Les instabilités thermo-acoustiques causent des problèmes récurrents dans les chambres de combustion pour une large gamme d'applications industrielles, allant des chaudières domestiques aux turbines à gaz, en passant par les moteurs fusées. Ces phénomènes résultent d’un couplage résonant entre la dynamique de la combustion et les modes acoustiques du foyer, et peuvent donner lieu à de fortes vibrations, un vieillissement prématuré des composants de la chambre, voire des dommages structurels. Les mécanismes physiques mis en jeu sont complexes et difficiles à modéliser, ainsi les oscillations thermo-acoustiques ne sont pas facilement prévisibles au stade de la conception d’une chambre de combustion. Dans de nombreux foyers, des systèmes d’amortissement passifs sont installés pour augmenter la dissipation d’énergie acoustique et empêcher le développement de ces instabilités. Dans ce travail, des systèmes d’amortissement basés sur des plaques perforées couplées à une cavité résonante et traversées par un écoulement moyen sont analysés. Les principaux objectifs sont : (i) d’améliorer et de simplifier la conception de systèmes d’amortissement robustes en maximisant leurs propriétés d’absorption acoustique en régime linéaire, (ii) d’analyser l’effet de l’amplitude des ondes sonores incidentes sur la réponse acoustique des plaques perforées et (iii) de développer des modèles capables de reproduire cette réponse aux hautes amplitudes. Tout d’abord, deux régimes asymptotiques intéressants sont identifiés où le système fonctionne à faibles et forts nombres de Strouhal respectivement. Dans ces régimes la conception d’un système d’amortissement maximisant l’absorption acoustique est grandement simplifiée, puisque les calculs de la vitesse optimale de l’écoulement et de la taille de la cavité sont découplés. Il est démontré qu’à faible nombre de Strouhal le système se comporte comme un résonateur quart d’onde, et dispose d’une bande d’absorption très large. À fort nombre de Strouhal, le système fonctionne comme un résonateur de Helmholtz, comportant une cavité de taille plus réduite, mais une bande d’absorption beaucoup plus étroite que dans le régime précédent. Ces prévisions sont confirmées par des mesures réalisées dans les différents régimes identifiés sur un dispositif expérimental dédié. L’évolution des propriétés acoustiques d’une plaque perforée lorsque l’amplitude de forçage augmente est ensuite examinée par le biais de simulations directes. Il est montré que la transition du régime linéaire au régime non linéaire se produit lorsque l’amplitude de la vitesse acoustique dans l’orifice est comparable à la vitesse de l’écoulement moyen dans les trous. Pour des amplitudes élevées, une inversion périodique de l’écoulement est observée dans l’orifice. Des anneaux tourbillonnaires sont alternativement éjectés en amont et en aval de l’orifice à une vitesse de convection qui augmente avec l’amplitude de la perturbation acoustique. Ces mécanismes influencent profondément l’absorption acoustique des plaques perforées dans le régime non linéaire. Deux nouveaux modèles décrivant la réponse non linéaire de ces systèmes sont ensuite développés en exploitant la trajectoire des vortex (modèle VC), et une approche quasi-stationnaire (modèle IDF). Les prévisions de ces modèles sont confrontées à des mesures effectuées dans le tube à impédance et aux résultats de simulations directes. Les résultats obtenus au cours de ces travaux peuvent être utilisés pour guider la conception de systèmes d’absorption robustes, capables de fonctionner dans des environnements difficiles avec des niveaux sonores élevés, comme ceux rencontrés lors d’instabilités thermo-acoustiques. / Thermo-acoustic instabilities are of primary concern in combustion chambers for a wide range of industrial applications, from domestic boiler to gas turbines or rocket engines. They are the consequence of a resonant coupling between the flame dynamics and the acoustic modes of the combustor, and can result in strong vibrations, early aging of combustor components and structural damage. The physical mechanisms involved are complex and difficult to model, thus thermo-acoustic oscillations are not easily predictable at the design stage of a combustor. In many combustors, passive dampers are implemented to increase the acoustic energy dissipation of the system and to hinder detrimental flame-acoustics interactions. In the present work, passive damping systems based on perforated screens backed by a resonant cavity and traversed by a bias flow are investigated. The main objectives are: (i) to improve and simplify the design of these dampers by maximizing their acoustic absorption properties in the linear regime, (ii) to analyze the effect of the sound wave amplitude on the acoustic response of these systems and (iii) to develop models capable of capturing absorption at high oscillation amplitudes. First, two interesting asymptotic regimes are identified where the plate operates at low and high Strouhal numbers respectively. In these regimes the design of a damper maximizing absorption is greatly simplified, since