The prevalence of gas turbines operating in primarily lean premixed modes is predicated on the need for lower emissions and increased efficiency. An enhancement in the mixing process through the introduction of swirl in the combustion reactants is also necessary for flame stabilization. The resulting lean swirling flames are often characterized by a susceptibility to feedback between velocity, pressure and heat release perturbations with a potential for unstable self-amplifying dynamics. The existing literature on combustion dynamics is predominantly dedicated to premixed flame configurations motivated by power generation and propulsive gas turbine applications. In the present research effort, an investigation into the response of atmospheric, non-premixed swirling flames to acoustic perturbations at various frequencies (fp = 0-315Hz) and swirl intensities (S=0.09 and S=0.34) is carried out. The primary objective of the research effort is to broaden the scope of fundamental understanding in flame dynamics in the literature to include non-premixed swirling flames. Applications of the research effort include control strategies to mitigate the occurrence of thermoacoustic instabilities in future power generation gas turbines. Flame heat release is quantitatively measured using a photomultiplier with a 430nm bandpass filter for observing CH* chemiluminescence which is simultaneously imaged with a phase-locked CCD camera. Acoustic perturbations are generated with a loudspeaker at the base of an atmospheric co-flow burner with resulting velocity oscillation amplitudes, u'/Uavg in the 0.03-0.30 range. The dependence of flame dynamics on the relative richness of the flame is investigated by studying various constant fuel flow rate flame configurations. The effect of varying fuel flow rates on the flame response is also examined using with dynamic time-dependent fuel supply rates over the data acquisition period. The Particle Image Velocimetry (PIV) method is used to study the isothermal flow field associated with acoustic pulsing. The acoustic impedance, wavelet analysis, Rayleigh criteria and phase conditioning methods are used to identify fundamental mechanisms common to highly responsive flame configurations.

The acoustic source structure, acoustic farfield, and duct terminating impedances fully describe the acoustics of a source within a duct. A main goal in the study of noise generated by turbulent combustion is to characterize the structure of the flame as an acoustic source. Data describing the farfield and duct terminating conditions allow for the testing of combustion noise models. The acoustic farfield of a premixed flame burner is documented for various power levels and air-to-fuel ratios. The terminating impedance of the burner exhaust is determined by a method using the transfer function between two microphones that communicate with the acoustic field inside the duct. High temperature probes isolate the microphones from extreme temperatures within the duct while only slightly distorting the results. The real part of the terminating impedance agrees with a correlation in the literature for hot flow leaving a duct. / M.S.

In dieser Arbeit wurde magnetische und elastische Dynamik in nanostrukturierten künstlichen Materialien mit Hilfe eines optischen, zeitaufgelösten Pumpprobe Messaufbaus untersucht. Die Absorption der ultraschnellen Laserpulse erzeugt einen Wärmegradienten auf einer Zeitskala von Pikosekunden. Dieser induziert kohärente dynamische Prozesse, welche mit einem zweiten, zeitverzögerten Puls beobachtet werden. In einem zweidimensionalen magnonischen Kristall, bestehend aus einem submikrometer großen Antidotgitter auf einer ferromagnetischen CoFeB Schicht, können Spinwellenmoden beobachtet werden, die eine schwache Frequenzabhängigkeit vom externen magnetischen Feld aufweisen. Dies lässt vermuten, dass Spinwellen in der Nähe von Inhomogenitäten des internen Feldes lokalisieren. Elastische Dynamik auf denselben Strukturen zeigt Frequenzen proportional zu charakteristischen Strukturgrößen (Antidotabstand und Antidotgröße), was auf die Anregung von Spannungswellen auf der Oberfläche hindeutet. Auf CoFeB/MgO Schichtstapeln mit ähnlicher akustischer Impedanz, können sowohl Oberflächenwellen als auch Wellen im Volumen in guter Übereinstimmungmit der Theorie beobachtet werden. Anregung der elastischen Dynamik in Reflektions- und Transmissionsgeometrie zeigen, dass durch das Brechen der Periodizität des Schichtstapels die Amplitude der hochfrequenten Oberflächenwelle effektiv unterdrückt wird. Außerdem sind im W/PC Schichtstapeln mit hohem akustischem Versatz innere Wellen unterdrückt.

