Articles de revista
http://hdl.handle.net/2117/2261
2017-11-21T21:45:45ZOptimal power flow for resistive DC networks: a port-hamiltonian approach
http://hdl.handle.net/2117/110148
Optimal power flow for resistive DC networks: a port-hamiltonian approach
Benedito Benet, Ernest; del Puerto Flores, Dunstano; Dòria Cerezo, Arnau; Scherpen, Jacquelien
This paper studies the optimal power flow problem for resistive DC networks. The gradient method algorithm is written in a port-Hamiltonian form and the stability of the resulting dynamics is studied. Stability conditions are provided for general cyclic networks and a solution, when these conditions fail, is proposed. In addition, the results are exemplified by means of numerical simulations.
2017-11-08T13:10:59ZBenedito Benet, Ernestdel Puerto Flores, DunstanoDòria Cerezo, ArnauScherpen, JacquelienThis paper studies the optimal power flow problem for resistive DC networks. The gradient method algorithm is written in a port-Hamiltonian form and the stability of the resulting dynamics is studied. Stability conditions are provided for general cyclic networks and a solution, when these conditions fail, is proposed. In addition, the results are exemplified by means of numerical simulations.A bi-objective parallel machine problem with eligibility, release dates and delivery times of the jobs
http://hdl.handle.net/2117/108800
A bi-objective parallel machine problem with eligibility, release dates and delivery times of the jobs
Mateo Doll, Manuel; Teghem, Jacques; Tuyttens, Daniel
The scheduling of parallel machines is a well-known problem in many companies. Nevertheless, not always all the jobs can be manufactured in any machine and the eligibility appears. Based on a real-life problem, we present a model which has m parallel machines with different level of quality from the highest level for the first machine till the lowest level for the last machine. The set of jobs to be scheduled on these m parallel machines are also distributed among these m levels: one job from a level can be manufactured in a machine of the same or higher level but a penalty, depending on the level, appears when a job is manufactured in a machine different from the highest level i.e. different from the first machine. Besides, there are release dates and delivery times associated to each job. The tackled problem is bi-objective with the criteria: minimisation of the final date – i.e. the maximum for all the jobs of their completion time plus the delivery time – and the minimisation of the total penalty generated by the jobs. In a first step, we analyse the sub-problem of minimisation of the final date on a single machine for jobs with release dates and delivery times. Four heuristics and an improvement algorithm are proposed and compared on didactic examples and on a large set of instances. In a second step an algorithm is proposed to approximate the set of efficient solutions and the Pareto front of the bi-objective problem. This algorithm contains two phases: the first is a depth search phase and the second is a backtracking phase. The procedure is illustrated in detail on an instance with 20 jobs and 3 machines. Then extensive numerical experiments are realised on two different sets of instances, with 20, 30 and 50 jobs, 3 or 4 machines and various values of penalties. Except for the case of 50 jobs, the results are compared with the exact Pareto front.
2017-10-18T09:58:35ZMateo Doll, ManuelTeghem, JacquesTuyttens, DanielThe scheduling of parallel machines is a well-known problem in many companies. Nevertheless, not always all the jobs can be manufactured in any machine and the eligibility appears. Based on a real-life problem, we present a model which has m parallel machines with different level of quality from the highest level for the first machine till the lowest level for the last machine. The set of jobs to be scheduled on these m parallel machines are also distributed among these m levels: one job from a level can be manufactured in a machine of the same or higher level but a penalty, depending on the level, appears when a job is manufactured in a machine different from the highest level i.e. different from the first machine. Besides, there are release dates and delivery times associated to each job. The tackled problem is bi-objective with the criteria: minimisation of the final date – i.e. the maximum for all the jobs of their completion time plus the delivery time – and the minimisation of the total penalty generated by the jobs. In a first step, we analyse the sub-problem of minimisation of the final date on a single machine for jobs with release dates and delivery times. Four heuristics and an improvement algorithm are proposed and compared on didactic examples and on a large set of instances. In a second step an algorithm is proposed to approximate the set of efficient solutions and the Pareto front of the bi-objective problem. This algorithm contains two phases: the first is a depth search phase and the second is a backtracking phase. The procedure is illustrated in detail on an instance with 20 jobs and 3 machines. Then extensive numerical experiments are realised on two different sets of instances, with 20, 30 and 50 jobs, 3 or 4 machines and various values of penalties. Except for the case of 50 jobs, the results are compared with the exact Pareto front.Using discrete-time mathematical programming to optimise the extraction rate of a durable non-renewabre resource with a single primary supplier
http://hdl.handle.net/2117/108642
Using discrete-time mathematical programming to optimise the extraction rate of a durable non-renewabre resource with a single primary supplier
Corominas Subias, Albert
A non-linear discrete-time mathematical program model is proposed to determining the optimal extrac- tion policy for a single primary supplier of a durable non-renewable resource, such as gemstones or some metals. Karush, Kuhn and Tucker conditions allow obtaining analytic solutions and general properties of them in some specific settings. Moreover, provided that the objective function (i.e., the discounted value of the incomes throughout the planning horizon) is concave, the model can be easily solved, even using standard commercial solver. However, the analysis of the solutions obtained for different assumptions of the values of the parameters show that the optimal extraction policies and the corresponding prices do not exhibit a general shape.
