Orientador: Lee Luan Ling / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-08T01:26:33Z (GMT). No. of bitstreams: 1 Vieira_FlavioHenriqueTeles_D.pdf: 4214611 bytes, checksum: 755dfe9865aff1214f8e551afde7541d (MD5) Previous issue date: 2006 / Resumo: A modelagem multifractal generaliza os modelos de tráfego existentes na literatura e se mostra apropriada para descrever as características encontradas nos fluxos de tráfego das redes atuais. A presente tese investiga abordagens para alocação de banda, predição de tráfego e estimação de probabilidade de perda de bytes considerando as características multifractais de tráfego. Primeiramente, um Modelo Multifractal baseado em Wavelets (MMW) é proposto. Levando em consideração as propriedades deste modelo, são derivados o parâmetro de escala global, a função de autocorrelação e a banda efetiva para processos multifractais. A capacidade de atualização em tempo real do MMW aliada à banda efetiva proposta permite o desenvolvimento de um algoritmo de estimação adaptativa de banda efetiva. Através deste algoritmo é introduzido um esquema de provisão adaptativo de banda efetiva. Estuda-se também a alocação de banda baseada em predição de tráfego. Para este fim, propõe-se um preditor adaptativo fuzzy de tráfego, o qual é aplicado em uma nova estratégia de alocação de banda. O preditor fuzzy adaptativo proposto utiliza funções de base ortonormais baseadas nas propriedades do MMW. Com relação à probabilidade de perda para tráfego multifractal, derivase uma expressão analítica para a estimação da probabilidade de perda de bytes considerando que o tráfego obedece ao MMW. Além disso, uma caracterização mais completa do comportamento de fila é efetuada pela obtenção de limitantes para a probabilidade de perda e para a ocupação média do buffer em termos da banda efetiva do MMW. Por fim, é apresentado um esquema de controle de admissão usando o envelope efetivo proposto para o MMW oriundo do cálculo de rede estatístico, que garante que os fluxos admitidos obedeçam simultaneamente aos requisitos de perda e de retardo. As simulações realizadas evidenciam a relevância das propostas apresentadas / Abstract: Multifractal modeling generalizes the existing traffic models and is believed to be appropriate to describe the characteristics of traffic flows of modern communication networks. This thesis investigates some novel approaches for bandwidth allocation, traffic prediction and byte loss probability estimation, by considering the multifractal characteristics of the network traffic. Firstly, a Wavelet based Multifractal Model (WMM) is proposed. Taking into account the properties of this multifractal model, we derive the global scaling parameter, the autocorrelation function and the effective bandwidth for multifractal processes. The real time updating capacity of the WMM in connection with our effective bandwidth proposal allows us to develop an algorithm for adaptive effective bandwidth estimation. Then, through this algorithm, an adaptive bandwidth provisioning scheme is introduced. In this work, we also study a prediction-based bandwidth allocation case. For this end, we develop an adaptive fuzzy predictor, which is incorporated into a novel bandwidth allocation scheme. The proposed adaptive fuzzy predictor makes use of orthonormal basis functions based on the properties of the WMM. Additionally, we derive an analytical expression for the byte loss probability estimation assuming that the traffic obeys the MMW. Besides, a more complete characterization of the queuing behavior is carried out through the estimation of the bounds for the loss probability and mean queue length in buffer in terms of the WMM based effective bandwidth. Finally, an admission control scheme is presented that uses the WMM based effective envelope derived through the statistical network calculus, guaranteeing that the admitted flows simultaneously attend the loss and delay requirements. The computer simulation results confirm the relevance of the presented proposals / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

