Evaluación del impacto de la generación distribuida en sistemas de distribución primaria de energía eléctrica

Del conjunto de retos técnicos y económicos que crea la introducción masiva aleatoria de GD en el sistema eléctrico de potencia, surge la motivación central de la presente tesis que es estudiar y contribuir al conocimiento del impacto de esta tecnología en la seguridad, fiabilidad y calidad del suministro eléctrico de los sistemas de distribución. La estructura operativa de los sistemas de distribución ha sido diseñada para que reciban potencia en alta tensión (AT) y la suministren a los consumidores en baja tensión (BT) todo ello sobre unos principios de economía, fiabilidad, seguridad y calidad de suministro. En esta estructura, la generación es instantáneamente ajustada de acuerdo con la demanda. La introducción de DG en el sistema de distribución puede impactar de forma importante en los flujos de potencia y en los niveles del voltaje en los consumidores, dando lugar a importantes problemas técnicos que deben ser considerados cuando realizamos estas conexiones. Por tanto es importante considerar que en la introducción aleatoria de la GD en los sistemas de distribución, además del beneficio económico se debe asegurar la fiabilidad, seguridad y calidad de suministro en el sistema de distribución, el cual debe cumplir las restricciones técnicas de los criterios operativos. Puesto que en un mercado competitivo existen distintos propietarios de GD y además en algunas de ellas su fuente primaria de energía es variable, como es el caso de la energía eólica o solar, no existe garantía de que se cumplan los criterios operativos mencionados. Por todo ello, el objetivo de la presente tesis ha sido el desarrollo de modelos que permiten determinar en todo instante la energía eléctrica que producen distintas plantas de generación distribuida (parques eólicos y plantas de cogeneración) y de esta forma poder evaluar en diferentes escenarios el impacto que supone la introducción masiva aleatoria de GD en el sistema de distribución, por una parte, con respecto a la operación delSegura Heras, I. (2005). Evaluación del impacto de la generación distribuida en sistemas de distribución primaria de energía eléctrica [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/1894Palanci

Evaluación de la tenacidad a fractura en aceros mediante el uso de probetas miniatura prefisuradas

En las últimas décadas han sido numerosos los autores que han centrado sus investigaciones en la utilización del Ensayo Miniatura de Punzonado (SPT) con el fin de obtener las propiedades mecánicas del material, en los casos que no se dispone de una cantidad suficiente de material para poder realizar ensayos normalizados. Actualmente, uno de los grandes retos es la posibilidad de obtener las propiedades a fractura del material con el ensayo de este tipo de probetas miniatura. Por otro lado, se está extendiendo el uso de los procedimientos de Integridad Estructural como herramienta para predecir el instante de la rotura en componentes fisurados, haciendo uso de un diagrama de fallo (FAD). El presente trabajo de investigación establece un procedimiento integrado entre el ensayo de probetas SPT prefisuradas y el diagrama FAD, con el objetivo de estimar y determinar cuantitativamente la tenacidad a fractura de aceros

Application of an energy management and control system to assess the potential of different control strategies in HVAC systems

[EN] The significant and continuous increment in the global electricity consumption is asking for energy saving strategies. Efficient control for heating, ventilation and air-conditioning systems (HVAC) is the most cost-effective way to minimize the use of energy in buildings. In this framework, an energy management and control system (EMCS) has been developed to schedule electricity end-uses in the campus of the Universidad Politecnica de Valencia (UPV), Spain. This paper presents an evaluation performed by using the EMCS of different control strategies for HVAC split systems. It analyzed the effect of different schedules for a common air-conditioning device and demand response strategies are tested in several situations. The economic saving is calculated taking into account the electricity contract clauses. Finally, a test is made for the control of a group of similar devices in order to reduce the maximum peak power in consumption and to obtain a flexible load shape with the HVAC loads. The studies are then extrapolated to a larger system, the whole University campus, for which energy and economic savings are quantified. (C) 2010 Published by Elsevier B.V.This research work has been possible with the support of Universidad Politecnica de Valencia (Spain) by the grant #CE 19990032.Escrivá-Escrivá, G.; Segura Heras, I.; Alcázar-Ortega, M. (2010). Application of an energy management and control system to assess the potential of different control strategies in HVAC systems. Energy and Buildings. 42(11):2258-2267. https://doi.org/10.1016/j.enbuild.2010.07.023S22582267421

Modelling alpha case formation and embrittlement for Ti-6Al-4V produced by additive manufacturing and subjected to thermomechanical post-processing

