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Uzoegbo, Herbert Chidozie. "Propagation of acoustic waves in concrete." Thesis, King's College London (University of London), 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321500.
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Reese, Owein. "Homogenization of acoustic wave propagation in a magnetorheological fluid." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0430104-101629.
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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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Schlottmann, Robert Brian. "A path integral formulation of elastic wave propagation /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004372.
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Seale, Michael David. "Propagation of guided acoustic waves in composite media." W&M ScholarWorks, 1996. https://scholarworks.wm.edu/etd/1539623884.
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Composite materials are being more widely used today by aerospace, automotive, and a number of other commercial industries because of their advantages over conventional metals. Composites are finding applications ranging from bicycle frames to the proposed High-Speed Civil Transport (HSCT). Determining the response to a variety of damage mechanisms is necessary for a complete understanding of the total use environment of composite structures. The objective of the research presented here is to provide a method of quantifying the amount of damage in composite materials for a number of different damage scenarios. Components which have non-visible damage, but have degraded performance, are of interest. at this level of damage, the safety margin designed into the structure may be compromised.;Nondestructive Evaluation (NDE) is a field of measurement physics where energy is imparted to a material and information is obtained from observing how the energy interacts with the system. Many different forms of energy can be used to obtain useful information from these measurements: acoustic, thermal, x-ray, optical, and electromagnetic. Among the many various techniques available, ultrasonic Lamb waves offer a convenient method of evaluating these composite materials. as a material is damaged, the elastic parameters of the structure change. Since the Lamb wave velocity depends on these properties, an effective tool exists to monitor damage in composites by measuring the velocity of these waves. Additionally, Lamb wave measurements are beneficial because they can propagate over long distances and are sensitive to the desired in-plane elastic properties of the material.;Presented in this study are the results involving the investigation of a variety of damage mechanisms (fatigue, thermal, and thermal-mechanical) using the Lamb wave technique. Two fatigue studies were conducted which showed that the change in modulus and change in velocity of the Lamb wave squared follow the same general trend. The Lamb wave velocity was also observed to decrease with increasing crack density. For the thermal damage study, the results showed that the velocity of the lowest order symmetric Lamb mode dropped significantly for extended thermal damage. When the experimental results were compared to model calculations, good agreement was observed for both fatigue and thermal damage. Finally, for thermal-mechanical damage, it was found that the Lamb wave technique was also able to predict a local defect in a specimen, which was later found to have a large delamination zone.;The Lamb wave velocity is a quantitative measurement and it has been shown by this work to be an effective tool in monitoring different types of damage in composites. Since the Lamb wave velocity depends on a variety of material properties, an ideal technique exists to monitor composites as damage is incurred. With the continued development of damage assessment techniques such as the Lamb wave method, the safety of such structures can be assured.
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Furnell, G. D. "A study of acoustic wave propagation within curved ducting systems /." Title page, table of contents and abstract only, 1989. http://web4.library.adelaide.edu.au/theses/09PH/09phf987.pdf.
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Norbert, Čeljuska. "Novel metamaterial stuctures for non-conventional propagation of acoustic waves." Phd thesis, Univerzitet u Novom Sadu, Fakultet tehničkih nauka u Novom Sadu, 2015. https://www.cris.uns.ac.rs/record.jsf?recordId=95690&source=NDLTD&language=en.
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Metamaterials are artificial media composed of subwavelength unit cells, specifically engineered to exhibit unusual properties in relation to wave propagation, generally not found in nature. Most research in this area has been dedicated to electromagnetic metamaterials, In this thesis we present results in a new multidisciplinary field of metamaterials in acoustics and realization of non-conventional wave propagation applying novel metamaterial unit cells. The scientific contribution of this dissertation comprises three new types of wave propagation modes and their control with newly designed metamaterial unit cells. In the thesis, a novel class of compressibility-near-zero (CNZ) acoustic propagation, achieved by using Helmholtz resonators, is theoretically analyzed and experimentally demonstrated. A closed analytical formula for the effective compressibility of the proposed unit cell is presented, and the existence of two frequencies which may support CNZ propagation is shown. Furthermore, a new unit cell with effective mass density with Lorentzian type behavior is proposed, a closed analytical formula for its effective mass density is found, and the evanescent, left-handed propagation and density-near-zero acoustic wave propagation are demonstrated. In the end it is demonstrated for the first time that a surface acoustic wave propagating at the boundary between a fluid and a hard grooved surface can be efficiently controlled by varying only the temperature of the fluid, while the geometry of the grooved surface remains unchanged. This opens up a way for a number of new applications, all easily tunable by external means. Following theoretical considerations, we demonstrate temperature-controlled sound trapping and its applications in acoustic spectral analysis and temperature sensing. We also present a temperature-controlled gradient refractive index (GRIN) acoustic medium and apply it to achieve temperature-controlled acoustic focusing.Метаматеријали су вештачки медијуми састављени од јединичних ћелија мањих од таласне дужине, пројектовани на посебан начин да при пропагацији таласа испољавају необичне особине које се иначе не срећу у природи. Већина истраживања у овој области фокусира се на електромагнетске метаматеријале. У овој дисертацији презентовани су резултати у новом мултидисциплинарном пољу метаматеријала у акустици и реализација нове неконвенционалне пропагације таласа применом јединичних ћелија метаматеријала. Научни допринос ове дисертације су три нова типа модова пропагације таласа и њихова контрола новим пројектованим јединичним ћелијама метаматеријала. У дисертацији је теоријски анализирана и експериментално показана нова класа CNZ (енг. compressibility-near-zero) акустичке пропагације постигнуте Хелмхолцовим резонатором. Дата је затворена аналитичка формула за ефективну стишљивост јединичне ћелије, а затим је показано да постоје две фреквенције које подржавају CNZ пропагацију. Такође, предложена је нова јединична ћелија са ефективном густином Лоренцовог типа, изведена је затворена аналитичка формула за њену ефективну густину и показане су „левoрука“, еванесцентна и DNZ (енг. density-near-zero) пропагација акустичких таласа. На крају, по први пут је показано да се површински акустични талас који се простире на граници између флуида и чврсте избраздане површи може ефикасно контро-лисати само променом температуре, док геометрија избраздане површи остаје непромењена. Ово отвара могућности за бројне нове примене где је потребна лакоћа екстерног подешавања. Пратећи изложену теорију, демонстрирано је заробљавање звука контролисано температуром, као и његова примена у акустичкој спектралној анализи и мерењу темпе-ратуре. Такође, презентован је акустички медијум са температуром кон-тролисаним градијентом индекса преламања, као и његова примену у температурно контролисаном акустичком фокусирању.
