Golden Gate Bridge

Summary

The Golden Gate Bridge is a suspension bridge spanning the Golden Gate, the strait connecting San Francisco Bay and the Pacific Ocean. The structure links the U.S. city of San Francisco, California—the northern tip of the San Francisco Peninsula—to Marin County, carrying both U.S. Route 101 and California State Route 1 across the strait. It also carries pedestrian and bicycle traffic, and is designated as part of U.S. Bicycle Route 95. Recognized by the American Society of Civil Engineers as one of the Wonders of the Modern World, the bridge is one of the most internationally recognized symbols of San Francisco and California. The idea of a fixed link between San Francisco and Marin had gained increasing popularity during the late 19th century, but it was not until the early 20th century that such a link became feasible. Joseph Strauss served as chief engineer for the project, with Leon Moisseiff, Irving Morrow and Charles Ellis making significant contributions to its design. The b

Official source

https://en.wikipedia.org/wiki/Golden_Gate_Bridge

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Multi-Objective Airport Gate Assignment Problem

Michel Bierlaire, Prem Kumar

In this paper, we consider the gate assignment for a large airline at its hub airport. It is considered to be a highly complex problem with the possibility of application in both planning as well as operations mode. There are various considerations that are involved while assigning gates to incoming and outgoing turns at an airport. Different gates have restrictions, such as adjacency, LIFO and push time, which is known in advance from the structure of the airport. When optimizing the assignment costs, we consider different and often conflicting objectives such as maximization of gate rest time between two turns, minimization of the cost of towing an aircraft with a long turn and minimization of overall costs that includes penalization for not assigning preferred gates to certain turns. One of the major contributions of this paper is gate assignment in the planning mode to assign airport gates dynamically to scheduled flights based on daily origin and destination passenger flow data ensuring that the number of passenger misconnects at the hub airport is minimized. We formulate these problems as mixed 0-1 integer program with a linear objective function and constraints. Due to the complexity in the problem size and formulation, we have resorted to relaxation for certain instances when a reasonable solution is not obtained within the time limit. In order to compare the performance of standard MIP, a set partitioning formulation is proposed. The advantage of attempting this alternate formulation is the capability to compare the performance of a normal MIP solution with a column generation algorithm. Implementation is done using OPL and computational results for actual data sets are presented.

2011

We consider the assignment of gates to arriving and departing flights at a large hub airport. It is considered to be a highly complex problem even in planning stage when all flight arrivals and departures are assumed to be known precisely in advance. There are various considerations that are involved while assigning gates to incoming and outgoing flights (such a flight pair for the same aircraft is called a turn) at an airport. Different gates have restrictions, such as adjacency, last-in-first-out gates and towing requirements, which are known from the structure and layout of the airport. When optimizing the gate assignment costs, we consider different, and often, conflicting objectives such as maximization of gate rest time between two turns, minimization of the cost of towing an aircraft with a long layover, minimization of overall costs that includes penalization for not assigning preferred gates to certain turns, among others. One of the major contributions of this paper is to mathematically model all these features that are observed in the real-life. Further we also attempt to study the problem in both planning and operations mode, which has rarely been accomplished in the literature. For planning, we sequentially introduce different objectives to our gate assignment problem such as maximization of connection revenues, minimization of zone usage at airport and maximization of schedule reliability and include them to the model along with the relevant constraints. For operations, the main consideration is recovery of schedule by minimizing schedule variations and maintaining feasibility in the event of major disruptions. Additionally the operations models must have very, very short run times, in the order of a few seconds. These models are then applied to a real airline at one of its most congested hubs. Implementation is done using OPL and computational results for actual data sets are reported. For the planning mode, analyst perception of weights for the different objectives in the multi-objective model is used wherever actual dollar value of the objective coefficient is not available. The results are also reported for large, reasonable changes in objective function coefficients. For the operations mode, flight delays are simulated and the performance of the model studied. The final results indicate that it is possible to solve even large instances of real-life problems to optimality within short run times with conventional continuous time assignment model.

2012

Rational approach for the management of a medium size bridge stock

Eugen Brühwiler

Infrastructure managers of medium size bridge stocks are being faced with the task of approximating short, mid to long term financial needs for their infrastructure. This task is particularly demanding due to the lack of relevant information, in particular in forecasting bridge condition and intervention costs. It can, therefore, be beneficial to make cost estimations based on structure types and present condition evaluation. In this article a rational approach for the management of the medium size bridge stock including 654 bridges of a regional road network is presented. The basic methodology is given and it is described how this methodology is adopted considering the available information (data base) on the bridge stock on the structures level. The use of age equivalents is suggested to describe bridge condition and to link directly intervention cost to condition

Taylor & Francis Group2008

2012