Embedding simulation in optimization algorithms will incur computational costs. For NP-hard problems the computational costs of the embedded simulation in the optimization algorithm are likely to be substantial. YC dispatching is NP-hard. So it is very important to be able to minimize simulation costs in YC dispatching algorithms. In the optimization algorithm for yard crane dispatching published, simulation of YC operations of the entire (partial) sequence of YC jobs are carried out each time the tardiness of a (partial) sequence needs to be evaluated. In this paper we study two approaches to reduce simulation costs in these embedded simulations in the optimization algorithm. Experimental results show that one approach significantly reduces the computational time of the optimization algorithm. We also analyze the reasons for the other approach which fails to reduce the computational time.

Ensuring congestion-free marine traffic is crucial for hub ports in the world. For these hub ports, there has been increasing demand in marine transport. Therefore a capacity-assessment tool that models and simulates the navigational network, the traffic flows and complex navigational behaviors of vessels is needed. The simulation model presented in this paper is unique in the scale and complexity of the waterway networks covered, the flexibility in defining the traffic flow patterns, and the degree of accuracy demanded of navigational behaviors. As such, none of the existing models and simulation tools is adequate for assessing the waterway capacity. The model was calibrated based on detailed analysis of historical records and consultations with domain experts. The model was used in the study of several future scenarios of a hob port. The simulation system built has laid a useful foundation for planning future marine traffic for hub ports.

A performance mark of a BDI agent is how fast it can react to and process incoming event sequences. To the best of our knowledge, few papers have been published about predicting an agent's average response time for an event sequence before the agent is applied in a real project. In this paper, we first introduce a simulation method. In simulation, a sequence of events with attributes, such as priorities and amounts of time needed to process the events, is input to the agent at designed insertion time. The events are processed by the agent according to the attributes. The statistics of processing time can be recorded. Then we make some theoretical analysis to estimate the average response time when an agent processes a sequence of events based on probability and queueing theory. Comparison experiments show that the results from analysis are quite matching with the results from simulation experiments. The analysis suggests a way to quickly estimate the performance of an agent if the attributes of the incoming event sequence are known in advance. The predicted average response time can help construct efficient BDI agents for various environments.

We address the problem of dispatching a yard crane in its appointed zone of a container terminal. The objective of yard crane dispatching is to determine a sequence for handling all coming jobs within the zone that minimizes the average vehicle waiting time. We propose 2 modified A* search algorithms with admissible heuristics to provide fast and optimal dispatching solution. Simulation results show that the algorithm using the improved heuristic is able to find the optimal solution over 2.4 times 1018possible dispatching sequences in about 3 to 4 seconds under heavy work load.

In this paper, a general framework for the parallel BDI model suitable for dynamic environments is proposed. It is a parallel agent architecture that supports the following agent abilities at architecture level: (1) the ability to monitor the environ

This paper discusses the problem of multi-robot exploration. The objective of this problem is to explore an unknown environment using a team of mobile robots in a minimum amount of time. We believe that in an unknown environment, it is very difficult to estimate the amount of new information expected from a frontier location. We propose a new objective for the assignment algorithm and introduce a new cost function to be used in the assignment algorithm that leads to better motion planning. For the sake of simplicity, we suggest to use greedy algorithm for the assignment algorithm. In this paper, we also proposed a method for exploration problem with robots' limited communication capability, by estimating the missing robots' position, so that the outcome will not degrade significantly

In conventional Automated Storage and Retrieval Systems (AS/RS), stacker cranes are used to deliver loads to the AS/RS racks and to retrieve loads from the racks. Stacker cranes travel simultaneously in the vertical and horizontal directions. However, the stacker cranes are inadequate for extra heavy loads. In this paper a new kind of Storage/Retrieval (S/R) mechanism is presented to handle such loads. Unlike stacker cranes, the new S/R mechanism has one vertical platform and N horizontal platforms to serve N tiers of an AS/RS rack. The vertical platform provides the vertical link among the tiers of the AS/RS rack, whereas the horizontal platforms transfer loads to the individual storage cells on a given tier. The operations of the vertical platform and the horizontal platforms may be independent and concurrent. In this paper, the design, operation and advantages of the new mechanism are presented. We present a travel-time model under the dwell point policy that the platforms remain where they are after completing a storage/retrieval operation. The model is validated by computer simulations. The results show that our model is reliable for the design and analysis of the new kind of AS/RS. We also present guidelines for the optimal design of a rectangular-in-time AS/RS rack with the new S/R mechanism.

The ever-increasing demand on container port throughput has mounted the necessity of a more efficient container storage structure, the requirements of which apparently can be met by AS/RS because of its abilities of fully automating material handling and the potentials for delivering high performance. In this study, we present an AS/RS for container storage, develop the travel time models for the proposed system, and confirm its feasibility in terms of throughput performance. A pre-processing scheme for operation scheduling that significantly improves AS/RS throughput is proposed and evaluated. Additional constraints arising from the container size and weight on AS/RS design and scheduling are taken into considerations, which in effect leads to a platform-based AS/RS.