On-line MRI sequences for the evaluation of apple internal quality.

On-line dynamic MRI, which is oriented to industrial grading lines, requires high-speed sequences with motion correction artefacts. In this study two different types of motion correction sequences have been used and have been implemented in real-time (FLASH and UFLARE). They are based on T2* and T2 respectively and their selection depends on the expected contrast effect of the disorder: while watercore enhances bright areas due to higher fluid mobility, internal breakdown potentiates low signal due to texture degradation. For watercore study, five different apple cultivars were used (Normanda-18-, Fuji-35-, Helada-36-, Verde Doncella-54-, Esperiega-75-) along two seasons (2011 and 2012). In total 218 fruits were measured under both, static conditions (20 slices per fruit) and under dynamic conditions (3 repetitions without slice selection). For internal breakdown, Braeburn cultivar has been studied (in total 106 fruits) under both static (20 slices per fruit) and dynamic conditions (3 replicates with slice selection). Metrological aspects such as repeatability of dynamic images and subsequent histogram feature stability become of major interest for further industrial application. Segregation ability among varying degrees of disorder is also analyzed.

Effects of traffic loads on reinforced concrete railroad culverts

In the context of the present conference paper culverts are defined as an opening or conduit passing through an embankment usually for the purpose of conveying water or providing safe pedestrian and animal crossings under rail infrastructure. The clear opening of culverts may reach values of up to 12m however, values around 3m are encountered much more frequently. Depending on the topography, the number of culverts is about 10 times that of bridges. In spite of this, their dynamic behavior has received far less attention than that of bridges. The fundamental frequency of culverts is considerably higher than that of bridges even in the case of short span bridges. As the operational speed of modern high-speed passenger rail systems rises, higher frequencies are excited and thus more energy is encountered in frequency bands where the fundamental frequency of box culverts is located. Many research efforts have been spent on the subject of ballast instability due to bridge resonance, since it was first observed when high-speed trains were introduced to the Paris/Lyon rail line. To prevent this phenomenon from occurring, design codes establish a limit value for the vertical deck acceleration. Obviously one needs some sort of numerical model in order to estimate this acceleration level and at that point things get quite complicated. Not only acceleration but also displacement values are of interest e.g. to estimate the impact factor. According to design manuals the structural design should consider the depth of cover, trench width and condition, bedding type, backfill material, and compaction. The same applies to the numerical model however, the question is: What type of model is appropriate for this job? A 3D model including the embankment and an important part of the soil underneath the culvert is computationally very expensive and hard to justify taking into account the associated costs. Consequently, there is a clear need for simplified models and design rules in order to achieve reasonable costs. This paper will describe the results obtained from a 2D finite element model which has been calibrated by means of a 3D model and experimental data obtained at culverts that belong to the high-speed railway line that links the two towns of Segovia and Valladolid in Spain

High isolation series-shunt photoconductive microwave switch

This article presents a wide band compact high isolation photoconductive switch, which is based on the series-shunt switch design with three photoconductive switches made of diced high-resistivity silicon wafer placed over a microstrip gap and activated by 808-nm near-infrared laser diodes. The switch shows an insertion loss of 1.2 dB and an isolation of 44.8 dB at 2 GHz. It is easy to operate and control by light, high-speed, electromagnetically transparent and it does not require any biasing circuits.

Caracterización de un robot para aplicaciones de mecanizado con requerimientos de tolerancias

