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Dissertations / Theses on the topic 'Sound Acoustical materials'
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Dai, Hin Man. "Light weight low frequency sound focus lens /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202005%20DAI.
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Ho, Kin-Ming. "Impedance measurement of resonant sonic crystals /." View Abstract or Full-Text, 2002. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202002%20HOK.
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Tan, Lin. "Development of micro-acoustic devices with applications of viscous effects." Diss., Online access via UMI:, 2006.
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Jackson, Christophe E. "Construction and characterization of a portable sound booth for onsite voice recording /." Birmingham, Ala. : University of Alabama at Birmingham, 2009. https://www.mhsl.uab.edu/dt/2010r/jackson.pdf.
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Thesis (M.S.)--University of Alabama at Birmingham, 2009.Title from PDF t.p. (viewed June 30, 2010). Additional advisors: Stephen A. Watts, Paul A. Richardson, John T. Tarvin. Includes bibliographical references (p. 36-38).
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Fung, Kin-Hung. "Phononic band gap of locally resonant sonic materials with finite thickness /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202004%20FUNG.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 73-74). Also available in electronic version. Access restricted to campus users.
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Anders, William S. "Structural acoustic analysis of shape memory alloy hybrid composite panels." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-11012008-063243/.
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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.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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Wu, Ruimeng. "UTILIZATION OF EMPIRICAL MODELS TO DETERMINE THE BULK PROPERTIES OF COMPRESSED SOUND ABSORPTIVE MATERIALS." UKnowledge, 2017. https://uknowledge.uky.edu/me_etds/106.
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Empirical models based on flow resistivity are commonly used to determine the bulk properties of porous sound absorbing materials. The bulk properties include the complex wavenumber and complex characteristic impedance which can be used directly in simulation models. Moreover, the bulk properties can also be utilized to determine the normal incidence sound absorption and specific acoustic impedance for sound absorbing materials of any thickness and for design of layered materials. The sound absorption coefficient of sound absorbing materials is measured in an impedance tube using wave decomposition and the measured data is used to determine the flow resistivity of the materials by least squares curve fitting to empirical equations. Results for several commonly used foams and fibers are tabulated to form a rudimentary materials database. The same approach is then used to determine the flow resistivity of compressed sound absorbing materials. The flow resistivities of the compressed materials are determined as a function of the compression ratio. Results are then used in conjunction with transfer matrix theory to predict the sound absorptive performance of layered compressed absorbers with good agreement to measurement.
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Huang, Weichun. "Acoustic properties of natural materials." Thesis, Le Mans, 2018. http://www.theses.fr/2018LEMA1031/document.
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Dans cette thèse, nous étudions un métamatériau inspiré de la paille de blé pour l'absorption parfaite du son. Une botte de paille estidéalisée comme un milieu poreux anisotrope, composé d’un arrangement périodique très concentré de tubes creux cylindriques. L’approche théorique de ce métamatériau repose sur l'homogénéisation asymptotique à deux échelles d'un réseau perméable de résonateursparfaitement rigides dont la physique est enrichi par des résonances internes. Les principales caractéristiques de ce milieu poreux sont lacompressibilité effective négative autour de la résonance du tube et la réduction drastique de la vitesse de propagation du son (slowsound) à très basse fréquence. Une configuration optimale est conçue, basée sur la condition de couplage critique, pour laquelle la fuited’énergie du système résonnant ouvert est parfaitement compensée par les pertes intrinsèques induites par les pertes viscothermiques.Des mesures en tube à impédance sont effectuées sur des échantillons fabriqués par impression additive pour valider les résultatsthéoriques. Nous montrons que ce métamatériau est un absorbeur sub-longueur d'onde capable d’une absorption parfaite à très bassefréquence et d'introduire une quasi-bande interdite autour de la résonance du tube. De plus, la nature anisotrope de ce matériau conduit àune absorption globalement élevée à basse fréquence et ce pour toutes les incidences. Cette étude offre la possibilité de concevoir unabsorbeur acoustique sélectif en angle et en fréquence. Pour conclure, les résultats de cette thèse montrent que la paille est un boncandidat pour une absorption acoustique parfaiteStraw-inspired metamaterials for sound absorption are investigated in this Thesis. A straw stack is idealized as a highly concentratedresonant anisotropic porous medium constituted of a periodic arrangement of densely packed cylindrical hollow tubes. The approach tothis metamaterial relies on the two-scale asymptotic homogenization of a permeable array of perfectly rigid resonators, where the physicsis further enriched by tailoring inner resonances. The main features of such sound absorbing medium are the possibility for the effectivecompressibility to become negative around the tube resonance and the drastic reduction of the effective sound speed (slow sound) at verylow frequency in the system. Moreover, an optimal configuration for sound absorption is designed, based on the critical couplingcondition, in which the energy leakage out of the open resonant system is perfectly compensated by the intrinsic losses induced by thevisco-thermal losses both in the anisotropic matrix and in the resonators. Impedance tube measurements are performed on 3-D printedsamples with controlled parameters to validate the theoretical results. This metamaterial is a sub-wavelength absorber that can achievetotal absorption at a very low frequency and possesses a quasi-band-gap around the tube resonance. Furthermore, the anisotropic nature ofthe configuration gives rise to high absorption at low-frequency range for all incidences and diffuse field excitation. It paves the way tothe design of angular and frequency selective sound absorber. To conclude, the results of this Thesis show that straw is a good candidatefor perfect sound absorption
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Caille, Gary W. "The acoustic field scattered from some approximate pressure release materials coating a finite cylinder." Thesis, Monterey, Calif. : Naval Postgraduate School, 1988. http://handle.dtic.mil/100.2/ADA194768.
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Meng, Han. "Acoustic properties of novel multifunctional sandwich structures and porous absorbing materials." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEC008/document.