2017-10-11T10:19:20ZCorominas Subias, AlbertA non-linear discrete-time mathematical program model is proposed to determining the optimal extrac- tion policy for a single primary supplier of a durable non-renewable resource, such as gemstones or some metals. Karush, Kuhn and Tucker conditions allow obtaining analytic solutions and general properties of them in some specific settings. Moreover, provided that the objective function (i.e., the discounted value of the incomes throughout the planning horizon) is concave, the model can be easily solved, even using standard commercial solver. However, the analysis of the solutions obtained for different assumptions of the values of the parameters show that the optimal extraction policies and the corresponding prices do not exhibit a general shape.Renewable microgrid projects for autonomous small-scale electrification in Andean countries
http://hdl.handle.net/2117/108424
Renewable microgrid projects for autonomous small-scale electrification in Andean countries
López González, Alejandro; Domenech Léga, Bruno; González Hernández, Dorian; Ferrer Martí, Laia
Nowadays, 84% of the world population without access to electricity is located in rural areas of developing countries. In particular, in the Andean countries, about 10.4 million people lack of access to electricity, mainly in isolated poor regions. Considering the relevance of electricity in overcoming poverty and promoting socioeconomic development, local-regional-national governments, supported by international organizations, are making efforts to achieve full rural electrification. In this regard, renewable microgrid projects are an effective alternative where the national grid extension has limitations. The literature on the design of such projects is significant. However, when evaluating experiences, most works focus on an analysis of projects’ performance from a technical and/or economical point of view. In contrast, very few literature has been reported on the comparison of such experiences from the perspective of the design process itself and how decisions are taken by project developers. In this article, five rural electrification experiences in Andean Countries (Bolivia, Ecuador, Peru and Venezuela) are reviewed, analyzing the decisions taken across the design process and showing the suitability of these technologies to extend access to electricity. In the target projects, first, a preliminary analysis is carried out to estimate the energy resources and demand. Next, the system is designed and implemented to meet the demand using the available resources. The five projects illustrate different options for the electrical generation (single, hybrid or combination of technologies), storage (battery or diesel backup) and distribution (microgrid or individual systems), as well as different methods for data gathering and systems design. In addition, a comparison of projects’ real behavior is carried out and their technical performance in terms of energy production and suitability of the technologies implemented is analyzed. These projects can be a good reference for the dissemination of such technologies in future projects in the Andean countries and abroad.