El presente Trabajo fin Fin de Máster, versa sobre una caracterización preliminar del comportamiento de un robot de tipo industrial, configurado por 4 eslabones y 4 grados de libertad, y sometido a fuerzas de mecanizado en su extremo. El entorno de trabajo planteado es el de plantas de fabricación de piezas de aleaciones de aluminio para automoción. Este tipo de componentes parte de un primer proceso de fundición que saca la pieza en bruto. Para series medias y altas, en función de las propiedades mecánicas y plásticas requeridas y los costes de producción, la inyección a alta presión (HPDC) y la fundición a baja presión (LPC) son las dos tecnologías más usadas en esta primera fase. Para inyección a alta presión, las aleaciones de aluminio más empleadas son, en designación simbólica según norma EN 1706 (entre paréntesis su designación numérica); EN AC AlSi9Cu3(Fe) (EN AC 46000) , EN AC AlSi9Cu3(Fe)(Zn) (EN AC 46500), y EN AC AlSi12Cu1(Fe) (EN AC 47100). Para baja presión, EN AC AlSi7Mg0,3 (EN AC 42100). En los 3 primeros casos, los límites de Silicio permitidos pueden superan el 10%. En el cuarto caso, es inferior al 10% por lo que, a los efectos de ser sometidas a mecanizados, las piezas fabricadas en aleaciones con Si superior al 10%, se puede considerar que son equivalentes, diferenciándolas de la cuarta. Las tolerancias geométricas y dimensionales conseguibles directamente de fundición, recogidas en normas como ISO 8062 o DIN 1688-1, establecen límites para este proceso. Fuera de esos límites, las garantías en conseguir producciones con los objetivos de ppms aceptados en la actualidad por el mercado, obligan a ir a fases posteriores de mecanizado. Aquellas geometrías que, funcionalmente, necesitan disponer de unas tolerancias geométricas y/o dimensionales definidas acorde a ISO 1101, y no capaces por este proceso inicial de moldeado a presión, deben ser procesadas en una fase posterior en células de mecanizado. En este caso, las tolerancias alcanzables para procesos de arranque de viruta se recogen en normas como ISO 2768. Las células de mecanizado se componen, por lo general, de varios centros de control numérico interrelacionados y comunicados entre sí por robots que manipulan las piezas en proceso de uno a otro. Dichos robots, disponen en su extremo de una pinza utillada para poder coger y soltar las piezas en los útiles de mecanizado, las mesas de intercambio para cambiar la pieza de posición o en utillajes de equipos de medición y prueba, o en cintas de entrada o salida. La repetibilidad es alta, de centésimas incluso, definida según norma ISO 9283. El problema es que, estos rangos de repetibilidad sólo se garantizan si no se hacen esfuerzos o éstos son despreciables (caso de mover piezas). Aunque las inercias de mover piezas a altas velocidades hacen que la trayectoria intermedia tenga poca precisión, al inicio y al final (al coger y dejar pieza, p.e.) se hacen a velocidades relativamente bajas que hacen que el efecto de las fuerzas de inercia sean menores y que permiten garantizar la repetibilidad anteriormente indicada. No ocurre así si se quitara la garra y se intercambia con un cabezal motorizado con una herramienta como broca, mandrino, plato de cuchillas, fresas frontales o tangenciales… Las fuerzas ejercidas de mecanizado generarían unos pares en las uniones tan grandes y tan variables que el control del robot no sería capaz de responder (o no está preparado, en un principio) y generaría una desviación en la trayectoria, realizada a baja velocidad, que desencadenaría en un error de posición (ver norma ISO 5458) no asumible para la funcionalidad deseada. Se podría llegar al caso de que la tolerancia alcanzada por un pretendido proceso más exacto diera una dimensión peor que la que daría el proceso de fundición, en principio con mayor variabilidad dimensional en proceso (y por ende con mayor intervalo de tolerancia garantizable). De hecho, en los CNCs, la precisión es muy elevada, (pudiéndose despreciar en la mayoría de los casos) y no es la responsable de, por ejemplo la tolerancia de posición al taladrar un agujero. Factores como, temperatura de la sala y de la pieza, calidad constructiva de los utillajes y rigidez en el amarre, error en el giro de mesas y de colocación de pieza, si lleva agujeros previos o no, si la herramienta está bien equilibrada y el cono es el adecuado para el tipo de mecanizado… influyen más. Es interesante que, un elemento no específico tan común en una planta industrial, en el entorno anteriormente descrito, como es un robot, el cual no sería necesario añadir por disponer de él ya (y por lo tanto la inversión sería muy pequeña), puede mejorar la cadena de valor disminuyendo el costo de fabricación. Y si se pudiera conjugar que ese robot destinado a tareas de manipulación, en los muchos tiempos de espera que va a disfrutar mientras el CNC arranca viruta, pudiese coger un cabezal y apoyar ese mecanizado; sería doblemente interesante. Por lo tanto, se antoja sugestivo poder conocer su comportamiento e intentar explicar qué sería necesario para llevar esto a cabo, motivo de este trabajo. La arquitectura de robot seleccionada es de tipo SCARA. La búsqueda de un robot cómodo de modelar y de analizar cinemática y dinámicamente, sin limitaciones relevantes en la multifuncionalidad de trabajos solicitados, ha llevado a esta elección, frente a otras arquitecturas como por ejemplo los robots antropomórficos de 6 grados de libertad, muy populares a nivel industrial. Este robot dispone de 3 uniones, de las cuales 2 son de tipo par de revolución (1 grado de libertad cada una) y la tercera es de tipo corredera o par cilíndrico (2 grados de libertad). La primera unión, de tipo par de revolución, sirve para unir el suelo (considerado como eslabón número 1) con el eslabón número 2. La segunda unión, también de ese tipo, une el eslabón número 2 con el eslabón número 3. Estos 2 brazos, pueden describir un movimiento horizontal, en el plano X-Y. El tercer eslabón, está unido al eslabón número 4 por la unión de tipo corredera. El movimiento que puede describir es paralelo al eje Z. El robot es de 4 grados de libertad (4 motores). En relación a los posibles trabajos que puede realizar este tipo de robot, su versatilidad abarca tanto operaciones típicas de manipulación como operaciones de arranque de viruta. Uno de los mecanizados más usuales es el taladrado, por lo cual se elige éste para su modelización y análisis. Dentro del taladrado se elegirá para acotar las fuerzas, taladrado en macizo con broca de diámetro 9 mm. El robot se ha considerado por el momento que tenga comportamiento de sólido rígido, por ser el mayor efecto esperado el de los pares en las uniones. Para modelar el robot se utiliza el método de los sistemas multicuerpos. Dentro de este método existen diversos tipos de formulaciones (p.e. Denavit-Hartenberg). D-H genera una cantidad muy grande de ecuaciones e incógnitas. Esas incógnitas son de difícil comprensión y, para cada posición, hay que detenerse a pensar qué significado tienen. Se ha optado por la formulación de coordenadas naturales. Este sistema utiliza puntos y vectores unitarios para definir la posición de los distintos cuerpos, y permite compartir, cuando es posible y se quiere, para definir los pares cinemáticos y reducir al mismo tiempo el número de variables. Las incógnitas son intuitivas, las ecuaciones de restricción muy sencillas y se reduce considerablemente el número de ecuaciones e incógnitas. Sin embargo, las coordenadas naturales “puras” tienen 2 problemas. El primero, que 2 elementos con un ángulo de 0 o 180 grados, dan lugar a puntos singulares que pueden crear problemas en las ecuaciones de restricción y por lo tanto han de evitarse. El segundo, que tampoco inciden directamente sobre la definición o el origen de los movimientos. Por lo tanto, es muy conveniente complementar esta formulación con ángulos y distancias (coordenadas relativas). Esto da lugar a las coordenadas naturales mixtas, que es la formulación final elegida para este TFM. Las coordenadas naturales mixtas no tienen el problema de los puntos singulares. Y la ventaja más importante reside en su utilidad a la hora de aplicar fuerzas motrices, momentos o evaluar errores. Al incidir sobre la incógnita origen (ángulos o distancias) controla los motores de manera directa. El algoritmo, la simulación y la obtención de resultados se ha programado mediante Matlab. Para realizar el modelo en coordenadas naturales mixtas, es preciso modelar en 2 pasos el robot a estudio. El primer modelo se basa en coordenadas naturales. Para su validación, se plantea una trayectoria definida y se analiza cinemáticamente si el robot satisface el movimiento solicitado, manteniendo su integridad como sistema multicuerpo. Se cuantifican los puntos (en este caso inicial y final) que configuran el robot. Al tratarse de sólidos rígidos, cada eslabón queda definido por sus respectivos puntos inicial y final (que son los más interesantes para la cinemática y la dinámica) y por un vector unitario no colineal a esos 2 puntos. Los vectores unitarios se colocan en los lugares en los que se tenga un eje de rotación o cuando se desee obtener información de un ángulo. No son necesarios vectores unitarios para medir distancias. Tampoco tienen por qué coincidir los grados de libertad con el número de vectores unitarios. Las longitudes de cada eslabón quedan definidas como constantes geométricas. Se establecen las restricciones que definen la naturaleza del robot y las relaciones entre los diferentes elementos y su entorno. La trayectoria se genera por una nube de puntos continua, definidos en coordenadas independientes. Cada conjunto de coordenadas independientes define, en un instante concreto, una posición y postura de robot determinada. Para conocerla, es necesario saber qué coordenadas dependientes hay en ese instante, y se obtienen resolviendo por el método de Newton-Rhapson las ecuaciones de restricción en función de las coordenadas independientes. El motivo de hacerlo así es porque las coordenadas dependientes deben satisfacer las restricciones, cosa que no ocurre con las coordenadas independientes. Cuando la validez del modelo se ha probado (primera validación), se pasa al modelo 2. El modelo número 2, incorpora a las coordenadas naturales del modelo número 1, las coordenadas relativas en forma de ángulos en los pares de revolución (3 ángulos; ϕ1, ϕ 2 y ϕ3) y distancias en los pares prismáticos (1 distancia; s). Estas coordenadas relativas pasan a ser las nuevas coordenadas independientes (sustituyendo a las coordenadas independientes cartesianas del modelo primero, que eran coordenadas naturales). Es necesario revisar si el sistema de vectores unitarios del modelo 1 es suficiente o no. Para este caso concreto, se han necesitado añadir 1 vector unitario adicional con objeto de que los ángulos queden perfectamente determinados con las correspondientes ecuaciones de producto escalar y/o vectorial. Las restricciones habrán de ser incrementadas en, al menos, 4 ecuaciones; una por cada nueva incógnita. La validación del modelo número 2, tiene 2 fases. La primera, al igual que se hizo en el modelo número 1, a través del análisis cinemático del comportamiento con una trayectoria definida. Podrían obtenerse del modelo 2 en este análisis, velocidades y aceleraciones, pero no son necesarios. Tan sólo interesan los movimientos o desplazamientos finitos. Comprobada la coherencia de movimientos (segunda validación), se pasa a analizar cinemáticamente el comportamiento con trayectorias interpoladas. El análisis cinemático con trayectorias interpoladas, trabaja con un número mínimo de 3 puntos máster. En este caso se han elegido 3; punto inicial, punto intermedio y punto final. El número de interpolaciones con el que se actúa es de 50 interpolaciones en cada tramo (cada 2 puntos máster hay un tramo), resultando un total de 100 interpolaciones. El método de interpolación utilizado es el de splines cúbicas con condición de aceleración inicial y final constantes, que genera las coordenadas independientes de los puntos interpolados de cada tramo. Las coordenadas dependientes se obtienen resolviendo las ecuaciones de restricción no lineales con el método de Newton-Rhapson. El método de las splines cúbicas es muy continuo, por lo que si se desea modelar una trayectoria en el que haya al menos 2 movimientos claramente diferenciados, es preciso hacerlo en 2 tramos y unirlos posteriormente. Sería el caso en el que alguno de los motores se desee expresamente que esté parado durante el primer movimiento y otro distinto lo esté durante el segundo movimiento (y así sucesivamente). Obtenido el movimiento, se calculan, también mediante fórmulas de diferenciación numérica, las velocidades y aceleraciones independientes. El proceso es análogo al anteriormente explicado, recordando la condición impuesta de que la aceleración en el instante t= 0 y en instante t= final, se ha tomado como 0. Las velocidades y aceleraciones dependientes se calculan resolviendo las correspondientes derivadas de las ecuaciones de restricción. Se comprueba, de nuevo, en una tercera validación del modelo, la coherencia del movimiento interpolado. La dinámica inversa calcula, para un movimiento definido -conocidas la posición, velocidad y la aceleración en cada instante de tiempo-, y conocidas las fuerzas externas que actúan (por ejemplo el peso); qué fuerzas hay que aplicar en los motores (donde hay control) para que se obtenga el citado movimiento. En la dinámica inversa, cada instante del tiempo es independiente de los demás y tiene una posición, una velocidad y una aceleración y unas fuerzas conocidas. En este caso concreto, se desean aplicar, de momento, sólo las fuerzas debidas al peso, aunque se podrían haber incorporado fuerzas de otra naturaleza si se hubiese deseado. Las posiciones, velocidades y aceleraciones, proceden del cálculo cinemático. El efecto inercial de las fuerzas tenidas en cuenta (el peso) es calculado. Como resultado final del análisis dinámico inverso, se obtienen los pares que han de ejercer los cuatro motores para replicar el movimiento prescrito con las fuerzas que estaban actuando. La cuarta validación del modelo consiste en confirmar que el movimiento obtenido por aplicar los pares obtenidos en la dinámica inversa, coinciden con el obtenido en el análisis cinemático (movimiento teórico). Para ello, es necesario acudir a la dinámica directa. La dinámica directa se encarga de calcular el movimiento del robot, resultante de aplicar unos pares en motores y unas fuerzas en el robot. Por lo tanto, el movimiento real resultante, al no haber cambiado ninguna condición de las obtenidas en la dinámica inversa (pares de motor y fuerzas inerciales debidas al peso de los eslabones) ha de ser el mismo al movimiento teórico. Siendo así, se considera que el robot está listo para trabajar. Si se introduce una fuerza exterior de mecanizado no contemplada en la dinámica inversa y se asigna en los motores los mismos pares resultantes de la resolución del problema dinámico inverso, el movimiento real obtenido no es igual al movimiento teórico. El control de lazo cerrado se basa en ir comparando el movimiento real con el deseado e introducir las correcciones necesarias para minimizar o anular las diferencias. Se