g-Chieh Chen

Modeling and Performance Assessment of a Transit-Based Evacuation Plan Within a Contraflow Simulation Environment

A bilevel optimization model is used to determine the waiting locations and corresponding shelters–in the case study, a combinatorial problem between bus stops and Metro stations–of a transit-based emergency evacuation plan and dispatch rescue buses toward the combinatorial locations. In additional, a contraflow simulation is elaborated to disperse the inside and ambient traffic of the target area. Results from the simulation can be used for modifying routing plans to avoid potential traffic bottlenecks. Findings indicate that the transit-based evacuation plan with the contraflow operations outperforms the same base plan without the contraflow operations. If more people select to evacuate via transit systems, the difficulties of dispersing traffic would be reduced and system performance remarkably improved.

Modeling and Performance Assessment of Intermodal Transfers at Cargo Terminals

This study develops an analytical model for coordinating vehicle schedules and cargo transfers at cargo terminals to improve system operational efficiency and minimize total system costs. The studied problem is formulated as a multihub, multimode, and multicommodities network problem with nonlinear time value functions for shipped cargo. This is done primarily by optimizing service frequencies and slack times for system coordination while also considering loading and unloading, storage, and cargo processing operations at the transfer terminals. In a series of case studies, the model has shown its ability to determine optimal service frequencies (or headways) and slack times based on given inputs. Numerical results are solved using sequential quadratic programming and a genetic algorithm.

Alleviating Schedule Disruptions at Intermodal Freight Transfer Terminals: Real-Time Dispatching Control

This study develops methods for countering schedule disruptions in intermodal or intramodal freight transportation systems operating in time-dependent, stochastic, and dynamic environments. When routine disruptions occur (e.g., traffic congestion, vehicle failures, or demand fluctuations) in preplanned intermodal timed-transfer systems, this dispatching control model determines through an optimization process whether each ready outbound vehicle should be dispatched immediately or held waiting for some late-incoming vehicles with connecting freight. Another submodel is developed to deal with the freight left over because of missed connections. Through a series of cases solved with a hybrid genetic algorithm–sequential quadratic programming algorithm, the model demonstrates its ability to minimize net costs through its dispatching decisions.

An evolutionary path planning algorithm for military applications

The path planning problem for military applications is discussed, with a review of relevant literature. An evolutionary algorithm originally designed for optimizing 3-dimensional highway alignments is adapted and tested for real-time military path planning applications in a changing environment. An optimization problem is formulated to seek a path for an autonomous agent or robot between given origin and destination points. The problempsilas decision variables and constraints are discussed. This problem maximizes the net benefit of reaching the destination while considering the probabilities of destroying hostile targets and getting destroyed by them during the mission. A hypothetical numerical example for a rescue operation at a location in hostile territory is presented. Minimizing time to destination, maximizing survivability and other measures of performance are also discussed. The solution algorithm is intended for real-world path planning for autonomous agents or robots.

A dispatching decision support system for countering delay propagation in intermodal logistics networks

ABSTRACT This paper specifies a dispatching decision support system devoted to managing intermodal logistics operations while countering delay and delay propagation. When service disruptions occur within a logistics network where schedule coordination is employed, a dispatching control model determines through an optimization process whether each ready outbound vehicle should be dispatched immediately or held to wait for some late incoming vehicles. Decisions should consider potential missed-connection costs that may occur not only at the next transfer terminals but also at hubs located further downstream. Numerical examples and a sensitivity analysis with different slack time settings for attenuating delay propagation are presented.

A hybrid heuristic technique for optimal coordination in intermodal logistics scheduling

This paper specifies a mixed integer nonlinear programming problem (MINLP) for assisting intermodal logistics operators with coordination decisions in freight transfer scheduling. An optimisation model is developed for coordinating vehicle schedules and cargo transfers at intermodal freight terminals, which is done primarily by optimising coordinated service frequencies and slack times, while also considering loading and unloading, storage and cargo processing operations. A hybrid technique combining sequential quadratic programming and genetic algorithms (GA-SQP) is developed to solve the proposed MINLP. This study also provides flexibility in managing general and perishable cargos with different cargo value functions that depend on dwell times. In a case study we derive insights which support intermodal logistics operators in planning their freight service schedules. Numerical results indicate that the developed algorithm is capable of producing optimal solutions efficiently for both small and large intermodal freight networks.

Dynamic Programming Model for Attended Delivery Time Slot Management

Offering customers the choice of delivery time slots is an emerging business strategy in attended home delivery service because this option has the potential to improve service level and reduce the risk of delivery failure. A dynamic programming model was developed for assisting attended delivery service providers with pricing decisions in managing time slots. Since the choice of delivery time slots involves both marketing and operational issues, a proposed dynamic pricing model maximizes the total system expected revenue while also improving the matches between customers’ and service providers’ preferred time slots and fees. The study started by managing homogeneous time slots with three kinds of customer behaviors (i.e., price taker, price negotiator, and leave-without-pay) and then considered heterogeneous time slots. The study found that the optimal price might vary depending on customers’ arrival rates in the system, the remaining capacities of available time slots, the percentages of customers who are price negotiators, and the time left in the sales periods.

A Simulation Framework for the Path Planning of Unmanned Autonomous Systems

This paper presents a simulation framework designed to plan the movements of unmanned autonomous systems (UAS’s) in hazardous environments, to coordinate their actions, predict their behavior and evaluate their mission success in various combat situations. Current simulation methods do not predict the complex interrelations among vehicles, operating environments, and paths, thus providing inadequate tests. A family of methods for coordinating, positioning, routing and assessing diverse military units or “agents” (such as unmanned ground vehicles) is described in this paper. The methods are tested and evaluated through computer simulations to ensure suitability for operating unmanned autonomous systems (UAS’s). The path evaluation is performed using a dynamic GIS, distance transform, and genetic algorithms. The optimization algorithms for use in testing future unmanned systems are based on multiple objectives and criteria, including: (1) timeliness, (2) detectability & exposure time, (3) probabilities of survival & mission completion; (4) energy use; and (5) obstacle avoidance. A series of tests are presented which mimics real-world combat situation to test the effectiveness of the developed