Application of PZT and FBG impedance sensors for structural health monitoring of reinforced concrete beams strengthened with FRP composite materials

Esta Tesis tiene como objetivo principal el desarrollo de m��todos de identificaci��n del da��o que sean robustos y fiables, enfocados a sistemas estructurales experimentales, fundamentalmente a las estructuras de hormig��n armado reforzadas externamente con bandas fibras de pol��meros reforzados (FRP). El modo de fallo de este tipo de sistema estructural es cr��tico, pues generalmente es debido a un despegue repentino y fr��gil de la banda del refuerzo FRP originado en grietas intermedias causadas por la flexi��n. La detecci��n de este despegue en su fase inicial es fundamental para prevenir fallos futuros, que pueden ser catastr��ficos. Inicialmente, se lleva a cabo una revisi��n del m��todo de la Impedancia Electro-Mec��nica (EMI), de cara a exponer sus capacidades para la detecci��n de da��o. Una vez la tecnolog��a apropiada es seleccionada, lo que incluye un analizador de impedancias as�� como novedosos sensores PZT para monitorizaci��n inteligente, se ha dise��ado un procedimiento autom��tico basado en los registros de impedancias de distintas estructuras de laboratorio. Bas��ndonos en el hecho de que las mediciones de impedancias son posibles gracias a una colocaci��n adecuada de una red de sensores PZT, la estimaci��n de la presencia de da��o se realiza analizando los resultados de distintos indicadores de da��o obtenidos de la literatura. Para que este proceso sea autom��tico y que no sean necesarios conocimientos previos sobre el m��todo EMI para realizar un experimento, se ha dise��ado e implementado un Interfaz Gr��fico de Usuario, transformando la medici��n de impedancias en un proceso f��cil e intuitivo. Se eval��a entonces el da��o a trav��s de los correspondientes ��ndices de da��o, intentando estimar no s��lo su severidad, sino tambi��n su localizaci��n aproximada. El desarrollo de estos experimentos en cualquier estructura genera grandes cantidades de datos que han de ser procesados, y algunas veces los ��ndices de da��o no son suficientes para una evaluaci��n completa de la integridad de una estructura. En la mayor��a de los casos se pueden encontrar patrones de da��o en los datos, pero no se tiene informaci��n a priori del estado de la estructura. En este punto, se ha hecho una importante investigaci��n en t��cnicas de reconocimiento de patrones particularmente en aprendizaje no supervisado, encontrando aplicaciones interesantes en el campo de la medicina. De ah�� surge una idea creativa e innovadora: detectar y seguir la evoluci��n del da��o en distintas estructuras como si se tratase de un c��ncer propag��ndose por el cuerpo humano. En ese sentido, las lecturas de impedancias se emplean como informaci��n intr��nseca de la salud de la propia estructura, de forma que se pueden aplicar las mismas t��cnicas que las empleadas en la investigaci��n del c��ncer. En este caso, se ha aplicado un algoritmo de clasificaci��n jer��rquica dado que ilustra adem��s la clasificaci��n de los datos de forma gr��fica, incluyendo informaci��n cualitativa y cuantitativa sobre el da��o. Se ha investigado la efectividad de este procedimiento a trav��s de tres estructuras de laboratorio, como son una viga de aluminio, una uni��n atornillada de aluminio y un bloque de hormig��n reforzado con FRP. La primera ayuda a mostrar la efectividad del m��todo en sencillos escenarios de da��o simple y m��ltiple, de forma que las conclusiones extra��das se aplican sobre los otros dos, dise��ados para simular condiciones de despegue en distintas estructuras. Demostrada la efectividad del m��todo de clasificaci��n jer��rquica de lecturas de impedancias, se aplica el procedimiento sobre las estructuras de hormig��n armado reforzadas con bandas de FRP objeto de esta tesis, detectando y clasificando cada estado de da��o. Finalmente, y como alternativa al anterior procedimiento, se propone un m��todo para la monitorizaci��n continua de la interfase FRP-Hormig��n, a trav��s de una red de sensores FBG permanentemente instalados en dicha interfase. De esta forma, se obtienen medidas de deformaci��n de la interfase en condiciones de carga continua, para ser implementadas en un modelo de optimizaci��n multiobjetivo, cuya soluci��n se haya por medio de una expansi��n multiobjetivo del m��todo Particle Swarm Optimization (PSO). La fiabilidad de este ��ltimo m��todo de detecci��n se investiga a trav��s de sendos ejemplos tanto num��ricos como experimentales. ABSTRACT This thesis aims to develop robust and reliable damage identification methods focused on experimental structural systems, in particular Reinforced Concrete (RC) structures externally strengthened with Fiber Reinforced Polymers (FRP) strips. The failure mode of this type of structural system is critical, since it is usually due to sudden and brittle debonding of the FRP reinforcement originating from intermediate flexural cracks. Detection of the debonding in its initial stage is essential thus to prevent future failure, which might be catastrophic. Initially, a revision of the Electro-Mechanical Impedance (EMI) method is carried out, in order to expose its capabilities for local damage detection. Once the appropriate technology is selected, which includes impedance analyzer as well as novel PZT sensors for smart monitoring, an automated procedure has been design based on the impedance signatures of several lab-scale structures. On the basis that capturing impedance measurements is possible thanks to an adequately deployed PZT sensor network, the estimation of damage presence is done by analyzing the results of different damage indices obtained from the literature. In order to make this process automatic so that it is not necessary a priori knowledge of the EMI method to carry out an experimental test, a Graphical User Interface has been designed, turning the impedance measurements into an easy and intuitive procedure. Damage is then assessed through the analysis of the corresponding damage indices, trying to estimate not only the damage severity, but also its approximate location. The development of these tests on any kind of structure generates large amounts of data to be processed, and sometimes the information provided by damage indices is not enough to achieve a complete analysis of the structural health condition. In most of the cases, some damage patterns can be found in the data, but none a priori knowledge of the health condition is given for any structure. At this point, an important research on pattern recognition techniques has been carried out, particularly on unsupervised learning techniques, finding interesting applications in the medicine field. From this investigation, a creative and innovative idea arose: to detect and track the evolution of damage in different structures, as if it were a cancer propagating through a human body. In that sense, the impedance signatures are used to give intrinsic information of the health condition of the structure, so that the same clustering algorithms applied in the cancer research can be applied to the problem addressed in this dissertation. Hierarchical clustering is then applied since it also provides a graphical display of the clustered data, including quantitative and qualitative information about damage. The performance of this approach is firstly investigated using three lab-scale structures, such as a simple aluminium beam, a bolt-jointed aluminium beam and an FRP-strengthened concrete specimen. The first one shows the performance of the method on simple single and multiple damage scenarios, so that the first conclusions can be extracted and applied to the other two experimental tests, which are designed to simulate a debonding condition on different structures. Once the performance of the impedance-based hierarchical clustering method is proven to be successful, it is then applied to the structural system studied in this dissertation, the RC structures externally strengthened with FRP strips, where the debonding failure in the interface between the FRP and the concrete is successfully detected and classified, proving thus the feasibility of this method. Finally, as an alternative to the previous approach, a continuous monitoring procedure of the FRP-Concrete interface is proposed, based on an FBGsensors Network permanently deployed within that interface. In this way, strain measurements can be obtained under controlled loading conditions, and then they are used in order to implement a multi-objective model updating method solved by a multi-objective expansion of the Particle Swarm Optimization (PSO) method. The feasibility of this last proposal is investigated and successfully proven on both numerical and experimental RC beams strengthened with FRP.

PSO and neural networks: Optimal combination to solve non linear complex problems

Swarm colonies reproduce social habits. Working together in a group to reach a predefined goal is a social behaviour occurring in nature. Linear optimization problems have been approached by different techniques based on natural models. In particular, Particles Swarm optimization is a meta-heuristic search technique that has proven to be effective when dealing with complex optimization problems. This paper presents and develops a new method based on different penalties strategies to solve complex problems. It focuses on the training process of the neural networks, the constraints and the election of the parameters to ensure successful results and to avoid the most common obstacles when searching optimal solutions.