aplican ganancias en forma de correcciones en posición y/o velocidad para eliminar esas diferencias. Se evalúa el error de posición como la diferencia, en cada punto, entre el movimiento teórico deseado en el análisis cinemático y el movimiento real obtenido para cada fuerza de mecanizado y una ganancia concreta. Finalmente, se mapea el error de posición obtenido para cada fuerza de mecanizado y las diferentes ganancias previstas, graficando la mejor precisión que puede dar el robot para cada operación que se le requiere, y en qué condiciones. -------------- This Master´s Thesis deals with a preliminary characterization of the behaviour for an industrial robot, configured with 4 elements and 4 degrees of freedoms, and subjected to machining forces at its end. Proposed working conditions are those typical from manufacturing plants with aluminium alloys for automotive industry. This type of components comes from a first casting process that produces rough parts. For medium and high volumes, high pressure die casting (HPDC) and low pressure die casting (LPC) are the most used technologies in this first phase. For high pressure die casting processes, most used aluminium alloys are, in simbolic designation according EN 1706 standard (between brackets, its numerical designation); EN AC AlSi9Cu3(Fe) (EN AC 46000) , EN AC AlSi9Cu3(Fe)(Zn) (EN AC 46500), y EN AC AlSi12Cu1(Fe) (EN AC 47100). For low pressure, EN AC AlSi7Mg0,3 (EN AC 42100). For the 3 first alloys, Si allowed limits can exceed 10% content. Fourth alloy has admisible limits under 10% Si. That means, from the point of view of machining, that components made of alloys with Si content above 10% can be considered as equivalent, and the fourth one must be studied separately. Geometrical and dimensional tolerances directly achievables from casting, gathered in standards such as ISO 8062 or DIN 1688-1, establish a limit for this process. Out from those limits, guarantees to achieve batches with objetive ppms currently accepted by market, force to go to subsequent machining process. Those geometries that functionally require a geometrical and/or dimensional tolerance defined according ISO 1101, not capable with initial moulding process, must be obtained afterwards in a machining phase with machining cells. In this case, tolerances achievables with cutting processes are gathered in standards such as ISO 2768. In general terms, machining cells contain several CNCs that they are interrelated and connected by robots that handle parts in process among them. Those robots have at their end a gripper in order to take/remove parts in machining fixtures, in interchange tables to modify position of part, in measurement and control tooling devices, or in entrance/exit conveyors. Repeatibility for robot is tight, even few hundredths of mm, defined according ISO 9283. Problem is like this; those repeatibilty ranks are only guaranteed when there are no stresses or they are not significant (f.e. due to only movement of parts). Although inertias due to moving parts at a high speed make that intermediate paths have little accuracy, at the beginning and at the end of trajectories (f.e, when picking part or leaving it) movement is made with very slow speeds that make lower the effect of inertias forces and allow to achieve repeatibility before mentioned. It does not happens the same if gripper is removed and it is exchanged by an spindle with a machining tool such as a drilling tool, a pcd boring tool, a face or a tangential milling cutter… Forces due to machining would create such big and variable torques in joints that control from the robot would not be able to react (or it is not prepared in principle) and would produce a deviation in working trajectory, made at a low speed, that would trigger a position error (see ISO 5458 standard) not assumable for requested function. Then it could be possible that tolerance achieved by a more exact expected process would turn out into a worst dimension than the one that could be achieved with casting process, in principle with a larger dimensional variability in process (and hence with a larger tolerance range reachable). As a matter of fact, accuracy is very tight in CNC, (its influence can be ignored in most cases) and it is not the responsible of, for example position tolerance when drilling a hole. Factors as, room and part temperature, manufacturing quality of machining fixtures, stiffness at clamping system, rotating error in 4th axis and part positioning error, if there are previous holes, if machining tool is properly balanced, if shank is suitable for that machining type… have more influence. It is interesting to know that, a non specific element as common, at a manufacturing plant in the enviroment above described, as a robot (not needed to be added, therefore with an additional minimum investment), can improve value chain decreasing manufacturing costs. And when it would be possible to combine that the robot dedicated to handling works could support CNCs´ works in its many waiting time while CNCs cut, and could take an spindle and help to cut; it would be double interesting. So according to all this, it would be interesting to be able to know its behaviour and try to explain what would be necessary to make this possible, reason of this work. Selected robot architecture is SCARA type. The search for a robot easy to be modeled and kinematically and dinamically analyzed, without significant limits in the multifunctionality of requested operations, has lead to this choice. Due to that, other very popular architectures in the industry, f.e. 6 DOFs anthropomorphic robots, have been discarded. This robot has 3 joints, 2 of them are revolute joints (1 DOF each one) and the third one is a cylindrical joint (2 DOFs). The first joint, a revolute one, is used to join floor (body 1) with body 2. The second one, a revolute joint too, joins body 2 with body 3. These 2 bodies can move horizontally in X-Y plane. Body 3 is linked to body 4 with a cylindrical joint. Movement that can be made is paralell to Z axis. The robt has 4 degrees of freedom (4 motors). Regarding potential works that this type of robot can make, its versatility covers either typical handling operations or cutting operations. One of the most common machinings is to drill. That is the reason why it has been chosen for the model and analysis. Within drilling, in order to enclose spectrum force, a typical solid drilling with 9 mm diameter. The robot is considered, at the moment, to have a behaviour as rigid body, as biggest expected influence is the one due to torques at joints. In order to modelize robot, it is used multibodies system method. There are under this heading different sorts of formulations (f.e. Denavit-Hartenberg). D-H creates a great amount of equations and unknown quantities. Those unknown quatities are of a difficult understanding and, for each position, one must stop to think about which meaning they have. The choice made is therefore one of formulation in natural coordinates. This system uses points and unit vectors to define position of each different elements, and allow to share, when it is possible and wished, to define kinematic torques and reduce number of variables at the same time. Unknown quantities are intuitive, constrain equations are easy and number of equations and variables are strongly reduced. However, “pure” natural coordinates suffer 2 problems. The first one is that 2 elements with an angle of 0° or 180°, give rise to singular positions that can create problems in constrain equations and therefore they must be avoided. The second problem is that they do not work directly over the definition or the origin of movements. Given that, it is highly recommended to complement this formulation with angles and distances (relative coordinates). This leads to mixed natural coordinates, and they are the final formulation chosen for this MTh. Mixed natural coordinates have not the problem of singular positions. And the most important advantage lies in their usefulness when applying driving forces, torques or evaluating errors. As they influence directly over origin variable (angles or distances), they control motors directly. The algorithm, simulation and obtaining of results has been programmed with Matlab. To design the model in mixed natural coordinates, it is necessary to model the robot to be studied in 2 steps. The first model is based in natural coordinates. To validate it, it is raised a defined trajectory and it is kinematically analyzed if robot fulfils requested movement, keeping its integrity as multibody system. The points (in this case starting and ending points) that configure the robot are quantified. As the elements are considered as rigid bodies, each of them is defined by its respectively starting and ending point (those points are the most interesting ones from the point of view of kinematics and dynamics) and by a non-colinear unit vector to those points. Unit vectors are placed where there is a rotating axis or when it is needed information of an angle. Unit vectors are not needed to measure distances. Neither DOFs must coincide with the number of unit vectors. Lengths of each arm are defined as geometrical constants. The constrains that define the nature of the robot and relationships among different elements and its enviroment are set. Path is generated by a cloud of continuous points, defined in independent coordinates. Each group of independent coordinates define, in an specific instant, a defined position and posture for the robot. In order to know it, it is needed to know which dependent coordinates there are in that instant, and they are obtained solving the constraint equations with Newton-Rhapson method according to independent coordinates. The reason to make it like this is because dependent coordinates must meet constraints, and this is not the case with independent coordinates. When suitability of model is checked (first approval), it is given next step to model 2. Model 2 adds to natural coordinates from model 1, the relative coordinates in the shape of angles in revoluting torques (3 angles; ϕ1, ϕ 2 and ϕ3) and distances in prismatic torques (1 distance; s). These relative coordinates become the new independent coordinates (replacing to cartesian independent coordinates from model 1, that they were natural coordinates). It is needed to review if unit vector system from model 1 is enough or not . For this specific case, it was necessary to add 1 additional unit vector to define perfectly angles with their related equations of dot and/or cross product. Constrains must be increased in, at least, 4 equations; one per each new variable. The approval of model 2 has two phases. The first one, same as made with model 1, through kinematic analysis of behaviour with a defined path. During this analysis, it could be obtained from model 2, velocities and accelerations, but they are not needed. They are only interesting movements and finite displacements. Once that the consistence of movements has been checked (second approval), it comes when the behaviour with interpolated trajectories must be kinematically analyzed. Kinematic analysis with interpolated trajectories work with a minimum number of 3 master points. In this case, 3 points have been chosen; starting point, middle point and ending point. The number of interpolations has been of 50 ones in each strecht (each 2 master points there is an strecht), turning into a total of 100 interpolations. The interpolation method used is the cubic splines one with condition of constant acceleration both at the starting and at the ending point. This method creates the independent coordinates of interpolated points of each strecht. The dependent coordinates are achieved solving the non-linear constrain equations with Newton-Rhapson method. The method of cubic splines is very continuous, therefore when it is needed to design a trajectory in which there are at least 2 movements clearly differents, it is required to make it in 2 steps and join them later. That would be the case when any of the motors would keep stopped during the first movement, and another different motor would remain stopped during the second movement (and so on). Once that movement is obtained, they are calculated, also with numerical differenciation formulas, the independent velocities and accelerations. This process is analogous to the one before explained, reminding condition that acceleration when t=0 and t=end are 0. Dependent velocities and accelerations are calculated solving related derivatives of constrain equations. In a third approval of the model it is checked, again, consistence of interpolated movement. Inverse dynamics calculates, for a defined movement –knowing position, velocity and acceleration in each instant of time-, and knowing external forces that act (f.e. weights); which forces must be applied in motors (where there is control) in order to obtain requested movement. In inverse dynamics, each instant of time is independent of the others and it has a position, a velocity, an acceleration and known forces. In this specific case, it is intended to apply, at the moment, only forces due to the weight, though forces of another nature could have been added if it would have been preferred. The positions, velocities and accelerations, come from kinematic calculation. The inertial effect of forces taken into account (weight) is calculated. As final result of the inverse dynamic analysis, the are obtained torques that the 4 motors must apply to repeat requested movement with the forces that were acting. The fourth approval of the model consists on confirming that the achieved movement due to the use of the torques obtained in the inverse dynamics, are in accordance with movements from kinematic analysis (theoretical movement). For this, it is necessary to work with direct dynamics. Direct dynamic is in charge of calculating the movements of robot that results from applying torques at motors and forces at the robot. Therefore, the resultant real movement, as there was no change in any condition of the ones obtained at the inverse dynamics (motor torques and inertial forces due to weight of elements) must be the same than theoretical movement. When these results are achieved, it is considered that robot is ready to work. When a machining external force is introduced and it was not taken into account before during the inverse dynamics, and torques at motors considered are the ones of the inverse dynamics, the real movement obtained is not the same than the theoretical movement. Closed loop control is based on comparing real movement with expected movement and introducing required corrrections to minimize or cancel differences. They are applied gains in the way of corrections for position and/or tolerance to remove those differences. Position error is evaluated as the difference, in each point, between theoretical movemment (calculated in the kinematic analysis) and the real movement achieved for each machining force and for an specific gain. Finally, the position error obtained for each machining force and gains are mapped, giving a chart with the best accuracy that the robot can give for each operation that has been requested and which conditions must be provided.