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La mise en oeuvre de matériaux acoustiques est une méthode efficace et très utilisée pour réduire le bruit le long de sa propagation. Les propriétés acoustiques de nouvelles structures sandwich multifonctionnelles et de matériaux absorbants poreux sont étudiées dans la thèse. Les principales contributions de la thèse sont les suivantes: Les panneaux sandwich ont généralement d'excellentes propriétés mécaniques et un bon indice de perte en transmission sonore (STL), mais aucune capacité d'absorption acoustique. De nouvelles structures sandwich multifonctionnelles sont développées en intégrant des microperforations et des matériaux absorbants poreux aux panneaux sandwich ondulés et en nid d’abeilles conventionnels, structurellement efficaces pour obtenir de bons STL et de bonnes absorptions en basses fréquences. Le coefficient d'absorption acoustique (SAC) et la perte en transmission (STL) des panneaux sandwich ondulés sont évalués numériquement et expérimentalement en basse fréquence pour différentes configurations de perforations. Les modèles éléments finis (EF) sont construits en tenant compte des interactions vibro-acoustiques sur les structures et des dissipations d'énergie, visqueuse et thermique, à l'intérieur des perforations. La validité des calculs FE est vérifiée par des mesures expérimentales avec les échantillons testés obtenus par fabrication additive. Par rapport aux panneaux sandwich ondulés classiques sans perforation, les panneaux sandwich perforés (PCSPs) avec des perforations dans leur plaque avant présentent non seulement un SAC plus élevé aux basses fréquences, mais aussi un meilleur STL, qui en est la conséquence directe. L'élargissement des courbes des indices d’absorption et de transmission doit être attribué à la résonance acoustique induite par les micro-perforations. Il est également constaté que les PCSPs avec des perforations dans les plaques avant et les parois internes onduleés ont les fréquences de résonance les plus basses de tous les PCSPs. En outre, les performances acoustiques des panneaux sandwich en nid d'abeilles avec une plaque avant microperforée sont également examinées. Un modèle analytique est présenté avec l'hypothèse que les déplacements des deux plaques sont identiques aux fréquences inférieures à la fréquence de résonance des plaques. Le modèle analytique est ensuite validé par des modèles d'éléments finis et des résultats expérimentaux existants. Contrairement aux panneaux sandwich en nid d'abeilles classiques qui sont de piètres absorbeurs de bruit, les sandwichs en nid d'abeilles perforés (PHSPs) conduisent à un SAC élevé aux basses fréquences, ce qui entraîne en conséquence un incrément dans le STL basse fréquence. Les influences de la configuration du noyau sont étudiées en comparant les PHSPs avec différentes configurations de noyaux en nids d'abeilles. […]Implementation of acoustic materials is an effective and popular noise reduction method during propagation. Acoustic properties of novel multifunctional sandwich structures and porous absorbing materials are studied in the dissertation. The main contributions of the dissertation are given as, Sandwich panels generally have excellent mechanical properties and good sound transmission loss (STL), but no sound absorption ability. Novel multifunctional sandwich structures are developed by integrating micro perforations and porous absorbing materials to the conventional structurally-efficient corrugated and honeycomb sandwich panels to achieve good SAC and STL at low frequencies. Low frequency sound absorption and sound transmission loss (STL) of corrugated sandwich panels with different perforation configurations are evaluated both numerically and experimentally. Finite element (FE) models are constructed with considerations of acousticstructure interactions and viscous and thermal energy dissipations inside the perforations. The validity of FE calculations is checked against experimental measurements with the tested samples provided by additive manufacturing. Compared with the classical corrugated sandwich panels without perforation, the perforated corrugated sandwich panels (PCSPs) with perforations in its face plate not only exhibits a higher SAC at low frequencies but also a better STL as a consequence of the enlarged SAC. The enlargement of SAC and STL should be attributed to the acoustical resonance induced by the micro perforations. It is also found that the PCSPs with perforations in both the face plates and corrugated cores have the lowest resonance frequencies of all the PCSPs. Besides, the acoustic properties of honeycomb sandwich panels with microperforated faceplate are also explored. An analytical model is presented with the assumption that displacements of the two faceplates are identical at frequencies below the faceplate resonance frequency. The analytical model is subsequently verified by finite element models and existing experimental results. Unlike classical honeycomb sandwich panels which are poor sound absorbers, perforated honeycomb sandwiches (PHSPs) lead to high SAC at low frequencies, which in turn brings about increment in the low frequency STL. Influences of core configuration are investigated by comparing PHSPs with different honeycomb core configurations. In order to enlarge the SAC bandwidth of perforated sandwich panels, porous absorbing materials are added to the cores of novel perforated sandwich panels. FE models are set up to estimate the SAC and STL of perforated sandwich panels with porous materials. Results show that perforated sandwich panels with porous material can provide SAC with broader bandwidth and lower resonance frequency than that without porous materials. Whereas the peak values in the SAC and STL curves are reduced due to the weakened acoustical resonance by the porous materials. […]
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Warren, Daniel. "The scattering of sound waves in two-dimensional ducts with discontinuities in height and material property." Thesis, Brunel University, 1999. http://bura.brunel.ac.uk/handle/2438/6618.
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Eigen-mode matching techniques offer a versatile approach for solving acoustic scattering problems in ducts. However, until recently, these techniques have been restricted to problems in which the boundary conditions contain at most one derivative, that is, Neumann, Dirichlet or Robin's conditions. Here a method is developed to solve scattering problems in ducts that are discontinuous in height and have at least one surface described by a high order boundary condition. Attention is focussed on the membrane condition, but the method can be extended to elastic plates and other higher order conditions. An original orthogonality condition is derived and used to solve two problems. Limiting cases of the results are compared with some special cases solveable by standard Fourier techniques and (for the case of no height discontinuity) the Wiener-Hopf technique.
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Rumpler, Romain. "Efficient Finite Element Approach for Structural-Acoustic Applications including 3D modelling of Sound Absorbing Porous Materials." Doctoral thesis, KTH, MWL Numerisk akustik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-90335.
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In the context of interior noise reduction, the present work aims at proposing Finite Element (FE) solution strategies for interior structural-acoustic applications including 3D modelling of homogeneous and isotropic poroelastic materials, under timeharmonic excitations, and in the low frequency range. A model based on the Biot-Allard theory is used for the poroelastic materials, which is known to be very costly in terms of computational resources. Reduced models offer the possibility to enhance the resolution of such complex problems. However, their applicability to porous materials remained to be demonstrated.First, this thesis presents FE resolutions of poro-elasto-acoustic coupled problems using modal-based approaches both for the acoustic and porous domains. The original modal approach proposed for porous media, together with a dedicated mode selection and truncation procedure, are validated on 1D to 3D applications.In a second part, modal-reduced models are combined with a Padé approximants reconstruction scheme in order to further improve the efficiency.A concluding chapter presents a comparison and a combination of the proposed methods on a 3D academic application, showing promising performances. Conclusions are then drawn to provide indications for future research and tests to be conducted in order to further enhance the methodologies proposed in this thesis.Dans le contexte de lutte contre les nuisances sonores, cette thèse porte sur le développement de méthodes de résolution efficaces par éléments finis, pour des problèmes de vibroacoustique interne avec interfaces dissipatives, dans le domaine des basses fréquences. L’étude se limite à l’utilisation de solutions passives telles que l’intégration de matériaux poreux homogènes et isotropes, modélisés par une approche fondée sur la théorie de Biot-Allard. Ces modèles étant coûteux en terme de résolution, un des objectifs de cette thèse est de proposer une approche modale pour la réduction du problème poroélastique, bien que l’adéquation d’une telle approche avec le comportement dynamique des matériaux poreux soit à démontrer.Dans un premier temps, la résolution de problèmes couplés élasto-poro-acoustiques par sous-structuration dynamique des domaines acoustiques et poreux est établie. L’approche modale originale proposée pour les milieux poroélastiques, ainsi qu’une procédure de sélection des modes significatifs, sont validées sur des exemples 1D à 3D.Une deuxième partie présente une méthode combinant l’utilisation des modèles réduits précédemment établis avec une procédure d’approximation de solution par approximants de Padé. Il est montré qu’une telle combinaison offre la possibilité d’accroître les performances de la résolution (allocation mémoire et ressources en temps de calcul).Un chapitre dédié aux applications permet d’évaluer et comparer les approches sur un problème académique 3D, mettant en valeur leurs performances encourageantes. Afin d’améliorer les méthodes établies dans cette thèse, des perspectives à ces travaux de recherche sont apportées en conclusion.
QC 20120224
FP6 Marie-Curie Smart Structures
FP7 Marie-Curie Mid-Frequency
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Rumpler, Romain. "Efficient finite element approach for structural-acoustic applicationns including 3D modelling of sound absorbing porous materials." Phd thesis, Conservatoire national des arts et metiers - CNAM, 2012. http://tel.archives-ouvertes.fr/tel-00726915.
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In the context of interior noise reduction, the present work aims at proposing Finite Element (FE) solution strategies for interior structural-acoustic applications including 3D modelling of homogeneous and isotropic poroelastic materials, under timeharmonic excitations, and in the low frequency range. A model based on the Biot-Allard theory is used for the poroelastic materials, which is known to be very costly in terms of computational resources. Reduced models offer the possibility to enhance the resolution of such complex problems. However, their applicability to porous materials remained to be demonstrated.First, this thesis presents FE resolutions of poro-elasto-acoustic coupled problems using modal-based approaches both for the acoustic and porous domains. The original modal approach proposed for porous media, together with a dedicated mode selection and truncation procedure, are validated on 1D to 3D applications.In a second part, modal-reduced models are combined with a Padé approximants reconstruction scheme in order to further improve the efficiency.A concluding chapter presents a comparison and a combination of the proposed methods on a 3D academic application, showing promising performances. Conclusions are then drawn to provide indications for future research and tests to be conducted in order to further enhance the methodologies proposed in this thesis.
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Parra, Martinez Juan Pablo. "On the ECO2 multifunctional design paradigm and tools for acoustic tailoring." Licentiate thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-161209.
