An Approach To And Validation Of Maize-seed-assembly Modelling Based On The Discrete Element Method

As the largest grain production crop in China,its output is largely affected by the performance of maize seeding machinery and equipment,and the interaction of maize seeds with seeding machine and other key components directly affects its performance.In order to study and optimize the performance of the planter by the numerical method of the discrete element method?DEM?,it is necessary to establish a precise analysis model of the maize-seed-assembly based on DEM.For this reason,this paper takes Jiping 1,Ping'an 11and Tiannong nine varieties of maize as research objects,and studies the mechanical parameters such as geometric shape,characteristic size and static friction coefficient of maize seeds.Based on this,An approach to maize-seed-assembly modelling is proposed.through the comparison of the simulation results of bulk density,static angle of repose,percentage passing and seeding performance with the experimental results,the rationality of the proposed approach to maize-seed-assembly modelling is preliminarily verified.Finally,the modeling method is applied in the optimization of the performance of the seeding meter,and the effectiveness of the modeling method is verified.The main work and findings of this paper are as follows.?1?The physical properties of maize seeds of Jiping 1,Ping'an 11 and Tiannong Jiu three varieties are tested,It can be found that each variety contains the horse-tooth,spherical-cone,spheroid,prism,and irregular shape maize seeds.Among them,the total number percentage of maize seeds of the three shapes of the horse-tooth shape,the spherical-cone shape and the spheroid shape is about 90%.As the sum of the percentages of the prism and irregular shape seeds by number is far less than that of the other three shaped seeds,to simplify the modelling of maize seed assemblies,they are ignored in this paper.Therefore,the geometrical shape of the maize seed assemblies can be simplified into horse-tooth,spherical-cone,and spheroid in the modelling;Futhermore,it can be found that the characteristic sizes of the maize seeds of these three varieties approximately obey a normal distribution,By analysing the correlations between characteristic sizes,it is found that there exists a relatively strong correlation between the upper base and the other characteristic sizes for horse-tooth and spherical-cone maize seeds,and the thickness of the spheroid maize seeds has a substantial correlation with their length and width.For the horse-toothed and spherical cone corn seeds;Therefore,in building the particle model of a maize seed,the upper base of the horse-tooth and spherical-cone seeds and the thickness of the spheroid seeds are selected as the primary sizes,and their other sizes are calculated according to the established functional relationships between sizes.In this way,the shape and size distribution of the analysis model of a maize seed assembly we built is very close to those of a natural one.?2?The effect of moisture content on the characteristic size of maize seeds is studied.It can be found that with the increase of the moisture content,the characteristic sizes of the maize seeds increase.In addition,the sphericity of the spheroid seeds increases from 0.89 to0.93 with increasing moisture content,when the moisture content of spheroid seeds is high,their shape can be regarded as a sphere.?3?A single maize seed particle modeling method is proposed.For the horse-tooth maize seeds,8,10,14,20,and 25 sub-spheres are built.The filling spheres are mainly distributed in two columns along the height direction of a horse-tooth seed.For the spherical-cone maize seeds,14,18,and 22 sub-spheres are built.One filling sphere is fixed at the bottom of the spherical-cone with a diameter of the averaged value of its lower base?W₂?and thickness?T₂?,and four filling spheres are filled in each layer above this bottom one.The number of the layers varies with the modelling accuracy.For the spheroid maize seeds,1,6,and 10 sub-spheres are built.The spheroid is filled symmetrically with two filling spheres in each direction,expect for the one sub-sphere model,and they are of the same diameters.According to the abovementioned filling method and the coordinates and radii of each filling sphere,the maize seeds of three varieties are filled with spheres.On this basis,an approach to maize-seed-assembly modelling is proposed,that is,first,the particle model of a single maize seed abovementioned is taken as a template;Second,the primary size is generated according to a normal distribution,and other characteristic sizes are calculated according to the functional relationship between them and the primary size.The particle model of a maize seed can be built using these generated sizes.By repeating the above process for each maize seed a particle assembly can be built;Finally,according to the ratio of the horse-tooth,spherical-cone,and spheroid seeds,a mixture of different shaped particles with a corresponding quantity is generated.In this way,the particle assembly model of maize seeds is close to the natural one.?4?The simulated results are close to the experimental results in terms of the bulk density test,static angle of repose tests,the percentage passing tests and seed meter performance test when 10 to 14 sub-spheres are used to represent the horse-tooth-shaped seeds,18 sub-spheres for the spherical-cone-shaped seeds,and 6 sub-spheres for the spheroid-shaped seeds.In addition,the computational efficiency is also reasonable.Therefore,the feasibility and validity of the modelling methods representing maize seeds that we propose are preliminarily verified.?5?Taking a scoop-wheel-type seed meter as the research object,optimizing the performance of the seed metering device by using the approach to maize-seed-assembly modelling,the analysis shows that when the seed wheel rotation speed,the seeding angle and the scoop-wheel diameter are 25r/min,40°and 7mm,respectively,the performance of the seed meter is optimal,which initially reflects the practical value of the established maize-seed-assembly model.