Nuevo "sistema de desexcitación rápida para máquinas síncronas con excitación brushless" (HSBDS) en un generador de 15 MVA

Las máquinas síncronas con excitación indirecta sin escobillas (tipo brushless) presentan el problema de que no es posible acceder al devanado de campo para desexcitar la máquina. Esto provoca que, a pesar de la operación correcta del sistema de protecciones, la lenta constante de tiempo de desexcitación pueda producir graves daños en el caso de un cortocircuito interno. En este documento se presentan las pruebas de un novedoso sistema de desexcitación rápida para este tipo de máquinas en un generador de 15 MVA. La desexcitación se consigue introduciendo una resistencia en el circuito de campo, obteniendo una respuesta dinámica similar a la que se consigue en las máquinas con excitación estática. La principal aportación de este estudio es la adaptación del método a máquinas de tamaño industrial y las diversas pruebas realizadas en un generador de 15 MVA validando el correcto funcionamiento de este sistema. Synchronous machines with brushless excitation have the disadvantage that the field winding is no accessible for the de-excitation. This means that, despite the proper operation of the protection system, the slow de-excitation time constant may produce severe damage in the event of an internal short circuit. In this paper the test in a 15 MVA generator of a novel high-speed de-excitation system for brushless synchronous machines is presented. The de-excitation is achieved by inserting a resistance in the field circuit, obtaining a dynamic response similar to that archived in machines with static excitation. The main novelty of this paper is the use of this method in a industrial size machine. This system has been validated through experimental tests on a 15 MVA generator, with satisfactory results.