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Nowadays vehicle design paradigm influences not only the effectiveness of the different means of transport, but also the environment and economy in a critical way. The assessment of the consequences that design choices have on society at large are necessary to understand the limits of the methods and techniques currently employed. One of the mechanisms set in motion is the planned obsolescence of products and services. This has affected vehicle design paradigm in such a way that the variety in the market has shadowed the primary function of vehicle systems: the transport of persons and goods. Amongst the consequences of the expansion of such market is the exponential rise on combustion emissions to the atmosphere, which has become a great hindrance for humans health and survival of ecosystems. The development of evaluation tools for such consequences and their piloting mechanisms is needed so as to implement an ECO2 (Ecological and Economical) vehicle design paradigm. Moreover, the multifunctional design paradigm that drives aeronautical and vehicle engineering is an ever-growing demand of smart materials and structures, able to fulfil multiple requirements in an effective way. The understanding of certain phenomena intrinsic to the introduction of novel materials has found certain limits due to the complexity of the models needed. This work presents as a first step an assessment of the causes and consequences of the vehicle exponential market growth based on the analysis of the planned obsolescence within. Furthermore, a method for the acoustic response analysis of multilayered structures including anisotropic poroelastic materials is introduced. The methodology consists in a plane wave approach as a base for introducing the complex mechanic and acoustic equations governing anisotropic homogeneous media, e.g. open-celled foams, into an alternative mathematical tool manipulating physical wave amplitudes propagation within the studied media. In addition, this method is coupled to a power partitioning and energetic assessment tool so as to understand the phenomena present in complex multilayered designs.QC 20150323
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Li, Wanlu. "EXPERIMENTAL STUDIES ON THE DETERMINATION OF ACOUSTIC BULK MATERIAL PROPERTIES AND TRANSFER IMPEDANCE." UKnowledge, 2014. http://uknowledge.uky.edu/me_etds/48.
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Soft trim absorbing parts (i.e., headliners, backwalls, side panels, etc.) are normally comprised of different layers including films, adhesives, foams and fibers. Several approaches to determine the complex wavenumber and characteristic impedance for porous sound absorbing materials are surveyed and the advantages and disadvantages of each approach are discussed. It is concluded that the recently documented three-point method produces the smoothest results. It is also shown that measurement of the flow resistance and the use of empirical equations is sufficient for many common materials. Following this, the transfer impedance of covers, adhesives, and densified layers are measured using an impedance difference approach. The transfer matrix method was then used to predict the sound absorption of a multi-layered materal which included a perforated cover, fiber layers, and an adhesive. The predicted results agree well with measurement.
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Victor, John Samuel. "Interaction of Low Frequency Sound with Glass and other Building Materials in the Design of a Concert Hall for Symphony Orchestra and Choir." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/33313.
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In the world today, Concert Halls for Symphony Orchestra and Choir are generally â enclosed performance spacesâ that are completely cut-off from the outside: Whether itâ s a time of daylight or moonlight, rain or shine, summer or winter, spring or autumn, the environment within remains the same all the time.
I asked the question: â What if a concert hall offers views outside?â
To be more specific, the question is: â What if a concert hall offers views outside through the use of glass, along with other building materials, despite the fact that glass offers lower reflectivity and lower transmission loss for lower frequencies of sound, compared to certain other materials?â
Hence the title: Interaction of Low Frequency Sound with Glass and other Building Materials in the Design of a Concert Hall for Symphony Orchestra and Choir.Master of Architecture
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LEE, JOON-HYUN. "DEVELOPMENT OF NEW TECHNIQUE FOR DAMPING IDENTIFICATION AND SOUND TRANSMISSION ANALYSIS OF VARIOUS STRUCTURES." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin985028187.
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Jenne, Kirk E. "Acoustic cymbal transducers-design, hydrostatic pressure compensation, and acoustic performance." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Mar%5FJenne.pdf.
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Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, March 2004.Thesis advisor(s): Thomas R. Howarth, Dehua Huang. Includes bibliographical references (p. 67-69). Also available online.
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Mahasaranon, Sararat. "Acoustic and thermal properties of recycled porous media." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5516.
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This thesis is concerned with developing porous materials from tyre shred residue and polyurethane binder for acoustic absorption and thermal insulation applications. The resultant materials contains a high proportion of open, interconnected cells that are able to absorb incident sound waves through viscous friction, inertia effects and thermal energy exchanges. The materials developed are also able to insulate against heat by suppressing the convection of heat and reduced conductivity of the fluid locked in the large proportion of close-cell pores. The acoustic absorption performance of a porous media is controlled by the number of open cells and pore size distribution. Therefore, this work also investigates the use of catalysts and surfactants to modify the pore structure and studies the influence of the various components in the chemical formulations used to produce these porous materials. An optimum type and amounts of catalyst are selected to obtain a high chemical conversion and a short expanding time for the bubble growth phase. The surfactant is used to reduce the surface tension and achieve a homogenous mixing between the solid particulates tyre shred residue, the water, the catalyst and the binder. It is found that all of the components significantly affect the resultant materials structure and its morphology. The results show that the catalyst has a particularly strong effect on the pore structure and the ensuing thermal and acoustical properties. In this research, the properties of the porous materials developed are characterized using standard experimental techniques and the acoustic and thermal insulation performance underpinned using theoretical models. The important observation from this research is that a new class of recycled materials with pore stratification has been developed. It is shown that the pore stratification can have a positive effect on the acoustic absorption in a broadband frequency range. The control of reaction time in the foaming process is a key function that leads to a gradual change in the pore size distribution, porosity, flow resistivity and tortuosity which vary as a function of sample depth. It is shown that the Pade approximation is a suitable model to study the acoustic behaviour of these materials. A good agreement between the measured data and the model was attained.
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Januševičius, Tomas. "Research on the acoustic qualities of building materials and structures and their use for noise reduction in premises." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2011~D_20110621_170924-08631.
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The dissertation analyses the sound-insulating qualities of building materials and structures. The aim of the dissertation is to investigate and indentify, under natural conditions and in a noise suppression chamber, the structures which, as internal and external components of buildings, would ensure the protection of inte-rior rooms against noise and to model on this basis the sound reduction indices of structures.
The work deals with several main tasks: investigations of the acoustic quali-ties of building materials and structures in a noise suppression chamber and under natural conditions; comparison of results obtained from measurements, and the evaluation of the sound reduction indices of perspective structures through model-ling.
The introductory chapter introduces the problem addressed and topicality of the work, describes the object of research, formulates aim and tasks of the work, describes research methodology, scientific novelty of the work, points out practi-cal value of the work’s results and specifies defended propositions. The introduc-tion ends with a list of articles on the dissertation topic published by the author and the structure of the dissertation.
The first chapter analyses literature relating with the dissertation topic. Con-clusions are formulated at the end of the chapter.
The beginning of each chapter presents research methodologies. The second chapter differentiates investigations which were carried out in a noise suppression chamber and... [to full text]Disertacijoje nagrinėjamos statybinių medžiagų ir konstrukcijų garso izoliaci-nės savybės. Disertacijos tikslas – natūrinėmis sąlygomis ir triukšmo slopinimo kameroje ištirti ir nustatyti konstrukcijas, kurios, kaip pastatų vidinės ir išorinės sudėtinės dalys, užtikrintų vidaus patalpų apsaugą nuo triukšmo, ir tuo pagrindu sumodeliuoti konstrukcijų garso izoliavimo rodiklius. Šiame darbe sprendžiami keli pagrindiniai uždaviniai: statybinių medžiagų ir konstrukcijų akustinių savybių tyrimai triukšmo slopinimo kameroje ir natūrinė-mis sąlygomis, matavimų rezultatų palyginimas, perspektyvių konstrukcijų garso izoliavimo rodiklių įvertinimas modeliavimo būdu. Disertaciją sudaro įvadas, aštuoni skyriai, rezultatų apibendrinimas, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašas. Įvadiniame skyriuje pristatoma tiriamoji problema, darbo aktualumas, apibū-dinamas tyrimų objektas, formuluojamas darbo tikslas bei uždaviniai, aprašoma tyrimų metodika, nusakomas darbo mokslinis naujumas ir darbo rezultatų praktinė reikšmė, išvardijami ginamieji teiginiai. Įvadas baigiamas disertacijos tema auto-riaus paskelbtų publikacijų ir pranešimų konferencijose pristatymu bei disertacijos struktūra. Pirmajame skyriuje analizuojama su disertacijos tema susijusi literatūra. Sky-riaus pabaigoje formuluojamos išvados. Tyrimų metodikos pateiktos kiekvieno skyriaus pradžioje. Antrajame skyriuje išdiferencijuojami triukšmo slopinimo kameroje vykdyti tyrimai ir analizuojami jų... [toliau žr. visą tekstą]
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Aslan, Gokhan. "Cepstral Deconvolution Method For Measurement Of Absorption And Scattering Coefficients Of Materials." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/3/12608021/index.pdf.
