# Influencing Factors Analysis and Simulation Calibration of Restitution Coefficient of Rice Grain
## 3 Results and Discussion
### Results Analysis of Simulation Calibration  
To avoid accidental errors in the test process, the bench test and simulation test were repeated three times, and the motion parameters were determined as the test results. The vertical falling direction of rice grain was \(X\) direction; the left and right direction was \(Y\) direction; and the front and back direction was \(Z\) direction. The bouncing state of rice grains obtained by the bench test and simulation test is shown in Figures 9 and 10. Figure 8: Effect of moisture content on restitution coefficient of rice grain. Note: In the test, the spring compression was 150 mm, and the contact material was plexiglass plate. Figure 9: Rice grain bouncing state of bench test. The picture shows the falling state of grains at different times: (**a**) 0.01 s; (**b**) 0.04 s; (**c**) 0.07 s; (**d**) 0.10 s; and (**e**) 0.13 s.  
To analyze intuitively and accurately the whole process of rice grain from falling to collision rebound, the regular curve of the relationship between vertical displacement, combined velocity (absolute value), and movement time in the process of the bench test and simulation test was drawn, as shown in Figure 11.  
It can be seen from Figures 9-11 that there was a certain initial velocity at 0 s in the bench test and simulation test, which was the velocity of rice grain after being ejected by the impact device. With the increased time, the vertical displacement and resultant velocity increased gradually. When the time was 0.10 s-0.12 s, the vertical displacement reached the maximum, and the combined velocity decreases sharply. At this time, the rice grain collided with the plexiglass plate, and the ratio of combined velocity after collision to that before collision was the restitution coefficient of rice grain. With the increased time, the  
Figure 11: Curve of rice grain collision. Figure 10: Rice grain bouncing state of simulation test. The picture shows the falling state of grains at different times: Y is the Y direction, and Z is the Z direction. (**a**) 0.01s; (**b**) 0.04 s; (**c**) 0.07 s; (**d**) 0.10 s; and (**e**) 0.13 s.  
rice grain rebounded to a certain height, but the direction of motion was opposite to the direction of gravity acceleration, resulting in the speed gradually decreased. The velocity of rice grain measured by the bench test was less than that of simulation test. The velocity before collision was 1.851 m/s, and the velocity after collision was 0.794 m/s in the bench test, so the restitution coefficient was 0.429. The velocity before collision was 1.895 m/s, and the velocity after collision was 0.802 m/s in the simulation test, so the restitution coefficient was 0.423. Compared with the preset value, the relative error was 1.40%. This may be due to the influence of air resistance in the bench test, while the influence of air resistance was ignored in the simulation test, or the discrete element model of rice grain was composed of several small spheres, which increased the surface area of rice grain and led to large energy loss in the contact part during the bouncing collision. At the same time, due to the irregular shape of rice grain, it was easy to produce displacement and velocity in other directions of the three-dimensional space after bouncing, which had a certain impact on the subsequent measurement and analysis results. Because the speed of rice grain before collision in the bench test was less than that before collision in the simulation test, the restitution coefficient in the bench test was greater than that in the simulation test, which also verified the conclusion in 3.1.2 that the greater the initial collision speed was, the smaller the coefficient of restitution was. The results were consistent with the research results of [PERSON] et al. [10] and [PERSON] et al. [11]. However, the overall difference between the bench test and the simulation test was small, which proved the validity and rationality of the determination and simulation of the calibration restitution of rice grain.