# Switch-Off Policies in Job Shop Controlled by Workload Control Concept
## 5 Simulation Environment  
The performance of the proposed switch-off policies is compared with the always-on model. The simulation model has the same characteristics as previous work proposed in the literature [27; 28]; Table 2 reports the model characteristics for the simulations conducted. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Switch-Off Policy** & **Off Condition Machine \(m\)** & **On Condition Machine \(m\)** \\ \hline
**Policy 1** & Queue\({}_{m}=0\) & Queue\({}_{m}=1\) \\ \hline
**Policy 2** & WL\({}_{m}<\) Threshold\({}_{1}\) & Queue\({}_{m}=1\) \\ \hline
**Policy 3** & WLmod\({}_{m}<\) Threshold\({}_{2}\) & Queue\({}_{m}=1\) \\ \hline
**Policy 4** & WLmod\({}_{m}<\) Threshold\({}_{3}\) & WLmod\({}_{m}>\) Threshold\({}_{4}\) \\ \hline
**Policy 5** & WL\({}_{m}<\) Threshold\({}_{5}\) & WL\({}_{m}>\) Threshold\({}_{6}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Switch-off policies investigated. \begin{table}
\begin{tabular}{c c} \hline \hline Number of machines & 6, including 1 bottleneck \\ \hline Inter-arrival & EXPO (0.642) \\ \hline Number of operations & Discrete Uniform [1; 6] \\ \hline Due date & (total processing time) \(\times\) Uniform [5; 10] \\ \hline Processing times, no bottlenecks & 2-Erlang with mean 1 \\ \hline Processing times bottlenecks & 2-Erlang with mean 1.15 (utilization about 90\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Model characteristics. The job shop consists of 6 work centers/machines with 1 bottleneck; the processing time of machines that have no bottlenecks follows a 2-Erlang distribution with a mean of 1 and a mean of 1.15 for the bottleneck to lead to an average utilization of 90%. The job's arrival follows an exponential distribution with a parameter of 0.642. The routing of the jobs is random, without any preferential sequence, with the number of operations extracted by a discrete uniform between 1 and 6. Due date is assigned to each job, considering the total processing time multiplied by a parameter extracted by a uniform distribution. Finally, the simulation length is 25,000 h.  
The simulation model described above was developed using the software package SIMUL(r) (version 29.0). Simul8 is a computer package for Discrete Event Simulation to simulate and model a wide variety of manufacturing systems, such as production lines, job shops, robotics cells, assembly systems, and complex product flows. The simulations conducted by SIMUL8 provide a series of statistics on the main performance measures of the manufacturing system tested. The effects of the power in the three states (idle, stop, and warm-up) of the machines and the warm-up time are considered to evaluate the proposed switch-off policies. The power of the work state is fixed because the objective is to evaluate the relation between the power in the work state and the other states. In detail, 3 values for the warm-up time are considered, 0.2, 0.4, and 0.6, which correspond to 20%, 40%, and 60% of the mean processing time of the machines. Table 3 shows the power cases evaluated for the states of work, idle, stop, and warm-up of the machines. The experiments concern 6 models (benchmark and 5 switch-off policies), 9 cases of power values, and 3 warm-up times, with a total of 162 cases. The simulations are repeated for several values of the thresholds (see Table 1) to obtain results similar to policy 1 proposed in the literature. For each class of experiment, a series of replicates were carried out capable of ensuring a confidence interval of 5% and 95% of the confidence level for each performance measure. Each combination of the experimental class features over 2000 replicas and approximately 6 h of computation time (4 GHz Intel Core i7 and 8 Gb RAM).