Hydraulic fracturing is essential for producing gas and oil at an economic rate from low permeability sands. Most fracturing treatments use water and polymers with a gelling agent as a fracturing fluid. The water is held in the small pore spaces by capillary pressure and is not recovered when drawdown pressures are low. The un-recovered water leaves a water saturated zone around the fracture face that stops the flow of gas into the fracture. This is a particularly acute problem in low permeability formations where capillary pressures are high. Depletion (lower reservoir pressures) causes a limitation on the drawdown pressure that can be applied. A hydraulic fracturing process can be energized by the addition of a compressible, sometimes soluble, gas phase into the treatment fluid. When the well is produced, the energized fluid expands and gas comes out of solution. Energizing the fluid creates high gas saturation in the invaded zone, thereby facilitating gas flowback. A new compositional hydraulic fracturing model has been created (EFRAC). This is the first model to include changes in composition, temperature, and phase behavior of the fluid inside the fracture. An equation of state is used to evaluate the phase behavior of the fluid. These compositional effects are coupled with the fluid rheology, proppant transport, and mechanics of fracture growth to create a general model for fracture creation when energized fluids are used. In addition to the fracture propagation model, we have also introduced another new model for hydraulically fractured well productivity. This is the first and only model that takes into account both finite fracture conductivity and damage in the invaded zone in a simple analytical way. EFRAC was successfully used to simulate several fracture treatments in a gas field in South Texas. Based on production estimates, energized fluids may be required when drawdown pressures are smaller than the capillary forces in the formation. For this field, the minimum CO2 gas quality (volume % of gas) recommended is 30% for moderate differences between fracture and reservoir pressures (2900 psi reservoir, 5300 psi fracture). The minimum quality is reduced to 20% when the difference between pressures is larger, resulting in additional gas expansion in the invaded zone. Inlet fluid temperature, flowrate, and base viscosity did not have a large impact on fracture production. Finally, every stage of the fracturing treatment should be energized with a gas component to ensure high gas saturation in the invaded zone. A second, more general, sensitivity study was conducted. Simulations show that CO2 outperforms N2 as a fluid component because it has higher solubility in water at fracturing temperatures and pressures. In fact, all gas components with higher solubility in water will increase the fluid’s ability to reduce damage in the invaded zone. Adding methanol to the fracturing solution can increase the solubility of CO2. N2 should only be used if the gas leaks-off either during the creation of the fracture or during closure, resulting in gas going into the invaded zone. Experimental data is needed to determine if the gas phase leaks-off during the creation of the fracture. Simulations show that the bubbles in a fluid traveling across the face of a porous medium are not likely to attach to the surface of the rock, the filter cake, or penetrate far into the porous medium. In summary, this research has created the first compositional fracturing simulator, a useful tool to aid in energized fracture design. We have made several important and original conclusions about the best practices when using energized fluids in tight gas sands. The models and tools presented here may be used in the future to predict behavior of any multi-phase or multi-component fracturing fluid system. / text

En transports guidés, la localisation précise des trains s’avère vitale pour une exploitation nominale du système de transport. Dans un environnement de propagation tel que celui d’une emprise ferroviaire, un capteur de localisation efficace est complexe à concevoir et à valider lorsqu’il doit opérer en présence de nombreux obstacles fixes et mobiles constitués par l’infrastructure et les trains. Afin de concevoir un tel capteur, nous proposons dans ce travail de thèse l’emploi de techniques innovantes dites de diversité spectrale que l’on retrouve également sous la dénomination de radio Ultra Large Bande (ULB). Dans ce travail, cette dernière est également associée à la technique de Retournement Temporel (RT) afin de tirer partie de cet environnement de propagation complexe. L’objectif visé est d’obtenir une localisation fiable et robuste des véhicules ferroviaires par focalisation de signaux ULB en direction des antennes sol ou trains. Des études théoriques alliées à des simulations ont été effectuées portant sur les propriétés de focalisation d’énergie de la technique de retournement temporel en tenant compte de plusieurs paramètres liés aux configurations antennaires, aux canaux de propagation rencontrés et à l’électronique utilisée. L’apport du retournement temporel sur la précision du système de localisation Ultra Large Bande a été quantifié en comparant le système de localisation ULB conventionnel, sans retournement temporel puis, en associant le RT. Les résultats théoriques et de simulations de la solution proposée ont été validés par des expérimentations menées en chambre anéchoïque ainsi qu’en environnement indoor. / In guided transport, the precise location of trains is vital for nominal operation of the transport system. In a propagation environment such as a railway line, an effective location sensor is complex to design and validate since it must operate in the presence of many fixed and mobile obstacles constituted by the infrastructure and the trains. In this thesis, to design such a sensor, we propose the use of so-called spectral diversity techniques also found under the name of Ultra Wideband radio (UWB). In this work, the latter is also associated with the Time Reversal (TR) technique to take advantage of the complex propagation environment. The objective is to obtain a reliable and robust location of rail vehicles by focusing UWB signals to antennas or ground trains. Theoretical studies combined with simulations were performed on the properties of energy focusing of TR technique taking into account several parameters related to antennal configurations, propagation channels and the railway environment. The contribution of TR on the accuracy of the positioning system was quantified by comparing the conventional UWB positioning system alone and then, combining it with TR. The theoretical results and simulations of the proposed solution have been validated by experiments carried out in an anechoic chamber and in indoor environment.