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Several methods are developed to measure absorption and scattering coefficients of materials. In this study, a new method based on cepstral deconvolution technique is proposed. A reverberation room method standardized recently by ISO (ISO 17497-1) is taken as the reference for measurements. Several measurements were conducted in a physically scaled reverberation room and results are evaluated according to these two methods, namely, the method given
in the standard and cepstral deconvolution method. Two methods differ from each other in the estimation of specular parts of room impulse responses essential for determination of scattering coefficients. In the standard method, specular part
is found by synchronous averaging of impulse responses. However, cepstral deconvolution method utilizes cepstral analysis to obtain the specular part instead of averaging. Results obtained by both of these two approaches are compared for five different test materials. Both of the methods gave almost same values for absorption coefficients. On the other hand, lower scattering coefficient values
have been obtained for cepstral deconvolution with respect to the ISO method.
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Sun, Chao. "Acoustic characterisation of ultrasound contrast agents at high frequency." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8093.
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This thesis aims to investigate the acoustic properties of ultrasound contrast agents (UCAs) at high ultrasound frequencies. In recent years, there has been increasing development in the use of high frequency ultrasound in the fields of preclinical, intravascular, ophthalmology and superficial tissue imaging. Although research studying the acoustic response of UCAs at low diagnostic ultrasonic frequencies has been well documented, quantitative information on the acoustical properties of UCAs at high ultrasonic frequencies is limited. In this thesis, acoustical characterisation of three UCAs was performed using a preclinical ultrasound scanner (Vevo 770, VisualSonics Inc., Canada). Initially the acoustical characterisation of five high frequency transducers was measured using a membrane hydrophone with an active element of 0.2 mm in diameter to quantify the transmitting frequencies, pressures and spatial beam profiles of each of the transducers. Using these transducers and development of appropriate software, high frequency acoustical characterisation (speed and attenuation) of an agar-based tissue mimicking material (TMM) was performed using a broadband substitution technique. The results from this study showed that the acoustical attenuation of TMM varied nonlinearly with frequency and the speed of sound was approximately constant 1548m·s-1 in the frequency range 12-47MHz. The acoustical properties of three commercially available lipid encapsulated UCAs including two clinical UCAs Definity (Lantheus Medical Imaging, USA) and SonoVue (Bracco, Italy) and one preclinical UCAs MicroMarker (untargeted) (VisualSonics, Canada) were studied using the software and techniques developed for TMM characterisation. Attenuation, contrast-to-tissue ratio (CTR) and subharmonic to fundamental ratio were measured at low acoustic pressures. The results showed that large off-resonance and resonant MBs predominantly contributed to the fundamental response and MBs which resonated at half of the driven frequency predominantly contributed to subharmonic response. The effect of needle gauge, temperature and injection rate on the size distribution and acoustic properties of Definity and SonoVue was measured and was found to have significant impacts. Acoustic characterisations of both TMM and UCAs in this thesis extend our understanding from low frequency to high frequency ultrasound and will enable the further development of ultrasound imaging techniques and UCAs design specifically for high frequency ultrasound applications.
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Grotta, Danubia de Lima. "Materiais e técnicas contemporâneas para controle de ruído aéreo em edifícios de escritórios: subsídios para especificações." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/18/18141/tde-26052009-112244/.
Full textAbstract:
A malha urbana das grandes cidades tem sido ocupada, principalmente nos grandes centros, por vários edifícios corporativos, localizados em pólos administrativos onde os ruídos urbanos são constantes. Além dos ruídos externos a que o edifício fica exposto, existem também os ruídos internos, ambos impactando no conforto e produtividade de seus ocupantes, trazendo problemas para a empresa. Tendo a situação brevemente descrita acima como preocupante, este trabalho tem por objetivo geral, investigar quais materiais industrializados para tratamento acústico e quais técnicas são utilizadas, para redução e controle, da propagação de ruídos aéreos em edifícios de escritórios, nos últimos dez anos. Incluem-se assim o estudo e apresentação das características técnicas para especificação de forros acústicos, barreiras acústicas, tratamento de paredes, pisos, layout e mobiliário, vidros acústicos, tratamento dos ruídos gerados pelo ar condicionado e mascaramento sonoro. O objetivo específico neste trabalho é analisar os materiais utilizados para tratamento acústico, baseado nos índices de classificação acústica, seja este de absorção ou isolamento, com relação ao desempenho do material. São eles: NRC (Índice de Redução Sonora), \'alfa\' (Coeficiente de Absorção), \'alfa\'w (Coeficiente de Absorção Sonora Ponderado) Rw (Índice de Redução Acústica) e STC (Classe de Transmissão Sonora). Esta pesquisa tem como resultado a centralização de dados técnicos referente à utilização de materiais acústicos para controle de ruídos aéreos em edifícios de escritórios; a análise das classificações e desempenhos e a avaliação da disponibilização de informações técnicas nos catálogos brasileiros de produtos. Tal resultado oferecerá uma base de consulta para obtenção de critérios durante a especificação e elaboração de projetos de espaços corporativos. O trabalho conclui apontando observações da autora, referentes à utilização dos materiais e técnicas e a necessidade de criação e produção de um maior portfólio de produtos.Big cities have been taken the ground thought freeways and avenues, where constant and loud noise takes place. At theses ways, corporate edifices are also often established, so they naturally become exposed to the external noise interference, regardless the own internal facilities noising. The consequence is that people how work at these places are more prone to be less productive, turning it into a drawback to the corporate. The scenario described above is very concerning. This general research objective is to study techniques and industrialized material in order to reduce and control the noise propagation thought the air on for corporate facilities, focused at the last ten years time frame. It will focus on study and present the technical characteristics for acoustic absorption and/or isolation of roof lining, acoustic barriers, walls, floor, office layout, furniture, glasses, air-conditioner, and sound masking techniques. The specific research objective is to analyze the materials for acoustic handling, based on acoustic classification indexes that relate to the material performance, for absorption and isolation, as listed: NRC (Noise Reduction Coefficient), \'alfa\' (Sound Absorption Coefficient), \'alfa\'w (Pounder Sound Absorption Coefficient), Rw (Noise Reduction Index) and STC (Sound Transmission Class). The objective of this research is to be a single point of reference for technical data regarding the utilization of materials that can be used to control the sound propagation thought the air on corporate edifices; the classification of analysis and performance as well as the evaluation of technical information available on Brazilian product catalogs. The research result offers a baseline for those who look for criteria during the speciation and implementation of corporative spaces. The conclusion of this work is done with the Authors considerations regarding the utilization of materials and techniques, as well the necessity of creation and production of wider product portfolio.
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Khodier, Nesma Magdy VCUQ. "The Future of Arabic Music: No sound without silence." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4170.
Full textAbstract:
For centuries, Arabic music has been intrinsically linked to Arab culture and by extension bonded to the environmental landscape of the region, reflecting their emotions, moods, and behaviors. Numerous technological advancements in the latter half of the twentieth century, have greatly affected the rich legacy of Arabic music, significantly impacting the natural progression of traditional Arabic musical genres, scales, and instrumentation.
This thesis serves as an introduction to generative methods of music production, specifically music generated through gestures. Through generative music, and its unique ability to map gestures to different musical parameters, music can be produced using computer algorithms.
The outcome of this thesis aims to demystify the intricacies of recent technological advancements to enable the musician and the audience to incorporate responsive technology into their ensembles. This approach aims to further evolve Arabic music, using the concepts of Arabic music creativity while addressing international accessibility through integration.
