A Multi-sphere Based Modelling Method For Maize Grain Assemblies

Maize grains are usually presented in a wide range of shapes and sizes.To establish a reasonable model based on Discrete Element Method(DEM)is become a hot topic nowadays.There is a need for further research on the analysis model of maize grain assemblies approximated to real maize grains.In this paper,two varieties of maize grains are chosen as research subjects to study physical and mechanical properties.The modelling method of single maize and maize assemblies based on multi-sphere method.The feasibility and validity of the modelling method of maize grains are verified through comparison of experimental and simulated data of piling,dropping and screening process.The main work and conclusions of this paper are as follows.(1)Two varieties of maize grains,Xianyu 335 and Baidan 678,are taken as examples to study the physical and mechanical properties,including geometric shape,dimensions,density,moisture content,static friction coefficient,rolling friction coefficient,and so on.The effect of moisture content on dimensions and density of maize grains are analyzed.The results indicate that the shapes of maize grains can be divided into wide wedge,narrow wedge,ellipsoidal-conical and irregular shapes.Maize particles of wide and narrow wedge shapes account for more than 90% of the total.Therefore,the geometric model of wedge shaped maize grains can be established for simplicity for the modelling of maize grain assemblies of the same variety.The upper base of the wedge shaped maize grains can be defined as the main and other sizes can be calculated on the basis of the relationship with the main size.(2)The maize grain is scanned using a 3D scanner and the results processed through encapsulation and noise reduction,and then imported into the EDEM software.By filling the sub-spheres based on the scanned results of the particles,the analysis model of maize is established.In addition,the modelling method of single maize grain based on the multi-sphere filling method is proposed.Sphere center distance is defined as the distance between two adjacent sub-spheres,according to different sphere center distance,4 kinds of maize model of wide wedge,narrow wedge and wedge of two varieties of maize grain are established.(3)The piling process of maize grain is observed experimentally by high speed camera technology,and the piling process of 4 kinds of maize model is simulated numerically by EDEM software.The feasibility and validity of the modelling method of maize grains are verified through comparison of simulation results and experimental results.In addition,the simulation results are compared with experimental results in terms of bulk density,at the same time,the CPU time of 4 kinds of model is also considered.The results indicate that the analysis model of maize grains is accepted for scenarios with 14-16 sub-spheres.In addition,the feasibility of modelling method of maize grains proposed in this paper is further verified through the study of dropping process,screening process and parameters sensitivity of maize model.