1,774 research outputs found
A Combined Adaptive Tabu Search and Set Partitioning Approach for the Crew Scheduling Problem with an Air Tanker Crew Application
This research develops the first metaheuristic approach to the complete air crew scheduling problem. It develops the first dynamic, integrated, set-partitioning based vocabulary scheme for metaheuristic search. Since no benchmark flight schedules exist for the tanker crew scheduling problem, this research defines and develops a Java™ based flight schedule generator. The robustness of the tabu search algorithms is judged by testing them using designed experiments. An integer program is developed to calculate lower bounds for the tanker crew scheduling problem objectives and to measure the overall quality of solutions produced by the developed algorithms
Reliable Reserve-Crew Scheduling for Airlines
We study the practical setting in which regular- and reserve-crew schedules
are dynamically maintained up to the day of executing the schedule. At each day
preceding the execution of the schedule, disruptions occur due to sudden
unavailability of personnel, making the planned regular and reserve-crew
schedules infeasible for its execution day. This paper studies the fundamental
question how to repair the schedules' infeasibility in the days preceding the
execution, taking into account labor regulations. We propose a robust repair
strategy that maintains flexibility in order to cope with additional future
disruptions. The flexibility in reserve-crew usage is explicitly considered
through evaluating the expected shortfall of the reserve-crew schedule based on
a Markov chain formulation. The core of our approach relies on iteratively
solving a set-covering formulation, which we call the Robust Crew Recovery
Problem, which encapsulates this flexibility notion for reserve crew usage. A
tailored branch-and-price algorithm is developed for solving the Robust Crew
Recovery Problem to optimality. The corresponding pricing problem is
efficiently solved by a newly developed pulse algorithm. Based on actual data
from a medium-sized hub-and-spoke airline, we show that embracing our approach
leads to fewer flight cancellations and fewer last-minute alterations, compared
to repairing disrupted schedules without considering our robust measure
Reliable reserve-crew scheduling for airlines
We study the practical setting in which regular- and reserve-crew schedules are dynamically maintained up to the day of executing the schedule. At each day preceding the execution of the schedule, disruptions occur due to sudden unavailability of personnel, making the planned regular and reserve-crew schedules infeasible for its execution day. This paper studies the fundamental question how to repair the schedules’ infeasibility in the days preceding the execution, taking into account labor regulations. We propose a robust repair strategy that maintains flexibility in order to cope with additional future disruptions. The flexibility in reserve-crew usage is explicitly considered through evaluating the expected shortfall of the reserve-crew schedule based on a Markov chain formulation. The core of our approach relies on iteratively solving a set-covering formulation, which we call the Robust Crew Recovery Problem, which encapsulates this flexibility notion for reserve crew usage. A tailored branch-and-price algorithm is developed for solving the Robust Crew Recovery Problem to optimality. The corresponding pricing problem is efficiently solved by a newly developed pulse algorithm. Based on actual data from a medium-sized hub-and-spoke airline, we show that embracing our approach leads to fewer flight cancellations and fewer last-minute alterations, compared to repairing disrupted schedules without considering our robust measure.</p
Lagrangian-based methods for single and multi-layer multicommodity capacitated network design
Le problème de conception de réseau avec coûts fixes et capacités (MCFND) et le problème
de conception de réseau multicouches (MLND) sont parmi les problèmes de
conception de réseau les plus importants. Dans le problème MCFND monocouche, plusieurs
produits doivent être acheminés entre des paires origine-destination différentes
d’un réseau potentiel donné. Des liaisons doivent être ouvertes pour acheminer les produits,
chaque liaison ayant une capacité donnée. Le problème est de trouver la conception
du réseau à coût minimum de sorte que les demandes soient satisfaites et que les capacités
soient respectées. Dans le problème MLND, il existe plusieurs réseaux potentiels,
chacun correspondant à une couche donnée. Dans chaque couche, les demandes pour un
ensemble de produits doivent être satisfaites. Pour ouvrir un lien dans une couche particulière,
une chaîne de liens de support dans une autre couche doit être ouverte. Nous
abordons le problème de conception de réseau multiproduits multicouches à flot unique
avec coûts fixes et capacités (MSMCFND), où les produits doivent être acheminés uniquement
dans l’une des couches.
