Gabriel Villa - Academia.edu (original) (raw)
Papers by Gabriel Villa
International Journal of Robust and Nonlinear Control, 2004
This work presents the results of a project aimed at verifying the applicability of industrial mo... more This work presents the results of a project aimed at verifying the applicability of industrial model predictive control (MPC) to thermal Power Plants. The research is motivated by the need to improve the efficiency of power plants so as to cope with the high levels of competition induced by the deregulation of the energy market. A detailed plant simulator, already used for operators training and controllers tuning, is coupled to an industrial software package implementing the dynamic matrix control algorithm. The achieved results witness the great potentialities of MPC, with respect to classical decentralized schemes, in terms of economical savings, reduction of pollutants, improved flexibility, easier tuning and better documentation. Copyright © 2004 John Wiley & Sons, Ltd.
New technological solutions for the power supply system of the RFX toroidal circuit
The new power supply system of the RFX (reversed field experiment) toroidal field coils, is based... more The new power supply system of the RFX (reversed field experiment) toroidal field coils, is based on recent high power semiconductor components named IGCTs (integrated gate commutated thyristor). It represents the first application in a thermonuclear fusion experiment of a static power supply based on IGCTs. The paper reports a detailed description of the main devices and of the complete electric circuits, the provisions adopted to increase the plant safety and the solutions aimed at reducing the overcurrents in case of fault.
Fusion Engineering and Design, 2005
The paper deals with the component and system tests performed on the new toroidal power supply sy... more The paper deals with the component and system tests performed on the new toroidal power supply system of the RFX experiment. The high technological innovation of the system required a deep experimental characterization and validation campaign; special factory tests were performed on prototypes of single components aimed at verifying the most critical design aspects. Consequently an articulated series of tests were performed, based on a step-by-step approach to achieve the desired coordinate operation of the whole system. The test procedures and the most significant results are described in the paper.
Measuring the performance of nations at the Summer Olympics using data envelopment analysis
Journal of The Operational Research Society, 2002
In this paper a well known tool for relative efficiency assessment, namely Data Envelopment Analy... more In this paper a well known tool for relative efficiency assessment, namely Data Envelopment Analysis (DEA), is used to measure the performance of the nations participating at the last five Summer Olympic games. The proposed approach considers two inputs (GNP and ...
Journal of Productivity Analysis, 2004
While conventional DEA models set targets separately for each DMU, in this paper we consider that... more While conventional DEA models set targets separately for each DMU, in this paper we consider that there is a centralized decision maker (DM) who “owns” or supervises all the operating units. In such intraorganizational scenario the DM has an interest in maximizing the efficiency of individual units at the same time that total input consumption is minimized or total output production is maximized. Two new DEA models are presented for such resource allocation. One type of model seeks radial reductions of the total consumption of every input while the other type seeks separate reductions for each input according to a preference structure. In both cases, total output production is guaranteed not to decrease. The two key features of the proposed models are their simplicity and the fact that both of them project all DMUs onto the efficient frontier. The dual formulation shows that optimizing total input consumption and output production is equivalent to finding weights that maximize the relative efficiency of a virtual DMU with average inputs and outputs. A graphical interpretation as well as numerical results of the proposed models are presented.
A Hybrid VNS/Tabu Search Algorithm for Apportioning the European Parliament
In a Proportional Representation (PR) electoral system it is assumed that seats are apportioned t... more In a Proportional Representation (PR) electoral system it is assumed that seats are apportioned to the different electoral districts/states according to the corresponding voters’ distribution. In a previous paper we proposed a MILP (Mixed Integer Linear Programming) model to apportion the seats in the European Parliament (EP). Since the exact solution to the problem is not computationally efficient, we have designed a hybrid metaheuristic algorithm based on Variable Neighborhood Search (VNS) and Tabu Search (TS). The proposed approach takes into account the existing situation, guaranteeing a minimum number of seats, independently of the population size of each member. The model is illustrated with actual data and its results are compared with the present apportionment. The results show that the proposed approach can significantly improve the proportionality of the present apportionment.
Integer Dea Models
Conventional Data Envelopment Analysis (DEA) models consider that inputs and outputs are continuo... more Conventional Data Envelopment Analysis (DEA) models consider that inputs and outputs are continuous (i.e. real-valued) amounts. However, there are many applications in which one or more inputs and/or outputs are necessarily integer quantities. Commonly, in these situations, the non-integer targets are rounded off. However, rounding off may easily lead to an infeasible target (i.e. out of the Production Possibility Set) or to a dominated operation point. In this chapter, a general framework to handle integer inputs and outputs is presented and a number of integer DEA models reviewed. We illustrate the working of the proposed approach with on a problem from the literature.