Análisis de registros de aceleraciones verticales en caja de grasa y correlación con la infraestructura

El sector ferroviario ha experimentado en los últimos años un empuje espectacular acaparando las mayores inversiones en construcción de nuevas líneas de alta velocidad. Junto a esta inversión inicial no se debe perder de vista el coste de mantenimiento y gestión de las mismas y para ello es necesario avanzar en el conocimiento de los fenómenos de interacción de la vía y el material móvil. En los nuevos trazados ferroviarios, que hacen del ferrocarril un modo de transporte competitivo, se produce un notable aumento en la velocidad directamente relacionado con la disminución de los tiempos de viaje, provocando por ello elevados esfuerzos dinámicos, lo que exige una elevada calidad de vía para evitar el rápido deterioro de la infraestructura. Resulta primordial controlar y minimizar los costes de mantenimiento que vienen generados por las operaciones de conservación de los parámetros de calidad y seguridad de la vía férrea. Para reducir las cargas dinámicas que actúan sobre la vía deteriorando el estado de la misma, debido a este aumento progresivo de las velocidades, es necesario reducir la rigidez vertical de la vía, pero igualmente este aumento de velocidades hace necesarias elevadas resistecias del emparrillado de vía y mejoras en las plataformas, por lo que es necesario buscar este punto de equilibrio en la elasticidad de la vía y sus componentes. Se analizan las aceleraciones verticales medidas en caja de grasa, identificando la rigidez vertical de la vía a partir de las frecuencias de vibración vertical de las masas no suspendidas, correlacionándola con la infraestructura. Estas aceleraciones verticales se desprenden de dos campañas de medidas llevadas a cabo en la zona de estudio. En estas campañas se colocaron varios acelerómetros en caja de grasa obteniendo un registro de aceleraciones verticales a partir de las cuales se ha obteniendo la variación de la rigidez de vía de unas zonas a otras. Se analiza la rigidez de la vía correlacionándola con las distintas tipologías de vía y viendo la variación del valor de la rigidez a lo largo del trazado ferroviario. Estos cambios se manifiestan cuando se producen cambios en la infraestructura, de obras de tierra a obras de fábrica, ya sean viaductos o túneles. El objeto principal de este trabajo es profundizar en estos cambios de rigidez vertical que se producen, analizando su origen y las causas que los provocan, modelizando el comportamiento de los mismos, para desarrollar metodologías de análisis en cuanto al diseño de la infraestructura. Igualmente se analizan los elementos integrantes de la misma, ahondando en las características intrínsecas de la rigidez vertical global y la rigidez de cada uno de los elementos constituyentes de la sección tipo ferroviaria, en cada una de las secciones características del tramo en estudio. Se determina en este trabajo si se produce y en qué medida, variación longitudinal de la rigidez de vía en el tramo estudiado, en cada una de las secciones características de obra de tierra y obra de fábrica seleccionadas analizando las tendencias de estos cambios y su homogeneidad a lo largo del trazado. Se establece así una nueva metodología para la determinación de la rigidez vertical de la vía a partir de las mediciones de aceleraciones verticales en caja de grasa así como el desarrollo de una aplicación en el entorno de Labview para el análisis de los registros obtenidos. During the last years the railway sector has experienced a spectacular growth, focusing investments in the construction of new high-speed lines. Apart from the first investment the cost of maintaining and managing them has to be considered and this requires more knowledge of the process of interaction between track and rolling stock vehicles. In the new high-speed lines, that make of the railway a competitive mode of transport, there is a significant increase in speed directly related to the shorten in travel time, and that produces high dynamic forces. So, this requires a high quality of the track to avoid quickly deterioration of infrastructure. It is essential to control and minimize maintenance costs generated by maintenance operations to keep the quality and safety parameters of the railway track. Due to this gradual increase of speed, and to reduce the dynamic loads acting on the railway track causing its deterioration, it is necessary to reduce the vertical stiffness of the track, but on the other hand this speed increase requires high resistance of the railway track and improvements of the railway platform, so we must find the balance between the elasticity of the track and its components. Vertical accelerations in axle box are measured and analyzed, identifying the vertical stiffness of the railway track obtained from the vertical vibration frequency of the unsprung masses, correlating with the infrastructure. These vertical accelerations are the result of two measurement campaigns carried out in the study area with the placement of several accelerometers located in the axle box. From these vertical accelerations the variation of the vertical stiffness from one area to another is obtained. The track stiffness is analysed relating with the different types of infrastructure and the change in the value of the stiffness along the railway line. These changes are revealed when changes in infrastructure occurs, for instance; earthworks to bridges or tunnels. The main purpose of this paper is to examine these vertical stiffness changes, analysing its origins and causes, modelling their behaviour, developing analytical methodologies for the design of infrastructure. In this thesis it is also reviewed the different elements of the superstructure, paying special attention to the vertical stiffness of each one. In this study is determined, if it happens and to what extent, the longitudinal variation in the stiffness of track along the railway line studied in every selected section; earthwork, bridges and tunnels. They are also analyzed trends of these changes and homogeneity along the path. This establishes a new method for determining the vertical stiffness of the railway track from the vertical accelerations measured on axle box as well as an application developed in LabView to analyze the recordings obtained.

Numerical Simulation of the Aerodynamic Behavior of High Velocity Trains under Synthetic Crosswinds of Different Shear and Turbulence Characteristics

A numerical simulation of the aerodynamic behavior of high-speed trains under synthetic crosswinds at a 90º yaw angle is presented. The train geometry is the aerodynamic train model (ATM). Flow description based on numerical simulations is obtained using large eddy simulation (LES) and the commercial code ANSYSFluent V14.5. A crosswind whose averaged velocity and turbulence characteristics change with distance to the ground is imposed. Turbulent fluctuations that vary temporally and spatially are simulated with TurbSim code. The crosswind boundary condition is calculated for the distance the train runs during a simulation period. The inlet streamwise velocity boundary condition is generated using Taylor?s frozen turbulence hypothesis. The model gives a time history of the force and moments acting on the train; this includes averaged values, standard deviations and extreme values. Of particular interest are the spectra of the forces and moments, and the admittance spectra. For comparison, results obtained with LES and a uniform wind velocity fluctuating in time, and results obtained with Reynolds averaged Navier Stokes equations (RANS), and the averaged wind conditions, are also presented.

