Abstract
This paper studies a complex parallel scheduling problem with non-crossing constraint, sequence dependent setup times, eligibility restrictions, and precedence relationships motivated by reclaimer scheduling in dry bulk terminals. In a stockyard of any dry bulk terminal, stockpiles are handled by reclaimers. Therefore, improving the operational efficiency of reclaimers is critical for the overall performance of these terminals which are struggling with increasing workload. We study the variants of this problem with and without stacking operations. For each variant, we present a lower and an upper bound. A strong lower bound is obtained by relaxing the non-crossing constraint and solving the resulting problem to the optimality. While this relaxation still addresses a challenging scheduling problem, proposed arc-time-indexed formulation copes with the instances of practical size. We develop a novel constraint programming formulation to provide an upper bound for the problem. Computational experiments show this robust approach is able to generate near-optimal schedules for different stockyard configurations within a minute.
Highlights
Bulk terminals are seaside facilities in which agricultural products and natural resources are stored and transshipped in very large volumes
To provide an upper bound for the problem, we propose a novel constraint programming formulation
This paper presents an effective lower and upper bound for reclaimer scheduling problem which is a variant of parallel machine scheduling problem (PMSP) with non-crossing constraint, sequence dependent setup times, eligibility restrictions, and precedence relationships
Summary
Bulk terminals are seaside facilities in which agricultural products and natural resources are stored and transshipped in very large volumes. After finishing the reclaiming of a stockpile, a reclaimer travels along the rail track to go to the area where its scheduled task is stacked (sequence dependent setup times [4]). We develop an arc-time-indexed mixed integer programming formulation as a relaxation of the considered problem This formulation provides a strong lower bound by solving the PMSP with sequence dependent setup times and eligibility restrictions to the optimality. This formulation allows the accurate evaluation of non-exact solution approaches for RSP, and provides an effective solution to a challenging scheduling problem with a practical relevance.
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