This thesis is motivated by the need for noise control in aircraft engine with orifices and perforated liner. The presence of high-level acoustic excitation, different flow situations either bias flow, grazing flow or any combination in the aircraft engine, makes the acoustic behavior complex due to the interaction between sound and flow over the lined wall. Both systematic acoustic prediction of aircraft engines and liner optimization necessitate progress in impedance measurement methods by including the effect of the complex flow situations. The aim of the present thesis is to experimentally study the change in acoustic properties of orifices and perforated liners under bias or grazing flow. In order to study the effect of different combinations of bias flow and high-level acoustic excitation, an in-duct orifice has been investigated with finely controlled acoustic excitation levels and bias flow speeds. This provides a detailed study of the transition from cases when high-level acoustic excitation causes flow reversal in the orifice to cases when the bias flow maintains the flow direction. Nonlinear impedance is measured and compared, and a scattering matrix and its eigenvalues are investigated to study the potentiality of acoustic energy dissipation or production. A harmonic method is proposed for modelling the impedance, especially the resistance, which captures the change in impedance results at low frequencies compared with experimental results. The presence of grazing flow can increase the resistance of acoustic liners and shift their resonator frequency. So-called impedance eduction technology has been widely studied during the past decades, but with a limited confidence due to the interaction of grazing flow and acoustic waves. A comparison has been performed with different test rigs and methods from the German Aerospace Center (DLR). Numerical work has been performed to investigate the effect of shear flow and viscosity. Our study indicates that the impedance eduction process should be consistent with that of the code of wave propagation computation, for example with the same assumption regarding shear flow and viscosity. A systematic analysis for measurement uncertainties is proposed in order to understand the essentials for data quality assessment and model validation. The idea of using different Mach numbers for wave dispersion and in the Ingard-Myers boundary condition has been tested regarding their effect on impedance eduction. In conclusion, a local Mach number based on friction velocity is introduced and validated using both our own experimental results and those of previous studies. / <p>QC 20150522</p>

The thermodynamic equation of seawater - 2010 (TEOS-10) is hampered by the inability to measure absolute salinity or density in situ. No new advances for in situ salinity or density measurement have taken place since the adoption of the practical salinity scale in 1978. In this thesis three possible technologies for in situ measurements are developed and assessed: phased conductivity, an in situ density sensor and sound speed sensors. Of these, only sound speed sensors showed the potential for an in situ TEOS-10 measurement solution. To be implemented, sensor response times need to be matched and the sound speed sensor accuracy must be improved. Sound speed sensor accuracy is primarily limited by the calibration reference, pure water. Test results indicate the TEOS-10 sound speed coefficients may also need to be improved. A calibration system to improve sound speed sensor accuracy and verify the TEOS-10 coefficients is discussed. / Graduate / 0415 / 0986 / TDakin@UVic.ca