The collisions frequency of dispersed phases (particles, droplets, bubbles) in a turbulent carrier phase is a fundamental quantity that is needed for modeling multiphase flows with applications to chemical processes, minerals flotation, food science, and many other industries. In this dissertation, numerical simulations are performed to determine collisions frequency of bi-dispersed particles (solid particles and bubbles) in homogeneous isotropic turbulence. Both direct numerical simulations (DNS) and Large Eddy simulations (LES) are conducted to determine velocity fluctuations of the carrier phase. The DNS results are used to validate existing theoretical models as well as the LES results. The dissertation also presents a CFD-based flotation model for predicting the pulp recovery rate in froth flotation machines. In the direct numerical simulations work, particles and bubbles suspended in homogeneous isotropic turbulence are tracked and their collisions frequency is determined as a function of particle Stokes number. The effects of the dispersed phases on the carrier phase are neglected. Particles and bubbles of sizes on the order of Kolmogorov length scale are treated as point masses. Equations of motion of dispersed phases are integrated simultaneously with the equations of the carrier phase using the same time stepping scheme. In addition to Stokes drag, the pressure gradient in the carrier phase and added-mass forces are also included. The collision model used here allows overlap of particles and bubbles. Collisions kernel, radial relative velocity, and radial distribution function found by DNS are compared to theoretical models over a range of particle Stokes number. In general, good agreement between DNS and recent theoretical models is obtained for radial relative velocity for both particle-particle and particle-bubble collisions. The DNS results show that around Stokes number of unity particles of the same group undergo expected preferential concentration while particles and bubbles are segregated. The segregation behavior of particles and bubbles leads to a radial distribution function that is less than one. Existing theoretical models do not account for effects of this segregation behavior of particles and bubbles on the radial distribution function. In the large-eddy simulations efforts, the dissertation addresses the importance of the subgrid fluctuations on the collisions frequency and investigates techniques for predicting those fluctuations. The cases studied are of particles-particles and particles-bubbles collisions at Reynolds number Re_λ = 96. A study is conducted first by neglecting the effects of subgrid velocity fluctuations on particles and bubbles motions. It is found that around Stokes number of unity solid particles of the same group undergo the well known preferential concentration as observed in the DNS. Effects of pressure gradient on the particles are negligible due to their small sizes. Bubbles as a low inertia particles are very sensitive to subgrid velocity and acceleration fields where the effects of pressure gradient in the carrier phase are dominant. However, particle-bubble radial distribution functions from LES are not as low as that from DNS. To account for the effects of subgrid field on the dispersion of particles and bubbles, a new multifractal methodology has been developed to construct a subgrid vorticity field from the resolved vorticity field in frame work of LES. A Poisson's solver is used to obtain the subgrid velocity field from the subgrid vorticity field. Accounting for the subgrid velocity fluctuations (but neglecting pressure gradient) produced minor changes in the radial distribution function for particle-particle and particle-bubble collisions. We conclude from this study that for accurate particle tracking in LES the subgrid velocity fluctuations must be dynamically realizable field (temporally and spatially correlated with the large scale motion). Adding random SGS velocity fluctuations is not enough to capture the correct radial distribution functions of dispersed phases especially for bubbles-particles collisions where the pressure gradient term ( or acceleration Du_f′/Dt) is responsible for particle-bubble segregation around particle Stokes number near one. A CFD-based model for minerals flotation machines has been developed in this dissertation. The objective of flotation models is to predict the recovery rate of minerals from a flotation cell. The developed model advances the state-of-the-art of pulp recovery rate prediction by incorporating validated theoretical collisions frequency models and detailed hydrodynamics from two-phase flow simulations. Spatial distributions of dissipation rate and air volume fraction are determined by the two-phase hydrodynamic simulations. Knowing these parameters throughout the machine is essential in understanding the effectiveness of different components of flotation machine (rotor, stator or disperser, jets) on the flotation efficiency. The developed model not only predicts the average pulp recovery rate but also it indicates regions of high/low recovery rates. The CFD-based flotation model presented here can be used to determine the dependence of recovery rate constant at any locality within the pulp based on particle diameter, particle specfic gravity, contact angle, and surface tension. / Ph. D.