Parameter determination and validation of discrete element model of seed potato mechanical seeding

Abstract: For optimizing the seed metering performance of the seed metering device for potato with the help of discrete element method, firstly the basic physical parameters of seed potato (density, elastic modulus, Poisson's ratio and coefficient of restitution) were obtained through the experiment and from the references. From references we know that coefficient between seed potato and potato, steel, plastic is 0.79, 0.71 and 0.66 respectively. From experimental results the average density of seed potato is 1 048 kg/m3 by the method of drainage, and the average moisture content of seed potato was 80.15% by drying method, and the volume density is 631.88 kg/m3. Using the self-made measuring apparatus of potato static friction coefficient, the static friction coefficients between potato and matierial including potato, plastic and steel were measured, and these were respectively 0.452, 0.445 and 0.517. By the inclined plane method, the dynamic friction coefficients between potato and other matierial including steel and plastic were determinated, and these were respectively 0.269 and 0.303. The shape, size and center of mass of the patotoes through the particle repose method had a certain error with that of the actual potatoes, therefore, taking the actual potato repose angle as the target value, and changing the dynamic friction coefficient, the simulation regression model of predicting dynamic friction coefficient of potato was establised. Predicted value of dynamic friction coefficient is 0.024 when potato stacking angle is 24.39°. For verifying the reliability of parameters of potato simulation model. Selection of seed potato which were close to the 3 types of statistical mean values were modeled respectively. The modeling process is as follows: the largest potato contour along the XY section is cut, and which was connected the section to the white paper, and draw the outline with pencil, and then trace the potato along the YZ cross section. The image is collected vertically to the tape of the sheet. The image was put into AutoCAD using the spline curve command will outline the stroke of potato, potato slices one by one in the order from the top into the datum on the corresponding. The outline of the whole potato is introduced into Solidworks and the potato is built with a lofting order. The parameters of simulation model were used to simulate the potato repose angle, which was then compared with the experimental potato repose angle of outer contour. The length and height of repose angle bottom edge in simulation and experiment are compared and they are 436 and 99 mm respectively, and their repose areas are basically the same. The repose angle in simulation and experiment is 24.72° and 24.39° respectively, and their relative error is 1.33%. It can be seen that the simulation and experimental repose angle are basically the same. Therefore, from the above comparison results, it is known that the simulated and experimental repose angle are basically the same. Moreover, spoon-chain seed potatoes metering device is used to validate the parameters of the potato repose angle simulation, and the replay rates in simulation and experiment are 11.90% and 13.10% respectively, and their relative error is 9.16%; the empty hole rates in simulation and test are 8.93% and 9.52% respectively, and their relative error is 6.20%, which satisfies the GB/T 6242-2006 Test method for potato planting machine in planting machinery. Comparison between simulation and experimental results shows that under the bench experiment condition, compared with the simulation results, the empty hole rate of the potato metering device increased by 0.59%, and the replay rate decreased by 1.2%. According to the analysis, it is due to the influence of the increase of the variation coefficient of the seed potato's size.