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  • Scheduling commercial advertisements for television

     García Villoria, Alberto; Salhi, Said
    International Journal of Production Research
    Vol. 53, num. 4, p. 1198-1215
    DOI: 10.1080/00207543.2014.951095
    Date of publication: 2015-02-16
    Journal article

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    The problem of scheduling the commercial advertisements in the television industry is investigated. Each advertiser client demands that the multiple airings of the same brand advertisement should be as spaced as possible over a given time period. Moreover, audience rating requests have to be taken into account in the scheduling. This is the first time this hard decision problem is dealt with in the literature. We design two mixed integer linear programming (MILP) models. Two constructive heuristics, local search procedures and simulated annealing (SA) approaches are also proposed. Extensive computational experiments, using several instances of various sizes, are performed. The results show that the proposed MILP model which represents the problem as a network flow obtains a larger number of optimal solutions and the best non-exact procedure is one that uses SA.

  • Desig of off-grid renewable energy community electrification projects: analysis of micro-scale resource variations and developement of optimization methods

     Ranaboldo, Matteo
    Department of Business Administration, Universitat Politècnica de Catalunya
    Theses

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    Los proyectos de electrificación basados en energías renovables han demostrado ser una opción adecuada y sostenible para abastecer comunidades aisladas de forma autónoma. Estos sistemas producen energía de manera limpia y respetuosa del medio ambiente y su coste es a menudo inferior al de extender la red eléctrica nacional. Las configuraciones de diseño más fiables y eficientes utilizan sistemas híbridos que combinan varios recursos (eólico y solar) y distribución mediante microrredes. El diseño de proyectos de electrificación rural considerando sistemas híbridos y microrredes se ha definido como el problema AVEREMS. La optimización del problema AVEREMS es una tarea compleja que requiere el uso de herramientas de soporte. Actualmente, el proceso de diseño de proyectos de electrificación basados en energía renovables presenta algunas limitaciones. Entre ellas, destacan la falta de conocimientos sobre estudios del recurso eólico y la necesidad de procedimientos para resolver el problema AVEREMS incluyendo la generación alejada de los puntos de consumo para aprovechar las áreas de mayor potencial.El principal objetivo de esta tesis es abordar dichas limitaciones, mediante: 1) la definición de un método para evaluar en detalle el recurso eólico en proyectos de electrificación rural; 2) el desarrollo y 3) la implementación de procedimientos para resolver el problema AVEREMS considerando la variación del recurso a micro-escala y generación en todos los puntos (sean estos de consumo o de no-consumo) de una determinada área.Primero se presenta un método para realizar estudios del recurso eólico mediante el uso de modelos de flujo de viento a micro-escala. El método se valida en dos comunidades montañosas y se aplica para el diseño de proyectos reales en Cabo Verde.Sucesivamente, se desarrollan diferentes procedimientos resolutivos: primero se definen unos indicadores de soporte al diseño, y sucesivamente se presentan dos algoritmos (uno heurístico y otro meta-heurístico) para resolver el problema AVEREMS. Se analizan diferentes versiones de los algoritmos para finalmente seleccionar las que obtienen los mejores resultados. Además de considerar generación en todos los puntos (de consumo o de no-consumo) de una cierta área, los algoritmos propuestos mejoran considerablemente las prestaciones de los métodos disponibles actualmente.Finalmente, se analiza el diseño de un proyecto de electrificación en una comunidad rural en Nicaragua incluyendo la evaluación de recurso a micro-escala y la aplicación del algoritmo meta-heurístico para la optimización del diseño.La metodología para la evaluación del recurso eólico y los algoritmos resolutivos desarrollados en esta tesis se pueden fácilmente aplicar para suportar el diseño de proyectos de electrificación rural con energías renovables. Su utilización permitirá mejorar la eficiencia y sostenibilidad de estos proyectos reduciendo algunos de los problemas técnicos que limitan su implementación en comunidades aisladas

  • Equilibrado de líneas de montaje con ventanas de visibilidad. Descripción del problema y procedimiento heurístico de resolución

     Calleja Sanz, Gema; Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
    Dyna
    Vol. 89, num. 5, p. 552-559
    DOI: 10.6036/7051
    Date of publication: 2014-09
    Journal article