the choice of the optimal bias flow velocity and back cavity size can be decoupled. It is shown that at low Strouhal numbers the damper behaves as a quarter-wave resonator, and features a wide absorption bandwidth. At high Strouhal numbers, the system operates as a Helmholtz resonator, featuring shorter optimal back cavity sizes but narrower absorption bandwidths. These predictions are compared to measurements in a dedicated experimental setup for the different operating regimes identified. The dependence of the acoustic properties of a perforated plate on the forcing amplitude is then examined by means of direct numerical simulations. It is shown that transition from linear to nonlinear regimes occurs when the acoustic velocity amplitude in the orifice is comparable to the mean bias flow velocity. At high amplitudes, periodic flow reversal is observed within the perforation, vortex rings are alternatively shed upstream and downstream of the hole and convected away at a velocity which is increasing with the forcing amplitude. These mechanisms greatly influence the acoustic absorption of the perforate in the nonlinear regime. Two novel models capturing this nonlinear response are then inferred based on an analysis of the vortex trajectory (VC model), and on a quasi-steady description of the flow (IDF model). Their predictions are finally compared to measurements conducted in an impedance tube, and to results from numerical simulations. The results obtained in this work can be used to ease the design of robust dampers capable of operating in harsh environments with high sound levels, such as those found during self-sustained thermo-acoustic instabilities.

La conception d’un moteur thermoacoustique dépend de façon critique de la fiabilité des outils de prédiction théorique de ses performances. Une tentative pour réussir cette prédiction consiste à exploiter les coefficients de la matrice de transfert du noyau thermoacoustique (NTA) dans les modèles analytiques du moteur considéré. La matrice de transfert peut être obtenue soit par modélisation analytique, soit par des mesures acoustiques. Ce dernier cas, cependant, se présente comme une option intéressante pour éviter d’avoir à considérer la complexité des éléments constitutifs du NTA. La méthode analytique est tout d’abord présentée; elle ne vise que les cas de matériaux à géométrie simple. En ce qui concerne l’approche expérimentale, une méthode classique à deux charges est appliquée dans deux configurations différentes et, en outre, une méthode alternative basée sur des mesures d’impédance est développée ici et appliquée également. Une comparaison entre ces deux approches est évaluée au moyen d’une analyse de sensibilité. Différents matériaux sont testés, chacun jouant le rôle de l’élément poreux à l’intérieur d’un NTA soumis à plusieurs gradients de température. Seulement la méthode alternative s’avère performante pour tous les matériaux. Les matrices de transfert mesurées sont utilisées dans des modèles dédiés à prédire la fréquence de fonctionnement et le gain d’amplification thermoacoustique intrinsèque d’une machine équipée du NTA caractérisé au préalable. Une analyse comparative montre dans quelles conditions le seuil de déclenchement thermoacoustique est prévu ou non pour chaque matériau; elle révèle aussi les limites dimensionnelles de l’appareil expérimental pour mieux répondre aux estimations de performances. / The design of a thermoacoustic (TA) engine is improved towards the reliability of its performance prediction. An attempt to succeed in this prediction comes from the knowledge of the TA core (TAC) transfer matrix, which can be exploited in analytical models for the given engine. The transfer (T) matrix itself may be obtained either by analytical modeling or acoustic measurements. The latter consist in an interesting option to avoid thermo-physical or geometrical considerations of complex structures, as the TAC is treated as a black box. However, before proceeding with the experimental approach, an analytical solution is presented for comparison purposes, but it contemplates only cases of materials of simple geometry. Concerning the experimental approach, a classical two-load method is applied in two different configurations and an alternative method based on impedance measurements is here developed and applied. A comparison between these approaches is evaluated by means of a sensitivity analysis. Different materials are tested, each one playing the porous element allotted inside the TAC, which is in its turn submitted to several different regimes of steady state temperature gradient. The alternative method is the only one successful for all materials. In this manner, the measured transfer matrices are applied into a proper modeling devoted to predict both the operating frequency and the intrinsic TA amplification gain. A comparative analysis shows in what conditions the TA threshold is expected or not for each material; it also reveals the limitations of the experimental apparatus in what concerns the appropriate dimensions to better fit the performance investigations.

