246,230 research outputs found

    An optimization model for the US Air-Traffic System

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    A systematic approach for monitoring U.S. air traffic was developed in the context of system-wide planning and control. Towards this end, a network optimization model with nonlinear objectives was chosen as the central element in the planning/control system. The network representation was selected because: (1) it provides a comprehensive structure for depicting essential aspects of the air traffic system, (2) it can be solved efficiently for large scale problems, and (3) the design can be easily communicated to non-technical users through computer graphics. Briefly, the network planning models consider the flow of traffic through a graph as the basic structure. Nodes depict locations and time periods for either individual planes or for aggregated groups of airplanes. Arcs define variables as actual airplanes flying through space or as delays across time periods. As such, a special case of the network can be used to model the so called flow control problem. Due to the large number of interacting variables and the difficulty in subdividing the problem into relatively independent subproblems, an integrated model was designed which will depict the entire high level (above 29000 feet) jet route system for the 48 contiguous states in the U.S. As a first step in demonstrating the concept's feasibility a nonlinear risk/cost model was developed for the Indianapolis Airspace. The nonlinear network program --NLPNETG-- was employed in solving the resulting test cases. This optimization program uses the Truncated-Newton method (quadratic approximation) for determining the search direction at each iteration in the nonlinear algorithm. It was shown that aircraft could be re-routed in an optimal fashion whenever traffic congestion increased beyond an acceptable level, as measured by the nonlinear risk function

    Platform Design For Fleet-Level Efficiency Under Uncertain Demand: Application For Military Cargo Aircraft And Fleet

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    The aircraft system\u27s role in the United Stated Air Force is crucial. For the U.S. Air Force to maintain its air superiority in the world, the constant maintenance, upgrade, and acquisition of the systems must follow. As the cost of fuel rises and with the recent budget situation, the emphasis is on both running the Air Force fleet more efficiently and acquiring the platform that can reduce the fleet level operating cost and the fuel usage and yet brings same capabilities. The approach presented in the thesis combines approaches from multidisciplinary design optimization and operations research to improve energy efficiency-related defense acquisition decisions. The work focuses upon problems that are relevant to the U.S. Air Force-Air Mobility Command (AMC), which is the largest consumer of fuel in the Department of Defense. To reflect AMC problems, the approach must consider the uncertainty in cargo demand; historical data shows that the cargo demand for AMC varies on a daily basis. The approach selects requirements for a new cargo aircraft; predicts size, weight and performance of that new aircraft; and allocates the new aircraft along with existing aircraft fleet to meet the cargo transportation demand. The approach successfully provides a description of a new cargo aircraft that, given the abstractions and assumptions used, will reduce the fleet-level operating cost and / or the fuel needed to meet air cargo demand. The allocation problem incorporates scheduling-like features to account for time driven operational constraints. The results of this study demonstrate the approach for a simple three-route network and 22-base network, using the Global Air Transportation Execution System (GATES) dataset. With addition of uncertainty in demand and random home base generation, the simulation result will suggest an aircraft design that is more flexible to the fluctuations in demand. The 22-base network represents one day of operation of the AMC randomly selected from the GATES data. The result from the 22-base network simulation under uncertain demand scenario for the strategic fleet suggests the introduction of five new aircraft that are capable of 24 pallets and 3,300 nautical miles of unrefueled design range which will save 1.10 percent in the expected direct operating cost and 4.20 percent in expected fuel usage compared to the baseline allocation result without introduction of the new aircraft

    Enriching the tactical network design of express service carriers with fleet scheduling characteristics

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    Express service carriers provide time-guaranteed deliveries of parcels via a network consisting of nodes and hubs. In this, nodes take care of the collection and delivery of parcels, and hubs have the function to consolidate parcels in between the nodes. The tactical network design problem assigns nodes to hubs, determines arcs between hubs, and routes parcels through the network. Afterwards, fleet scheduling creates a schedule for vehicles operated in the network. The strong relation between flow routing and fleet scheduling makes it difficult to optimise the network cost. Due to this complexity, fleet scheduling and network design are usually decoupled. We propose a new tactical network design model that is able to include fleet scheduling characteristics (like vehicle capacities, vehicle balancing, and drivers' legislations) in the network design. The model is tested on benchmark data based on instances from an express provider, resulting in significant cost reductions

    Cargo Consolidation and Distribution Through a Terminals-Network: A Branch-And-Price Approach

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    Less-than-truckload is a transport modality that includes many practical variations to convey a number of transportation-requests from the origin locations to their destinations by using the possibility of goods-transshipments on the carrier?s terminals-network. In this way logistics companies are required to consolidate shipments from different suppliers in the outbound vehicles at a terminal of the network. We present a methodology for finding near-optimal solutions to a less-than-truckload shipping modality used for cargo consolidation and distribution through a terminals-network. The methodology uses column generation combined with an incomplete branch-and-price procedure.Fil: Dondo, Rodolfo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

    The Northern Arc: The Outer Perimeter Reincarnated?

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    Plans for the proposed Outer Perimeter were scaled back after the Regional Transportation Plan (RTP) and State Implementation Plan (SIP) lapsed in 1998 due to non-compliance with national clean air standards. In place of the 200-mile circumferential route, a dramatically modified Northern Arc emerged as an alternative in the revised alternative of the Regional Transportation Plan released in the Spring of 1999 by the Atlanta Regional Commission. In the Summer of 1999 the State Department of Transportation held a series of Public Hearings on the proposed 59 mile route extending from I-75 in the Cartersville area eastward to I-85 and GA Route 316 in the Lawrenceville area. Without advocating a position on the project, this paper examines several issues requiring resolution prior to action for or against its ultimate construction.Research Atlanta released a report in 1993 discussing issues for consideration in the public debate on the highway's fate. The current report lends some updated perspective on these issues and the text of the original report is contained in an appendix
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