Coordinated scheduling of production and delivery from multiple plants and with time windows using genetic algorithms
Abstract This paper deals with the problem of selecting and scheduling a set of orders to be manu... more Abstract This paper deals with the problem of selecting and scheduling a set of orders to be manufactured and immediately delivered to the customer site. We provide m plants for production and V vehicles for distribution. Furthermore, another constraints to be ...
Centralised reallocation of emission permits using DEA
European Journal of Operational Research, 2009
In this paper a data envelopment analysis (DEA) approach to the problem of emission permits reall... more In this paper a data envelopment analysis (DEA) approach to the problem of emission permits reallocation is presented. It can be used with conventional command and control as well as with an allowance market. It uses a centralized point of view, which represents the common good. In the model it is assumed that firms produce two types of outputs: desirable outputs (i.e. good outputs with positive value for consumers) and undesirable outputs (i.e. bad outputs with negative value for consumers, such as emissions of pollutants). The proposed approach has three phases, which correspond to three objectives that are pursued lexicographically. The three objectives are maximizing aggregated desirable production, minimizing undesirable total emissions and minimizing the consumption of input resources. The relative priority of these objectives is defined by the regulator. The whole approach is units-invariant and does not require information on input and output prices. The approach is applied on a dataset from the Swedish pulp and paper industry.
Computers & Operations Research, 2006
This paper addresses DEA scenarios whose inputs and outputs are naturally restricted to take inte... more This paper addresses DEA scenarios whose inputs and outputs are naturally restricted to take integer values. Conventional DEA models would project the DMU onto targets that generally do not respect such type of integrality constraints. Although integer-valued inputs and outputs can be considered as a special case of ordinal inputs and outputs, the use of that type of models has many drawbacks. In this paper a MILP DEA model that guarantees the required integrality of the computed targets is proposed.
Determining a sequence of targets in DEA
Journal of The Operational Research Society, 2005
ABSTRACT Data Envelopment Analysis (DEA) can be used for assessing the relative efficiency of a n... more ABSTRACT Data Envelopment Analysis (DEA) can be used for assessing the relative efficiency of a number of operating units, finding, for each inefficient unit, a target operating point lying on the efficient frontier. Most DEA models project an inefficient unit onto a most distant target, which makes its attainment more difficult. In this paper, we advocate determining a sequence of targets, each one within an appropriate, short distance of the preceding. The proposed Constant Returns to Scale approach has two interesting features: (a) the sequence of targets ends in the efficient frontier and (b) the final, efficient target is generally closer to the original unit than the one-step projection is.Journal of the Operational Research Society (2005) 56, 1439–1447. doi:10.1057/palgrave.jors.2601964 Published online 16 March 2005
Centralised target setting for regional recycling operations using DEA
Omega-international Journal of Management Science, 2004
This paper presents an application of data envelopment analysis for analysing the performance of ... more This paper presents an application of data envelopment analysis for analysing the performance of a number of spanish municipalities in terms of the amount of glass recycled. The inputs considered are the number of glass containers assigned to each municipality on one hand and the population and the number of bars and restaurants in town on the other. The number
Centralized DEA models with the possibility of downsizing
Journal of The Operational Research Society, 2005
ABSTRACT
Computers & Operations Research, 2009
In this paper two new target setting DEA approaches are proposed. The first one is an interactive... more In this paper two new target setting DEA approaches are proposed. The first one is an interactive multiobjective method that at each step of the process asks the decision maker (DM) which inputs and outputs he wishes to improve, which ones are allowed to worsen and which ones should stay at their current level. The local relative priorities of these inputs and outputs changes are computed using the analytic hierarchy process (AHP). After obtaining the candidate target, the DM can update his preferences for improving, worsening or maintaining current inputs and outputs levels and obtain a new candidate target. Thus continuing, until a satisfactory operating point is computed. The second method proposed uses a lexicographic multiobjective approach in which the DM specifies a priori a set of priority levels and, using AHP, the relative importance given to the improvements of the inputs and outputs at each priority level. This second approach requires solving a series of models in order, one model for each priority level. The models do not allow for worsening of neither inputs nor outputs. After the lowest priority model has been solved the corresponding target operating point is obtained. The application of the proposed approach to a port logistics problem is presented.