Na prática clínica, nota-se uma dificuldade em identificar a rigidez do sistema tímpano-ossicular decorrente da Otosclerose por meio dos métodos de avaliação rotineiramente empregados. Assim, as medidas de imitância acústica de banda larga podem fornecer mais informações sobre a condição do sistema tímpano-ossicular por avaliarem uma ampla faixa de frequência. O objetivo do estudo foi caracterizar as medidas de imitância acústica de banda larga com os estímulos tom puro e chirp em indivíduos com diagnóstico de Otosclerose submetidos à estapedectomia ou estapedotomia. Foram avaliados 40 indivíduos na faixa etária de 33 a 80 anos, totalizando 54 orelhas operadas e 22 orelhas não operadas. A avaliação audiológica foi realizada por meio da otoscopia, audiometria tonal liminar, logoaudiometria e imitanciometria. As medidas de imitância acústica de banda larga foram obtidas por meio do sistema de medidas Middle-Ear Power Analyzer MEPA3, versão 5.0 (Mimosa Acoustics), utilizando os estímulos tom puro e chirp. Os dados obtidos foram submetidos à análise estatística descritiva e inferencial, com nível de significância de 0,05. As orelhas com Otosclerose apresentaram maior absorvância em 750 Hz, uma tênue diminuição até 3000 Hz, acentuando-se a partir desta frequência. A magnitude da admitância foi maior na faixa de frequência de 1992 a 4008 Hz, assim como a magnitude da impedância foi maior nas frequências baixas com diminuição até 4008 Hz e aumento em 6000 Hz. Estas orelhas foram dominadas pela rigidez nos sons graves e médios, por resistência entre 3000 e 4008 Hz e a partir desta frequência pela massa. A fase da impedância foi maior em 258 Hz e o delay da reflectância (slope) apresentou uma variação de comportamento entre as frequências, não sendo possível caracterizar um padrão de resposta. Conclui-se que há diferenças nas medidas obtidas nas orelhas com Otosclerose submetidas à cirurgia, quando analisadas as frequências baixas e médias, o que demonstra o impacto positivo da intervenção cirúrgica na funcionalidade do sistema tímpano-ossicular. / In clinical practice, there is a difficulty in identifying the rigidity of the tympano-ossicular system resulting from Otosclerosis through the routinely employed evaluation methods. Thus, wideband acoustic immitance measurements can provide more information on the condition of the tympanic-ossicle system by evaluating a wide frequency range. This study aimed at characterizing the wideband acoustic immitance measurements with the pure tone and chirp stimuli in individuals diagnosed with Otosclerosis submitted to stapedectomy or stapedotomy. Forty individuals aged 33 to 80 years were evaluated, totaling 54 operated and 22 non-operated ears. Audiology assessment was performed through otoscopy, pure-tone audiometry, logoaudiometry and imitanciometry. Wideband acoustic immitance measurements were obtained using the Middle-Ear Power Analyzer (MEPA3), version 5.0 (Mimosa Acoustics), by means of pure tone and chirp stimuli. Data were submitted to descriptive and inferential statistical analysis, with a significance level of 0.05. The ears with Otosclerosis presented a greater absorbance in 750 Hz, a slight diminution until 3000 Hz, being accentuated from this frequency. The admittance magnitude was higher in the frequency range from 1992 to 4008 Hz, as well as the impedance magnitude was higher in the low frequencies with a decrease up to 4008 Hz and an increase in 6000 Hz. These ears were dominated by rigidity in the low and medium sounds, by resistance between 3000 and 4008 Hz, and from this frequency, by the mass. The impedance phase was higher at 258 Hz and the reflectance delay (slope) showed a behavioral variation between the frequencies, a response not being characterized. It can be concluded that there are differences in the measurements obtained in Otosclerosis ears submitted to surgery, when the low and medium frequencies were analyzed, which demonstrates the positive impact of the surgical intervention on the tympano-ossicle system.

