Dynamic merge of discrete goods flow – Impact on throughput and efficiency

Continuous conveyors with a dynamic merge were developed with adaptable control equipment to differentiate these merges from competing Stop-and-Go merges. With a dynamic merge, the partial flows are manipulated by influencing speeds so that transport units need not stop for the merge. This leads to a more uniform flow of materials, which is qualitatively observable and verifiable in long-term measurements. And although this type of merge is visually mesmerizing, does it lead to advantages from the view of material flow technology? Our study with real data indicates that a dynamic merge shows a 24% increase in performance, but only for symmetric or nearly symmetric flows. This performance advantage decreases as the flows become less symmetric, approaching the throughput of traditional Stop-and-Go merges. And with a cost premium for a continuous merge of approximately 10% due to the additional technical components (belt conveyor, adjustable drive engines, software, etc.), this restricts their economical use.

Flow disturbances in stent-related coronary evaginations: a computational fluid-dynamic simulation study

Aims: Angiographic ectasias and aneurysms in stented segments have been associated with late stent thrombosis. Using optical coherence tomography (OCT), some stented segments show coronary evaginations reminiscent of ectasias. The purpose of this study was to explore, using computational fluid-dynamic (CFD) simulations, whether OCT-detected coronary evaginations can induce local changes in blood flow. Methods and results: OCT-detected evaginations are defined as outward bulges in the luminal vessel contour between struts, with the depth of the bulge exceeding the actual strut thickness. Evaginations can be characterised cross ectionally by depth and along the stented segment by total length. Assuming an ellipsoid shape, we modelled 3-D evaginations with different sizes by varying the depth from 0.2-1.0 mm, and the length from 1-9 mm. For the flow simulation we used average flow velocity data from non-diseased coronary arteries. The change in flow with varying evagination sizes was assessed using a particle tracing test where the particle transit time within the segment with evagination was compared with that of a control vessel. The presence of the evagination caused a delayed particle transit time which increased with the evagination size. The change in flow consisted locally of recirculation within the evagination, as well as flow deceleration due to a larger lumen - seen as a deflection of flow towards the evagination. Conclusions: CFD simulation of 3-D evaginations and blood flow suggests that evaginations affect flow locally, with a flow disturbance that increases with increasing evagination size.

Static and dynamic characteristics of cerebral blood flow during the resting state in schizophrenia

Background: The cerebral network that is active during rest and is deactivated during goal-oriented activity is called the default mode network (DMN). It appears to be involved in self-referential mental activity. Atypical functional connectivity in the DMN has been observed in schizophrenia. One hypothesis suggests that pathologically increased DMN connectivity in schizophrenia is linked with a main symptom of psychosis, namely, misattribution of thoughts. Methods: A resting-state pseudocontinuous arterial spin labeling (ASL) study was conducted to measure absolute cerebral blood flow (CBF) in 34 schizophrenia patients and 27 healthy controls. Using independent component analysis (ICA), the DMN was extracted from ASL data. Mean CBF and DMN connectivity were compared between groups using a 2-sample t test. Results: Schizophrenia patients showed decreased mean CBF in the frontal and temporal regions (P < .001). ICA demonstrated significantly increased DMN connectivity in the precuneus (x/y/z = -16/-64/38) in patients than in controls (P < .001). CBF was not elevated in the respective regions. DMN connectivity in the precuneus was significantly correlated with the Positive and Negative Syndrome Scale scores (P < .01). Conclusions: In schizophrenia patients, the posterior hub-which is considered the strongest part of the DMN-showed increased DMN connectivity. We hypothesize that this increase hinders the deactivation of the DMN and, thus, the translation of cognitive processes from an internal to an external focus. This might explain symptoms related to defective self-monitoring, such as auditory verbal hallucinations or ego disturbances.

Estimation of cooling of lavas from Serocki volcano

A dynamic crystallization study was undertaken to provide a framework for linking the textural variations observed in the Hole 648B lavas with the size and morphology of cooling units inferred from drilling and submersible observation. The textures produced in cooling rate experiments carried out using a Serocki lava (ALV-1690-20) are comparable to the groundmass textural characteristics of lavas from Serocki volcano. The results of the dynamic crystallization study provide a quantitative link between texture, cooling rate, and eruption temperature. The maximum half-width of cooling units estimated from textural characteristics is on the order of 3 m, a value consistent with constraints from drilling and submersible observation. Textural characteristics indicate that the temperature from which cooling began was slightly above the liquidus. The relation between cooling rate and texture are also tested on a drill core sample of basalt of similar composition from a 9-m-thick flow in DSDP Hole 396B.

Detection and Tracking of Dynamic Objects. A MultiRobot approach to Critical Infrastructures Surveillance.