Submitted by Filipe dos Santos (fsantos@pucsp.br) on 2018-06-15T12:32:33Z No. of bitstreams: 1 Jéssica Raignieri.pdf: 1240538 bytes, checksum: 94c6dfb67614061048d3c5cfdd8ce0c9 (MD5) / Made available in DSpace on 2018-06-15T12:32:34Z (GMT). No. of bitstreams: 1 Jéssica Raignieri.pdf: 1240538 bytes, checksum: 94c6dfb67614061048d3c5cfdd8ce0c9 (MD5) Previous issue date: 2018-03-14 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Introduction: Audiological monitoring is aimed at monitoring children from six months to three years old, due to the risk of late or progressive hearing loss. Objective: To study the results of the Wideband Tympanometry in acoustic absorbance measurements and the Transient Evoked Otoacoustic Emissions and Distortion Product record in children with risk indicators for hearing loss during audiological monitoring. Method: Fifty-eight children with risk indicators for hearing loss were evaluated in the audiological monitoring process, with a mean age of 16.7 months. In order to contact the families of the children, phone calls were made, with information obtained from a database of four public maternity hospitals in São Paulo. Subjects were characterized in normal auditory status and conductive altered auditory status, in the groups with and without risk indicators for auditory deficiency, and according to the audiological results of auditory monitoring. Transient Otoacoustic Emissions and Distortion Product tests were performed, in addition to the Wideband Tympanometry. For the analysis of the absorbance in the Wideband Tympanometry, seven frequency bands were selected from 1 kHz to 8 kHz, similar to the Otoacoustic Emission Frequency bands. Results: In this study, the absorbance curves presented similar results for the right and left ears, both for children with normal hearing, and for those with conductive hearing loss, as well as for females and males. It was observed that in the frequencies between 1500 Hz and 6000 Hz, the subjects with normal hearing status, the absorbance was between 0.92 and 0.98, and the best results obtained for this age group being in this frequency range. Absorbance is higher in the group of children without risk indicators for hearing loss (RIHL) when compared to the group of children with (RIHL). The recording of Transient Otoacoustic Emissions (TOAE) and Distortion Product Otoacoustic Emissions (DPOAE) showed a strong agreement with the measured absorbance in all frequency bands in both ears. Conclusion: Absorbance values are higher in males, and for children with normal hearing status. 13 There was an agreement for the results of Evoked Otoacoustic Emissions level and absorbance measurements, and the higher the absorbance, the higher the TOAE and DPOAE levels / Introdução: o monitoramento audiológico visa ao acompanhamento de crianças de seis meses até três anos de idade, devido ao risco de perdas auditivas de início tardio ou progressivo. Objetivo: estudar os resultados da Timpanometria de Banda Larga nas medidas de absorvância acústica e do registro das Emissões Otoacústicas Evocadas Transiente e Produto de Distorção, em crianças com indicadores de risco para a deficiência auditiva durante o monitoramento audiológico. Método: foram avaliadas 58 crianças com indicadores de risco para a deficiência auditiva no processo de monitoramento audiológico, com idade média de 16,7 meses de vida. Para contato com as famílias das crianças, ligações telefônicas foram realizadas, com informações obtidas de um banco de dados de quatro maternidades públicas de São Paulo. Os sujeitos foram caracterizados em status auditivo normal e status auditivo alterado condutivo nos grupos com e sem indicadores de risco para a deficiência auditiva e de acordo com os resultados audiológicos do monitoramento auditivo. Foram realizados testes de Emissões Otoacústicas Transientes e Produto de Distorção, além da Timpanometria de Banda Larga. Para análise da absorvância na Timpanometria de Banda Larga, foram selecionadas sete bandas de frequências que variam de 1 kHz a 8 kHz similares às bandas de frequências. Resultados: neste estudo, as curvas de absorvância apresentaram-se de forma similar para as orelhas direita e esquerda, tanto para as crianças com audição dentro da normalidade, como para aquelas com perdas auditivas condutivas e, também, no sexo feminino e masculino. Observou-se que, na frequência de 1500 Hz a 6000 Hz, nos sujeitos com status auditivos normal, a absorvância estava entre 0,92 a 0,98, podendo estar, nessa faixa de frequência, os melhores resultados obtidos para essa faixa etária estudada. A absorvância foi maior no grupo de crianças sem 11 indicadores de risco para a deficiência auditiva (IRDA) quando comparado com o grupo de crianças com IRDA. O registro das Emissões Otoacústicas Transientes (EOAT) e Emissões Otoacústicas Produto de Distorção (EOAPD) apresentou uma forte concordância com a medida de absorvância registrada, em todas as bandas de frequências, em ambas as orelhas. Conclusão: os valores de absorvância são maiores no sexo masculino e em crianças com status auditivo normal. Houve concordância para os resultados de nível de Emissões Otoacústicas Evocadas e medidas de absorvância, sendo que, quanto maior a absorvância, maior o nível de EOAT e EOPD

