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.

The objective of this doctoral thesis is to study three different innovative noise control techniques in ducts namely: acoustic metamaterials, porous absorbers and microperforates. There has been a lot of research done on all these three topics in the context of duct acoustics. This research will assess the potential of the acoustic metamaterial technique and compare to the use of conventional methods using microperforated plates and/or porous materials.  The objective of the metamaterials part is to develop a physical approach to model and synthesize bulk moduli and densities to feasibly control the wave propagation pattern, creating quiet zones in the targeted fluid domain. This is achieved using an array of locally resonant metallic patches. In addition to this, a novel thin slow sound material is also proposed in the acoustic metamaterial part of this thesis. This slow sound material is a quasi-labyrinthine structure flush mounted to a duct, comprising of coplanar quarter wavelength resonators that aims to slow the speed of sound at selective resonance frequencies. A good agreement between theoretical analysis and experimental measurements is demonstrated. The second technique is based on acoustic porous foam and it is about modeling and characterization of a novel porous metallic foam absorber inside ducts. This material proved to be a similar or better sound absorber compared to the conventional porous absorbers, but with robust and less degradable properties. Material characterization of this porous absorber from a simple transfer matrix measurement is proposed.The last part of this research is focused on impedance of perforates with grazing flow on both sides. Modeling of the double sided grazing flow impedance is done using a modified version of an inverse semi-analytical technique. A minimization scheme is used to find the liner impedance value in the complex plane to match the calculated sound field to the measured one at the microphone positions. / <p>QC 20160923</p>

Abstract Interacting many-body problems are central to most fields of physics. In condensed matter physics, the systems of interest consists of a number of bodies on the order of Avogadro's constant, ~10²³. The precise modeling of such systems is usually impossible. Under certain circumstances however, even these problems can become tractable. One such circumstance is that of a Fermi liquid. At sufficiently low temperatures, in describing the dynamics of a system of interacting fermions, it is possible to forgo description of the fermions themselves, and instead concentrate on the collective excitations of the entire fermion system. These collective excitations are called quasiparticles. In this thesis we study two phenomena related to the motion of objects in a Fermi liquid. First, we study the transmission of transverse oscillations through a thin film of normal Fermi liquid. The dynamics of normal Fermi liquid are described by Landau's Fermi liquid theory. Landau's theory predicts the existence of new modes of sound under conditions where sound ordinarily would not propagate. Using the equations of motion for the Fermi liquid quasiparticles, we calculate the linear response of a Fermi liquid film to the transverse oscillations of a planar substrate under a wide range of conditions. We present the linear response in terms of the film's acoustic impedance and study the effects of quasiparticle collisions and of the Fermi liquid interactions. The second phenomenon we study is the supercritical motion of a wire in a superfluid Fermi liquid. The prevailing assumption is that if the velocity of an object moving in a superfluid Fermi liquid surpasses a characteristic critical velocity, the object experiences a sudden onset of viscous forces. This viscosity is caused by the escape of quasiparticles, produced by pair breaking on the surface of the object, into the surrounding superfluid. We study Andreev reflection of the quasiparticles by the surrounding superfluid flow field, and modifications to the flow caused by pair breaking, as possible mechanisms for low-dissipation motion above the critical velocity. / Original publications The original publications are not included in the electronic version of the dissertation. Kuorelahti, J. A., Tuorila, J. A., &amp; Thuneberg, E. V. (2016). Fermi liquid theory applied to a film on an oscillating substrate. Physical Review B, 94(18). https://doi.org/10.1103/physrevb.94.184103 Kuorelahti, J. A., &amp; Thuneberg, E. V. (2018). Two-parameter boundary condition applied to transverse acoustic impedance of a Fermi liquid. Journal of Physics: Conference Series, 969, 12010. https://doi.org/10.1088/1742-6596/969/1/012010 http://jultika.oulu.fi/Record/nbnfi-fe2018060425173 Kuorelahti, J. A., Laine, S. M., &amp; Thuneberg, E. V. (2018). Models for supercritical motion in a superfluid Fermi liquid. Physical Review B, 98(14). https://doi.org/10.1103/physrevb.98.144512 http://jultika.oulu.fi/Record/nbnfi-fe2018112148794