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2015-10-22T10:13:08Z No. of bitstreams: 2 Dissertação - Diego Cruz Abrahão - 2015.pdf: 9765017 bytes, checksum: 6f29592215e8451edda4aa5ad24238f4 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-10-22T10:15:40Z (GMT) No. of bitstreams: 2 Dissertação - Diego Cruz Abrahão - 2015.pdf: 9765017 bytes, checksum: 6f29592215e8451edda4aa5ad24238f4 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2015-10-22T10:15:40Z (GMT). No. of bitstreams: 2 Dissertação - Diego Cruz Abrahão - 2015.pdf: 9765017 bytes, checksum: 6f29592215e8451edda4aa5ad24238f4 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-03-19 / In this paper we propose two schemes for allocating resource blocks for transmission LTE downlink to maximize the throughput of the system, to guarantee QoS (Quality of Service) parameters for the users and reduce the data loss rate of network. The first proposed scheme uses the Max-min criterion and the second employs a fuzzy inference system to calculate the priorities of users and make scheduling decisions. Both schemes use an estimated effective bandwidth of traffic flows of users. The effective bandwidth of a traffic flow is the rate required to meet a criterion of probability of data loss rate. In this work, the effective bandwidth is estimated adaptively by the parameters of multifractal modeling βMWM (β-Multifractal Wavelet Mode). Are made simulations of the algorithms proposed, considering different propagation models with multipath fading and with different numbers of users in the network. The simulation results are compared with other algorithms presented in the literature, using parameters such as: throughput of the system, data loss rate and fairness index. It is also proposed to use predict of the SNR (Signal-to-Noise Ratio) of users, in the scheduling algorithms, using linear prediction of multi-step filter, in view of the delay in receipt of the channel quality information of the users in the base station and the variation of the signal propagation conditions. The multi-step prediction filter is used with the algorithms of allocation of resource blocks proposed in this work to estimate the signal-to-noise-ratio of users and set well, modulation schemes and code to be used in the LTE network. / Neste trabalho são propostos dois esquemas de alocação de blocos de recurso para a transmissão de downlink LTE, visando maximizar a vazão de dados total do sistema, garantir parâmetros de QoS (Quality of Service) dos usuários e diminuir a taxa de perda de dados da rede. O primeiro esquema proposto utiliza o critério Max-min e o segundo emprega um sistema de inferência fuzzy para calcular as prioridades dos usuários e tomar decisões de escalonamento. Ambos os esquemas utilizam estimações de banda efetiva dos fluxos de tráfego dos usuários. A banda efetiva de um fluxo de tráfego é a taxa necessária para atender a um critério de probabilidade de perda de dados. Neste trabalho, a banda efetiva é estimada de forma adaptativa, através dos parâmetros da modelagem multifractal βMWM (β-Multifractal Wavelet Mode). São realizadas simulações dos algoritmos propostos de alocação de blocos de recurso, considerando diferentes modelos de propagação com desvanecimento de multipercursos e com diferentes quantidades de usuários na rede. Os resultados das simulações são comparados com outros algoritmos apresentados na literatura, através de parâmetros, como: vazão de dados do sistema, taxa de perda de dados e índice de justiça. É proposta ainda, a utilização da predição da relação sinalruído (SNR - Signal-to-Noise Ratio) dos usuários nos algoritmos de escalonamento, utilizando filtro de predição linear de multi-passos, tendo em vista o atraso no recebimento da informação da qualidade do canal dos usuários na estação base e a variação das condições de propagação do sinal. O filtro de predição de multi-passos é utilizado junto com os algoritmos de alocação de blocos de recurso propostos neste trabalho, para estimar a relação sinal-ruído dos usuários e definir, assim, os esquemas de modulação e código a serem utilizados na rede LTE.