Αντικείμενο της παρούσας διπλωματικής εργασίας είναι η μελέτη των μεθόδων βελτιστοποίησης της ποιότητας των παρεχομένων υπηρεσιών των δικτύων κυτταρικής τηλεφωνίας τρίτης γενιάς σε διαλειπτικό περιβάλλον. Αρχικά γίνεται μια σύντομη ιστορική αναδρομή στην εξέλιξη των συστημάτων κινητών επικοινωνιών και παρουσιάζεται το σημαντικότερο πρότυπο τρίτης γενιάς, το UMTS και τα ιδιαίτερα τεχνικά χαρακτηριστικά του. Στην συνέχεια αναλύεται το LTE το οποίο αποτελεί την τελευταία εξέλιξη των δικτύων τρίτης γενιάς και αναμένεται να αντικαταστήσει το UMTS στο άμεσο μέλλον αποτελώντας στην πραγματικότητα τον πρόδρομο των συστημάτων τέταρτης γενιάς. Στην συνέχεια εστιάζουμε στα διαλειπτικά κανάλια αναλύοντας τα φαινόμενα που παρατηρούνται σε αυτά και τα στατιστικά μοντέλα μέσα από τα οποία περιγράφονται. Παράλληλα διερευνάται η επίδραση των φαινομένων αυτών (θετική ή αρνητική) στο QoS των δικτύων τρίτης γενιάς βάσει των χαρακτηριστικών τους (όπως παρουσιάστηκαν στο κεφάλαιο 1) και οι δυνατότητες για περαιτέρω βελτιστοποίηση κατα τον σχεδιασμό των δικτύων και την σωστή εκμετάλλευση των χαρακτηριστικών του περιβάλλοντος όδευσης. Ιδιαίτερη αναφορά γίνεται στα μοντέλα εσωτερικού χώρου λόγω του μεγάλου φορτίου κίνησης που καλούνται να εξυπηρετήσουν. Στο τελευταίο μέρος παρουσιάζεται η διαδικασία παραμετροποίησης κάποιων σημαντικών μοντέλων και τα αποτελέσματα των εξομοιώσεων που έγιναν στον χώρο του κτηρίου των Ηλεκτρολόγων Μηχανικών. / The subject of this diploma thesis is the study of the optimization techniques of the quality of service for third generation cellular telephony networks in fading enviroment. After a short presentation of the evolution of the systems of wireless telecommunications, it is discussed UMTS the most important third generation system which dominated the european market and its technical features. LTE is also introduced, the system which is expected to replace UMTS in the near future while being the predecessor of the fourth generation systems. Then we focus on the fading channels analysing the phenomena wich are related to them and analysing the statistical models that describe them. It is also studied the effect (positive or negative) of these phenomena on the QoS of the third generation networks and the optimization methods which can be applied during the network designing process with special reference to the indoor propagation models because of the big amount of traffic load that they are asked to serve. At the last chapter of the thesis there is a presentation of the parameter setting procedure for some important models and the outcomes of the simulation that took place in the building of Electronic Engineering.