Despite that Critical Infrastructures (CIs) security and surveillance are a growing concern for many countries and companies, Multi Robot Systems (MRSs) have not been yet broadly used in this type of facilities. This dissertation presents a novel study of the challenges arisen by the implementation of this type of systems and proposes solutions to specific problems. First, a comprehensive analysis of different types of CIs has been carried out, emphasizing the influence of the different characteristics of the facilities in the design of a security and surveillance MRS. One of the most important needs for the surveillance of a CI is the detection of intruders. From a technical point of view this problem can be abstracted as equivalent to the Detection and Tracking of Mobile Objects (DATMO). This dissertation proposes algorithms to solve this specific problem in a CI environment. Using 3D range images of the environment as input data, two detection algorithms for ground robots have been developed. These detection algorithms provide a list of moving objects in the robot detection area. Direct image differentiation and computer vision techniques are used when the robot is static. Alternatively, multi-layer ground reconstructions are compared to detect the dynamic objects when the robot is moving. Since CIs usually spread over large areas, it is very useful to incorporate aerial vehicles in the surveillance MRS. Therefore, a moving object detection algorithm for aerial vehicles has been also developed. This algorithm compares the real optical flow obtained from a down-face oriented camera with an artificial optical flow computed using a RANSAC based homography matrix. Two tracking algorithms have been developed to follow the moving objects trajectories. These algorithms can efficiently handle occlusions and crossings, as well as exchange information among robots. The multirobot tracking can be applied to any type of communication structure: centralized, decentralized or a combination of both. Even more, the developed tracking algorithms are independent of the detection algorithms and could be potentially used with other detection procedures or even with static sensors, such as cameras. In addition, using the 3D point clouds available to the robots, a relative localization algorithm has been developed to improve the position estimation of a given robot with observations from other robots. All the developed algorithms have been extensively tested in different simulated CIs using the Webots robotics simulator. Furthermore, the algorithms have also been validated with real robots operating in real scenarios. In conclusion, this dissertation presents a multirobot approach to Critical Infrastructure Surveillance, mainly focusing on Detecting and Tracking Dynamic Objects.

E-Flow: A communication system for user notification in dynamic evacuation scenarios

Most of the current evacuation plans are based on static signaling, fixed monitoring infrastructure, and limited user notification and feedback mechanisms. These facts lead to lower situation awareness, in the case event of an emergency, such as blocked emergency exits, while delaying the reaction time of individuals. In this context, we introduce the E-Flow communication system, which improves the user awareness by integrating personal, mobile and fixed devices with the existing monitoring infrastructure. Our system broadens the notification and monitoring alternatives, in real time, among, safety staff, end-users and evacuation related devices, such as sensors and actuators.