Les précipitations ont une très grande variabilité sur une large gamme d'échelles tant spatiale que temporelle. Cette variabilité est une source importante d'incertitude pour la mesure, les applications et la modélisation, et au-delà pour la simulation et la prévision. De plus, les précipitations sont des processus extrêmement intermittents et possèdent plusieurs régimes d’invariance d’échelle. Le générateur de champ précipitant développé au cours de la thèse est basé sur la modélisation statistique de l’hétérogénéité et de l’intermittence des précipitations à fine échelle. L’originalité de la modélisation repose en partie sur l’analyse de données observées par un disdromètre à très fine résolution. Cette modélisation qui diffère des modèles existants dont la résolution est plutôt de l’ordre de la minute, voire de l’heure ou du jour, permet d’obtenir des simulations dont les propriétés sont réalistes sur une large gamme d’échelle. Ce simulateur permet de produire des séries chronologiques dont les caractéristiques statistiques sont similaires aux observations aussi bien à l’échelle de simulation (15s) qu’après dégradation (1h et 1 jour). Les propriétés multi-échelles du simulateur sont obtenues grâce à une approche hybride qui repose sur une simulation à fine échelle des évènements de pluie par un générateur multifractal associé à une simulation du support basée sur une hypothèse de type Poissonienne. Une étape de re-normalisation des taux de pluie assure l’adaptation du générateur à la zone climatique considérée.Le simulateur permet la génération de cartes 2D de lames d’eau. La méthodologie développée pour les séries chronologiques est étendue au cas 2D. Le simulateur stochastique multi-échelle 2D ainsi développé reproduit les caractéristiques géostatistiques et topologiques à la résolution de 1x1 km2. Ce générateur est utilisé dans le cadre d’une étude de faisabilité d’un nouveau système d’observation des précipitations en milieu urbain. Le principe de ce système repose sur l’utilisation de mesures opportunistes de l’affaiblissement subit par les ondes radios émises par les satellites géostationnaires TV-SAT dans la bande 10.7-12.7 GHz. De façon plus spécifique on suppose que les terminaux de réception TVSAT installés en ville chez les particuliers sont capables de mesurer de tels affaiblissements. A ce stade de l’étude nous ne disposons pas de telles observations. L’étude s’appuie donc sur des cartes de précipitations issues du générateur 2D et d’un réseau de capteur hypothétique. Le système d’observation envisagé permettra d’estimer les champs de précipitation (30x30 Km2) et avec une résolution spatiale de 0.5x0.5 Km2. / Precipitations are highly variable across a wide range of both spatial and temporal scales. This variability is a major source of uncertainty for the measurement and modeling, also for the simulation and prediction. Moreover, rainfall is an extremely intermittent process with multiple scale invariance regimes. The rain-field generator developed during the thesis is based on the fine-scale statistic modeling of rain by the mean of its heterogeneity and intermittency. The modeling originality partially rest on the analysis of fine-scale disdrometer data. This model differs from other existing models whose resolution is roughly a minute or even an hour or a day. It provides simulations with realistic properties across a wide range ofscales. This simulator produces time series with statistical characteristics almost identical to the observations both at the 15s resolution and, after degradation, at hourly or daily resolutions. The multi-scale properties of our simulator are obtained through a hybrid approach that relies on a fine scale simulation of rain events using a multifractal generator associated with a rain support simulation based on a Poissonian-type hypothesis. A final re-normalization step of the rain rate is added in order to adapt the generator to the relevant climate area. The simulator allows the generation of 2D water-sheets. The methodology developed in the first part is extended to the 2 Dimension case. The multi-scale 2D stochastic simulator thus developed can reproduce geostatistical and topological characteristics at the spatial resolution of 1x1 km2.This generator is used in the scope of the feasability study of a new observation system for urban area. The principle of this system is based on the opportunistic use of attenuation measurements provided by geostationary TV satellites which radio waves lay in the 10.7 to 12.7 GHz bandwidth. More specifically it is assumed that the SAT-TV reception terminals installed in private homes are able to measure such attenuations. At this stage of the study we do not have such observations. The study is therefore based on rainfall maps generated using the 2D generator in addition to a hypothetical sensor network. The considered observation system will allow to estimate precipitation fields (30 x 30 km2) with a spatial resolution of 0.5x0.5 km2.