[pt] Neste trabalho, um - software - foi desenvolvido para prover predições do sinal em ambientes exteriores e interiores. O programa inclui dois diferentes modelos de propagação. Para situações urbanas com antenas baixas (Microcélulas) e para situações urbanas onde o receptor pode ser posicionado numa área - indoor - e o transmissor numa área urbana ( - outdoor -). O procedimento automatizado combina técnicas de várias diferentes disciplinas, incluindo computação gráfica e teoria eletromagnética assintótica, para reduzir o tempo de computação sem comprometer a precisão. Usando técnicas de computação gráfica, o tempo necessário para o lançamento de raios através da geometria urbana é grandemente reduzido. Os dados teóricos foram testados e validados por comparação com dados experimentais. Para modelar os diferentes mecanismos de propagação, a aproximação eletromagnética usada foi a OG/UTD. / [en] In this work, a software tool has been developed that provides accurate, sitespecific radio signal predictions for outdoor to indoor/outdoor locations. The program includes two different propagation models. For urban calculations with low antennas (Microcells) and for urban situations where receiver can be located at indoor area and transmitter antennas can be located at Urban area (outdoor). The software combines techniques from several different disciplines, including computer graphics and asymptotic electromagnetic theory, to reduce the calculation time without compromising accuracy. Using computer graphics techniques, the time necessary for shooting the rays through the urban geometry is greatly reduced. The calculation engine used has been tested and validated by comparison with measured data. In order to model the diferent propagation mechanisms, the eletromagnetic approach considered has been the GO/UTD combination.

No description available.

Submitted by Carolina Neves (carolinapon@uefs.br) on 2016-08-09T01:01:22Z No. of bitstreams: 1 Karine_Souza_de_Almeida_Dissertacao_Final.pdf: 13569698 bytes, checksum: 81752dfa3be4ee9493654f5c61524c5a (MD5) / Made available in DSpace on 2016-08-09T01:01:22Z (GMT). No. of bitstreams: 1 Karine_Souza_de_Almeida_Dissertacao_Final.pdf: 13569698 bytes, checksum: 81752dfa3be4ee9493654f5c61524c5a (MD5) Previous issue date: 2016-05-24 / Funda??o de Amparo ? Pesquisa do Estado da Bahia - FAPEB / By using the Orthogonal Frequency Division Multiplexing (OFDM), it is possible to transmit by a channel a more robust signal and less susceptible to interferences. When such technique, based on orthogonal subcarriers, is combined with the use of propagation models, which are relevant tools for simulating the signal behavior in respect to environmental parameters and antenna configurations, it is feasible to have an evaluation about the performance of these systems, improving their project phase. Therefore, this work presents the use of OFDM technique applied to two propagation models: a two-ray geometric model and a microcellular model adapted to the Paulista Avenue, S?o Paulo, SP, having as objective the analysis of a mobile communication system through Bit Error Rate (BER). In the developed application using the MAtrix LABoratory (MATLAB) software, the mobile communication system based on OFDM admits several scenarios during the simulation, so that scenarios are related to positioning of the antennas, heights, type of modulation, size of the bit sequence to be sent, and others. The adopted OFDM architecture has been the IFFT/FFT and based on it, the system performs the transmission and reception of a bit set through a channel with interference by using different digital modulations, making appropriate comparisons. / Atrav?s da utiliza??o da t?cnica de Multiplexa??o por Divis?o de Frequ?ncias Ortogonais (OFDM, do ingl?s, Orthogonal Frequency Division Multiplexing), ? poss?vel transmitir por um canal um sinal mais robusto e menos propenso a interfer?ncias. Quando tal t?cnica, baseada na utiliza??o de subportadoras ortogonais, ? aliada ao uso de modelos de propaga??o, que s?o ferramentas relevantes para a simula??o do comportamento do sinal em rela??o aos par?metros do ambiente e as configura??es das antenas, ? poss?vel ter uma avalia??o a respeito do desempenho desses sistemas, melhorando a fase de projeto dos mesmos. Sendo assim, este trabalho apresenta o uso da t?cnica OFDM aplicada a dois modelos de propaga??o: um modelo geom?trico de dois raios e um modelo microcelular adaptado para a Avenida Paulista, S?o Paulo, SP, possuindo como objetivo a an?lise de um sistema de comunica??o m?vel atrav?s do c?lculo da Taxa de Erro de Bit (BER, do ingl?s, Bit Error Rate). Na aplica??o desenvolvida utilizando o software MATLAB (MATrix LABoratory), o sistema de comunica??o m?vel baseado em OFDM assume diversos cen?rios durante as simula??es, de forma que esses cen?rios s?o relacionados ao posicionamento das antenas, alturas, tipo de modula??o, tamanho da sequ?ncia de bits a ser enviada, entre outras. A arquitetura OFDM adotada foi a IFFT/FFT e baseado nela, o sistema realiza a transmiss?o e a recep??o de um conjunto de bits por um canal com interfer?ncias utilizando diferentes modula??es digitais, fazendo as devidas compara??es.

