## 4 Empirical Examples
### Results and Discussion  
The simulation results under PERT network schedule of this case and the simulation results including various combinations of different elements under DBR scheduling technique is shown in Figure 4. The data comparison of a variety of simulation results obtained by different progress planning methods are shown in Table 2.  
The expected duration in the project progress network diagram is 1211.63 days, but uncertainty of duration in the network schedule in terms of PERT schedule technique is as high as 33.56 days (SD. 33.56 days, Min. 1092.29 days, and Max. 348.92 days). Additionally, when the DBR technology is applied in PERT network diagram, compared to the traditional PERT network technology, drum technology reduces the expected project completion time by 2.68 percent (31.59 days), while the uncertainty of the project completion duration has decreased by 3.8 days (SD. 29.76 days, Min. 1083.51 days, Max. 1288.12 days). Application of buffer technology in projects increases the average completion time by 6.03% (73.01 days), but the degree of uncertainty of the project completion period has decreased by 16.78 days (SD. 16.78 days, Min. 1220.30 days, Max. 1344.39 days). Similarly, the application of rope technology also increases the average completion time of the project, and the rate of increasing was 1.27% (15.44 days), but the uncertainty of project completion period has decreased by 6.97 days (SD. 26.59 days, Min. 1132.12 days, Max. 1322.37 days). When putting two of schedule control elements into the traditional PERT project schedule network diagram, drum-buffer technology increases the expectations of the project completion time, the rate of increasing was 3.59 % (43.52 days), but uncertainty of project completion period has decreased by 22.16 days (SD. 11.40 days, Min. 1213.72 days, Max. 1303.21 days). Drum-rope technology reduces the average completion time of the project 1.27% (15.44 days), while the uncertainty of completion period reduces 10.45 days (SD. 23.11 days, Min. 1117.47 days, Max.1271.83 days). Buffer-rope technology reduces the average completion time of the project 1.91% (23.17 days), while the uncertainty of completion period reduces 24.38 days (SD. 9.18 days, Min. 1152.89 days, Max. 1216.75 days). As for the comparison between drum-buffer-rope and traditional PERT schedule technology, the DBR reduces the average completion time of the project 2.6% (27.38 days), while the uncertainty of completion period reduces 25.64 days (SD. 7.92 days; Min. 1156.38 days; Max. 1212.46 days). Observing the comparison chart of completion period distribution of various project schedule network simulation under different combinations (Figure 5), and comparison \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Number**} & **Control** & **Average** & \multirow{2}{*}{\begin{tabular}{c} **The Most** \\ **Completion** \\ **Period** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **The Most** \\ **Optimistic** \\ **Completion** \\ **Completion Time** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **The Most** \\ **Pessimistic** \\ **Completion Time** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Uncertainty** \\ **Reducing Compared** \\ **with PERT** \\ \end{tabular} } \\ \hline
1 & PERT & 1211.63 & 33.56 & 1092.29 & 1348.92 & - \\
2 & drum & 1180.04 & 29.76 & 1083.51 & 1288.12 & 3.8 \\
3 & buffer & 1284.64 & 16.78 & 1220.30 & 1344.39 & 16.78 \\
4 & rope & 1227.07 & 26.59 & 1132.12 & 1322.37 & 6.97 \\
5 & drum-buffer & 1255.15 & 11.40 & 1213.72 & 1303.21 & 22.16 \\
6 & drum-rope & 1196.19 & 23.11 & 1117.47 & 1271.83 & 10.45 \\
7 & buffer-rope & 1188.46 & 9.18 & 1152.89 & 1216.75 & 24.38 \\
8 & drum-buffer-rope & 1184.25 & 7.92 & 1156.38 & 1212.46 & 25.64 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison table of simulation uncertainty of various combinations. Figure 4: Simulation results under different combinations.