Wind tunnel analysis of the flow topology over complex topographies

El principal objetivo de este trabajo es aportar conocimiento para contestar la pregunta: ¿hasta que punto los ensayos en túnel aerodinámico pueden contribuir a determinar las características que afectan la respuesta dinámica de los aerogeneradores operando en terreno complejo?. Esta pregunta no es nueva, de hecho, el debate en la comunidad científica comenzó en el primer tercio del siglo pasado y aún está intensamente vivo. El método generalmente aceptado para enfrentar el mencionado problema consiste en analizar un caso de estudio determinado en el cual se aplican tanto ensayos a escala real como análisis computacionales y ensayos en túnel aerodinámico. Esto no es ni fácil ni barato. Esta es la razón por la cual desde el experimento de Askervein en 1988, los modelizadores del flujo atmosférico tuvieron que esperar hasta 2007 a que el experimento de Bolund fuese puesto en marcha con un despliegue de medios técnicos equivalentes (teniendo en cuenta la evolución de las tecnologías de sensores y computación). El problema contempla tantos aspectos que ambas experiencias fueron restringidas a condiciones de atmósfera neutra con efectos de Coriolis despreciables con objeto de reducir la complejidad. Este es el contexto en el que se ha desarrollado la presente tesis doctoral. La topología del flujo sobre la isla de Bolund ha sido estudiada mediante la reproducción del experimento de Bolund en los túneles aerodinámicos A9 y ACLA16 del IDR. Dos modelos de la isla de Bolund fueron fabricados a dos escalas, 1:230 y 1:115. El flujo de entrada en el túnel aerodinámico simulando la capa límite sin perturbar correspondía a régimen de transición (transitionally rough regime) y fue usado como situación de referencia. El modelo a escala 1:230 fue ensayado en el túnel A9 para determinar la presión sobre su superficie. La distribución del coeficiente de presión sobre la isla proporcionó una visualización y estimación de una región de desprendimiento sobre el pequeño acantilado situado al frente de la misma. Las medidas de presión instantánea con suficiente grado de resolución temporal pusieron de manifiesto la no estacionariedad en la región de desprendimiento. El modelo a escala 1:115 fue ensayado utilizando hilo caliente de tres componentes y un sistema de velocimetría por imágenes de partículas de dos componentes. El flujo fue caracterizado por el ratio de aceleración, el incremento normalizado de energía cinética turbulenta y los ángulos de inclinación y desviación horizontal. Los resultados a lo largo de la dirección 270°y alturas de 2 m y 5 m presentaron una gran similitud con los resultados a escala real del experimento de Bolund. Los perfiles verticales en las localizaciones de las torres meteorológicas mostraron un acuerdo significativo con los resultados a escala real. El análisis de los esfuerzos de Reynolds y el análisis espectral en las localizaciones de los mástiles meteorológicos presentaron niveles de acuerdo variados en ciertas posiciones, mientras que en otras presentaron claras diferencias. El mapeo horizontal del flujo, para una dirección de viento de 270°, permitió caracterizar el comportamiento de la burbuja intermitente de recirculación sobre el pequeño acantilado existente al frente de la isla así como de la región de relajación y de la capa de cortadura en la región corriente abajo de Bolund. Se realizaron medidas de velocidad con alta resolución espacial en planos perpendiculares a la dirección del flujo sin perturbar. Estas medidas permitieron detectar y caracterizar una estructura de flujo similar a un torbellino longitudinal con regiones con altos gradientes de velocidad y alta intensidad de turbulencia. Esta estructura de flujo es, sin duda, un reto para los modelos computacionales y puede considerarse un factor de riesgo para la operación de los aerogeneradores. Se obtuvieron y analizaron distribuciones espaciales de los esfuerzos de Reynolds mediante 3CHW y PIV. Este tipo de parámetros no constituyen parte de los resultados habituales en los ensayos en túnel sobre topografías y son muy útiles para los modelizadores que utilizan simulación de grades torbellinos (LES). Se proporciona una interpretación de los resultados obtenidos en el túnel aerodinámico en términos de utilidad para los diseñadores de parques eólicos. La evolución y variación de los parámetros del flujo a lo largo de líneas, planos y superficies han permitido identificar como estas propiedades del flujo podrían afectar la localización de los aerogeneradores y a la clasificación de emplazamientos. Los resultados presentados sugieren, bajo ciertas condiciones, la robustez de los ensayos en túnel para estudiar la topología sobre terreno complejo y su comparabilidad con otras técnicas de simulación, especialmente considerando el nivel de acuerdo del conjunto de resultados presentados con los resultados a escala real. De forma adicional, algunos de los parámetros del flujo obtenidos de las medidas en túnel son difícilmente determinables en ensayos a escala real o por medios computacionales, considerado el estado del arte. Este trabajo fue realizado como parte de las actividades subvencionadas por la Comisión Europea como dentro del proyecto FP7-PEOPLE-ITN-2008WAUDIT (Wind Resource Assessment Audit and Standardization) dentro de la FP7 Marie-Curie Initial Training Network y por el Ministerio Español de Economía y Competitividad dentro del proyecto ENE2012-36473, TURCO (Determinación en túnel aerodinámico de la distribución espacial de parámetros estadísticos de la turbulencia atmosférica sobre topografías complejas) del Plan Nacional de Investigación (Subprograma de investigación fundamental no orientada 2012). El informe se ha organizado en siete capítulos y un conjunto de anexos. En el primer capítulo se introduce el problema. En el capítulo dos se describen los medios experimentales utilizados. Seguidamente, en el capítulo tres, se analizan en detalle las condiciones de referencia del principal túnel aerodinámico utilizado en esta investigación. En el capítulo tres se presentan resultados de ensayos de presión superficial sobre un modelo de la isla. Los principales resultados del experimento de Bolund se reproducen en el capítulo cinco. En el capítulo seis se identifican diferentes estructuras del flujo sobre la isla y, finalmente, en el capitulo siete, se recogen las conclusiones y una propuesta de lineas de trabajo futuras. ABSTRACT The main objective of this work is to contribute to answer the question: to which extend can the wind tunnel testing contribute to determine the flow characteristics that affect the dynamic response of wind turbines operating in highly complex terrains?. This question is not new, indeed, the debate in the scientific community was opened in the first third of the past century and it is still intensely alive. The accepted approach to face this problem consists in analysing a given case study where full-scale tests, computational modelling and wind tunnel testing are applied to the same topography. This is neither easy nor cheap. This is is the reason why since the Askervein experience in 1988, the atmospheric flow modellers community had to wait till 2007 when the Bolund experiment was setup with a deployment of technical means equivalent (considering the evolution of the sensor and computing techniques). The problem is so manifold that both experiences were restricted to neutral conditions without Coriolis effects in order to reduce the complexity. This is the framework in which this PhD has been carried out. The flow topology over the Bolund Island has been studied by replicating the Bolund experiment in the IDR A9 and ACLA16 wind tunnels. Two mock-ups of the Bolund island were manufactured at two scales of 1:230 and 1:115. The in-flow in the empty wind tunnel simulating the incoming atmospheric boundary layer was in the transitionally rough regime and used as a reference case. The 1:230 model was tested in the A9 wind tunnel to measure surface pressure. The mapping of the pressure coefficient across the island gave a visualisation and estimation of a detachment region on the top of the escarpment in front of the island. Time resolved instantaneous pressure measurements illustrated the non-steadiness in the detachment region. The 1:115 model was tested using 3C hot-wires(HW) and 2C Particle Image Velocimetry(PIV). Measurements at met masts M3, M6, M7 and M8 and along Line 270°were taken to replicate the result of the Bolund experiment. The flow was characterised by the speed-up ratio, normalised increment of the turbulent kinetic energy, inclination angle and turning angle. Results along line 270°at heights of 2 m and 5 m compared very well with the full-scale results of the Bolund experiment. Vertical profiles at the met masts showed a significant agreement with the full-scale results. The analysis of the Reynolds stresses and the spectral analysis at the met mast locations gave a varied level of agreement at some locations while clear mismatch at others. The horizontal mapping of the flow field, for a 270°wind direction, allowed to characterise the behaviour of the intermittent recirculation bubble on top of the front escarpment followed by a relaxation region and the presence of a shear layer in the lee side of the island. Further detailed velocity measurements were taken at cross-flow planes over the island to study the flow structures on the island. A longitudinal vortex-like structure with high mean velocity gradients and high turbulent kinetic energy was characterised on the escarpment and evolving downstream. This flow structure is a challenge to the numerical models while posing a threat to wind farm designers when siting wind turbines. Spatial distribution of Reynold stresses were presented from 3C HW and PIV measurements. These values are not common results from usual wind tunnel measurements and very useful for modellers using large eddy simulation (LES). An interpretation of the wind tunnel results in terms of usefulness to wind farm designers is given. Evolution and variation of the flow parameters along measurement lines, planes and surfaces indicated how the flow field could affect wind turbine siting. Different flow properties were presented so compare the level of agreement to full-scale results and how this affected when characterising the site wind classes. The results presented suggest, under certain conditions, the robustness of the wind tunnel testing for studying flow topology over complex terrain and its capability to compare to other modelling techniques especially from the level of agreement between the different data sets presented. Additionally, some flow parameters obtained from wind tunnel measurements would have been quite difficult to be measured at full-scale or by computational means considering the state of the art. This work was carried out as a part of the activities supported by the EC as part of the FP7- PEOPLE-ITN-2008 WAUDIT project (Wind Resource Assessment Audit and Standardization) within the FP7 Marie-Curie Initial Training Network and by the Spanish Ministerio de Economía y Competitividad, within the framework of the ENE2012-36473, TURCO project (Determination of the Spatial Distribution of Statistic Parameters of Flow Turbulence over Complex Topographies in Wind Tunnel) belonging to the Spanish National Program of Research (Subprograma de investigación fundamental no orientada 2012). The report is organised in seven chapters and a collection of annexes. In chapter one, the problem is introduced. In chapter two the experimental setup is described. Following, in chapter three, the inflow conditions of the main wind tunnel used in this piece of research are analysed in detail. In chapter three, preliminary pressure tests results on a model of the island are presented. The main results from the Bolund experiment are replicated in chapter five. In chapter six, an identification of specific flow strutures over the island is presented and, finally, in chapter seven, conclusions and lines for future works related to the presented one are included.