The intention of this thesis is to bridge between the contemporary and the traditional Arabic audiences and provides insight into a possible future of Arabic music based on its own fundamental principles.
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Farooqui, Maaz. "Innovative noise control in ducts." Doctoral thesis, KTH, Farkost och flyg, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-192927.
Full textAbstract:
The objective of this doctoral thesis is to study three different innovative noise control techniques in ducts namely: acoustic metamaterials, porous absorbers and microperforates. There has been a lot of research done on all these three topics in the context of duct acoustics. This research will assess the potential of the acoustic metamaterial technique and compare to the use of conventional methods using microperforated plates and/or porous materials. The objective of the metamaterials part is to develop a physical approach to model and synthesize bulk moduli and densities to feasibly control the wave propagation pattern, creating quiet zones in the targeted fluid domain. This is achieved using an array of locally resonant metallic patches. In addition to this, a novel thin slow sound material is also proposed in the acoustic metamaterial part of this thesis. This slow sound material is a quasi-labyrinthine structure flush mounted to a duct, comprising of coplanar quarter wavelength resonators that aims to slow the speed of sound at selective resonance frequencies. A good agreement between theoretical analysis and experimental measurements is demonstrated. The second technique is based on acoustic porous foam and it is about modeling and characterization of a novel porous metallic foam absorber inside ducts. This material proved to be a similar or better sound absorber compared to the conventional porous absorbers, but with robust and less degradable properties. Material characterization of this porous absorber from a simple transfer matrix measurement is proposed.The last part of this research is focused on impedance of perforates with grazing flow on both sides. Modeling of the double sided grazing flow impedance is done using a modified version of an inverse semi-analytical technique. A minimization scheme is used to find the liner impedance value in the complex plane to match the calculated sound field to the measured one at the microphone positions.QC 20160923
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Bergweiler, Steffen. "Körperoszillation und Schallabstrahlung akustischer Wellenleiter unter Berücksichtigung von Wandungseinflüssen und Kopplungseffekten : Verändern Metalllegierung und Wandungsprofil des Rohrresonators den Klang der labialen Orgelpfeife?" Phd thesis, Universität Potsdam, 2005. http://opus.kobv.de/ubp/volltexte/2006/656/.
Full textAbstract:
Am Beispiel der Orgelpfeife wurde der Einfluss der Wandungsgeometrie
des akustischen Wellenleiters auf die Schallabstrahlung untersucht.
Für verschiedene Metalllegierungen wurden unterschiedliche Profile
der Orgelpfeifenwandung verglichen: ein konisches Wandungsprofil mit
zur Mündung hin abnehmender Wandungsstärke und ein paralleles
Wandungsprofil mit konstanter Wandungsstärke. Für eine hohe
statistische Sicherheit der Ergebnisse wurden sämtliche
Untersuchungen an vier mal zehn Testpfeifen durchgeführt. Mit
Ausnahme der beschriebenen Unterschiede sind die Pfeifen von
gleichen Abmessungen und auf gleichen Klang intoniert.Die Überprüfung der Wandungseinflüsse auf den Klang besteht aus drei verschiedenen Untersuchungen: Erstens, einer subjektiven Hinterfragung der Wahrnehmbarkeit in einem Hörtest. Zweitens wurde der abgestrahlte Luftschall objektiv gemessen und das Spektrum der Pfeifen in seinen Komponenten (Teiltöne, Grundfrequenz) verglichen. Drittens wurde mit einer neuartigen Messtechnik die Oszillation des Pfeifenkörpers (ein einem akustischen Monopol entsprechendes "Atmen" des Querschnitts) untersucht. Die Ergebnisse belegen die Wahrnehmbarkeit unterschiedlicher Wandungsprofile als auch klare objektive Differenzen zwischen den emittierten Schallspektren. Ein Atmen mit guter Korrelation zur inneren Druckanregung bestätigt den Einfluss wandungsprofilabhängiger Oszillationen auf den Klang der Orgelpfeife. Schließlich wurde die Interaktion zweier in Abstand und Grundfrequenz nah beieinander liegender Orgelpfeifen überprüft. Als Ursache des dabei wahrnehmbaren Oktavsprung des Orgeltons konnte eine gegenphasiger Oszillation des Grundtons beider Pfeifen nachgewiesen werden.
The influence of the wall geometry of an acoustic waveguide on the sound radiation has been investigated on the example of the steady sound quality of an organ pipe. At the example of two different pipe materials two different pipe wall geometries were compared: a wedge-shaped conical wall profile with a decreasing wall strength towards the pipes open end and a constant wall profile with no change in wall strength, respectively. For statistic safety all investigations were exercised on a large test pipe series of 4 by 10 pipes, unique to our knowledge. Apart from the described differences, all pipes are produced and intonated to be as equal as possible.
The verification of the wall geometries influences is based on three investigations: First, a subjective evaluation of the audible differences was performed. Second, differences in the broad spectra, the level of the harmonics partials and in the fundamental frequency were detected in an anechoic chamber. Third, with a new measurement technique we examined the oscillation of the pipe body (monopolic breathing of the pipe bodies cross-section) as source of the detected differences in the sound. The results show clear audible difference which are supported by measurable differences in airborne sound and body oscillations of the investigated pipes. Finally the interaction of two organ pipes closely space in frequency and distance has been investigated. The subjective impression of frequency doubling was detected as an anti-phase phase oscillation of the fundamental tone of both pipes leading to a dominance of the second harmonic.
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Windisch, Thomas. "Laser-akustische Messtechnik in der Materialcharakterisierung." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-209721.
Full textAbstract:
Testing equipment based on the propagation of elastic waves are commonly used for measuring specific material properties. As a prerequisite for accurate measurements a reliable acoustic coupling of probe and specimen is highly important. Therefore, high-resolution testing equipment is using fluids as couplant. In certain conditions, only non-contacting methods can be considered. This is the case for example, if particular high or low temperatures are present, if topographic features impede the use of ultrasonic probes, diffusion or solubility processes exist, measurements at vacuum are addressed and if high purity requirements need to be fulfilled. Hence, subject of this work is a method which offers to handle these constraints. With the emergence of modern laser systems the scientific basics for a non-contacting, laser-acoustic excitation of ultrasound were discovered. The tremendous development of commercially available laser systems during the last decade was taken as reason to investigate, to which extent former scientifically designed laboratory setups can now be merged into one single application oriented measuring system. All considerations are based on the thermoelastic excitation of ultrasound in combination with a likewise laser-based detection. By this, a self-contained measuring chain is built which combines the attributes non-destructive, non-contacting and application oriented within one ultrasonic measurement system for the first time. Thermal calculations lead to more precise equations which predict a laser-induced, local temperature rise of about 100 K. The examination of sound field simulations, as a prerequisite for the design of ultrasonic systems, identified an additional complex of problems. Although existing calculation approaches presuppose laser intensity profiles what can be described in analytical terms, real-world laser sources exhibit a complex shaped spatial distribution of laser energy. Based on a preceding CEFIT simulation, the developed CPSS method enables the calculation of the time resolved, 3D wave propagation of arbitrary shaped sources. A comparison to measured data successfully validated the results of simulation. By presenting selected scenario of measurements, the practical suitability of this non-contacting method is demonstrated. Using a transmission setup enables the characterization of open-pore ceramic coatings as well as the deduction of longitudinal and transversal speeds of sound. Equally, the imaging and estimation of the depth position of artificial defects with 0.7 mm in diameter is shown. Measurements based on a reflection setup provided evidence of a resolution limit of at least FBH = 1 mm in 4.5 mm depth. Additional examples demonstrate the ability to detect close-surface