published journal article
published journal article
published journal article
published journal article
published journal article
published journal article
published journal article
Recent research has demonstrated and established the viability of applying path-based algorithms to the traffic equilibrium problem in reasonably large networks. Much of the attention has been focused on two particular algorithms: the disaggregate simplicial decomposition (DSD) algorithm and the gradient projection (GP) algorithm. The purpose of this paper is to evaluate the performance of these two path-based algorithms using networks of realistic size. Sensitivity analysis is performed on randomly generated networks to examine the performance of the algorithms with respect to network sizes, congestion levels, number of origin-destination (OD) pairs, and accuracy levels. In order to be empirically convincing, a realistic large-scale network, known as the ADVANCE network, is also used to show that path-based algorithms are a viable alternative in practice. (C) 2002 IMACS. Published by Elsevier Science B.V. All rights reserved.
published journal article
This work assesses the feasibility of Solid Oxide Fuel Cell-Gas Turbine (SOFC-GT) hybrid power systems for use as the prime mover in freight locomotives. The available space in a diesel engine-powered locomotive is compared to that required for an SOFC-GT system, inclusive of fuel processing systems necessary for the SOFC-GT. The SOFC-GT space requirement is found to be similar to current diesel engines, without consideration of the electrical balance of plant. Preliminary design of the system layout within the locomotive is carried out for illustration. Recent advances in SOFC technology and implications of future improvements are discussed as well. A previously-developed FORTRAN model of an SOFC-GT system is then augmented to simulate the kinematics and power notching of a train and its locomotives. The operation of the SOFC-GT-powered train is investigated along a representative route in Southern California, with simulations presented for diesel reformate as well as natural gas reformate and hydrogen as fuels. Operational parameters and difficulties are explored as are comparisons of expected system performance to modern diesel engines. It is found that even in the diesel case, the SOFC-GT system provides significant savings in fuel and CO2 emissions, making it an attractive option for the rail industry. (C) 2012 Elsevier B.V. All rights reserved.
conference paper
A new facility location model and a solution algorithm are proposed that feature 1) itinerary-interception instead of flow-interception; 2) stochastic demand as dynamic service requests; and 3) queueing delay. These features are essential to analyze battery-powered electric shared-ride taxis operating in a connected, centralized dispatch manner. The model and solution method are based on a bi-level, simulation-optimization framework that combines an upper level multiple-server allocation model with queueing delay and a lower level dispatch simulation based on earlier work by Jung and Jayakrishnan. The solution algorithm is tested on a fleet of 600 shared-taxis in Seoul, Korea, spanning 603 km2, a budget of 100 charging stations, and up to 22 candidate charging locations, against a benchmark â??naïveâ?? genetic algorithm that does not consider cyclic interactions between the taxi charging demand and the charger allocations with queue delay. Results show not only that the proposed model is capable of locating charging stations with stochastic dynamic itinerary-interception and queue delay, but that the bi-level solution method improves upon the benchmark algorithm in terms of realized queue delay, total time of operation of taxi service, and service request rejections. Furthermore, the authors show how much additional benefit in level of service is possible in the upper-bound scenario when the number of charging stations is unbounded.
published journal article