Output Impedance Correction Circuit (OICC): A New Concept to Improve the Dynamic Response of DC/DC Converters with Additional Energy Path

El desarrollo da las nuevas tecnologías permite a los ingenieros llevar al límite el funcionamiento de los circuitos integrados (Integrated Circuits, IC). Las nuevas generaciones de procesadores, DSPs o FPGAs son capaces de procesar la información a una alta velocidad, con un alto consumo de energía, o esperar en modo de baja potencia con el mínimo consumo posible. Esta gran variación en el consumo de potencia y el corto tiempo necesario para cambiar de un nivel al otro, afecta a las especificaciones del Módulo de Regulador de Tensión (Voltage Regulated Module, VRM) que alimenta al IC. Además, las características adicionales obligatorias, tales como adaptación del nivel de tensión (Adaptive Voltage Positioning, AVP) y escalado dinámico de la tensión (Dynamic Voltage Scaling, DVS), imponen requisitos opuestas en el diseño de la etapa de potencia del VRM. Para poder soportar las altas variaciones de los escalones de carga, el condensador de filtro de salida del VRM se ha de sobredimensionar, penalizando la densidad de energía y el rendimiento durante la operación de DVS. Por tanto, las actuales tendencias de investigación se centran en mejorar la respuesta dinámica del VRM, mientras se reduce el tamaño del condensador de salida. La reducción del condensador de salida lleva a menor coste y una prolongación de la vida del sistema ya que se podría evitar el uso de condensadores voluminosos, normalmente implementados con condensadores OSCON. Una ventaja adicional es que reduciendo el condensador de salida, el DVS se puede realizar más rápido y con menor estrés de la etapa de potencia, ya que la cantidad de carga necesaria para cambiar la tensión de salida es menor. El comportamiento dinámico del sistema con un control lineal (Control Modo Tensión, VMC, o Control Corriente de Pico, Peak Current Mode Control, PCMC,…) está limitado por la frecuencia de conmutación del convertidor y por el tamaño del filtro de salida. La reducción del condensador de salida se puede lograr incrementando la frecuencia de conmutación, así como incrementando el ancho de banda del sistema, y/o aplicando controles avanzados no-lineales. Usando esos controles, las variables del estado se saturan para conseguir el nuevo régimen permanente en un tiempo mínimo, así como el filtro de salida, más específicamente la pendiente de la corriente de la bobina, define la respuesta de la tensión de salida. Por tanto, reduciendo la inductancia de la bobina de salida, la corriente de bobina llega más rápido al nuevo régimen permanente, por lo que una menor cantidad de carga es tomada del condensador de salida durante el tránsito. El inconveniente de esa propuesta es que el rendimiento del sistema es penalizado debido al incremento de pérdidas de conmutación y las corrientes RMS. Para conseguir tanto la reducción del condensador de salida como el alto rendimiento del sistema, mientras se satisfacen las estrictas especificaciones dinámicas, un convertidor multifase es adoptado como estándar para aplicaciones VRM. Para asegurar el reparto de las corrientes entre fases, el convertidor multifase se suele implementar con control de modo de corriente. Para superar la limitación impuesta por el filtro de salida, la segunda posibilidad para reducir el condensador de salida es aplicar alguna modificación topológica (Topologic modifications) de la etapa básica de potencia para incrementar la pendiente de la corriente de bobina y así reducir la duración de tránsito. Como el transitorio se ha reducido, una menor cantidad de carga es tomada del condensador de salida bajo el mismo escalón de la corriente de salida, con lo cual, el condensador de salida se puede reducir para lograr la misma desviación de la tensión de salida. La tercera posibilidad para reducir el condensador de salida del convertidor es introducir un camino auxiliar de energía (additional energy path, AEP) para compensar el desequilibrio de la carga del condensador de salida reduciendo consecuentemente la duración del transitorio y la desviación de la tensión de salida. De esta manera, durante el régimen permanente, el sistema tiene un alto rendimiento debido a que el convertidor principal con bajo ancho de banda es diseñado para trabajar con una frecuencia de conmutación moderada para conseguir requisitos estáticos. Por otro lado, el comportamiento dinámico durante los transitorios es determinado por el AEP con un alto ancho de banda. El AEP puede ser implementado como un camino resistivo, como regulador lineal (Linear regulator, LR) o como un convertidor conmutado. Las dos primeras implementaciones proveen un mayor ancho de banda, acosta del incremento de pérdidas durante el transitorio. Por otro lado, la implementación del convertidor computado presenta menor ancho de banda, limitado por la frecuencia de conmutación, aunque produce menores pérdidas comparado con las dos anteriores implementaciones. Dependiendo de la aplicación, la implementación y la estrategia de control del sistema, hay una variedad de soluciones propuestas en el Estado del Arte (State-of-the-Art, SoA), teniendo diferentes propiedades donde una solución ofrece más ventajas que las otras, pero también unas desventajas. En general, un sistema con AEP ideal debería tener las siguientes propiedades: 1. El impacto del AEP a las pérdidas del sistema debería ser mínimo. A lo largo de la operación, el AEP genera pérdidas adicionales, con lo cual, en el caso ideal, el AEP debería trabajar por un pequeño intervalo de tiempo, solo durante los tránsitos; la otra opción es tener el AEP constantemente activo pero, por la compensación del rizado de la corriente de bobina, se generan pérdidas innecesarias. 2. El AEP debería ser activado inmediatamente para minimizar la desviación de la tensión de salida. Para conseguir una activación casi instantánea, el sistema puede ser informado por la carga antes del escalón o el sistema puede observar la corriente del condensador de salida, debido a que es la primera variable del estado que actúa a la perturbación de la corriente de salida. De esa manera, el AEP es activado con casi cero error de la tensión de salida, logrando una menor desviación de la tensión de salida. 3. El AEP debería ser desactivado una vez que el nuevo régimen permanente es detectado para evitar los transitorios adicionales de establecimiento. La mayoría de las soluciones de SoA estiman la duración del transitorio, que puede provocar un transitorio adicional si la estimación no se ha hecho correctamente (por ejemplo, si la corriente de bobina del convertidor principal tiene un nivel superior o inferior al necesitado, el regulador lento del convertidor principal tiene que compensar esa diferencia una vez que el AEP es desactivado). Otras soluciones de SoA observan las variables de estado, asegurando que el sistema llegue al nuevo régimen permanente, o pueden ser informadas por la carga. 4. Durante el transitorio, como mínimo un subsistema, o bien el convertidor principal o el AEP, debería operar en el lazo cerrado. Implementando un sistema en el lazo cerrado, preferiblemente el subsistema AEP por su ancho de banda elevado, se incrementa la robustez del sistema a los parásitos. Además, el AEP puede operar con cualquier tipo de corriente de carga. Las soluciones que funcionan en el lazo abierto suelen preformar el control de balance de carga con mínimo tiempo, así reducen la duración del transitorio y tienen un impacto menor a las pérdidas del sistema. Por otro lado, esas soluciones demuestran una alta sensibilidad a las tolerancias y parásitos de los componentes. 