# Alfafa Stalk Crushing Simulation Test and Parameter Optimization Method
## 4 Key Steps in Discrete Element Simulation and Results
### Discrete Element Analysis Results  
#### 4.3.1 The Influence of Crushing Structure and Rotation Speed on Stalk Crushing Effect  
The simulation process (Figure 9) revealed that the stalk particles were randomly distributed at the bottom of the trommel screen. Additionally, some stalk adhesive blocks were broken upon impact with the knife, while others remained in the adhesive block state. Thus, the fracture of bonds could serve as an evaluation index for the effectiveness of stalk crushing.  
In the EDEM post-processing module, a specific particle was randomly chosen, and the trajectories of other particles were concealed. The movement trajectory of the selected particle was then displayed (Figure 10). From the particle's movement trajectory, it is evident that the device effectively accomplished the task of crushing and discharging stalks.  
After the simulation was completed, the state of bond breaking was determined through post-processing. In this context, a value of one indicated that the bond remained  
Figure 8: Discrete element model of the crushing device.  
Figure 10: Particle movement trajectory. (**a**) +X direction; (**b**) +Y direction.  
Figure 9: The crushing state of alfalfa stems at a certain moment.  
inact, while a value of zero indicated that the bond was broken. The data regarding the number of bonds changing over time were exported and visualized through plotted curves.  
Based on Figure 11, it is evident that the number of bonds decreased noticeably over time within the range of 0 s to 0.8 s. Upon observing the simulation process, it was observed that the stalk entered the feed inlet from the conveyor belt between 0 s and 0.4 s, subsequently entered the crushing chamber, and made contact with the crushing blade. This led to a rapid decrease in the bonds. After 1 s, the graph plateaued, although it did not reach zero.  
When comparing the five crushing structures, it was observed that the bonds of the hob crushing structure, A4, and the roller crushing structure, A5, had decreased. However, the number of unbroken bonds was higher in these structures, leading to a poor crushing effect.  
Figure 11: Changes in the number of bonds under five crushing structures at different rotational speeds. (**a**) 1800 r/min; (**b**) 2400 r/min; (**c**) 3000 r/min; (**d**) 3600 r/min; (**e**) 4200 r/min; (**f**) 4800 r/min; (**g**) 5400 r/min.  
Through simulation, it was discovered that the cutters in these two crushing structures were arranged horizontally, resulting in a large crushing blind area and limited contact between the stalks and the cutters. Overall, the hammer-type crushing structure, A1, with blades exhibited the most effective crushing.  
Based on preliminary research, it was discovered that alfalfa stalks can be effectively crushed within 2 s. Therefore, during the simulation post-processing, data pertinent to the initial 2 s duration were extracted. Figure 12 illustrates the average speed of particles at a rotation speed of 3600 r/min for five different crushing structures. The average velocity of particles under the influence of A1, A2, and A3 gradually increased from 0 s to 1 s and then reached a stable state. This observation aligns with the gradual breaking of bonds over time, as seen in Figure 7. However, for the two crushing structures of A5 and A6, the average particle speed continued to increase between 0 s and 2 s. In conclusion, the changing pattern of average velocity for stalk particles was not necessarily consistent with the changing pattern of bond breakage, depending on the specific crushing structure.