International Journal of Robust and Nonlinear Control, 2004
This work presents the results of a project aimed at verifying the applicability of industrial mo... more This work presents the results of a project aimed at verifying the applicability of industrial model predictive control (MPC) to thermal Power Plants. The research is motivated by the need to improve the efficiency of power plants so as to cope with the high levels of competition induced by the deregulation of the energy market. A detailed plant simulator, already used for operators training and controllers tuning, is coupled to an industrial software package implementing the dynamic matrix control algorithm. The achieved results witness the great potentialities of MPC, with respect to classical decentralized schemes, in terms of economical savings, reduction of pollutants, improved flexibility, easier tuning and better documentation. Copyright © 2004 John Wiley & Sons, Ltd.
New technological solutions for the power supply system of the RFX toroidal circuit
The new power supply system of the RFX (reversed field experiment) toroidal field coils, is based... more The new power supply system of the RFX (reversed field experiment) toroidal field coils, is based on recent high power semiconductor components named IGCTs (integrated gate commutated thyristor). It represents the first application in a thermonuclear fusion experiment of a static power supply based on IGCTs. The paper reports a detailed description of the main devices and of the complete electric circuits, the provisions adopted to increase the plant safety and the solutions aimed at reducing the overcurrents in case of fault.
Fusion Engineering and Design, 2005
The paper deals with the component and system tests performed on the new toroidal power supply sy... more The paper deals with the component and system tests performed on the new toroidal power supply system of the RFX experiment. The high technological innovation of the system required a deep experimental characterization and validation campaign; special factory tests were performed on prototypes of single components aimed at verifying the most critical design aspects. Consequently an articulated series of tests were performed, based on a step-by-step approach to achieve the desired coordinate operation of the whole system. The test procedures and the most significant results are described in the paper.
Measuring the performance of nations at the Summer Olympics using data envelopment analysis
Journal of The Operational Research Society, 2002
In this paper a well known tool for relative efficiency assessment, namely Data Envelopment Analy... more In this paper a well known tool for relative efficiency assessment, namely Data Envelopment Analysis (DEA), is used to measure the performance of the nations participating at the last five Summer Olympic games. The proposed approach considers two inputs (GNP and ...
Journal of Productivity Analysis, 2004
While conventional DEA models set targets separately for each DMU, in this paper we consider that... more While conventional DEA models set targets separately for each DMU, in this paper we consider that there is a centralized decision maker (DM) who “owns” or supervises all the operating units. In such intraorganizational scenario the DM has an interest in maximizing the efficiency of individual units at the same time that total input consumption is minimized or total output production is maximized. Two new DEA models are presented for such resource allocation. One type of model seeks radial reductions of the total consumption of every input while the other type seeks separate reductions for each input according to a preference structure. In both cases, total output production is guaranteed not to decrease. The two key features of the proposed models are their simplicity and the fact that both of them project all DMUs onto the efficient frontier. The dual formulation shows that optimizing total input consumption and output production is equivalent to finding weights that maximize the relative efficiency of a virtual DMU with average inputs and outputs. A graphical interpretation as well as numerical results of the proposed models are presented.
A Hybrid VNS/Tabu Search Algorithm for Apportioning the European Parliament
In a Proportional Representation (PR) electoral system it is assumed that seats are apportioned t... more In a Proportional Representation (PR) electoral system it is assumed that seats are apportioned to the different electoral districts/states according to the corresponding voters’ distribution. In a previous paper we proposed a MILP (Mixed Integer Linear Programming) model to apportion the seats in the European Parliament (EP). Since the exact solution to the problem is not computationally efficient, we have designed a hybrid metaheuristic algorithm based on Variable Neighborhood Search (VNS) and Tabu Search (TS). The proposed approach takes into account the existing situation, guaranteeing a minimum number of seats, independently of the population size of each member. The model is illustrated with actual data and its results are compared with the present apportionment. The results show that the proposed approach can significantly improve the proportionality of the present apportionment.
Integer Dea Models
Conventional Data Envelopment Analysis (DEA) models consider that inputs and outputs are continuo... more Conventional Data Envelopment Analysis (DEA) models consider that inputs and outputs are continuous (i.e. real-valued) amounts. However, there are many applications in which one or more inputs and/or outputs are necessarily integer quantities. Commonly, in these situations, the non-integer targets are rounded off. However, rounding off may easily lead to an infeasible target (i.e. out of the Production Possibility Set) or to a dominated operation point. In this chapter, a general framework to handle integer inputs and outputs is presented and a number of integer DEA models reviewed. We illustrate the working of the proposed approach with on a problem from the literature.