5. El AEP debería inyectar la corriente a la salida en una manera controlada, así se reduce el riesgo de unas corrientes elevadas y potencialmente peligrosas y se incrementa la robustez del sistema bajo las perturbaciones de la tensión de entrada. Ese problema suele ser relacionado con los sistemas donde el AEP es implementado como un convertidor auxiliar. El convertidor auxiliar es diseñado para una potencia baja, con lo cual, los dispositivos elegidos son de baja corriente/potencia. Si la corriente no es controlada, bajo un pico de tensión de entrada provocada por otro parte del sistema (por ejemplo, otro convertidor conectado al mismo bus), se puede llegar a un pico en la corriente auxiliar que puede causar la perturbación de tensión de salida e incluso el fallo de los dispositivos del convertidor auxiliar. Sin embargo, cuando la corriente es controlada, usando control del pico de corriente o control con histéresis, la corriente auxiliar tiene el control con prealimentación (feed-forward) de tensión de entrada y la corriente es definida y limitada. Por otro lado, si la solución utiliza el control de balance de carga, el sistema puede actuar de forma deficiente si la tensión de entrada tiene un valor diferente del nominal, provocando que el AEP inyecta/toma más/menos carga que necesitada. 6. Escalabilidad del sistema a convertidores multifase. Como ya ha sido comentado anteriormente, para las aplicaciones VRM por la corriente de carga elevada, el convertidor principal suele ser implementado como multifase para distribuir las perdidas entre las fases y bajar el estrés térmico de los dispositivos. Para asegurar el reparto de las corrientes, normalmente un control de modo corriente es usado. Las soluciones de SoA que usan VMC son limitadas a la implementación con solo una fase. Esta tesis propone un nuevo método de control del flujo de energía por el AEP y el convertidor principal. El concepto propuesto se basa en la inyección controlada de la corriente auxiliar al nodo de salida donde la amplitud de la corriente es n-1 veces mayor que la corriente del condensador de salida con las direcciones apropiadas. De esta manera, el AEP genera un condensador virtual cuya capacidad es n veces mayor que el condensador físico y reduce la impedancia de salida. Como el concepto propuesto reduce la impedancia de salida usando el AEP, el concepto es llamado Output Impedance Correction Circuit (OICC) concept. El concepto se desarrolla para un convertidor tipo reductor síncrono multifase con control modo de corriente CMC (incluyendo e implementación con una fase) y puede operar con la tensión de salida constante o con AVP. Además, el concepto es extendido a un convertidor de una fase con control modo de tensión VMC. Durante la operación, el control de tensión de salida de convertidor principal y control de corriente del subsistema OICC están siempre cerrados, incrementando la robustez a las tolerancias de componentes y a los parásitos del cirquito y permitiendo que el sistema se pueda enfrentar a cualquier tipo de la corriente de carga. Según el método de control propuesto, el sistema se puede encontrar en dos estados: durante el régimen permanente, el sistema se encuentra en el estado Idle y el subsistema OICC esta desactivado. Por otro lado, durante el transitorio, el sistema se encuentra en estado Activo y el subsistema OICC está activado para reducir la impedancia de salida. El cambio entre los estados se hace de forma autónoma: el sistema entra en el estado Activo observando la corriente de condensador de salida y vuelve al estado Idle cunado el nuevo régimen permanente es detectado, observando las variables del estado. La validación del concepto OICC es hecha aplicándolo a un convertidor tipo reductor síncrono con dos fases y de 30W cuyo condensador de salida tiene capacidad de 140μF, mientras el factor de multiplicación n es 15, generando en el estado Activo el condensador virtual de 2.1mF. El subsistema OICC es implementado como un convertidor tipo reductor síncrono con PCMC. Comparando el funcionamiento del convertidor con y sin el OICC, los resultados demuestran que se ha logrado una reducción de la desviación de tensión de salida con factor 12, tanto con funcionamiento básico como con funcionamiento AVP. Además, los resultados son comparados con un prototipo de referencia que tiene la misma etapa de potencia y un condensador de salida físico de 2.1mF. Los resultados demuestran que los dos sistemas tienen el mismo comportamiento dinámico. Más aun, se ha cuantificado el impacto en las pérdidas del sistema operando bajo una corriente de carga pulsante y bajo DVS. Se demuestra que el sistema con OICC mejora el rendimiento del sistema, considerando las pérdidas cuando el sistema trabaja con la carga pulsante y con DVS. Por lo último, el condensador de salida de sistema con OICC es mucho más pequeño que el condensador de salida del convertidor de referencia, con lo cual, por usar el concepto OICC, la densidad de energía se incrementa. En resumen, las contribuciones principales de la tesis son: • El concepto propuesto de Output Impedance Correction Circuit (OICC), • El control a nivel de sistema basado en el método usado para cambiar los estados de operación, • La implementación del subsistema OICC en lazo cerrado conjunto con la implementación del convertidor principal, • La cuantificación de las perdidas dinámicas bajo la carga pulsante y bajo la operación DVS, y • La robustez del sistema bajo la variación del condensador de salida y bajo los escalones de carga consecutiva. ABSTRACT Development of new technologies allows engineers to push the performance of the integrated circuits to its limits. New generations of processors, DSPs or FPGAs are able to process information with high speed and high consumption or to wait in low power mode with minimum possible consumption. This huge variation in power consumption and the short time needed to change from one level to another, affect the specifications of the Voltage Regulated Module (VRM) that supplies the IC. Furthermore, additional mandatory features, such as Adaptive Voltage Positioning (AVP) and Dynamic Voltage Scaling (DVS), impose opposite trends on the design of the VRM power stage. In order to cope with high load-step amplitudes, the output capacitor of the VRM power stage output filter is drastically oversized, penalizing power density and the efficiency during the DVS operation. Therefore, the ongoing research trend is directed to improve the dynamic response of the VRM while reducing the size of the output capacitor. The output capacitor reduction leads to a smaller cost and longer life-time of the system since the big bulk capacitors, usually implemented with OSCON capacitors, may not be needed to achieve the desired dynamic behavior. An additional advantage is that, by reducing the output capacitance, dynamic voltage scaling (DVS) can be performed faster and with smaller stress on the power stage, since the needed amount of charge to change the output voltage is smaller. The dynamic behavior of the system with a linear control (Voltage mode control, VMC, Peak Current Mode Control, PCMC,…) is limited by the converter switching frequency and filter size. The reduction of the output capacitor can be achieved by increasing the switching frequency of the converter, thus increasing the bandwidth of the system, and/or by applying advanced non-linear controls. Applying nonlinear control, the system variables get saturated in order to reach the new steady-state in a minimum time, thus the output filter, more specifically the output inductor current slew-rate, determines the output voltage response. Therefore, by reducing the output inductor value, the inductor current reaches faster the new steady state, so a smaller amount of charge is taken from the output capacitor during the transient. The drawback of this approach is that the system efficiency is penalized due to increased switching losses and RMS currents. In order to achieve both the output capacitor reduction and high system efficiency, while satisfying strict dynamic specifications, a Multiphase converter system is adopted as a standard for VRM applications. In order to ensure the current sharing among the phases, the multiphase converter is usually implemented with current mode control. In order to overcome the limitation imposed by the output filter, the second possibility to reduce the output capacitor is to apply Topologic modifications of the basic power stage topology in order to increase the slew-rate of the inductor current and, therefore, reduce the transient duration. Since the transient is reduced, smaller amount of charge is taken from the output capacitor under the same load current, thus, the output capacitor can be reduced to achieve the same output voltage deviation. The third possibility to reduce the output capacitor of the converter is to