Evaluating the Performance of a Loading-and-Unloading Operations System with an Imbalanced Workload Layout Via a Two-Node Closed Queueing Network Model

Abstract

Imbalanced workloads commonly occur in container terminal loading and unloading operations and significantly affect terminal performance. However, little is reported in the literature about terminal performance under this imbalanced workload setting. In this paper, we study the performance of operations in a container vessel bay with imbalanced yard crane workloads under the quay crane double cycling and mixed storage strategies. To address this problem, we develop a two-node closed queueing network to model the interactions between yard trucks and the equipment using the yard truck pooling rule. This model measures imbalanced workload using probabilities that a truck is assigned to a yard crane. Our proposed model can be flexibly applied to different loading-and-unloading processes and yard truck assignment rules. We develop Markov chain formulations and a simulation framework to compute the resulting model with equipment service times following exponential and general distributions, respectively. We show that the imbalanced workload layout at the yard side can cause a large reduction in throughput. Fortunately, for approximately 50% of the types of imbalanced workload layouts, the resulting performance reduction can be effectively mitigated by applying the yard truck pooling rule. Our proposed model and method are practical and efficient for evaluating the performance of a workload-sensitive terminal handling system.

Keywords: Terminal performance evaluation, closed queueing networks, Markov chain, numerical simulations