defects, the analysis of the challenging lamb waves zero-group-velocity S1 mode as well as the utilization of buried laser-acoustic sourcesPrüfsysteme, welche die Ausbreitungseigenschaften elastischer Wellen zur Ableitung spezifischer Messgrößen nutzen, sind etablierte Messverfahren. Voraussetzung für zuverlässige Ergebnisse ist stets die sichere akustische Kopplung zwischen Sensor und Material. Daher arbeiten hochauflösende Prüfsysteme mit Fluiden als Koppelmedium. Unter bestimmten Bedingungen scheiden kontaktierende Ultraschallsysteme allerdings ersatzlos aus. Dies ist beispielsweise der Fall, wenn die Probe eine besonders niedrige oder hohe Temperatur besitzt, topografische Eigenschaften ein sicheres Ankoppeln der Kontaktprüfköpfe erschweren, Diffusionsvorgänge oder Löslichkeiten zu beachten sind, in Vakuum zu arbeiten ist oder erhöhte Reinheitsanforderungen vorliegen. Gegenstand der vorliegenden Arbeit ist eine Technik welche hilft, diese Einschränkungen zu umgehen. Mit dem Aufkommen der ersten Laserquellen entstanden die wissenschaftlichen Grundlagen zur kontaktlosen Anregung und Detektion von Ultraschall. Die rasante Entwicklung kommerziell verfügbarer Lasersysteme der vergangenen Dekade wurde zum Anlass genommen zu untersuchen, in wie weit sich die einst wissenschaftlich orientierte Laboraufbauten zu einem anwendungsnahen Messsystem zusammenführen lassen. Basis der Arbeiten ist die thermoelastische Anregung von Ultraschall in Kombination mit einer ebenfalls kontaktlosen Detektion. Damit entsteht eine geschlossene Messkette welche erstmals die Eigenschaften zerstörungsfrei, kontaktlos und anwendungsorientiert in einem Ultraschallmesssystem vereint. Ausgangspunkt stellt die thermische Simulation der Anregung dar. Mit Hilfe präzisierter Gleichungen wird eine lokale Erwärmung von lediglich 100 K vorausgesagt. Für die zur Auslegung eines akustischen Messsystems notwendige Schallfeldsimulation wurde eine weitere Problematik identifiziert. Während bekannte Rechenansätze stets analytisch beschreibbare Strahlprofile des Lasers voraussetzen, zeigen reale Laserquellen kompliziert gestaltete räumliche Intensitätsverteilungen. Auf Basis einer vorangestellten CEFIT-Simulation ist mit der entwickelten CPSS-Methode eine zeitdiskrete Berechnung der 3D-Wellenausbreitung beliebiger Quellgeometrien möglich. Vergleiche mit realen Messdaten bestätigen die Simulationsrechnungen. Anhand ausgewählter Messszenarien wird die Praxistauglichkeit der kontaktlosen Arbeitsweise demonstriert. Neben der Charakterisierung einer offenporigen keramischen Beschichtung erlauben Transmissionsmessungen die Berechnung der longitudinalen und transversalen Schallgeschwindigkeiten. Ebenso ist die Abbildung wie auch die Beurteilung der Tiefenlage von Referenzfehlern mit lediglich 0,7 mm Durchmesser möglich. In Reflexionsmessungen wurde eine Auflösungsgrenze von mindestens KSR = 1 mm in 4,5 mm Tiefe nachgewiesen. Weitere Beispiele zeigen die Sensitivität hinsichtlich oberflächennaher Fehler, die Auswertung der anspruchsvollen „Zero Group Velocity“ S1-Mode der Lambwelle wie auch die Nutzung eingebetteter Quellen
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Almansour, Amjad Saleh Ali. "USE OF SINGLE TOW CERAMIC MATRIX MINICOMPOSITES TO DETERMINE FUNDAMENTAL ROOM AND ELEVATED TEMPERATURE PROPERTIES." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron148640184494135.
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Oliver, Serna Clara. "Vibroacoustic analysis of car door and window seals." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEC023.
Full textAbstract:
Les joints de porte et de vitrage des voitures jouent un rôle très important dans la réduction du bruit d’origine aérodynamique, à la fois par transmission directe et de par son rôle en tant que condition limite ees autres éléments transmetteurs (portes et fenêtres). Par conséquent, sa conception est fondamentale pour l’optimisation du confort de passager. Néanmoins, la méthode traditionnelle pour sa conception, basée sur une approche par tâtonnement de tests en soufflerie, est très coûteuse et insuffisante. Une approche différente est envisagée dans ce manuscrit, par la création d’un modèle capable de prédire la transmission du bruit jusqu’`a la cavité du véhicule, qui puisse être appliqué ultérieurement dans une routine d’optimisation. La modélisation des joints de vitrage et des fenêtres fait face à plusieurs difficultés. La fermeture de la porte subie par le joint de porte avant d’être soumis à l’excitation acoustique, ainsi que le comportement hyperélastique du caoutchouc, mènent à des déformations non-linéaires. Ce comportement change les propriétés (telles que la rigidité) du joint comprimé lors qu’il est soumis à l’excitation acoustique. De plus, l’interaction du son transmis par les joints avec la cavité du véhicule doit être prise en compte. Néanmoins, la taille réduite et la géométrie complexe du joint appellent à une approche telle que la méthode EF, tandis que la grande taille de la cavité véhicule nécessite d’une approche plus grossière, pour ne pas aboutir sur un modèle trop lourd. La solution proposée dans ce manuscrit implique la création d’un modèle hybride capable de modéliser le joint et la cavité séparément, avec l’approche la plus adaptée `a chaque cas, et de les coupler dans un seul modèle. Les comportements hyperélastique et viscoélastique des joints, avant et durant l’excitation acoustique, sont modélisés à l’aide du code commercial ABAQUS, tandis qu’une méthode énergétique appelée Méthode Energétique Simplifiée est utilisée pour la propagation ´ du son depuis les joints jusqu’au reste de la cavité. Cette méthode, adaptée aux besoins de l’application souhaitée, et couplée aux résultats du modèle EF, permet l’obtention rapide et locale du niveau de pression acoustique en n’importe quel point de la cavité. Finalement, des campagnes expérimentales sont mises en œuvre pour la validation des modèles. Les mises en place et les résultats sont détaillés dans ce manuscritCar door and window seals have been proven to be of utmost importance to reduce aerodynamic noise, both through direct transmission and through their role as boundary conditions of the other transmitting elements (car doors and windows). As consequence, their design has become of great relevance when it comes to passenger comfort optimization. However, the traditional method for their conception, based on a trial and error approach through wind-tunnel testing, has been found to be insufficient and costly. A different approach is contemplated in this dissertation, through the development of a model capable of predicting sound transmission through seals and into the vehicle cavity, for its subsequent application into an optimization procedure. Several difficulties arise from the modeling of car door and window seals. Indeed, the door closure imposed on the door seal before any acoustic excitation, as well as the hyperelasticity of the rubber lead to a non-linear deformation behavior. This behavior changes the seal properties (e.g. stiffness) which have to be modeled under acoustic excitation. Additionally, the interaction of the transmitted sound with the vehicle cavity must be taken into account. However, the small, precise geometry of the seal would call for an approach such as FE method, whereas the big dimensions of a vehicle cavity demand a much coarser approach so that the problem doesn’t become unmanageable in size. The solution that is proposed in this dissertation, implies the creation of an hybrid model capable of modeling the seal and the vehicle cavity separately, with the most adequate approach to each case, and coupling them afterward into a single model. As consequence, the hyperelastic and viscoelastic behaviors of the seals, prior to and during the acoustic excitation, are modeled through FE software ABAQUS, whereas an energy method called Méthode Energétique Simplifiée is used for the propagation ´ of the sound from the seal to the rest of the cavity. This method, improved to better suit the requirements of the discussed application, and coupled to the results of the FE model, allows a fast and local computation of the sound pressure level at any point inside the cavity. Finally, some experimental tests are put in place for the validation of the models. The different setups and results are detailed in this dissertation
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Austin, Travis R. "Laminated PAINT." VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5462.
Full textAbstract:
Though we may not perceive it, we are surrounded by material-in-flux. Inert materials degrade and the events that comprise our natural and social environments causally thread into a duration that unifies us in our incomprehension. Sounds reveal ever-present vibrations of the landscape: expressions of the flexuous ground on which we stand.
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Yang, Erh-Hsien, and 楊二憲. "The sound isolation and experimental error study of acoustical materials." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/32232109719443448682.