Metamaterijali su veštački medijumi sastavljeni od jediničnih ćelija manjih od talasne dužine, projektovani na poseban način da pri propagaciji talasa ispoljavaju neobične osobine koje se inače ne sreću u prirodi. Većina istraživanja u ovoj oblasti fokusira se na elektromagnetske metamaterijale. U ovoj disertaciji prezentovani su rezultati u novom multidisciplinarnom polju metamaterijala u akustici i realizacija nove nekonvencionalne propagacije talasa primenom jediničnih ćelija metamaterijala. Naučni doprinos ove disertacije su tri nova tipa modova propagacije talasa i njihova kontrola novim projektovanim jediničnim ćelijama metamaterijala. U disertaciji je teorijski analizirana i eksperimentalno pokazana nova klasa CNZ (eng. compressibility-near-zero) akustičke propagacije postignute Helmholcovim rezonatorom. Data je zatvorena analitička formula za efektivnu stišljivost jedinične ćelije, a zatim je pokazano da postoje dve frekvencije koje podržavaju CNZ propagaciju. Takođe, predložena je nova jedinična ćelija sa efektivnom gustinom Lorencovog tipa, izvedena je zatvorena analitička formula za njenu efektivnu gustinu i pokazane su „levoruka“, evanescentna i DNZ (eng. density-near-zero) propagacija akustičkih talasa. Na kraju, po prvi put je pokazano da se površinski akustični talas koji se prostire na granici između fluida i čvrste izbrazdane površi može efikasno kontro-lisati samo promenom temperature, dok geometrija izbrazdane površi ostaje nepromenjena. Ovo otvara mogućnosti za brojne nove primene gde je potrebna lakoća eksternog podešavanja. Prateći izloženu teoriju, demonstrirano je zarobljavanje zvuka kontrolisano temperaturom, kao i njegova primena u akustičkoj spektralnoj analizi i merenju tempe-rature. Takođe, prezentovan je akustički medijum sa temperaturom kon-trolisanim gradijentom indeksa prelamanja, kao i njegova primenu u temperaturno kontrolisanom akustičkom fokusiranju.
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Ead, Richard M. "Predicting the effects of sea surface scatter on broad band pulse propagation with an ocean acoustic parabolic equation model." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FEad.pdf.
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Wojcik, Stefanie E. "Effects of internal waves and turbulent fluctuations on underwater acoustic propagation." Link to electronic thesis, 2006. http://www.wpi.edu/Pubs/ETD/Available/etd-030906-152505/.
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Nagaraj, Nagaraj. "Effects of Dissipation on Propagation of Surface Electromagnetic and Acoustic Waves." Thesis, University of North Texas, 2012. https://digital.library.unt.edu/ark:/67531/metadc115126/.
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With the recent emergence of the field of metamaterials, the study of subwavelength propagation of plane waves and the dissipation of their energy either in the form of Joule losses in the case of electomagnetic waves or in the form of viscous dissipation in the case of acoustic waves in different interfaced media assumes great importance. with this motivation, I have worked on problems in two different areas, viz., plasmonics and surface acoustics. the first part (chapters 2 & 3) of the dissertation deals with the emerging field of plasmonics. Researchers have come up with various designs in an efort to fabricate efficient plasmonic waveguides capable of guiding plasmonic signals. However, the inherent dissipation in the form of Joule losses limits efficient usage of surface plasmon signal. a dielectric-metal-¬dielectric planar structure is one of the most practical plasmonic structures that can serve as an efficient waveguide to guide electromagnetic waves along the metal-dielectric boundary. I present here a theoretical study of propagation of surface plasmons along a symmetric dielectric-metal-dielectric structure and show how proper orientation of the optical axis of the anisotropic substrate enhances the propagation length. an equation for propagation length is derived in a wide range of frequencies. I also show how the frequency of coupled surface plasmons can be modulated by changing the thickness of the metal film. I propose a Kronig-Penny model for the plasmonic crystal, which in the long wavelength limit, may serve as a homogeneous dielectric substrate with high anisotropy which do not exist for natural optical crystals. in the second part (chapters 4 & 5) of the dissertation, I discuss an interesting effect of extraordinary absorption of acoustic energy due to resonant excitation of Rayleigh waves in a narrow water channel clad between two metal plates. Starting from the elastic properties of the metal plates, I derive a dispersion equation that gives resonant frequencies, which coincide with those observed in the experiment that was performed by Wave Phenomena Group at Polytechnic University of Valencia, Spain. Two eigenmodes with different polarizations and phase velocities are obtained from the dispersion equation. at certain critical aperture of the channel, an interesting cutoff effect, which is unusual for an acoustic wave, is observed for one of the eigenmodes with symmetric distribution of the pressure field. the theoretical prediction of the coupling and synchronization of Rayleigh waves strongly supports the experimentally measured shift of the resonant frequencies in the transmission spectra with channel aperture. the observed high level of absorption may find applications in designing metamaterial acoustic absorbers.
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Reynolds, Eric W. "Laboratory observation of evolution of IEDD-wave-modified equilibrium and density-gradient effects on SMIA wave propagation." Morgantown, W. Va. : [West Virginia University Libraries], 2009. http://hdl.handle.net/10450/10471.
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Thesis (Ph. D.)--West Virginia University, 2009.Title from document title page. Document formatted into pages; contains xxviii, 307 p. : ill. Includes abstract. Includes bibliographical references (p. 118-131).
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Baylosis, Benito E. "Acoustic imaging of ultrasonic wave propagation." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA290390.
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Bacon, David R. "Finite amplitude propagation in acoustic beams." Thesis, University of Bath, 1986. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.483000.
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Xu, Jinshan. "Effects of internal waves on low frequency, long range, acoustic propagation in the deep ocean." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42295.
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Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2007.Includes bibliographical references (p. 183-191).
This thesis covers a comprehensive analysis of long-range, deep-ocean, low-frequency, sound propagation experimental results obtained from the North Pacific Ocean. The statistics of acoustic fields after propagation through internal-wave-induced sound-speed fluctuations are explored experimentally and theoretically. The thesis starts with the investigation of the North Pacific Acoustic Laboratory 98-99 data by exploring the space-time scales of ocean sound speed variability and the contributions from different frequency bands. The validity of the Garret & Munk internal-wave model is checked in the upper ocean of the eastern North Pacific. All these results impose hard bounds on the strength and characteristic scales of sound speed fluctuations one might expect in this region of the North Pacific for both internal-wave band fluctuations and mesoscale band fluctuations. The thesis then presents a detailed analysis of the low frequency, broadband sound arrivals obtained in the North Pacific Ocean. The observed acoustic variability is compared with acoustic predictions based on the weak fluctuation theory of Rytov, and direct parabolic equation Monte Carlo simulations. The comparisons show that a resonance condition exists between the local acoustic ray and the internal wave field such that only the internal-waves whose crests are parallel to the local ray path will contribute to acoustic scattering: This effect leads to an important filtering of the acoustic spectra relative to the internal-wave spectra. We believe that this is the first observational evidence for the acoustic ray and internal wave resonance. Finally, the thesis examined the evolution with distance, of the acoustic arrival pattern of the off-axis sound source transmissions in the Long-range Ocean Acoustic Propagation EXperiment.
(cont.) The observations of mean intensity time-fronts are compared to the deterministic ray, parabolic equation (with/without internal waves) and (one-way coupled) normal mode calculations. It is found the diffraction effect is dominant in the shorter-range transmission. In the longer range, the (internal wave) scattering effect smears the energy in both the spatial and temporal scales and thus has a dominant role in the finale region.
by Jinshan Xu.
Ph.D.
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Young, Aaron C. "Two dimensional acoustic propagation through oceanic internal solitary waves weak scattering theory and numerical simulation." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Jun%5FYoung.pdf.