Coordinated scheduling of production and delivery from multiple plants and with time windows using genetic algorithms
Abstract This paper deals with the problem of selecting and scheduling a set of orders to be manu... more Abstract This paper deals with the problem of selecting and scheduling a set of orders to be manufactured and immediately delivered to the customer site. We provide m plants for production and V vehicles for distribution. Furthermore, another constraints to be ...
Centralised reallocation of emission permits using DEA
European Journal of Operational Research, 2009
In this paper a data envelopment analysis (DEA) approach to the problem of emission permits reall... more In this paper a data envelopment analysis (DEA) approach to the problem of emission permits reallocation is presented. It can be used with conventional command and control as well as with an allowance market. It uses a centralized point of view, which represents the common good. In the model it is assumed that firms produce two types of outputs: desirable outputs (i.e. good outputs with positive value for consumers) and undesirable outputs (i.e. bad outputs with negative value for consumers, such as emissions of pollutants). The proposed approach has three phases, which correspond to three objectives that are pursued lexicographically. The three objectives are maximizing aggregated desirable production, minimizing undesirable total emissions and minimizing the consumption of input resources. The relative priority of these objectives is defined by the regulator. The whole approach is units-invariant and does not require information on input and output prices. The approach is applied on a dataset from the Swedish pulp and paper industry.
Computers & Operations Research, 2006
This paper addresses DEA scenarios whose inputs and outputs are naturally restricted to take inte... more This paper addresses DEA scenarios whose inputs and outputs are naturally restricted to take integer values. Conventional DEA models would project the DMU onto targets that generally do not respect such type of integrality constraints. Although integer-valued inputs and outputs can be considered as a special case of ordinal inputs and outputs, the use of that type of models has many drawbacks. In this paper a MILP DEA model that guarantees the required integrality of the computed targets is proposed.
Determining a sequence of targets in DEA
Journal of The Operational Research Society, 2005
ABSTRACT Data Envelopment Analysis (DEA) can be used for assessing the relative efficiency of a n... more ABSTRACT Data Envelopment Analysis (DEA) can be used for assessing the relative efficiency of a number of operating units, finding, for each inefficient unit, a target operating point lying on the efficient frontier. Most DEA models project an inefficient unit onto a most distant target, which makes its attainment more difficult. In this paper, we advocate determining a sequence of targets, each one within an appropriate, short distance of the preceding. The proposed Constant Returns to Scale approach has two interesting features: (a) the sequence of targets ends in the efficient frontier and (b) the final, efficient target is generally closer to the original unit than the one-step projection is.Journal of the Operational Research Society (2005) 56, 1439–1447. doi:10.1057/palgrave.jors.2601964 Published online 16 March 2005
Centralised target setting for regional recycling operations using DEA
Omega-international Journal of Management Science, 2004
This paper presents an application of data envelopment analysis for analysing the performance of ... more This paper presents an application of data envelopment analysis for analysing the performance of a number of spanish municipalities in terms of the amount of glass recycled. The inputs considered are the number of glass containers assigned to each municipality on one hand and the population and the number of bars and restaurants in town on the other. The number
Centralized DEA models with the possibility of downsizing
Journal of The Operational Research Society, 2005
ABSTRACT
Computers & Operations Research, 2009
In this paper two new target setting DEA approaches are proposed. The first one is an interactive... more In this paper two new target setting DEA approaches are proposed. The first one is an interactive multiobjective method that at each step of the process asks the decision maker (DM) which inputs and outputs he wishes to improve, which ones are allowed to worsen and which ones should stay at their current level. The local relative priorities of these inputs and outputs changes are computed using the analytic hierarchy process (AHP). After obtaining the candidate target, the DM can update his preferences for improving, worsening or maintaining current inputs and outputs levels and obtain a new candidate target. Thus continuing, until a satisfactory operating point is computed. The second method proposed uses a lexicographic multiobjective approach in which the DM specifies a priori a set of priority levels and, using AHP, the relative importance given to the improvements of the inputs and outputs at each priority level. This second approach requires solving a series of models in order, one model for each priority level. The models do not allow for worsening of neither inputs nor outputs. After the lowest priority model has been solved the corresponding target operating point is obtained. The application of the proposed approach to a port logistics problem is presented.