Orientadores: Maria Francisca Colella dos Santos, Sergio Tadeu Martins Marba / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciencias Medicas / Made available in DSpace on 2018-08-15T13:54:09Z (GMT). No. of bitstreams: 1 Tazinazzio_TatianaGuilhermino_M.pdf: 808223 bytes, checksum: a6dc55813f9697cacf282acb5759a681 (MD5) Previous issue date: 2010 / Resumo: Objetivo: Analisar os resultados encontrados na imitanciometria com tons de sonda de 226 e 1.000Hz em neonatos sem indicadores de risco para perda auditiva (IRPA) e correlaciona-los com as Emissões Otoacústicas Transitórias (EOAT), além de estudar o reflexo acústico com tom de sonda de 226Hz. Métodos: Foram avaliados 52 neonatos a termo, 27 do sexo masculino e 25 do feminino, com faixa etária de 11 a 51 dias de vida. Foram realizadas anamnese, meatoscopia, EOAT, Timpanometria com tons de sonda de 226 e 1000Hz e pesquisa do Reflexo Acústico Ipsilateral. Resultados: Os dados foram analisados independentes de sexo e orelha. Em relação à EOAT, 78,8% estavam presentes. As curvas timpanométricas encontradas com tom de sonda de 226 Hz foram: A (55,8%), D (40,4%), Ar (1,0%), B (2,9%); já com tom de sonda de 1000 Hz encontramos: A (74%), D(1%), B (14,4%) e Bloqueada (10,6%). O reflexo acústico ipsilateral com tom de sonda de 226 Hz estava presente na maioria dos neonatos sem IRPA. Conclusões: Uma relação estatisticamente significante foi encontrada quando comparamos as curvas timpanométricas do tipo A e D (com tom de sonda de 226Hz). E quando comparamos a sonda tipo A e a bloqueada (sonda de 1.000Hz) com a curva tipo B e as relacionarmos com a EOAT foi também estatisticamente significante. Além disso, verificamos uma maior detecção de alteração de orelha média quando a imitanciometria foi realizada com tom de sonda de 1000Hz, do que com a realizada com a de 226Hz. A curva timpanométrica usando a sonda de 1.000Hz mostrou ser mais adequada para detecção de alterações da orelha média que a sonda de 226Hz / Abstract: Objective: To assess the results found in Immittance measurements using 226Hz and 1000Hz in neonates without Hearing Loss Risks Indicators (HLRI) and to correlate them to Transient Evoked Otoacoustic Emissions (EOAT) and also to study Acoustic Reflex using 226Hz probe tones. Methods: Assessments of 52 full - term neonates, being 27 males and 25 females on an age group from 11 to 51 days of life. Anamnese, Meatoscopy, EOAT, Tympanometry using 226 and 1000 probe tones and Ipsilateral Acoustic Reflex Research were performed. Results: Data were analyzed regardless gender and ears. In relation to EOAT (78,8%) were present. Tympanometric curves using 226Hz probe tone found were: A ( 55,8%), D (40,4%) and Ar (1,0%), B (2,9%); and the ones found using 1000Hz probe tone were: A (74%), D (1%), B (14,4%) and Blocked (10,6%). According to p-value, there has been a relation among Tympanometric and general reproductivity. On the sample, 81,7% of the ears indicated presence of Acoustic Reflex. Conclusions: A significant statistically relation was found when it was compared Tympanometric curves types A and D using 226Hz. When it was compared the probe tones types A and blocked (using 1000Hz) to tympanometric curves type B, they were related to the EOAT emissions, which were also statistically significant. Besides, it was also verified a greater detection of changes on middle ear when the immitanciometry was performed using 1000Hz probe tone than the one performed using 226Hz probe tone. Tympanometric curve using 1000Hz probe tone showed to be more adequated for the detection of changes of middle ear than 226Hz probe tone / Mestrado / Saude da Criança e do Adolescente / Mestre em Saude da Criança e do Adolescente

Indivíduos com audição normal entre 250 e 8.000 Hz podem apresentar zumbido. Além da avaliação audiológica convencional, a audiometria de altas freqüências tem sido aplicada nestes casos. O objetivo desta pesquisa foi avaliar os limiares de audibilidade nas altas freqüências em indivíduos com audição normal entre 250 e 8.000 Hz com e sem queixa de zumbido. A pesquisa foi realizada em 33 indivíduos com zumbido e 33 sem zumbido. Houve piora estatisticamente significante entre os limiares de audibilidade dos indivíduos com zumbido em relação aos indivíduos sem zumbido para as seguintes freqüências: 9.000, 10.000, 12.500, 14.000, 16.000, 18.000 e 20.000 Hz / Subjects with