A Bi-objective green tugboat scheduling problem with the tidal port time windows

Tugboat assistance is essential when large ships are berthing and unberthing, and requires ports to produce efficient tugboat schedules considering various constraints. Few studies optimize tugboat scheduling from multiple vectors simultaneously, however. This paper thus constructs a bi-objective, mixed-integer linear programming, green tugboat scheduling model in order to minimize the maximum completion time and total fuel consumption, which improves port service levels, decreases tugboat company operating expenditures and thus environmental pollution emissions. The proposed model also considers the time window characteristics of the tidal port. We use the non-dominated sorting genetic algorithm II (NSGA-II) framework integrating the characteristics of tugboat scheduling to solve the model. Finally, we make a case study about Guangzhou Port to validate the model and the algorithm via a comparison of results solved by NSGA-II and CPLEX solver. The Pareto fronts obtained show the trade-off relationship between the two objectives, and provide a basis for port tugboat scheduling plans.