Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Exploracionistas tem grande interesse em sistemas turbidíticos, pois em geral estes compõem prolíficos plays exploratórios. No entanto, estes potenciais reservatórios se encontram muitas vezes perto ou abaixo de resolução sísmica. Dessa forma, no processo de inversão, é importante integrar os dados sísmicos com qualidade de resolução obtida a partir do seu pré-condicionamento, para que o resultado final possua características detalhadas das camadas. O pré-condicionamento possibilita melhora na resolução dos dados sísmicos, através da atenuação dos ruídos aleatórios. Como objetivo final, foi realizada a inversão acústica em dados sísmicos post stack, migrados em tempo, a um sistema de turbiditos na Bacia de Campos. O principal objetivo da inversão sísmica é transformar o dado de reflexão em propriedades petrofísicas quantitativas. A inversão para impedância acústica é comumente utilizada para predição de porosidade. O fluxo de trabalho proposto foi dividido em cinco estágios principais: pré-condicionamento sísmico do dado 3D, correlação poço-sísmica, construção do modelo de baixa frequência, inversão do dado, e estimativa da porosidade. Os resultados mostraram que o cubo de impedância acústica invertido possui resolução muito superior quando comparado com o dado em amplitude sísmica, possibilitando melhor visualização das feições geológicas do Campo de Marlim. Além de suas limitações, como desconsiderando os efeitos das variações de fluido e variações litológicas complexas sobre a relação porosidade/impedância, o método fornece uma ferramenta confiável para exploração sísmica. Detalhes mais precisos das propriedades petrofísicas podem ser obtidos através de métodos de inversão mais sofisticados, a partir de dados pre stack. / Exploracionists has great interest in turbidite systems, since these generally comprise prolific exploration plays. However, these potential reservoirs are often near or below seismic resolution. Thus, the inversion process is important to integrate the seismic data quality of the resolution obtained from its preconditioning, so that the end result has detailed characteristics of the layers. The preconditioning enables improved resolution of seismic data, through mitigation of random noise. As the final goal, the inversion was performed acoustic post stack seismic data, migrated time, to a system of turbidites in Campos Basin. The main purpose of seismic inversion is to transform the given reflection in quantitative petrophysical properties. The inversion for acoustic impedance is commonly used to predict porosity. The flow of the proposed work was divided into five main stages: pre-conditioning the seismic 3D data, well-tie correlation, construction of the model of low frequency, inversion of data and estimation of porosity. The results showed that the inverted acoustic impedance cube has much higher resolution compared to the seismic amplitude data, allowing greater visualization of geological features in the Marlim Field. Besides its limitations as ignoring the effects of changing the fluid and complex lithological variations on the relationship porosity / impedance, the method provides a reliable tool for seismic exploration. More precise details of petrophysical properties can be obtainedthrough inversion methods starting from sophisticated pre-stack data.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Exploracionistas tem grande interesse em sistemas turbidíticos, pois em geral estes compõem prolíficos plays exploratórios. No entanto, estes potenciais reservatórios se encontram muitas vezes perto ou abaixo de resolução sísmica. Dessa forma, no processo de inversão, é importante integrar os dados sísmicos com qualidade de resolução obtida a partir do seu pré-condicionamento, para que o resultado final possua características detalhadas das camadas. O pré-condicionamento possibilita melhora na resolução dos dados sísmicos, através da atenuação dos ruídos aleatórios. Como objetivo final, foi realizada a inversão acústica em dados sísmicos post stack, migrados em tempo, a um sistema de turbiditos na Bacia de Campos. O principal objetivo da inversão sísmica é transformar o dado de reflexão em propriedades petrofísicas quantitativas. A inversão para impedância acústica é comumente utilizada para predição de porosidade. O fluxo de trabalho proposto foi dividido em cinco estágios principais: pré-condicionamento sísmico do dado 3D, correlação poço-sísmica, construção do modelo de baixa frequência, inversão do dado, e estimativa da porosidade. Os resultados mostraram que o cubo de impedância acústica invertido possui resolução muito superior quando comparado com o dado em amplitude sísmica, possibilitando melhor visualização das feições geológicas do Campo de Marlim. Além de