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    Assembly line balancing problems (ALBPs) arise when designing or modifying an assembly or production line and usually consist in assigning the tasks to the workstations along the line in order to meet some given objectives. Traditionally, it is assumed that there is exactly one workpiece in each workstation and that the workstation has access to the entire workpiece. In practice, this assumption may be sometimes too restrictive. An example is the case of the automated assembly of printed circuit boards. In this type of lines the length of the workpiece might be larger than the width of the workstation. Therefore, each workstation can only access to the limited portion of the workpieces that fall inside its accessibility window. In this work we present an extension of the ALBP to the case of workstations with accessibility windows (AWALBP). The problem is described and a simple-to-implement solving procedure is proposed, which consists of i) an algorithm to obtain a good initial solution and ii) a simulated annealing algorithm for improving the obtained solution. Finally, a computational experience that validates the proposed procedure is reported.

  • A heuristic method to design autonomous village electrification projects with renewable energies

     Ranaboldo, Matteo; García Villoria, Alberto; Ferrer Marti, Laia; Pastor Moreno, Rafael
    Energy
    Vol. 73, p. 96-109
    DOI: 10.1016/j.energy.2014.05.099
    Date of publication: 2014-08-14
    Journal article

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    Systems relying on renewable energies demonstrated to be a reliable and sustainable option to electrify isolated communities autonomously. Hybrid systems that combine different energy resources and distribution microgrids are the most efficient design configurations. The design of these systems requires the use of decision support tools, while projects' promoters generally dispose of low design resources. This study presents a heuristic method to design off-grid electrification projects based on wind and solar energies considering micro-scale resource variations and a combination of independent generation points and microgrids. The method considers generation far from users and a pre-selection process is presented in order to screen the initial pool of potentially infinite generation points. Different algorithm versions are evaluated and performances are compared with existing tools: VIPOR, known software for microgrids design, and a recently developed mixed integer linear programming (MILP) model. The proposed heuristic performs better than VIPOR with mean improvements of around 6% and, for communities of more than 40 users, considerably enhances solutions obtained by the MILP model with a much lower computational time (1 min against 1 h). The method is a complete and simple tool that can efficiently support the design of stand-alone community electrification projects with renewable energies. (C) 2014 Elsevier Ltd. All rights reserved.

  • Combining matheuristics and MILP to solve the accessibility windows assembly line balancing problem level 2 (AWALBP-L2)

     Calleja Sanz, Gema; Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
    Computers & operations research
    Vol. 48, p. 113-123
    DOI: 10.1016/j.cor.2014.03.009
    Date of publication: 2014-08-01
    Journal article

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    We propose an approach combining a matheuristic and a MILP model to solve the variant Level 2 of the Accessibility Windows Assembly Line Balancing Problem (AWALBP-L2). This is a novel problem that arises in those real-world assembly lines where, in contrast to the most common ones, the length of the workpieces is larger than the widths of the workstations. This means that, at any time, a workstation cannot access an entire workpiece, but only a restricted portion of a workpiece or two consecutive workpieces. As a result, a workstation can only perform, at any time, the subset of tasks that fall inside its accessible area. The problem is to solve the task assignment and the movement scheme subproblems, while minimizing the cycle time. The proposed solving approach consists of (i) a matheuristic to generate good feasible solutions and compute bounds and (ii) a MILP model that makes use of the obtained bounds. A computational study is carried out to compare the performance of the proposed approach with the existing literature. (C) 2014 Elsevier Ltd. All rights reserved.

  • The accessibility windows assembly line balancing problem (AWALBP): a review of advances and trends

     Calleja Sanz, Gema; Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
    Triennial Conference of the International Federation of Operational Research Societies
    p. 191
    Presentation's date: 2014-07-17
    Presentation of work at congresses

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    We investigate the Accessibility Windows Assembly Line Balancing Problem (AWALBP), where, in sharp contrast to traditional assembly line problems, only a portion of the workpieces can be reached from each workstation. The literature distinguishes different variants of the problem, and several formulations and solution approaches have been proposed. This talk gives an overview on recent advances in the methods used to solve AWALBP, including exact, heuristic and hybrid methods. An extensive set of computational experiments, along with some guidelines for further lines of research are reported.

