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Dissertations / Theses on the topic 'Acoustics'
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1
Liddy, David W. Holmes John F. "Acoustic room de-reverberation using time-reversal acoustics /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA374579.
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Thesis (M.S. in Applied Physics) Naval Postgraduate School, September 1999.<br>"September 1999". Thesis advisor(s):, Andrés Larraza, Bruce C. Denardo. Includes bibliographical references (p. 49). Also available online.
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Liddy, David W., and John F. Holmes. "Acoustic room de-reverberation using time-reversal acoustics." Thesis, Monterey, California: Naval Postgraduate School, 1999. http://hdl.handle.net/10945/13698.
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This thesis probes the performance of one-channel time-reversal acoustics in a chamber in terms of the geometry of the cavity. In particular, a rectangular chamber is compared to an enclosure that has a stadium shape. The mode structure in the rectangular cavity is highly symmetric, while it is highly irregular in the stadium-shaped cavity. Time- reversal acoustic techniques produce an improved focus in the latter. The focusing quality is determined as a function of frequency, time-reversal window size, and spatial extent. A scheme for encrypted acoustic communication, both in air and underwater, that uses multiple broadband signals with identical bandwidth, Hanning window source spectra, and center frequencies separated by half the bandwidth, allowing for null detection between adjacent signals, is successfully investigated.
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Smurzynski, Jacek. "Acoustic Foundations of Signal Enhancement and Room Acoustics." Digital Commons @ East Tennessee State University, 2007. https://www.amzn.com/1597565628.
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Book Summary: Chermak and Musiek's two-volume, award-winning handbooks are back in newly revised editions. Extensively revised and expanded, Volume II provides expanded coverage of rehabilitative and professional issues, detailing intervention strategies for children and adults. Volume I provides comprehensive coverage of the auditory neuroscience and clinical science needed to accurately diagnose the range of developmental and acquired central auditory processing disorders in children, adults, and older adults.
Building on the excellence achieved with the best-selling 1st editions which earned the 2007 Speech, Language, and Hearing Book of the Year Award the second editions include contributions from world-renowned authors detailing major advances in auditory neuroscience and cognitive science; diagnosis; best practice intervention strategies in clinical and school settings; as well as emerging and future directions in diagnosis and intervention.
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Ajaz, Mahnoor. "Finite Difference Time Domain Modelling of Ultrasonic Parametric Arrays in Two-Dimensional Spaces." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1619109761801613.
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Alenius, Emma. "Flow Duct Acoustics : An LES Approach." Doctoral thesis, KTH, MWL Strömningsakustik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-104777.
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The search for quieter internal combustion engines drives the quest for a better understanding of the acoustic properties of engine duct components. Simulations are an important tool for enhanced understanding; they give insight into the flow-acoustic interaction in components where it is difficult to perform measurements. In this work the acoustics is obtained directly from a compressible Large Eddy Simulation (LES). With this method complex flow phenomena can be captured, as well as sound generation and acoustic scattering. The aim of the research is enhanced understanding of the acoustics of engine gas exchange components, such as the turbocharger compressor.In order to investigate methods appropriate for such studies, a simple constriction, in the form of an orifice plate, is considered. The flow through this geometry is expected to have several of the important characteristics that generate and scatter sound in more complex components, such as an unsteady shear layer, vortex generation, strong recirculation zones, pressure fluctuations at the plate, and at higher flow speeds shock waves. The sensitivity of the scattering to numerical parameters, and flow noise suppression methods, is investigated. The most efficient method for reducing noise in the result is averaging, both in time and space. Additionally, non-linear effects were found to appear when the amplitude of the acoustic velocity fluctuations became larger than around 1~\% of the mean velocity, in the orifice. The main goal of the thesis has been to enhance the understanding of the flow and acoustics of a thick orifice plate, with a jet Mach number of 0.4 to 1.2. Additionally, we evaluate different methods for analysis of the data, whereby better insight into the problem is gained. The scattering of incoming waves is compared to measurements with in general good agreement. Dynamic Mode Decomposition (DMD) is used in order to find significant frequencies in the flow and their corresponding flow structures, showing strong axisymmetric flow structures at frequencies where a tonal sound is generated and incoming waves are amplified.The main mechanisms for generating plane wave sound are identified as a fluctuating mass flow at the orifice openings and a fluctuating force at the plate sides, for subsonic jets. This study is to the author's knowledge the first numerical investigation concerning both sound generation and scattering, as well as coupling sound to a detailed study of the flow.With decomposition techniques a deeper insight into the flow is reached. It is shown that a feedback mechanism inside the orifice leads to the generation of strong coherent axisymmetric fluctuations, which in turn generate a tonal sound.<br><p>QC 20121113</p>
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Zou, Chengzhe. "Structural Acoustics of Reconfigurable Tessellated Arrays for Acoustic Energy Guiding." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1574285872850491.
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Kriewaldt, Hannah A. "Communications performance of an undersea acoustic wide-area network." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Mar%5FKriewaldt.pdf.
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Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, March 2006.<br>Thesis Advisor(s): Joseph A. Rice. "March 2006." Includes bibliographical references (p.57-59). Also available online.
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Chen, Zhixin. "An investigation of acoustic impulse response measurement and modeling for small rooms." Diss., Montana State University, 2007. http://etd.lib.montana.edu/etd/2007/chen/ChenZ1207.pdf.
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Ward, Gareth Paul. "The manipulation of sound with acoustic metamaterials." Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/29774.
