| Abstract: | How quay cranes (QC) are scheduled is vital to the productivity of seaside container port operations. Double cycling concept is an operation strategy of loading the containers into ships as they are unloaded, thus improving the efficiency of a QC as well as the container port. Goodchild and Daganzo (Transp Sci 40(4):473–483, 2006) first described QC double cycling problem and solved the problem after formulating it into a two machine flow shop problem. Song (Port Technol Int 36:50–52, 2007) studied the formula to determine the optimal starting sequence for double cycling while reflecting on the practical issue of QC working direction. The above studies focused on a single QC double cycling and their empirical trials showed the double cycling could improve the productivity of each QC approximately by between 10 and 20 %. In Zhang and Kim (Comput Ind Eng 56(3):979–992, 2009), a multiple QC double cycling model was first suggested by formulating a mixed integer programming model to maximise the number of double cycles between multiple QCs. In the present paper we point out a flaw with the existing multiple QC double cycling model that lets cycles that are not implementable. In addition, the paper discusses the need for imposing constraints arising from real world requirements to the formulations aiming at double cycling. |