  • MILP-based tabu search using corridor method for an assembly line balancing problem with accessibility windows

     Corominas, Albert; García Villoria, Alberto; Calleja Sanz, Gema; Pastor Moreno, Rafael
    Triennial Conference of the International Federation of Operational Research Societies
    p. 192
    Presentation's date: 2014-07-17
    Presentation of work at congresses

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    In this work, we present an MILP-TS matheuristic for an assembly line balancing problem with accessibility windows. The proposed matheuristic uses an MILP model embedded in a tabu search (TS) algorithm to iteratively solve reduced portions of the original solution space. We use the paradigm of the corridor method to impose exogenous constraints of the original mathematical formulation and, subsequently, we apply an MILP solver to optimally solve the constrained problem. Computational results show the effectiveness of the proposed matheuristic.

  • Journal of heuristics

     García Villoria, Alberto
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    A GRASP based method to design off-grid community electrification projects with renewable energies  Open access

     Ranaboldo, Matteo; García Villoria, Alberto; Ferrer Marti, Laia; Pastor Moreno, Rafael
    Date: 2014
    Report

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    The design of off-grid electrification projects considering hybrid systems and distribution microgrids is a complex task that requires the use of decision support tools. Most of existing tools focus on the design of hybrid systems without defining generator locations and distribution through microgrids. Recently a deterministic heuristic was developed to solve the complete problem. In this study we present an improved deterministic heuristic and then a meta-heuristic procedure, based on the GRASP, for designing community off-grid electrification projects based on renewable energies considering micro-scale resource variations and a combination of independent generation points and microgrids. Both algorithms improve performance of the previous existing procedure. The new deterministic heuristic can rapidly (computational time lower than 1 minute) obtain a good solution. On the other hand, the proposed GRASP based method considerably enhances solutions obtained by the deterministic heuristic with a computational time of 1 hour on a standard PC. The improvement tends to increase as the problem complexity increases: improvements of more than 1% were obtained in more than 30% of the instances bigger than 40 users. The proposed algorithm is a complete design tool that can efficiently support the design of stand-alone community electrification projects requiring of low computational resources.

  • Renewable energy projects to electrify rural communities in Cape Verde

     Ranaboldo, Matteo; Domenech Lega, Bruno; Vilar, David; Ferrer Marti, Laia; Pastor Moreno, Rafael; García Villoria, Alberto
    Applied energy
    Vol. 118, p. 280-291
    Date of publication: 2014
    Journal article

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    Even though Cape Verde has high wind and solar energy resources, the conventional strategy for increasing access to electricity in isolated rural areas is by centralized microgrids with diesel generators. In this study, the design of 2 off-grid electrification projects based on hybrid wind–photovoltaic systems in Cape Verde is developed and analyzed. The design considers some significant novelty features in comparison with previous studies. First a detailed wind resource assessment is carried out combining meso-scale wind climate data and a specialized micro-scale wind flow model. Then a mathematical model is used for the design of off-grid projects considering a combination of individual systems and microgrids. In this study, locations far from the demand points are also considered as possible generation points. Various design configurations are analyzed and compared. The proposed configurations exploit the highest wind potential areas and are economically beneficial in comparison with diesel generator systems.

    Even though Cape Verde has high wind and solar energy resources, the conventional strategy for increasing access to electricity in isolated rural areas is by centralized microgrids with diesel generators. In this study, the design of 2 off-grid electrification projects based on hybrid wind–photovoltaic systems in Cape Verde is developed and analyzed. The design considers some significant novelty features in comparison with previous studies. First a detailed wind resource assessment is carried out combining meso-scale wind climate data and a specialized micro-scale wind flow model. Then a mathematical model is used for the design of off-grid projects considering a combination of individual systems and microgrids. In this study, locations far from the demand points are also considered as possible generation points. Various design configurations are analyzed and compared. The proposed configurations exploit the highest wind potential areas and are economically beneficial in comparison with diesel generator systems.