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The original work presented in this thesis pertains to the design and characterisation of resonant-cavity-based acoustic metamaterials, with a focus on airborne sound. There are five separate experimental chapters, each with a unique approach to the design of periodic structures that can support and manipulate air-bound acoustic surface waves via diffractive coupling between resonant-cavities. The first two chapters concern measurement of the acoustic transmission though various kinds of periodic slit-arrays, whilst the latter three chapters utilise a near-field imaging technique to directly record and characterise the dispersion of trapped acoustic surface waves. The first experimental chapter investigates the effect that thermodynamic boundary layers have on the Fabry-Perot-like cavity resonances that are so often utilised in acoustic metamaterial design. At audio frequencies, these boundary layers have a decay length that is typically more than two orders of magnitude smaller than the width of the resonating slit-cavities, hence it may naively be assumed that their effect can be ignored. However, by studying in detail the effect that reducing slit-cavity width has on the frequency of the measured cavity-resonance, for both a single slit cavity and a slit-cavity array, it is found that these boundary layer effects become significant on a far larger scale than their characteristic thickness. This is manifested in the form of a reduction in the resonant frequency as the slit-width is narrowed. Significant attenuation of the resonance and a 5% reduction in the effective speed of sound through the cavity is measured when the boundary layers form only 5% of the total width of each slit. Hence, it is both shown that the prevalent loss free treatment of acoustic slit-cavities is unrealistic, and that one may control the effective speed of sound through the slit-cavities with a simple change in slit-width. The second chapter explores the effect of ‘compound’ grating structure on trapped acoustic surface waves, a compound grating having a basis comprised of more than one resonating element. The angle dependent acoustic transmission spectra of four types of aluminium slit-array are recorded, and for the compound gratings, it is found that sharp dips appear in the spectra that result from the excitation of a ‘phase-resonance’. This occurs as new degrees-of-freedom available to the acoustic near-field allow the fields of adjacent cavities within a unit-cell to be both out-of-phase and strongly enhanced. By mapping the transmission spectra as a function of in-plane wavevector, the dispersions of the modes supported by each sample are determined. Hence, the origin of the phase-resonant features may be described as acoustic surface waves that have been band-folded back into the radiative regime via diffraction from higher in-plane wavevectors than possible on a simple grating. One of the samples is then optimised via numerical methods that account for thermodynamic boundary layer attenuation, resulting in the excitation of a sharp, deep transmission minimum in a broad maximum that may be useful in the design of an acoustic filter. The third chapter introduces the near-field imaging technique that can be utilised to directly characterise acoustic surface waves, via spatial fast Fourier transform algorithms of high-resolution pressure field maps. The acoustic response of a square-lattice open-ended hole array is thus characterised. It is found that over a narrow frequency band, the lattice symmetry causes the acoustic surface power flow to be channelled into specific, predictable directions, forming ‘beams’ with a well defined width. In chapter four, the existence of the ‘acoustic line mode’ is demonstrated, a type of acoustic surface wave that may be supported by a simple line of open-ended hole cavities. The near-field imagine technique is again used to extract the mode dispersion. This acoustic line mode may be readily manipulated, demonstrated by arrangement of the line of holes into the shape of a ring. The existence of this type of mode offers a great deal of potential for the control of acoustic energy. Chapter five explores the effect of ‘glide-symmetry’ on a pair of acoustic line modes arranged side-by-side. A control sample not possessing glide- symmetry is first characterised, where measurement of the acoustic near- fields show that this sample supports two separate modes at different frequencies, with their phase either symmetric or anti-symmetric about the mirror plane between the lines of holes. One of these lines is then shifted along its periodicity by half of a grating pitch, thus creating glide-symmetry. The resulting sample is found to support a single hybrid mode, capable of reaching a much larger in-plane wavevector than possible on a simple grating with no gaps in its band-structure, and displaying a region of negative dispersion. The third sample demonstrates how one may increase the coupling strength between the two lines of holes via manipulation of the cavity shape, thus enhancing the glide-symmetry effect. The thesis concludes with preliminary investigations into other possible ways of manipulating acoustic surface waves, such as with the use of ‘screw-symmetry’.
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Susbilla, Robert Tayag. "Casimir acoustics." Thesis, Monterey, California. Naval Postgraduate School, 1996. http://hdl.handle.net/10945/8062.
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Approved for public release; distribution is unlimited<br>When the indirect manifestations of the electromagnetic ZPF are interpreted as due to radiation pressure, acoustic noise can render an excellent analog to probe previous as well as recently proposed behavior. An acoustic chamber for isotropic and homogeneous acoustic noise of controllable spectral shape has been built. The noise can be driven up to levels of 130 dB (re 20 microPa) in a band of frequencies up to 50 kHz wide. When driving the system with broadband noise, it will be used (1) to test the Galilean invariance of a spectral shape proportional to the square of the frequency, (2) the force of attraction between parallel plates (analog to Casimir force), (3) the acoustic radiation emitted by a cavity that is made to oscillate at high frequencies (analog to the proposed Casimir radiation), (4) the change in the frequency of oscillation of a pendulum as the noise intensity is varied (analog to the proposed origin of inertia), and (5) the force of attraction between two spheres due to the acoustic shadow that each one casts onto the other (analog to van der Waals force and the proposed origin of gravitation).
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Chang, Ding-chen. "Underwater acoustic pulse propagation using the Recursive Ray Acoustics (RRA) Algorithm." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA303441.
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Durany, Vendrell Jaume. "Geometrical room acoustics: ray based simulation for room acoustics." Doctoral thesis, Universitat Pompeu Fabra, 2016. http://hdl.handle.net/10803/395190.
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L’acústica de sales és la ciència encarregada d’estudiar la propagació del so en
entorns tancats. La informació acústica de qualsevol entorn, coneguda com la
resposta impulsional, s’expressa en termes del camp acústic com una funció de
l’espai i el temps. La formulació analítica de la distribució de les variables del so és,
en general, extremadament complexa d’obtenir i només existeixen solucions
d’escenaris molt simples i irreals. Per tant, l’ús d’ordinadors per solucionar aquest
tipus de problemes ha emergit com una alternativa adequada per calular funcions de
resposta.
En aquesta Tesi ens hem centrat en l’ús de mètodes basats en rajos per calcular
funcions de resposta. Més concretament, presentem el disseny i la implementació
d’un motor de traçat de rajos que calcula funcions de resposta en cualsevol entorn
virtual, obtenint no només la funció de resposta per la presió sinó també pel vector de
velocitats del camp acústic. Amb aquesta informació extra tenim totes les dades
necessàries per modelar la propagació del so i podem de forma natural espacialitzar
un so per qualsevol configuració d’altaveus.