normal hearing between 250 and 8.000 Hz may show tinnitus. Beyond the conventional audiological evaluation, the high frequency audiometry has been applied in these cases. The research's goal was to evaluate the audibility thresholds in high frequencies in subjects with normal hearing between 250 and 8.000 Hz with and with no tinnitus complaint. The research was carried through in 33 individuals with tinnitus and 33 with no tinnitus. A significant statistical worsening occurred between hearing thresholds of subjects with tinnitus with relation to subjects with no tinnitus for the following frequencies: 9.000, 10.000, 12.500, 14.000, 16.000, 18.000 and 20.000 Hz

Orientadores: José Roberto de França Arruda, Pierrick Lotton, Guillaume Penelet / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-24T19:14:04Z (GMT). No. of bitstreams: 1 Bannwart_FlaviodeCampos_D.pdf: 33288736 bytes, checksum: 8166e34982ed775a474e0817a4157baf (MD5) Previous issue date: 2014 / Resumo: O projeto de um motor termoacústico (TA) se torna viabilizado à medida da con?abilidade de sua previsão de desempenho. Uma tentativa para o êxito nessa previsão vem do conhecimento da matriz de transferência do núcleo termoacústico (NTA), que pode ser explorada em modelos analíticos para o motor considerado. A matriz de transferência por si só pode ser obtida ou por modelagem analítica ou medições acústicas. As últimas, no entanto, consistem em uma opção interessante para se evitar considerações termo-físicas ou geométricas de estruturas complexas, uma vez que o NTA é tratado como uma caixa preta. No entanto, antes de se prosseguir com a abordagem experimental, uma solução analítica é apresentada, apenas para ?ns de comparação, mas que contempla somente os casos de materiais de geometria simples, tal como um catalisador de cerâmica, por exemplo. Em relação à abordagem experimental, três diferentes métodos são apresentados. Um método clássico de duas cargas é aplicado em duas con?gurações distintas e, além disso, um método alternativo com base em medições de impedância é aqui desenvolvido e aplicado. Uma comparação entre estas três abordagens é realizada por meio de uma avaliação de performance experimental e também por uma análise de sensibilidade, de modo a se conhecer as perspectivas de viabilidade de cada método. Quatro diferentes materiais são testados, cada um sendo usado como o elemento poroso colocado no interior do NTA, que é por sua vez submetido a diferentes regimes de gradiente de temperatura. Estes materiais são escolhidos de tal maneira a cobrir uma vasta gama de porosidades compreendidas entre esperados stack puro e regenerador puro. O método alternativo foi bem sucedido no seu objectivo para todos os materiais, ao contrário do método clássico de duas cargas. Desta forma, as matrizes de transferência medidas são aplicadas em uma modelagem dedicada a prever tanto a frequência operacional como o ganho de ampli?ca- ção TA intrínseca. Tais parâmetros são otimizados em simulações para dois modelos de motores TA básicos, um de onda estacionária e outro progressiva, variando-se parâmetros geométricos dos componentes anexos ao NTA. Uma análise comparativa mostra em que condições o limiar TA é esperado ou não para cada material, e também revela as limitações do aparato experimental no que se refere às dimensões adequadas para melhor se ajustarem às investigações de desempenho / Abstract: The design of a thermoacoustic (TA) engine is improved towards the reliability of its performance prediction. An attempt to succeed in this prediction comes from the knowledge of the TA core (TAC) transfer matrix, which can be exploited in analytical models for the given engine. The transfer (T) matrix itself may be obtained either by analytical modeling or acoustic measurements. The latter consist in an interesting option to avoid thermo-physical or geometrical considerations of complex structures, as the TAC is treated as a black box. However, before proceeding with the experimental approach, an analytical solution is presented for comparison purposes, but it contemplates only cases of materials of simple geometry such as a ceramic catalyst. Concerning the experimental approach, three different methods are put forward. A classical two-load method is applied in two different con?gurations and an alternative method based on impedance measurements is here developed and