  • Metodología para el diseño de proyectos de electrificación autónomos con energías eólica y solar, y consideraciones técnicas y sociales

     Ranaboldo, Matteo; Domenech Lega, Bruno; Ferrer Marti, Laia; García Villoria, Alberto; Pastor Moreno, Rafael
    Simposio internacional en energía eolica de pequeña escala
    Presentation's date: 2013-11
    Presentation of work at congresses

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  • Erratum to “A solution procedure for type E simple assembly line balancing problem"

     García Villoria, Alberto; Pastor Moreno, Rafael
    Computers and industrial engineering
    Vol. 66, num. 1, p. 201-202
    DOI: 10.1016/j.cie.2013.05.015
    Date of publication: 2013-10-01
    Journal article

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    The objective of SALBP-E is to minimize the product on the number of workstations by the cycle time. Recently Wei and Chao [Comput. Ind. Eng. 61 (2011) 824–830] have proposed an exact procedure for solving this problem. It is based on solving iteratively SALBP-2 by means of a MILP model. SALBP-E has not been much studied and hence the high interest of their work. However, the article has several errors that make its understanding harder and, moreover, impede the correct implementation of their procedure for solving SALBP-E. Therefore, it is important to correct them.

  • Minimising maximum response time

     García Villoria, Alberto; Pastor Moreno, Rafael
    Computers & operations research
    Vol. 40, num. 10, p. 2314-2321
    DOI: 10.1016/j.cor.2013.03.014
    Date of publication: 2013-10
    Journal article

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    The minmax response time problem (mRTP) is a scheduling problem that has recently appeared in the literature and can be considered as a fair sequencing problem. This kind of problems appears in a wide range of real-world applications in mixed-model assembly lines, computer systems, periodic maintenance and others. The mRTP arises whenever products, clients or jobs need to be sequenced in such a way that the maximum time between the points at which they receive the necessary resources is minimised. The mRTP has been solved in the literature with a greedy heuristic. The objective of this paper is to improve the solution of this problem by means of exact and heuristic methods. We propose one mixed integer linear programming model, nine local search procedures and five metaheuristic algorithms. Extensive computational experiments are carried out to test them.

  • Using tabu search and MILP for the accessibility windows assembly line balancing problem (AWALBP)

     Calleja Sanz, Gema; Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
    Congreso Nacional de Estadística e Investigación Operativa
    p. 117
    DOI: 10.6035/e-TIiT.2013.16
    Presentation's date: 2013-09-12
    Presentation of work at congresses

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    The AWALBP arises in those assembly lines where, in contrast to standard ones, the length of the workpieces is larger than the accessibility windows of the workstations. Because of this, only a limited portion of one or two consecutive workpieces can be reached from each station at any moment. In our problem, the cycle decomposes into stationary stages separated between them by forward steps, according to a cyclic movement scheme. Several procedures were previously proposed to solve the problem to optimality and instances up to a certain size limit were solved. In this study, we propose a tabu search (TS) and a combination procedure using TS and a mixed integer linear programming (MILP) model in order to solve larger instances. The neighborhood search is performed in the space of the movement schemes. Results show that a better solution is obtained in most of the cases that could not be previously solved optimally.

  • Corridor method heuristics to solve rural electrification projects

     Triado Aymerich, Joan; Ferrer Marti, Laia; García Villoria, Alberto; Pastor Moreno, Rafael
    International Workshop on Simulation-Optimization & Internet Computing
    Presentation's date: 2013-07-11
    Presentation of work at congresses

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  • MILP based heuristics to solve rural electrification projects

     Triado Aymerich, Joan; Ferrer Marti, Laia; García Villoria, Alberto; Pastor Moreno, Rafael
    European Conference on Operational Research
    p. 39
    Presentation's date: 2013-07-03
    Presentation of work at congresses

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  • Using simulated annealing and MILP for the accessibility windows assembly line balancing problem (AWALBP)

     Calleja Sanz, Gema; Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
    European Conference on Operational Research
    p. 38
    Presentation's date: 2013-07-01
    Presentation of work at congresses

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    The AWALBP is an assembly line balancing problem where the length of the workpieces is larger than the width of the workstations. A procedure using a matheuristic and a mixed integer linear programming (MILP) model was previously tested to solve the AWALBP and it succeeded in finding optimal solutions to instances up to a certain size. We propose simulated annealing (SA) and a hybrid procedure using SA and MILP in order to find good quality solutions for larger instances. Results show that a better solution is obtained in most of the cases that could not be previously solved optimally.