Comunicación presentada en: 5th Iberian Conference on Structural Integrity que corresponde con el 38 Congreso del Grupo Español de Fractura GEF2022 celebrado en Coimbra, Portugal del 30 de marzo al 1 de abril de 2022La Fabricación Aditiva permite la producción optimizada de geometrías complejas. Las propiedades de tracción entallada de la aleación Ti-6Al-4V se estudian numéricamente en este trabajo considerando el método de Selective Laser Melting (SLM) y diferentes condiciones de post-proceso. La formación de una capa frágil enriquecida con oxígeno o “alpha case” también se reproduce aquí para atmósferas no inertes aprovechando esquemas numéricos para el agrietamiento asistido por hidrógeno. La reducción local de la energía de fractura en función de la concentración de oxígeno se implementa en un modelo de Phase Field para la nucleación y propagación de grietas. Se modelizan diferentes probetas de tracción entallada en Comsol Multiphysics. El análisis es secuencial: la entrada y difusión de oxígeno se simulan para diferentes temperaturas y tiempos de permanencia, reproduciendo procesos típicos de SLM y HIP y diferentes presiones parciales de oxígeno. En un segundo paso, se simula el ensayo mecánico de tracción y se resuelve el problema de Phase Field considerando una reducción lineal de la tenacidad a fractura en función de la concentración de oxígeno. Se evalúan los efectos del valor de la longitud característica y del comportamiento plástico. Los resultados muestran que el marco numérico actual, después de una necesaria calibración de parámetros, es capaz de predecir la influencia del post-proceso termomecánico en la fractura de componentes entallados.Additive Manufacturing enables cost-effective production of complex geometries. Notched tensile properties of Ti-6Al4V alloy are here numerically studied considering the Selective Laser Melting (SLM) method and different postprocessing conditions. The formation of an oxygen-enriched brittle layer or an “alpha case” in Ti-6Al-4V is also reproduced for non-inert atmospheres. Exploiting other Finite Element frameworks for environmentally assisted cracking, e.g. hydrogen embrittlement models, the local reduction of fracture energy as a function of oxygen concentration is implemented in a Phase Field model for crack nucleation and propagation. Different notched tensile specimens are modelled in Comsol Multiphysics. The analysis is sequential: oxygen uptake and diffusion are simulated for different temperatures and dwell times, reproducing typical SLM and HIP processes and different partial pressures of oxygen. In a second step, mechanical tensile testing is simulated, and the damage Phase Field scheme is solved considering a linear reduction of fracture toughness as a function of oxygen concentration. The effects of the characteristic length value and of plastic behaviour are evaluated. Results show that the present framework, after parameter calibration, is able to predict the influence of thermomechanical post-processing on notch fracture.The authors gratefully acknowledge financial support from the Junta of Castile and Leon through grant BU002-P20, co-financed by FEDER funds

Stress-intensity factor solutions for embedded elliptical cracks in round bars subjected to tensile load

In this paper, stress-intensity factor solutions are presented for an embedded elliptical crack in a round bar subjected to tensile load. The stress-intensity factors (SIF) are presented in a tabulated form and were obtained from three-dimensional finite-element analyses of this crack configuration. The solutions provide the stress-intensity factor as a function of three dimensionless parameters representative of the crack size, the crack aspect ratio of the elliptical flaw and its relative position in the cross section. The dimensionless parameters cover ranges that allow most internal flaw shapes in practice to be considered. In order to validate the numerical model developed, some particular cases are compared with solutions of embedded elliptical flaws in different geometries available in the literature. Afterwards, a sequential methodology for fatigue crack growth is presented, including the conditions for the recategorization from the internal elliptical crack to a semi-elliptical surface crack. A comparison of the predicted crack paths with experimental results of fatigue crack propagation initiated from internal defects in round bars is also presented. This experimental validation shows the capability of the proposed SIF solutions for the study of the fatigue crack propagation initiated from internal defects in this geometry.JCyL project reference BU-002-P20, co-financed with FEDER funds

Stress-intensity factor solutions for the simulation of fish-eye fatigue crack growth in round bars subjected to tensile load

Trabajo presentado en: The 7th International Conference on Crack Paths (CP 2021), organised by TC3 Fatigue of Engineering Materials and Structures of the European Structural Integrity Society (ESIS). The CP 2021 edition will take place in a virtual format (September 21st to 24th, 2021)The fatigue crack growth in round bars initiated from internal defects leads to the formation of a circular crack pattern usually so-called fish-eye. This failure mechanism is found in the current additive manufacturing techniques in which internal defects, such as pores or lack of fusion, are the main cause of fatigue crack initiation. Moreover, this fatigue mechanism becomes the predominant failure mode in the Very High Cycle Fatigue (VHCF) regime. With the aim of adequately studying these fatigue crack situations, this paper presents a set of solutions for the stress-intensity factor calculation for embedded elliptical cracks in a round bar subjected to tensile load. The stress-intensity factors (SIF) are presented in a tabulated form and were obtained from three-dimensional finite-element analyses. The SIF solutions are provided as a function of three dimensionless parameters that include the crack size, the crack aspect ratio, and its relative position in the cross section. After that, a sequential methodology for fatigue crack growth simulation is presented, and a comparison with experimental results of fatigue crack propagation initiated from internal defects in round bars is also presented. Finally, by varying the initial crack position and the initial crack aspect ratio, several aspects related to the evolution of the fatigue crack shape in this geometry are analyzed.The authors gratefully acknowledge financial support from the Junta de Castilla y Leon (Spain) through grant BU-002-P20, co-financed by FEDER funds