Les algorithmes basés sur la relaxation lagrangienne sont l’une des méthodes de résolution
les plus efficaces pour résoudre les problèmes de conception de réseau. Nous
présentons de nouvelles relaxations à base de noeuds, où le sous-problème résultant se
décompose par noeud. Nous montrons que la décomposition lagrangienne améliore significativement
les limites des relaxations traditionnelles.
Les problèmes de conception du réseau ont été étudiés dans la littérature. Cependant,
ces dernières années, des applications intéressantes des problèmes MLND sont apparues,
qui ne sont pas couvertes dans ces études. Nous présentons un examen des problèmes de
MLND et proposons une formulation générale pour le MLND. Nous proposons également
une formulation générale et une méthodologie de relaxation lagrangienne efficace
pour le problème MMCFND. La méthode est compétitive avec un logiciel commercial
de programmation en nombres entiers, et donne généralement de meilleurs résultats.The multicommodity capacitated fixed-charge network design problem (MCFND) and
the multilayer network design problem (MLND) are among the most important network
design problems. In the single-layer MCFND problem, several commodities have to
be routed between different origin-destination pairs of a given potential network. Appropriate
capacitated links have to be opened to route the commodities. The problem
is to find the minimum cost design and routing such that the demands are satisfied and
the capacities are respected. In the MLND, there are several potential networks, each
at a given layer. In each network, the flow requirements for a set of commodities must
be satisfied. However, the selection of the links is interdependent. To open a link in a
particular layer, a chain of supporting links in another layer has to be opened. We address
the multilayer single flow-type multicommodity capacitated fixed-charge network
design problem (MSMCFND), where commodities are routed only in one of the layers.
Lagrangian-based algorithms are one of the most effective solution methods to solve
network design problems. The traditional Lagrangian relaxations for the MCFND problem
are the flow and knapsack relaxations, where the resulting Lagrangian subproblems
decompose by commodity and by arc, respectively. We present new node-based
relaxations, where the resulting subproblem decomposes by node. We show that the
Lagrangian dual bound improves significantly upon the bounds of the traditional relaxations.
We also propose a Lagrangian-based algorithm to obtain upper bounds.
Network design problems have been the object of extensive literature reviews. However,
in recent years, interesting applications of multilayer problems have appeared that
are not covered in these surveys. We present a review of multilayer problems and propose
a general formulation for the MLND. We also propose a general formulation and
an efficient Lagrangian-based solution methodology for the MMCFND problem. The
method is competitive with (and often significantly better than) a state-of-the-art mixedinteger
programming solver on a large set of randomly generated instances
Combining and Analyzing the Tanker and Aircrew Scheduling Heuristics
Air refueling is an integral part of U.S. air power across a wide range of military operations. It is an essential capability in the conduct of air operations worldwide and is especially important when overseas basing is limited or not available. The planning, tasking, and scheduling of aerial refueling require solution of two major problems: assigning and scheduling of tankers to refueling points and efficiently assigning crews to each tanker. To address the scheduling of tankers, Wiley (2001) developed an efficient tabu search approach. Combs (2002) developed another tabu search approach to assign crews to tankers. This research combines the two scheduling heuristics so that the tanker schedules generated by the tanker scheduling heuristics can feed the crew scheduling heuristic
Optimisation simultanée des rotations et des blocs mensuels des équipages aériens
R´esum´e
Le probl`eme int´egr´e de la construction des rotations et des blocs mensuels des pilotes
consiste `a d´eterminer un ensemble de rotations et de blocs mensuels pour les pilotes tels
que chaque segment de vol est couvert par une seule rotation et un seul bloc, et ce, tout en
satisfaisant des contraintes suppl´ementaires comme la disponibilit´e des pilotes dans chaque
base. Une rotation est une s´equence de vols effectu´ee par un ´equipage durant une p´eriode
donn´ee partant et revenant `a la mˆeme base. Un bloc (ou horaire) mensuel est une s´equence
de rotations s´epar´ees par des p´eriodes de repos. La construction des rotations et des blocs
mensuels doit ˆetre conforme aux r`egles de la s´ecurit´e a´erienne, aux r`egles d’op´eration de la
compagnie et aux r`egles contenues dans les conventions collectives entre les employ´es et la
compagnie a´erienne. `A part l’introduction, la revue de litt´erature et la conclusion, cette th`ese
est compos´ee de trois chapitres principaux dont chacun pr´esente les travaux r´ealis´ees pour un
objectif de recherche bien pr´ecis. Ces trois chapitres utilisent les mˆemes instances du probl`eme
bas´ees sur des donn´ees r´eelles fournies par une grande compagnie a´erienne am´ericaine.