  • Metaheuristic algorithms hybridized with variable neighbourhood search for solving the response time variability problem

     Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
    TOP
    Vol. 21, num. 2, p. 296-312
    DOI: 10.1007/s11750-011-0175-y
    Date of publication: 2013-07
    Journal article

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  • A MILP model for the Accessibility Windows Assembly Line Balancing Problem (AWALBP).

     Calleja Sanz, Gema; Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
    International Journal of Production Research
    Vol. 51, num. 12, p. 3549-3560
    DOI: 10.1080/00207543.2012.751514
    Date of publication: 2013-06
    Journal article

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    This work studies a novel assembly line balancing problem that has recently appeared in the literature, which we name Accessibility Windows Assembly Line Balancing Problem (AWALBP). AWALBP is a real-world industrial problem that arises in those assembly lines where, as opposed to the most common ones, the length of the workpiece is larger than the widths of the workstation. This means that, at any time, a workstation cannot access one whole workpiece, but only a restricted portion of one or two consecutive workpiece. In our problem the cycle decomposes into stationary stages separated by forward steps, according to a cyclic movement scheme. The aim of this paper is (i) to formalise the AWALBP and its variants, and (ii) to propose a Mixed Integer Linear Programming (MILP) model using two alternative formulations to solve the variant AWALBP-L2. This variant involves solving the task assignment and the movement scheme sub-problems (with the objective of minimising the cycle time). An extensive computational experiment is carried out to study the behaviour of the proposed model for different instance sizes. To the best of our knowledge, this is the first work in the literature which provides optimal solutions for AWALBP-L2. In addition, a set of benchmark instances is provided, which can be further used by the research community.

  • Simulated annealing for improving the solution of the response time variability problem

     García Villoria, Alberto; Pastor Moreno, Rafael
    International Journal of Production Research
    Vol. 51, num. 16, p. 4911-4920
    DOI: 10.1080/00207543.2013.775522
    Date of publication: 2013-05-29
    Journal article

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  • A MILP model to design hybrid wind–photovoltaic isolated rural electrification projects in developing countries

     Ferrer Marti, Laia; Domenech Lega, Bruno; García Villoria, Alberto; Pastor Moreno, Rafael
    European journal of operational research
    Vol. 226, num. 2, p. 293-300
    DOI: 10.1016/j.ejor.2012.11.018
    Date of publication: 2013-04-16
    Journal article

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    Electrification systems based on the use of renewable energy sources are a suitable option for providing electricity to isolated communities autonomously. Wind and hybrid wind-photovoltaic (PV) systems are increasingly getting attention. To electrify scattered communities, designs that combine individual systems and microgrids have recently proven advantageous. In this paper we present a mathematical programming model to optimize the design of hybrid wind-PV systems that solves the location of the wind-PV generators and the design of the microgrids, taking into account the demand of the consumption points and the energy potential. The criterion is the minimization of the initial investment cost required to meet the demand. The proposed hybrid model is tested with realistic size instances and results show the instances are efficiently solved.

    Electrification systems based on the use of renewable energy sources are a suitable option for providing electricity to isolated communities autonomously. Wind and hybrid wind–photovoltaic (PV) systems are increasingly getting attention. To electrify scattered communities, designs that combine individual systems and microgrids have recently proven advantageous. In this paper we present a mathematical programming model to optimize the design of hybrid wind–PV systems that solves the location of the wind–PV generators and the design of the microgrids, taking into account the demand of the consumption points and the energy potential. The criterion is the minimization of the initial investment cost required to meet the demand. The proposed hybrid model is tested with realistic size instances and results show the instances are efficiently solved. Moreover, the model is applied to real case studies in Peru; obtained results verify that the hybrid model efficiently finds solutions that significantly reduce cost.

