## 5 Conclusions  
In order to reduce the cutting resistance of wave-type disc cutters in the picking devices of castor harvesters, this study used the SPH-FEM coupling algorithm and LS-DYNA software to simulate the dynamic process of cutting castor. Based on the orthogonal rotation combination test, the effects of disc cutter thickness, disc cutter rotation speed, feeding speed, and disc cutter edge angle on the maximum cutting force were simulated. The simulation results were optimized using the response surface method, and the optimal combination of parameters was verified using experimental tests. The conclusions were as follows:  
1. Simulation tests showed that the disc cutter rotation speed, feeding speed, disc cutter thickness, and edge angle had a highly significant influence on the maximum cutting force. The influence of each factor on the maximum cutting force was in the order of disc cutter rotation speed > feeding speed > edge angle > disc cutter thickness. The following optimal parameters were obtained: disc cutter thickness of 2.71-3.15 mm, disc cutter rotation speed of 844.2-942.1 r/min\({}^{-1}\), feeding speed of 0.89-1.01 m\(\cdot\)s\({}^{-1}\), and edge angle of 29.2-33.9\({}^{\circ}\), where the maximum cutting force was less than 50 N;
2. The operating parameters were set as follows: disc cutter thickness at 3 mm, disc cutter rotation speed at 942 r/min, feeding speed at 1.0 m/s, and edge angle at 30\({}^{\circ}\)  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Item**} & \multirow{2}{*}{**Optimization Value**} & \multicolumn{5}{c}{**Verification Test**} \\ \cline{3-7}  & & **1** & **2** & **3** & **4** & **5** \\ \hline Maximum cutting force (N) & 42.64 & 43.5 & 45.8 & 46.1 & 41.5 & 46.2 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Bench test results.  
Figure 8: Verification test device. (**a**) Schematic diagram. (**b**) Cutting test bench—1. measurement and control system; 2. cutting system; 3. feeding device; and 4. dynamical system.  
with a predicted maximum cutting force of 42.64 N. The verification test indicated that the maximum cutting force obtained by the SPH-FEM coupling simulation method was generally consistent with the castor-cutting bench test using the optimized combination of parameters and that there was no significant difference in the data obtained using the two methods. The simulation method can, therefore, be used to study castor harvester disc cutters and provides an effective method for further parameter optimization of castor disc cutters.  
Conceptualization, F.K., D.W. and L.S.; methodology, Q.X., Y.S. and C.C.; software, Q.X., H.H. and T.W.; validation, D.W., L.S. and Y.S.; writing--original draft preparation, F.K., D.W. and T.W.; writing--review and editing, F.K., D.W. and H.H. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Agricultural Science and Technology Innovation Program of Chinese Academy of Agricultural Sciences (CAAS-ASTIP-31-NIAM-05) and supported by National Natural Science Foundation of China (52205261).  
Not applicable.  
We greatly appreciate the careful and precise reviews provided by the anonymous reviewers and editors.  
The authors declare no conflict of interest.