An experimental evaluation of normal, sonic, helium injection from a wedgeshaped nozzle and a circular nozzle into a Mach 3 free stream with a total pressure of 6.5 atm and a total temperature of 294 K was conducted. The expansion ratio and the mass rate of flow of both nozzles were matched in order to determine the effect of the geometric difference only. 'Decay rate, penetration, and jet area growth rate were used to compare the mixing performance of the nozzles. Oil flow photography was used to determine the size of the three-dimensional boundary layer separation zone in front of each nozzle, and nanoshadowgraph photography was used to visualize the system of shocks and the flow field of each nozzle. Mean flow quantity profiles at several lateral stations were made at three downstream locations. The profiles were used to calculate helium concentration, Mach number, static temperature, static pressure, density, flow velocity, local speed of sound, mass flux, and total pressure. The two nozzles were then compared on the basis of maximum helium concentration decay, core center and overall penetration, and the growth rate and centroid penetration of a defined jet area. Although the decay rate of the jet from the circular nozzle was slightly higher than the decay rate of the jet from the wedge-shaped nozzle, the mixing performance of the wedge-shaped nozzle exceeded that of the circular nozzle in all other comparison parameters. The jet from the wedge-shaped nozzle penetrated further and its area grew more rapidly than the same parameters for the jet from the circular nozzle. The oil flow photography showed that the wedge-shaped nozzle also had no separation zone in front of it, whereas the circular nozzle had a large separation zone. A separation zone in front of a fuel injector in a scramjet engine can result in damage to the combustor from the extreme heat fluxes to the wall. Also, the total pressure loss in the combustor should be lower for fuel injection through a wedge-shaped nozzle due to the elimination of the normal shock. It was concluded that wedge-shaped fuel injectors should perform better than circular fuel injectors in supersonic combustors. / Master of Science

Active Structural Acoustic Control (ASAC) has been previously demonstrated for systems excited by single and multiple frequency disturbances. This work is an extension of ASAC techniques to the control of sound radiation from structures excited by a disturbance with broadband frequency content. An adaptive, multi-input multi-output (MIMO), feedforward broadband acoustic control system has been developed. The control approach is the least mean squares (LMS) algorithm. The compensators are adaptive finite impulse response (FIR) digital filters. The system identification of the control loop transfer functions were implemented with infinite impulse response (IIR) digital filters. The control inputs were implemented with piezoelectric ceramic actuators (PZT). Both far-field microphones and polyvinylidene fluoride (PVDF) structural sensors designed to optimally control the efficient acoustic radiating modes were used as error sensors. The disturbance was band-limited zero mean white noise and was input with a point force shaker. In the control of harmonically excited systems, satisfactory attenuation is possible with a single-input single-output (SISO) controller. In contrast, for Systems excited with broadband disturbances, a MIMO controller is necessary for significant acoustic attenuation. Experimental results for the control of two simplySupported plates are presented. Aspects addressed include the evaluation of the microphone and PVDF error sensors, optimization of sensors and actuators, FIR compensator size, controller sample rate, and convergence time. Thus this work provides a methodology for controlling broadband acoustic radiation from a structure with regard to the practical aspects of ASAC. / Master of Science

Comprehensive studies are needed to better understand the original acoustical features of historical baths in order to uncover the historical technologies that enabled the acoustical performance for which they are renowned and to ensure they retain this performance with time. In this study, acoustic performances of Seng&uuml / l Hamami and Kadi Hamami, two 15th century historical baths belonging to the Ottoman period, were examined to discover their original acoustical features and to assess their present situation by taking into consideration the recent incompatible repair work. The analyses were done by using 3D computer modeling and acoustical simulation methods supported by laboratory analyses. The results were evaluated in terms of sound absorption characteristics of historical lime-based plasters, the original acoustical features of historical Turkish baths and acoustical failures related to recent repairs. The study showed that these baths had originally well-designed acoustical features provide for a proper environment for musical performances. This success was attributed to the conscious use of historical materials having high sound absorption characteristics. It was seen that these original acoustical features had been destroyed by wrong repairs using cement-based plasters. These plasters demonstrated incompatible acoustical properties, such as less porosity and lower sound absorption coefficients. This study also helped to define acoustical specifications for such historical baths to be maintained in restoration work.