Submitted by Filipe dos Santos (fsantos@pucsp.br) on 2017-04-17T10:43:29Z No. of bitstreams: 1 Cibelle Duarte Vilela.pdf: 2348062 bytes, checksum: 27c7e277821fda172bafebbcf2051b08 (MD5) / Made available in DSpace on 2017-04-17T10:43:29Z (GMT). No. of bitstreams: 1 Cibelle Duarte Vilela.pdf: 2348062 bytes, checksum: 27c7e277821fda172bafebbcf2051b08 (MD5) Previous issue date: 2017-04-07 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Introduction: Acoustic absorbance measures by wideband tympanometry are performed using the chirp stimulus using a stimulus with frequency spectrum of 226 Hz to 8000 Hz. Objective: To study the results of acoustic absorbance measures using wideband tympanometry in neonates. Method: the sample consisted of 269 subjects who underwent NHS (group I) and eleven who had failed NHS (group II), all of whom were evaluated before hospital discharge. The subjects were characterized in normal auditory status, slight change in the test and changed test, according to the results of screening tests. For the absorbance analysis, eleven frequency bands ranging from 226 to 8000 Hz were selected. Percentile analysis was performed among subjects who presented normal auditory status. Results: Absorbance curves varied between the frequencies of 226 Hz and 8000 Hz, from 0.3 to 0.7 for subjects with normal hearing status in the right ear, from 0,4 to 0,6 for subjects with normal hearing status in the left ear. The subjects in group II had values of absorbance between 0.3 and 0.5 in the right ear and between 0.3 and 0.4 in the left ear. The frequencies from 749.15 to 2000 Hz show significant differences in absorbances. Conclusion: Absorbance values were higher in subjects with normal hearing status and in subjects with changed auditory status before maternity discharge, but normal tests results who were evaluated after 15 days. The percentile curve may contribute to the clinical analysis of the data specially neonates absorvance between 749.15 and 2000 Hz / Introdução: as medidas de absorvância acústica pela timpanometria de banda larga é realizada utilizando o estímulo chirp, com um espectro de frequência de 226 Hz a 8000 Hz. Objetivo: Estudar os resultados das medidas de absorvância acústica por meio da timpanometria de banda larga em neonatos. Método: a casuística foi composta por 269 sujeitos que passaram na TAN (grupo I) e onze que falharam na TAN (grupo II), sendo todos avaliados antes da alta hospitalar. Os sujeitos foram caracterizados em status auditivo normal, alterado leve e alterado, de acordo com os resultados dos testes da triagem. Para a análise da absorvância foram selecionadas onze bandas frequências que variaram de 226 a 8000 Hz. A análise do percentil foi realizada entre os sujeitos que apresentaram status auditivo normal. Resultados: as curvas de absorvância variaram, entre as frequências de 226 Hz a 8000 Hz, de 0,3 a 0,7 para os sujeitos com status auditivo normal na orelha direita, e 0,4 a 0,6 na orelha esquerda. Os sujeitos do grupo II tiveram os valores de absorvância entre 0,3 e 0,5 na orelha direita e entre 0,3 e 0,4 para os sujeitos com status auditivo normal na orelha esquerda. As frequências de 749,15 a 2000 Hz apresentam diferenças significativas nas absorvâncias. Conclusão: os valores de absorvância foram maiores nos sujeitos com status auditivo normal, assim como para os sujeitos com status auditivo alterados no nascimento, mas que no retorno aos 15 dias, obtiveram resultados normais. A curva do percentil pode contribuir para análise clínica dos dados, especialmente entre a faixa de frequência entre 749,15 a 2000 Hz, podendo ser considerada a melhor faixa de frequência para interpretação dos resultados de absorvância para neonatos

Bibliography : leaves 237-251. / x, 251 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1994

