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Constrained Vehicle Routing and speed optimization Problem (CVRsoP) for electric vehicles. Bay, Maud ; Limbourg, Sabine Conference (2015, July) Detailed reference viewed: 33 (4 ULg)TSP model for electric vehicle deliveries, considering speed, loading and road grades Bay, Maud ; Limbourg, Sabine Conference (2015, June 05) The objective usually considered in sustainable transportation is to minimize pollution due to emissions, and equivalently energy consumption. Turning to electric mobility, pollution is related to ... [more ▼] The objective usually considered in sustainable transportation is to minimize pollution due to emissions, and equivalently energy consumption. Turning to electric mobility, pollution is related to electricity production technology, not considered in this research; driving range is the major concern nowadays, due to the limited capacity of batteries and long recharge times . Maximizing the driving range or the level of energy (state of charge of the battery) at destination leads to consider the main factors of energy consumption which are : vehicle weight, engine efficiency and consumption models, drive speed and acceleration, drive pattern, road grade, and payload. We define the electric vehicle travelling salesman problem (EV-TSP) and the electric vehicle routing problem (E-VRP) based on the classical TSP and on the Pollution Routing Problem (PRP) and present models and preliminary results for those problems. [less ▲] Detailed reference viewed: 75 (7 ULg)TSP model for electric vehicle deliveries, considering speed, loading and path slope. Bay, Maud ; Limbourg, Sabine Conference (2015, April 17) In the current Transport White Paper, the European Union presents a roadmap for a more competitive and sustainable European transport system. Concerning Urban Freight Transport, responsible for about a ... [more ▼] In the current Transport White Paper, the European Union presents a roadmap for a more competitive and sustainable European transport system. Concerning Urban Freight Transport, responsible for about a quarter of CO2 emissions of the transport sector, one of the goals of the EU is to achieve essentially CO2-free city logistics in major urban centres by 2030 by developing and deploying new and sustainable fuels and propulsion systems. The gradual phasing out of ‘conventionally-fuelled’ vehicles from the urban environment contributes to reduce oil dependence, greenhouse gas emissions and local air and noise pollution. To meet European air quality standards, authorities of some major European cities have already introduced Low Emissions Zones where access to urban areas is limited to freight vehicles that meet certain emissions standards. Greater use of low-emission urban trucks based on electric, hydrogen and hybrid technologies would reduce air emissions, but also noise, letting to use road infrastructure more efficiently by making night deliveries and avoiding morning and afternoon peak periods. In addition to their role in the reduction of polluting emissions, the development of low-emission vehicles also allows to mitigate the dependence of the transportation sector to high fossil fuel prices. Electric vehicles have the potential to be powered by renewable energy sources such as wind and solar energy. However, weaknesses can be found in the limited capacity of the battery and the time needed to recharge, and consequently, the limited driving range of electric vehicle. The main sources for final energy consumption are the vehicle size and the engine characteristics, the load factor, the driving pattern, the gradient which represent the average topology of the country, the speed and the acceleration. To maximize the driving range, a routing model, which aims at minimizing the energy consumption, has to be developed. Our paper focus on the Electric Vehicle Traveling Salesman Problem (EV-TSP): given n cities, find the shortest tour, i.e., the shortest directed cycle containing all cities. The classical objective is to minimize the cost tour scheduling to fulfill delivery requests at each location. In this paper we consider the energy cost and we present an extension of the classical problem to minimize the remaining storage capacity of all electric vehicles at the destination node, knowing that there is no recharge operation on the tour. The objective function accounts not just for the travel distance but also on the load of the vehicle and on its speed while the energy consumption of the engine additionally depends on the path to travel, on the slope of the roads and on the vehicle specifications. Moreover, negative consumption that may happen due to regenerative breaking and kinetic energy capture on downhill paths is taken into consideration. Mathematical model is described and computational experiments are performed. [less ▲] Detailed reference viewed: 97 (4 ULg)A global optimization method for naval structure op- timization Bay, Maud ; Crama, Yves ; Rigo, Philippe Conference (2013, July 01) The paper proposes a global optimization method for the preliminary structural