suas limitações, como desconsiderando os efeitos das variações de fluido e variações litológicas complexas sobre a relação porosidade/impedância, o método fornece uma ferramenta confiável para exploração sísmica. Detalhes mais precisos das propriedades petrofísicas podem ser obtidos através de métodos de inversão mais sofisticados, a partir de dados pre stack. / Exploracionists has great interest in turbidite systems, since these generally comprise prolific exploration plays. However, these potential reservoirs are often near or below seismic resolution. Thus, the inversion process is important to integrate the seismic data quality of the resolution obtained from its preconditioning, so that the end result has detailed characteristics of the layers. The preconditioning enables improved resolution of seismic data, through mitigation of random noise. As the final goal, the inversion was performed acoustic post stack seismic data, migrated time, to a system of turbidites in Campos Basin. The main purpose of seismic inversion is to transform the given reflection in quantitative petrophysical properties. The inversion for acoustic impedance is commonly used to predict porosity. The flow of the proposed work was divided into five main stages: pre-conditioning the seismic 3D data, well-tie correlation, construction of the model of low frequency, inversion of data and estimation of porosity. The results showed that the inverted acoustic impedance cube has much higher resolution compared to the seismic amplitude data, allowing greater visualization of geological features in the Marlim Field. Besides its limitations as ignoring the effects of changing the fluid and complex lithological variations on the relationship porosity / impedance, the method provides a reliable tool for seismic exploration. More precise details of petrophysical properties can be obtainedthrough inversion methods starting from sophisticated pre-stack data.

>Magister Scientiae - MSc / Velocity modelling forms an integral part of the seismic interpretation process initially completed in two-way time. In order for a representative depth conversion, it is obligatory to construct a velocity model that serves the bridge between velocity and respective two-way time. This study deals with the investigation of subsurface heterogeneities and its impact on the variation of velocities. Interpretation of time domain reflection data results in one or more seismic horizons, however these horizons should represent the variation in subsurface geology as a result of acoustically different layers displaying varying reflection amplitudes. The purpose of this study was fulfilled by examining the variation of these velocities in relation to the geology and its significance towards building a velocity model. It is evident that complexities, such as an existing heterogeneous subsurface is present in the study area. Using velocities only considered at formation well tops, as a result, does not completely honour the variation in these velocities. The velocity profile as calculated from the sonic log was characterized into zones representing unique velocity trends. The analyses to understand the impact of subsurface heterogeneities on the velocities was completed by the application of seismic facies analysis which entailed the study of the seismic reflector patterns and amplitudes; a study of the lithologies present and the generation of mineral plots using available wireline logs, all of which in close relation to the variation in velocities. The characterized zones, as a result have shown that shaly sediments are typically associated with higher velocities (~2800 – 4600m/s) compared to sandstones of lower densities. Mineral plots however, have also indicated that where quartz minerals were present (specifically zone L), sandstones as a result have shown higher velocities (~4800m/s) as compared to the shales (~3600m/s). These higher velocities are also associated with more organised seismic reflectors with brighter amplitudes and strong contrasts in acoustic impedance as shown by the seismic. Uniform velocities were observed in zones such as zone Ia, typically associated with a low acoustic impedance contrast and minimal variation in its lithological make-up. The integrated investigation of subsurface heterogeneities has shown that velocities vary to a substantial degree as a result of existing subsurface heterogeneities. The variation of these velocities are hence significant enough that it should be considered when constructing a velocity model which aims to respect the geology of the study area. The result of understanding the relation between the geology and resultant velocities may prove to advance the results of the velocity model in a manner that it is more complete and representative of the subsurface.

