Queue-based local scheduling and global coordination for real-time operation control in a container terminal

To maximize the productivity of a container terminal, the operations of various types of equipments should be optimized and synchronized in real time. However, use of optimization techniques such as mathematical programming or search-based meta-heuristics becomes difficult when given a large-scaled problem due to their high computational cost. Addressing this problem, the queue-based local scheduling and global coordination method proposed in this paper stands as a viable alternative. The method consists of the following steps. First, separate schedules are locally generated for each equipment type using a queue-based dispatching heuristic which pays attention to the queue lengths of the quay cranes (QCs) under service. Next, the schedules are executed via a simulation and a notable QC delay is identified. Based on the analysis on the causes of this delay, some compromising adjustments are made to the priorities of relevant jobs. Then, the localized scheduling followed by the adjustment is repeated until the termination condition is met. Adopting simple heuristics in the local scheduling phase, the overall process easily meets the real-time constraint, yet producing an integrated schedule with a better global perspective than the myopic heuristic-only approach.