Le probl`eme de construction des rotations se r´esout traditionnellement en trois phases
de mani`ere s´equentielle : un probl`eme journalier, un probl`eme hebdomadaire et un probl`eme
mensuel. Cette approche interdit la r´ep´etition du mˆeme num´ero de vol dans une rotation. Le
premier objectif de cette th`ese est de mettre en ´evidence deux faiblesses de cette approche
s´equentielle et proposer `a la place une approche alternative qui permet la r´ep´etition des vols
dans une mˆeme rotation. Premi`erement, nous montrons que lorsque l’horaire des vols est
irr´egulier, les deux premi`eres phases ne sont qu’une perte de temps et on peut obtenir de
meilleures solutions en moins de temps si le probl`eme mensuel est r´esolu directement en utilisant
une approche d’horizon fuyant faisant appel `a une m´ethode de g´en´eration de colonnes.
En effet, cette approche a permis de diminuer le gras de la solution de 34% en moyenne o`u le
gras est une mesure de qualit´e portant sur le pourcentage du temps non travaill´e mais pay´e
durant un horizon. Deuxi`emement, mˆeme si l’horaire des vols est compl`etement r´egulier, la
qualit´e de la solution est meilleure si le probl`eme hebdomadaire est trait´e directement sans
exploiter le probl`eme journalier. En effet, les diff´erents tests ont montr´e qu’une moyenne de
48.8% des rotations contiennent des r´ep´etitions causant une r´eduction moyenne de 16% dans
le gras.----------Abstract
The integrated crew pairing and crew assignment problem for pilots consists of producing
a minimum-cost set of pairings and schedules such that each flight leg is covered once by one
pairing and one schedule, and side constraints are satisfied such as pilot availability in each
crew base station. A pairing is a sequence of duties separated by rest periods that must start
and end at the same crew base. A duty is a sequence of flights separated by connections and
ground waiting times, forming a working day for a crew. The construction of pairings and
schedules must respect all safety and collective agreement rules. Besides the introduction,
literature review and conclusion, this thesis is composed of three main chapters where each
one presents the performed work for a specific research objective. These three chapters use
the same problem instances based on real-data provided by a major US airline.
The crew pairing problem has been traditionally solved in the industry by a heuristic
three-phase approach that solves sequentially a daily, a weekly, and a monthly problem.
This approach prohibits the repetition of the same flight number in a pairing. The first objective
in this thesis is to highlight two weaknesses of the three-phase approach and propose
an alternative solution approach that exploits flight number repetitions in pairings. First,
when the flight schedule is irregular, we show that better quality solutions can be obtained
in less computational times if the first two phases are skipped and the monthly problem is
solved directly using a rolling horizon approach based on column generation. In fact, this approach
has reduced the solution fat by 34%. The solution fat is a quality measure that shows
the percentage of time not worked but paid. Second, even if the flight schedule is completely
regular, we show that better quality solutions can be derived by skipping the daily problem
phase and solving the weekly problem directly. Indeed, the proportion of pairings with such
repetitions represents 48.8% causing a mean reduction in the solution fat by 16%.
In practice, both the crew pairing and crew assignment problems are independently modeled
and sequentially solved. The use of a sequential approach considerably reduces the
complexity of the global problem but produces solutions that may not be conform with airline
desires. The second objective in this thesis is to propose a model that fully integrates
the crew pairing and crew assignment problems and solve it in a single step. Due to the
large size of this integrated model, we propose a solution method that combines a column
generation and a dynamic constraint aggregation method. Since the latter method requires a
good initial partition, this partition is provided by a set of pairings found with the sequentia
Aircraft Maintenance Routing Problem – A Literature Survey
The airline industry has shown significant growth in the last decade according to some indicators such as annual average growth in global air traffic passenger demand and growth rate in the global air transport fleet. This inevitable progress makes the airline industry challenging and forces airline companies to produce a range of solutions that increase consumer loyalty to the brand. These solutions to reduce the high costs encountered in airline operations, prevent delays in planned departure times, improve service quality, or reduce environmental impacts can be diversified according to the need. Although one can refer to past surveys, it is not sufficient to cover the rich literature of airline scheduling, especially for the last decade. This study aims to fill this gap by reviewing the airline operations related papers published between 2009 and 2019, and focus on the ones especially in the aircraft maintenance routing area which seems a promising branch
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