Closed-form equations for the calculation of stress intensity factors for embedded cracks in round bars subjected to tensile load

Fatigue crack propagation initiated from internal defects is a typical mechanism observed in high cycle fatigue (HCF) and very high cycle fatigue (VHCF) of cylindrical tensile specimens subjected to uniaxial cyclic loads. To study the fatigue crack propagation of these embedded cracks by means of a fracture mechanics approach, solutions for the Stress Intensity Factor (SIF) for different crack configurations are needed. In this paper, a set of closed-form equations for the calculation of the SIF of embedded cracks in round bars subjected to tensile load is presented. Two sets of solutions are provided, which allow for different levels of approach to be considered. The first solution provides the SIF for the vertex points of an internal elliptical crack as a function of three dimensionless parameters related to crack size, crack position and crack aspect ratio. The second solution is a simplification for eccentric circular cracks located at any position of the cross section. The methodology necessary for the application to the study of fatigue crack propagation is also presented, and a comparison with those obtained from experimental tests is included, which exhibits a very good capacity for prediction.The authors gratefully acknowledge financial support from the Junta de Castilla y Leon (Spain) through grant BU-002-P20, co-financed by FEDER funds

Implementation of the GTN Damage Model to Simulate the Small Punch Test on Pre-Cracked Specimens

11th International Conference on the Mechanical Behavior of Materials (ICM11), Como (Italy), 2011Nowadays, pre-cracked Small Punch Tests (P-SPT) are used in those cases where there is not enough material for conducting conventional tests. In this paper, P-SPT has been used to determine the fracture properties of the 15.5PH steel, using the micromechanical model, developed by Gurson-Tvergaard-Needleman (GTN). The effect of variation of damage parameters on the numerical simulation has been analyzed. This numerical simulation is based on the sequential adjustment of the experimental load-displacement curves obtained from P-SPT. Interrupted test have been also developed in order to know the cracking process during loading and the damage evolution until fracture.Project MCI Ref: MAT2008-06879-C03-03/MA

Mechanical behaviour of stamped aluminium alloy components by means of response surfaces

In the automotive industry, the use of stamped aluminium alloy components has become a very common occurrence. For the appropriate design of these components, it is necessary to know how the manufacturing process a ects the material properties. In the first place, high plastic strains ("p) can be generated during the stamping process, which can result in a change in the residual stress and mechanical properties in the plastically deformed areas. Furthermore, if a last coat of paint that is usually subjected to a thermal cycle, characterized by temperature (T) and exposure time (t), is applied, it can also influence mechanical behaviour. Consequently, this paper studies how both processes a ect the mechanical behaviour of an aluminium alloy of the 5000 series, commonly used in these types of components. In particular, the mechanical properties such as the yield stress at 0.2% ( 0.2), the ultimate tensile strength (sut) and the engineering strain at break (e f ) have been analysed. To achieve this, a response surface technique, based on the design of experiments, has been used. The response surfaces obtained allow for the prediction of mechanical properties 0.2, sut and e f for any combination of values of t, T and "p.Junta of Castile and Leon through grant ref. BU053U1

Hydrogen uptake and diffusion kinetics in a quenched and tempered low carbon steel: experimental and numerical study

To better understand hydrogen uptake kinetics, electrochemical permeation tests have been performed in a quenched and tempered low-alloy steel. Hydrogen uptake and transport has been studied with three different surface roughness, in four different solutions (1 M H2SO4, 1 M H2SO4+As2O3, 0.1 M NaOH and 3.5% NaCl) and two different hydrogen charging current densities (1 and 5 mA/cm2). A strong effect of the charging solution, current density and surface roughness has been demonstrated. In 1 M H2SO4 + As2O3 solution and 5 mA/cm2, hydrogen recombination on the surface of the samples is strongly reduced and interstitial diffusion prevails due to the trap saturation ( ). However, in 1 M H2SO4, 0.1 M NaOH and 3.5% NaCl, hydrogen transport is dominated by trapping and detrapping processes ( ). Permeation transients are numerically reproduced through Finite Element simulations and compared to the experimental results. The relationship between hydrogen diffusion kinetics at the microstructural level and surface effects is clearly established by a mapping strategy obtained from the wide range of experimental results, combined with a numerical approach.The authors would like to thank the Spanish Government for the financial support received to perform the research projects RTI2018-096070-B-C33 and PID2021-124768OB-C21. This work was supported by the Regional Government of Castilla y León (Junta de Castilla y León) and by the Ministry of Science and Innovation MICIN and the European Union Next Generation EU/PRTR (MR4W.P2 and MR5W.P3). L.B. Peral is also grateful for his Margarita Salas Postdoctoral contract (Ref.: MU-21-UP2021-030) funded by the University of Oviedo through the Next Generation European Union