introduce an additional energy path (AEP) to compensate the charge unbalance of the output capacitor, consequently reducing the transient time and output voltage deviation. Doing so, during the steady-state operation the system has high efficiency because the main low-bandwidth converter is designed to operate at moderate switching frequency, to meet the static requirements, whereas the dynamic behavior during the transients is determined by the high-bandwidth auxiliary energy path. The auxiliary energy path can be implemented as a resistive path, as a Linear regulator, LR, or as a switching converter. The first two implementations provide higher bandwidth, at the expense of increasing losses during the transient. On the other hand, the switching converter implementation presents lower bandwidth, limited by the auxiliary converter switching frequency, though it produces smaller losses compared to the two previous implementations. Depending on the application, the implementation and the control strategy of the system, there is a variety of proposed solutions in the State-of-the-Art (SoA), having different features where one solution offers some advantages over the others, but also some disadvantages. In general, an ideal additional energy path system should have the following features: 1. The impact on the system losses should be minimal. During its operation, the AEP generates additional losses, thus ideally, the AEP should operate for a short period of time, only when the transient is occurring; the other option is to have the AEP constantly on, but due to the inductor current ripple compensation at the output, unnecessary losses are generated. 2. The AEP should be activated nearly instantaneously to prevent bigger output voltage deviation. To achieve near instantaneous activation, the converter system can be informed by the load prior to the load-step or the system can observe the output capacitor current, which is the first system state variable that reacts on the load current perturbation. In this manner, the AEP is turned on with near zero output voltage error, providing smaller output voltage deviation. 3. The AEP should be deactivated once the new steady state is reached to avoid additional settling transients. Most of the SoA solutions estimate duration of the transient which may cause additional transient if the estimation is not performed correctly (e.g. if the main converter inductor current has higher or lower value than needed, the slow regulator of the main converter needs to compensate the difference after the AEP is deactivated). Other SoA solutions are observing state variables, ensuring that the system reaches the new steady state or they are informed by the load. 4. During the transient, at least one subsystem, either the main converter or the AEP, should be in closed-loop. Implementing a closed loop system, preferably the AEP subsystem, due its higher bandwidth, increases the robustness under system tolerances and circuit parasitic. In addition, the AEP can operate with any type of load. The solutions that operate in open loop usually perform minimum time charge balance control, thus reducing the transient length and minimizing the impact on the losses, however they are very sensitive to tolerances and parasitics. 5. The AEP should inject current at the output in a controlled manner, thus reducing the risk of high and potentially damaging currents and increasing robustness on the input voltage deviation. This issue is mainly related to the systems where AEP is implemented as auxiliary converter. The auxiliary converter is designed for small power and, as such, the MOSFETs are rated for small power/currents. If the current is not controlled, due to the some unpredicted spike in input voltage caused by some other part of the system (e.g. different converter), it may lead to a current spike in auxiliary current which will cause the perturbation of the output voltage and even failure of the switching components of auxiliary converter. In the case when the current is controlled, using peak CMC or Hysteretic Window CMC, the auxiliary converter has inherent feed-forwarding of the input voltage in current control and the current is defined and limited. Furthermore, if the solution employs charge balance control, the system may perform poorly if the input voltage has different value than the nominal, causing that AEP injects/extracts more/less charge than needed. 6. Scalability of the system to multiphase converters. As commented previously, in VRM applications, due to the high load currents, the main converters are implemented as multiphase to redistribute losses among the modules, lowering temperature stress of the components. To ensure the current sharing, usually a Current Mode Control (CMC) is employed. The SoA solutions that are implemented with VMC are limited to a single stage implementation. This thesis proposes a novel control method of the energy flow through the AEP and the main converter system. The proposed concept relays on a controlled injection of the auxiliary current at the output node where the instantaneous current value is n-1 times bigger than the output capacitor current with appropriate directions. Doing so, the AEP creates an equivalent n times bigger virtual capacitor at the output, thus reducing the output impedance. Due to the fact that the proposed concept reduces the output impedance using the AEP, it has been named the Output Impedance Correction Circuit (OICC) concept. The concept is developed for a multiphase CMC synchronous buck converter (including a single phase implementation), operating with a constant output voltage and with AVP feature. Further, it is extended to a single phase VMC synchronous buck converter. During the operation, the main converter voltage loop and the OICC subsystem capacitor current loop is constantly closed, increasing the robustness under system tolerances and circuit parasitic and allowing the system to operate with any load-current shape or pattern. According to the proposed control method, the system operates in two states: during the steady-state the system is in the Idle state and the OICC subsystem is deactivated, while during the load-step transient the system is in the Active state and the OICC subsystem is activated in order to reduce the output impedance. The state changes are performed autonomously: the system enters in the Active state by observing the output capacitor current and it returns back to the Idle state when the steady-state operation is detected by observing the state variables. The validation of the OICC concept has been done by applying it to a 30W two phase synchronous buck converter with 140μF output capacitor and with the multiplication factor n equal to 15, generating during the Active state equivalent output capacitor of 2.1mF. The OICC subsystem is implemented as single phase PCMC synchronous buck converter. Comparing the converter operation with and without the OICC the results demonstrate that the 12 times reduction of the output voltage deviation is achieved, for both basic operation and for the AVP operation. Furthermore, the results have been compared to a reference prototype which has the same power stage and a fiscal output capacitor of 2.1mF. The results show that the two systems have the same dynamic behavior. Moreover, an impact on the system losses under the pulsating load and DVS operation has been quantified and it has been demonstrated that the OICC system has improved the system efficiency, considering the losses when the system operates with the pulsating load and the DVS operation. Lastly, the output capacitor of the OICC system is much smaller than the reference design output capacitor, therefore, by applying the OICC concept the power density can be increased. In summary, the main contributions of the thesis are: • The proposed Output Impedance Correction Circuit (OICC) concept, • The system level control based on the used approach to change the states of operation, • The OICC subsystem closed-loop implementation, together with the main converter implementation, • The dynamic losses under the pulsating load and the DVS operation quantification, and • The system robustness on the capacitor impedance variation and consecutive load-steps.