2017-10-06T07:35:04ZLópez González, AlejandroDomenech Léga, BrunoGonzález Hernández, DorianFerrer Martí, LaiaNowadays, 84% of the world population without access to electricity is located in rural areas of developing countries. In particular, in the Andean countries, about 10.4 million people lack of access to electricity, mainly in isolated poor regions. Considering the relevance of electricity in overcoming poverty and promoting socioeconomic development, local-regional-national governments, supported by international organizations, are making efforts to achieve full rural electrification. In this regard, renewable microgrid projects are an effective alternative where the national grid extension has limitations. The literature on the design of such projects is significant. However, when evaluating experiences, most works focus on an analysis of projects’ performance from a technical and/or economical point of view. In contrast, very few literature has been reported on the comparison of such experiences from the perspective of the design process itself and how decisions are taken by project developers. In this article, five rural electrification experiences in Andean Countries (Bolivia, Ecuador, Peru and Venezuela) are reviewed, analyzing the decisions taken across the design process and showing the suitability of these technologies to extend access to electricity. In the target projects, first, a preliminary analysis is carried out to estimate the energy resources and demand. Next, the system is designed and implemented to meet the demand using the available resources. The five projects illustrate different options for the electrical generation (single, hybrid or combination of technologies), storage (battery or diesel backup) and distribution (microgrid or individual systems), as well as different methods for data gathering and systems design. In addition, a comparison of projects’ real behavior is carried out and their technical performance in terms of energy production and suitability of the technologies implemented is analyzed. These projects can be a good reference for the dissemination of such technologies in future projects in the Andean countries and abroad.Improving the resolution of the simple assembly line balancing problem type E
http://hdl.handle.net/2117/103425
Improving the resolution of the simple assembly line balancing problem type E
Corominas Subias, Albert; García Villoria, Alberto; Pastor Moreno, Rafael
The simple assembly line balancing problem type E (abbreviated as SALBP-E) occurs when the number of workstations and the cycle time are variables and the objective is to maximise the line efficiency. In contrast with other types of SALBPs, SALBP-E has received little attention in the literature. In order to solve optimally SALBP-E, we propose a mixed integer liner programming model and an iterative procedure. Since SALBP-E is NP-hard, we also propose heuristics derived from the aforementioned procedures for solving larger instances. An extensive experimentation is carried out and its results show the improvement of the SALBP-E resolution.
2017-04-06T11:10:36ZCorominas Subias, AlbertGarcía Villoria, AlbertoPastor Moreno, RafaelThe simple assembly line balancing problem type E (abbreviated as SALBP-E) occurs when the number of workstations and the cycle time are variables and the objective is to maximise the line efficiency. In contrast with other types of SALBPs, SALBP-E has received little attention in the literature. In order to solve optimally SALBP-E, we propose a mixed integer liner programming model and an iterative procedure. Since SALBP-E is NP-hard, we also propose heuristics derived from the aforementioned procedures for solving larger instances. An extensive experimentation is carried out and its results show the improvement of the SALBP-E resolution.The multi-objective assembly line worker integration and balancing problem of type-2
http://hdl.handle.net/2117/101447
The multi-objective assembly line worker integration and balancing problem of type-2
Moreira, Mayron César O.; Pastor Moreno, Rafael; Costa, Alysson E.; Miralles, Cristobal
The consideration of worker heterogeneity in assembly lines has received a fair amount of attention in the literature in the past decade. Most of this exploration uses as motivation the example of assembly lines in sheltered work centers for the disabled. Only recently has the community started looking at the situation faced in assembly lines in the general industrial park, when in the presence of worker heterogeneity. This step raises a number of questions around the best way to incorporate heterogeneous workers in the line, maximizing their integration while maintaining productivity levels. In this paper we propose the use of Miltenburg’s regularity criterion and cycle time as metrics for integration of workers and productivity, respectively. We then define, model and develop heuristics for a line balancing problem with these two goals. Results obtained through an extensive set of computational experiments indicate that a good planning can obtain trade-off solutions that perform well in both objectives.