Near-field Acoustical Holography is a tool that is conventionally used to visualize sound fields through an inverse process in a three-dimensional space so that either sound field projections or sound source localization can be performed. The visualization is conducted by using sound pressure measurements taken in the near-field region close to the surface of the unknown sound source. Traditional Fourier-based Near-field Acoustical Holography requires a large number of measurement inputs to avoid spatial truncation effects. However, the use of a large number of measurements is usually not feasible since having a large number of microphones is costly, and usually the array is limited in size by the physical environment, thus limiting the practicality of this method. In the present work, because of the desire to reduce the number of microphones required to conduct acoustical holography, a method known as Statistically Optimized Near-field Acoustical Holography initially proposed by Steiner and Hald was analyzed. The main difference between the present work and the concept mentioned by Steiner and Hald is the cylindrical coordinate system employed here for the purpose of experimenting on a bladeless fan, which resembles a cylindrical structure and which could be assumed to be a cylindrical source. The algorithm was first verified <i>via</i> simulations and measurements, and was then applied to experimental data obtained <i>via</i> pressure measurements made with a cylindrical microphone array. Finally, suggestions for noise control strategies for the bladeless fan are described, based on the measurement results.<br>

[Truncated abstract] This thesis presents three different methods to investigate flexural wave propagation and scattering, power flow and transmission efficiencies, and dynamic stress concentration and fatigue failures in structural dynamics. The first method is based on the acoustical wave propagator (AWP) technique, which is the main part described in this thesis. Through the numerical implementation of the AWP, the complete information of the vibrating structure can be obtained including displacement, velocity, acceleration, bending moments, strain and stresses. The AWP technique has been applied to systems consisting of a one-dimensional stepped beam, a two-dimensional thin plate, a thin plate with a sharp change of section, a heterogeneous plate with multiple cylindrical patches, and a Mindlin?s plate with a reinforced rib. For this Mindlin?s plate structure, through the comparison of the results obtained by Mindlin?s thick plate theory and Kirchhoff?s classical thin plate theory, the difference of theoretical predicted results is investigated. As part of these investigations, reflection and transmission coefficients, power flow and transmission efficiencies in a onedimensional stepped beam, and power flow in a two-dimensional circular plate structure, are studied. In particular, this technique has been successfully extended to investigate wave propagation and scattering, and dynamic stress concentration at discontinuities. Potential applications are fatigue failure prediction and damage detection in complex structures. The second method is based on experimental techniques to investigate the structural response under impact loads, which consist of the waveform measuring technique in the time domain by using the WAVEVIEW software, and steady-state measurements by using the Polytec Laser Scanning Vibrometer (PLSV) in the frequency domain. The waveform measuring technique is introduced to obtain the waveform at different locations in the time domain. These experimental results can be used to verify the validity of predicted results obtained by the AWP technique. Furthermore, distributions of dynamic strain and stress in both near-field (close to discontinuities) and far-field regions are investigated for the study of the effects of the discontinuities on reflection and transmission coefficients in a one-dimensional stepped beam structure. Experimental results in the time domain can be easily transferred into those in the frequency domain by the fast Fourier transformation, and compared with those obtained by other researchers. This PLSV technique provides an accurate and efficient tool to investigate mode shape and power flow in some coupled structures, such as a ribbed plate. Through the finite differencing technique, autospectral and spatial of dynamic strain can be obtained. The third method considered uses the travelling wave solution method to solve reflection and transmission coefficients in a one-dimensional stepped beam structure in the time domain. In particular, analytical exact solutions of reflection and transmission coefficients under the given initial-value problem are derived. These analytical solutions together with experimental results can be used to compare with those obtained by the AWP technique.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Pleural effusion is a common respiratory condition that is characterized by an abnormal collection of fluid in the lung cavity. In this study, an innovation using the transmission of sound into the respiratory system as a novel tool to detect fluid in the lung was developed. First, the method was evaluated on a phantom model of a lung. Based on the results of this test model, the appropriate technique was used in a clinical study. This method has several advantages, such as that is non-invasive, low cost, and easy for clinical review. Two techniques, including analysis of the frequency response of the model and the transient time of transmitted sound in the lung, were evaluated in the phantom models of the human lung. Two phantom models with similar geometry to the human lung, including a healthy model (without fluid in the model) and a pleural effusion model (with bulk of fluid in the model) were developed. These models have acoustical properties similar to the lung parenchyma. To obtain the frequency responses of the model, a sine sweep signal was transmitted into the model and the frequency response of the model was then calculated using the fast Fourier transform. The transient time of the transmitted sound was calculated using a cross correlation method. The results show that the locations of fluid in the model were detectable using both techniques. However, the transient time technique is better than the frequency response technique because it is simple, fast, and has potential for use in