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Gacto M.J.,University of Jaén | Galende M.,CARTIF Centro Tecnologico | Alcala R.,University of Granada | Herrera F.,University of Granada | Herrera F.,King Abdulaziz University
Information Sciences | Year: 2014

In this contribution, we propose a two-stage method for Accurate Fuzzy Modeling in High-Dimensional Regression Problems using Approximate Takagi-Sugeno-Kang Fuzzy Rule-Based Systems. In the first stage, an evolutionary data base learning is performed (involving variables, granularities and slight fuzzy partition displacements) together with an inductive rule base learning within the same process. The second stage is a post-processing process to perform a rule selection and a scatter-based tuning of the membership functions for further refinement of the learned solutions. Moreover, the second stage incorporates an efficient Kalman filter to learn the coefficients of the consequent polynomial function in the Takagi-Sugeno-Kang rules. Both stages include mechanisms that significantly improve the accuracy of the model and ensure a fast convergence in high-dimensional and large-scale regression datasets. We tested our approach on 28 real-world datasets with different numbers of variables and instances. Five well-known methods have been executed as references. We compared the different approaches by applying non-parametric statistical tests for pair-wise and multiple comparisons. The results confirm the effectiveness of the proposed method, showing better results in accuracy within a reasonable computing time. © 2013 Elsevier Inc. All rights reserved.

Velez F.,CARTIF Centro Tecnologico | Segovia J.J.,University of Valladolid | Martin M.C.,University of Valladolid | Antolin G.,CARTIF Centro Tecnologico | And 2 more authors.
Renewable and Sustainable Energy Reviews | Year: 2012

This paper presents an overview of the technical and economic aspects, as well as the market evolution of the Organic Rankine Cycle (ORC). This is an unconventional but very promising technology for the conversion of thermal energy, at low and medium temperatures, into electrical and/or mechanical energy on a small scale. As it makes a greater and/or more intensive use of its energy source, this technology could facilitate an electricity supply to unconnected areas, the self-production of energy, the desalination of seawater for human consumption, or even to increase the energy efficiency in the industrial sector respecting the environment. A look at the scientific publications on this topic shows an open research line, namely the selection of a suitable working fluid for these systems, since there is as yet none that provides all aspects that must be taken into account in ORCs. Furthermore, a description and an analysis of the applications of the proposed technology is carried out, specifying the main providers, which at the present time is limited mainly to the range 0.2-2 MWe with a cost of around 1 and 4 × 10 3 /kWe. Lower powers are in pre-commercial status. © 2012 Elsevier Ltd. All right reserved.

Barrientos F.,CARTIF Centro Tecnologico | Sainz G.,CARTIF Centro Tecnologico | Sainz G.,University of Valladolid
Knowledge-Based Systems | Year: 2012

Nowadays, call centers are common in different areas of activity providing customer services, medical attention, security services, etc. Each type of call center has its own particularities but all call centers have to plan the availability of resources at each time period to support the incoming calls. The emergency call centers are a special case with extra restrictions. In this context, this work is devoted to providing support for the decision making about resource planning of an emergency call center in order to reach its mandatory quality of service. This is carried out by the extraction of interpretable knowledge from the activity data collected by an emergency call center. A linguistic prediction, categorization and description of the days based on the call center activity and information permits the workload for each category of day to be known. This has been generated by a fuzzy version of an unsupervised decision tree (FUDT), merging decision trees and clustering. This involves quality indexes to reach an adequate trade-off between the tree complexity and the category quality in order to guarantee interpretability and performance. This unsupervised approach deals correctly with the real management of this type of centers generating and preserving expert knowledge. © 2011 Elsevier B.V. All rights reserved.

Bujedo L.A.,CARTIF Centro Tecnologico | Rodriguez J.,Fraunhofer Institute for Building Physics | Martinez P.J.,University Miguel Hernández
Solar Energy | Year: 2011

In this article, different control strategies used in a solar cooling installation are presented and compared, publishing real working data from three summer periods, with the system working at part load.The facility consists of two solar fields that feed a heating system during the winter and a 35. kW Li-Br absorption chiller during the summer period to cool part of an office building.The improvements obtained using control based on critical radiation and a variable flow mass have been compared on the solar plant with a conventional constant flow control. In the same way, the improvements obtained in the yields of a cooling production plant have been compared when programming three different controls: the first one with fixed flow masses, the second adapting the temperature on the condenser as a function of the generator temperature (constant flow mass), and the third adapting the condenser temperature and the flow mass on the generator as a function of the system loads. © 2011 Elsevier Ltd.

Velez F.,CARTIF Centro Tecnologico | Segovia J.,University of Valladolid | Chejne F.,National University of Colombia | Antolin G.,CARTIF Centro Tecnologico | And 2 more authors.
Energy | Year: 2011

The main results of a theoretical work on the use of a low temperature heat source for power generation through a carbon dioxide transcritical power cycle are reported in this paper. The procedure for analyzing the behaviour of the proposed cycle consisted in modifying the input pressure to the turbine from 66 bar, maintained constant each evaluated temperature (60 °C, 90 °C, 120 °C and 150 °C) until the net work was approximately zero. As a result, the maximum exergy efficiency was 50%, while the energy efficiencies obtained were 9.8%, 7.3%, 4.9% and 2.4% and the net specific work was 18.2 kJ/kg, 12.8 kJ/kg, 7.8 kJ/kg and 3.5 kJ/kg, respectively. Furthermore, the effect of the addition of an internal heat exchanger, which obviously supposed an increase in the efficiency, was analyzed. The analysis of the proposed system shows the viability of implementing this type of process as an energy alternative and/or strengthener of non-conventional energy sources in non-provided zones, or for increasing the energy efficiency in the industry. © 2011 Elsevier Ltd.