Aquesta recerca contribueix als aspectes principals del càlcul de funcions de resposta
utilitzant mètodes basats en rajos. El motor de traçat de rajos que presentem inclou un
mètode desenvolupat per aplicar la solució analítica de la Funció de Distribució
Acústica de Reflectància Bidireccional (A-BRDF) al Model de Dispersió Basat en
Vectors (VBS), fet que redueix molt notablement el cost computacional.<br>Room acoustics is the science devoted to study sound propagation in enclosures
where the sound conduction medium is bounded on all sides by walls, ceiling and
floor. The acoustic information of any room, the so-called impulse response, is expressed
in terms of the acoustic field as a function of space and time. The analytical
formulation of the sound variables distribution is, in general, extremely hard to obtain
and there only exist solutions of very simple and unrealistic scenarios. Therefore the
use of computers for solving this type of problems has emerged as a proper
alternative to calculate impulse responses.
In this Thesis we focus on the use of the ray-based methods to compute impulse
responses. More precisely, we present the design and implementation of a sound ray
tracing engine that computes the impulse response in any given environment not only
for the pressure but also for the velocity vector of the acoustic field. With this extra
information we have all the necessary data to model the propagation of sound and we
can then naturally spatialize the sound to any speakers layout.
This research contributes to the main aspects in the computation of impulse responses
using a ray-based approach. The presented ray tracing engine includes a method
developed to apply the analytical solution for the Acoustic Bidirectional Reflectance
Distribution Function (A-BRDF) in the Vector Based Scattering Model (VBS), which
reduces dramatically the computational cost.
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Wu, Xiao-Feng. "Variational principles for acoustic radiation and diffraction from underwater structures." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/17377.
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Keeser, Christopher Corson. "Shallow under water communication with passive phase conjugation and iterative demodulation and decoding." Pullman, Wash. : Washington State University, 2008. http://www.dissertations.wsu.edu/Thesis/Fall2008/c_keeser_112408.pdf.
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Thesis (M.S. in electrical engineering)--Washington State University, December 2008.<br>Title from PDF title page (viewed on Jan. 21, 2009). "School of Electrical Engineering and Computer Science." Includes bibliographical references (p. 51-53)
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Jung, Du San. "Detection of binary phase-shift keying signal in multioath propagation." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Jun%5FJung.pdf.
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Angelopoulos, Pavlos. "Direct-sequence spread-spectrum acoustic communications with CRV Decomposition." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FAngelopoulos.pdf.
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Thesis (M.S. in Electrical Engineering and M.S. in Engineering Acoustics)--Naval Postgraduate School, June 2004.<br>Thesis advisor(s): Roberto Cristi, Kevin B. Smith. Includes bibliographical references (p. 91-94). Also available online.
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Hurrell, Andrew M. "Finite difference modelling of acoustic propagation and its applications in underwater acoustics." Thesis, University of Bath, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250842.
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Cates, Andrew Thomas. "Nonlinear diffractive acoustics." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315809.
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Onur, Cagla. "Acoustic Tracking Of Ship Wakes." Phd thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615656/index.pdf.
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Theories about ship wake structure, bubble dynamics, acoustic propagation through bubble clouds, backscattering and target strength of bubble clouds have been investigated and related Matlab simulations have been carried on. Research has been carried on algorithms for ship wake acoustic detection and tracking. Particle filter method has been simulated with Matlab for target tracking using wake echo measurements. Simulation results are promising.
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Kenney, Debra M. "A short water-filled pulse tube for the measurement of the acoustic properties of materials at low frequencies." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/16671.
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Root, Joseph Andrew. "Capabilities of an underwater acoustic volumetric array using time-reversal." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/18944.
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Woods, Simon Nicholas. "Acoustic Inspection of Timber." Thesis, University of Canterbury. Electrical and Computer Engineering, 2006. http://hdl.handle.net/10092/3679.
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The ability to determine wood quality using non-destructive tests has enormous potential for the forestry industry in both research and commercial applications. This thesis describes some of the theory of acoustic waves in wood and how wood stiffness can be estimated by measuring the velocity of acoustic waves. Attention is paid to both resonance and stress wave timer technologies and the benefits and problems with both. A detailed description is given of the design of a new tool (Treetap 5.0) to aid in future, acoustic based, timber inspection research.
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Kumon, Ronald Edward. "Nonlinear surface acoustic waves in cubic crystals /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Sineiro, Guilherme da Silva. "Underwater multimode directional transducer evaluation." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FSineiro.pdf.
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Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, December 2003.<br>Thesis advisor(s): Thomas J. Hofler, Joseph A. Rice. Includes bibliographical references (p. 53-54). Also available online.
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Dessalermos, Spyridon. "Undersea acoustic propagation channel estimation." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Jun%5FDessalermos.pdf.
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Thesis (M.S. in Electrical Engineering and M.S. in Applied Physics)--Naval Postgraduate School, June 2005.<br>Thesis Advisor(s): Joseph Rice, Roberto Cristi. Includes bibliographical references (p. 117-119). Also available online.
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Fabre, Josette. "Representative Environments for Reduced Estimation Time of Wide Area Acoustic Performance." ScholarWorks@UNO, 2010. http://scholarworks.uno.edu/td/1156.
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Advances in ocean modeling (Barron et al., 2006) have improved such that ocean forecasts and even ensembles (e.g., Coelho et al., 2009) representing ocean uncertainty are becoming more widely available. This facilitates nowcasts (current time ocean fields / analyses) and forecasts (predicted ocean fields) of acoustic propagation conditions in the ocean which can greatly improve the planning of acoustic experiments. Modeling of acoustic transmission loss (TL) provides information about how the environment impacts acoustic performance for various systems and system configurations of interest. It is, however, very time consuming to compute acoustic propagation to and from many potential source and receiver locations for multiple locations on an area-wide grid for multiple analysis / forecast times, ensembles and scenarios of interest. Currently, to make such wide area predictions, an area is gridded and acoustic predictions for multiple directions (or radials) at each grid point for a single time period or ensemble, are computed to estimate performance on the grid. This grid generally does not consider the environment and can neglect important environmental acoustic features or can overcompute in areas of environmental acoustic isotropy. This effort develops two methods to pre-examine the area and time frame in terms of the environmental acoustics in order to prescribe an environmentally optimized computational grid that takes advantage of environmental-acoustic similarities and differences to characterize an area, time frame and ensemble with fewer acoustic model predictions and thus less computation time. Such improvement allows for a more thorough characterization of the time frame and area of interest. The first method is based on critical factors in the environment that typically indicate acoustic response, and the second method is based on a more robust full waveguide mode-based description of the environment. Results are shown for the critical factors method and show that this proves to be a viable solution for most cases studied. Limitations are at areas of high loss, which may not be of concern for exercise planning. The mode-based method is developed for range independent environments and shows significant promise for future development.