Determination of critical slip surfaces using mutative scale chaos optimization

Limit equilibrium is a common method used to analyze the stability of a slope, and minimization of the factor of safety or identification of critical slip surfaces is a classical geotechnical problem in the context of limit equilibrium methods for slope stability analyses. A mutative scale chaos optimization algorithm is employed in this study to locate the noncircular critical slip surface with Spencer���s method being employed to compute the factor of safety. Four examples from the literature���one homogeneous slope and three layered slopes���are employed to identify the efficiency and accuracy of this approach. Results indicate that the algorithm is flexible and that although it does not generally provide the minimum FS, it provides results that are close to the minimum, an improvement over other solutions proposed in the literature and with small relative errors with respect to other minimum factor of safety (FS) values reported in the literature.

Flujo de potencia entre estructuras complejas sometidas a excitaciones de alta frecuencia y aplicaciones a la detecci��n de da��o estructural

El tema central de investigaci��n en esta Tesis es el estudio del comportamientodin��mico de una estructura mediante modelos que describen la distribuci��n deenerg��a entre los componentes de la misma y la aplicaci��n de estos modelos parala detecci��n de da��os incipientes.Los ensayos din��micos son un modo de extraer informaci��n sobre las propiedadesde una estructura. Si tenemos un modelo de la estructura se podr��a ajustar ��stepara que, con determinado grado de precisi��n, tenga la misma respuesta que elsistema real ensayado. Despu��s de que se produjese un da��o en la estructura,la respuesta al mismo ensayo variar�� en cierta medida; actualizando el modelo alas nuevas condiciones podemos detectar cambios en la configuraci��n del modeloestructural que nos condujeran a la conclusi��n de que en la estructura se haproducido un da��o.De este modo, la detecci��n de un da��o incipiente es posible si somos capacesde distinguir una peque��a variaci��n en los par��metros que definen el modelo. Unr��gimen muy apropiado para realizar este tipo de detecci��n es a altas frecuencias,ya que la respuesta es muy dependiente de los peque��os detalles geom��tricos,dado que el tama��o caracter��stico en la estructura asociado a la respuesta esdirectamente proporcional a la velocidad de propagaci��n de las ondas ac��sticas enel s��lido, que para una estructura dada es inalterable, e inversamente proporcionala la frecuencia de la excitaci��n. Al mismo tiempo, esta caracter��stica de la respuestaa altas frecuencias hace que un modelo de Elementos Finitos no sea aplicable enla pr��ctica, debido al alto coste computacional.Un modelo ampliamente utilizado en el c��lculo de la respuesta de estructurasa altas frecuencias en ingenier��a es el SEA (Statistical Energy Analysis). El SEAaplica el balance energ��tico a cada componente estructural, relacionando la energ��ade vibraci��n de estos con la potencia disipada por cada uno de ellos y la potenciatransmitida entre ellos, cuya suma debe ser igual a la potencia inyectada a cadacomponente estructural. Esta relaci��n es lineal y viene caracterizada por los factoresde p��rdidas. Las magnitudes que intervienen en la respuesta se consideranpromediadas en la geometr��a, la frecuencia y el tiempo.Actualizar el modelo SEA a datos de ensayo es, por lo tanto, calcular losfactores de p��rdidas que reproduzcan la respuesta obtenida en ��ste. Esta actualizaci��n,si se hace de manera directa, supone la resoluci��n de un problema inversoque tiene la caracter��stica de estar mal condicionado. En la Tesis se propone actualizarel modelo SEA, no en t��rmino de los factores de p��rdidas, sino en t��rminos depar��metros estructurales que tienen sentido f��sico cuando se trata de la respuestaa altas frecuencias, como son los factores de disipaci��n de cada componente, susdensidades modales y las rigideces caracter��sticas de los elementos de acoplamiento.Los factores de p��rdidas se calculan como funci��n de estos par��metros. Estaformulaci��n es desarrollada de manera original en esta Tesis y principalmente sefunda en la hip��tesis de alta densidad modal, es decir, que en la respuesta participanun gran n��mero de modos de cada componente estructural.La teor��a general del m��todo SEA, establece que el modelo es v��lido bajounas hip��tesis sobre la naturaleza de las excitaciones externas muy restrictivas,como que ��stas deben ser de tipo ruido blanco local. Este tipo de carga es dif��cil dereproducir en condiciones de ensayo. En la Tesis mostramos con casos pr��cticos queesta restricci��n se puede relajar y, en particular, los resultados son suficientementebuenos cuando la estructura se somete a una carga arm��nica en escal��n.Bajo estas aproximaciones se desarrolla un algoritmo de optimizaci��n por pasosque permite actualizar un modelo SEA a un ensayo transitorio cuando la carga esde tipo arm��nica en escal��n. Este algoritmo actualiza el modelo no solamente parauna banda de frecuencia en particular sino para diversas bandas de frecuencia demanera simult��nea, con el objetivo de plantear un problema mejor condicionado.Por ��ltimo, se define un ��ndice de da��o que mide el cambio en la matriz dep��rdidas cuando se produce un da��o estructural en una localizaci��n concreta deun componente. Se simula num��ricamente la respuesta de una estructura formadapor vigas donde producimos un da��o en la secci��n de una de ellas; como se tratade un c��lculo a altas frecuencias, la simulaci��n se hace mediante el M��todo delos Elementos Espectrales para lo que ha sido necesario desarrollar dentro de laTesis un elemento espectral de tipo viga da��ada en una secci��n determinada. Losresultados obtenidos permiten localizar el componente estructural en que se haproducido el da��o y la secci��n en que ��ste se encuentra con determinado grado deconfianza.AbstractThe main subject under research in this Thesis is the study of the dynamic behaviourof a structure using models that describe the energy distribution betweenthe components of the structure and the applicability of these models to incipientdamage detection.Dynamic tests are a way to extract information about the properties of astructure. If we have a model of the structure, it can be updated in order toreproduce the same response as in experimental tests, within a certain degree ofaccuracy. After damage occurs, the response will change to some extent; modelupdating to the new test conditions can help to detect changes in the structuralmodel leading to the conclusi��n that damage has occurred.In this way incipient damage detection is possible if we are able to detect srnallvariations in the model parameters. It turns out that the high frequency regimeis highly relevant for incipient damage detection, because the response is verysensitive to small structural geometric details. The characteristic length associatedwith the response is proportional to the propagation speed of acoustic waves insidethe solid, but inversely proportional to the excitation frequency. At the same time,this fact makes the application of a Finite Element Method impractical due to thehigh computational cost.A widely used model in engineering when dealing with the high frequencyresponse is SEA (Statistical Energy Analysis). SEA applies the energy balance toeach structural component, relating their vibrational energy with the dissipatedpower and the transmitted power between the different components; their summust be equal to the input power to each of them. This relationship is linear andcharacterized by loss factors. The magnitudes considered in the response shouldbe averaged in geometry, frequency and time.SEA model updating to test data is equivalent to calculating the loss factorsthat provide a better fit to the experimental response. This is formulated as an illconditionedinverse problem. In this Thesis a new updating algorithm is proposedfor the study of the high frequency response regime in terms of parameters withphysical meaning such as the internal dissipation factors, modal densities andcharacteristic coupling stiffness. The loss factors are then calculated from theseparameters. The approach is developed entirely in this Thesis and is mainlybased on a high modal density asumption, that is to say, a large number of modescontributes to the response.General SEA theory establishes the validity of the model under the asumptionof very restrictive external excitations. These should behave as a local white noise.This kind of excitation is difficult to reproduce in an experimental environment.In this Thesis we show that in practical cases this assumption can be relaxed, inparticular, results are good enough when the structure is excited with a harmonicstep function.Under these assumptions an optimization algorithm is developed for SEAmodel updating to a transient test when external loads are harmonic step functions.This algorithm considers the response not only in a single frequency band,but also for several of them simultaneously.A damage index is defined that measures the change in the loss factor matrixwhen a damage has occurred at a certain location in the structure. The structuresconsidered in this study are built with damaged beam elements; as we are dealingwith the high frequency response, the numerical simulation is implemented witha Spectral Element Method. It has therefore been necessary to develop a spectralbeam damaged element as well. The reported results show that damage detectionis possible with this algorithm, moreover, damage location is also possible withina certain degree of accuracy.

