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See detailOptimization Methods for the design and production of Naval Structures
Bay, Maud ULg

Doctoral thesis (2011)

In the past decades the marine industry has undergone significant evolution and the production of large passenger ships faced dramatic changes. The size, the complexity and the security standards of the ... [more ▼]

In the past decades the marine industry has undergone significant evolution and the production of large passenger ships faced dramatic changes. The size, the complexity and the security standards of the ships have increased and the ship-owners have become less and less willing to wait once the order is placed. In the meantime, due to growing intense competition, the shipyards have had to improve their efficiency and master their production costs: they progressively moved from manufacture to automated production processes. As a consequence, the shipyards have now to meet this difficult challenge: produce more complex ships, cheaper and faster. In the first part of the thesis we consider the structural optimization problem that arises in the early design phase of a project. Given a vessel overall dimensions and form, structural optimization consists in defining the scantling of the structure’s constitutive elements so as to minimize its total weight or cost, while taking weight, robustness and security issues into account. Designers have to make the most adequate choices within a very short period of time. The decisions made during the design phase have a major impact on the final structure and on its production cost. We propose new algorithms to compute near-optimal solutions of the discrete structural optimization problem. In the second part of the thesis, we turn to the building process of large ships and we present new methods to improve production facility management of shipyards. The ship building process requires the production and the assembly of tens, or even hundreds of thousands of steel elements. We define a space and time allocation problem that arises in assembly halls producing large building blocks and we develop algorithms for its solution. A successful implementation of a flexible and robust application is nowadays in use at a shipyard. [less ▲]

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See detailSpace and time allocation in a shipyard assembly hall
Bay, Maud ULg; Crama, Yves ULg; Langer, Yves et al

in Annals of Operations Research (2010), 179(1), 57-76

We present a space and time allocation problem that arises in assembly halls producing large building blocks (namely, a shipyard which assembles prefabricated keel elements). The building blocks are very ... [more ▼]

We present a space and time allocation problem that arises in assembly halls producing large building blocks (namely, a shipyard which assembles prefabricated keel elements). The building blocks are very large, and, once a block is placed in the hall, it cannot be moved until all assembly operations on this block are complete. Each block must be processed during a predetermined time window. The objective is to maximize the number of building blocks produced in the hall. The problem is modeled as a 3-dimensional bin packing problem (3D-BPP) and is handled by a Guided Local Search heuristic initially developed for the 3D-BPP. Our com- putational experiments with this heuristic demonstrate that excellent results can be found within minutes on a workstation, and that the heuristic outperforms a standard constraint programming approach. We also describe some additional real-life constraints arising in the industrial application and show how these constraints can be conveniently integrated in the model. [less ▲]

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See detailAimms - Tutoriel en une heure à l’usage des débutants
Bay, Maud ULg; François, Véronique ULg

Learning material (2009)

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See detailLocal search heuristics for large-scale discrete structural optimization with expensive black-box evaluations
Bay, Maud ULg; Crama, Yves ULg; Rigo, Philippe ULg

Report (2009)

This paper considers large-scale structural optimization problems featuring discrete variables, as well as nonlinear implicit constraints which can only be evaluated through time-expensive computations. A ... [more ▼]

This paper considers large-scale structural optimization problems featuring discrete variables, as well as nonlinear implicit constraints which can only be evaluated through time-expensive computations. A prominent application consists in the preliminary structural design of large ships, where many of the variables take their values in discrete sets which model standard element dimensions to be selected from catalogs, and where the evaluation of the constraints involves a complex structural analysis performed by black-box software. The resulting large-scale nonlinear combinatorial problems are particularly hard, and even nding a discrete feasible solution may prove challenging for some instances. In this paper, we propose two heuristics that combine local search methods and a sequential optimization method based on approximations of the implicit constraints. The heuristics are applied to the structural optimization of several large ships. For these instances, the heuristics provide discrete feasible solutions whose value is close to the optimal value of the continuous relaxation obtained by disregarding the discrete nature of the variables. [less ▲]

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See detailAlimentation durable : De la promotion des filières courtes à la promotion d’emplois durables
Ozer, Pierre ULg; Bay, Maud ULg