L’étude présentée dans cette thèse se situe dans le domaine de l’acoustique modale des conduits avec des parois absorbantes et un écoulement moyen. Nous considérons une source de bruit en amont avec une fréquence fixe. Avec cela, nous étudions les modes propres acoustiques du conduit en terme de nombre d’onde qui sont présents.Avec cette étude, nous contribuons à la meilleure compréhension de la propagation du sondans ce type de configuration. Parmi les applications, il y a la réduction du bruit des moteurs des aéronefs.Une analyse numérique par la méthode pseudospectrale de collocation, sur la base de polynômes de Chebyshev, a été mise en ouvre pour obtenir le spectre des modes, dans un domaine transversal.Pour cela, deux programmes ont été utilisés : le programme FiEStA, qui a été développé dans le cadre de cette thèse, et qui résout les équations d’Euler linéarisées, en considérant un problème à une ou deux une ou deux dimensions. D’autre part, le programme MAMOUT, a été utilisé pour résoudre les équations de Navier-Stokes linéarisées, pour étudier plus spécifiquement les effets de la viscosité.Avec ces outils, on a constaté les effets de trois paramètres : lorsque le rapport d’aspect augmente, la densité des modes, en particulier des modes propagatifs, se développe également.Quand le nombre de Mach de l’écoulement moyen augmente, on observe les effets suivants sur les valeurs propres : un déplacement vers la partie réelle négative, une amplification de leur valeur absolue et un déplacement vers les modes d’indice inférieur. Le profil d’écoulement moyen induit aussi un déplacement dans les valeur propres, pas facilement prévisible. Il modifie également la forme des fonctions propres ; ce qui est notamment visible pour le mode d’onde plane. Les changements d’impédance induisent un échange cyclique de valeurs propres entre les valeurs de parois rigides des modes consécutifs. Avec certaines valeurs d’impédance, les modes acoustiques de paroi apparaissent. Ils sont caractérisés par la forme exponentielle de leurs fonctions propres.En plus des modes acoustiques, il existe des modes hydrodynamiques de surface qui se sont révélés avec quelques valeurs d’impédance et forme et nombre de Mach de l’écoulement moyen. Pour un ensemble de données de référence, ces modes ont été étudiés. L’impédance a été considérée avec un modèle basé sur des données de la littérature, tout comme le profil d’écoulement moyen.Un mode hydrodynamique a été trouvé. Avec certaines valeurs de la fréquence, l’ensemble des paramètres donne lieu à une instabilité. En utilisant le critère Briggs Bres pour la stabilité,l’instabilité a été jugée absolue.À partir du comportement des modes avec différentes valeurs de l’impédance, et conformément aux résultats publiés, nous avons défini la condition que le spectre doit remplir pour réduire autant que possible le bruit. C’est cela qu’on appelle l’impédance optimale. Nous avons calculé cette valeur pour différents fréquences et écoulements moyens. / The study presented in this thesis is within the domain of modal acoustics of lined ducts withgrazing flow. We consider an upstream source of noise with a fixed frequency, within a lined duct.From this, we study the eigenmodes in terms of wavenumber that are present in this system.With this study, we contribute to the better understanding of sound propagation in thedescribed configuration. Within its main applications, we can find the noise reduction fromaeroengines.A numerical analysis with the pseudospectral collocation method, based on Chebyshevpolynomials was used to obtain the spectrum of modes within the duct, in a domain transversalto the mean flow. For this, two programs were used: On one hand, within the frame of this thesis,the program FiEStA was developed. It solves the linearized Euler Equations, considering eitherone or two dimensions of the transversal plane. On the other hand, the already existing programMAMOUT was used for verification and to solve also the linearized Navier-Stokes Equations toobserve the effects of viscosity.With these tools, the first result was to notice the effects of three parameters: When theaspect ratio grows, the density of modes in the spectrum grows also. In particular, we havemore propagative modes. As the mean flow Mach number grows, we observe these effects on theeigenvalues: a displacement to the negative real part, a slight amplification of their absolute valueand a displacement towards the modes of lower index. The difference in mean flow profile inducesanother displacement in modes, not easily predictable. It changes also the shape of eigenfunctions,which is clearly seen for the planewave mode. The impedance changes induce a cyclic exchange ofeigenvalues from their hard wall value to the hard wall value of a consecutive mode. The changeof eigenfunction is gradually change in wavelength, to obtain the shape of the destination mode.With some impedance values, a pair of modes, called the acoustic surface modes arise. They arecharacterized by the exponential shape of their eigenfunctions.Besides these acoustic surface modes, there are also a pair of hydrodynamic surface modeswhich come to light with some values of impedance and shape and Mach number of the meanflow. With a benchmark data, these modes were studied. The impedance was considered from themodel of a measured liner while the mean flow profile was taken from experimental values. Withthis, the hydrodynamic mode was found. With specific values of frequency, the set of parametersgives rise to an instability. Using the Briggs-Bers criterion for stability, the instability was foundto be absolute for a given frequency.From the comportment of modes with different values of impedance, and in accordance withpublished results, we defined the condition that the spectrum has to fulfill to reduce as much aspossible the upstream noise. This is what we called the optimal impedance. We obtained it forseveral flow profiles and frequencies, in both 1D and 2D domains.