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Yildirim, Baran. "Acoustic Wave Analysis Using Different Wave Propagation Models." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/3/12609527/index.pdf.
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In this study in order to simulate the acoustic waves, Ray Theory and Normal Mode models are used. These methods are analyzed using MATLAB simulation tooldifferences between two models are examined and a region with a known bottom profile and sound velocity profiles is investigated. The Ray Theory is used in acoustic systems which is the one of the applications of wave modeling. Ray theory is solved with standard Ordinary Differential Equation solvers and normal mode with finite element method. Different bottom profiles and sound velocity profiles previously taken are interpolated to form an environment and examined in the case study. in the case study.
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Foda, Mosaad A. "Propagation and interaction of finite amplitude acoustic waves generated by a dual frequency transducer." Diss., Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/16720.
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Shmelev, Alexey Alexandrovich. "Three-dimensional acoustic propagation through shallow water internal, surface gravity and bottom sediment waves." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/69241.
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Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 185-193).
This thesis describes the physics of fully three-dimensional low frequency acoustic interaction with internal waves, bottom sediment waves and surface swell waves that are often observed in shallow waters and on continental slopes. A simple idealized model of the ocean waveguide is used to analytically study the properties of acoustic normal modes and their perturbations due to waves of each type. The combined approach of a semi-quantitative study based on the geometrical acoustics approximation and on fully three-dimensional coupled mode numerical modeling is used to examine the azimuthal dependence of sound wave horizontal reflection from, transmission through and ducting between straight parallel waves of each type. The impact of the natural crossings of nonlinear internal waves on horizontally ducted sound energy is studied theoretically and modeled numerically using a three-dimensional parabolic equation acoustic propagation code. A realistic sea surface elevation is synthesized from the directional spectrum of long swells and used for three-dimensional numerical modeling of acoustic propagation. As a result, considerable normal mode amplitude scintillations were observed and shown to be strongly dependent on horizontal azimuth, range and mode number. Full field numerical modeling of low frequency sound propagation through large sand waves located on a sloped bottom was performed using the high resolution bathymetry of the mouth of San Francisco Bay. Very strong acoustic ducting is shown to steer acoustic energy beams along the sand wave's curved crests.
by Alexey Alexandrovich Shmelev.
Ph.D.
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Udawalpola, Rajitha. "Shape Optimization for Acoustic Wave Propagation Problems." Doctoral thesis, Uppsala universitet, Avdelningen för teknisk databehandling, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-112549.
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Boundary shape optimization is a technique to search for an optimal shape by modifying the boundary of a device with a pre-specified topology. We consider boundary shape optimization of acoustic horns in loudspeakers and brass wind instruments. A horn is an interfacial device, situated between a source, such as a waveguide or a transducer, and surrounding space. Horns are used to control both the transmission properties from the source and the spatial power distribution in the far-field (directivity patterns). Transmission and directivity properties of a horn are sensitive to the shape of the horn flare. By changing the horn flare we design transmission efficient horns. However, it is difficult to achieve both controllability of directivity patterns and high transmission efficiency by using only changes in the horn flare. Therefore we use simultaneous shape and so-called topology optimization to design a horn/acoustic-lens combination to achieve high transmission efficiency and even directivity. We also design transmission efficient interfacial devices without imposing an upper constraint on the mouth diameter. The results demonstrate that there appears to be a natural limit on the optimal mouth diameter. We optimize brasswind instruments with respect to its intonation properties. The instrument is modeled using a hybrid method between a one-dimensional transmission line analogy for the slowly flaring part of the instrument, and a finite element model for the rapidly flaring part. An experimental study is carried out to verify the transmission properties of optimized horn. We produce a prototype of an optimized horn and then measure the input impedance of the horn. The measured values agree reasonably well with the predicted optimal values. The finite element method and the boundary element method are used as discretization methods in the thesis. Gradient-based optimization methods are used for optimization, in which the gradients are supplied by the adjoint methods.
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Sheard, John Daniel. "Acoustic wave propagation in ice covered oceans." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319827.
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Wadbro, Eddie. "Topology optimization for acoustic wave propagation problems." Licentiate thesis, Uppsala universitet, Avdelningen för teknisk databehandling, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-86427.
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The aim of this study is to develop numerical techniques for the analysis and optimization of acoustic horns for time harmonic wave propagation. An acoustic horn may be viewed as an impedance transformer, designed to give an impedance matching between the feeding waveguide and the surrounding air. When modifying the shape of the horn, the quality of this impedance matching changes, as well as the angular distribution of the radiated wave in the far field (the directivity). The dimensions of the horns considered are in the order of the wavelength. In this wavelength region the wave physics is complicated, and it is hard to apply elementary physical reasoning to enhance the performance of the horn. Here, topology optimization is applied to improve the efficiency and to gain control over the directivity of the acoustic horn.
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Gandhi, Navneet. "Determination of dispersion curves for acoustoelastic lamb wave propagation." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37158.
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The effect of stress on Lamb wave propagation is relevant to both nondestructive evaluation and structural health monitoring because of changes in received signals due to both the associated strain and the acoustoelastic effect. A homogeneous plate that is initially isotropic becomes anisotropic under biaxial stress, and dispersion of propagating waves becomes directionally dependent. The problem is similar to Lamb wave propagation in an anisotropic plate, except the fourth order tensor in the resulting wave equation does not have the same symmetry as that for the unstressed anisotropic plate, and the constitutive equation relating incremental stress to incremental strain is more complicated. Here we review the theory of acoustoelastic and develop theory for acoustoelastic Lamb wave propagation and show how dispersion curves shift anisotropically for an aluminum plate under biaxial tension. We also develop an approximate method using the effective elastic constants (EECs) and show that existing commercial tools to generate dispersion curves can be used under restricted conditions to describe wave propagation in biaxially stressed plates. Predictions of changes in phase velocity as a function of propagation direction using theory and the EEC method are compared to experimental results for a single wave mode.
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Malléjac, Matthieu. "Metamaterials with extreme properties for the control of acoustic waves." Thesis, Le Mans, 2020. http://cyberdoc-int.univ-lemans.fr/Theses/2020/2020LEMA1024.pdf.
