# Integrated Simulation-Based Optimization of Operational Decisions at Container Terminals
## 2 Materials and Methods
### Simulation Model  
In the following, the created simulation model of the container terminal and its restrictions are presented. The discrete-event simulation model is implemented in Tecnomatix Plant Simulation and is based on the data of a real terminal. The layout of the terminal is shown in Figure 2.  
The terminal has a quay length of 800 m and a total of 20 YBs. The simulation model represents container handling between the quayside and container yard. As displayed in Figure 2, the specifics of the design of the land-side transport interface as well as the berths are not considered in detail. In this study, parallel handling of several ships is not modeled. Consequently, the simulation model of the container terminal is stressed by the arrival of a single ship. For this, 12 bays of the ship with a total of 4000 containers have to be handled. About half of them are import containers to be unloaded and the other half are export containers to be loaded. The container transport orders are pre-defined and contain details such as the origin and destination of the containers at the terminal and the availability time for handling in the yard or quayside by gantry cranes. To reduce the execution time of a simulation run, three variations for each parameter combination are generated before all experiments. Depending on the experiment, at least 3 and at most 6 QCs are available for loading and unloading the ship. The ship is unloaded and loaded bay by bay, whereby the QC always handles the entire bay that is assigned to it. Thus, the QC moves after the unloading of a bay and before the loading of the next bay. These bay changes are represented by a delay between the handling of two containers of the same QC. When fewer QCs are used for one ship, more bays are served by each QC. In the simulation model, an average quayside handling rate of 30 containers per hour is assumed, which is represented by an expected handling frequency of 120 s by each QC. To model stochastic influences, a triangular distribution of the QC handling times is assumed with a minimum handling time of 80 s and a maximum value of 180 s. YTs carry out horizontal transport between the quay and yard. Since YTs are unable to lift containers themselves, the transfer between the QC and YT must be synchronized. The travel times of the YTs are determined by the distances between QCs and YBs, as specified by the terminal layout. For calculating the travel times, an average speed of 8.4 m/s is assumed for the YTs. By inserting a triangular distribution, stochastic influences are taken into account when calculating the travel times. The total number of YTs used per experiment is generated in the yard at the beginning of the simulation. The inbound and outbound yard operations are performed by RTGs. For the simulation model, it is assumed that RTGs can handle an average of 15 containers per hour, which corresponds to an expected value of 240 s per handling. Deviations and irregularities in the process are modeled by a triangular distribution with a minimum handling time of 180 s and a maximum value of 420 s. For all experiments, at least two YBs are required for each active QC. Thus, it can be ensured that sufficient storage space is available for the containers to be handled. Depending on the experiment, one of the two storage policies  
Figure 2: Layout and process illustration of the simulation model. random YB assignment_ and _close YB assignment_ is investigated with the simulation model. For the storage policy _random YB assignment_, containers from all active YBs can be transported to and from each of the QCs. In addition, import containers are randomly assigned to YBs, regardless of which QC is used for the unloading. All active YBs are ensured to be equally burdened as much as possible. The second storage policy is _close YB assignment_, which seeks to minimize the distance between QCs and YBs. YBs with the shortest possible distance for horizontal transport are assigned to every QC.