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Bechwati, Fouad. "Acoustics of activated carbon." Thesis, University of Salford, 2008. http://usir.salford.ac.uk/26573/.
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This thesis describes a study into how sound interacts with activated carbon, a material that exhibits adsorbing and desorbing properties. Adsorption is where molecules from the surrounding gas are attracted to the material microstructure and held in place by a weak physical attraction force named after the scientist van der Waals\ desorption is the opposite process. Activated carbons include a complex porous structure, with a large internal surface area, and a considerable adsorption capacity caused by free electrons in the deformed graphene layers. The process of adsorption and desorption is usually associated with energy exchanges, caused by transfers of heat between the adsorbate molecules and the adsorbent surface. The study of acoustic interactions with granular activated carbons at normal conditions makes the subject of this doctoral thesis. Two main physical phenomena were seen to accompany sound propagation through the material: (i) an increase in volume compliance which is assumed to be caused by a change in the density of the interacting gas, and (ii) excess absorption at low frequencies thought to be due to the energy lost in the adsorption/desorption hysteresis. For the former, measurements on the impedance of low frequency Helmholtz resonators reveal significant shifts in resonance when activated carbon is used as a porous liner in the backing volume. At constant aperture dimensions, these shifts are attributed to a larger apparent volume of the resonator as compared to an empty backing volume. This phenomenon is in direct contravention of the physical theory associated with Helmholtz resonators as the resonant frequency of a device increases slightly when a porous solid is placed in the backing volume. An upper frequency limit of SOOHz is also determined where sorption effects in activated carbon are assumed to become almost negligible in relation to sound propagation. For the latter, the excess absorption at low frequency, a series of experiments to reveal the physical cause of the phenomenon have been undertaken. Hysteresis was observed during the sorption of humid air onto activated carbon at room temperature. At such conditions, the different rates of adsorption and desorption lead to a disturbance in the system equilibrium and cause a change in entropy. The return of the system to equilibrium is an exothermic process hence involves energy losses between activated carbon and the surrounding gas. This is suggested as a possible cause of the excess attenuation. However,the relaxation times are rather long for acoustic propagation, and further work is needed to examine this. An experimental apparatus to explore sound propagation through the material was devised. Results showed a violation of the equation of state for the relationship between volume and pressure: as the volume in a sealed chamber was reduced at constant temperature, the measured pressure change was found to be lower for a sample of activated carbon than when the chamber was empty; a phenomenon assumed due to the differences between adsorption and desorption rates. A new method for determining the porosity of a material exhibiting adsorption at acoustic pressures has been devised and found to be 81 ±7% for the granular sample examined. BET analysis and examination of electron microscope pictures allowed the pore size distribution to be found. Although the activated carbon sample has many very small pores (0.7nm in width), the BET isotherm showed that these will be saturated with water vapour in normal conditions. Consequently, the pores that affect sound propagation are those between the grains of the activated carbon, and the macropores (>50nm) on the surface of the grains. A theoretical model is developed and outlined based on the Langmuir isotherm. This was used to predict the sound propagation within the material and is compared to acoustic impedance measured in a large low frequency impedance tube, which was constructed especially for this project. The match between theory and measurement is rather poor, thought to be due to the lack of modelling the hysteresis effects in the adsorption- desorption cycle. Two applications of the material are examined, within a Helmholtz resonator and the cups of hearing defenders. In both cases, improved performance is seen. For instance, the use of the material in hearing defenders showed that activated carbon could be used to improve the attenuation at low frequencies in comparison to conventional foam liners.
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Kang, Jian. "Acoustics of long enclosures." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266240.
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James, Duncan Stuart. "Acoustics of cohesive sediments." Thesis, University of East Anglia, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323344.
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Thompson, Philip R. Z. (Philip Reed Zane). "Space, time and acoustics." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/78997.
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Thesis (M. Arch.)--Massachusetts Institute of Technology, Dept. of Architecture, 1988.<br>Includes bibliographical references (leaves 156-159).<br>This thesis describes the development of new concepts in acoustical analysis from their inception to implementation as a computer design tool. Research is focused on a computer program which aids the designer to visually conceive the interactions of acoustics within a geometrical~y defined environment by synthesizing the propagation of sound in a three dimensional space over time. Information is communicated through a unique use of images that are better suited for interfacing with the design process. The first part of this thesis describes the concepts behind the development of a graphic acoustical rendering program to a working level. This involves the development of a computer ray tracing prototype that is sufficiently powerful to explore the issues facing this new design and analysis methodology. The second part uses this program to evaluate existing performance spaces in order to establish qualitative criteria in a new visual format. Representational issues relating to the visual perception of acoustic spaces are also explored. In the third part, the program is integrated into the design process. I apply this acoustical tool to an actual design situation by remodeling a large performance hall in Medford, Massachusetts. Chevalier Auditorium is a real project, commissioned by the city of Medford, whose program requirements closely match my intentions in scope, scale and nature of a design for exploring this new acoustical analysis and design methodology. Finally, I summarize this program's effectiveness and discuss its potential in more sophisticated future design environments.<br>by Philip R.Z. Thompson.<br>M.Arch.
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Rendón, Pablo Luis. "Problems in nonlinear acoustics." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621365.
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Deal, Thomas J. "Reciprocity in vector acoustics." Thesis, Monterey, California: Naval Postgraduate School, 2017. http://hdl.handle.net/10945/52968.