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Les métamatériaux à indice nul, pour lesquels au moins un des paramètres effectifs s’annule (densité ou compressibilité dynamique pour l’acoustique), ont fait l’objet d’une attention considérable au cours de ces dernières années. Ces matériaux ont la particularité d’induire une augmentation remarquable de la longueur d’onde effective, offrant ainsi de nombreuses possibilités d’application, incluant entre autres la propagation sans changement de phase, la dissimulation acoustique de diffuseurs, le contrôle de la directivité, etc. Ce travail de doctorat se concentre particulièrement sur le régime de densité effective quasi-nulle dans des métamatériaux acoustiques constitués de plaques fines dans l’air. Grâce à une étude approfondie d’un arrangement périodique de fines plaques élastiques encastrées dans un guide d’onde, nous avons pu explorer analytiquement, numériquement et expérimentalement certains des effets ci-dessus. Une attention particulière est portée sur les pertes inhérentes à ce type de système et à leurs conséquences sur les comportements attendus. Nous débutons par l’étude numérique et l’observation expérimentale d’une propagation sans changement de phase à travers le métamatériau, à une fréquence située dans une bande interdite du système fini. Nous transposons ensuite le concept de dopage photonique à l’acoustique. L’ajout dans le système d’une impureté, ici un résonateur de Helmholtz bien choisi, permet de transformer le régime de densité nulle en un régime où la densité et la compressibilité sont simultanément quasi-nulles. Ainsi, la propagation sans changement de phase est accompagnée d’une transmission unitaire, due à l’accord d’impédance du système avec l’air environnant. Nous étudions enfin la possibilité de réaliser une dissimulation ou un masquage acoustique d’un objet en utilisant l’extension de la longueur d’onde acoustique, offerte par la densité nulleZero-index metamaterials, for which at least one of the effective parameters (density or dynamic compressibility for acoustics) vanishes, have received considerable attention in recent years. These materials have the particularity of inducing a considerable increase in the effective wavelength, thus offering numerous application possibilities, including, among others, propagation without phase change, acoustic hiding of diffusers, directivity control, etc. This PhD work focuses particularly on the near-zero effective density regime in acoustic metamaterials made of thin plates in air. Through an in-depth study of a periodic arrangement of thin elastic plates embedded in a waveguide, we have been able to explore analytically, numerically and experimentally some of the above effects. Particular attention is paid to the losses inherent to this type of system and their consequences on the expected behavior. We begin by studying numerically and experimentally observing a phase-change-free propagation through the metamaterial at a frequency in a stopband of the finite system. We then transpose the concept of photonic doping to acoustics. The addition of an impurity, here a well-chosen Helmholtz resonator, to the system allows to transform the regime of zero density into one where density and compressibility are simultaneously near zero. Thus, propagation without phase change is accompanied by a unitary transmission, due to the impedance matching of the system with the surrounding air. Finally, we study the possibility of performing acoustic hiding or masking of an object using the acoustic wavelength stretching offered by the zero density
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Ananda, Agus A. "Propagation of Rayleigh waves in thin films." W&M ScholarWorks, 1997. https://scholarworks.wm.edu/etd/1539623914.
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With the advent of thin film technology and more recently its applications in microelectronics and control of surface properties, the interest in mechanical properties of thin films has grown tremendously. Mechanical defects such as creep, fracture and adhesion loss, play a very important role in physical instabilities of thin film materials. An acoustic microscope has been built to study mechanical properties of thin-films. The microscope operates at a nominal frequency of 50 MHz. Rayleigh surface waves velocities on the surface of film-substrate systems were measured from V(z) curves generated by the acoustic microscope. V(z) curves are produced from interference between the Rayleigh surface wave and the specularly reflected waves. Technologically important materials, non-stoichiometric titanium nitride (TiN{dollar}\sb{lcub}\rm x{rcub}{dollar}) films and diamond films, were fabricated by using magnetron plasma deposition and hot filament chemical vapor deposition (HFCVD) on Si (100) and Si (111) substrates. Spectra from XPS (X-ray Photoelectron Spectroscopy) were used to determine the chemical composition of the films and SEM (Scanning Electron Microscope) micrographs were taken to study the morphology of the films. Rayleigh surface wave velocity measurements on TiN{dollar}\sb{lcub}\rm x{rcub}{dollar} films show a sharp increase in velocity at x = 0.7. A comparison with the phase diagram of TiN {dollar}\sb{lcub}\rm x{rcub}{dollar} suggests that the sharp increase in velocity might be due to a crystal structural transition from tetragonal {dollar}\varepsilon{dollar}-Ti{dollar}\sb2{dollar}N to fcc {dollar}\delta{dollar}-TiN.
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Vetreno, JoAnna Ruth. "ANALYTIC MODELS FOR ACOUSTIC WAVE PROPAGATION IN AIR." NCSU, 2008. http://www.lib.ncsu.edu/theses/available/etd-01032008-114426/.
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Ultrasound waves have been used for imaging purposes for many years. However, a liquid interface has always been necessary between the transducer and the object being imaged due to a high mechanical resistance at the air-transducer interface. Recent advances in transducers have made it possible to omit the liquid interface, allowing imaging to be done through air interfaces. Because this is a relatively new field, research into ultrasound propagation in air is very limited. A comprehensive model of how an ultrasound wave propagates through air would expedite the study of air-coupled ultrasound for imaging. This thesis presents a mathematical model of two-dimensional linear acoustic wave propagation in air. The model takes as input the frequency and amplitude of an acoustic signal and outputs the pressure field over varying longitudinal and lateral distances from the source. The benefits of a mathematical model over a finite element model are first discussed, then the mathematical model for acoustic propagation in air is developed using both computer simulations and physical experiments in an anechoic chamber. Results are presented and compared to experimental data to confirm the validity of the mathematical model.
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Wang, TingTing. "Acoustic / elastic wave propagation in coupled-resonator waveguides." Thesis, Bourgogne Franche-Comté, 2020. http://www.theses.fr/2020UBFCD061.
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Lorsqu'un défaut est introduit dans un cristal phononique, des états apparaissent dans les bandes interdites et se localisent au niveau des défauts. Ils décroissent rapidement loin du défaut. Par conséquent, il est possible de localiser et de guider la propagation des ondes en concevant des défauts dans un cristal phononique parfait. Le guide d’onde à résonateurs couplés, fondé sur le couplage d'une séquence de cavités, présente simultanément un fort confinement des ondes et une faible vitesse de groupe ; il peut être utilisé pour concevoir des circuits plutôt arbitraires. En outre, la propagation des ondes élastiques dans une matrice solide peut être contrôlée en remplissant des cavités d'un fluide, sur la base des systèmes couplés fluides-solides. Ils ont des applications essentielles pour la réduction des vibrations et l’isolation acoustique. Dans cette thèse, les ondes acoustiques et élastiques se propageant dans les guides d’ondes à résonateurs couplés périodiques et apériodiques sont étudiées. L’interaction fluide-solide dans les cristaux phononiques fluide / solide est étudiée. Les travaux sont menés en combinant simulation numérique, analyse par modèles théoriques et investigation expérimentaleWhen a defect is introduced into a phononic crystal, states localized at the defect appear in the band gaps. They decay rapidly far away from the defect. Therefore, it is possible to localize and guide wave propagation by designing defects in the perfect phononic crystal. Coupled-resonator waveguides based on the coupling effect between a sequence of defect cavities have simultaneously strong wave confinement and low group velocity, and can be used to design rather arbitrary circuits. Furthermore, the propagation of elastic waves in a solid matrix can be controlled through changing fluid fillings based on fluid-solid interaction. Thus, they have essential applications in vibration reduction and noise isolation. In this thesis, the acoustic and elastic waves propagating in both periodic and aperiodic coupled-resonator waveguides are investigated. The fluid-solid interaction in fluid/solid phononic crystals is studied. The work is conducted by combining numerical simulations, theoretical model analysis and experimental investigations
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Klymko, Victor. "Propagation of plate acoustic waves in z-cut lithium niobate : single crystal and periodically poled wafers /." Full text available from ProQuest UM Digital Dissertations, 2009. http://0-proquest.umi.com.umiss.lib.olemiss.edu/pqdweb?index=0&did=1799143161&SrchMode=1&sid=7&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1269366078&clientId=22256.