2017-02-23T11:14:14ZMoreira, Mayron César O.Pastor Moreno, RafaelCosta, Alysson E.Miralles, CristobalThe consideration of worker heterogeneity in assembly lines has received a fair amount of attention in the literature in the past decade. Most of this exploration uses as motivation the example of assembly lines in sheltered work centers for the disabled. Only recently has the community started looking at the situation faced in assembly lines in the general industrial park, when in the presence of worker heterogeneity. This step raises a number of questions around the best way to incorporate heterogeneous workers in the line, maximizing their integration while maintaining productivity levels. In this paper we propose the use of Miltenburg’s regularity criterion and cycle time as metrics for integration of workers and productivity, respectively. We then define, model and develop heuristics for a line balancing problem with these two goals. Results obtained through an extensive set of computational experiments indicate that a good planning can obtain trade-off solutions that perform well in both objectives.Efficient heuristics for the parallel blocking flow shop scheduling problem
http://hdl.handle.net/2117/100670
Efficient heuristics for the parallel blocking flow shop scheduling problem
Ribas Vila, Immaculada; Companys Pascual, Ramon; Tort-Martorell Llabrés, Xavier
We consider the NP-hard problem of scheduling n jobs in F identical parallel flow shops, each consisting of a series of m machines, and doing so with a blocking constraint. The applied criterion is to minimize the makespan, i.e., the maximum completion time of all the jobs in F flow shops (lines). The Parallel Flow Shop Scheduling Problem (PFSP) is conceptually similar to another problem known in the literature as the Distributed Permutation Flow Shop Scheduling Problem (DPFSP), which allows modeling the scheduling process in companies with more than one factory, each factory with a flow shop configuration. Therefore, the proposed methods can solve the scheduling problem under the blocking constraint in both situations, which, to the best of our knowledge, has not been studied previously. In this paper, we propose a mathematical model along with some constructive and improvement heuristics to solve the parallel blocking flow shop problem (PBFSP) and thus minimize the maximum completion time among lines. The proposed constructive procedures use two approaches that are totally different from those proposed in the literature. These methods are used as initial solution procedures of an iterated local search (ILS) and an iterated greedy algorithm (IGA), both of which are combined with a variable neighborhood search (VNS). The proposed constructive procedure and the improved methods take into account the characteristics of the problem. The computational evaluation demonstrates that both of them –especially the IGA– perform considerably better than those algorithms adapted from the DPFSP literature.
2017-02-08T11:54:07ZRibas Vila, ImmaculadaCompanys Pascual, RamonTort-Martorell Llabrés, XavierWe consider the NP-hard problem of scheduling n jobs in F identical parallel flow shops, each consisting of a series of m machines, and doing so with a blocking constraint. The applied criterion is to minimize the makespan, i.e., the maximum completion time of all the jobs in F flow shops (lines). The Parallel Flow Shop Scheduling Problem (PFSP) is conceptually similar to another problem known in the literature as the Distributed Permutation Flow Shop Scheduling Problem (DPFSP), which allows modeling the scheduling process in companies with more than one factory, each factory with a flow shop configuration. Therefore, the proposed methods can solve the scheduling problem under the blocking constraint in both situations, which, to the best of our knowledge, has not been studied previously. In this paper, we propose a mathematical model along with some constructive and improvement heuristics to solve the parallel blocking flow shop problem (PBFSP) and thus minimize the maximum completion time among lines. The proposed constructive procedures use two approaches that are totally different from those proposed in the literature. These methods are used as initial solution procedures of an iterated local search (ILS) and an iterated greedy algorithm (IGA), both of which are combined with a variable neighborhood search (VNS). The proposed constructive procedure and the improved methods take into account the characteristics of the problem. The computational evaluation demonstrates that both of them –especially the IGA– perform considerably better than those algorithms adapted from the DPFSP literature.Social networks and performance in distributed learning communities
http://hdl.handle.net/2117/100653
Social networks and performance in distributed learning communities
Cadima, Rita; Ojeda Rodríguez, Jordi; Monguet Fierro, José María
Social networks play an essential role in learning environments as a key channel for knowledge sharing and students' support. In distributed learning communities, knowledge sharing does not occur as spontaneously as when a working group shares the same physical space; knowledge sharing depends even more on student informal connections. In this study we analyse two distributed learning communities' social networks in order to understand how characteristics of the social structure can enhance students' success and performance. We used a monitoring system for social network data gathering. Results from correlation analyses showed that students' social network characteristics are related to their performance
