Parameter Determination And Verification Of Discrete Element Simulation Model For Fodder Rapeseed Chopping Process

Rapeseed is a multi-purpose oil crop.Under the situation of agriculture reform about grain and industrial and forage crops,nutrient-rich fodder rapeseed is gradually known as a new type of fodder.Compared with other fodder crops,fodder rapeseed can be planted in autumn and winter fallow fields to increase production of fodder without occupying grain land.Fodder rapeseed has a large biomass,but the main harvesting method is manual or semi-mechanized harvesting,which consumes a lot of manpower and material resources and low work efficiency.Some aquaculture enterprises have attempted mechanized harvesting of fodder rapeseed by silage corn harvester,which is prone to blockage of transport channels,oxidation and mildew of fodder rapeseed for deucedly kneaded,and so on.So suitable research on chopping technology of fodder rapeseed is imperative.Crop shredding methods are diverse,and trial production costs are high and seasonally restricted.Computer simulation is not only limited by seasons and site restrictions,but also convenient to adjust test conditions,and can study chopping problems in various aspects with high efficiency,with economic and security features.Due to the different nature of various materials,the physical parameters of different materials also have large differences.It is the key to virtual simulation to determine the correctness of the parameters of the simulation model.Based on the systematic analysis of the calibration methods of simulation parameters at home and abroad,this paper proposes a method based on Hertz-Mindlin with bonding contact model to construct the chopping process of fodder rapeseed stalk with continuous tissue structure.The method of meta-simulation was used to design the calibration method of fodder rapeseed stalk parameters.The test of characteristics of feed rapeseed material,the calibration of basic contact parameters of the simulation model,the calibration of particle bond model parameter,the simulation test and verification of bench test,the optimization of the working parameters of the roller chopper and so on were carried out.The main research contents are as follows:(1)Characteristics test of fodder rapeseed stalk material.The parameters required for the simulation experiment of discrete element software were clarified,and the differences between the characteristics of fodder rapeseed stalk materials in different growth stages were analyzed.The physical characteristics of fodder rapeseed stalk in different growth stages were combined,and the diameter,water content,density,elastic modulus,shear modulus,Poisson’s ratio of fodder rapeseed stalks and the angle of repose of fodder rapeseed stalk under chopped conditions were tested.(2)Calibration of discrete element contact parameters of fodder rapeseed stalk.Based on the basic model between particles named Hertz-Mindlin(no slip)of EDEM software,the angle of repose of rapeseed stalk was selected as the experimental index.The factors and range of factors were determined by factor significance test and Steepest Ascent test.Finally the regression equation between the angle of repose and the saliency parameters was obtained by the Box-Behnken Design experiment.In order to ensure the accuracy of the parameter calibration,the relative error of the angle of repose in the simulation test and the actual test is used as the response value to calibrate the contact parameters,and the static friction coefficient,dynamic friction coefficient and collision recovery coefficient of steel or plastic and fodder rapeseed stalk are determined respectively.By testing the contact parameters after calibration,the relative error between the simulation test and the angle of repose in the actual test is 2.27%.(3)The stalk discrete element simulation model construction and contact model parameter calibration.Through the observation and analysis of the crushing test process,the test indexes of fracture displacement and maximum pressing force were selected.Based on the bond model between particles named Hertz-Mindlin with bonding,the rapeseed stalk model was discretized,and the simulation experiment of pressing the fodder rapeseed stalk was carried out.The parameters of the contact model were calibrated by the Central Composite Design test,and the feasibility of the maximum pressing force as the test index was determined.Four parameters of normal contact stiffness,tangential contact stiffness,critical normal stress and critical tangential stress are calibrated in the model.By testing the calibration contact parameters,the relative error between the simulation test and the actual test results is 1.28%.In order to ensure the reliability of the results,different diameter stem models were established,and the actual pressing test of the corresponding diameter stalk was carried out.The relative error of the maximum pressing force between the corresponding diameter stalk was 2.74%,3.13%,3.86% and 4.04% respectively,indicating that the calibration parameters are reliable and effective.(4)Actual test and simulation test of chopping fodder rapeseed stalk on roller chopper bench.Through the analysis of the pass rate of the fodder rapeseed stalk bench test,the influence of the speed of feed roller and the roller chopper on the pass rate during the chopping process was determined.The simulation and chopping analysis of fodder rapeseed stalk was carried out.The feasibility of the simulation test was determined by single factor test.The optimal combination of speed of feed roller and roller chopper was calibrated by Box-Behnken Design test,which was 467.32r/min and 770.71r/min.Through the examination of the contact parameters after calibration,the relative error between the simulation test and the actual test results is 0.38%.