A novel methodology for planning reliable wireless sensor networks

Wireless sensor networks (WSNs) have shown their potentials in various applications, which bring a lot of benefits to users from both research and industrial areas. For many setups, it is envisioned thatWSNs will consist of tens to hundreds of nodes that operate on small batteries. However due to the diversity of the deployed environments and resource constraints on radio communication, sensing ability and energy supply, it is a very challenging issue to plan optimized WSN topology and predict its performance before real deployment. During the network planning phase, the connectivity, coverage, cost, network longevity and service quality should all be considered. Therefore it requires designers coping with comprehensive and interdisciplinary knowledge, including networking, radio engineering, embedded system and so on, in order to efficiently construct a reliable WSN for any specific types of environment. Nowadays there is still a lack of the analysis and experiences to guide WSN designers to efficiently construct WSN topology successfully without many trials. Therefore, simulation is a feasible approach to the quantitative analysis of the performance of wireless sensor networks. However the existing planning algorithms and tools, to some extent, have serious limitations to practically design reliable WSN topology: Only a few of them tackle the 3D deployment issue, and an overwhelming number of works are proposed to place devices in 2D scheme. Without considering the full dimension, the impacts of environment to the performance of WSN are not completely studied, thus the values of evaluated metrics such as connectivity and sensing coverage are not sufficiently accurate to make proper decision. Even fewer planning methods model the sensing coverage and radio propagation by considering the realistic scenario where obstacles exist. Radio signals propagate with multi-path phenomenon in the real world, in which direct paths, reflected paths and diffracted paths contribute to the received signal strength. Besides, obstacles between the path of sensor and objects might block the sensing signals, thus create coverage hole in the application. None of the existing planning algorithms model the network longevity and packet delivery capability properly and practically. They often employ unilateral and unrealistic formulations. The optimization targets are often one-sided in the current works. Without comprehensive evaluation on the important metrics, the performance of planned WSNs can not be reliable and entirely optimized. Modeling of environment is usually time consuming and the cost is very high, while none of the current works figure out any method to model the 3D deployment environment efficiently and accurately. Therefore many researchers are trapped by this issue, and their algorithms can only be evaluated in the same scenario, without the possibility to test the robustness and feasibility for implementations in different environments. In this thesis, we propose a novel planning methodology and an intelligent WSN planning tool to assist WSN designers efficiently planning reliable WSNs. First of all, a new method is proposed to efficiently and automatically model the 3D indoor and outdoor environments. To the best of our knowledge, this is the first time that the advantages of image understanding algorithm are applied to automatically reconstruct 3D outdoor and indoor scenarios for signal propagation and network planning purpose. The experimental results indicate that the proposed methodology is able to accurately recognize different objects from the satellite images of the outdoor target regions and from the scanned floor plan of indoor area. Its mechanism offers users a flexibility to reconstruct different types of environment without any human interaction. Thereby it significantly reduces human efforts, cost and time spent on reconstructing a 3D geographic database and allows WSN designers concentrating on the planning issues. Secondly, an efficient ray-tracing engine is developed to accurately and practically model the radio propagation and sensing signal on the constructed 3D map. The engine contributes on efficiency and accuracy to the estimated results. By using image processing concepts, including the kd-tree space division algorithm and modified polar sweep algorithm, the rays are traced efficiently without detecting all the primitives in the scene. The radio propagation model iv is proposed, which emphasizes not only the materials of obstacles but also their locations along the signal path. The sensing signal of sensor nodes, which is sensitive to the obstacles, is benefit from the ray-tracing algorithm via obstacle detection. The performance of this modelling method is robust and accurate compared with conventional methods, and experimental results imply that this methodology is suitable for both outdoor urban scenes and indoor environments. Moreover, it can be applied to either GSM communication or ZigBee protocol by varying frequency parameter of the radio propagation model. Thirdly, WSN planning method is proposed to tackle the above mentioned challenges and efficiently deploy reliable WSNs. More metrics (connectivity, coverage, cost, lifetime, packet latency and packet drop rate) are modeled more practically compared with other works. Especially 3D ray tracing method is used to model the radio link and sensing signal which are sensitive to the obstruction of obstacles; network routing is constructed by using AODV protocol; the network longevity, packet delay and packet drop rate are obtained via simulating practical events in WSNet simulator, which to the best of our knowledge, is the first time that network simulator is involved in a planning algorithm. Moreover, a multi-objective optimization algorithm is developed to cater for the characteristics of WSNs. The capability of providing multiple optimized solutions simultaneously allows users making their own decisions accordingly, and the results are more comprehensively optimized compared with other state-of-the-art algorithms. iMOST is developed by integrating the introduced algorithms, to assist WSN designers efficiently planning reliable WSNs for different configurations. The abbreviated name iMOST stands for an Intelligent Multi-objective Optimization Sensor network planning Tool. iMOST contributes on: (1) Convenient operation with a user-friendly vision system; (2) Efficient and automatic 3D database reconstruction and fast 3D objects design for both indoor and outdoor environments; (3) It provides multiple multi-objective optimized 3D deployment solutions and allows users to configure the network properties, hence it can adapt to various WSN applications; (4) Deployment solutions in the 3D space and the corresponding evaluated performance are visually presented to users; and (5) The Node Placement Module of iMOST is available online as well as the source code of the other two rebuilt heuristics. Therefore WSN designers will be benefit from v this tool on efficiently constructing environment database, practically and efficiently planning reliable WSNs for both outdoor and indoor applications. With the open source codes, they are also able to compare their developed algorithms with ours to contribute to this academic field. Finally, solid real results are obtained for both indoor and outdoor WSN planning. Deployments have been realized for both indoor and outdoor environments based on the provided planning solutions. The measured results coincide well with the estimated results. The proposed planning algorithm is adaptable according to the WSN designer���s desirability and configuration, and it offers flexibility to plan small and large scale, indoor and outdoor 3D deployments. The thesis is organized in 7 chapters. In Chapter 1, WSN applications and motivations of this work are introduced, the state-of-the-art planning algorithms and tools are reviewed, challenges are stated out and the proposed methodology is briefly introduced. In Chapter 2, the proposed 3D environment reconstruction methodology is introduced and its performance is evaluated for both outdoor and indoor environment. The developed ray-tracing engine and proposed radio propagation modelling method are described in details in Chapter 3, their performances are evaluated in terms of computation efficiency and accuracy. Chapter 4 presents the modelling of important metrics of WSNs and the proposed multi-objective optimization planning algorithm, the performance is compared with the other state-of-the-art planning algorithms. The intelligent WSN planning tool iMOST is described in Chapter 5. RealWSN deployments are prosecuted based on the planned solutions for both indoor and outdoor scenarios, important data are measured and results are analysed in Chapter 6. Chapter 7 concludes the thesis and discusses about future works. vi Resumen en Castellano Las redes de sensores inal��mbricas (en ingl��s Wireless Sensor Networks, WSNs) han demostrado su potencial en diversas aplicaciones que aportan una gran cantidad de beneficios para el campo de la investigaci��n y de la industria. Para muchas configuraciones se prev�� que las WSNs consistir��n en decenas o cientos de nodos que funcionar��n con bater��as peque��as. Sin embargo, debido a la diversidad de los ambientes para desplegar las redes y a las limitaciones de recursos en materia de comunicaci��n de radio, capacidad de detecci��n y suministro de energ��a, la planificaci��n de la topolog��a de la red y la predicci��n de su rendimiento es un tema muy dif��cil de tratar antes de la implementaci��n real. Durante la fase de planificaci��n del despliegue de la red se deben considerar aspectos como la conectividad, la cobertura, el coste, la longevidad de la red y la calidad del servicio. Por lo tanto, requiere de dise��adores con un amplio e interdisciplinario nivel de conocimiento que incluye la creaci��n