Made available in DSpace on 2014-07-29T15:08:17Z (GMT). No. of bitstreams: 1 Dissertacao_mestrado_josemar.pdf: 1807801 bytes, checksum: b47a17ed3732deb7f34a3e310ec05477 (MD5) Previous issue date: 2011-09-29 / The multifractal modeling is more appropriate in describing some features finding in traffic flows in real networks than other models. This work investigates the behavior of the traffic modeling based policing algorithms found in the literature (Leaky Bucket, Fractal Leaky Bucket, Gaussian Multifractal Leaky Bucket) regarding the buffer utilization, the efficiency for the use of buffer efficiency in describing the accumulated traffic (envelope process), packet dropping and data loss (bytes). First, we compare the envelope process of the considered policing algorithms and the proposed algorithm MAPM (Multifractal Arrival Policing Mechanism), with traffic without policing. Next, it was calculated the system loss rate for a finity buffer system with and without policing algoritm. Using the deterministic Network Calculus, it is also estimated the average queue length (backlog) and delay of bytes by applying the concept of the Min-Plus algebra that presents some differences against the conventional algebra. The proposed policing algorithm was applied to a transmission system based on OFDM (Orthogonal Frequency - Division Multiplexing) / TDMA (Time Division Multiplexing Access) system, where it was evaluated the network performance of the considered policing algorithms. Simulations were carried out with real wireless network trace (Wi-Fi) and wired network trace in order to demonstrate the efficiency of the algorithm proposed in relation to policing algorithms in the literature. The simulations shown the efficiency of the MAPM policing algorithm with traces from wired and wireless networks. We also propose the use of deterministic Network Calculus associated to multifractal envelope process to analyze the traffic behavior in terms of delay and backlog before policing algorithms application in the network. Finally we present the results of buffer utilization, link utilization, delay and backlog to a WiMAX system where the policing algorithm MAPM in general shown delay and backlog increasing in the traffic compared with anothers algorithms and low link utilization / A modelagem multifractal tem se mostrado mais apropriada para descrever algumas características encontradas nos fluxos de tráfego de redes reais que outros modelos, tais como o modelo de Poisson e Markov. Este trabalho investiga o comportamento dos algoritmos de policiamento baseados em modelagem de tráfego (Balde Furado, Balde Furado Fractal, Balde Furado Multifractal Gaussiano) em relação à utilização do buffer, eficiência em descrever o tráfego acumulado (processo envelope) e descarte de pacotes e perda de dados (bytes). Primeiramente, compara-se o processo envelope dos algoritmos de policiamento considerados e do algoritmo proposto neste trabalho, o MAPM (Multifractal Arrival Policing Mechanism), com o tráfego sem policiamento. Em seguida, a taxa de perda em um enlace simples com buffer finito com e sem algoritmo de policiamento é calculada. Utilizando o Cálculo de Rede Determinístico, estima-se o tamanho da fila (backlog) e retardo (delay) de bytes, conforme o conceito da álgebra Min-Plus. O algoritmo de policiamento proposto foi aplicado em um sistema de transmissão OFDM (Orthogonal Frequency - Division Multiplexing) / TDMA (Time Division Multiplexing Access) baseado no sistema WiMAX simplificado, onde se avaliou o desempenho da rede com os algoritmos de policiamento considerados. Realizam-se simulações com séries reais de tráfego de redes sem fio (Wi-Fi) e de redes com fio a fim de demonstrar a eficiência do algoritmo proposto em relação aos algoritmos de policiamento encontrados na literatura. As simulações realizadas evidenciam a eficiência do algoritmo MAPM em policiar séries reais de tráfego de redes com fio e redes sem fio. Propôs-se também, a utilização do Cálculo de Rede Determinístico associado ao processo envelope multifractal para se analisar o comportamento do tráfego em termos de retardo e backlog após a aplicação dos algoritmos de policiamento de rede. Por fim, são apresentados os resultados de retardo, backlog, utilização média do buffer e utilização do enlace para um sistema WiMAX onde o algoritmo de policiamento MAPM que apresentou em geral, acréscimo no retardo e backlog do tráfego em relação aos outros algoritmos e baixa utilização do enlace.