Estudio de la respuesta dinámica transversal de viaductos altos de líneas de ferrocarril de alta velocidad bajo la acción de cargas de uso

Es conocido que las dimensiones de los puentes de ferrocarril han ido cambiando debido a las estrictas condiciones de trazado impuestas en las líneas de alta velocidad. Además, la creciente preocupación de la sociedad por cuidar y proteger el medio ambiente, reflejado en la correspondiente normativa, ha generado nuevos condicionantes en el diseño de estas infraestructuras. En concreto, se ha limitado el movimiento de grandes volúmenes de terreno particularmente en los espacios protegidos. Por estas razones, hoy en día se proyectan y construyen puentes de ferrocarril más altos y más largos en todo el mundo. En España se han construido varios viaductos de pilas altas para líneas de alta velocidad. Ejemplos de estas infraestructuras son el Viaducto O’Eixo y el Viaducto de Barbantiño, situados en la línea de alta velocidad Madrid-Galicia, Estos viaductos altos se caracterizan por tener una mayor flexibilidad lateral y una frecuencia fundamental de oscilación baja, de hasta 0.2 Hz. La respuesta dinámica de este tipo de estructura puede aumentar como consecuencia de la aproximación entre la frecuencias propias de la misma y las de excitación debidas al paso del tren y a la acción del viento. Por lo tanto, estas estructuras pueden presentar problemas a la hora de cumplir con las limitaciones impuestas en las normas de diseño de puentes de ferrocarril, y otras, para garantizar la seguridad del tráfico y el confort de los viajeros. La respuesta dinámica lateral de viaductos de pilas altas no ha sido suficientemente estudiada en la literatura científica. Se pueden intuir varios de los motivos para explicar esta carencia. El primero es la relativamente reciente aparición de este tipo de viaductos asociados al desarrollo de la alta velocidad. Por otro lado, se hace necesario, para estudiar este tema, construir nuevos modelos numéricos adecuados para el estudio de la interacción dinámica lateral del puente y del tren. La interacción entre el puente y un tren viajando sobre él es un problema dinámico no lineal, dependiente del tiempo y de acoplamiento entre los dos subsistemas que intervienen (vehículo y puente). Los dos subsistemas, que pueden ser modelados como estructuras elásticas, interaccionan el uno con el otro a través de las fuerzas de contacto, que tiene una marcada naturaleza no lineal por el rozamiento entre rueda y carril, y por la geometría de los perfiles de estos dos elementos en contacto. En esta tesis, se desarrolla la formulación completa de un modelo no lineal de interacción tren-vía-puente-viento que reproduce adecuadamente las fuerzas laterales de contacto rueda-carril, fuerzas que van a tener una gran influencia en los índices de seguridad del tráfico. Este modelo se ha validado a partir de casos resueltos en la literatura científica, y de medidas experimentales tomadas en eventos dinámicos ocurridos en los viaductos de Arroyo de Valle y Arroyo de las Piedras. Puentes altos que han estado monitorizados en servicio durante dos años. En los estudios realizados en este trabajo, se cuantifican, empleando el modelo construido, los niveles de seguridad del tráfico y de confort de los pasajeros de trenes ligeros de alta velocidad, como el tren articulado AVE S-100, que viajan sobre viaductos altos sometidos, o no, a fuertes vientos laterales racheados. Finalmente, se ha obtenido el grado de mejora de la seguridad del tráfico y del confort de los viajeros, cuando se emplean pantallas anti-viento en el tablero y amortiguadores de masa sintonizados en la cabeza de las pilas de un viaducto alto. Resultando, el uso simultaneo de estos dos dispositivos (pantallas y amortiguadores de masa), en puentes altos de líneas de alta velocidad, una opción a considerar en la construcción de estas estructuras para elevar significativamente el nivel de servicio de las mismas. It is known that dimensions of railway bridges have been changing due to the strict high-speed lines layout parameters. Moreover, the growing concern of society to take care of and protect the environment, reflected in the corresponding regulations, has created new environment requirements for the design of these infrastructures. Particularly, the mentioned regulations do not allow designers to move far from terrain to build these railway lines. Due to all these reasons, longer and higher railway bridges are being designed and built around the world. In Spain, several high pier railway viaducts have been built for high speed lines. Barbantiño Viaduct and Eixo Viaduct, belonging to the Madrid-Galicia high speed line, are examples of this kind of structures. These high viaducts have great lateral flexibility and a low fundamental vibration frequency of down to 0.2 Hz. The dynamic response of high speed railway bridges may increase because of the approximation between the natural viaduct frequencies and the excitation ones due to the train travel and the wind action. Therefore, this bridge response could not satisfy the serviceability limits states, for traffic safety and for passenger comfort, considered by the design standards of high speed bridges. It is difficult to find papers in the scientific literature about the lateral response of high-speed trains travel over long viaducts with high piers. Several reasons could explain this issue. On one hand, the construction of this kind of viaduct is relatively recent and it is associated to the development of the high speed railway. On the other hand, in order to study the dynamic lateral interaction between the train and the high bridge, it is necessary to build new numerical and complex models. The interaction between the bridge-track subsystem and the vehicle subsystem travelling over the bridge is a coupling, nonlinear and time dependent problem. Both subsystems, train and bridge, which can be modelled as elastic structures, interact each other through the contact forces. These forces have a strong nonlinear nature due to the friction and the geometry of rail and wheel profiles. In this thesis, the full formulation of a train-track-bridge-wind nonlinear interaction model is developed. This model can reproduce properly the lateral contact wheel-rail forces, which have a great influence on traffic safety indices. The validation of the model built has been reached through interaction solved cases found in the scientific literature and experimental measures taken in dynamic events which happened at Arroyo de las Piedras and Arroyo del Valle Viaducts. These high bridges have been controlled during two years of service by means of structural health monitoring. In the studies carried out for this thesis, the levels of traffic safety and passenger comfort are quantified using the interaction model built, in the cases of high speed and light trains, as AVE S-100, travelling over high pier bridges and with or without lateral turbulent winds acting. Finally, the improvement rate of the traffic safety and passenger comfort has been obtained, when wind barriers are used at the bridge deck and tuned mass dampers are installed at the pier heads of a high viaduct. The installation of both devices, wind barriers and tuned mass damper, at the same time, turned out to be a good option to be considered in the design of high pier railway viaducts, to improve significantly the serviceability level of this kind of structures.

