## 3 Results and Discussion
### Analysis of EDEM Simulation Results and Wear Mechanism Investigation  
The EDEM approach was used to simulate the interaction between abrasive particles and five different geometric structured surfaces. In the EDEM post-processing module, the \"geometry bin\" function was used to divide the geometry area (as shown in Figure 10). The particle flow impact area was included in the divided geometry bin. The averaged abraded depth of the divided geometry area was exported. The simulation results are shown in Table 2; it was found that the abraded depth of the conventional smooth surface was the highest, and the average abraded depth reached 1.9766 \(\times\) 10\({}^{-7}\) mm. The average abraded depth of Bionic Type 1 was 1.7221 \(\times\) 10\({}^{-7}\) mm, and the wear resistance performance was better than that of the smooth surface, but worse than the micro-thorn and convex hull coupled structured surfaces. Among the micro-thorn and convex hull coupled structured surfaces, Bionic Type 3 showed the lowest abraded depth, which was 1.5656 \(\times\) 10\({}^{-7}\) mm. It was further proved that among all the test samples, Bionic Type 3 had the best abrasive wear resistance performance. The results obtained from the EDEM simulations generally agreed well with the real scenario experiments. Figure 9: Surface wear patterns of different bionic geometrically structured surfaces. The worn cloud maps of the five different surfaces are shown in Figure 11. For the conventional smooth surface, the wear severity at different positions of this surface were relatively uniform. For Bionic Type 1 of the convex hull surface without micro-thorn, the worn area was concentrated at the edge of the convex hull that faced the particle flow, while the wear severity of other areas was light. For the micro-thorn and convex hull coupled structured surfaces, the worn area was not only concentrated at the edge of the convex hull that faced the particle flow, but also the micro-thorms that showed a certain degree of signs of wear. In the process of the abrasive wear test, the abrasive particles had an impact on the sample surface. As a result, a particle-surface contact system was formed. The movement of a single abrasive particle was not only affected by the geometrical structures on the contact surface, but also the surrounding abrasive particles. The wear mechanism of a particle-surface contact system was related to the abrasive particles group and the movement state of each single of abrasive particle. The sliding behavior of abrasive particles played a fundamental role in the wear of the sample surface. The rolling behavior of abrasive particles on the sample surface could substantially mitigate the wear severity of the sample surface [49; 51]. The movement of abrasive particles on different types of surfaces is shown in Figure 12. When the abrasive particles were in contact with the smooth surface, the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Type of Samples** & **Bionic Type 1** & **Bionic Type 2** & **Bionic Type 3** & **Bionic Type 4** & **Smooth** \\ \hline Averaged wear & 1.7221 & 1.5741 & 1.5656 & 1.6293 & 1.9766 \\ depth/\(10^{-7}\) mm & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Averaged abraded depth. Figure 11: Cloud map of worn surface morphology (the direction of abrasive movement is indicated by the arrow). Figure 10: Geometry bin for analysis divided from geometry region. abrasive particles mainly slid on the surface. Therefore, the smooth surface was subjected to high impact force and cutting force. Therefore, the surface wear was more serious. When the abrasive particles were in contact with the bionic Type 1 surface, the edge of the convex hull geometrical structure that faced the particle flow was firstly hit by an incoming flow of particles. Thus, this area was subjected to severe impact force and cutting force, and resulted in being seriously worn. However, the convex hull geometrical structures could alter the contact condition of the abrasive particles in the particle-surface system.