Research On Analysis Method Of Corn Threshing Based On3D DEM

Corn is a typical multipurpose and high yield crop. After years of development, the cornplanting area of China has become the second largest crops after rice, the annual output ofcorn is nearly a billion fifty million tons. Due to local geography, climate and other factors,most of corn will be dried first and then threshed after harvesting. Therefore, there is awildly use of corn thresher, and it plays an important role to guarantee the quality of cornafter harvesting and also to improve the farmers’income.However, due to the complexity of working process, up to now most of the researchesand designs of corn thresher were carried out by experimental methods, statistical analysismethods or traditional continuum mechanics analysis methods at home and abroad. In thispaper, the discrete element method (DEM) is adopted to research the corn threshing process.Based on the review of the principle and the structure of the corn threshers as well as theresearch status of the corn threshing, a drum type corn thresher is taken as research object. Inthis paper the physical and mechanical properties of the corn ears is tested, the modelingmethod of corn ears is researched, the3D DEM boundary modeling software is developed,researches the DEM calculation methods of the corn threshing process is researched. Basedon above work, a corn threshing process simulation analysis software using3D DEM isdeveloped. The simulation analysis of the corn threshing process is carried out by using thissoftware and the bench test of the corn threshing process is finished. By comparing thesimulation results with the test results, the feasibility and effectiveness of the new methodare validated. Thus this paper presents a novel method for the research of the corn threshingprocess and the optimal design of the corn thresher. The main work and results of this paperare as follows.1) The physical and mechanical properties of the corn ear of xianfeng8have been tested,including corn ear length, corn ear both ends of diameter, corn cob both ends of diameter,corn ear row number, kernel number per row, kernel angle per row, kernel offset between therows, parameters of each segment corn ear, density and moisture content of the kernel andthe cob, connection stiffness coefficient and connection force between the kernel and the cobof each segment and so on. The calculation method of the connection force between thekernel and the cob and the conditions for the corn kernel threshing are proposed. Thus wehave laid the foundation for using the DEM to analyze the corn threshing process.2) Based on deep researching of the structure of corn ear, cob and kernel, the modelingmethod of corn ears based on particles agglomerate is proposed. By comparing the corn ears’entities with the analysis models, the feasibility of the new method is validated.3) Based on deep researching of the UG software and the second development,researching of the method of getting boundary information for regular surface, the3D boundary modeling software for corn thresher based on UG software is developed. Bybuilding the corn thresher’s analysis model, the feasibility and effectiveness of the boundarymodeling software are validated.4) The DEM analysis theory of corn threshing process has been established, and theDEM calculating method of corn threshing process has been deeply researched, includingthe neighbor search collision detecting methods and the contact force calculation methodsbetween the particles and between the particle and the boundary, the collision detectingmethods and force calculation methods in one corn ear, and the calculation method forparticle motion.5) With the application of object-oriented technology, a corn threshing processsimulation analysis software based on3D DEM is developed after the requirements analysisand the preliminary design as well as the detailed design. The following functions are tested,including the connecting process function test between corn ear models and the boundaries,the methods of the neighbor search collision detecting and the function of performancepresentation function of the threshing machines. From the test cases, the feasibility andeffectiveness of analysis on the threshing simulation software is verified.6) Through the bench experiments of the drum-type corn threshing machine, the impactof different factors on the corn threshing process and the threshing machines performance isstudied. Conclusions are as follows.①Threshed rate during the test increases with increasing rotary speed of the rollerwithin65.5~500r/min. Rotary speed of the roller less than250r/min has a great impact onthreshed rate which is then very unstable. Threshing performance is greatly improved andthe threshed rate reaches96%when rotary speed of the roller is more than250r/min. Rotaryspeed of the roller on threshed rate is not significant and it also adds stability to threshingperformance. The corn ear number between5to20and the different parts of the corn earsfrom top to bottom don’t affect largely on threshed rate.②It has a less threshed kernels distribution axially in different rotary speed of theroller with different rotary speed of the roller. There are big differences quantitativelybetween the first part and the last part of the cylinder. The threshed rate in last part of thecylinder increases with increasing rotary speed of the roller. In addition, it has a less fallenkernels distribution axially in different rotary speed of the roller with different numbers ofthe corn ears. There is few differences of the distribution curve of the fallen kernels axiallywith different rotary speed of the roller, different numbers of the corn ears and different partsof the corn ears.7) Simulation analysis on the working process of corn threshing is conducted by thesimulation analysis software based on DEM developed independently. And the results acquired by experiment of corn threshing machine are analyzed contrastively. Conclusionsare as follows.①It is the same that threshed rate during the test increases with increasing rotary speedof the roller within65.5~500r/min. Threshed rates in the simulation analysis are just underthose in the bench experiments when the rotary speed of the roller is less than252.10r/min.The maximum discrepancy is9.99%in122.70r/min. Threshed rates in the simulationanalysis are higher than those in the bench experiments as the rotary speed of the rollerincreases. It also follows the same trend with the bench experiments that threshed ratesincrease with increasing numbers of corn ears in simulation tests. The number of the cornears and the different parts of the corn ears don’t play an important role on the threshingprocess.②It has a less shedding kernel distribution axially in the simulation analysis and thedistribution of the threshed kernel is similar to that in the bench experiments. Mostly, thebiggest error (about10%) occurs in the first part of the cylinder. There is few differences ofthe distribution curve of the fallen kernels axially with different rotary speed of the roller,different numbers of the corn ears and different parts of the corn ears.③The threshed rate increases with the increasing stiffness coefficient while thesimulation parameters are acquired in the physical and mechanical tests. The threshed rate isless affected by the friction coefficient in the selected three friction coefficients as thethreshed rate is all higher than98%.④It also follows basically the same trend with the bench experiments that it has a lessthreshing kernels distribution axially with different stiffness coefficient and frictioncoefficient while the simulation parameters are acquired in the physical and mechanicaltests.⑤It is the same for the changed threshing machine CAD model in the simulation withthe original model that the threshed rate increases with increasing rotary speed of the rollerand it has a less shedding kernel distribution axially. The changed threshing machine modelincreases the chance of collision between nail teeth and corn ears, so the threshed rates withthe changed threshing machine model are higher than those in the original model in thesimulation and there are more kernels in the first part of the cylinder.8) By comparing the simulation results with the test results, the feasibility andeffectiveness of the new method and the corn threshing process simulation analysis softwareis validated. Thus we have put forward a novel method for the research of the corn threshing a nd the optimal design of the corn thresher.