Análisis y optimización de la resistencia de interferencia en multicascos

Esta tesis presenta un estudio de la resistencia de interferencia en multicascos, término que engloba las variaciones en la resistencia al avance debidas a la interacción entre cascos. Su característica más notable es que puede ser tanto positiva como negativa, contribuyendo favorablemente en este último caso a la reducción de la resistencia total. Su análisis permanece como un área activa dentro de la comunidad hidrodinámica, si bien se ha detectado una significativa falta de información experimental sobre el flujo entre cascos. En primer lugar se incluye una caracterización de los fenómenos de interferencia, evaluando su impacto en las diferentes componentes de la resistencia al avance. Al igual que la resistencia total, su predicción requiere el uso de técnicas experimentales o numéricas al ser inviable su solución analítica. Ambos procedimientos han sido considerados en esta tesis. El análisis experimental de la resistencia de interferencia supone el núcleo central del trabajo realizado. Se han ensayado dos geometrías diferentes, un catamarán de servicio comercial PESBO junto con un catamarán compuesto por dos Serie 60 (S60) en paralelo. Los ensayos se han llevado a cabo en dos canales de experiencias, CEHINAV y CEHIPAR, midiéndose resistencia al avance, asiento y trimados dinámicos, y cortes de olas en la zona entre cascos. Mención especial a estos últimos, dado que a pesar de ser en la zona central donde ocurren los principales efectos de interferencia, no se encontró información previa publicada en la literatura. Su medición requirió la fabricación de un sistema de soporte especifico para las probetas de medición. Por otro lado, aunque el Serie 60 es una geometría bien conocida en la comunidad hidrodinámica, a conocimiento del autor su comportamiento como multicasco no había sido aun caracterizado experimentalmente. Los bastidores de unión se fabricaron de forma que permitieran variar la separación entre cascos. Además, los multicascos son en general embarcaciones de alta velocidad mostrando asientos y trimados dinámicos significativos. Para cuantificar su efecto en la resistencia total y de interferencia se construyo un sistema de fijación del modelo al carro que los restringiera, posibilitando comparar los resultados en esta condición con los del modelo libre. Como resultado, se han obtenido resultados experimentales de las dos geometrías estudiadas con múltiples separaciones, incluyendo un solo casco, y con modelo fijo y libre. Una de las principales utilidades de los resultados experimentales es servir como referencia para validar modelos de predicción. Como primera aplicación, los datos experimentales obtenidos con el catamarán S60 se han contrastado con las predicciones numéricas de Yeung et al. (2004). El análisis numérico de la resistencia de interferencia se completa con la realización de simulaciones numéricas utilizando dos códigos substancialmente diferentes: Tdynlin y CD--‐Adapco Star--‐CCM+. Los cortes de olas obtenidos en las simulaciones se comparan con los valores experimentales, mostrándose además los campos de presiones y velocidades calculados sobre el casco. La principal aportación de esta tesis es una extensa caracterización experimental de los fenómenos de interferencia, con la intención de servir de referencia para futuros estudios con multicascos. El análisis de los resultados permite comprender mejor el impacto que la interacción entre cascos, así como las variaciones dinámicas de las condiciones de navegación, tienen en las diferentes componentes de la resistencia. Por otro lado, permite apreciar la dependencia de la resistencia de interferencia con la velocidad y separación entre cascos, de cara a su utilización como parámetro de diseño. ABSTRACT This thesis presents a study of the interference resistance in multihulls, which comprises all the variations in the ship resistance due to the interaction between hulls. Its most remarkable characteristic is that it can be positive or negative, contributing in the second case to the reduction of the total ship resistance. Its study remains an active area in the hydrodynamic community, although there is a significant lack of published experimental data regarding the flow between hulls. First of all, the interference phenomena are characterized, evaluating the impact in the different components of the ship resistance. Similar to the total resistance, their prediction requires experimental or numerical techniques, as no analytic solutions are known. Both procedures have been considered in this thesis. The experimental analysis of the interference resistance is the core of the work done. Two different geometries have been tested, a commercial catamaran PESBO and a catamaran composed by two parallel Series 60 (S60). The tests have been carried out in two towing tanks, CEHINAV and CEHIPAR, measuring ship resistance, dynamic sinkage and trim, and wave cuts in--‐between the hulls. Special mention to the wave cuts, as no previous published information was found regarding this zone, even if it is where the main interference effects happen. Their measurement required building a support tripod for the probes, specifically designed for this experimental campaign. In addition, although the Series 60 is a well known hull for experimental and computational analyses, to the author’s knowledge its behavior as a multihull had not yet been experimentally described. The connection frames between the hulls were built so they allowed adjusting the hull spacing. Furthermore, multihulls are usually high--‐speed vessels, acquiring significant dynamic sinkage and trim. To quantify the effect of these dynamic variations of the interference resistance, a clamping system was developed to fixed the model and compare the results with the free model condition. Thus, experimental results have been obtained for various hull separations with the two geometries analyzed, including a single hull, and with free and fixed model. One of the main applications of experimental results is to serve as a reference to validate prediction models. As a first step, the obtained experimental data with the catamaran S60 have been compared with the numerical predictions of Yeung et al. (2004). The numerical analysis of the interference resistance is completed with the inclusion of numerical simulations using two codes substantially different: Tdynlin and CD--‐Adapco Star--‐CCM+. The wave cuts obtained from the simulations are compared with the experimental ones, showing also the pressure and velocity fields over the hulls. The main contribution of this thesis is an extensive experimental characterization of the interference phenomena, aiming to serve as reference for future studies about multihulls. The analysis of the results provides insights into the impact that the interaction between hulls, as well as the dynamic variations of the sailing conditions, have in the different components of the ship resistance. Moreover, it allows us to observe the dependence of the interference resistance on the velocity and hull spacing, useful towards its use as a design parameter.

Influência da rigidez vertical no comportamento mecânico e dimensionamento da via permanente ferroviária.

A via permanente representa um elemento imprescindível na composição do transporte ferroviário e seu desempenho deve ser adequado, de forma a garantir tanto segurança quanto conforto. Assim, diversos aspectos devem ser analisados ainda na fase de projeto, através de dimensionamentos que confrontem diferentes parâmetros da resposta da via e os limites estabelecidos. Dessa forma, o conhecimento do comportamento mecânico da via, devido aos esforços impostos pela passagem do material rodante, passa a ser essencial no projeto de uma estrutura que garanta os requisitos necessários, sem ser inviável economicamente. Visto que esse comportamento mecânico é muito sensível à rigidez vertical da estrutura, o presente trabalho apresenta análises da influência desse parâmetro na resposta da via e, consequentemente, no seu dimensionamento. Nesse contexto, o trabalho abrange tanto o caso de vias em lastro solicitadas por trens de carga, quanto o caso de vias em laje solicitadas por trens de passageiros em meios urbanos. No primeiro caso são realizados estudos paramétricos, por meio de modelos clássicos e um modelo mecanicista, para a análise de momentos fletores e deflexões nos trilhos, bem como tensões verticais nas camadas de lastro, sub-lastro e subleito. Já no segundo caso, são realizados estudos paramétricos relativos à transmissibilidade e à atenuação de vibrações causadoras de ruído secundário. Também é feita uma análise da influência da rigidez vertical na amplificação dinâmica das cargas estáticas, que pode ser aplicada a ambos os casos citados e até extrapolada para casos de vias de alta velocidade. Os resultados mostraram que aumentos de rigidez vertical resultam em ganhos do ponto de vista de momentos fletores e deflexões nos trilhos, além de maior resistência e capacidade de dissipação de tensões verticais nas camadas de lastro, sub-lastro e subleito. Por outro lado, esses aumentos também levaram a maiores tensões nas camadas subjacentes à grade citadas, além de atenuações de vibrações em menores intervalos de frequência e maiores amplificações dinâmicas das cargas estáticas em vias de alta velocidade. Assim, é mostrado que a influência da rigidez vertical, tanto da via como um todo quanto de alguns elementos específicos, não deve ser analisada de forma genérica, pois, dependendo do parâmetro da resposta da via considerado no dimensionamento, seu aumento pode representar uma influência positiva ou negativa.

On the development of advanced techniques for mixed-elastohydrodynamic lubrification modelling of journal and sliding bearing systems.