a clinical enviorment. Based on the results obtained from the phantoms, the transient time method was performed on both 22 healthy participants and four patients diagnosed with pleural effusion. To perform this technique on human subjects, a data acquisition system was developed. Two types of sound, including a complex chirp sound and a polyphonic sound, were transmitted into the respiratory systems of the participants. The time delay between a reference microphone, located on the trachea of the subject, and eight microphones attached to the chest was computed using a cross correlation method, and the effect of inhalation and lung size on the transient time of transmitted sound on the healthy subject was evaluated. The results show that using transmission of sound in the lung is a promising technique in the diagnosis of pleural effusion. / AFRIKAANSE OPSOMMING: Pleurale effusie is 'n algemene respiratoriese toestand wat gekenmerk word deur 'n abnormale versameling van vloeistof in die longholte. In hierdie studie is 'n innoverende manier ontwikkel om vloeistof in die long met behulp van die transmissie van klank te bespeur. Die metode is eers op 'n fantoommodel van 'n long geëvalueer. Op grond van die resultate van hierdie toetsmodel is die geskikte tegniek in 'n kliniese studie gebruik. Hierdie metode het verskeie voordele, soos dat dit ingreepsvry is, nie duur is nie en kliniese evaluering moontlik maak. Twee tegnieke, naamlik ontleding van die frekwensierespons van die model en die oorgangstyd van versende klank in die long, is in die fantoommodel van die menselong geëvalueer. Twee fantoommodelle met soortgelyke geometrie aan die menselong, met inbegrip van 'n gesonde model (sonder vloeistof in die model) en 'n pleurale-effusie-model (met 'n massa vloeistof in die model), is ontwikkel. Hierdie modelle het akoestiese eienskappe soortgelyk aan die longparenchiem. Om die frekwensieresponse van die model te verkry, is 'n sinuskrommesein tot in die model versend. Die frekwensierespons van die model is met behulp van die vinnige Fourier-transformasie bereken. Die oorgangstyd van die versende klank is deur 'n kruiskorrelasie-metode bereken. Die resultate toon dat die ligging van die vloeistof in die model met albei tegnieke bespeur kan word. Die oorgangstyd-tegniek is egter beter as die frekwensierespons-tegniek, aangesien dit eenvoudig en vinnig is en maklik in 'n kliniese omgewing gebruik kan word. Op grond van die resultate wat van die fantome verkry is, is die oorgangstyd-metode op 22 gesonde deelnemers en vier pasiënte wat met pleurale effusie gediagnoseer is, uitgevoer. 'n Dataverkrygingstelsel is ontwikkel ten einde hierdie tegniek op proefpersone uit te voer. Twee soorte klank, naamlik 'n komplekse tjirpgeluid en 'n polifoniese klank, is na die respiratoriese stelsels van die deelnemers versend. Die tydvertraging tussen 'n verwysingsmikrofoon in die tragea van die proefpersoon en agt mikrofone wat aan die bors vasgeheg is, is met 'n kruiskorrelasie-metode bereken, en die uitwerking van inaseming en longgrootte op die oorgangstyd van versende klank op die gesonde proefpersone is geëvalueer. Die resultate toon dat die gebruik van transmissie van klank in die long 'n belowende tegniek vir die diagnose van pleurale effusie is.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Telephony has developed substantially over the years, but the fundamental auditory model of mixing all the audio from di erent sources together into a single monaural stream has not changed since the telephone was rst invented. Monaural audio is very di cult to follow in a multiple-source situation such as a conference call. Sound originating from a speci c point in space will travel along a slightly di erent path to each ear. Although we are not consciously aware of it, our brain processes these spatial cues to help us to locate sounds in space. It is this spatial information that allows us to focus our attention and listen to a single speaker in an environment where many di erent sources may be active at the same time; a phenomenon known as the \cocktail party e ect". It is possible to reproduce these spatial cues in a sound recording, using Head-Related Transfer Functions (HRTFs) to allow a listener to experience localised audio, even when sound is reproduced through a headset. In this thesis, spatial audio is implemented in a telephony application as well as in a virtual world. Experiments were conducted which demonstrated that spatial audio increases the intelligibility of speech in a multiple-source environment and aids active speaker identi cation. Resource usage measurements show that these bene ts are, however, not without a cost. In conclusion, spatial audio was shown to be an improvement over the monaural audio model traditionally implemented in telephony. / AFRIKAANSE OPSOMMING: Telefonie het ansienlik ontwikkel oor die jare, maar die basiese ouditiewe model waarin die klank van alle verskillende bronne bymekaar gemeng word na een enkelouditoriese stroom het nie verander sedert die eerste telefoon gebou is nie. Enkelouditoriese klank is baie moeilik om te volg in 'n meervoudigebron situasie, soos byvoorbeeld in 'n konferensie oproep. Klank met oorsprong by 'n sekere punt in die ruimte sal 'n e ens anderse pad na elke oor volg. Selfs is ons nie aktief bewus hiervan nie, verwerk ons brein hierdie ruimtelike aanduidinge om ons te help om klanke in die ruimte te vind. Dit is hierdie ruimtelike inligting wat ons toelaat om ons aandag te vestig en te luister na 'n enkele spreker in 'n omgewing waar baie verskillende bronne terselfdertyd aktief mag wees, 'n verskynsel wat bekend staan as die \skemerkelkiepartytjiee ek". Dit is moontlik om hierdie ruimtelike leidrade na 'n klank te reproduseer met behulp van hoofverwandeoordragfunksies (HRTFs) en om daardeur 'n luisteraar gelokaliseerde klank te laat ervaar, selfs wanneer die klank deur middel van oorfone gespeel word. In hierdie tesis word ruimtelike klank ge mplementeer in 'n telefonieprogram, sowel as in 'n virtuelew^ereld. Eksperimente is uitgevoer wat getoon het dat ruimtelike klank die verstaanbaarheid van spraak in 'n meerderebronomgewing verhoog en help met aktiewe spreker identi kasie. Hulpbrongebruiks metings toon aan dat hierdie voordele egter nie sonder 'n koste kom nie. Ter afsluiting, dit is bewys dat ruimtelike klank 'n verbetering tewees gebring het oor die enkelouditorieseklankmodel wat tradisioneel in telefonie gebruik het.