Comparison among monitoring strategies to assess water flow dynamic and soil hydraulic properties in agricultural soils

Irrigated agriculture is usually performed in semi-arid regions despite scarcity of water resources. Therefore, optimal irrigation management by monitoring the soil is essential, and assessing soil hydraulic properties and water flow dynamics is presented as a first measure. For this purpose, the control of volumetric water content, θ, and pressure head, h, is required. This study adopted two types of monitoring strategies in the same experimental plot to control θ and h in the vadose zone: i) non-automatic and more time-consuming; ii) automatic connected to a datalogger. Water flux was modelled with Hydrus-1D using the data collected from both acquisition strategies independently (3820 daily values for the automatic; less than 1000 for the non-automatic). Goodness-of-fit results reported a better adjustment in case of automatic sensors. Both model outputs adequately predicted the general trend of θ and h, but with slight differences in computed annual drainage (711 mm and 774 mm). Soil hydraulic properties were inversely estimated from both data acquisition systems. Major differences were obtained in the saturated volumetric water content, θs, and the n and α van Genuchten model shape parameters. Saturated hydraulic conductivity, Ks, shown lower variability with a coefficient of variation range from 0.13 to 0.24 for the soil layers defined. Soil hydraulic properties were better assessed through automatic data acquisition as data variability was lower and accuracy was higher.