de redes, la ingenier��a de radio y los sistemas embebidos entre otros, con el fin de construir de manera eficiente una WSN confiable para cualquier tipo de entorno. Hoy en d��a todav��a hay una falta de an��lisis y experiencias que orienten a los dise��adores de WSN para construir las topolog��as WSN de manera eficiente sin realizar muchas pruebas. Por lo tanto, la simulaci��n es un enfoque viable para el an��lisis cuantitativo del rendimiento de las redes de sensores inal��mbricos. Sin embargo, los algoritmos y herramientas de planificaci��n existentes tienen, en cierta medida, serias limitaciones para dise��ar en la pr��ctica una topolog��a fiable de WSN: S��lo unos pocos abordan la cuesti��n del despliegue 3D mientras que existe una gran cantidad de trabajos que colocan los dispositivos en 2D. Si no se analiza la dimensi��n completa (3D), los efectos del entorno en el desempe��o de WSN no se estudian por completo, por lo que los valores de los par��metros evaluados, como la conectividad y la cobertura de detecci��n, no son lo suficientemente precisos para tomar la decisi��n correcta. A��n en menor medida los m��todos de planificaci��n modelan la cobertura de los sensores y la propagaci��n de la se��al de radio teniendo en cuenta un escenario realista donde existan obst��culos. Las se��ales de radio en el mundo real siguen una propagaci��n multicamino, en la que los caminos directos, los caminos reflejados y los caminos difractados contribuyen a la intensidad de la se��al recibida. Adem��s, los obst��culos entre el recorrido del sensor y los objetos pueden bloquear las se��ales de detecci��n y por lo tanto crear ��reas sin cobertura en la aplicaci��n. Ninguno de los algoritmos de planificaci��n existentes modelan el tiempo de vida de la red y la capacidad de entrega de paquetes correctamente y pr��cticamente. A menudo se emplean formulaciones unilaterales y poco realistas. Los objetivos de optimizaci��n son a menudo tratados unilateralmente en los trabajos actuales. Sin una evaluaci��n exhaustiva de los par��metros importantes, el rendimiento previsto de las redes inal��mbricas de sensores no puede ser fiable y totalmente optimizado. Por lo general, el modelado del entorno conlleva mucho tiempo y tiene un coste muy alto, pero ninguno de los trabajos actuales propone alg��n m��todo para modelar el entorno de despliegue 3D con eficiencia y precisi��n. Por lo tanto, muchos investigadores est��n limitados por este problema y sus algoritmos s��lo se pueden evaluar en el mismo escenario, sin la posibilidad de probar la solidez y viabilidad para las implementaciones en diferentes entornos. En esta tesis, se propone una nueva metodolog��a de planificaci��n as�� como una herramienta inteligente de planificaci��n de redes de sensores inal��mbricas para ayudar a los dise��adores a planificar WSNs fiables de una manera eficiente. En primer lugar, se propone un nuevo m��todo para modelar demanera eficiente y autom��tica los ambientes interiores y exteriores en 3D. Seg��n nuestros conocimientos hasta la fecha, esta es la primera vez que las ventajas del algoritmo de _image understanding_se aplican para reconstruir autom��ticamente los escenarios exteriores e interiores en 3D para analizar la propagaci��n de la se��al y viii la planificaci��n de la red. Los resultados experimentales indican que la metodolog��a propuesta es capaz de reconocer con precisi��n los diferentes objetos presentes en las im��genes satelitales de las regiones objetivo en el exterior y de la planta escaneada en el interior. Su mecanismo ofrece a los usuarios la flexibilidad para reconstruir los diferentes tipos de entornos sin ninguna interacci��n humana. De este modo se reduce considerablemente el esfuerzo humano, el coste y el tiempo invertido en la reconstrucci��n de una base de datos geogr��fica con informaci��n 3D, permitiendo as�� que los dise��adores se concentren en los temas de planificaci��n. En segundo lugar, se ha desarrollado un motor de trazado de rayos (en ingl��s ray tracing) eficiente para modelar con precisi��n la propagaci��n de la se��al de radio y la se��al de los sensores en el mapa 3D construido. El motor contribuye a la eficiencia y la precisi��n de los resultados estimados. Mediante el uso de los conceptos de procesamiento de im��genes, incluyendo el algoritmo del ��rbol kd para la divisi��n del espacio y el algoritmo _polar sweep_modificado, los rayos se trazan de manera eficiente sin la detecci��n de todas las primitivas en la escena. El modelo de propagaci��n de radio que se propone no s��lo considera los materiales de los obst��culos, sino tambi��n su ubicaci��n a lo largo de la ruta de se��al. La se��al de los sensores de los nodos, que es sensible a los obst��culos, se ve beneficiada por la detecci��n de objetos llevada a cabo por el algoritmo de trazado de rayos. El rendimiento de este m��todo de modelado es robusto y preciso en comparaci��n con los m��todos convencionales, y los resultados experimentales indican que esta metodolog��a es adecuada tanto para escenas urbanas al aire libre como para ambientes interiores. Por otra parte, se puede aplicar a cualquier comunicaci��n GSM o protocolo ZigBee mediante la variaci��n de la frecuencia del modelo de propagaci��n de radio. En tercer lugar, se propone un m��todo de planificaci��n de WSNs para hacer frente a los desaf��os mencionados anteriormente y desplegar redes de sensores fiables de manera eficiente. Se modelan m��s par��metros (conectividad, cobertura, coste, tiempo de vida, la latencia de paquetes y tasa de ca��da de paquetes) en comparaci��n con otros trabajos. Especialmente el m��todo de trazado de rayos 3D se utiliza para modelar el enlace de radio y se��al de los sensores que son sensibles a la obstrucci��n de obst��culos; el enrutamiento de la red se construye utilizando el protocolo AODV; la longevidad de la red, retardo de paquetes ix y tasa de abandono de paquetes se obtienen a trav��s de la simulaci��n de eventos pr��cticos en el simulador WSNet, y seg��n nuestros conocimientos hasta la fecha, es la primera vez que simulador de red est�� implicado en un algoritmo de planificaci��n. Por otra parte, se ha desarrollado un algoritmo de optimizaci��n multi-objetivo para satisfacer las caracter��sticas de las redes inal��mbricas de sensores. La capacidad de proporcionar m��ltiples soluciones optimizadas de forma simult��nea permite a los usuarios tomar sus propias decisiones en consecuencia, obteniendo mejores resultados en comparaci��n con otros algoritmos del estado del arte. iMOST se desarrolla mediante la integraci��n de los algoritmos presentados, para ayudar de forma eficiente a los dise��adores en la planificaci��n de WSNs fiables para diferentes configuraciones. El nombre abreviado iMOST (Intelligent Multi-objective Optimization Sensor network planning Tool) representa una herramienta inteligente de planificaci��n de redes de sensores con optimizaci��n multi-objetivo. iMOST contribuye en: (1) Operaci��n conveniente con una interfaz de f��cil uso, (2) Reconstrucci��n eficiente y autom��tica de una base de datos con informaci��n 3D y dise��o r��pido de objetos 3D para ambientes interiores y exteriores, (3) Proporciona varias soluciones de despliegue optimizadas para los multi-objetivo en 3D y permite a los usuarios configurar las propiedades de red, por lo que puede adaptarse a diversas aplicaciones de WSN, (4) las soluciones de implementaci��n en el espacio 3D y el correspondiente rendimiento evaluado se presentan visualmente a los usuarios, y (5) El _Node Placement Module_de iMOST est�� disponible en l��nea, as�� como el c��digo fuente de las otras dos heur��sticas de planificaci��n. Por lo tanto los dise��adores WSN se beneficiar��n de esta herramienta para la construcci��n eficiente de la base de datos con informaci��n del entorno, la planificaci��n pr��ctica y eficiente de WSNs fiables tanto para aplicaciones interiores y exteriores. Con los c��digos fuente abiertos, son capaces de comparar sus algoritmos desarrollados con los nuestros para contribuir a este campo acad��mico. Por ��ltimo, se obtienen resultados reales s��lidos tanto para la planificaci��n de WSN en interiores y exteriores. Los despliegues se han realizado tanto para ambientes de interior y como para ambientes de exterior utilizando las soluciones de planificaci��n propuestas. Los resultados medidos coinciden en gran medida con los resultados estimados. El algoritmo de planificaci��n x propuesto se adapta convenientemente al deise��o de redes de sensores inal��mbricas, y ofrece flexibilidad para planificar los despliegues 3D a peque��a y gran escala tanto en interiores como en exteriores. La tesis se estructura en 7 cap��tulos. En el Cap��tulo 1, se presentan las aplicaciones de WSN y motivaciones de este trabajo, se revisan los algoritmos y herramientas de planificaci��n del estado del arte, se presentan los retos y se describe brevemente la metodolog��a propuesta. En el Cap��tulo 2, se presenta la metodolog��a de reconstrucci��n de entornos 3D propuesta y su rendimiento es evaluado tanto para espacios exteriores como para espacios interiores. El motor de trazado de rayos desarrollado y el m��todo de modelado de propagaci��n de radio propuesto se describen en detalle en el Cap��tulo 3, evalu��ndose en t��rminos de eficiencia computacional y precisi��n. En el Cap��tulo 4 se presenta el modelado de los par��metros importantes de las WSNs y el algoritmo de planificaci��n de optimizaci��n multi-objetivo propuesto, el rendimiento se compara con los otros algoritmos de planificaci��n descritos en el estado del arte. La herramienta inteligente de planificaci��n de redes de sensores inal��mbricas, iMOST, se describe en el Cap��tulo 5. En el Cap��tulo 6 se llevan a cabo despliegues reales de acuerdo a las soluciones previstas para los escenarios interiores y exteriores, se miden los datos importantes y se analizan los resultados. En el Cap��tulo 7 se concluye la tesis y se discute acerca de los trabajos futuros.