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Approved for public release; distribution is unlimited<br>Reissued 30 May 2017 with Second Reader’s non-NPS affiliation added to title page.<br>The scalar reciprocity equation commonly stated in underwater acoustics relates pressure fields and monopole sources. It is often used to predict the pressure measured by a hydrophone for multiple source locations by placing a source at the hydrophone location and calculating the field everywhere for that source. That method, however, does not work when calculating the orthogonal components of the velocity field measured by a fixed receiver. This thesis derives a vector-scalar reciprocity equation that accounts for both monopole and dipole sources. This equation can be used to calculate individual components of the received vector field by altering the source type used in the propagation calculation. This enables a propagation model to calculate the received vector field components for an arbitrary number of source locations with a single model run for each received field component instead of requiring one model run for each source location. Application of the vector-scalar reciprocity principle is demonstrated with analytic solutions for a range-independent environment and with numerical solutions for a range-independent and a range-dependent environment using a parabolic equation model.<br>Electronics Engineer, Naval Undersea Warfare Center
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Ozgenel, Caglar Firat. "Developing A Tool For Acoustical Performance Evaluation Throughout The Design." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614066/index.pdf.
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Performance of the buildings has always been a concern for the architects. With the enhancements in the technology, it is possible to measure, analyze and evaluate the performance of an architectural design before it is built via simulation tools developed. With the evaluation of the analysis performance of the concerned space can be upgraded if simulation tools are employed throughout the design process. However, even though the simulation tools are developed for the acoustical simulation and performance analysis, it is not always simple to integrate the simulation tools to whole design process because of both specific knowledge required for the usage of the tools and the nature of the acoustical simulation tools. Within the scope of the thesis, a simulation tool, which does not require advanced knowledge on acoustics and which provides rapid feedbacks about the performance of the design for the enhancement of the performance is developed using method of image sources.
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HAND, SCOTT ANTHONY. "ADAPTABLE ACOUSTICS IN MULTI-USE MUSIC PERFORMANCE SPACES." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1083634977.
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Zagala, Franck. "Simplified Acoustic Simulations and Virtual Acoustics : Contributions to Virtual Navigation for the Visually Impaired." Electronic Thesis or Diss., Sorbonne université, 2022. http://www.theses.fr/2022SORUS254.
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Cette thèse s'inscrit dans projet RASPUTIN et s'intéresse au développement, à l'évaluation et à l'utilisation d'outils de simulation pour la réalité virtuelle acoustique dans le but d'aider les déficients visuels à préparer des navigations dans des lieux non-familiers. Alors que plusieurs outils d'assistance tels que des dispositifs de substitution sensorielle permettent de fournir des informations spatiales lors de navigations, une approche alternative consiste à concevoir un moteur de simulation et d'auralisation de l'acoustique d'un lieu en temps réel que les déficients visuels pourraient utiliser chez eux, leur permettant ainsi de naviguer virtuellement dans différents lieux, le tout dans des conditions contrôlées. Trois aspects de ce sujet sont abordés. La première partie se concentre sur la simulation et l'auralisation efficace de volumes couplés, qui sont présents dans de nombreux lieux d'intérêt pour la préparation à la navigation (mairies, hôpitaux ou musées) et où la simulation et l'auralisation peuvent s'avérer délicates. La deuxième partie s'intéresse à l'individualisation des fonctions de transfert relatives à la tête, une étape nécessaire pour délivrer une expérience auditive convaincante à chaque sujet. La dernière partie s'intéresse à certains aspects de la cognition de l'espace en fonction du paradigme utilisé pour l'exploration d'un lieu<br>This thesis takes place within the RASPUTIN project and focuses on the development, evaluation and use of immersive acoustic virtual reality simulation tools for the purpose of helping blind individuals prepare in-situ navigations in unfamiliar reverberant environments. While several assistive tools, such as sensory substitution devices, can provide spatial information during navigation, an alternative approach is to devise a real-time room acoustic simulation and auralization engine for use by blind individuals at home to enable them to virtually navigate in unfamiliar environments under controlled circumstances, hence building mental representations of these spaces prior to in-situ navigation. In this thesis, I tackle three aspects of this subject. The first part focuses on efficient simulations and auralizations of coupled volumes, which occur in many buildings of interest for navigation preparation (e.g. city halls, hospitals, or museums) and whose simulation and auralization can be challenging. The second part focuses on the individualization of head related transfer functions, which is a necessary step in providing individualized and convincing auditory experiences. Finally, the last part investigates some aspects of the space cognition following use of different learning paradigms, such as tactile maps
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Barsanti, Robert J. "Denoising of ocean acoustic signals using wavelet-based techniques." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA329379.
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Thesis (M.S. in Electrical Engineering and M.S. in Engineering Acoustics) Naval Postgraduate School, December 1996.<br>Thesis advisor(s): Monique P. Fargues and Ralph Hippenstiel. "December 1996." Includes bibliographical references (p. 99-101). Also available online.
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Abrahamson, Scott. "Automated psycho-acoustic experimental station." Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/19566.
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Fountoulakis, Radamanthis P. "Oceanographic and acoustical survey of the East Ionian Sea." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA241360.
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Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, September 1990.<br>Thesis Advisor(s): Bourke, Robert H. ; Coppens, Alan B. "September 1990." Description based on title screen as viewed on December 30, 2009. DTIC Identifiers: Raymode model, PE model. Author(s) subject terms: Oceanographic, acoustic survey, East Ionian Sea, PEmodel. Includes bibliographical references (p. 86-88). Also available in print.
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Goates, Caleb Burley. "Analytical Expressions for Acoustic Radiation Modes of Simple Curved Structures." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7494.
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The search for a convenient connection between vibration patterns on a structure and the sound radiated from that structure is ongoing in structural acoustics literature. Common techniques are wavenumber domain methods, or representation of the vibration in terms of some basis, such as structural modes or elementary radiators, and calculating the sound radiation in terms of the basis. Most choices for a basis in this situation exhibit strong coupling between the basis functions, but there is one choice which does not: Acoustic radiation modes are by definition the basis that orthogonalizes the radiation operator, meaning the radiation modes do not exhibit any coupling in radiation of sound.Acoustic radiation modes are coming up on their 30th anniversary in the literature, but still have not found wide use. This is largely due to the fact that most radiation modes must be calculated through the computationally intensive boundary element method or boundary integral equations. Analytical expressions for radiation modes, or for the radiation resistance matrix from which they are derived, are only available for a few geometries. This thesis meets this problem head on, to develop additional analytical expressions for radiation resistance matrices of cylindrically curved structures.Radiation modes are developed in the context of their use to calculate sound power. Experimental and computational sound power calculations are presented in order to validate the use of the modes developed here. In addition, the properties and trends of the developed modes are explored.