2017-02-08T08:20:59ZCadima, RitaOjeda Rodríguez, JordiMonguet Fierro, José MaríaSocial networks play an essential role in learning environments as a key channel for knowledge sharing and students' support. In distributed learning communities, knowledge sharing does not occur as spontaneously as when a working group shares the same physical space; knowledge sharing depends even more on student informal connections. In this study we analyse two distributed learning communities' social networks in order to understand how characteristics of the social structure can enhance students' success and performance. We used a monitoring system for social network data gathering. Results from correlation analyses showed that students' social network characteristics are related to their performanceCalibrating cross-training to meet demand mix variation and employee absence
http://hdl.handle.net/2117/100267
Calibrating cross-training to meet demand mix variation and employee absence
Olivella Nadal, Jordi; Nembhard, David
We address the problem of determining the cross-training that a work team needs in order to cope with demand mix variation and absences. We consider the case in which all workers can be trained on all tasks, the workforce is a resource that determines the capacity and a complete forecasting of demand is not available. The demand mix variation that the organization wants to be able to cope with is fixed by establishing a maximum time to devote to each product. We contend that this approach is straightforward, has managerial practicality and can be applied to a broad range of practical scenarios. It is required that the demand mix variation be met, even if there are a certain level of absences. To numerically solve the mathematical problem, a constraint-based selection procedure is developed, which we term CODEMI. We provide illustrated examples demonstrating solution quality for the approximation, and we report on an illustrative set of computational cases. (C) 2015 Elsevier B.V. and Association of European Operational Research Societies (EURO) within the International Federation of Operational Research Societies (IFORS). All rights reserved.
2017-01-30T11:17:19ZOlivella Nadal, JordiNembhard, DavidWe address the problem of determining the cross-training that a work team needs in order to cope with demand mix variation and absences. We consider the case in which all workers can be trained on all tasks, the workforce is a resource that determines the capacity and a complete forecasting of demand is not available. The demand mix variation that the organization wants to be able to cope with is fixed by establishing a maximum time to devote to each product. We contend that this approach is straightforward, has managerial practicality and can be applied to a broad range of practical scenarios. It is required that the demand mix variation be met, even if there are a certain level of absences. To numerically solve the mathematical problem, a constraint-based selection procedure is developed, which we term CODEMI. We provide illustrated examples demonstrating solution quality for the approximation, and we report on an illustrative set of computational cases. (C) 2015 Elsevier B.V. and Association of European Operational Research Societies (EURO) within the International Federation of Operational Research Societies (IFORS). All rights reserved.Una visión sobre secuencias regulares
http://hdl.handle.net/2117/99559
Una visión sobre secuencias regulares
Bautista Valhondo, Joaquín; Companys Pascual, Ramon; Corominas Subias, Albert
En los últimos años el laboratorio de Organización de la Producción (LOP) del departamento de Organización de Empresas de la UPC ha venido desarrollando una serie de trabajos sobre diversos problemas en el campo de la Organización Industrial (planificación y programación de la producción, diseño de sistemas productivos, entre otros), empleando indistintamente procedimientos exactos (programación lineal continua, entera, mixta, BDP, etc.) y heurísticos (algoritmos genéticos, heurísticas greedy y procedimientos de mejora basados en la búsqueda tabú y el recocido simulado). Uno de los problemas que ha merecido una atención especial es el de las secuencias regulares., línea de trabajo encuadrada en los proyectos de investigación DGICYT PB-0504 y CAICYT TAP95-0420.
2017-01-18T07:33:06ZBautista Valhondo, JoaquínCompanys Pascual, RamonCorominas Subias, AlbertEn los últimos años el laboratorio de Organización de la Producción (LOP) del departamento de Organización de Empresas de la UPC ha venido desarrollando una serie de trabajos sobre diversos problemas en el campo de la Organización Industrial (planificación y programación de la producción, diseño de sistemas productivos, entre otros), empleando indistintamente procedimientos exactos (programación lineal continua, entera, mixta, BDP, etc.) y heurísticos (algoritmos genéticos, heurísticas greedy y procedimientos de mejora basados en la búsqueda tabú y el recocido simulado). Uno de los problemas que ha merecido una atención especial es el de las secuencias regulares., línea de trabajo encuadrada en los proyectos de investigación DGICYT PB-0504 y CAICYT TAP95-0420.