applied. A comparison between these approaches is evaluated by means of a sensitivity analysis, in order to investigate the feasibility of each method in further explorations. Four different materials are tested, each one playing the porous element allotted inside the TAC, which is in its turn submitted to several different regimes of steady state temperature gradient. These materials are chosen in such a way as to cover the wide range of porosities comprised between expected pure stack and pure regenerator. The alternative method succeeds on its purpose for all materials, contrarily to the classical two-load method. In this manner, the measured transfer matrices are applied into a proper modeling devoted to predict both the operating frequency and the intrinsic TA ampli?cation gain. Such parameters are optimized for two basic TA engine models, either standing or traveling-wave con?guration, by searching for the corresponding geometrical parameters of the TAC surrounding components. A comparative analysis shows in what conditions the TA threshold is expected or not for each material, but it also reveals the limitations of the experimental apparatus in what concerns the appropriate dimensions to better ?t the performance investigations / Doutorado / Mecanica dos Sólidos e Projeto Mecanico / Doutor em Engenharia Mecânica

Orientadores: Emilson Pereira Leite, Alexandre Campane Vidal / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociências / Made available in DSpace on 2018-08-20T11:46:52Z (GMT). No. of bitstreams: 1 Acquaviva_LeticiadeAvila_M.pdf: 3409962 bytes, checksum: cb41ac297ccc22f2e5e7c89007df133f (MD5) Previous issue date: 2011 / Resumo: Os substratos que constituem um reservatório são identificados com a utilização de dados sísmicos. O processo consiste na determinação de propriedades petrofísicas dos reservatórios. Entretanto, camadas de estruturas subsísmica são mascaradas devido à limitação do dado sísmico convencional. A falha proporcionada por esses dados produz um modelo comprometido para o reservatório. A falta de resolução vertical do dado sísmico pode ser superada através da integração do mesmo com todas as informações disponíveis do reservatório (Sancevero, 2006). A maneira mais efetiva de reunir esses dados encontra-se na geração de modelos de impedância acústica originados do processo de inversão. Como foco principal, foi produzido um algoritmo de inversão sísmica para impedância acústica, manuseado com o software MATLAB. Nesse algoritmo, o dado sísmico foi modelado como sendo a convolução da resposta refletiva do meio com o pulso sísmico sonoro, conhecido como wavelet. A assinatura do pulso sonoro faz com que o dado sísmico seja de banda limitada no domínio da frequência. O método proposto permite acrescentar nos dados sísmicos valores de baixas frequências providos de dados de perfis de poços. Tal método também permite analisar o impacto da extração da wavelet por meio da amarração sísmica-poço, bem como o valor limite de frequências utilizadas do dado de poço. O algoritmo foi aplicado em dados do Campo de Namorado da bacia de Campos, Brasil. Os resultados mostram dados de impedância acústica com banda de frequências mais larga que o dado sísmico e, portanto, imagens com maior resolução e com conteúdo petrofísico do reservatório / Abstract: The substrates that constitute a reservoir are identified using seismic data. The process consists of determining reservoir petrophysical properties. However, sub-seismic layers structures are masked due to the limitation of conventional seismic data. The failure provided by these data produces an erroneous model of reservoir. The lack of vertical resolution of seismic data can be overcome by integrating it with all available information from the reservoir (Sancevero, 2006). The most effective way to gather such data lies in the generation of acoustic impedance models derived from seismic inversion methods. As a main focus an inversion algorithm for seismic acoustic impedance have been produced, handled with MATLAB software. In this algorithm, the seismic data have been modeled as the convolution of the reflective response of the medium with the wavelet noise known as wavelet. The signature of the sound pulse makes the seismic data be a limited bandwidth in the frequency domain. The proposed method allows add low-frequencies data from well logs into seismic data. This method also analyzes the impact of the wavelet extraction through the well-seismic tie, and the limit of frequencies used from well data. The model was applied on data from the Namorado Field of the Campos Basin, Brazil. The results show the acoustic impedance data with a frequencies band wider than the seismic data and, therefore, images with higher resolution and with petrophysical content reservoir / Mestrado / Reservatórios e Gestão / Mestre em Ciências e Engenharia de Petróleo