The present thesis is focused on the development of a thorough mathematical modelling and computational solution framework aimed at the numerical simulation of journal and sliding bearing systems operating under a wide range of lubrication regimes (mixed, elastohydrodynamic and full film lubrication regimes) and working conditions (static, quasi-static and transient conditions). The fluid flow effects have been considered in terms of the Isothermal Generalized Equation of the Mechanics of the Viscous Thin Films (Reynolds equation), along with the massconserving p-Ø Elrod-Adams cavitation model that accordingly ensures the so-called JFO complementary boundary conditions for fluid film rupture. The variation of the lubricant rheological properties due to the viscous-pressure (Barus and Roelands equations), viscous-shear-thinning (Eyring and Carreau-Yasuda equations) and density-pressure (Dowson-Higginson equation) relationships have also been taken into account in the overall modelling. Generic models have been derived for the aforementioned bearing components in order to enable their applications in general multibody dynamic systems (MDS), and by including the effects of angular misalignments, superficial geometric defects (form/waviness deviations, EHL deformations, etc.) and axial motion. The bearing exibility (conformal EHL) has been incorporated by means of FEM model reduction (or condensation) techniques. The macroscopic in fluence of the mixedlubrication phenomena have been included into the modelling by the stochastic Patir and Cheng average ow model and the Greenwood-Williamson/Greenwood-Tripp formulations for rough contacts. Furthermore, a deterministic mixed-lubrication model with inter-asperity cavitation has also been proposed for full-scale simulations in the microscopic (roughness) level. According to the extensive mathematical modelling background established, three significant contributions have been accomplished. Firstly, a general numerical solution for the Reynolds lubrication equation with the mass-conserving p - Ø cavitation model has been developed based on the hybridtype Element-Based Finite Volume Method (EbFVM). This new solution scheme allows solving lubrication problems with complex geometries to be discretized by unstructured grids. The numerical method was validated in agreement with several example cases from the literature, and further used in numerical experiments to explore its exibility in coping with irregular meshes for reducing the number of nodes required in the solution of textured sliding bearings. Secondly, novel robust partitioned techniques, namely: Fixed Point Gauss-Seidel Method (PGMF), Point Gauss-Seidel Method with Aitken Acceleration (PGMA) and Interface Quasi-Newton Method with Inverse Jacobian from Least-Squares approximation (IQN-ILS), commonly adopted for solving uid-structure interaction problems have been introduced in the context of tribological simulations, particularly for the coupled calculation of dynamic conformal EHL contacts. The performance of such partitioned methods was evaluated according to simulations of dynamically loaded connecting-rod big-end bearings of both heavy-duty and high-speed engines. Finally, the proposed deterministic mixed-lubrication modelling was applied to investigate the in fluence of the cylinder liner wear after a 100h dynamometer engine test on the hydrodynamic pressure generation and friction of Twin-Land Oil Control Rings.

Image processing for safety assessment in Civil Engineering

Behaviour analysis of construction safety systems is of fundamental importance to avoid accidental injuries. Traditionally, measurements of dynamic actions in Civil Engineering have been done through accelerometers, but high-speed cameras and image processing techniques can play an important role in this area. Here, we propose using morphological image filtering and Hough transform on high-speed video sequence as tools for dynamic measurements on that field. The presented method is applied to obtain the trajectory and acceleration of a cylindrical ballast falling from a building and trapped by a thread net. Results show that safety recommendations given in construction codes can be potentially dangerous for workers.

A high-resolution binocular video-oculography system: assessment of pupillary light reflex and detection of an early incomplete blink and an upward eye movement

Background: The pupillary light reflex characterizes the direct and consensual response of the eye to the perceived brightness of a stimulus. It has been used as indicator of both neurological and optic nerve pathologies. As with other eye reflexes, this reflex constitutes an almost instantaneous movement and is linked to activation of the same midbrain area. The latency of the pupillary light reflex is around 200 ms, although the literature also indicates that the fastest eye reflexes last 20 ms. Therefore, a system with sufficiently high spatial and temporal resolutions is required for accurate assessment. In this study, we analyzed the pupillary light reflex to determine whether any small discrepancy exists between the direct and consensual responses, and to ascertain whether any other eye reflex occurs before the pupillary light reflex. Methods: We constructed a binocular video-oculography system two high-speed cameras that simultaneously focused on both eyes. This was then employed to assess the direct and consensual responses of each eye using our own algorithm based on Circular Hough Transform to detect and track the pupil. Time parameters describing the pupillary light reflex were obtained from the radius time-variation. Eight healthy subjects (4 women, 4 men, aged 24–45) participated in this experiment. Results: Our system, which has a resolution of 15 microns and 4 ms, obtained time parameters describing the pupillary light reflex that were similar to those reported in previous studies, with no significant differences between direct and consensual reflexes. Moreover, it revealed an incomplete reflex blink and an upward eye movement at around 100 ms that may correspond to Bell’s phenomenon. Conclusions: Direct and consensual pupillary responses do not any significant temporal differences. The system and method described here could prove useful for further assessment of pupillary and blink reflexes. The resolution obtained revealed the existence reported here of an early incomplete blink and an upward eye movement.

A Cloud-based Framework for Security Analysis of Browser Extensions

In today's internet world, web browsers are an integral part of our day-to-day activities. Therefore, web browser security is a serious concern for all of us. Browsers can be breached in different ways. Because of the over privileged access, extensions are responsible for many security issues. Browser vendors try to keep safe extensions in their official extension galleries. However, their security control measures are not always effective and adequate. The distribution of unsafe extensions through different social engineering techniques is also a very common practice. Therefore, before installation, users should thoroughly analyze the security of browser extensions. Extensions are not only available for desktop browsers, but many mobile browsers, for example, Firefox for Android and UC browser for Android, are also furnished with extension features. Mobile devices have various resource constraints in terms of computational capabilities, power, network bandwidth, etc. Hence, conventional extension security analysis techniques cannot be efficiently used by end users to examine mobile browser extension security issues. To overcome the inadequacies of the existing approaches, we propose CLOUBEX, a CLOUd-based security analysis framework for both desktop and mobile Browser EXtensions. This framework uses a client-server architecture model. In this framework, compute-intensive security analysis tasks are generally executed in a high-speed computing server hosted in a cloud environment. CLOUBEX is also enriched with a number of essential features, such as client-side analysis, requirements-driven analysis, high performance, and dynamic decision making. At present, the Firefox extension ecosystem is most susceptible to different security attacks. Hence, the framework is implemented for the security analysis of the Firefox desktop and Firefox for Android mobile browser extensions. A static taint analysis is used to identify malicious information flows in the Firefox extensions. In CLOUBEX, there are three analysis modes. A dynamic decision making algorithm assists us to select the best option based on some important parameters, such as the processing speed of a client device and network connection speed. Using the best analysis mode, performance and power consumption are improved significantly. In the future, this framework can be leveraged for the security analysis of other desktop and mobile browser extensions, too.

Manufacture of high pressure die-cast radio frequency filter bodies

The manufacture of a radio frequency filter box using high pressure die casting (HPDC) is compared to the traditional high speed machining route. This paper describes an industrial exercise that concluded HPDC to be an economical and appropriate method to produce larger volumes of thin-walled telecommunications components. Modifications to the component design were made to make the component suitable for the HPDC process. Development of the die design through simulation modelling is described. The wrought alloy was replaced by near-eutectic Al-Si die casting alloy that was found to give better temperature stability performance. Apart from the economic benefits, HPDC was found to give lower filter efficiency losses through better surface finish. The effects of HPDC process variables, such as intensification pressure and injection piston velocity, on component quality, particularly porosity levels, were investigated. The pressure was analysed in terms of HPDC machine set pressure and the pressure measured in the die cavity by pressure sensors. Porosity was found to decrease with increased pressure and slightly increase with higher casting velocities.