design of large vessels in shipbuilding industry. We face a combinatorial problem of large size, with constraints modeled as ... [more ▼] The paper proposes a global optimization method for the preliminary structural design of large vessels in shipbuilding industry. We face a combinatorial problem of large size, with constraints modeled as implicit functions with nonlinear behavior. We present a heuristic method that performs a global search over the feasible solution space, combining a large neighborhood search and a heuristic local search. Experiments on actual structural optimization problems show that the heuristic converges towards discrete feasible solutions of good quality. [less ▲] Detailed reference viewed: 21 (1 ULg)Elective Course Allocation with numerical preferences Bay, Maud ; Homburg, David Conference (2013, February 14) In Universities, students have to select a specified number of elective courses to be included in their curriculum. Elective courses are a good way to increase students motivation and improve their ... [more ▼] In Universities, students have to select a specified number of elective courses to be included in their curriculum. Elective courses are a good way to increase students motivation and improve their academic success. At HEC- Management School of the University of Liège, each student has to set a preference value for each course offered and taking a number of courses is mandatory to fulfill his curriculum. The Elective Course Allocation with Numerical Preferences (ECANP) is the problem of assigning to each student the requested number of courses such as to maximize the total preference score (i.e. the overall sum of preference values associated by each student to the courses he has been granted). The course assignment problem often comes along with the course time tabling problem. This issue is not considered in this work as a complete course schedule is available at the time of registration. Each student provides his own schedule availability and can only attend one course at a time. An additional constraint is that a course cannot be granted to a student if his preference value for this course is null. We present the set of rules defined to ensure that a feasible assignment can be obtained for each student. The ECANP problem is modeled as a mixed integer programming model and we use CPLEX to obtain optimal solutions for a set of realistic instances. The ECANP problem is compared to the Elective Course Planning problem solved with heuristic methods in [2], to the course Allocation problem for which a bidding mechanism is described in [1] and to the College Admission (CA) problem as presented in [3]. In particular in the CA each student provides a preference order instead of numerical values and each student must be granted only one college. We discuss the differences between the mathematical formulations of theses problems and the ECANP problem, and their properties. [less ▲] Detailed reference viewed: 32 (0 ULg)Optimization Methods for the design and production of Naval Structures Bay, Maud 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 ▲] Detailed reference viewed: 95 (9 ULg)Space and time allocation in a shipyard assembly hall Bay, Maud ; Crama, 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 ▲] Detailed reference viewed: 179 (37 ULg)Aimms - Tutoriel en une heure à l’usage des débutants Bay, Maud ; François, Véronique Learning material (2009) Detailed reference viewed: 81 (15 ULg)Local search heuristics for large-scale discrete structural optimization with expensive black-box evaluations Bay, Maud ; Crama, Yves ; Rigo, Philippe 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 ▲] Detailed reference viewed: 91 (13 ULg)Alimentation durable : De la promotion des filières courtes à la promotion d’emplois durables Ozer, Pierre ; Bay, Maud 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 ▲] Detailed reference viewed: 554 (43 ULg)Multicriterion Scantling Optimization of the Midship Section of a Passenger Vessel considering IACS Requirements ; Caprace, Jean-David ; Losseau, Nicolas 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 ▲] Detailed reference viewed: 337 (50 ULg)Avoir le véhicule vert Bay, Maud ; Ozer, Pierre ; Perrin, Dominique 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 ▲] Detailed reference viewed: 96 (21 ULg)A mixed-integer heuristic for the structural optimization of a cruise ship Bay, Maud ; Crama, Yves ; 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 ▲] Detailed reference viewed: 119 (16 ULg)A branch and bound framework applied to naval structure optimization problems Bay, Maud 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 ▲] Detailed reference viewed: 151 (21 ULg)Optimization of Surface Utilization Using Heuristic Approaches ; Bay, Maud ; Crama, Yves 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 ▲] Detailed reference viewed: 115 (30 ULg)Optimization of Surface Allocation using Heuristic Approaches ; Bay, Maud ; Crama, Yves 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: 86 (22 ULg) |
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