Full textAbstract:
碩士國立臺灣海洋大學
系統工程暨造船學系
98
This thesis is to design a low-frequency sound-insulation mechanisms, and for noise and vibration measurement and analysis. We used finite element method with ANSYS software to simulate acoustic materials vibration. In this thesis, we used sound intensity probe measure the sound transmission with different measurement methods. Transmission loss values were obtained and compared analysis of potential errors. The experimental proper way and the accuracy of experimental values are assured. We also used different spring coefficients with the same impulse force to calculate modes, and displacement, and radiation of sound pressure. In simulation results, we found that the proper structure (stiffness) damping can enhance transmission values of low frequency.
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Khan, Amir, Mostafa H. A. Mohamed, Halo N. Al, and Hadj Benkreira. "Acoustical properties of novel sound absorbers made from recycled granulates." 2017. http://hdl.handle.net/10454/12167.
Full textAbstract:
YesThis study investigates the acoustic performance of materials made using various amounts of bio-binder (cis-1,4-polyisoprene). The filler used in making these materials was from recycled tyres which consist of nylon 6,6 fibres bonded to rubber grains known as tyre shred residue (TSR). The materials have shown high acoustical performance especially at low binder levels, due mainly to the open porosity of the tested samples. The paper begins with a discussion of materials made using recycled granulates. The macroscopic properties (e.g. flow resistivity, porosity, tortuosity, etc.) that control the acoustical behaviour of these materials are then defined as are methods for their measurements. The acoustical characterisation of porous media is considered next, followed by discussion of the acoustic performance of the materials. The characteristics of these novel materials are illustrated through experimental and theoretical models involving sound absorption and transmission.
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(7500887), Yutong Xue. "MODELING AND DESIGN METHODOLOGIES FOR SOUND ABSORBING POROUS MATERIALS WHEN USED AS LAYERED VIBRATION DAMPERS." Thesis, 2019.
Find full textAbstract:
Modeling methodologies based on state-of-the-art and classic theories of acoustics have been developed to provide a comprehensive toolbox, which can be used to model multilayer systems that involve acoustical and/or damping treatments, and to optimize these treatments' performance by designing their geometrical structures. The objective of this work was to understand, predict and optimize conventional sound absorbing porous media's near-field damping performance, so that automotive and aerospace industries can take full advantage of layered porous treatments' lightness and multi-functionality: i.e., absorption of airborne sound and reduction of structure-borne vibration, for noise control applications. First, acoustical models that include the Transfer Matrix Method and the Arbitrary Coefficient Method were developed to build connections between the bulk properties and acoustical properties of porous media when coupled into layered systems. Given a specified layered system consisting of a vibrating panel and a porous damping treatment, the acoustics models were then incorporated into the Near-field Damping model to predict the acoustical near-field and spatial response of the panel, based on which the near-field damping performance can be evaluated for a limp or an elastic porous layer when applied on different structures including an infinitely-extended panel, a partially-constrained panel, an aircraft fuselage-like structure and a vehicle floor pan-like structure. Furthermore, the relations between the material's microstructural details and bulk properties were established via an Air-Flow Resistivity model for porous media that are made of fibers, and the optimal fiber size that provides the largest damping for certain vibrating structures was identified. Relatively large fibers were found to be better at reducing lower frequency vibrations; fibers made of polymer were found to have manufacturing benefits over fibers made of glass to achieve equivalent optimal damping performance; and elastic fibers were found to have both manufacturing and damping advantages over limp fibers.
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shie, howard, and 施世豪. "Effect of Sound Absorbing Materials on Acoustic Field." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/43141910078228207495.
Full textAbstract:
碩士逢甲大學
機械工程學所
91
Abstract The purpose of this paper is to investigate the measuring method of the impedance characteristics of the sound absorbing materials and also the effect of sound materials in the acoustic field. Instead of the previous Transfer function method, in this research the Two-cavity method has been applied to measure the characteristic impedance and the propagation constant of the sound absorbing materials. Besides, in order to prove that the result from the experiment is correct and confident, the experimental results have been compared with the results from the theoretical method and the analytical solutions. With the database of the impedance characteristics of the sound absorbing materials and a boundary element model, the designer can make the acoustic field analysis through simulation according to the real case condition. Besides, through tests of various sound absorbing materials from the database, the better sound absorbing materials can be chosen to improve the manufacturing process or product quality. In this research a computer simulation program has been used to find the effect in acoustic field through a real test using various sheet metal parts in a car. The result from the computer simulation is that in the low frequency range (128-600Hz), different sheet parts with different sound absorbing materials at the same frequency achieve different sound absorbing effect. Therefore a better sound absorbing effect can be obtained through the use of different sound absorbing materials. Another result from the computer simulation through total noise measurement is that the sound absorbing effect of the sound absorbing material on the car firewall is the best one, following the ones on front seats, on rear seats and on car roof. The sound absorbing material on the car floor has almost no sound absorbing effect.
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Lee, Po-Lin, and 李柏霖. "Investigation of Sound Absorbing Materials and Complex Acoustic Properties." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/n66axz.
Full textAbstract:
碩士逢甲大學
機械工程學所
91
Abstract This thesis is based on cylindrical sound field to analyze the sound filed effect of absorbing material, while the calculation procedure is proposed in the form of quantitative analysis. The acoustic impedance data of absorbing material are obtained from practical measurements, transformed into functions of frequencies by polynomial regression. Meanwhile, the eigenvalues of sound filed characteristic equation are obtained using Newton’s method. The analysis of acoustic energy loss is focused on the interactive relationship between the thickness of absorbing material and the geometry of sound field. Simulation results both show that natural frequencies of sound field and wave number are complex form. The thickness of absorbing material affects the shift of natural frequencies significantly. The absorptivity of absorbing material will be reduced when the sound filed geometry is expended. Moreover, the imaginary parts of the complex natural frequency and complex wave number are important factors to evaluate acoustic energy loss. Reverberation time can be calculated by the imaginary part of the complex natural frequency. At the same time, the transmission loss of sound filed is computed by the imaginary part of complex wave number with transfer matrix method. The effectiveness of the calculation procedure proposed in this thesis is verified by using the INAP software.
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(6622235), Hyunjun Shin. "Weight Minimization of Sound Packages by Balancing Absorption and Transmission Performance." Thesis, 2019.
Find full textAbstract:
Generally, heavier noise control treatments are favored over lighter ones since heavier acoustical materials tend to insulate (block) noise sources more effectively than do lighter materials. In automotive applications, however, heavier materials cannot always be adopted because of concerns over the total weight of the vehicle. Thus, it would be useful to identify lightweight acoustical treatments that can mitigate vehicle interior noise. Automotive sound packages have both absorption and barrier characteristics, and there is inevitably a trade-off between these two. Therefore, it is important to study the exchange between the absorption and transmission of acoustical materials particularly as it pertains to weight. Here, a procedure based on plane wave analysis is described that can be used to identify weight reduction opportunities by adjusting the acoustical properties of a generic sound package, consisting of a fibrous layer and a flexible microperforated panel surface treatment, so that it meets a target sound pressure level in a downstream interior space. It has been found, for the configuration studied here, that there are lightweight sound package configurations that can maintain acoustical performance equivalent to that of heavier noise treatments, and further, it has been found that the lightest treatments tend to favor barrier performance rather than absorption. Further, the impact of acoustical leaks has been considered, and it has been found that even very small leaks can result in a very substantial weight penalty if a specified level of acoustical performance is to be ensured. Further, the impact of changing the underlying panel mass and altering the frequency weighting used in the optimization process has also been considered.