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Thesis (Ph.D.)--University of Mississippi, 2009.Typescript. Vita. "February 2009." Major Professor: Dr. Igor Ostrovskii Includes bibliographical references (leaves 98-104). Also available online via ProQuest to authorized users.
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Leissing, Thomas. "Nonlinear acoustic wave propagation in complex media : application to propagation over urban environments." Phd thesis, Université Paris-Est, 2009. http://tel.archives-ouvertes.fr/tel-00584398.
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Dans cette recherche, un modèle de propagation d'ondes de choc sur grandes distances sur un environnement urbain est construit et validé. L'approche consiste à utiliser l'Equation Parabolique Nonlinéaire (NPE) comme base. Ce modèle est ensuite étendu afin de prendre en compte d'autres effets relatifs à la propagation du son en milieu extérieur (surfaces non planes, couches poreuses, etc.). La NPE est résolue en utilisant la méthode des différences finies et donne des résultats en accord avec d'autres méthodes numériques. Ce modèle déterministe est ensuite utilisé comme base pour la construction d'un modèle stochastique de propagation sur environnements urbains. La Théorie de l'Information et le Principe du Maximum d'Entropie permettent la construction d'un modèle probabiliste d'incertitudes intégrant la variabilité du système dans la NPE. Des résultats de référence sont obtenus grâce à une méthode exacte et permettent ainsi de valider les développements théoriques et l'approche utilisée
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Rallabhandi, Sriram Kishore. "Sonic Boom Minimization through Vehicle Shape Optimization and Probabilistic Acoustic Propagation." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6937.
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Sonic boom annoyance is an important technical showstopper for commercial supersonic aircraft operations. It has been proposed that aircraft can be shaped to alleviate sonic boom. Choosing the right aircraft shape reflecting the design requirements is a fundamental and most important step that is usually over simplified in the conceptual stages of design by resorting to a qualitative selection of a baseline configuration based on historical designs and designers perspective. Final aircraft designs are attempted by minor shape modifications to this baseline configuration. This procedure may not yield large improvements in the objectives, especially when the baseline is chosen without a rigorous analysis procedure.
Traditional analyses and implementations tend to have a complex algorithmic flow, tight coupling between tools used and computational limitations. Some of these shortcomings are overcome in this study and a diverse mix of tools is seamlessly integrated to provide a simple, yet powerful and automatic procedure for sonic boom minimization. A shape optimization procedure for supersonic aircraft design using better geometry generation and improved analysis tools has been successfully demonstrated. The geometry engine provides dynamic reconfiguration and efficient manipulation of various components to yield unstructured watertight geometries. The architecture supports an assimilation of different components and allows configuration changes to be made quickly and efficiently because changes are localized to each component. It also enables an automatic way to combine linear and non-linear analyses tools. It has been shown in this study that varying atmospheric conditions could have a huge impact on the sonic boom annoyance metrics and a quick way of obtaining probability estimates of relevant metrics was demonstrated. The well-accepted theoretical sonic boom minimization equations are generalized to a new form and the relevant equations are derived to yield increased flexibility in aircraft design process. Optimum aircraft shapes are obtained in the conceptual design stages weighing in various conflicting objectives. The unique shape optimization procedure in conjunction with parallel genetic algorithms improves the computational time of the analysis and allows quick exploration of the vast design space. The salient features of the final designs are explained. Future research recommendations are made.
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Dai, Ji-Dong. "Acoustic and optical wave propagation in anisotropic fiber waveguides." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39525.
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In this thesis analyses of the optical wave propagation characteristics in uniaxial and weakly biaxial fibers are presented. Analytical closed form solutions are obtained for optical wave propagation in uniaxial fibers with field and modal power distributions investigated in detail for the first time. Optical dispersion characteristics in weakly biaxial fibers are studied by a perturbation method with the exact solution for the uniaxial fibers as the perturbation base. The analysis of optical second harmonic generation in LiNbO$ sb3$ fibers of practical interest is also carried out by a scalar coupled mode theory where the quasi-phase match grating design for cladded fiber geometry is obtained.Pioneer work of fundamental value on the investigation of acoustic wave propagation properties in hexagonal, trigonal and cubic fibers has also been carried out. Exact analytical solutions are achieved for acoustic wave propagation in hexagonal fibers and simplified closed form formulas are deduced for the weakly guiding case. Acoustic wave propagation in a three-layer structure consisting of a hexagonal-core, a thin isotropic interface layer and an isotropic cladding is analyzed by a perturbation method based on the exact solutions for hexagonal and isotropic acoustic fibers. Based on the exact results for acoustic wave propagation in hexagonal and isotropic fibers respectively, coupled mode equations are applied to acoustic wave propagation analyses in trigonal and cubic fibers.
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Spring, Christopher Todd 1965. "Acoustic wave propagation in a cylindrical borehole with fractures." Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/277313.
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We study the problem of acoustic wave propagation in a cylindrical borehole possessing a finite number of transverse discontinuities. We model the field behavior through Green's function techniques. We formulate an integral equation whose solution will enable us to solve for the acoustic field everywhere within our structure. We investigate asymptotic forms to speed the numerical convergence of our solution. To solve the integral equation we employ both the method of moments and the low frequency approximation. We study the reflection coefficient in the time and frequency domains. Finally after presenting solutions for the one and two fracture case, we generalize our analysis for many fractures.
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Horne, Michael R. "Rayleigh Wave Acoustic Emission during Crack Propagation in Steel." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/28780.
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An investigation was conducted of the existence of seismic surface pulses (SSP) on crack faces in near-failure fatigue. An SSP has components of various modes of wave propagation. The component with the largest amplitude is a Rayleigh surface wave pulse. The possibility that these surface modes have much higher amplitudes than bulk modes of acoustic emission (AE) was illustrated by an idealized thought experiment relating an SSP on a half-space to the response of crack faces to crack extension.
A number of aspects of AE monitoring in finite objects were investigated. Attributes of surface wave propagation on the edge of a specimen were found to be easier to monitor than other modes of wave propagation. Wavelet analysis was used to compare the characteristics of brittle AE with other sources.
A new testing paradigm was developed to reduce interference from secondary sources of AE and enhance the investigation of AE from critical crack behavior. Unique specimen design features were developed, data acquisition features sought and validated, a dead weight load frame was modified, and data analysis procedures were developed. Criteria based on velocity, frequency content, amplitude and shape were devised to determine if an AE event is an SSP. The tests were designed to mimic load conditions on structures such as bridges and hence investigate the difference between AE generated in field conditions and that of typical laboratory conditions. Varieties of steel, from very ductile to very brittle, were tested.
It was concluded that plastic zone formation, considered a secondary source of AE, was found not to interfere with the SSP activity. The SSP was found experimentally to have 2-3 times the amplitude of the bulk wave AE. The lack of sufficient AE did not allow for determination of conclusive changes in the AE as the specimens approached failure. However, it was found that brittle crack extension in fatigue and ductile failure can produce wave propagation resembling the SSP.Ph. D.