A análise precisa dos resultados da timpanometria é essencial para determinar a condição da orelha média, principalmente em crianças nos primeiros anos de vida. Assim, o objetivo deste estudo foi apresentar um padrão de análise da timpanometria com sonda de 226 Hz para a faixa etária de seis meses a três anos, considerando a pressão do pico de máxima compliância e a compliância estática. Foram analisados prontuários de crianças de seis meses a três anos de idade atendidas no período de outubro de 2012 a fevereiro de 2016 no Centro de Pesquisas Audiológicas - Seção de Implante Coclear do Hospital de Reabilitação de Anomalias Craniofaciais e na Clínica de Audiologia Infantil da Clínica de Fonoaudiologia da Faculdade de Odontologia de Bauru, ambos da Universidade de São Paulo. A casuística foi dividida em dois grupos: grupo sem alteração de orelha média, composto por 224 orelhas, e o grupo com alteração de orelha média, composto por 59 orelhas. Foram considerados para análise os valores de pressão do pico de máxima compliância (daPa) e de compliância estática (ml) obtidos na timpanometria com sonda de 226Hz. No grupo sem alteração, o Teste Correlação Mann Whitney revelou que não houve diferença significante entre os sexos para pressão do pico de máxima compliância (p=0,782) e para a compliância estática (p=0,085). Também não houve correlação dos valores de pressão (p=0,678) e compliância (p=0,079) com a idade, de acordo com o Teste Correlação de Spearman. Considerando o intervalo entre os percentis 2,5 e 97,5 obtidos para a pressão e compliância nos grupos sem e com alteração, observou-se uma faixa de valores comum aos dois grupos, ou seja, os valores contidos nesta faixa não conseguiram classificar a orelha média como normal ou alterada. De acordo com os percentis 2,5 e 97,5, foi possível estabelecer uma faixa de normalidade para a pressão do pico de máxima compliância, de +52 daPa a -100 daPa, e para compliância estática, de 0,20 ml a 0,68 ml. Enquanto que na faixa de alteração, os valores variaram de -259 a 17,52 daPa para pressão e de 0,04 a 0,41 ml para a compliância. Assim, uma faixa de intersecção foi identificada, correspondente ao intervalo de -100 a 17,52 daPa para pressão do pico de máxima compliância e de 0,2 a 0,41 ml para a compliância estática. A análise dos dados demonstrou que a timpanometria com sonda de 226 Hz apresentou alta sensibilidade e baixa especificidade na faixa etária de seis meses a três anos. / Accurate analysis of tympanometry results is essential to determine the condition of the middle ear, especially in children in their first years of life. Thus, this study aimed at presenting a standard analysis of tympanometry with a 226 Hz probe for the age range six months to three years, taking into account the pressure of the peak of maximum compliance and static compliance. The records of 6-month to three-year old children assisted from October 2012 to February 2016 at the Audiology Research Center - Cochlear Implant Section of the Craniofacial Anomalies Rehabilitation Hospital and at the Children\'s Audiology Clinic of the Audiology and Speech-Language Pathology Clinic of the Bauru Dentistry School, both of the University of São Paulo, were analyzed. The sample was divided into two groups: a group with no middle ear alteration comprising 224 ears and the group with middle ear alteration composed of 59 ears. For analysis, the pressure values of the maximum compliance peak (daPa) and static compliance (ml) obtained in the tympanometry with a 226Hz probe were considered. In the group with no alteration, the Mann Whitney Correlation Test showed no significant difference between the genders for the maximum compliance peak pressure (p = 0.782) and for static compliance (p = 0.085). No difference was seen, either, for pressure (p = 0.678) and compliance (p = 0.079) values, according to age, by using the Spearman Correlation Test. Considering the interval between percentiles 2,5 and 97,5 obtained for pressure and compliance in the groups without and with alteration, a range of values common for the two groups was observed, that is, the values contained in this range could not classify the Middle ear as normal or altered. According to percentiles 2,5 and 97,5, it was possible to establish a range of normality for the pressure of the maximum compliance peak, from +52 daPa to -100 daPa, and for static compliance, from 0.20 ml to 0.68 ml, while in the alteration range, values ranged from -259 to 17,52 daPa for pressure and from 0,04 to 0,41 ml for compliance. Thus, an intersection range was identified, corresponding to the interval of -100 to 17,52 daPa for the pressure of the maximum compliance peak and 0,2 to 0,41 ml for the static compliance. Data analysis showed that tympanometry with a 226 Hz probe presented high sensitivity and low specificity in the 6-month to 3-year age range.