  • Design of autonomous rural electrification systems for isolated Spanish communities

     Domenech Lega, Bruno; Ranaboldo, Matteo; Ferrer Marti, Laia; García Villoria, Alberto; Pastor Moreno, Rafael
    International Conference on Microgeneration and Related Technologies
    p. 88
    Presentation's date: 2013-04-15
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  • A branch and bound algorithm for the response time variability problem

     García Villoria, Alberto; Corominas Subias, Albert; Delorme, Xavier; Dolgui, Alexandre; Kubiak, Wieslaw; Pastor Moreno, Rafael
    Journal of scheduling
    Vol. 16, num. 2, p. 243-252
    DOI: 10.1007/s10951-012-0277-x
    Date of publication: 2013-04
    Journal article

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    The response time variability problem (RTVP) is an NP-hard scheduling problem that has been studied intensively recently and has a wide range of real-world applications in mixed-model assembly lines, multithreaded computer systems, network environments and others. The RTVP arises whenever products, clients or jobs need to be sequenced in order to minimise the variability in the time between two successive points at which they receive the necessary resources. To date, the best exact method for solving this problem is a mixed integer linear programming (MILP) model, which solves to optimality most of instances with up to 40 units to be scheduled in a reasonable amount of time. The goal of this paper is to increase the size of the instances that can be solved to optimality. We have designed an algorithm based on the branch and bound (B&B) technique to take advantage of the particular features of the problem. Our computational experiments show that the B&B algorithm is able to solve larger instances with up to 55 units to optimality in a reasonable time.

    The response time variability problem (RTVP) is an NP-hard scheduling problem that has been studied intensively recently and has a wide range of real-world applications in mixed-model assembly lines, multithreaded computer systems, network environments and others. The RTVP arises whenever products, clients or jobs need to be sequenced in order to minimise the variability in the time between two successive points at which they receive the necessary resources. To date, the best exact method for solving this problem is a mixed integer linear programming (MILP) model, which solves to optimality most of instances with up to 40 units to be scheduled in a reasonable amount of time. The goal of this paper is to increase the size of the instances that can be solved to optimality. We have designed an algorithm based on the branch and bound (B&B) technique to take advantage of the particular features of the problem. Our computational experiments show that the B&B algorithm is able to solve larger instances with up to 55 units to optimality in a reasonable time

  • Dyna

     García Villoria, Alberto
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  • Technical note: A systematic procedure based on CALIBRA and the Nelder & Mead algorithm for fine-tuning metaheuristics

     Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
    Journal of the Operational Research Society
    Vol. 64, num. 2, p. 276-282
    DOI: 10.1057/jors.2012.51
    Date of publication: 2013-02
    Journal article

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  • Heuristic indicators for the design of community off-grid electrification systems based on multiple renewable energies

     Ranaboldo, Matteo; Ferrer Marti, Laia; García Villoria, Alberto; Pastor Moreno, Rafael
    Energy
    Vol. 50, p. 501-512
    Date of publication: 2013
    Journal article

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    Off-grid rural electrification project configurations which consider hybrid generation systems based on multiple renewable sources and the implementation of micro-grids are the most promising design solutions. The efficient design of those systems is a complex task that is facing several technical issues such as limited time and resources available for the purpose, especially in developing countries. This study proposes indicators for supporting and improving the design of community off-grid electrification projects considering hybrid generation and micro-grids. A (Grid Generation Score) GGS is defined in order to identify most promising locations for being the generation point of a micro-grid. The (No- Generation Score) NGS and the (Independent Generation Score) IGS evaluate respectively if a point should be reliably connected to a micro-grid or should better be an independent generation point. All indicators could be easily and quickly calculated at a very first stage of the plan of a community project requiring as input data only demand and resource distributions in the studied area. It is shown that the utilization of proposed indictors can enhance the design of stand-alone community electrification projects based on renewable energies.

  • Journal of scheduling

     García Villoria, Alberto
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  • Pure and hybrid metaheuristics for the response time variability problem

     García Villoria, Alberto; Corominas Subias, Albert; Pastor Moreno, Rafael
    DOI: 10.4018/978-1-4666-2086-5.ch010
    Date of publication: 2012-08-16
    Book chapter

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  • Modelo de PLEM mejorado para el Accessibility Windows Assembly Line Balancing Problem (AWALBP)

     Calleja Sanz, Gema; Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
    International Conference on Industrial Engineering and Industrial Management. Congreso de Ingeniería de Organización
    p. 879-886
    Presentation's date: 2012-07-18
    Presentation of work at congresses

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    The Accessibility Windows Assembly Line Balancing Prob-lem (AWALBP) occurs in those assembly lines where the length of the workpiec-es is large relative to the width of the workstations. As a result, each workstation can only access to the limited portion of workpiece(s) that is inside its accessibil-ity window. In previous works we proposed a mixed-integer linear programming (MILP) model and a heuristic decomposition approach to solve AWALBP. Com-putational results revealed the size limits of the instances that could be solved. In this work, we provide an enhanced MILP model using reformulations and addi-tional bound contraints, which significantly improves the percentage of the in-stances optimally solved.

