A decomposition-based approach to the scheduling of identical automated yard cranes at container terminals

In today’s ports, the storage area is often the bottleneck in the serving of a vessel. It is therefore an important influencing factor in the minimization of the turnaround time of the vessels, which is the main objective in operational planning in container terminals. The operational planning of the yard cranes strongly impacts the yard’s efficiency. This planning task comprises the assignment of jobs to cranes, the sequencing of jobs per crane and the scheduling of crane movement and job executions subject to time windows and precedence constraints. A common yard configuration is a block storage system with two identical automated gantry cranes, called twin cranes. These cranes are subject to non-crossing constraints and therefore often exclusively serve either the landside or the seaside of the terminal. A polynomial-time algorithm for the scheduling subproblem of the cranes is introduced. As the sequencing and assignment part of this planning task is NP-hard, the overall problem is solved heuristically with a branch and bound procedure that includes the introduced scheduling algorithm as an evaluation subroutine. A computational study is presented to test the performance of this approach against a mathematical program solved by CPLEX.