Estudio num��rico de flujo turbulento cargado con part��culas s��lidas a trav��s de canales y tuber��as de secci��n variable

La presente Tesis Doctoral tiene como objetivo el estudio de flujo turbulento cargado con part��culas s��lidas a trav��s de canales y tuber��as de secci��n constante usando un enfoque Euleriano-Lagrangiano. El campo de flujo de la fase de transporte (aire) se resuelve usando simulaci��n de grandes escalas (LES), implementada en un programa de vol��menes finitos mientras que las ecuaciones gobernantes de la fase dispersa son resueltas por medio de un algoritmo de seguimiento Lagrangiano de part��culas que ha sido desarrollado y acoplado al programa que resuelve el flujo. Se estudia de manera sistem��tica y progresiva la interacci��n fluido���part��cula (one-way coupling), a trav��s de diferentes configuraciones geom��tricas en coordenadas cartesianas (canales de secci��n constante y variable) y en coordenadas cil��ndricas (tuber��as de secci��n constante y secci��n variable) abarcando diferentes n��meros de Reynolds y diferentes tama��os de part��culas; todos los resultados obtenidos han sido comparados con datos publicados previamente. El estudio de flujo multif��sico a trav��s de, tuber��as de secci��n variable, ha sido abordada en otras investigaciones mayoritariamente de forma experimental o mediante simulaci��n usando modelos de turbulencia menos complejos y no mediante LES. El patr��n de flujo que se verifica en una tuber��a con expansi��n es muy complejo y dicha configuraci��n geom��trica se halla en m��ltiples aplicaciones industriales que involucran el transporte de part��culas s��lidas, por ello es de gran inter��s su estudio. Como hecho innovador, en esta tesis no solo se resuelven las estad��sticas de velocidad del fluido y las part��culas en tuber��as con diferentes tama��os de expansi��n y diferentes reg��menes de flujo sino que se caracteriza, usando diversas formulaciones del n��mero de Stokes y el par��metro de arrastre, el ingreso y acumulaci��n de part��culas dentro de la zona de recirculaci��n, obteni��ndose resultados coincidentes con datos experimentales. ABSTRACT The objective of this Thesis research is to study the turbulent flow laden with solid particles through channels and pipes with using Eulerian-Lagrangian approach. The flow field of the transport phase (air ) is solved using large eddy simulation ( LES ) implemented in a program of finite volume while the governing equations of the dispersed phase are resolved by means of a particle Lagrangian tracking algorithm which was developed and coupled to principal program flow solver . We studied systematically and progressively the fluid interaction ��� particle ( one- way coupling ) , through different geometric configurations in Cartesian coordinates ( channel with constant and variable section) and in cylindrical coordinates ( pipes with constant section and variable section ) covering different Reynolds numbers and different particle sizes, all results have been compared with previously published data . The study of multiphase flow through, pipes with variable section has been addressed in other investigations predominantly experimentally or by simulation using less complex models and no turbulence by LES. The flow pattern is verified in a pipe expansion is very complex and this geometry is found in many industrial applications involving the transport of solid particles, so it is of great interest to study. As an innovator fact , in this Thesis not only finds fluid velocity statistics and particles with different sizes of pipe expansion and different flow regimes but characterized, using various formulations of the Stokes number and the drag parameter are resolved, the entry and accumulation of particles within the recirculation zone , matching results obtained with experimental data.

Two design methods for radial line slot antennas with arbitrary or beam pattern

Two design procedures for Radial Line Slot Antennas (RLSAs) with circular polarization and either maximum gain or an arbitrary shaped pattern are proposed. Firstly, a method to design a RLSA with any desired pattern is presented. It is based on an optimization algorithm and some measures to ensure its fast convergence and stability need to be taken. Secondly, a fast technique to calculate the length and the position of every slot in a high gain RLSA with uniform field distribution is described. Both procedures are vali dated with the design of three antennas with different characteristics.

Microstructure-based numerical modeling of the mechanical behavior of Mg alloys

Dentro de los materiales estructurales, el magnesio y sus aleaciones est��n siendo el foco de una de profunda investigaci��n. Esta investigaci��n est�� dirigida a comprender la relaci��n existente entre la microestructura de las aleaciones de Mg y su comportamiento mec��nico. El objetivo es optimizar las aleaciones actuales de magnesio a partir de su microestructura y dise��ar nuevas aleaciones. Sin embargo, el efecto de los factores microestructurales (como la forma, el tama��o, la orientaci��n de los precipitados y la morfolog��a de los granos) en el comportamiento mec��nico de estas aleaciones est�� todav��a por descubrir. Para conocer mejor de la relaci��n entre la microestructura y el comportamiento mec��nico, es necesaria la combinaci��n de t��cnicas avanzadas de caracterizaci��n experimental como de simulaci��n num��rica, a diferentes longitudes de escala. En lo que respecta a las t��cnicas de simulaci��n num��rica, la homogeneizaci��n policristalina es una herramienta muy ��til para predecir la respuesta macrosc��pica a partir de la microestructura de un policristal (caracterizada por el tama��o, la forma y la distribuci��n de orientaciones de los granos) y el comportamiento del monocristal. La descripci��n de la microestructura se lleva a cabo mediante modernas t��cnicas de caracterizaci��n (difracci��n de rayos X, difracci��n de electrones retrodispersados, as�� como con microscopia ��ptica y electr��nica). Sin embargo, el comportamiento del cristal sigue siendo dif��cil de medir, especialmente en aleaciones de Mg, donde es muy complicado conocer el valor de los par��metros que controlan el comportamiento mec��nico de los diferentes modos de deslizamiento y maclado. En la presente tesis se ha desarrollado una estrategia de homogeneizaci��n computacional para predecir el comportamiento de aleaciones de magnesio. El comportamiento de los policristales ha sido obtenido mediante la simulaci��n por elementos finitos de un volumen representativo (RVE) de la microestructura, considerando la distribuci��n real de formas y orientaciones de los granos. El comportamiento del cristal se ha simulado mediante un modelo de plasticidad cristalina que tiene en cuenta los diferentes mecanismos f��sicos de deformaci��n, como el deslizamiento y el maclado. Finalmente, la obtenci��n de los par��metros que controlan el comportamiento del cristal (tensiones cr��ticas resueltas (CRSS) as�� como las tasas de endurecimiento para todos los modos de maclado y deslizamiento) se ha resuelto mediante la implementaci��n de una metodolog��a de optimizaci��n inversa, una de las principales aportaciones originales de este trabajo. La metodolog��a inversa pretende, por medio del algoritmo de optimizaci��n de Levenberg-Marquardt, obtener el conjunto de par��metros que definen el comportamiento del monocristal y que mejor ajustan a un conjunto de ensayos macrosc��picos independientes. Adem��s de la implementaci��n de la t��cnica, se han estudiado tanto la objetividad del metodolog��a como la unicidad de la soluci��n en funci��n de la informaci��n experimental. La estrategia de optimizaci��n inversa se us�� inicialmente para obtener el comportamiento cristalino de la aleaci��n AZ31 de Mg, obtenida por laminado. Esta aleaci��n tiene una marcada textura basal y una gran anisotrop��a pl��stica. El comportamiento de cada grano incluy�� cuatro mecanismos de deformaci��n diferentes: deslizamiento en los planos basal, prism��tico, piramidal hc+ai, junto con el maclado en tracci��n. La validez de los par��metros resultantes se valid�� mediante la capacidad del modelo policristalino para predecir ensayos macrosc��picos independientes en diferentes direcciones. En segundo lugar se estudi�� mediante la misma estrategia, la influencia del contenido de Neodimio (Nd) en las propiedades de una aleaci��n de Mg-Mn-Nd, obtenida por extrusi��n. Se encontr�� que la adici��n de Nd produce una progresiva isotropizaci��n del comportamiento macrosc��pico. El modelo mostr�� que este incremento de la isotrop��a macrosc��pica era debido tanto a la aleatoriedad de la textura inicial como al incremento de la isotrop��a del comportamiento del cristal, con valores similares de las CRSSs de los diferentes modos de deformaci��n. Finalmente, el modelo se emple�� para analizar el efecto de la temperatura en el comportamiento del cristal de la aleaci��n de Mg-Mn-Nd. La introducci��n en el modelo de los efectos non-Schmid sobre el modo de deslizamiento piramidal hc+ai permiti�� capturar el comportamiento mec��nico a temperaturas superiores a 150_C. Esta es la primera vez, de acuerdo con el conocimiento del autor, que los efectos non-Schmid han sido observados en una aleaci��n de Magnesio. The study of Magnesium and its alloys is a hot research topic in structural materials. In particular, special attention is being paid in understanding the relationship between microstructure and mechanical behavior in order to optimize the current alloy microstructures and guide the design of new alloys. However, the particular effect of several microstructural factors (precipitate shape, size and orientation, grain morphology distribution, etc.) in the mechanical performance of a Mg alloy is still under study. The combination of advanced characterization techniques and modeling at several length scales is necessary to improve the understanding of the relation microstructure and mechanical behavior. Respect to the simulation techniques, polycrystalline homogenization is a very useful tool to predict the macroscopic response from polycrystalline microstructure (grain size, shape and orientation distributions) and crystal behavior. The microstructure description is fully covered with modern characterization techniques (X-ray diffraction, EBSD, optical and electronic microscopy). However, the mechanical behaviour of single crystals is not well-known, especially in Mg alloys where the correct parameterization of the mechanical behavior of the different slip/twin modes is a very difficult task. A computational homogenization framework for predicting the behavior of Magnesium alloys has been developed in this thesis. The polycrystalline behavior was obtained by means of the finite element simulation of a representative volume element (RVE) of the microstructure including the actual grain shape and orientation distributions. The crystal behavior for the grains was accounted for a crystal plasticity model which took into account the physical deformation mechanisms, e.g. slip and twinning. Finally, the problem of the parametrization of the crystal behavior (critical resolved shear stresses (CRSS) and strain hardening rates of all the slip and twinning modes) was obtained by the development of an inverse optimization methodology, one of the main original contributions of this thesis. The inverse methodology aims at finding, by means of the Levenberg-Marquardt optimization algorithm, the set of parameters defining crystal behavior that best fit a set of independent macroscopic tests. The objectivity of the method and the uniqueness of solution as function of the input information has been numerically studied. The inverse optimization strategy was first used to obtain the crystal behavior of a rolled polycrystalline AZ31 Mg alloy that showed a marked basal texture and a strong plastic anisotropy. Four different deformation mechanisms: basal, prismatic and pyramidal hc+ai slip, together with tensile twinning were included to characterize the single crystal behavior. The validity of the resulting parameters was proved by the ability of the polycrystalline model to predict independent macroscopic tests on different directions. Secondly, the influence of Neodymium (Nd) content on an extruded polycrystalline Mg-Mn-Nd alloy was studied using the same homogenization and optimization framework. The effect of Nd addition was a progressive isotropization of the macroscopic behavior. The model showed that this increase in the macroscopic isotropy was due to a randomization of the initial texture and also to an increase of the crystal behavior isotropy (similar values of the CRSSs of the different modes). Finally, the model was used to analyze the effect of temperature on the crystal behaviour of a Mg-Mn-Nd alloy. The introduction in the model of non-Schmid effects on the pyramidal hc+ai slip allowed to capture the inverse strength differential that appeared, between the tension and compression, above 150_C. This is the first time, to the author's knowledge, that non-Schmid effects have been reported for Mg alloys.

