kinds of speed,the maximum error of single grain rate and double grain rate is9.89%in simulation and test;②The simulation values of clear seed starting angle and clear seed ending angle are smallerthan experimental values, its absolute maximum error is8.49°,19.8°respectively, its relativemaximum error is12.38%;③Little difference between simulation and experimental valuesof casting angle, its absolute maximum error is2.78°, relative maximum error is14.11%;④Little difference between filling seed trajectory and casting seed trajectory in simulationand experiment, its relative error is less;⑤Value of seed resultant velocity in simulation and experiment is similar(in0.1unit),its relative error is almost less than10%, the varietytrend of simulation and experiment value is almost same;⑥Taking corn seed Changdan228for example, the effects of the simulation results of three different corn seed particle modelsare analyzed under three different stiffness coefficients(300、3000、30898N/m), threedifferent coefficients of friction and three different particle module methods.In summary, although a little errors exist between simulation and experiment results,but the variety trend is similar and little difference between simulation and experimentvalues. From these, the feasibility and effectiveness of analysis on the corn seed meteringdevice through DEM and self-developed CAE software is verified. A kind of new method foroptimized simulation design is realized.更多还原