2010년 대한산업공학회/한국경영과학회 춘계공동학술대회
A Simulation Study for Evaluating Multi-lifting Operations by Quay Cranes Vu Duc Nguyen and Kap Hwan Kim* Department of Industrial Engineering, Pusan National University Busan, South Korea Tel.: +82-51-510-2419. Fax: +82-51-512-7603 Email:
[email protected] and
[email protected] *
Corresponding author
Abstract The capacities of containerships have been increased recently up to 15,000 TEU (Twenty-foot Equivalent Unit) and even larger. Therefore, it makes efficient ship operation be more challenging for operators of modern container terminals. This paper analyses the effect of multi-lifting operations by quay cranes on the productivity of ship operation for various sizes of ships. Types of operations by quay crane considered includes single, tandem, and triple lifts. Simulation model was developed and run to evaluate and analyze the performance measures such as the completion time of ship operation and the quay crane productivity. Keywords: container terminal, quay crane operation, containership size, simulation.
1. Introduction Nowadays, because of the globalization of economy, the demand of cargos transportation between countries has been increased rapidly since the last decade. For the cost-effective transportation, containerships have been used to transport cargos among port container terminals. The capacity of containership has been increased recently up to 15,000 TEU and even larger. Thus, the seaport container terminals become to have more opportunities and challenges. The governments of many countries such as Korea, China, Hong Kong, and Singapore have recognized the importance of the development of seaport container to meet the increasing demand of transferring containers. The most important issue in container terminals is how to reduce the turnaround time of ships by speeding up the ship operation. The ship operation consists of unloading and loading operations, which transport containers between vessels and the storage yard. In this paper, three main types of equipment in container terminals, such as quay cranes (QCs), vehicles, and yard cranes (YCs), are used for ship operations. Nowadays, there are various types of handling equipments investigated for improving the ship operation in container terminals. This paper considers the multi-lifting operations by QCs, which are capable of transferring up to six 20-ft containers or three 40-ft containers. A triple-lift QC is shown in Figure 1. Recently, some modern container terminals have applied the multi-lifts by QCs to improve the
ship operation. Therefore, with such multi-lifting operations, the ship operations for large-sized vessels can be speeded up in order to reduce the turnaround time of the vessels. During an unloading operation, up to three 40-ft containers are picked up by a triple QC and put onto the vehicles and waiting under the QC in the apron. Next, vehicles deliver the containers to the storage yard. In the yard, the vehicles arrive at a transfer point (TP) of the yard. Then, a YC picks up and stacks it in an empty slot in a bay. A loading operation is performed in the reverse order of the unloading process. Figure 1 illustrates the layout of a seaport container terminal which consists of quay, vehicle driving, and yard area. Researches on the development of the simulation models of container terminals have been published for a long time (Cho 1985; Jang & Park 1988; Kim 1988; Ramani 1996; Yun & Choi 1999; Tahar & Hussain 2000; Saanen 2004). Hartmann (2004) introduced an approach for generating scenarios that can be used as input data for the simulation models of port container terminals. Simulation is a suitable and powerful tool for evaluating the performance of container terminals in detail level. This paper develops a simulation model for analyzing the effects of multi-lifting operations by QCs on the productivity of ship operation for ships of various sizes. The types of operations by QCs considered in this paper are single, tandem, and triple
2010년 대한산업공학회/한국경영과학회 춘계공동학술대회
lifts operations. This paper is organized as follows. The ship operations with multi-lifting operations by QCs are introduced in section 2. Section 3 introduces some results of simulation experiments for evaluating the effects of multi-lifting operations by QCs on the productivity of ship operation for ships of various sizes. Finally, section 4 discusses some conclusion remarks.