M��todos computacionales para visco-hiperelasticidad anis��tropa en grandes deformaciones

El comportamiento mec��nico de muchos materiales biol��gicos y polim��ricos en grandes deformaciones se puede describir adecuadamente mediante formulaciones isoc��ricas hiperel��sticas y viscoel��sticas. Las ecuaciones de comportamiento el��stico y viscoel��stico y las formulaciones computacionales para materiales incompresibles is��tropos en deformaciones finitas est��n ampliamente desarrolladas en la actualidad. Sin embargo, el desarrollo de modelos anis��tropos no lineales y de sus correspondientes formulaciones computacionales sigue siendo un tema de investigaci��n de gran inter��s. Cuando se consideran grandes deformaciones, existen muchas medidas de deformaci��n disponibles con las que poder formular las ecuaciones de comportamiento. Los modelos en deformaciones cuadr��ticas facilitan la implementaci��n en c��digos de elementos finitos, ya que estas medidas surgen de forma natural en la formulaci��n. No obstante, pueden dificultar la interpretaci��n de los modelos y llevar a resultados pocos realistas. El uso de deformaciones logar��tmicas permite el desarrollo de modelos m��s simples e intuitivos, aunque su formulaci��n computacional debe ser adaptada a las exigencias del programa. Como punto de partida, en esta tesis se demuestra que las deformaciones logar��tmicas representan la extensi��n natural de las deformaciones infinitesimales, tanto axiales como angulares, al campo de las grandes deformaciones. Este hecho permite explicar la simplicidad de las ecuaciones resultantes. Los modelos hiperel��sticos predominantes en la actualidad est��n formulados en invariantes de deformaciones cuadr��ticas. Estos modelos, ya sean continuos o microestructurales, se caracterizan por tener una forma anal��tica predefinida. Su expresi��n definitiva se calcula mediante un ajuste de curvas a datos experimentales. Un modelo que no sigue esta metodolog��a fue desarrollado por Sussman y Bathe. El modelo es s��lo v��lido para isotrop��a y queda definido por una funci��n de energ��a interpolada con splines, la cual reproduce los datos experimentales de forma exacta. En esta tesis se presenta su extensi��n a materiales transversalmente is��tropos y ort��tropos utilizando deformaciones logar��tmicas. Asimismo, se define una nueva propiedad que las funciones de energ��a anis��tropas deben satisfacer para que su convergencia al caso is��tropo sea correcta. En visco-hiperelasticidad, aparte de las distintas funciones de energ��a disponibles, hay dos aproximaciones computational t��picas basadas en variables internas. El modelo original de Sim�� est�� formulado en tensiones y es v��lido para materiales anis��tropos, aunque s��lo es adecuado para peque��as desviaciones con respecto al equilibrio termodin��mico. En cambio, el modelo basado en deformaciones de Reese y Govindjee permite grandes deformaciones no equilibradas pero es, en esencia, is��tropo. Las formulaciones anis��tropas en este ��ltimo contexto son microestructurales y emplean el modelo is��tropo para cada uno de los constituyentes. En esta tesis se presentan dos formulaciones fenomenol��gicas viscoel��sticas definidas mediante funciones hiperel��sticas anis��tropas y v��lidas para grandes desviaciones con respecto al equilibrio termodin��mico. El primero de los modelos est�� basado en la descomposici��n multiplicativa de Sidoroff y requiere un comportamiento viscoso is��tropo. La formulaci��n converge al modelo de Reese y Govindjee en el caso especial de isotrop��a el��stica. El segundo modelo se define a partir de una descomposici��n multiplicativa inversa. Esta formulaci��n est�� basada en una descripci��n co-rotacional del problema, es sustancialmente m��s compleja y puede dar lugar a tensores constitutivos ligeramente no sim��tricos. Sin embargo, su rango de aplicaci��n es mucho mayor ya que permite un comportamiento anis��tropo tanto el��stico como viscoso. Varias simulaciones de elementos finitos muestran la gran versatilidad de estos modelos cuando se combinan con funciones hiperel��sticas formadas por splines. ABSTRACT The mechanical behavior of many polymeric and biological materials may be properly modelled be means of isochoric hyperelastic and viscoelastic formulations. These materials may sustain large strains. The viscoelastic computational formulations for isotropic incompressible materials at large strains may be considered well established; for example Ogden���s hyperelastic function and the visco-hyperelastic model of Reese and Govindjee are well known models for isotropy. However, anisotropic models and computational procedures both for hyperelasticity and viscohyperelasticity are still under substantial research. Anisotropic hyperelastic models are typically based on structural invariants obtained from quadratic strain measures. These models may be microstructurallybased or phenomenological continuum formulations, and are characterized by a predefined analytical shape of the stored energy. The actual final expression of the stored energy depends on some material parameters which are obtained from an optimization algorithm, typically the Levenberg-Marquardt algorithm. We present in this work anisotropic spline-based hyperelastic stored energies in which the shape of the stored energy is obtained as part of the procedure and which (exactly in practice) replicates the experimental data. These stored energies are based on invariants obtained from logarithmic strain measures. These strain measures preserve the metric and the physical meaning of the trace and deviator operators and, hence, are interesting and meaningful for anisotropic formulations. Furthermore, the proposed stored energies may be formulated in order to have material-symmetries congruency both from a theoretical and from a numerical point of view, which are new properties that we define in this work. On the other hand, visco-hyperelastic formulations for anisotropic materials are typically based on internal stress-like variables following a procedure used by Sim��o. However, it can be shown that this procedure is not adequate for large deviations from thermodynamic equilibrium. In contrast, a formulation given by Reese and Govindjee is valid for arbitrarily large deviations from thermodynamic equilibrium but not for anisotropic stored energy functions. In this work we present two formulations for visco-hyperelasticity valid for anisotropic stored energies and large deviations from thermodynamic equilibrium. One of the formulations is based on the Sidoroff multiplicative decomposition and converges to the Reese and Govindjee formulation for the case of isotropy. However, the formulation is restricted to isotropy for the viscous component. The second formulation is based on a reversed multiplicative decomposition. This last formulation is substantially more complex and based on a corotational description of the problem. It can also result in a slightly nonsymmetric tangent. However, the formulation allows for anisotropy not only in the equilibrated and non-equilibrated stored energies, but also in the viscous behavior. Some examples show finite element implementation, versatility and interesting characteristics of the models.