Casado C.M.,CARTIF Centro Tecnologico | Diaz I.M.,University of Castilla - La Mancha | De Sebastian J.,CARTIF Centro Tecnologico | Poncela A.V.,University of Valladolid | Lorenzana A.,University of Valladolid
Structural Control and Health Monitoring | Year: 2013

The current trend toward lighter and slender pedestrian structures, with new aesthetic requirements and high-performance materials, has resulted in structures with increased susceptibility to vibration. Notable vibrations under human-induced excitations might appear, and the vibration serviceability requirements might not be accomplished. The Valladolid Science Museum Footbridge (Spain) is an example of a lively structure that might achieve excessive vertical acceleration under walking or running excitation. The control of excessive footbridge vibrations via passive and active devices is dealt with in this work. More specifically, this paper is concerned with the design and experimental implementation of a passive tuned mass damper (TMD) and an active mass damper (AMD) to mitigate human-induced vibrations on this in-service footbridge. The TMD, with a mass ratio of 1%, is designed by a numerical method based on H∞ controllers. The AMD consists of a proof-mass actuator, with a mass ratio of approximately 0.2%, controlled by a strategy based on acceleration feedback with a phase-lag network. The performance of both devices has been assessed. Copyright © 2011 John Wiley & Sons, Ltd.

Meiss A.,University of Valladolid | Feijo-Munoz J.,University of Valladolid | Garcia-Fuentes M.A.,CARTIF Centro Tecnologico
Energy and Buildings | Year: 2013

The ventilation air in rooms is generally kept moving due to a constant difference in pressure. This gradient is generated through a general ventilation system (hybrid or mechanical), with minimum ventilation flow being established by the normative. However, there are cases in which, even if the established flows are fulfilled, certain indoor areas exhibit an excess or shortage of ventilation. The excess or deficit depends on the flow pattern that the air follows in the room, and its characterisation is possible using the indoor local and mean calculation of the age of the air. The flow pattern of air is conditioned by the energy transfer processes; therefore, analysis of air's behaviour under two extreme situations (summer and winter) was performed to compare the results with a previous isothermal model. For the development of this work, a double study (numerical and experimental) was conducted. The numerical calculations were developed using a CFD tool, which is notably useful for this type of research work. © 2013 Elsevier B.V. All rights reserved.

Belver A.V.,CARTIF Centro Tecnologico | Iban A.L.,University of Valladolid | Lavin Martin C.E.,CARTIF Centro Tecnologico
Journal of Wind Engineering and Industrial Aerodynamics | Year: 2012

A simplified fluid-structure interaction approach is used to study the dynamic behaviour of a particular 90. m steel chimney under vortex-induced vibrations. Navier-Stokes equations for incompressible flow are solved in 2D in several transverse planes of the line-like structure. The resultant pressure field is introduced using standard FEM interpolation techniques, together with the dynamical behaviour of the structure and its boundary conditions. A fractional step scheme is used to solve the fluid field. In each fluid plane, the displacements are taken into account considering an Arbitrary Lagrangian Eulerian approach. The stabilisation of incompressibility and convection is achieved through orthogonal quasi-static subscales, an approach that is believed to provide a first step towards turbulence modelling. In order to solve the structural problem, a special one-dimensional element for thin walled cross-section beams is implemented. The standard second-order Bossak method is used for the time integration of the dynamic problem. The wind is modelled as an incompressible fluid acting on the structure in a series of planes, transverse to the structure that are supposed to be independent among them. For each period of time, the fluid problem is solved, the aeroelastic analysis is carried out and the geometry of the mesh of each fluid plane is updated according to the structure displacements. © 2011 Elsevier Ltd.

Velez F.,CARTIF Centro Tecnologico | Segovia J.J.,University of Valladolid | Martin M.C.,University of Valladolid | Antolin G.,CARTIF Centro Tecnologico | And 2 more authors.
Fuel Processing Technology | Year: 2012

The main results of a thermodynamic study on the use of a low temperature heat source (150 °C as maximum) for power generation through a basic Rankine are reported in this paper. Different working fluids such as water and some hydrocarbons and coolants are studied. The procedure consisted in modifying the input pressure and temperature to the turbine. The efficiency for these fluids is a weak function of temperature, i.e., overheating the inlet fluid to the turbine does not cause a significant change in the efficiency. However, when the pressure ratio in the turbine increases, much larger values of efficiency are obtained, and also, as the input temperature to the turbine rises, the efficiency increases more sharply. As result, a maximum efficiency of 9% was obtained. It is shown the technical viability of implementing this type of process for recovering residual wastes for very low temperature, as well as an energy alternative and/or strengthener of non-conventional energy sources in non-provided zones. © 2011 Elsevier B.V. All rights reserved.

Velez F.,CARTIF Centro Tecnologico | Chejne F.,National University of Colombia | Antolin G.,CARTIF Centro Tecnologico | Quijano A.,CARTIF Centro Tecnologico
Energy Conversion and Management | Year: 2012

The present paper reports the results obtained on a carbon dioxide transcritical power cycle using an energy and exergy analysis. The procedure consisted of modifying the inlet pressure to the turbine from 66 bar, by means of the software HYSYS®, maintaining constant each evaluated turbine inlet temperature (60, 90, 120 and 150 °C) until the net work was approximately zero. As a result, an increase up to 25% for the exergy efficiency, and up to 300% for the energy efficiency are obtained when the inlet temperature to the turbine is risen from 60 to 150 °C. Consequently, the analysis shows the viability of implementing this process as alternative energy, because of the possibility to recovery energy from waste heat from industrial processes. © 2012 Elsevier Ltd. All rights reserved.

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