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Kim, Yoonkee. "Surface acoustic wave propagation in multilayered and multichannel waveguide structures." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/15060.
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MEN'SHOV, Igor, and Yoshiaki NAKAMURA. "On Instability of Acoustic Waves Propagating in Stratified Vortical Flows." The Japan Society of Mechanical Engineers, 2002. http://hdl.handle.net/2237/9091.
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Suchivoraphanpong, Varanyu. "Fast integral equation methods for large acoustic scattering analyses." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312269.
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Berry, David Leonard. "Acoustic scattering by near-surface inhomogeneities in porous media." Thesis, Open University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254021.
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Mehta, Hiren Mukundroy. "Simulation of nonlinear optical, magnetic and acoustic envelope pulse propagation." Thesis, University of Salford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308209.
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Nieberding, Zachary J. "An Investigation of Acoustic Wave Propagation in Mach 2 Flow." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406881591.
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Weng, Chenyang. "Theoretical and numerical studies of sound propagation in low-Mach-number duct flows." Doctoral thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-168031.
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When sound waves propagate in a duct in the presence of turbulent flow, turbulent mixing can cause attenuation of the sound waves extra to that caused by the viscothermal effects. Experiments show that compared to the viscothermal effects, this turbulent absorption becomes the dominant contribution to the sound attenuation at sufficiently low frequencies. The mechanism of this turbulent absorption is attributed to the turbulent stress and the turbulent heat transfer acting on the coherent perturbations (including the sound waves) near the duct wall, i.e. sound-turbulence interaction. The purpose of the current investigation is to understand the mechanism of the sound-turbulence interaction in low-Mach-number internal flows by theoretical modeling and numerical simulations. The turbulence absorption can be modeled through perturbation turbulent Reynolds stresses and perturbation turbulent heat flux in the linearized perturbation equations. In this thesis, the linearized perturbation equations are reviewed, and different models for the turbulent absorption of the sound waves are investigated. A new non–equilibrium model for the perturbation turbulent Reynolds stress is also proposed. The proposed model is validated by comparing with experimental data from the literature, and with the data from Direct Numerical Simulations (DNS) of pulsating turbulent channel flow. Good agreement is observed.QC 20150526
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Macedo, Daniel Leal 1975. "Scattering-based decomposition of sensitivity kernels of acoustic full waveform inversion = Decomposição baseada em teoria de espalhamento dos núcleos de sensibilidade da inversão de onda completa acústica." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265785.
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Orientador: Dietrich Wilhelm SchleicherTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica, Instituto de Geociências
Made available in DSpace on 2018-08-26T05:18:51Z (GMT). No. of bitstreams: 1 Macedo_DanielLeal_D.pdf: 16481305 bytes, checksum: 3d47b0427882ec03cc38bd035feee293 (MD5) Previous issue date: 2014
Resumo: A inversão de onda completa (FWI, do inglês ''full waveform inversion'') nãolinear baseada em gradientes (métodos de descida) é, a princípio, capaz de levar em conta todos os aspectos da propagação de onda contida nos dados síismicos. Porém, FWI baseada em gradientes é limitada pela sua bem conhecida sensibilidade no que diz respeito à escolha do modelo inicial. Com o intuito de melhor entender algumas questões relacionadas à convergência do modelo na FWI, nós estudamos uma decomposição baseada na teoria de espalhamento que permite dividir os núcleos de sensibilidade dos campos de onda acústica em função dos parâmetros do modelo em duas partes: uma relativa ao componente de fundo, outra relativa à componente singular do modelo. Estimativas para a perturbação de fundo, bem como para a perturbação da parte singular do modelo obtidas com os adjuntos destes subnúcleos são componentes da estimativa obtida com o adjunto do núcleo total de sensibilidade. Os experimentos numéricos suportam a tese de que a decomposiçao em subnúcleos permite que se retroprojete somente os resíduos do campo de onda espalhado de modo a obter estimativas razoáveis da perturbação de fundo do modelo. Em um experimento com geometria de aquisição restrita (dados de reflexão com afastamento curto), os subnúcleos baseados em espalhamento múltiplo se aproveitam da autoiluminacão do meio devido às ondas multiplamente espalhadas. A autoiluminação fornece estimativas melhores com conteúdo espectral mais rico nas baixas frequências
Abstract: While in principle nonlinear gradient-based full-waveform inversion (FWI) is capable of handling all aspects of wave propagation contained in the data, including full nonlinearity, in practice, it is limited due to its notorious sensitivity to the choice of the starting model. To help addressing model-convergence issues in FWI, we study a decomposition based on the scattering theory that allows to break the acoustic-wavefield sensitivity kernels with respect to model parameters into background and singular parts. The estimates for both background perturbation and/or singular-part perturbation obtained with the subkernels' adjoints are components of the estimate obtained with the total kernel's adjoint. Our numerical experiments shows the feasibility of our main claim: the decomposition into subkernels allows to backproject the scattered-wavefield residuals only so as to obtain reasonable background-model perturbation estimates. In an experiment with restricted acquisition geometry (reflection data, narrow offset), the multiple-scattering subkernels take advantage of medium self-illumination provided by the scattered wavefields. This self-illumination provides better estimates, with longer wavelengh content
Doutorado
Reservatórios e Gestão
Doutor em Ciências e Engenharia de Petróleo
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Stamp, Gregory Carlton. "Experimental characterization of acoustic wave propagation through a supersonic ducted flow." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3934.
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Thesis (M.S.) -- University of Maryland, College Park, 2006.Thesis research directed by: Dept. of Aerospace Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Stabile, Tony Alfredo <1977>. "High frequency seismic and underwater acoustic wave propagation and imaging techniques." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1145/.
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Moon, Kihyo. "Immersed Discontinuous Galerkin Methods for Acoustic Wave Propagation in Inhomogeneous Media." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/70906.
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We present immersed discontinuous Galerkin finite element methods for one and two dimensional acoustic wave propagation problems in inhomogeneous media where elements are allowed to be cut by the material interface. The proposed methods use the standard discontinuous Galerkin finite element formulation with polynomial approximation on elements that contain one fluid while on interface elements containing more than one fluid they use specially-built piecewise polynomial shape functions that satisfy appropriate interface jump conditions. The finite element spaces on interface elements satisfy physical interface conditions from the acoustic problem in addition to extended conditions derived from the system of partial differential equations. Additional curl-free and consistency conditions are added to generate bilinear and biquadratic piecewise shape functions for two dimensional problems. We established the existence and uniqueness of one dimensional immersed finite element shape functions and existence of two dimensional bilinear immersed finite element shape functions for the velocity.
The proposed methods are tested on one dimensional problems and are extended to two dimensional problems where the problem is defined on a domain split by an interface into two different media. Our methods exhibit optimal $O(h^{p+1})$ convergence rates for one and two dimensional problems. However it is observed that one of the proposed methods is not stable for two dimensional interface problems with high contrast media such as water/air. We performed an analysis to prove that our immersed Petrov-Galerkin method is stable for interface problems with high jumps across the interface. Local time-stepping and parallel algorithms are used to speed up computation.
Several realistic interface problems such as ether/glycerol, water/methyl-alcohol and water/air with a circular interface are solved to show the stability and robustness of our methods.Ph. D.