Determining electric vehicle charging point locations considering drivers' daily activities

In this paper the daily temporal and spatial behavior of electric vehicles (EVs) is modelled using an activity-based (ActBM) microsimulation model for Flanders region (Belgium). Assuming that all EVs are completely charged at the beginning of the day, this mobility model is used to determine the percentage of Flemish vehicles that cannot cover their programmed daily trips and need to be recharged during the day. Assuming a variable electricity price, an optimization algorithm determines when and where EVs can be recharged at minimum cost for their owners. This optimization takes into account the individual mobility constraint for each vehicle, as they can only be charged when the car is stopped and the owner is performing an activity. From this information, the aggregated electric demand for Flanders is obtained, identifying the most overloaded areas at the critical hours. Finally it is also analyzed what activities EV owners are underway during their recharging period. From this analysis, different actions for public charging point deployment in different areas and for different activities are proposed.

A methodology to analyze, design and implement very fast and robust controls of Buck-type converters

La electr��nica digital moderna presenta un desaf��o a los dise��adores de sistemas de potencia. El creciente alto rendimiento de microprocesadores, FPGAs y ASICs necesitan sistemas de alimentaci��n que cumplan con requirimientos din��micos y est��ticos muy estrictos. Espec��ficamente, estas alimentaciones son convertidores DC-DC de baja tensi��n y alta corriente que necesitan ser dise��ados para tener un peque��o rizado de tensi��n y una peque��a desviaci��n de tensi��n de salida bajo transitorios de carga de una alta pendiente. Adem��s, dependiendo de la aplicaci��n, se necesita cumplir con otros requerimientos tal y como proveer a la carga con ���Escalado din��mico de tensi��n���, donde el convertidor necesitar cambiar su tensi��n de salida tan r��pidamente posible sin sobreoscilaciones, o ���Posicionado Adaptativo de la Tensi��n��� donde la tensi��n de salida se reduce ligeramente cuanto m��s grande sea la potencia de salida. Por supuesto, desde el punto de vista de la industria, las figuras de m��rito de estos convertidores son el coste, la eficiencia y el tama��o/peso. Idealmente, la industria necesita un convertidor que es m��s barato, m��s eficiente, m��s peque��o y que a��n as�� cumpla con los requerimienos din��micos de la aplicaci��n. En este contexto, varios enfoques para mejorar la figuras de m��rito de estos convertidores se han seguido por la industria y la academia tales como mejorar la topolog��a del convertidor, mejorar la tecnolog��a de semiconducores y mejorar el control. En efecto, el control es una parte fundamental en estas aplicaciones ya que un control muy r��pido hace que sea m��s f��cil que una determinada topolog��a cumpla con los estrictos requerimientos din��micos y, consecuentemente, le da al dise��ador un margen de libertar m��s amplio para mejorar el coste, la eficiencia y/o el tama��o del sistema de potencia. En esta tesis, se investiga c��mo dise��ar e implementar controles muy r��pidos para el convertidor tipo Buck. En esta tesis se demuestra que medir la tensi��n de salida es todo lo que se necesita para lograr una respuesta casi ��ptima y se propone una gu��a de dise��o unificada para controles que s��lo miden la tensi��n de salida Luego, para asegurar robustez en controles muy r��pidos, se proponen un modelado y un an��lisis de estabilidad muy precisos de convertidores DC-DC que tienen en cuenta circuiter��a para sensado y elementos par��sitos cr��ticos. Tambi��n, usando este modelado, se propone una algoritmo de optimizaci��n que tiene en cuenta las tolerancias de los componentes y sensados distorsionados. Us ando este algoritmo, se comparan controles muy r��pidos del estado del arte y su capacidad para lograr una r��pida respuesta din��mica se posiciona seg��n el condensador de salida utilizado. Adem��s, se propone una t��cnica para mejorar la respuesta din��mica de los controladores. Todas las propuestas se han corroborado por extensas simulaciones y prototipos experimentales. Con todo, esta tesis sirve como una metodolog��a para ingenieros para dise��ar e implementar controles r��pidos y robustos de convertidores tipo Buck. ABSTRACT Modern digital electronics present a challenge to designers of power systems. The increasingly high-performance of microprocessors, FPGAs (Field Programmable Gate Array) and ASICs (Application-Specific Integrated Circuit) require power supplies to comply with very demanding static and dynamic requirements. Specifically, these power supplies are low-voltage/high-current DC-DC converters that need to be designed to exhibit low voltage ripple and low voltage deviation under high slew-rate load transients. Additionally, depending on the application, other requirements need to be met such as to provide to the load ���Dynamic Voltage Scaling��� (DVS), where the converter needs to change the output voltage as fast as possible without underdamping, or ���Adaptive Voltage Positioning��� (AVP) where the output voltage is slightly reduced the greater the output power. Of course, from the point of view of the industry, the figures of merit of these converters are the cost, efficiency and size/weight. Ideally, the industry needs a converter that is cheaper, more efficient, smaller and that can still meet the dynamic requirements of the application. In this context, several approaches to improve the figures of merit of these power supplies are followed in the industry and academia such as improving the topology of the converter, improving the semiconductor technology and improving the control. Indeed, the control is a fundamental part in these applications as a very fast control makes it easier for the topology to comply with the strict dynamic requirements and, consequently, gives the designer a larger margin of freedom to improve the cost, efficiency and/or size of the power supply. In this thesis, how to design and implement very fast controls for the Buck converter is investigated. This thesis proves that sensing the output voltage is all that is needed to achieve an almost time-optimal response and a unified design guideline for controls that only sense the output voltage is proposed. Then, in order to assure robustness in very fast controls, a very accurate modeling and stability analysis of DC-DC converters is proposed that takes into account sensing networks and critical parasitic elements. Also, using this modeling approach, an optimization algorithm that takes into account tolerances of components and distorted measurements is proposed. With the use of the algorithm, very fast analog controls of the state-of-the-art are compared and their capabilities to achieve a fast dynamic response are positioned de pending on the output capacitor. Additionally, a technique to improve the dynamic response of controllers is also proposed. All the proposals are corroborated by extensive simulations and experimental prototypes. Overall, this thesis serves as a methodology for engineers to design and implement fast and robust controls for Buck-type converters.