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

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.

A análise precisa dos resultados da timpanometria é essencial para determinar a condição da orelha média, principalmente em crianças nos primeiros anos de vida. Assim, o objetivo deste estudo foi apresentar um padrão de análise da timpanometria com sonda de 226 Hz para a faixa etária de seis meses a três anos, considerando a pressão do pico de máxima compliância e a compliância estática. Foram analisados prontuários de crianças de seis meses a três anos de idade atendidas no período de outubro de 2012 a fevereiro de 2016 no Centro de Pesquisas Audiológicas - Seção de Implante Coclear do Hospital de Reabilitação de Anomalias Craniofaciais e na Clínica de Audiologia Infantil da Clínica de Fonoaudiologia da Faculdade de Odontologia de Bauru, ambos da Universidade de São Paulo. A casuística foi dividida em dois grupos: grupo sem alteração de orelha média, composto por 224 orelhas, e o grupo com alteração de orelha média, composto por 59 orelhas. Foram considerados para análise os valores de pressão do pico de máxima compliância (daPa) e de compliância estática (ml) obtidos na timpanometria com sonda de 226Hz. No grupo sem alteração, o Teste Correlação Mann Whitney revelou que não houve diferença significante entre os sexos para pressão do pico de máxima compliância (p=0,782) e para a compliância estática (p=0,085). Também não houve correlação dos valores de pressão (p=0,678) e compliância (p=0,079) com a idade, de acordo com o Teste Correlação de Spearman. Considerando o intervalo entre os percentis 2,5 e 97,5 obtidos para a pressão e compliância nos grupos sem e com alteração, observou-se uma faixa de valores comum aos dois grupos, ou seja, os valores contidos nesta faixa não conseguiram classificar a orelha média como normal ou alterada. De acordo com os percentis 2,5 e 97,5, foi possível estabelecer uma faixa de normalidade para a pressão do pico de máxima compliância, de +52 daPa a -100 daPa, e para compliância estática, de 0,20 ml a 0,68 ml. Enquanto que na faixa de alteração, os valores variaram de -259 a 17,52 daPa para pressão e de 0,04 a 0,41 ml para a compliância. Assim, uma faixa de intersecção foi identificada, correspondente ao intervalo de -100 a 17,52 daPa para pressão do pico de máxima compliância e de 0,2 a 0,41 ml para a compliância estática. A análise dos dados demonstrou que a timpanometria com sonda de 226 Hz apresentou alta sensibilidade e baixa especificidade na faixa etária de seis meses a três anos. / Accurate analysis of tympanometry results is essential to determine the condition of the middle ear, especially in children in their first years of life. Thus, this study aimed at presenting a standard analysis of tympanometry with a 226 Hz probe for the age range six months to three years, taking into account the pressure of the peak of maximum compliance and static compliance. The records of 6-month to three-year old children assisted from October 2012 to February 2016 at the Audiology Research Center - Cochlear Implant Section of the Craniofacial Anomalies Rehabilitation Hospital and at the Children\'s Audiology Clinic of the Audiology and Speech-Language Pathology Clinic of the Bauru Dentistry School, both of the University of São Paulo, were analyzed. The sample was divided into two groups: a group with no middle ear alteration comprising 224 ears and the group with middle ear alteration composed of 59 ears. For analysis, the pressure values of the maximum compliance peak (daPa) and static compliance (ml) obtained in the tympanometry with a 226Hz probe were considered. In the group with no alteration, the Mann Whitney Correlation Test showed no significant difference between the genders for the maximum compliance peak pressure (p = 0.782) and for static compliance (p = 0.085). No difference was seen, either, for pressure (p = 0.678) and compliance (p = 0.079) values, according to age, by using the Spearman Correlation Test. Considering the interval between percentiles 2,5 and 97,5 obtained for pressure and compliance in the groups without and with alteration, a range of values common for the two groups was observed, that is, the values contained in this range could not classify the Middle ear as normal or altered. According to percentiles 2,5 and 97,5, it was possible to establish a range of normality for the pressure of the maximum compliance peak, from +52 daPa to -100 daPa, and for static compliance, from 0.20 ml to 0.68 ml, while in the alteration range, values ranged from -259 to 17,52 daPa for pressure and from 0,04 to 0,41 ml for compliance. Thus, an intersection range was identified, corresponding to the interval of -100 to 17,52 daPa for the pressure of the maximum compliance peak and 0,2 to 0,41 ml for the static compliance. Data analysis showed that tympanometry with a 226 Hz probe presented high sensitivity and low specificity in the 6-month to 3-year age range.

