Ta-Hui Yang

A hub location inventory model for bicycle sharing system design: Formulation and solution

This study addresses a strategic design problem for bicycle sharing systems incorporating bicycle stock considerations. The problem is formulated as a hub location inventory model. The key design decisions considered are: the number and locations of bicycle stations in the system, the creation of bicycle lanes between bicycle stations, the selection of paths of users between origins and destinations, and the inventory levels of sharing bicycles to be held at the bicycle stations. The design decisions are made with consideration for both total cost and service levels (measured both by the availability rate for rental requests at the pick-up rental stations and coverage of the origins and destinations). The optimal design of this system requires an integrated view of the travel costs of users, bicycle inventory costs and facility costs of bicycle stations and bicycle lanes as well as service levels. The purpose of this study is to create a formal model that provides such an integrated view, and to develop methods for obtaining solutions for the design variables in practical situations. The complexity of the problem precludes the exact solution of the optimization problem for instances of realistic size, and so we propose a heuristic method for efficiently finding near-optimal solutions. In the test problem for which enumeration is possible, the heuristic solution is within 2% optimal. Finally, a numerical example is created to illustrate the model and proposed solution algorithm.

Stability issues for dynamic traffic assignment

Abstract This paper explores stability issues for operational route guidance control strategies for vehicular traffic networks equipped with advanced information systems, and develops a general procedure for the stability analysis of the associated dynamic traffic assignment (DTA) problems. The route guidance control strategies are modeled as dynamical systems, and the associated solution procedure enables computational tractability for real-time deployment. An important study insight is that the Lyapunov functions for the route guidance control models are their corresponding objective functions under DTA. This overcomes the key difficulty of constructing meaningful Lyapunov functions for DTA problems.

An airline maintenance manpower planning model with flexible strategies

An effective maintenance manpower supply plan not only reduces operating costs but ensures greater aviation safety and punctuality. A variety of flexible management strategies have been widely applied in other industries; however, little research has stressed flexible management strategies for airline crew scheduling problems. Here, we introduce a model that includes various flexible strategies so that an airline can effectively manage its maintenance manpower supply. The model is formulated as a mixed integer program that is solved using a commercial software package, CPLEX. In order to evaluate the model performance, we use the operating data from a leading Taiwan airline.

AIRLINE NETWORK DESIGN PROBLEM WITH DIFFERENT AIRPORT CAPACITY CONSTRAINTS

Shortages of resources at airports have become a serious problem, however most past studies in airline network design have not taken into consideration capacity restrictions at airports. This study addressed the capacitated fixed charge hub location problems. Two models with different capacity constraints are proposed to determine the hub location and service network; capacity constraints in the first model take into account total volumes that pass through airports, including inbound, outbound, and transshipped traffic, while those in the second model only account for transshipment flows. Both models take into consideration most possible services, including non-stop and hub-connected, and the coexistence of both services. This provides maximal flexibility for the construction of airline service networks. A network based on the air freight market between Taiwan and China will be used to illustrate the proposed models, while analyses show that the use of different capacity constraints will result in different hub locations and network structures.

A two-stage stochastic model for airline network design with uncertain demand

This study addresses airline network design problems with stochastic demand. The airline network design problem aims to determine hub location, flight routes and flow allocation. The hub location decision is a long-term investment and will not vary according to different demand levels. On the other hand, the determination of flight routes and flow allocation are short-term decisions and may change due to seasonal demand variation. A two-stage stochastic model was proposed to formulate the problem. The first-stage problem corresponds to hub location decision, while the second-stage corresponds to flight route determination and flow allocation based upon the hub location from the first stage and realised uncertain demand. Finally, a contrived network and a real network are used to test the proposed model.

A model and a solution algorithm for airline line maintenance manpower supply planning with multiple aircraft type maintenance certificates

Abstract Traditionally, aircraft maintenance manpower supply planning in Taiwan is based on staff experience, which is neither efficient nor effective. In this research, we developed a model to help airlines to efficiently and effectively plan their maintenance manpower supplies to deal with multiple aircraft type maintenance certifications. The model is formulated as a mixed integer program which is characterized as NP‐hard. Because the problem size of the proposed model was expected to be huge, we developed a heuristic algorithm to solve the problem. To evaluate the model and the solution algorithm, we performed a case study using the operating data from a Taiwan airline. The preliminary results indicate that the proposed model and the solution algorithm are both efficient and effective.

Hub-and-spoke airline network design under competitive market

This study proposed a hub-and-spoke network design model with the uncertainty of a competitor’s information in a duopolistic airline market. The market share is affected by the prices of both players in the market and the prices are assumed to be proportional to their transportation costs. The source of uncertainty in the problem is due to the imperfect information on the competitor’s price setting. The stochastic programming was applied to formulate the system randomness. An illustrative example from air freight data was used to test the proposed model. The sensitivity analysis was used to investigate the interactions between the stochastic factors.

SETZ logistics models and system framework for manufacturing and exporting large engineering assets

Given the dynamic and increasingly competitive nature of international commerce, manufacturing companies must plan global logistics operations for sustainable competitive advantage. Many enterprises build collaborative manufacturing networks across multinational regions to reduce production costs and gain access to new and often unfamiliar markets. Recognizing the strategic importance of globalization, government agencies are developing Special Economic Trade Zones (SETZ). These zones are regulated industrial districts which encourage manufacturing by offering incentives such as new logistic designs linked with the latest information technologies. The objective of this paper is to analyze and design SETZ logistics hub models and system framework for linking manufacturers. By defining the characteristics of the different types of specialized trade zones, and briefly discussing the older types of trade models that are no longer competitive, this research uses the case of a Taiwan power transformer manufacturer to analyze the supply chain logistics processes for manufacturing and exporting large engineering assets within a SETZ. The logistics models and information system framework developed provide a general reference for other governments, companies, and industrial sectors that intend to design export-oriented industrial parks incorporating IT-centric and globally oriented SETZ techniques.

Airline hub-and-spoke system design under stochastic demand and hub congestion

This study addresses the hub network design problem considering demand uncertainty and hub congestion effects. The problem is formulated as a two-stage stochastic program with recourse model. The model provides a consistent set of hub locations, while adjusting network configuration in response to different demand realizations. A case study collected from real-world data was used to test the proposed model, and a sensitivity analysis was performed to know how several important parameters affected the solution.

Insights on a stable route guidance model for real-time deployment

This paper explores the stability issues for a dynamical system based traffic assignment model for vehicular traffic networks equipped with advanced information systems and develops a real-time deployable solution algorithm. Experimental analysis suggests that the algorithm can efficiently provide real-time stable solutions while accounting for time-dependent variations in the system. The results are compared to those of the benchmark deterministic dynamic traffic assignment and the rolling horizon implementation based models.