## 3 Results and Discussion of RSM Experiments  
### Plackett-Burman Design and Significance Analysis  
The Plackett-Burman experimental design was employed to identify statistically significant factors influencing the repose angle of wheat straw feed, a key response variable in discrete element method (DEM) simulations [21]. By comparing the effects of each factor at two levels--minimum (\(-1\)) and maximum (\(+1\))--non-significant parameters were systematically eliminated to enhance the accuracy of material calibration. Seven contact parameters, including interparticle friction coefficients and JKR surface energy, were selected for evaluation, with their respective ranges detailed in Table 5.  
The experimental matrix and results (Table 6) demonstrate the efficacy of this screening approach in isolating critical factors governing particle interactions. Parameters exhibiting negligible impact on the repose angle (e.g., rolling friction coefficients) were excluded from subsequent optimization, streamlining the calibration process. This rigorous methodology ensures that DEM simulations prioritize parameters with measurable influence on bulk material behavior, aligning computational models with empirical observations of wheat straw dynamics. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value/Range** \\ \hline
**Wheat straw feed** & \\ Density (kg/m\({}^{3}\)) & 45.82 \\ Poisson’s ratio & 0.3 \\ Shear modulus (MPa) & 1 \\ \hline
**Steel plate** & \\ Density (kg/m\({}^{3}\)) & 7850 \\ Poisson’s ratio & 0.3 \\ Shear modulus (GPa) & 75 \\ \hline
**Inter-particle interactions** & \\ Coefficient of restitution (straw–straw) & 0.25–0.33 \\ Static friction coefficient (straw–straw) & 0.46–0.62 \\ Rolling friction coefficient (straw–straw) & 0.14–0.29 \\ Coefficient of restitution (straw–steel) & 0.41–0.54 \\ Coefficient of restitution (straw–steel) & 0.43–0.53 \\ Rolling friction coefficient (straw–steel) & 0.11–0.27 \\ JKR surface energy (J/m\({}^{2}\)) & 0.01–0.11 \\ \hline \hline \end{tabular} Notes: This table divides the parameters into three parts: the first part being the wheat straw feed parameters, the second part the steel plate parameters, and the third part the inter-particle interaction parameters.  
\end{table} 
Table 4: DEM simulation parameters for the repose angle of wheat straw particles. Figure 8: Stacking-angle simulation test. (**a**) Feed dispersal process; (**b**) feed dispersal process. The experimental results were subjected to Analysis of Variance (ANOVA) using Design-Expert 13 software to evaluate the significance of contact parameters, with outcomes summarized in Table 7.  
As demonstrated in Tables 2-7, the rolling friction coefficient between wheat straw feed particles exhibited a highly significant impact (\(p\)! 0.01) on the simulated repose angle, emphasizing its critical role in governing particle rearrangement and energy dissipation. The JKR surface energy (\(0.05<p<0.1\)) and the static friction coefficient between wheat straw feed and steel plates (\(0.05<p<0.1\)) showed moderate significance, indicating their measurable contributions to particle-substrate interactions and cohesive agglomeration. Conversely, all remaining parameters (\(p>0.1\)) demonstrated negligible effects on the repose angle, validating their exclusion from subsequent calibration steps to streamline computational efficiency.