Energy-based acoustic quantities provide vital information about acoustic fields and the characterization of acoustic sources. Recently, the phase and amplitude gradient estimator (PAGE) method has been developed to reduce error and extend bandwidth of energy-based quantity estimates. To inform uses and applications of the method, analytical and experimental characterizations of the method are presented. Analytical PAGE method bias errors are compared with those of traditional estimation for two- and three-microphone one-dimensional probes. For a monopole field when phase unwrapping is possible, zero bias error is achieved for active intensity using three-microphone PAGE and for specific acoustic impedance using two-microphone PAGE. A method for higher-order estimation in reactive fields is developed, and it is shown that a higher-order traditional method outperforms higher-order PAGE for reactive intensity in a standing wave field. Extending the applications of PAGE, the unwrapped phase gradient is used to develop a method for directional sensing with improved bandwidth and arbitrary array response.

Traditional means of controlling sound radiated by electrical power transformers involve the construction of large expensive barriers or full enclosures, which cause maintainability and cooling problems. One promising alternative is to use active noise control to cancel the noise. This thesis is concerned with one of the many problems which need to be investigated to develop a practical active noise cancellation system for transformers. This work, in particular, is concerned with the physical system design which includes the selection of the control source types and the evaluation of the near-field sensing strategies. Loudspeakers have been widely used in the past as an acoustic source for canceling transformer noise. The principal disadvantage of using loudspeakers is that to achieve global noise control, a large number, driven by a multi-channel controller, are required. However, if large panels are used in place of loudspeakers as control sources, it is possible that the number of the control sources and complexity of the controller could be reduced substantially. In addition to reducing the number of control sources and simplifying their application, panel sound sources could also overcome some disadvantages of the loudspeakers, such as limited life and deterioration due to the weather. Thus, part of the work described in this thesis is concerned with the development of a resonant curved panel with a backing cavity as an acoustic type source. The advantages of using a curved panel rather than a flat panel are twofold: first a curved panel is more easily excited by the extensional motion of the piezoelectric patch actuators; and second, it is more difficult to adjust the resonance frequencies of the efficient modes of a flat panel than of a curved panel. The analytical models for the design of the panel cavity systems have been developed. As an example, a resonant curved panel with a backing cavity system was constructed and the sound radiation of the system was measured. Results show that a resonant panel-cavity sound source could be used as an alternative to a number of loudspeakers for active cancellation of electric power transformer noise. Due to the advantages of using the vibration type control sources, two types of vibration control sources (inertial electrodynamic shakers and piezoelectric patch actuators) were considered and the mechanical output of the inertial shakers has been compared with that of the piezoelectric actuators. In contrast with the piezoelectric actuators, the resonance frequencies of the inertial shakers can be tuned to the frequencies of interest using simple tuning procedures, so that the output efficiency of the shakers can be increased. The output performance was evaluated for two types of actuators by measuring the structural response of either a panel or a transformer when excited by the actuators at half their rated voltage input. Results demonstrated that a much larger output amplitude at the frequency of interest can be achieved by the tuned inertial type actuators. Two near-field sensing strategies, the minimization of the sum of the sound intensities and the minimization of the sum of the squared sound pressures, have been studied. A quadratic expression was derived for the minimization of the sum of the sound intensities in the near-field. To evaluate the control performances achieved using both sensing strategies, a flat-panel was modelled with a harmonic point force disturbance and several point