5. Results and discussion
The mathematical model was solved using GAMS software
(CPLEX solver) version 24.3.3 on a computer with 2.60 GHz Intel
i5 processor and RAM 8.0 GB 64-bit. For all scenarios, the solved
MIPs contain 7720 constraints and 28,039 variables among which
there are 448 binary variables and 10 discrete variables. The computational
time for the base case is 10.81 s.
The solution is graphically presented in Figs. 2 and 3, which
represents the location of the inspection centers and remanufacturing
plants as well as the materials’ flow in the base case at the
beginning and end of the planning horizon. The detailed solution of
the base case is included in Table 1, which demonstrates at which
time period an inspection center or remanufacturing plant was
opened and the capacity level of the installed module (denoted
by ‘High’ or ‘Low’). Furthermore, Table 2 shows the number of
purchased trucks, as well as economic parameters at each time
period.