Calibration of simulation parameters of flaxed seeds using discrete element method and verification of seed-metering test

In order to optimize the mechanized production equipment of flax seeds by means of discrete element method to provide the basic parameters of flax seeds, the basic physical parameters and partial contact mechanical parameters of flax seeds were determined by the experimental method for 3 kinds of flax seeds, Dingya 22, Longya 10 and Longya 13, which are widely planted in Gansu Province of China. The basic physical parameters include three directions of size, mass density, bulk density, Poisson's ratio, 1,000-kernel weight, seed moisture content, and elastic modulus of flax seeds. Three kinds of flax seeds were randomly selected from 500 flax seeds, and the triaxial size of the flax was measured by Vernier calipers. The statistical results showed that the long average of Dingya 22 was 4.83 mm, the width was 2.39 mm, and the thickness was 0.85 mm. The average length was 4.43 mm, the width was 2.38 mm, and the thickness was 0.95 mm. The average length of Longya 13 was 5.13 mm, the width was 2.47 mm, and the thickness was 1.02 mm. The volume of the flax seed was calculated by the 3-axis size. Distribution of 3-dimensional volume of 3 kinds of flax seeds were basically normal distribution. With the pressure deformation experiment of flax seeds was carried out by electric double column tension test bench, and the Poisson's ratio was calculated by measuring the deformation amount of width and thickness before and after loading flax seeds, and Poisson's ratio of flax seed was 0.403, 0.410 and 0.409, respectively. The coefficient of static friction of flax seed was measured by the bevel method, and the coefficient of static friction between flax seeds were 0.240, 0.201 and 0.204, respectively. The collision recovery coefficient between flax seeds was determined by free fall experiment, and the collision recovery coefficient was 0.433, 0.389, 0.430, respectively. The elastic modulus of the load-displacement curve of the flax seeds obtained by the flax pressure experiment was 370.16, 558.28, 370.18 MPa. By the simulation repose angle of flax models under the different coefficient of rolling friction of flax seeds that were put to the actual repose angle of flax seeds, the coefficient of rolling friction of flax seeds was predicted, and the result was that the coefficient of rolling friction of flax seeds was 0.0415, 0.0425 and 0.042 0 for Dingya 22, Longya 10, and Longya 13, respectively. The influence of the coefficient of rolling friction on the repose process of flax seeds was analyzed. With the decrease of the coefficient of rolling friction, the contact quantity of flax seeds and bottom plate increased. The rotational kinetic energy of flax seed population increased first, and then decreased during the accumulation process. At the same time point, the coefficient of rolling friction of flax seeds decreased and the rotational kinetic energy increased. Based on the calibration parameters of flax seeds, the arrangement of heterosexous hole seeding device with flax seeds was carried out. The simulation results showed that the number of granules was 8-11, the average number of granules was 9.5, and the standard deviation was 0.5. Through the field trial experiment of flax combined planter, the number of seeds in the hole of the 81 hole in the collection area was counted. The results showed that the number of seeds in the first, second and third rows of seedlings fluctuated between 8 and 12, with an average of 9, standard deviation of 1. The average value of the simulated and experimental granules was 0.5, and the relative error was 5.26%. The flax seeds were small, and the number of leaks in the process of flax mining statistics occurred, resulting in certain errors in the experiment and simulation results. The flax simulation parameters calibrated in this paper have certain significance in guiding optimizing the seeding working parameters of the flax seeder.