Scientific conference (2009, March)

Consommation durable ? Le thème de la consommation durable est relativement neuf. Il trouve ses origines au Sommet de la Terre qui s’est tenu en 1992 à Rio de Janeiro. Ce thème part du constat que les ... [more ▼]

Consommation durable ? Le thème de la consommation durable est relativement neuf. Il trouve ses origines au Sommet de la Terre qui s’est tenu en 1992 à Rio de Janeiro. Ce thème part du constat que les politiques publiques ne peuvent plus seulement se contenter d’agir sur la production ; infléchir également les modes de consommation écologiquement et socialement non soutenables étant devenu indispensable pour parvenir à un développement durable. Mais cela pose une série de questions. Quelles sont actuellement les spécificités des modes de consommation des ménages ? Quelles sont leurs capacités à évoluer vers la prise en compte des critères du développement durable ? Quels sont les rôles que doivent jouer les pouvoirs publics, les acteurs économiques et associatifs dans la consommation durable ? [less ▲]

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See detailMulticriterion Scantling Optimization of the Midship Section of a Passenger Vessel considering IACS Requirements
Richir, Thomas; Caprace, Jean-David ULg; Losseau, Nicolas ULg et al

in The 10th International Symposium on Practical Design of Ships and Other Floating Structures (PRADS) (2007, October)

In the scantling design of a passenger ship, minimum production cost, minimum weight and maximum moment of inertia (stiffness) are conflicting objectives. For that purpose, recent improvements were made ... [more ▼]

In the scantling design of a passenger ship, minimum production cost, minimum weight and maximum moment of inertia (stiffness) are conflicting objectives. For that purpose, recent improvements were made to the LBR-5 software (French acronym of “Stiffened Panels Software”, version 5.0) to optimize the scantling of ship sections by considering production cost, weight and moment of inertia in the optimization objective function. Moreover, IACS requirements regarding bending, shearing and buckling strength are currently available in LBR-5. Until now, only raw scantling optimizations were performed with LBR-5. Thanks to new developments using heuristics, it is now possible to realize discrete optimization so that a standardized and “ready to use” set of optimum scantlings can be obtained. [less ▲]

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See detailAvoir le véhicule vert
Bay, Maud ULg; Ozer, Pierre ULg; Perrin, Dominique ULg et al

Article for general public (2007)

L'argument est séduisant d'acquérir un nouveau véhicule, plus propre en émission de CO2, mais il faut aussi se débarrasser de son ancien. Attention au bilan CO2 total de l'opération ! [...] De plus en ... [more ▼]

L'argument est séduisant d'acquérir un nouveau véhicule, plus propre en émission de CO2, mais il faut aussi se débarrasser de son ancien. Attention au bilan CO2 total de l'opération ! [...] De plus en plus d'entreprises s'emparent des problématiques environnementales pour vanter leurs produits "plus écologiques". Il faut bien avouer que, suite au film d'Al Gore sur le réchauffement climatique et aux interventions très médiatisées de Nicolas Hulot sur l'urgence écologique, le sujet est très à la mode dans notre pays. D'autant plus qu'au cours des trois dernières années de divers constructeurs automobiles devenues très "vertes" nous incitent à remplacer notre ancien véhicule "polluant" par un nouveau, plus économe en carburant et donc plus propre également en émissions de CO2. Certes l'argument est séduisant. Il faut cependant prendre garde de ne pas oublier que la production, le transport, le marketing et le démantèlement d'un nouveau véhicule émettent aussi beaucoup de CO2 et doivent donc être pris en compte dans le "bilan CO2" total de l'opération. [...] [less ▲]

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See detailA mixed-integer heuristic for the structural optimization of a cruise ship
Bay, Maud ULg; Crama, Yves ULg; Richir, Thomas et al

in COMPIT 2007 , Cortona, Italy (2007, April 23)

A heuristic approach is proposed to solve the structural optimization problem of a cruise ship. The challenge of optimization is to define the scantling of the structure of a ship in order to minimize the ... [more ▼]