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Tripathi, Bharat. "Discontinuous Galerkin Method for Propagation of Acoustical Shock Waves in Complex Geometry." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066344/document.
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Un nouveau code de simulation numérique pour la propagation des ondes de choc acoustiques dans des géométries complexes a été développé. Le point de départ a été la méthode de Galerkin discontinu qui utilise des maillages non structurés (ici des éléments triangulaires), particulièrement adaptés aux géométries complexes. Cependant, cette discrétisation conduit à l'apparition d'oscillation de Gibbs. Pour pallier ce problème, nous avons choisi d'introduire de la viscosité artificielle au voisinage des chocs. Cela a nécessité le développement de trois outils originaux : (i) un nouveau détecteur de choc sensible aux ondes de chocs acoustiques sur des maillages non structurés, (ii) un nouveau terme de viscosité artificielle dans les équations de l'acoustique non linéaire défini élément par élément et (iii) un nouveau terme permettant de régler le niveau de viscosité locale à partir du raidissement des fronts d'onde. Le code de calcul a été utilisé pour étudier deux configurations différentes. La première concerne la réflexion d'ondes de choc acoustiques sur des surfaces rigides. Différents régimes de réflexion ont alors été observés allant, de la réflexion classique de Snell Descartes jusqu'à celui dit de réflexion faible de Von Neumann. La deuxième configuration était consacrée à la focalisation d'ondes de choc acoustiques produites par un transducteur à haute intensité (comme ceux utilisés en HIFU). Un soin particulier a été pris pour étudier le calcul de l'intensité et pour étudier l'interaction entre les ondes de choc et des obstacles placés dans la région du foyerA new numerical solver for the propagation of acoustical shock waves in complex geometry has been developed. This is done starting from the discontinuous Galerkin method. This method is based on unstructured mesh (triangular elements here), and so, naturally it is well-adapted for complex geometries. Nevertheless, the discretization induces Gibbs oscillations. To manage this problem, we choose to introduce some artificial viscosity only in the vicinity of the shocks. This necessitates the development of three original tools. First of all, a new shock sensor for unstructured mesh sensitive to acoustical shock waves has been designed. It senses where the local artificial viscosity has to be introduced thanks to a reformulation of a new element centred smooth artificial viscosity term in the equations. Finally, the amount of viscosity is computed by the introduction of an original notion of gradient factor linked to the steepening of the waveform. The numerical solver has been used to investigate two different physical situations. The first one is the nonlinear reflection of acoustical shock waves on rigid surfaces. Different regimes of reflection have been observed ranging from the linear Snell Descartes reflection to the weak von Neumann case. The second configuration deals with the focusing of shock waves produced by high intensity transducers (like in HIFU). Special attention has been given to the careful computation of intensity and to the interaction between the shock waves and obstacles in the region of the focus
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Atkinson, Chris M. (Chris Mark). "Acoustic wave propagation and non-intrusive velocity measurements in highly concentrated suspensions." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/111044.
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Reinwald, Michael. "Wave propagation in mammalian skulls and its contribution to acoustic source localization." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS244.
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La précision avec laquelle le dauphin localise les sources sonores est excellente, que les sources soient situées dans le plan médial ou dans le plan transverse. Cette faculté est contre-intuitive étant donné que les dauphins n’ont pas d’oreille externe (pavillon), qui joue un rôle important chez les autres mammifères pour la localisation de sources en élévation. Dans cette thèse, des simulations tridimensionnelles ont été réalisées pour déterminer l’influence de la conduction osseuse du son dans le crâne d’un dauphin commun à bec court sur la pression acoustique au voisinage de l’oreille. La modalisation n’a pas permis de mettre en évidence d’encoches spectrales telles que celles créées par le pavillon de l’oreille externe des humains et qui codent chez celui-ci l’élévation de la source sonore. Une série d’expériences sur un crâne de dauphin, immergé dans une piscine, a permis de mesurer directement la conduction osseuse dans la mandibule. Les formes d’ondes complètes des sons reçus aux récepteurs fixés sur la mandibule, et particulièrement la coda du signal, a pu être utilisée avec succès pour obtenir la position de sources en utilisant un algorithme de corrélation. Ce résultat, qui devra être conforté par la réalisation d’autres expériences, suggère que le système auditif du dauphin pourrait utiliser la coda des signaux reçus lors de l’écholocation. Enfin, des simulations 2D ont permis de mettre en évidence le potentiel bénéfice du couplage de la conduction osseuse du son avec la propagation dans des structures graisseuses de la tête du dauphinThe spatial accuracy of source localization by dolphins has been observed to be equally accurate independent of source azimuth and elevation. This ability is counter-intuitive if one considers that humans and other species have presumably evolved pinnae to help determine the elevation of sound sources, while cetaceans have actually lost them. In this work, 3D numerical simulations are carried out to determine the influence of bone-conducted waves in the skull of a short-beaked common dolphin on sound pressure in the vicinity of the ears. The skull is not found to induce any salient spectral notches, as pinnae do in humans, that the animal could use to differentiate source elevations in the median plane. Experiments are conducted in a water tank by deploying sound sources on the horizontal and median plane around a skull of a dolphin and measuring bone-conducted waves in the mandible. Their full waveforms, and especially the coda, can be used to determine source elevation via a correlation-based source localization algorithm. While further experimental work is needed to substantiate this speculation, the results suggest that the auditory system of dolphins might be able to localize sound sources by analyzing the coda of biosonar echoes. 2D numerical simulations show that this algorithm benefits from the interaction of bone-conducted sound in a dolphin's mandible with the surrounding fats
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Nguyen, The Anh. "Acoustic waves in porous media : numerical study of wave propagation in porous media with one or many mineral components : applications to real Fontainebleau and STATOIL samples." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066205/document.
