## 3 Results and Discussion
### Simulation Results and Analysis of S-U-S
#### 3.1.2 Forces Affected by the Different Arrangement Spacing of the Optimal Structure  
The structural parameters of No. 14 in Table 2 were \(l\) = 7 mm, \(h\) = 3.5 mm when the arrangement spacing was fixed at \(S_{1}\) = \(S_{2}\) = 1 mm. We followed the steps of the simulation experimental design for the S-U-S as stated in the design of simulation experiments section. Here, the next simulation was performed by changing the arranged spacing of the bionic structure, which was labeled S-U-S-_I/h_3.5. According to Table 3, 16 groups of discrete element simulations were performed with different arranged spacings for S-U-S-_I/h_3.5. Because the draft force was consistent with the tractor traction in format (they are both along the direction of movement), in this research, the draft force was used as the reference value to study the influence of the arranged spacing of the scalelike unit on the drag reduction performance. The simulation results are listed in Table 5.  
To investigate the influence of the arrangement of the scalelike unit structure on the drag reduction performance, a single factor, such as the lateral spacing or the longitudinal spacing, was analyzed according to the predesigned test plan. As shown in Figure 12, when the longitudinal spacing was fixed (\(S_{2}\) = 1 mm), the total force tended to increase as the lateral spacing increased. As shown in Figure 12, when the transversal spacing was fixed (\(S_{1}\) = 1 mm), the total force tended to increase as the longitudinal spacing increased. The above results showed that the arrangement of scalelike unit structures also had a great influence on the drag reduction performance. Theoretically, the smaller the spacing is, the greater the drag reduction. This finding was consistent with the theoretical analysis. As the spacing size and structural size continue to decrease, the manufacturing cost and design  
Figure 11: Variation of the total force versus the height when \(l\) = 3 mm. cost are significantly increased, which is impossible in agricultural engineering applications. Hence, the recommended values of the range of the arranged spacing used in engineering applications are 1 mm \(\leq S_{1}\leq\) 4 mm, 1 mm \(\leq S_{2}\leq\) 4 mm. The above preliminary analysis means that, for the scalelike unit structure, the recommended structural parameters for engineering applications are 5 mm \(\leq\)1\(\leq\) 8 mm and 2.5 mm \(\leq\) h \(\leq\) 3.5 mm, and the recommended ranges of the arrangement spacings are 1 mm \(\leq\) S1 \(\leq\) 4 mm and 1 mm \(\leq\) S2 \(\leq\) 4 mm. To adapt to the engineering applications, the structural parameters can be further optimized based on the resulting suggestions. In summary, it can be inferred that, when the height exceeds a critical value (h \(>\) 3.5 mm), the biomimetic structure is detrimental to the formation of a composite contact interface. On the contrary, when the bionic structure exceeds a critical value of 3.5 mm, the composite interface cannot be created, and a barrier will form, hindering the continuous movement of soil. Thus, an accumulation of soil at the contacting barrier is formed, resulting in increasing resistance. This result is consistent with the conclusions of the literature [36]. Figure 12: Variation of the draft force versus the transversal spacing of the S-U-S-I/3.5.