  • Access to the full text
    Heurística basada en PLEM para resolver proyectos de electrificación rural  Open access

     Triadó-Aymerich, Joan; Ferrer Marti, Laia; García Villoria, Alberto; Pastor Moreno, Rafael
    International Conference on Industrial Engineering and Industrial Management
    p. 1137-1144
    Presentation's date: 2012-07
    Presentation of work at congresses

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    En la literatura se ha propuesto un modelo matemático para diseños de electrificación rural con generación eólica y solar en el que tiene que decidirse la localización de cada uno de los componentes de generación y distribución de energía eléctrica. Cuando la cantidad de viviendas a electrificar excede de un cierto número, la resolución del modelo matemático requiere un tiempo computacional que puede ser inviable en la práctica. En este artículo se presenta un método heurístico basado en programación lineal entera y mixta para la resolución de ejemplares con gran número de viviendas. Para ello proponemos un proceso en dos etapas. En la primera etapa se resuelve el modelo con algunas de las variables relajadas. En la segunda etapa se fijan algunas variables enteras resultado de la etapa 1 y se resuelve el modelo sin relajar. En este artículo se presenta una extensa experiencia computacional para evaluar la heurística propuesta y se constata una mejora de las soluciones obtenidas.

  • Access to the full text
    Heurística basada en un indicador de demanda y potencial para diseñar sistemas de electrificación  Open access

     Ranaboldo, Matteo; Ferrer Marti, Laia; García Villoria, Alberto; Pastor Moreno, Rafael
    International Conference on Industrial Engineering and Industrial Management
    p. 1057-1066
    Presentation's date: 2012-07
    Presentation of work at congresses

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  • Premi extraordinari de doctorat en l'ambit d'Enginyeria Industrial

     García Villoria, Alberto
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  • Cocktail of heuristics for solving hard problems

     Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
    Dyna
    Vol. 87, num. 3, p. 275-278
    DOI: 10.6036/4508
    Date of publication: 2012-05
    Journal article

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  • Enhanced MILP model for the Accessibility Windows Assembly Line Balancing Problem (AWALBP)

     Calleja Sanz, Gema; Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
    Congrès Annuel de la Société Française de Recherche Opérationnelle et d'Aide à la Décision
    p. 117-118
    Presentation's date: 2012-04-13
    Presentation of work at congresses

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    The Accessibility Windows Assembly Line Balancing Problem (AWALBP) arises in those assembly lines where, as opposed to traditional assembly lines, the dimensions of the workpieces are larger than the width of the workstations. This means that, at any cycle, a workstation cannot access to one whole workpiece, but only to a restricted portion of one or two consecutive workpieces [1]. In our problem the cycle decomposes into stationary stages separated between them by forward steps, according to a cyclic movement scheme.

  • An Adaptive search for the response time variability problem

     Salhi, Said; García Villoria, Alberto
    Journal of the Operational Research Society
    Vol. 63, num. 5-6, p. 597-605
    DOI: 10.1057/jors.2011.46
    Date of publication: 2012
    Journal article

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    The Response Time Variability Problem (RTVP) is an NP-hard combinatorial scheduling problem, which has recently been reported and formalised in the literature. This problem has a wide range of real-world applications in mixed-model assembly lines, multi-threaded computer systems, broadcast of commercial videotapes and others. The RTVP arises whenever products, clients or jobs need to be sequenced in such a way that the variability in the time between the points at which they receive the necessary resources is minimised. We propose a greedy but adaptive heuristic that avoids being trapped into a poor solution by incorporating a look ahead strategy suitable for this particular scheduling problem. The proposed heuristic outperforms the best existing methods, while being much faster and easier to understand and to implement.

