# Multi-Level Site Selection of Mobile Emergency Logistics Considering Safety Stocks
## 4 Analysis of Examples
### Result Analysis  
The coordinates of mobile emergency facilities in 148 counties and districts were selected in Sichuan and Chongqing. The emergency logistics centers were chosen using the improved immune optimization algorithm. As shown in Figure 6, two logistics centers were deployed in Jinniu District, Chengdu and Hechuan District, Chongqing. Distribution warehouses were selected among the alternative sites in the remaining districts and communities. Materials were transported to the distribution warehouses through the logistics centers. The relationship between the affinity value, solution time, and the number of warehouses is shown in Figure 7.  
An increase in the number of warehouses will increase the level of mobile emergency logistics. Affinity decreases as the number of warehouses increases. Still, the affinity curve decreases with the increase in the number of warehouses, slows down significantly, and  
Figure 6: Emergency logistics center site selection map. Figure 7: Folding line diagram of growth site selection for distribution storage silos. levels off around the number of warehouses equal to 18. Due to the intelligent optimization algorithm, the solution time becomes longer as the number of allocated storage points increases. The solution time also fluctuates occasionally as the number of allocated storage bins increases. Generally speaking, the higher the safety stock coefficient of the distribution warehouse, the larger the safety stock is. The larger the safety stock, the lower the transit cost. The statistics of the number of emergencies at all levels in the last 20 years in all districts and counties of Sichuan and Chongqing are shown in Table 5 and plotted as shown in Figure 8.  
Level 1 to 4 emergencies have approximately the same probability of occurring in each region. Each region's safety stock factor assignment is based on a summary of the number of emergencies. The safety stock coefficients were assigned to four intervals (0.2, 0.3, 0.4, 0.5) for the total number of emergencies in the last 20 years (0-16, 17-30, 31-45, 46-70). The number of warehouses is equal to 18. Warehouses in each region are assigned safety stock coefficients according to Table 4 for site selection. The results of the warehouse sitting are shown in Figure 9. In summary, further analysis leads to the following:  
Figure 8: Folding line chart of emergency statistics by county in Sichuan and Chongqing in the past 20 years. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Number** & **Political Districts and Counties** & **Level 1** & **Level 2** & **Level 3** & **Level 4** & **Total** \\ \hline
1 & Jingyang & 5 & 8 & 10 & 15 & 38 \\
2 & Mianzhu & 3 & 5 & 7 & 11 & 26 \\
3 & Luojiang & 2 & 4 & 6 & 9 & 21 \\
4 & Zhongjiang & 4 & 7 & 9 & 14 & 34 \\
5 & Guanghan & 6 & 9 & 11 & 16 & 42 \\ \(\cdots\) & \(\cdots\) & \(\cdots\) & \(\cdots\) & \(\cdots\) & \(\cdots\) \\
155 & Wushan & 1 & 3 & 5 & 7 & 16 \\
156 & Wuxi & 1 & 3 & 5 & 7 & 16 \\
161 & Fuling & 1 & 3 & 5 & 7 & 16 \\
162 & Shijiazhuang & 1 & 3 & 5 & 7 & 16 \\
163 & Wanzhou & 1 & 3 & 5 & 7 & 16 \\
164 & Tongnan & 1 & 3 & 5 & 7 & 16 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Frequency of emergencies in Sichuan and Chongqing in the past 20 years. Based on the above site selection results, the relationship between inventory, transshipment, and total costs is measured by adjusting the safety factor, as shown in Figure 10.  
Figure 10: Safety stock factor contingency logistics cost chart. Figure 9: Site selection map of distribution and storage silos. Inventory costs include contingency and safety inventory costs, and transshipment costs include horizontal and vertical transportation costs. In general, inventory costs become higher as the safety stock factor increases. Transit costs decrease as the safety stock factor increases. The total cost of emergency logistics is mainly affected by transshipment costs. Total emergency logistics costs increase with the rise in the safety stock factor.