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Wan, Lin. "Matched field processing based geo-acoustic inversion in shallow water." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37266.
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Shallow water acoustics is one of the most challenging areas of underwater acoustics; it deals with strong sea bottom and surface interactions, multipath propagation, and it often involves complex variability in the water column. The sea bottom is the dominant environmental influence in shallow water. An accurate solution to the Helmholtz equation in a shallow water waveguide requires accurate seabed acoustic parameters (including seabed sound speed and attenuation) to define the bottom boundary condition. Direct measurement of these bottom acoustic parameters is excessively time consuming, expensive, and spatially limited. Thus, inverted geo-acoustic parameters from acoustic field measurements are desirable.
Because of the lack of convincing experimental data, the frequency dependence of attenuation in sandy bottoms at low frequencies is still an open question in the ocean acoustics community. In this thesis, geo-acoustic parameters are inverted by matching different characteristics of a measured sound field with those of a simulated sound field. The inverted seabed acoustic parameters are obtained from long range broadband acoustic measurements in the Yellow Sea '96 experiment and the Shallow Water '06 experiment using the data-derived mode shape, measured modal attenuation coefficients, measured modal arrival times, measured modal amplitude ratios, measured spatial coherence, and transmission loss data. These inverted results can be used to test the validity of many seabed geo-acoustic models (including Hamilton model and Biot-Stoll model) in sandy bottoms at low frequencies. Based on the experimental results in this thesis, the non-linear frequency dependence of seabed effective attenuation is justified.
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Recalde, Salas Angela Paola. "Variability in Baleen Whale Acoustical Ecology: Implications for Optimal Monitoring Using Passive Acoustics." Thesis, Curtin University, 2020. http://hdl.handle.net/20.500.11937/80627.
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This study aimed to improve the acoustical ecology knowledge of humpback and pygmy blue whales migrating through Geographe Bay - Western Australia. Vocalisations produced by each species were described. Vocalisation rates and detection probabilities varied between species and were dependent on temporal, behavioural and ecological parameters. Correlations between sound energy and visual observations were low for both species. This information suggests that optimal monitoring protocols for passive acoustics should be species specific.
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Holm, Sebastian, and Petra Lagerberg. "En effektiv lektion : En interventionsstudie kring akustikåtgärder och taluppfattbarhet hos en femteklass." Thesis, KTH, Byggvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-174028.
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Detta är en interventionsstudie av hur rumsakustiken i ett klassrum påverkar en lektion beträffande tidseffektivisering samt taluppfattbarhet. Studien jämför resultat av olika mätningar och tester före och efter en rumsakustisk åtgärd i form av ett nedpendlat akustiktak. Åtgärden utförs i ett klassrum på S:t Hansskolan i Visby, i syfte att undersöka huruvida en förbättring av ljudmiljön i klassrummet kan ge positiva samhällsekonomiska effekter. De mätningar och tester som genomförts ger tillsammans en bild av klassrummets akustiska egenskaper före och efter åtgärden. Mätningarna innefattar tidtagning av uppstartstid av en lektion samt olika rumsakustiska mätningar och tester beträffande taluppfattbarhet. Mätningar visar att klassrummets ljudmiljö efter den rumsakustiska åtgärden har förbättrats med kortare efterklangstider, förbättrade förhållanden med rummets reflexer samt ett förbättrat talöverföringsindex. Även ett lyssningstest har genomförts och resultaten visar att taluppfattbarheten har ökats. Lärarens tidtagning visar att uppstartstiden förkortats med åtminstone 15 minuter per vecka. Sammantaget visar studien att den rumsakustiska åtgärden inneburit en ökning i nyttjad lektionstid som dessutom blivit mer effektiv genom en uppmätt ökad taluppfattbarhet. Observerade nyttoeffekter anses väga tyngre än investeringskostnaden till den grad att installationen rekommenderas till befintliga skolmiljöer och inte bara vid nyproduktion.<br>This is an interventional study of how classroom acoustics affects a class in regards to time effectiveness and speech intelligibility. The study compares results of measurements and tests before and after acoustical treatments in the form of a new acoustic ceiling. The treatments are made in a classroom in S:t Hansskolan elementary school, with the aim to see whether an improvement in room acoustics can lead to socio economic gains through an increase in the effective time for a lesson. The combined measurements and tests show the state of the acoustical environment before and after the treatments. Measurements includes the time it takes to get a lesson going, as well as various acoustical measurements and tests regarding speech intelligibility. Results shows that the room acoustics have improved with reduced reverberation times, an increase in early reflexes compared to late, as well as improved speech transmission index values. The class also scores higher on hearing in noise tests, which implies an increase in speech intelligibility. The teacher’s timekeeping shows that the time it takes to start classes has shortened by at least 15 minutes per week. On a whole the study shows that the acoustic treatments has led to an increase in use of planned time for each lesson, which through increased speech intelligibility also has become more effective. Observed socio economic effects outweigh the cost of the installation to the point that it is recommended not only to new classrooms but also to existing school environments.
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Tam, Joseph. "Methods of Characterizing Gas-Metal Arc Welding Acoustics for Process Automation." Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/859.
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Recent developments in material joining, specifically arc-welding, have increased in scope and extended into the aerospace, nuclear, and underwater industries where complex geometry and hazardous environments necessitate fully automated systems. Even traditional applications of arc welding such as off-highway and automotive manufacturing have increased their demand in quality, accuracy, and volume to stay competitive. These requirements often exceed both skill and endurance capacities of human welders. As a result, improvements in process parameter feedback and sensing are necessary to successfully achieve a closed-loop control of such processes. <br ><br /> One such feedback parameter in gas-metal arc welding (GMAW) is acoustic emissions. Although there have been relatively few studies performed in this area, it is agreed amongst professional welders that the sound from an arc is critical to their ability to control the process. Investigations that have been performed however, have been met with mixed success due to extraneous background noises or inadequate evaluation of the signal spectral content. However, if it were possible to identify the salient or characterizing aspects of the signal, these drawbacks may be overcome. <br ><br /> The goal of this thesis is to develop methods which characterize the arc-acoustic signal such that a relationship can be drawn between welding parameters and acoustic spectral characteristics. Three methods were attempted including: Taguchi experiments to reveal trends between weld process parameters and the acoustic signal; psycho-acoustic experiments that investigate expert welder reliance on arc-sounds, and implementation of an artificial neural network (ANN) for mapping arc-acoustic spectral characteristics to process parameters. <br ><br /> Together, these investigations revealed strong correlation between welding voltage and arc-acoustics. The psycho-acoustic experiments confirm the suspicion of welder reliance on arc-acoustics as well as potential spectral candidates necessary to spray-transfer control during GMA welding. ANN performance shows promise in the approach and confirmation of the ANN?s ability to learn. Further experimentation and data gathering to enrich the learning data-base will be necessary to apply artificial intelligence such as artificial neural networks to such a stochastic and non-linear relationship between arc-sound and GMA parameters.