Figure 1: A QC with triple-lift capability.
may be allowed among all the loading and the unloading operations. When the vessel actually arrives, ship operations are usually performed on the basis of the sequence list of loading and discharging. In this study, various types of operations by QCs are illustrated in Figure 3. Figure 3c illustrates the triple lifts by QCs. In this figure, there are six possible combinations of triple lifts, lifting up to three 40-ft containers or six 20-ft containers. For tandem lifts, two 40-ft containers or four 20-ft containers can be lifted simultaneously (Figure 3b). While single lifts can only handle one 40-ft container or two 20-ft containers (Figure 3a). The ability of tandem or triple lift to handle a larger number of containers than the single lift is expected to enhance the efficiency of the ship operations in container terminals. Recently, because the size of ship becomes larger and larger up to 15,000 TEU, the time that a ship stays at the berth for the ship operation becomes longer and longer. In order to speed up the ship operation, the multi-lifting operations by QCs are used in many practices. The effects of the multi-lifting operations by QC on the ship operation for various sizes of ships are analyzed by a simulation study.
(a) Single lifts.
(b) Tandem lifts.
(c) Triple lifts. Figure 3: Various types of multi-lifting operations by QCs.
3. Simulation Experiments 3.1. Simulation Modeling
Figure 2: Layout of a seaport container terminal.
2. Ship Operation with Multi-lifting Operations by QCs Before a vessel arrives at a port container terminal, a sequence list of the unloading and loading operations for individual containers is prepared. In most of the stowing plans, a percentage of tandem and triple lifts
In this section, the operation of a container terminal was modeled in detail. When a ship arrives, it is assigned to a berth if there is an available berth for the ship. Otherwise, the ship must wait until a berth becomes available. When the ship enters a berth, 2-6 QCs are assigned to the ship. An unloading and loading sequence is then generated for each QC. By referring to the specified sequence, QCs can start to unload and load containers. Four to seven vehicles are usually assigned to each QC to transport containers between the quay and
2010년 대한산업공학회/한국경영과학회 춘계공동학술대회
the yard. All QCs share all vehicles together, that is, a pooling strategy is used to dispatch vehicles. The operation scenario modeled in the simulation program is described below. At the quay side, QCs unload or load containers only when vehicles are available under QCs. When a vehicle arrives at a designated QC, it must wait for either pickup or drop-off of a container by a QC. At the yard side, a vehicle first arrives at a transfer point (TP) at a side of the block. The vehicle waits for a YC to pick up an inbound container or release an outbound container. When a vehicle finishes transporting a container, it returns to a parking area to await the next assignment. For loading, a YC picks up a loading container from a specified slot in the yard. For unloading, when a YC receives an inbound container from a vehicle, it stacks the container in a slot in the yard. The loading and unloading operations continue until all containers are transferred between the ship and the storage yard. When all operations are completed, the ship leaves the berth. The simulation model developed may be described as follows. The layout of a hypothetical container terminal is shown in Figure 2. The wharf has one berth and three QCs. The yard consists of six storage blocks; two YCs of the same size are deployed to each block. Each block has TPs on which YTs can wait for transferring containers. The total number of vehicles in the system is 24. The travel times of YTs between pickup and drop-off points are assumed to be constant, and traffic congestion for YTs in driving lanes is not considered. To test the effect of the multi-lifting operations by QC as shown in Figure 3, various combinations of the multi-lifts are used in simulation experiments. In simulation experiments, the percentage of multi-lifts by QC ranged from 0 to 40%. The size of vessel varied from 1,000 TEU to 8,000 TEU. Additional, in respect of the number of containers transferred per each multi-lifting operation by QCs, the total average number of containers per move is considered as a parameter in the experiments, which ranged between 1.0 and 1.4. The ratio of the number loading operations to the number unloading operations by multi-lifts varied from 0.85 to 1.10. The performance measures considered in the simulation experiments were the completion time of the ship operation and the throughput rate of QCs.
increased. The improvements in the completion time increased from 4.19% to 12.91% when the percentage of multi-lifts increased from 10% to 40%.
Figure 4: Effects of the multi-lifting operations by QCs on the completion time of vessel.
Figure 5: Effects of the multi-lifting operations by QCs on the QC throughput.
3.2 Simulation Results and Analyses Figures 4-5 show the effects of the multi-lifting operations by QCs on the completion time of vessels and QC throughput rate. From the results shown in Figure 4, it was found that the completion of vessels reduced rapidly as the multi-lifting operations
Figure 6: Effects of the total number of vehicles on the QC throughput.