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L’objectif de ma thèse est d'étudier la propagation des ondes acoustiques dans les milieux poreux. La théorie de l'homogénéisation (Boutin et Auriault, 1990; Malinouskaya, 2007; Li, 2010) est utilisée avec les modèles de réseaux tels que LBM, LSM, LSM2S, LBM-LSM, LBM-LSM2S. Ces modèles nous permettent de déterminer les propriétés macroscopiques, les vitesses acoustiques et les effets d'atténuation dans les échantillons Fontainebleau avec deux composants (pores et quartz) et les échantillons STATOIL avec trois composantes (pores, quartz et d'argile). La modélisation numérique vise à résoudre 3 problèmes. Le premier problème est la caractérisation des échantillons; par la détermination de la porosité et des fonctions de corrélation avec les composantes de Fourier correspondantes (Adler, 1992; Nguyen, 2013). Le second porte sur la propagation des ondes dans les échantillons secs; les vitesses sont dérivées du tenseur de rigidité efficace C(eff) qui peut être calculé par LSM (Pazdniakou, 2012) ou LSM2S. Le troisième problème correspond aux échantillons saturés par un fluide incompressible ou compressible; les vitesses sont obtenues par résolution de l'équation de Christoffel après les déterminations de C(eff), fr la perméabilité dynamique K et ses réactions à la pression de fluide α et β. Pour les échantillons de Fontainebleau, les calculs sont effectués avec des modèles pré-existents tels que LSM, LBM, LBM-LSM. Ces modèles de bases sont étendus pour milieux avec plusieurs composants solides; ils sont validés via des comparaisons avec d’autres méthodes (Nemat-Nasser et Iwakuma, 1982; Torquato, 1998, 2000; Cohen, 2004). Les vitesses, le module d’élasticité et cisaillement efficace de tous les échantillons secs ainsi que les vitesses et l'atténuation des ondes dans les échantillons saturés sont déterminés. Les séries de résultats obtenues concordent bien avec des corrélations empiriques et théoriques, tels que le modèle d’IOS d’ Arns (1996), les modèles empiriques de Nur et al. (1991), Krief (1990) et avec le modèle de Gassmann. Les résultats numériques sont un peu plus grands que les données expérimentales d’ Han (1986) et de Gomez et al. (2010); les raisons de cette petite différence ont été provisoirement analysées, mais sa cause n'a pas été identifiée sans ambiguïtéThe purpose of this Ph.D. thesis is to study acoustic waves in porous media. The homogenization theory (Boutin and Auriault, 1990; Malinouskaya, 2007; Li, 2010) is used together with the lattice models such as LBM, LSM, LSM2S, LBM-LSM, LBM-LSM2S in order to determine the macroscopic properties, the acoustic velocities, the attenuation effects in Fontainebleau samples with two components (pore and quartz) and in STATOIL samples with three components (pore, quartz and clay). Three problems are studied numerically in this work. The first problem is devoted to characterizations of samples; this is done with the determination of the porosity and of the correlation functions with the corresponding Fourier components (Adler, 1992; Nguyen, 2013). The second one addresses wave propagation in dry samples; the velocities are derived from the effective stiffness tensor C(eff) which can be calculated by LSM (Pazdniakou, 2012) or LSM2S. The third one corresponds to samples saturated by incompressible or compressible fluids; the velocities can be obtained from the Christoffel equation after determining C(eff) , the dynamic permeability K and the reactions to fluid pressure α and β. For Fontainebleau samples, the calculations are performed with basic existing models such as LSM, LBM, LBM-LSM. These basic models are extended to solids with multiple components; they are validated by comparisons with others (Nemat-Nasser and Iwakuma, 1982; Torquato, 1998, 2000; Cohen, 2004). The velocities, the effective bulk and shear modulus of all the dry samples as well as the velocities and the attenuation effected in saturated samples are determined. These results are in good agreement compared with existing models and results, such as the IOS model of Arns (1996), the empirical models of Nur et al. (1991), Krief (1990) and with Gassmann’ s model. The numerical results are slightly larger than the experimental data of Han (1986) and Gomez et al. (2010); the origin of this small discrepancy has been tentatively analyzed, but its cause has not been unambiguously identified
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Bailey, Jermaine A. "UNIFORM AND MULTI-GRID MODELING OF ACOUSTIC WAVE PROPAGATION WITH CELLULAR AUTOMATON TECHNIQUES." Monterey, California. Naval Postgraduate School, 2013. http://hdl.handle.net/10945/32789.
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The Cellular Automaton (CA) method is an alternative computational technique used in understanding the behavioral response of dynamic systems. It allows great flexibility in the application of various types of boundary conditions. As such, this method is used in developing an alternative propagation model for ocean acoustics. The modeling scheme creates a profile of propagation losses versus range, in an acoustic medium. Moreover, the chosen complex boundary conditions, which are not easily modeled by ordinary numerical techniques, are shown to perform with remarkable ease with CA methods. Accordingly, like any other modeling method, the computational time increases when a refined solution is desired. As such, an alternative multi-grid modeling scheme is shown to increase the performance time of the CA method significantly. This improvement is dependent upon the total number of global grid points inside the multi-grid domain. The end result show a multi-grid, with fewer nodal points, producing accurate results that replicate a uniform grid, which utilizes a larger quantity of nodal points.
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Kameni, Carole. "Etude et optimisation d’une source sonore pour la sollicitation acoustique fort niveau des satellites." Thesis, Le Mans, 2017. http://www.theses.fr/2017LEMA1008.
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Avant leur lancement dans l'espace, les satellites font l'objet de tests afin d'éprouver leurs comportements à diverses sollicitations (thermiques, acoustiques, etc.). Pour les essais acoustiques, la société Intespace soumet les satellites à de forts niveaux sonores (de l'ordre de 145 dB SPL dans la chambre réverbérante) comparables à ceux existant lors du décollage du lanceur. Elle utilise pour cela des sources électropneumatiques couplées à des pavillons débouchant dans une chambre réverbérante. Ce système acoustique assure sa mission avec succès mais la société Intespace s'interroge sur ses possibilités d'amélioration. Deux prototypes de sources pneumatiques (à disque oscillant ou rotatif, à l'échelle 1 sur 5) sont développés et construits. Les prédictions théoriques avec vena contracta sont comparées aux données expérimentales issues d'un banc de mesure. Leurs différences concernant les niveaux sonores à la sortie de la source n'excèdent pas 1 dB pour des pressions d'alimentation de 1 à 3,5 bars absolus. Un prototype de pavillon de géométrie optimisée a été construit à l'échelle 1 sur 5. Les mesures montrent des performances intéressantes. Compte tenu des niveaux sonores générés par la source, une étude de la propagation dans le pavillon met en évidence des phénomènes non linéaires, qui s'avèrent peu influencés par la présence d'un écoulement moyen pour les vitesses envisagées dans l'étude. Finalement, des mesures sont réalisées sur l'ensemble du système à l'échelle 1 sur 5, afin d'en évaluer les performances. Les niveaux sonores mesurés sont comparés aux prédictions d'un modèle issu de la théorie de Sabine. Les différences n'excèdent pas plus ou moins 3 dBBefore their launch in space, satellites are the object of tests in order to test their behaviors with diverse constraints (thermal, acoustic, etc.). In terms of acoustic qualification, the Intespace company submits the satellites to high sound levels (of the order of 145 dB SPL in the reverberating room) comparable to those existing during the take-off phase of the launcher. For this purpose, it uses electropneumatic sources coupled to horns opening into a reverberating room. This acoustic system ensures its mission successfully but Intespace is wondering about the possibilities of improving the system. Two prototypes of pneumatic sources (oscillating or rotating disk, 1 on 5 scale) are developed and constructed. Theoretical predictions taking into account the vena contracta are compared with the experimental data from an instrumented measuring bench. Their differences in the sound levels at the source outlet do not exceed 1 dB at supply pressures of 1 to 3.5 bars absolute. A horn prototype whose shapes have been optimized was built on a 1 on 5 scale. The measurements show interesting performances. Considering the sound levels generated by the source, a study of the propagation in the horn highlights nonlinear phenomena. The latter are not influenced by the presence of an average flow for the velocities envisaged in the study. Finally, measurements are realized on the whole system at 1 on 5 scale, in order to evaluate their performance. The measured sound levels are compared to the predictions of a model derived from the Sabine theory. The differences do not exceed 3 dB or less
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Wang, Hui. "Boundary integral modelling of transient wave propagation with application to acoustic radiation from loudspeakers." Thesis, University of Brighton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404067.
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