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Kalscheuer, Jon M. "A selective automatic repeat request protocol for undersea acoustic links." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FKalscheuer.pdf.
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Kuster, Martin. "Inverse methods in room acoustics with under-determined data and applications to virtual acoustics." Thesis, Queen's University Belfast, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486233.
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With the advent of commercial surround sound systems there is a growing demand for 11 system that can convert existing mono and stereo recor~ings into a surround sound recording. A part of this problem is to generate the reverberation for the additional audio channels from the reverberation in the mono or stereo recording. . , In thi~ thesis, it is investigated whether a room model can be constructed from one or two room impulse responses and in which a virtual surround sound recording can then be perfonned. The estimation of the room model parameters is based on the three well-mown room acoustic models; the geometrical acoustic model with specular reflections, the eigenmode model and the diffuse field model. It is shown that the scope with the geometrical acoustic and the eigenmode model is limited but it is possible to obtain useful and consistent results for the room volume and the source-to-receiver distance from the diffuse field model. Based on these findings, the problem of generating multiple room impulse responses from one or two input room impulse response(s) is approached slightly differently. The very early part of the room impulse responses (the early reflections) is generated by a geometrical model with specular and diffuse reflections. The remainder of the room impulse responses are copies of the input room impulses obtained by convolution with a set of filters that control the coherence between them. The values for the coherence are given by expressions for the coherence between microphones with first-order directivity in a diffuse field and these expressions are derived in the thesis. The results from objective and subjective tests indicate that this method works successfully.
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Lee, Iljae. "Acoustic characteristics of perforated dissipative and hybrid silencers." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1117631229.
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Thesis (Ph. D.)--Ohio State University, 2005.<br>Title from first page of PDF file. Document formatted into pages; contains xvi, 195 p.; also includes graphics. Includes bibliographical references (p. 183-195). Available online via OhioLINK's ETD Center
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Jackson, Edward James. "Modelling and monitoring nonlinear acoustic phenomena in high-intensity focused ultrasound therapy." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:cea762cf-8a12-4265-b1b1-a15214c58ac3.
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High intensity focused ultrasound (HIFU) provides a wide range of noninvasive therapies ranging from drug delivery to the destruction of kidney stones. In particular, thermal ablation by HIFU presents an effective noninvasive method for the treatment of deep seated solid tumours. HIFUâs further uptake is limited by a need for improved treatment planning and monitoring. Two nonlinear acoustic phenomena that play key roles in HIFU treatment: finite amplitude effects that lead to the generation of harmonics and steepening of wavefronts, and acoustic cavitation. The former must be taken into careful consideration for treatment planning purposes, while the latter has the potential to provide fast, real-time, cost effective treatment monitoring. The first half of this thesis provides new measurements for the nonlinear acoustic properties of tissue, assesses the validity of two common modelling techniques for simulating HIFU fields. The second half develops a new method for combining passive acoustic mapping- an ultrasound monitoring technique- with MR thermometry, to assess estimates of cavitation enhanced heating derived from passive acoustic maps. In the first results chapter B/A was measured in ex-vivo bovine liver, over a heating/ cooling cycle replicating temperatures reached during HIFU ablation, adapting a finite amplitude insertion technique (FAIS), which also allowed for measurement of sound-speed and attenuation. The method measures the nonlinear progression of a plane-wave through liver and B/A was chosen so that numerical simulations matched measured waveforms. Results showed that attenuation initially decreased with heating then increased after denaturation, sound-speed initially increased with temperature and then decreased, and B/A showed an increase with temperature but no significant post-heating change. These data disagree with other reports that show a significant change and suggest that any nonlinear enhancement in the received ultrasound signal post-treatment is likely due to acoustic cavitation rather than changes in tissue nonlinearity. In the second results chapter two common methods of modelling HIFU fields were compared with hydrophone measurements of nonlinear HIFU fields at a range of frequencies and pressures. The two methods usedwere the KZK equation and the commercial package PZFlex. The KZK equation has become the standard method for modelling focused fields, while the validity of PZFlex for modelling these types of transducers is unclear. The results show that the KZK equation is able to match hydrophone measurements, but that PZFlex underestimates the magnitude of the harmonics. Higher order harmonics in PZFlex are not the correct shape, and do not peak around the focus. PZFlex performs worse at higher pressures and frequencies, and should be used with caution. In the final two chapters a system for estimating cavitation-enhanced heating from acoustic maps is developed and benchmarked against magnetic resonance thermometry methods. The first chapter shows that the ultrasound and MR monitoring systems are compatible, and registers the two imaging systems. The HIFUfocus is clearly visible in passive maps acquired in the absence of cavitation and these coincide with the centre of heating in MR temperature images. When cavitation occurs, it coincides spatially and temporally with the appearance of a clear spike in temperature, especially when the passive maps are processed using the Robust Capon Beamformer algorithm. The final chapter shows how passive maps can be converted into thermal heating inputs, and used to estimate cavitation-enhanced temperature increases. These estimates have the potential to closely match maximum temperature rise, and estimated thermal dose after the estimated temperature rise is spatially averaged. However, themethod is not always successful. This is partly due to uncertainties in MR thermometry estimates, partly due to uncertainties in the acoustic properties of tissue.
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Pearson, Charlie. "Vertical axis wind turbine acoustics." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245256.