A caracterização das patologias da laringe até o presente momento é predominantemente realizada de forma qualitativa. Alguns trabalhos recentes têm quantificados parâmetros acústicos no intuito de discriminar as diversas patologias. Este trabalho verifica os valores médios das diversas medidas acústicas da voz e as relaciona com as diferentes patologias. Desta forma, futuramente será possível utilizar estes valores para quantificar e acompanhar diferentes estágios do tratamento da patologia. O conjunto de valores médios compõem o que chamamos de perfil acústico. / Until now the characterization of larynx pathologies has been done in a subjective manner. Recently some researches have been conducted in order to quantify acoustic parameters mainly to discriminate the larynx pathologies. In this work several acoustic parameters of voice was evaluated and their correlation with the pathologies were established. In the future, would be possible to use these parameters to quantify and to follow the therapy procedures. These values constitute the acoustic profile of the pathologies.

<div>Fluid power is widely used in a variety of applications such as construction machines, aerospace, automotive, agricultural machinery, manufacturing, etc. Although this technology has many obvious advantages such as compactness, robustness, high power density, and so forth, there is much room for improvement, of which one of the most important and challenging problems is the noise.</div><div><br></div><div>Different institutes have been researching fluid power noise for decades. However, much of the experimental investigation was based on simple measurement and analysis techniques, which left the designers/researchers no method of understanding the complicated phenomena. A microphone array is a powerful tool that unfortunately has not been introduced to the fluid power noise research. By capturing the magnitude and phase information in space, a microphone array enables the noise source identification, separation, localization and so forth.</div><div><br></div><div>This thesis focuses on implementing the microphone array processing techniques on a synthetic microphone array for fluid power noise diagnostics. Differing from traditional scan-based approaches, the synthetic array is created by synchronizing the non-synchronous measurements to achieve the equivalent effect of a multi-microphone snapshot. The final results will show the power of microphone arrays and provide an economical solution to achieve approximate results when a real microphone array is not available.</div>

Boundary layers are regions where turbulence develops easily. In the case where the flow occurs on a surface showing a certain degree of roughness, turbulence eddies will interact with the roughness elements and will produce an acoustic field. This thesis aims at predicting this type of noise with the help of the Computational Fluid Dynamics (CFD) simulation of a wall jet using the Reynolds Average Navier-Stokes (RANS) equations. A frequency spectrum is reconstructed using a representation of the turbulence with uncorrelated sheets of vorticity. Both aerodynamic and acoustic results are compared to experimental measurements of the flow. The CFD simulation of the flow returns consistent results but would benefit from a refinement of the grid. The surface pressure spectrum presents a slope in the high frequencies close to the experimental spectrum. The far field noise spectrum has a 5dB difference to the experiments. / by Jean-Baptiste Blanc. / Thesis (M.S.C.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.