An iterative method for solving nonsymmetric linear systems with dynamic estimation of parameters /

Vita.

Estimation of flow through offshore breakwater gaps generated by wave overtopping /

"December 1980."

A study of the dynamic flue-gas temperature and off-period mass flow rate of a residential gas-fired furnace /

Includes bibliographical references (p. 31).

A Novel Framework for Real-time Traffic Flow Parameter Estimation from Aerial Videos

Thesis (Master's)--University of Washington, 2016-06

Prediction of slurry transport in SAG mills using SPH fluid flow in a dynamic DEM based porous media

DEM modelling of the motion of coarse fractions of the charge inside SAG mills has now been well established for more than a decade. In these models the effect of slurry has broadly been ignored due to its complexity. Smoothed particle hydrodynamics (SPH) provides a particle based method for modelling complex free surface fluid flows and is well suited to modelling fluid flow in mills. Previous modelling has demonstrated the powerful ability of SPH to capture dynamic fluid flow effects such as lifters crashing into slurry pools, fluid draining from lifters, flow through grates and pulp lifter discharge. However, all these examples were limited by the ability to model only the slurry in the mill without the charge. In this paper, we represent the charge as a dynamic porous media through which the SPH fluid is then able to flow. The porous media properties (specifically the spatial distribution of porosity and velocity) are predicted by time averaging the mill charge predicted using a large scale DEM model. This allows prediction of transient and steady state slurry distributions in the mill and allows its variation with operating parameters, slurry viscosity and slurry volume, to be explored. (C) 2006 Published by Elsevier Ltd.