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Increasing awareness of the issues of climate change and sustainable energy use has led to growing levels of interest in small-scale, decentralised power generation. Small-scale wind power has seen significant growth in the last ten years, partly due to the political support for renewable energy and the introduction of Feed In Tariffs, which pay home owners for generating their own electricity. Due to their ability to respond quickly to changing wind conditions, small-scale vertical axis wind turbines (VAWTs) have been proposed as an efficient solution for deployment in built up areas, where the wind is more gusty in nature. If VAWTs are erected in built up areas they will be inherently close to people; consequently, public acceptance of the turbines is essential. One common obstacle to the installation of wind turbines is noise annoyance, so it is important to make the VAWT rotors as quiet as possible. To date, very little work has been undertaken to investigate the sources of noise on VAWTs. The primary aim of this study was therefore to gather experimental data of the noise from various VAWT rotor configurations, for a range of operating conditions. Experimental measurements were carried out using the phased acoustic array in the closed section Markham wind tunnel at Cambridge University Engineering Department. Beamforming was used in conjunction with analysis of the measured sound spectra in order to locate and identify the noise sources on the VAWT rotors. Initial comparisons of the spectra from the model rotor and a full-scale rotor showed good qualitative agreement, suggesting that the conclusions from the experiments would be transferable to real VAWT rotors. One clear feature observed in both sets of spectra was a broadband peak around 1-2kHz, which spectral scaling methods demonstrated was due to laminar boundary layer tonal noise. Application of boundary layer trips to the inner surfaces of the blades on the model rotor was found to eliminate this noise source, and reduced the amplitude of the spectra by up to 10dB in the region of the broadband peak. This method could easily be applied to a full-scale rotor and should result in measurable noise reductions. At low tip speed ratios (TSR) the blades on a VAWT experience dynamic stall and it was found that this led to significant noise radiation from the upstream half of the rotor. As the TSR was increased the dominant source was seen to move to the downstream half of the rotor; this noise was thought to be due to the interaction of the blades in the downstream half of the rotor with the wake from the blades in the upstream half. It was suggested that blade wake interaction is the dominant noise source in the typical range of peak performance for the full-scale QR5 rotor. Different solidity rotors were investigated by using 2-, 3- and 4-bladed rotors and it was found that increasing the solidity had a similar effect to increasing the TSR. This is due to the fact that the induction factor, which governs the deflection of the flow through the rotor, is a function of both the rotor solidity and the TSR. With a large body of experimental data for validation, it was possible to investigate computational noise prediction methods. A harmonic model was developed that aimed to predict the sound radiated by periodic fluctuations in the blade loads. This model was shown to agree with similar models derived by other authors, but to make accurate predictions very high resolution input data was required. Since such high resolution blade loading data is unlikely to be available, and due to the dominance of stochastic sources, the harmonic model was not an especially useful predictive tool. However, it was used to investigate the importance of the near-field components of the sound radiated by the wind tunnel model to the acoustic array. It was shown that the near-field terms were significant over a wide range of frequencies, and the total spectrum was always greater than that of the far-field component. This implied that the noise levels measured by the acoustic array represented an upper bound on the sound radiated to the far-field, and hence that the latter would also be dominated by stochastic components. An alternative application of the harmonic model, which attempted to determine the blade loading harmonics from the harmonics in the sound field was proposed. This inversion method utilised a novel convex optimisation technique that was found to generate good solutions in the simulated test cases, even in the presence of significant random noise. The method was found to be insensitive at low frequencies, which made it ineffective for inverting the real microphone data, although this was shown to be at least partly due to the limitations imposed by the array size. In addition to the harmonic models, an empirical noise prediction method using the spectral scaling laws derived by \citet*{Brooks_1989} was trialled, and was found to be capable of making predictions that were in agreement with the measured data. The model was shown to be sensitive to the exact choice of turbulence parameters used and was also found to require good quality aerodynamic data to make accurate noise predictions. If such data were available however, it is expected that this empirical model would be able to make useful predictions of the noise radiated by a VAWT rotor.
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Prentice, Philip Ridley. "Asymptotic waveforms in propeller acoustics." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282923.
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Maier, Christian. "Experimental and theoretical aero-acoustics." Thesis, Glasgow Caledonian University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601630.
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Acoustic noise problems are encountered in many fields and are very often undesirable. The localisation of sound sources is the first step 10 reducing noise problems. In this thesis, the ability and feasibility of an acoustic camera in this regard is demonstrated The acoustic camera deals with the problem of sound sources coming from different directions by estimating the sound contributions incident to the acoustic camera. One example of an aero-acoustic noise problem is an air plane with its air foil. These cause unwanted noise due 10 the flowed air. Or another example is the current collector on trains which causes unwanted noise as well as affecting driving. Another problem, dealt with later in this thesis, is a cylinder flowed by air in a wind tunnel. A practical case 0/ this problem is a car antenna in the form of a cylinder; this causes noise due to the driving wind Fans can be optimised for aero-acoustics as well - an example is a cooling fan in a computer, or larger fans for air conditioners that can transport the noise over the whole tunnel in which they are built. Some processing techniques are used and implemented in the acoustic camera. The first technique is the "classical" Delay-and-Sum Beam/arming technique and the improved orthogonal beamforming, with the ability to separate non-correlated sound sources in a Single measurement. The second technique is based on the decomposition of the Eigenvalues of the cross spectral matrix. In addition to the experimental section of this thesis, the results are compared to a simulation, where a flowed object measured with the acoustic camera is compared to a suitable simulation with the same parameters like dimensions and velocity. Here f/owed means that a suitable object, a cylinder for example, is placed in the wind tunnel and flowed by air. The outcome of this thesis is the analysing of a flow induced problem, a fan for example. First steps were done with 2D flow simulations of a cylinder to become familiar with the topic program and implementing MATLAB® code to process the points of interest. This analysing could be done with a simulation or with the acoustic camera. The aim of this work is concerned with sound sources and the mechanism behind it. Suitable aero-acoustic experiments were chosen that can be analysed with the acoustic camera and with numerical simulation as well. With the acoustic camera, these sound sources can be visualised using the beamforming method A similar procedure should be done to the numerical simulations. These simulations are done and the sound sources are visualised there as well by rebuilt an array of microphones, which acts as acoustic camera, in the numerical simulations.