Heuristic Methods for the Unrestricted Dynamic Container Relocation Problem

In this work, we address the unrestricted Dynamic Container Relocation Problem (DCRP). The DCRP is an extension of the Container Relocation Problem (CRP) that is NPhard. The CRP aims to empty a single yard-bay, which contains containers with a given retrieval sequence from the yardbay, such that the total number of relocations is minimized. The DCRP extends the CRP so that containers both arrive and depart at the yard-bay. The unrestricted DCRP relaxes a common assumption which enforces container relocations are performed only to retrieve containers that needs to leave the yard-bay. A mathematical formulation is suggested for the unrestricted DCRP. Then, three efficient heuristic methods are offered. An extensive set of computational experiments is performed on standard test instances. Our results indicate that savings can be achieved by using the suggested heuristic methods.