  • International Journal of Engineering, Science and Technology

     García Villoria, Alberto
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  • Desarrollo metodológico para la ubicación de microaerogeneradores a escala comunal

     Domenech Lega, Bruno; Ferrer Marti, Laia; Pastor Moreno, Rafael; García Villoria, Alberto
    Simposio Internacional de Energía Eólica de Pequeña Escala
    Presentation's date: 2011-11
    Presentation of work at congresses

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  • Assembly automation

     García Villoria, Alberto
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  • Heurísticas para el Visibility Windows Assembly Line Balancing Problem (VWALBP)

     Calleja Sanz, Gema; Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
    Congreso de Ingeniería de Organización
    p. 201-205
    Presentation's date: 2011-09-08
    Presentation of work at congresses

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    En este trabajo se trata el problema conocido como problema de equilibrado de líneas de montaje con ventanas de visibilidad o Visibility Windows Assembly Line Balancing Problem (VWALBP), que ocurre en varios entornos de producción automatizados. En particular este problema surge, por ejemplo, en la producción de placas de circuito impreso (PCIs) en líneas pick&place. Este tipo de líneas consta de varias estaciones en paralelo que montan los componentes en posiciones predefinidas sobre la superficie de la placa. El montaje se realiza de modo cíclico (en cada ciclo se completa una pieza) y consiste en escoger (pick) un componente de un alimentador, trasladarlo hacia la placa, y colocarlo (place) en su posición correspondiente

  • Omega: the international journal of management science

     García Villoria, Alberto
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  • A Heuristic procedure for solving the Lexicographic Bottleneck Assembly Line Balancing Problem (LB-ALBP)

     Pastor Moreno, Rafael; Chueca, Ignacio; García Villoria, Alberto
    International Journal of Production Research
    Vol. 50, num. 7, p. 1862-1876
    DOI: 10.1080/00207543.2011.578164
    Date of publication: 2011-07-25
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  • SORT: statistics and operations research transactions

     García Villoria, Alberto
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  • Hyper-heuristic approaches for the response time variability problem

     García Villoria, Alberto; Salhi, Said; Corominas Subias, Albert; Pastor Moreno, Rafael
    European journal of operational research
    Vol. 211, num. 1, p. 160-169
    DOI: 10.1016/j.ejor.2010.12.005
    Date of publication: 2011-05-16
    Journal article

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  • Promoció de sistemes micro-eólics i solars per l'electrificació de comunitats de forma autònoma: anàlisis i desenvolupament d'eines de disseny i planificació per a diferents contextos i paisos II

     Ferrer Marti, Laia; Pastor Moreno, Rafael; García Villoria, Alberto; Corominas Subias, Albert; Villafafila Robles, Roberto; Ranaboldo, Matteo; Domenech Lega, Bruno; Triadó, Joan; Travesset, Oriol
    Competitive project

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  • Exact and heuristic approaches for the Visibility Windows Assembly Line Balancing Problem (VWALBP)

     Calleja Sanz, Gema; Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
    French National Society of Operations Research and Decision Science
    p. 583-584
    Presentation's date: 2011-03-04
    Presentation of work at congresses

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    In this paper, we consider the problem that we name Visibility Windows Assembly Line Balancing Problem (VWALBP) [1], which arises in some actual automated production lines. In contrast to traditional assembly lines, the length of the workpieces may be larger than the visibility windows of the workstations, and because of this, only a limited portion of the unit can be reached from any station at any time.

  • Journal of the Operational Research Society

     García Villoria, Alberto
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  • Programación de tareas para la obtención de la polivalencia, teniendo en cuenta el aprendizaje y el olvido

     García Villoria, Alberto; Calleja Sanz, Gema; Corominas Subias, Albert; Cuatrecasas Arbos, Luis; Pastor Moreno, Rafael; Olivella Nadal, Jorge
    Competitive project

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  • Electrificación rural con energía eólica y solar

     García Villoria, Alberto; Pastor Moreno, Rafael; Coves Moreno, Anna Maria; Santos Lopez, M. Antonia de Los; Villafafila Robles, Roberto; Domenech Lega, Bruno; Ranaboldo, Matteo; Ferrer Marti, Laia
    Competitive project

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  • Comparing ways of breaking symmetries in mathematical models for SALBP-1

     Pastor Moreno, Rafael; García Villoria, Alberto; Corominas Subias, Albert
    Assembly automation
    Vol. 31, num. 4, p. 385-387
    DOI: 10.1108/01445151111172970
    Date of publication: 2011
    Journal article

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  • IEEE intelligent systems

     García Villoria, Alberto
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