Optimizaci��n del consumo de combustible de un veh��culo dependiendo de las condiciones de la carretera

El consumo de combustible en un autom��vil es una caracter��stica que se intenta mejorar continuamente debido a los precios del carburante y a la creciente conciencia medioambiental. Esta tesis doctoral plantea un algoritmo de optimizaci��n del consumo que tiene en cuenta las especificaciones t��cnicas del veh��culo, el perfil de orograf��a de la carretera y el tr��fico presente en ella. El algoritmo de optimizaci��n calcula el perfil de velocidad ��ptima que debe seguir el veh��culo para completar un recorrido empleando un tiempo de viaje especificado. El c��lculo del perfil de velocidad ��ptima considera los valores de pendiente de la carretera as�� como tambi��n las condiciones de tr��fico vehicular de la franja horaria en que se realiza el recorrido. El algoritmo de optimizaci��n reacciona ante condiciones de tr��fico cambiantes y adapta continuamente el perfil ��ptimo de velocidad para que el veh��culo llegue al destino cumpliendo el horario de llegada establecido. La optimizaci��n de consumo es aplicada en veh��culos convencionales de motor de combusti��n interna y en veh��culos h��bridos tipo serie. Los datos de consumo utilizados por el algoritmo de optimizaci��n se obtienen mediante la simulaci��n de modelos cuasi-est��ticos de los veh��culos. La t��cnica de minimizaci��n empleada por el algoritmo es la Programaci��n Din��mica. El algoritmo divide la optimizaci��n del consumo en dos partes claramente diferenciadas y aplica la Programaci��n Din��mica sobre cada una de ellas. La primera parte corresponde a la optimizaci��n del consumo del veh��culo en funci��n de las condiciones de tr��fico. Esta optimizaci��n calcula un perfil de velocidad promedio que evita, cuando es posible, las retenciones de tr��fico. El tiempo de viaje perdido durante una retenci��n de tr��fico debe recuperarse a trav��s de un aumento posterior de la velocidad promedio que incrementar��a el consumo del veh��culo. La segunda parte de la optimizaci��n es la encargada del c��lculo de la velocidad ��ptima en funci��n de la orograf��a y del tiempo de viaje disponible. Dado que el consumo de combustible del veh��culo se incrementa cuando disminuye el tiempo disponible para finalizar un recorrido, esta optimizaci��n utiliza factores de ponderaci��n para modular la influencia que tiene cada una de estas dos variables en el proceso de minimizaci��n. Aunque los factores de ponderaci��n y la orograf��a de la carretera condicionan el nivel de ahorro de la optimizaci��n, los perfiles de velocidad ��ptima calculados logran ahorros de consumo respecto de un perfil de velocidad constante que obtiene el mismo tiempo de recorrido. Las simulaciones indican que el ahorro de combustible del veh��culo convencional puede lograr hasta un 8.9% mientras que el ahorro de energ��a el��ctrica del veh��culo h��brido serie un 2.8%. El algoritmo fusiona la optimizaci��n en funci��n de las condiciones del tr��fico y la optimizaci��n en funci��n de la orograf��a durante el c��lculo en tiempo real del perfil ��ptimo de velocidad. La optimizaci��n conjunta se logra cuando el perfil de velocidad promedio resultante de la optimizaci��n en funci��n de las condiciones de tr��fico define los valores de los factores de ponderaci��n de la optimizaci��n en funci��n de la orograf��a. Aunque el nivel de ahorro de la optimizaci��n conjunta depende de las condiciones de tr��fico, de la orograf��a, del tiempo de recorrido y de las caracter��sticas propias del veh��culo, las simulaciones indican ahorros de consumo superiores al 6% en ambas clases de veh��culo respecto a optimizaciones que no logran evitar retenciones de tr��fico en la carretera. ABSTRACT Fuel consumption of cars is a feature that is continuously being improved due to the fuel price and an increasing environmental awareness. This doctoral dissertation describes an optimization algorithm to decrease the fuel consumption taking into account the technical specifications of the vehicle, the terrain profile of the road and the traffic conditions of the trip. The algorithm calculates the optimal speed profile that completes a trip having a specified travel time. This calculation considers the road slope and the expected traffic conditions during the trip. The optimization algorithm is also able to react to changing traffic conditions and tunes the optimal speed profile to reach the destination within the specified arrival time. The optimization is applied on a conventional vehicle and also on a Series Hybrid Electric vehicle (SHEV). The fuel consumption optimization algorithm uses data obtained from quasi-static simulations. The algorithm is based on Dynamic Programming and divides the fuel consumption optimization problem into two parts. The first part of the optimization process reduces the fuel consumption according to foreseeable traffic conditions. It calculates an average speed profile that tries to avoid, if possible, the traffic jams on the road. Traffic jams that delay drivers result in higher vehicle speed to make up for lost time. A higher speed of the vehicle within an already defined time scheme increases fuel consumption. The second part of the optimization process is in charge of calculating the optimal speed profile according to the road slope and the remaining travel time. The optimization tunes the fuel consumption and travel time relevancies by using two penalty factors. Although the optimization results depend on the road slope and the travel time, the optimal speed profile produces improvements of 8.9% on the fuel consumption of the conventional car and of 2.8% on the spent energy of the hybrid vehicle when compared with a constant speed profile. The two parts of the optimization process are combined during the Real-Time execution of the algorithm. The average speed profile calculated by the optimization according to the traffic conditions provides values for the two penalty factors utilized by the second part of the optimization process. Although the savings depend on the road slope, traffic conditions, vehicle features, and the remaining travel time, simulations show that this joint optimization process can improve the energy consumption of the two vehicles types by more than 6%.

Two-dimensional isostatic meshes in the finite element method

In a Finite Element (FE) analysis of elastic solids several items are usually considered, namely, type and shape of the elements, number of nodes per element, node positions, FE mesh, total number of degrees of freedom (dot) among others. In this paper a method to improve a given FE mesh used for a particular analysis is described. For the improvement criterion different objective functions have been chosen (Total potential energy and Average quadratic error) and the number of nodes and dof's of the new mesh remain constant and equal to the initial FE mesh. In order to find the mesh producing the minimum of the selected objective function the steepest descent gradient technique has been applied as optimization algorithm. However this efficient technique has the drawback that demands a large computation power. Extensive application of this methodology to different 2-D elasticity problems leads to the conclusion that isometric isostatic meshes (ii-meshes) produce better results than the standard reasonably initial regular meshes used in practice. This conclusion seems to be independent on the objective function used for comparison. These ii-meshes are obtained by placing FE nodes along the isostatic lines, i.e. curves tangent at each point to the principal direction lines of the elastic problem to be solved and they should be regularly spaced in order to build regular elements. That means ii-meshes are usually obtained by iteration, i.e. with the initial FE mesh the elastic analysis is carried out. By using the obtained results of this analysis the net of isostatic lines can be drawn and in a first trial an ii-mesh can be built. This first ii-mesh can be improved, if it necessary, by analyzing again the problem and generate after the FE analysis the new and improved ii-mesh. Typically, after two first tentative ii-meshes it is sufficient to produce good FE results from the elastic analysis. Several example of this procedure are presented.

Debonding detection of FRP strengthened concrete beams by using impedance measurements and an ensemble PSO adaptive spectral model

An impedance-based midspan debonding identification method for RC beams strengthened with FRP strips is presented in this paper using piezoelectric ceramic (PZT) sensor?actuators. To reach this purpose, firstly, a two-dimensional electromechanical impedance model is proposed to predict the electrical admittance of the PZT transducer bonded to the FRP strips of an RC beam. Considering the impedance is measured in high frequencies, a spectral element model of the bonded-PZT?FRP strengthened beam is developed. This model, in conjunction with experimental measurements of PZT transducers, is used to present an updating methodology to quantitatively detect interfacial debonding of these kinds of structures. To improve the performance and accuracy of the detection algorithm in a challenging problem such as ours, the structural health monitoring approach is solved with an ensemble process based on particle of swarm. An adaptive mesh scheme has also been developed to increase the reliability in locating the area in which debonding initiates. Predictions carried out with experimental results have showed the effectiveness and potential of the proposed method to detect prematurely at its earliest stages a critical failure mode such as that due to midspan debonding of the FRP strip.

Self-organizing Routing Algorithm fo Wireless Sensors Networks (WSN) using Ant Colony Optimization (ACO) with Tinyos.

This paper describes the basic tools to work with wireless sensors. TinyOShas a componentbased architecture which enables rapid innovation and implementation while minimizing code size as required by the severe memory constraints inherent in sensor networks. TinyOS's component library includes network protocols, distributed services, sensor drivers, and data acquisition tools ? all of which can be used asia or be further refined for a custom application. TinyOS was originally developed as a research project at the University of California Berkeley, but has since grown to have an international community of developers and users. Some algorithms concerning packet routing are shown. Incar entertainment systems can be based on wireless sensors in order to obtain information from Internet, but routing protocols must be implemented in order to avoid bottleneck problems. Ant Colony algorithms are really useful in such cases, therefore they can be embedded into the sensors to perform such routing task.