A heuristic approach is proposed to solve the structural optimization problem of a cruise ship. The challenge of optimization is to define the scantling of the structure of a ship in order to minimize the weight or the production cost. The variables are the dimensions and positions of the constitutive elements of the structure: they are discrete by nature. The objective functions are nonlinear functions. The structure is submitted to geometric constraints and to structural constraints. The geometric constraints are linear functions and the structural constraints are implicit functions requiring a high computation cost. The problem belongs to the class of mixed-integer nonlinear problems (MINLP). A local heuristic of the type “dive and fix” is combined with a solver based on approximation methods. The solver is used as a black-box tool to perform the structural analysis and solve the nonlinear optimization problems (NLP) defined by the heuristic. The heuristic is designed to always provide a discrete feasible solution. Experiments on a real-size structure demonstrate that the optimal value of the mixed-integer problem is of the same magnitude as the optimal value of the optimization problem for which all the variables can take continuous values. [less ▲]

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See detailA branch and bound framework applied to naval structure optimization problems
Bay, Maud ULg

Master of advanced studies dissertation (2005)

Naval structure optimization consists of defining the optimum scantling of the constitutive elements of a structure with given general dimensions and form of the hull. Amathematical formulation leads to ... [more ▼]

Naval structure optimization consists of defining the optimum scantling of the constitutive elements of a structure with given general dimensions and form of the hull. Amathematical formulation leads to non linear problem with mixed (discrete continuos) variables and implicit constraints that are evaluated with a "black-box" software. The evaluation of the constraints is vry expensive in computation time. A non-linear branch and bound framework is presented to solve this problem. The method is first tested on a small example to set up the parameters of the algorithm and then is applied to a real size structures. It performs very well to provide good solutions in a reasonable time. [less ▲]

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See detailOptimization of Surface Utilization Using Heuristic Approaches
Langer, Yves; Bay, Maud ULg; Crama, Yves ULg et al

in Ship Technology Research = Schiffstechnik (2005), 52(3), 141-147

We present a scheduling problem that arises in factories producing large building blocks. This is a three dimensional bin-packing problem with two spatial dimensions and a time dimension. We propose an ... [more ▼]

We present a scheduling problem that arises in factories producing large building blocks. This is a three dimensional bin-packing problem with two spatial dimensions and a time dimension. We propose an algorithm based on the guided local search heuristic of Faroe and al. (Informs Journal of Computing,vol.15, 2003). The algorithm is especially developped to consider real-life issues. Finally the algorithm is applied on an industrial problem and shows excellent performances in speed and quality of the solution. [less ▲]

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See detailOptimization of Surface Allocation using Heuristic Approaches
Langer, Yves; Bay, Maud ULg; Crama, Yves ULg et al

in COMPIT 2005 , Hambourg, Germany (2005, May)

In this paper, we present a scheduling problem that arises in factories producing large building blocks (in our case, a shipyard workshop producing prefabricated keel elements). The factory is divided in ... [more ▼]

In this paper, we present a scheduling problem that arises in factories producing large building blocks (in our case, a shipyard workshop producing prefabricated keel elements). The factory is divided in several equal size areas. The blocks produced in the factory are very large, and, once a building block is placed in the factory, it cannot be moved until all processes on the building block are finished. The blocks cannot overlap. The objective is to maximize the number of building blocks produced in the factory during a certain time window. To solve this problem, we propose heuristics inspired by techniques initially developed for the three-dimensional bin packing problem, e.g. Faroe and al. (2003), since constraints for both problems are quite similar. Starting from an unfeasible solution, where blocks can overlap, a Guided Local Search (GLS) heuristic is used to minimize the sum of total overlap. If a solution with zero overlap is found, then it is a feasible solution; otherwise the block with the biggest overlap is removed and the procedure is restarted. The GLS algorithm has been improved by Fast Local Search (FST) tech- niques in order to speed up convergence to a local minimum. Additionally, neighborhoods are restricted to their smallest size so as to allow their evaluation in polynomial-time. In a last step, we explain the additional real-life issues arising in the industrial application and how firm-specific constraints can be conveniently considered by the model. [less ▲]

Detailed reference viewed: 77 (22 ULg)