# Towards a Digital Twin Warehouse through the Optimization of Internal Transport
## 4 Conclusions  
A way to digital twin applied to non-stacking warehouse management by combination of RFID technology and spatial-operational multivariate simulation has been carried out. The warehouse is intended for the storage of recycled bags, and the variables analyzed are the reallocated bags and the forklift time use. All the simulations have been repeated five times, and their computing time is around 117 h. Two logics have been applied, finding that logic S1 provides a more efficient solution with any degree of occupancy, although \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**Reallocated Bags (Units)**} & \multicolumn{4}{c}{**Time of Forklift Use (s)**} \\ \hline Occupancy & 50\% & 55\% & 60\% & 65\% & 70\% & 75\% & 50\% & 55\% & 60\% & 65\% & 70\% & 75\% \\ Layout & & & & & & & & & & & & \\ \hline
3 \(\times\) 3 & 173 & 194 & 2206 & 233 & 258 & 285 & 41,236 & 42,805 & 44,292 & 46,026 & 47,184 & 48,815 \\
3 \(\times\) 4 & 175 & 208 & 229 & 251 & 276 & 290 & 41,443 & 43,705 & 45,357 & 46,409 & 48,435 & 48,806 \\
4 \(\times\) 3 & 101 & 112 & 126 & 141 & 157 & 175 & 32,866 & 34,120 & 34,480 & 36,145 & 36,465 & 38,554 \\
3 \(\times\) 5 & 186 & 214 & 234 & 263 & 283 & **308** & 41,546 & 44,444 & 45,380 & 47,367 & 48,669 & **49,807** \\
5 \(\times\) 3 & 59 & 71 & 85 & **93** & **106** & **117** & 29,727 & 30,096 & 31,154 & 32,034 & **32,467** & **33,854** \\
4 \(\times\) 4 & 109 & 121 & 140 & 157 & 169 & 33,155 & 34,818 & 351,956 & 36,987 & 37,361 & \\
3 \(\times\) 6 & **197** & **223** & **251** & **279** & **297** & **42,708** & **44,798** & **46,203** & **48,587** & **50,037** & \\ Layouts & 5 \(\times\) 4 & 65 & 82 & 94 & 104 & & 29,363 & 30,798 & 31,983 & **31,947** & \\
4 \(\times\) 5 & 119 & 131 & 153 & 166 & & & 34,327 & 34,820 & 36,414 & 37,029 & \\
4 \(\times\) 6 & 125 & 137 & 157 & & & 35,328 & 35,228 & 36,612 & & & \\
6 \(\times\) 3 & **41** & **50** & **51** & & & **27,177** & **28,047** & **28,375** & & \\
5 \(\times\) 5 & 77 & 91 & 101 & & & 30,067 & 31,488 & 31,858 & & & \\
5 \(\times\) 6 & 84 & 98 & & & & 30,763 & 31,355 & & & & \\
6 \(\times\) 4 & 43 & 55 & & & & 27,256 & 28,419 & & & & \\
6 \(\times\) 5 & 52 & & & & & 28,216 & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Reallocated bags and time of forklift use in layouts with different equivalent occupancies. the differences with respect to logic S2 are reduced when this occupancy rate increases. In addition, the time of use of the forklift follows a similar pattern. The results of the simulations indicate that for occupancy rates below 65%, the 6 \(\times\) 3 configuration is recommended. Moreover, this layout has provided fewer reallocated bags and, consequently, shorter forklift usage times. However, its reverse configuration, 3 \(\times\) 6, is the least recommended. As storage capacity increases, the number of viable designs decreases, being those with the greatest number of \"transverse zones\" and the least number of \"longitudinal zones\" as the most suitable. With storage requirements greater than 80%, the number of available alternatives is greatly reduced. The integration of internal transport with warehouse management indicates that the maximum use of space does not lead to an improvement in internal movements, which implies that a digital warehouse would facilitate its management. As future work, several immediate lines are open, completing the transition to the digital twin in this particular warehouse by connecting to the physical system and integrating this system with the maintenance management and manufacturing execution systems (MES), all of which could be studied to continue progressing towards Industry 4.0. Conceptualization, J.S.F.-C.; methodology, J.S.F.-C.; software, J.S.F.-C.; validation, J.S.F.-C. and R.D. ; formal analysis, J.S.F.-C. and R.D. ; investigation, J.S.F.-C.; resources, J.S.F.-C. and R.D; data curation, J.S.F.-C.; writing--original draft preparation, J.S.F.-C. and R.D. ; writing--review and editing, J.S.F.-C. and R.D. ; supervision, R.D.