Experimental Study And Simulation Analysis Of The Working Process Of The Precision Seeding Unit And Its Key Parts

There are contacts between the working components(i.e.,opener,fertilizer apparatus,seeding device,as well as the covering and compacting parts)and the bulk materials(i.e.,soil particles,fertilizers,and seeds)and the granular flow in the working process of the precise seeder.The final positions of the seeds sowed by the precise seeder are determined as a result of the profiling mechanism,opener,seeder,as well as the covering and compacting parts.Due to the complexity of the precise seeding,the design,performance analysis,and the optimization of the precise seeding devices are mostly dependent on the designers’ experience,experiments,or traditional continuum mechanics analysis methods(i.e.,Newtonian mechanics,multi-body dynamics,and Smooth Particle Hydrodynamics).However,the issues in the performance analysis and optimization design of precise seeding devices cannot be well-addressed by the abovementioned methods.For this consideration,in this paper,the effects of various factors on the working process of the seeding device,the collisions between sowed seeds and soil particles,as well as the covering and compacting processes are studied by conducting experiments.On this basis,the working process of the seeding device,the collisions between sowed seeds and soil particles,as well as the covering and compacting processes are analyzed by the Discrete Element Method(DEM)and the coupled method of Discrete Element Method with Multi-Body Dynamics(DEM-MBD)at a mesoscopic scale.The validity and effectiveness of the analysis of a precise seeding device and its key parts using the DEM and DEM-MBD are verified by the comparison of the simulated results and those obtained experimentally.The main work and conclusions of this paper are as follows.(1)The physical and mechanical properties of soil particles are measured and analyzed.The models of three soil particles with different shapes and sizes are built by the composite spheres approach.The Hertz-Mindlin with JKR model is used to calculate the contact force between soil particles.The soil modelling is verified by the comparison of experiments and simulations in terms of the angle of repose in cylinder piling test and the resistance force in the cone penetration test.It can be found that the decrease of both the friction coefficient and the surface energy between soil particles increases their fluidity,which makes them more likely to flow.The penetration speed has a great impact on the penetration resistance.The bigger the penetration speed,the bigger the penetration resistance.(2)Four varieties of soybean seeds are taken as the research objects.The similarity between the shape of a soybean seed and an ellipsoid with the same size to the seed is analyzed quantitatively.The shape of a soybean seed is so close to the ellipsoid that the soybean seed can be approximated as an ellipsoid in the particle modelling.The dimensions of soybean seeds are measured and analyzed.On this basis,the multi-sphere-based modelling methods for the single soybean seed and the soybean seed assembly are proposed.The pilling process and the “self-flow” screening process are simulated using the soybean seed model built in this paper.The validity of the particle modelling methods of soybean seeds is verified by the good agreement between the simulated results and the experimental results in terms of the piling angle,flow pattern,and the percentage passing.(3)Two seeding devices are taken as the research objects.The experimental study of the working process of these seeding devices and their performance are carried out using the bench test.The working process of these seeding devices and their performance are simulated using the EDEM software.The effects of various factors on the seeding performance are analyzed.By the comparisons of the simulated results with those obtained experimentally in terms of the seeding performance and the motion of seed assembly,it can be found that their values are close and their variations are consistent,which gives a further verification of the modelling method of soybean seeds.(4)The bench tests of the bouncing and rolling of sowed soybean seeds after contacting with the soil are conducted.The effects of the moisture content of soil,seed-sowing height,conveyor belt speed,and the circular speed of the seeding-wheel on the bouncing and rolling displacements of soybean seeds.By the analysis of the experimental results,it can be seen that the primary-secondary factors affecting the non-uniformity in the spacing of seeds are the seed-sowing height,conveyor belt speed,moisture content of soil,and the circular speed of the seeding-wheel successively.The bouncing and rolling processes of the soybean seeds after contacting with the soil are simulated using the EDEM software.By the comparisons of the experimental results with the simulated results in terms of the transverse and longitudinal offsets of seeds after contacting with the soil,it can be found that their values are close and their variations are consistent,which verifies the feasibility of the analysis of the bouncing and rolling displacements of seeds after contacting with the soil using the Discrete Element Method.(5)The soil-bin tests of the covering after seeding and the compacting after seeding and covering are conducted,respectively.The effects of the vehicle speed and the opening angle of covering discs on the experimental results are studied.The coupling algorithm of DEM with MBD is deduced.The covering and compacting processes are simulated by the coupling of the discrete element method software EDEM with the multibody dynamics software ADAMS.This coupling method is verified by the good agreement between the simulated results and the experimental results.