This paper deals with the propagation of waves. Here is the wavelength distribution according to the wavelength. It focuses on the UHF and SHF band in which IEEE802.11n operates. Contains model breakdown by cell type. Describes which propagation methods are dominant in the cell type. Several propagation patterns are presented, which are then modeled in Matlab environment.The models are then compared to experimental measurements.

The diploma thesis „Analysis and prediction of data traffic in mobile Ad Hoc network“ focuses on the radio propagation models of services in MANET (Mobile Ad-hoc) networks. It describes MANET networks and covers the theoretical analysis of routing protocols, radio wave propagation and propagation models of simulation enviroment NS-3 (Network Simulator 3). Furthermore, there is processed the creation process of model MANET networks with the routing protocol AODV (Ad Hoc On Demand Distance Vector) in the simulation environment NS-3. For analysis purposes there were implemented new functions to capture value of SNR (Signal to Noise Ratio) and throughtput. For this reason a physical layer of one of NS-3 model was modified. As an result there is a simulation build that compared several number of propagaion models.

Résumé : Tout comme l’aéronautique, l’industrie aérospatiale s’est tournée progressivement vers l’emploi des coques à base des matériaux composites. Cette transition a permis d’alléger considérablement les structures aéronautiques et aérospatiales, et par conséquent, a réduit la consommation de carburants ainsi que l’impact écologique des aéronefs et des lanceurs. Toutefois, la loi de masse stipule que cela ne peut être sans conséquence sur la perte par transmission acoustique des panneaux, surtout sur les basses fréquences. Que ce soit pour la conformité aux exigences des normes aéronautiques en terme de niveau de pression acoustique à l’intérieur des cabines ou la protection des charges utiles dans les coiffes des lanceurs, les traitements acoustiques ciblant les basses fréquences s’avèrent un défi d’envergure. En effet, avec des contraintes très strictes de minimum de masse et de volume ajoutés, il est difficile de traiter les problèmes d’absorption acoustique basses-fréquences, avec les traitements phoniques classiques. Afin de tirer avantage des effets résonants pour améliorer l’absorption sur les basses fréquences, ce projet se propose d’étudier l’intégration d’écrans résistifs à très faibles épaisseurs dans les revêtements acoustiques, tout en minimisant le poids. Il a été proposé dans le cadre de la chaire industrielle de recherche en aéroacoustique dont les principaux bailleurs de fonds sont Bombardier aerospace, Pratt & whitney et Bell helicopter. Aussi, des travaux de recherche connexes se sont déroulés en partenariat avec ULA (United Launch Alliance). Ce travail de maîtrise comporte une partie bibliographique qui présente une étude exhaustive des traitements basses-fréquences existants, tout en y portant un regard critique. La partie théorique met particulièrement l’emphase sur les différents modèles de propagation d’onde et les phénomènes de dissipations dans les milieux poreux. Dans cette partie, on dénombre également les différents types d’écrans ainsi que les modèles de propagation correspondants. Des critères permettant une étude comparative objective du point de vue masse/performance ont été proposés. En plus des paramètres non acoustiques, les conditions de montage et d’agencement des couches ont été étudiées avec des simulations numériques appuyées par des mesures expérimentales. Dans l’avant dernier chapitre, un modèle SEA (Statical Energy Analysis) d’une coiffe de lanceur a été construit avec tous ses détails à partir d’un exemple concret. Les simulations se sont terminées avec une étude comparative de la réduction de niveau de pression acoustique dans la coiffe. Le dernier chapitre résume les principaux résultats et conclusions de cette étude. / Abstract : Over the last few decades, the aerospace industry has witnessed a significant emergence of the use of composite shells. The latter are continuously replacing the metallic ones. This transition allowed a significant weight reduction of flying structures. Consequently, it substantially lessened the fuel consumption and mitigated the environmental footprint of aircrafts and space launch vehicles. However, evoking the mass law, this transition clearly cannot be without consequences on the acoustic transmission loss of fuselage panels. Neither can it be on payload fairings, especially over the low frequencies. Whether to meet with the standards and regulations in terms of acoustic pressure levels inside the pressurized cabins or to protect the payloads inside the launchers fairings, acoustic treatments design targeting the low frequencies seems to be a challenging issue. Indeed, with very stringent constraints in terms of added weight and volume, it is difficult to deal with the low frequencies noise and vibration, using passive monolayers. In order to take advantage of the resonant effects in enhancing low frequencies absorption, this work intends to investigate the integration of heavy treatments of very low thicknesses in acoustic coatings while minimizing weight. It was conducted within the frame work of the industrial research chair in aeroacoustics, whose main funders are : Bombardier Aerospace, Pratt & Whitney and Bell Helicopter. Also, other related researches were jointly carried out in partnership with ULA (United Launch Alliance). This master thesis includes a bibliographical section which consists of an overview of the existing low-frequencies solutions while keeping a critical eye on most of them. The following theoretical part focuses on the different models describing wave s’ propagation and dissipation phenomena in porous media. In the same section, we also list the different types of screens and the corresponding propagation models. Criteria for an objective comparative study in terms of weight versus performance were suggested. In addition to non-acoustic parameters, the layout and the mounting conditions of the acoustic packages were also investigated by means of numerical simulations, seconded by experimental measurements. In the penultimate chapter, an SEA detailed model of a launcher fairing was built based on data taken from a concrete example. The simulations ended with a comparative study of the sound pressure level reduction in the inner fairing cavity. The final chapter summarizes the main findings, conclusions and perspectives of this study.