Orientador: Jose Maria Campos dos Santos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-07-25T19:56:09Z (GMT). No. of bitstreams: 1 Nunes_RonaldoFernandes_M.pdf: 5604429 bytes, checksum: 3e2d42b8a7421a42a727f76195057b6e (MD5) Previous issue date: 1999 / Resumo: Neste trabalho foi estudado o controle ativo de ruído em dutos usando técnicas de filtragem adaptativa. Foi utilizado o método de controle adaptativo do Mínimo Erro Médio Quadrático (Least Mean Square - LMS) normalizado com sinal de referência filtrado, NFXLMS. Três geometrias de dutos montados em uma bancada experimental para os casos de controle monocanal, multierro e multiexcitação foram verificados. Os sinais de perturbação investigados foram: tonal (seno), aleatório e uma com composição de duas senoidais no caso multiexcitação. Avaliações das impedâncias analíticas e experimentais foram verificadas no estudo de uma configuração do duto para o caso de controle monocanal. Simulações e experimentos foram realizados para diversas geometrias de dutos e diferentes tipos de excitação. Parâmetros do algoritmo, como o número de pesos do filtro adaptativo, faixa de frequência de perturbação, fator de convergência do algoritmo e freqüência de amostragem foram investigados nos casos tratados. Os resultados encontrados nos experimentos realizados para o controlador monocanal e multierro confirmaram as avaliações efetuadas nas simulações. Para o caso multiexcitação, limitações da placa de processamento de sinal não permitiram a obtenção de resultados conclusivos / Abstract: In this work was investigated the active control of noise in ducts using the techniques of adaptive filtering. The normalized, filtered reference Least Mean Square algorithm control method - NXLMS was used. Three shapes of duct system in a supported experimental test rig for the cases of control mono-channel, multi-error, and multi-input were verified. The investigated disturbance signals were: tonal (sine), random, and a composition of two sinusoids for the case of multi-input. Evaluations of analytical and experimental impedances were verified in a configuration study of mono-channel duct contraI case. Simulations and experiments were accomplished for several duct shapes and different types of excitations. AIgorithm parameters, such as the weight number of adaptive filter, the disturbance frequency range, the convergence factor of the algorithm, and the sampling frequency were investigated in the treated cases. The experimental results obtained for the mono-channel and multi-error controller confirm the evaluations obtained in the simulations. For the multi-input case, limitations of the DSP board didn't allow to obtain conclusive results / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

No

No / A novel technique for the laboratory characterization of the frequency-dependent acoustic surface admittance of partly saturated samples of sands is presented. The technique is based on a standard laboratory de-watering apparatus coupled with a standard acoustic impedance tube. The dependence of the surface admittance on the degree of water saturation is investigated for two samples of sand with widely different flow resistivities. It is shown that a relatively small change (e.g., from 0% to 11% by volume) in the degree of water saturation can result in a much larger change (e.g., twofold) in the acoustic surface admittance. An empirical relationship is found between the peaks observed in the real part of admittance spectra for the low flow resistivity sand and the degree of water saturation. The data are compared with predictions of two widely used ground impedance models: a semiempirical single parameter model and a two parameter model. A modified two-parameter version of a single-parameter model is found to give comparable fit to the two-parameter model. However, neither model provides an accurate fit.