force control sources. Simulation results show that the control performance could be improved by minimizing the sum of the sound intensities in the hydrodynamic near-field, provided that a very large number of error sensors were used, otherwise better results were achieved using near-field squared pressure sensing. Both sensing strategies were used to predict the noise reductions that resulted for the active noise control of a small transformer in the laboratory environment and for a large electrical power transformer on site. To optimize the locations of the control sources (for the large transformer on site) and the locations of the error sensors (for the small transformer in the laboratory environment), a genetic algorithm (GA), which is an evolutionary optimization technique, was employed as a search procedure to optimize the control source and error sensor locations. The results showed that the control source locations and/or the error sensor locations must be optimized to achieve the maximum sound reduction for either error sensing strategy, especially for the sound intensity minimization; otherwise, the sound field level may increase after control due to the character of the cost function (the sum of the sound intensities). The simulation results were experimentally validated for the small transformer in the laboratory environment. Due to the limitation of the number of controller channels, the control performance was only evaluated for squared pressure minimization. The results demonstrated that for the case of 8 control sources and 8 error sensors, at 100 Hz, an average sound pressure reduction of 15.8 dB was achieved when evaluated at 528 monitoring locations at 0.25 m intervals on a surface that surrounded the transformer. / Thesis (Ph.D.)--Engineering (Department of Mechanical Engineering), 2000.

Increased national and international travel over the lastdecades has caused an increase in the global number ofpassengers using different means of transportation. Greateffort is being directed to improving the noisy environment inthe residential community. This is to face the growing strictnoise requirements which are implemented by international noiseregulatory authorities, governments, and local airports. Thereis also a strong competition between different manufacturers tomake their products quieter. The propulsion system in anaircraft is the major source of noise during relevant flightconditions. The engine noise in a vehicle dominates the totalradiated noise at low speeds especially inside cities. Manyrecent studies on noise reduction involve the use of perforatedplates in the air and gas flow ducting connected to the engine.This thesis deals with the modelling of perforates as anabsorbent. There are many difficulties in using liners in theseapplications. The most important is that there is no largesurface area to which the linings may be applied. Equally, theenvironment in which linings have to survive is hostile.Therefore, liners have to be carefully tailored in order toachieve the most efficient attenuation. The full-scalesimulation testing, which is usually necessary to define thenoise attenuation produced by a liner installation, is bothtime-consuming and expensive. Therefore, a need for accuratemodels is a must. This thesis fills some gaps in the impedancemodelling of perforated liners. It also concentrates on thosecomplicated situations of sound propagation in ducts that weresolved earlier using Finite Element Methods. Alternateanalytical solutions to these problems are developed here,which gives more physical insight into the results. The key design parameter of perforates is the acousticimpedance. The impedance is what determines their efficiency toabsorb sound waves. A semi empirical impedance model wasdeveloped to be capable of accurately predicting the linerimpedance as a function of its physical properties and thesurrounding conditions. It was compared to all previous modelsin the literature. Nothing in the literature has been reportedon the effect of temperature on the perforate impedance,therefore a complete study was performed. A new inverseanalytical impedance measurement technique was proposed. It isbased on educing the impedance value based on the measurementof the attenuation across a lined duct section. Twoapplications were further considered: The effect of hard stripsin lined ducts on there attenuation properties; and themodelling of perforations in a complicated automotive mufflersystem. Keywords:Perforates–Liners–Acousticimpedance–Hot stream liners–Hard splices–Mufflers–Lined ducts–Collocation–Flowduct.