Manufacturers of commercial, power-generating, gas turbine engines continue to develop combustors that produce lower emissions of nitrogen oxides (NOx) in order to meet the environmental standards of governments around the world. Lean, premixed combustion technology is one technique used to reduce NOx emissions in many current power and energy generating systems. However, lean, premixed combustors are susceptible to thermo-acoustic oscillations, which are pressure and heat-release fluctuations that occur because of a coupling between the combustion process and the natural acoustic modes of the system. These pressure oscillations lead to premature failure of system components, resulting in very costly maintenance and downtime. Therefore, a great deal of work has gone into developing methods to prevent or eliminate these combustion instabilities. This dissertation presents the results of a theoretical and experimental investigation of a novel Fuel System Tuner (FST) used to damp detrimental combustion oscillations in a gas turbine combustor by changing the fuel supply system impedance, which controls the amplitude and phase of the fuel flowrate. When the FST is properly tuned, the heat release oscillations resulting from the fuel-air ratio oscillations damp, rather than drive, the combustor acoustic pressure oscillations. A feasibility study was conducted to prove the validity of the basic idea and to develop some basic guidelines for designing the FST. Acoustic models for the subcomponents of the FST were developed, and these models were experimentally verified using a two-microphone impedance tube. Models useful for designing, analyzing, and predicting the performance of the FST were developed and used to demonstrate the effectiveness of the FST. Experimental tests showed that the FST reduced the acoustic pressure amplitude of an unstable, model, gas-turbine combustor over a wide range of operating conditions and combustor configurations. Finally, combustor acoustic pressure amplitude measurements made in using the model combustor were used in conjunction with model predicted fuel system impedances to verify the developed design rules. The FST concept and design methodology presented in this dissertation can be used to design fuel system tuners for new and existing gas turbine combustors to reduce, or eliminate altogether, thermo-acoustic oscillations.

This thesis considers applications of gradient-based optimization algorithms to the design and control of some mechanics systems. The material distribution approach to topology optimization is applied to design two different acoustic devices, a reactive muffler and an acoustic horn, and optimization is used to control a ball pitching robot. Reactive mufflers are widely used to attenuate the exhaust noise of internal combustion engines by reflecting the acoustic energy back to the source. A material distribution optimization method is developed to design the layout of sound-hard material inside the expansion chamber of a reactive muffler. The objective is to minimize the acoustic energy at the muffler outlet. The presence or absence of material is represented by design variables that are mapped to varying coefficients in the governing equation. An anisotropic design filter is used to control the minimum thickness of materials separately in different directions. Numerical results demonstrate that the approach can produce mufflers with high transmission loss for a broad range of frequencies. For acoustic devices, it is possible to improve their performance, without adding extended volumes of materials, by an appropriate placement of thin structures with suitable material properties. We apply layout optimization of thin sound-hard material in the interior of an acoustic horn to improve its far-field directivity properties. Absence or presence of thin sound-hard material is modeled by a surface transmission impedance, and the optimization determines the distribution of materials along a “ground structure” in the form of a grid inside the horn. Horns provided with the optimized scatterers show a much improved angular coverage, compared to the initial configuration. The surface impedance is handled by a new finite element method developed for Helmholtz equation in the situation where an interface is embedded in the computational domain. A Nitschetype method, different from the standard one, weakly enforces the impedance conditions for transmission through the interface. As opposed to a standard finite-element discretization of the problem, our method seamlessly handles both vanishing and non-vanishing interface conditions. We show the stability of the method for a quite general class of surface impedance functions, provided that possible surface waves are sufficiently resolved by the mesh. The thesis also presents a method for optimal control of a two-link ball pitching robot with the aim of throwing a ball as far as possible. The pitching robot is connected to a motor via a non-linear torsional spring at the shoulder joint. Constraints on the motor torque, power, and angular velocity of the motor shaft are included in the model. The control problem is solved by an interior point method to determine the optimal motor torque profile and release position. Numerical experiments show the effectiveness of the method and the effect of the constraints on the performance.