Simulation model for stacking area
۳. Simulation model for stacking area
3.1 Introduction
Since port operations in a container terminal are costly and complicated, simulation models have been used to test different terminal process. Simulation models are used for both process designing and decision making in container terminals. The purpose of simulation in this study is to assess operational and idle time of equipments in two layouts with vertical and horizontal stacks. Three kinds of operational scenarios are generally considered for container terminals, i.e. unloading, loading and combined unloading and loading. This article simulation model focuses solely on loading process.Yard layout determines the routing and route network of the terminal. A poor layout will have its effect on transfer cycle and other aspects of terminal. In this study we present a simulation model using "Show flow" software covers 3 cycles of the container terminal operation namely Quay Cranes (QCs), Rubber tyred Gantry cranes (RTGs) and Trucks.
3.2 Layouts
Anzalis' port dedicated space for stacking area is about eight hectare. Before moving into details of the layouts, the following which is defined bellow are common for both vertical and horizontal stacks layouts (see figures 1 and 2):
Cell: is the position and space for two TEU.
Lane: is a narrow road with a breadth of 8 feet or a road made of some cells
Stack: is set of parallel lanes next to each other
Block: is a set of stacks which are surrounded by some main roads in a container terminal
Road: is a space on which trucks move. The breadth of the roads differs. The roads can be vertical or horizontal with respect to the berth.
Port equipment: the equipments used in the terminals are QCs, TGs and trucks.
Import/export area: the area of the terminal is divided to two parts, export area is the area in which the export containers are stacked, and import area is the area in which import containers are stacked. Export containers are stacked near the berth.
Stacking the containers: in each block, the containers are supposed to be stacked only in one direction, i.e. the container doors should be placed in one direction.
Locating the containers: the location for the containers is determined randomly from the import area. The same is assumed for the export containers which are selected randomly from the export area.
Trucks speed: A fixed speed of 8 kilometers per hour for loaded trucks and 14 kilometers per hour for unloaded trucks is assumed.
RTGs speed: A fixed speed of 8 kilometers per hour is assumed as the traveling speed of each RTG. For each container handling the RTG takes an average of 65.
3.2.1 Layout A
In this type of layout the containers are stacked horizontally, that is parallel to the berth. This is clearly illustrated in Fig 1.
The following specification and assumptions hold for layout A:
Type of stacks: the stacks are parallel to the berth, also called horizontal.
Breadth of each stack: the breadth is 10 lanes but only containers are stacked in 9 of them. The free lane is used for trucks to get loaded and unloaded.
Length of the stacks: each stack of layout A is 40 TEUs long.
Number of stacks: there are 12 stacks in this layout; in each stack either import or export containers are stacked. In fact the yard is divided into import and export area.
Horizontal roads: All horizontal roads of this layout are 2-lane roads and unidirectional. The roads are used for loading and unloading of trucks (they park on the tenth lane of the stack) and also as transit roads. There are seven horizontal roads in this layout.
Vertical roads: there are three vertical roads in this layout shown in Fig 1. Roads one and three are 3-lane and unidirectional but road two is 6-lane and bidirectional
Movement of trucks: the movement of the trucks is always clockwise.
Distance that the trucks move: the distance is randomly selected as the cells in which containers should be discharged are determined randomly.
Number of QCs: there are two QC or ship-to-shore cranes operating in this layout. The performance of each gantry crane is assumed to be 40 moves per hour. They supposed to be fixed without movement along the birth.
Number of RTGs: each stack is given one RTG. Therefore layout A enjoys having a total of 12 RTGs, four of which operate in import area and the other eight operate in export area. The cranes serve the trucks based on first in first out.
Number of trucks: The optimal number of trucks will be determined based on the performance indicators that the simulation program on loading operations provides us.
Assigning the trucks and gantry cranes to stacks: For loading operation each of the two QCs is assigned to the nearest four neighboring stacks of each block.
3.2.2 Layout B
The following specification and assumptions hold for layout B:
Type of stacks: the stacks are perpendicular to the berth, also called vertical.
Horizontal roads: All horizontal roads of this layout are 3-lane roads and unidirectional.The roads are used for loading and unloading of trucks (they park on the tenth lane of the stack) and also as transit roads. There are two horizontal roads in this layout.
Vertical roads: there are 13 vertical roads in this layout shown in Fig: 2. All roads except road seven are unidirectional and 2-lane. Road seven is 3-lane and bidirectional.
Other assumptions are the same as layout A.
3.3 Comparison of layouts' operational and idle time
Fig 3 Illustrates that layout A has approximately less average operational time than layout B, and increasing the number of trucks decreases the difference between layouts' average operational time.
