# Triangular Position Multi-Bolt Layout Structure Optimization
## 3 Results
### Optimized Stress Comparison between Front and Rear Bolts  
The ABAQUS-based simulation design can verify the correctness of the optimal solution selection of the gray wolf algorithm to reduce the stress concentration phenomenon in the structure and thus improve the safety performance of the aerostructure. The stress clouds of the upper nickel steel plate, lower nickel steel plate and bolts before and after optimization are shown in Figures 10-12. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Algorithm** &
\begin{tabular}{c} **Fastest Iteration** \\ **(Generation)** \\ \end{tabular} & **Stable Value** \\ \hline Fruit Fly Optimization Algorithm & 70 & \(-\)42.8195 \\ Particle Swarm Optimization & 77 & \(-\)42.8195 \\ Gray Wolf Optimization Algorithm & 342 & \(-\)42.8195 \\ Multiverse Optimization Algorithm & 315 & \(-\)42.8195 \\ Wind Driven Optimization Algorithm & 150 & \(-\)42.8195 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The number of fastest iterations. Figure 9: Algorithm optimization results. The stress cloud diagram of the nickel steel plate above is shown in Figure 10. In order to make the stress nephogram visually compare the stress change and stress concentration through images, this paper takes the stress extreme value before optimization as the standard and changes the mechanism of the optimized nephogram. Before and after  
Figure 11: Lower nickel steel plate stress cloud. (**a**) Optimized pre-stress nephogram; (**b**) Optimized stress nephogram. Figure 12: Stress clouds for bolt sets in triangular positions. (**a**) Optimized pre-stress nephogram; (**b**) Optimized stress nephogram. Figure 10: Upper nickel steel plate stress cloud. (**a**) Optimized pre-stress nephogram; (**b**) Optimized stress nephogram. optimization, the maximum stress of the nickel steel plate is 304.0 MPa and 230.9 MPa, respectively, and the maximum stress is reduced by 73.1 MPa, with an optimization rate of 24%. A previous study [8] optimized the layout of the bolts on the connection structure based on the improved genetic algorithm, and the results showed that the optimized bolt layout reduces the maximum equivalent stress at corners constructed by 20.4%. In another study [11], the firefly algorithm was used to optimize bolts with double and triple rows, and the results showed that after optimization, the stress around the hole of the plate structure with triple rows of bolts was reduced by about 20%, and the stress reduction effect in this paper was better. [PERSON] et al. [31] adopted the improved genetic algorithm to optimize the equivalent stress of the aviation connection structure under the position of three rows of bolts under severe working conditions. The results showed that the maximum pore circumference stress was reduced by 31.03% under a static pressure load of 30 MPa, while the optimization efficiency only reached 23.36% under severe working conditions. Under the conditions of 15 KN tension and pressure studied in this paper, it is already a serious condition, and the optimization effect of both is the same, which proves the reliability and accuracy of the analysis in this paper. Among them, the stress around bolt hole B decreased significantly after optimization, and the maximum stress value around bolt hole B decreased from 304.0 MPa to 112.1 MPa, with a decrease rate of 63.1%, which greatly reduced the stress around bolt hole B. The stress around bolt hole C before and after optimization is 309.2 MPa and 302.8 MPa, respectively. Bolt hole C was originally the most stressed bolt, and its optimization effect is not obvious. The stress around bolt hole A is increased by 27.9 MPa, mainly because after optimization, the position of bolt hole A is closer to the edge of the nickel steel plate, and the position of concentrated force is closer to the vicinity of bolt A. Figure 11 shows the stress cloud map of the lower nickel steel plate.