2010년 대한산업공학회/한국경영과학회 춘계공동학술대회
Figure 5 shows that the QC throughput rate increased rapidly when the percentage of the multilifting operations by QCs increased. In Figure 6, the QC throughput rate increased as the total number of vehicles deployed to the ship operation increased. When the total number of vehicles reached about 30, the changing rate was reduced. In general, the terminal operations depend on not only operation of quay side, but also the other operations, such as vehicle operation. However, from the results as shown in Figure 6, when the total number of vehicles was sufficient to support the vessel operation, the increase of total number of vehicles did not make any improvement in the QC throughput. Figure 7 illustrates the effects of the average number of containers per move on the completion time of vessels. Obviously, the completion time of vessels reduced rapidly as the average number of containers per move increased. However, the reduction in the completion time of vessels (19.60%) was about a half of the increase of the average number of containers per move (40%). Figure 8 shows the effects of the number of containers per move on the average waiting time of QCs and vehicles at quay side. The results show that the average waiting time of vehicles reduced as the number of containers per move increased. The average waiting time of QCs increased rapidly as the number of containers per move increased. This means that vehicles cannot meet the requirements on arrival times because of high productivity of QCs. When the number of containers per move increased from 1.0 to 1.4, the average waiting time of QCs increased from 0% to 70.80%.
operation always takes more time to handle than the loading operation because of difficulties of management of vehicles. The reduction in QC throughput increased from 0% to 6.05% as the ratio of the number loading operations to the number unloading operations increased from 0.85 to 1.10.
Figure 8: Effects of the number of containers per move on the average waiting time of QCs and vehicles at quay side.
Figure 9: Effects of the ratio of the number of loading operations to the number of unloading operations on the QC throughput.
4. Conclusions
Figure 7: Effects of the average number of containers per move on the completion time of vessel Figure 9 shows that the increase in the ratio of the number loading operations to the number unloading operations slows down the speed of QC operation. It comes from the fact that the loading
This paper discusses the effects of multi-lifting operations by QCs on the productivity of the ship operation for ships of various sizes. The types of operations by QC considered are single, tandem, and triple lifts. A simulation model was developed to evaluate and analyze the performance measures of the completion time of the ship operation and the quay crane productivity. From the simulation results, it can be concluded that the multi-lifting operations by QCs affected the completion time of vessels. The QC
2010년 대한산업공학회/한국경영과학회 춘계공동학술대회
throughput rate increased rapidly as the percentage of multi-lifting operations by QCs increased. In addition, the completion time of vessel reduced rapidly as the average number of containers per move increased. However, the reduction in the completion time of vessel was about a half of the increase of the average number of containers per move. When the number of containers per move increased, the average waiting time of vehicles reduced and the average waiting time of QCs increased rapidly. The QC throughput rate decreased by the increase of the ratio of the number loading operations to the number unloading operations, because the loading operation always takes more time to handle than the unloading operation. This study only evaluated the effects of QC operations. Moreover, the operations of YCs and YTs should also be considered in a further extension of this study.
Acknowledgments This study was supported by the Korean Ministry of Education & Human Resources Development through the Regional Research Centers Program (Research Center for Logistics Information Technology).
References Cho, D.W. (1985) A computer simulation model for container terminal systems, Journal of the Korean Institute of Industrial Engineers, 11, 173–187. Hartmann, S. (2004) Generating scenarios for simulation and optimization of container logistics, OR Spectrum, 26, 171–192. Jang, S. Y. and Park, J. W. (1988) Determination of container terminal operating system using computer simulation, IE Interfaces, 1, 49–62. Kim, H. (1988) A systematic analysis on the operation of Busan container terminal by computer simulation. Master Thesis. Busan, South Korea: Korea Maritime University. Ramani, K. V. (1996) An interactive simulation model for the logistics planning of container operations in seaports, Simulation, 66, 291–300. Saanen, Y. A. (2004) An approach for designing robotized marine container terminals. Ph. D. Thesis. Delft, The Netherlands: Delft University of Technology. Tahar, R. M. and Hussain, K. (2000) Simulation and analysis for the Kelang container terminal operations, Logistics Information Management, 13, 14–20. Yun, W.Y. and Choi, Y.S. (1999) A simulation model for container-terminal operation analysis using an object-oriented approach. International Journal of Production Economics, 59, 221–230.