Cette thèse porte sur l’étude théorique du transport d’un faisceau intense d’électrons relativistes dans une cible solide. Dans la première partie nous présentons les interprétations théoriques d’une partie des résultats d’une campagne d’expérience portant sur la production et le transport d’électrons relativistes dans une cible d’aluminium. Nous y démontrons la prédominance des e?ets collectifs sur les e?ets collisionels dans la première dizaine de microns de propagation grâce à des modèles de transports déjà existant au début de cette thèse. Ces modèles deviennent insu?sants dans le cas du transport de faisceau dans un isolant. Aussi, dans la deuxième partie, nous présentons un modèle de propagation du faisceau d’électrons relativistes dans un diélectrique incluant l’e?et de l’ionisation de la cible par le faisceau. Nous y quanti?ons les pertes d’énergies des électrons en fonction des paramètres du faisceau et du milieu environnant, et nous démontrons l’existence d’un régime de propagation pour lequel les électrons du plasma ne sont pas à l’équilibre thermodynamique local avec les ions. Ces résultats ont été comparés et con?rmés avec un code cinétique qui prend en compte l’ionisation par champ électrique et par collisions entre les électrons du plasma et les ions. Nous avons examiné la stabilité du faisceau et montré que ce dernier pouvait exciter deux types d’instabilités transverses sur des longueurs de propagation de l’ordre de 30 à 300 µm en fonction de la taille de la perturbation. / This PhD thesis is a theoretical study of high-current relativistic electron beam transport through solid targets. In the ?rst part, we present an interpretation of a part of experimental results of laser– produced electron beam transport in aluminium foil targets. We have estimated the fast electron beam characteristics and we demonstrated that the collective e?ects dominate the transport in the ?rst tens of µm of propagation. These quantitative estimates were done with the transport models already existing at the beginning of this thesis. These models are no longer su?cient in the case a fast electron beam propagation in insulator targets. Thus, in the second part, we have developed a propagation model of the beam that includes the e?ects of electric ?eld ionization and the collisional ionization by the plasma electrons. We present estimates of the electron energy loss induced by the target ionization, and we discuss its dependence on the beam and target parameters. In the case of a relatively low fast electron density, we demonstrated that the beam creates a plasma where the electons are not in a local thermodynamic equilibrium with ions. We have examined the beam stability and we demonstrated that transverse instabilities can be excited by the relativistic electron beam over the propagation distances of 30 - 300 µm depending on the perturbation wavelength.