The optimizer used in the proposed procedure requires considerable calculation time; hence, the acoustic pressure calculation time needs to be minimized to enhance the efficiency of the solution process. Thus, the transfer matrix method (TMM) for a two-dimensional case was used to calculate the interior acoustic pressure for a simple geometry as a starting point in the process of identifying the minimum-weight sound packages. The TMM is a widely used analytical approach to predicting the sound pressure (and particle velocity) for a system that can be represented as a series of subsystems. Although the TMM can offer fast and simple calculations for the acoustic system, its application is limited to a plane-wave-based model. Thus, the TMM is not the best option for the acoustic pressure prediction in a complex geometry such as a vehicle interior, that involves non-planar wave propagation. Therefore, a hybrid TMM-FEA method is proposed in this research to evaluate the acoustical performance of the sound package in more complex geometries (here, a vehicle-like cavity). So, in this research, the TMM was introduced to obtain the initial solutions that can be used in conjunction with the FEA tool to calculate the sound pressure field in the complex geometry case. The correlation between the results of these two approaches was then analyzed to develop a space-averaged pressure prediction model for various absorptive cases in the interior space. Finally, this SAP prediction model was used to generate an acoustic map that can be used to graphically estimate the SAPs in the complex geometry case.
In order to validate the usage of the developed equation for different sets of boundary conditions, several case studies were performed to study the effects of the surface impedance arrangements, geometrical shapes, and, lastly, the presence of extra features in the interior space. Finally, the SAP difference between the area near the driver’s right ear and the total interior cavity was studied to show that the SAP of the total cavity can be adjusted to evaluate the acoustic performance of the sound packages along the lines of conventional industry practice.
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Huang, An-Jiun, and 黃安均. "Research of Acoustical Characteristics of Sound-Absorbing Material Covering Fiber Fabric." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/53abse.
Full textAbstract:
碩士國立臺灣海洋大學
系統工程暨造船學系
102
Today, under this living environment of concentrated community society, it is important to prevent people from interference of noise. Prevention of noise can be achieved normally by reducing sound level of noise source and cutting off the transmission path. In order to reduce the noise, acoustic absorption material can absorbs and decays sound wave propagation energy. Fiberglass cotton is the most common acoustic material, which has characteristics of incombustible, incorruptible, and non-erodible. However, it has defects of fragile fiber, dust appearance, and indecomposable. Therefore, we usually use fiber fabric to cover this acoustic cotton which could prevent environment pollution. This also has utility to control reverberation time and speech intelligibility clarity etc. This study focuses on investigating the analysis of acoustic characteristics of acoustic material covered by fiber fabric. We combine different physical properties fiber cotton and different density of fiberglass cotton to do the comparison in sound absorption coefficient, then analyze and compare the relation of characteristics. The sound absorption experiment included impedance tube method and reverberation room method. While other physical properties test included light transmission rate, pore rate, water absorption rate, and water absorption speed etc. The results indicate that fiber fabric has notable effect on sound absorbance.
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Chung, Wen, and 鍾文. "The Automatic Measurement Analysis for Sound Insulation of Acoustic Materials." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/49460939870975383497.
Full textAbstract:
碩士國立臺灣海洋大學
系統工程暨造船學系
100
This thesis is to design an automatic sound insulation measurement system, and compare with artificial intensity set. The design of automatic sound insulation measurement system is use the step motor to drive and PLC(Programmable Logic Controller)for programming and control. Compare with two ways of experiment in same number of measure points and same material, to find out what was the cause of the errors and improve it to achieve completely automatic control.
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Lin, Guan-Yen, and 林冠言. "Study on Insulation Characteristics of Acoustic Materials in Scale Model Sound Field." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/268pa6.
Full textAbstract:
碩士國立臺灣海洋大學
系統工程暨造船學系
107
This study will use the scale model and the sound insulation performance analysis as the starting point, and find out the experimental method of sound insulation energy measurement using the scale model. The beginning of the research will introduce how the scale model is made, and the theory of the scale model for frequency. The basic definition of sound insulation performance and the calculation of the reverberation time in space will also be introduced in the text, and explore the similarity between using the simulation software calculation and the measurement results the scale model. The experiment on the sound insulation performance of the scale model will be divided into two steps. The first step will analyze the sound field characteristics of the scale model. Firstly,we use the CNS15160 and related specifications to evaluate the sound field characteristics of the scale reverberation chamber, and then test the radiation direction performance of the scale speaker. After confirming the correctness of the sound field and the instrument of the scale model, the second step is to study the effect of the sound insulation material barrier property on the scale model, and explore the sound insulation performance of the scale model for various soundproof materials.We find problems of the soundproofing model for the scale model and propose corresponding solutions. The sound insulation performance measurement experiment through the scale model can indeed have a certain degree of similarity with the prototype model sound insulation performance. Keywords: scale model, sound field characteristics, directivity test, sound insulation performance.
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Cops, Mark. "Engineered metallic foam for controlling sound and vibration." Thesis, 2020. https://hdl.handle.net/2144/41014.
Full textAbstract:
Many structural acoustic and vibration designs rely extensively on materials that are light-weight, stiff, and highly damped. Advanced materials such as metallic foams can be engineered to achieve these properties in order to control sound and vibration for a variety of aerospace, maritime, and ground transportation applications.
In this work, the structural and acoustic properties of commercially available and digitally designed metallic foams are analyzed through numerical and experimental methods. Furthermore as a post-manufacturing process, metallic foams can be engineered in order to preferentially alter the microstructure and achieve material property enhancements. In this work, the following engineering methods are proposed and investigated: plastic deformation and material saturation.
When a metallic foam is plastically deformed, the foam's porosity and pore shape are dramatically altered. This transformation in microstructure can lead directly to changes in bulk properties. In this work, a method for triaxial hydrostatic compression of metallic foams is proposed and demonstrated experimentally. The structural properties of transformed foams are tested using a load cell with digital image correlation. Transformed foams exhibit higher compliance, higher toughness, and a reduced Poisson ratio. Measurement and analysis of acoustic properties indicate that the transformed foams can absorb significantly more sound than the conventional samples of equal thickness in the test range of 0.25 - 4.50 kHz.
Due to their open-cell microstructure, metallic foams can be filled with saturating materials. In this work, metallic foams saturated with viscous liquids are investigated for reducing vibration transmissibility in a structure. For the best performing saturated foam subject to a transient excitation, an order of magnitude increase in damping ratio is measured. Additionally, a composite foam (consisting of metallic foam saturated with polyurethane foam) is fabricated to enhance acoustic properties. For the best performing composite foam at normal incidence, the sound absorption coefficient is improved by a factor of 6 near 0.60 kHz and by a factor of 2 up to 4.5 kHz.
Lastly, two methods for estimating acoustic absorption in metallic foams are presented which utilize finite element analysis and boundary layer theory. The proposed methods are discussed for commercially available foams as well as for representative digital designs. Limitations and assumptions of the methods pertaining to size scales and boundary layer features are addressed.
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Lee, Fan-Ching, and 李芳慶. "The study of porous plates / acoustic absorbent materials with roughness surface in sound absorption." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/92657382288180268707.
Full textAbstract:
碩士國立清華大學
動力機械學系
84
The objective of this work is to study the influence of porous plates / acoustic absorbent materials with various shapes of roughness surface on the sound absorption using finite element method and two-microphone impedance tube experiment. Four roughness surface shapes of acoustic absorbent materials, say, triangle, semi-circle, convex rectangle and plate shape, are chosen. Different porous plates are also placed in front of the above acoustic absorbent materials to study the effect of acoustic absorption in each assembly. It is found that the variation of roughness surface shapes has more influence on the acoustic absorption coefficients at higher frequency. However, as the porous plates are placed in front of the acoustic absorbent materials, the influence of roughness surface shapes on the acoustic absorption coefficient is less than the amoumt of acoustic absorbent materials contained. The properties of porous plates, such as porosity, thickness, shapes of holes and the location of back air gap, also affect the acoustic absorption coefficients distinctly. Finally, the noise reduction coefficient is adopted to simply indicate the acoustic absorbent ability of the entire structure , and would be of help for the design of acoustic absorbent structure.
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Chen, Yu-Wen, and 陳鈺文. "Research on Applying Composition of Acoustic Flooring Materials to Improve Floor Impact Sound Insulation Performance." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/3aefn4.
Full textAbstract:
碩士國立臺灣海洋大學
系統工程暨造船學系
105
The noise can be found everywhere, and the modern people pay more and more attention to noise problem. With the development of high-rise buildings, the impact sound of the floor has become one of the important topics of noise. The domestic building technical rules also incorporate technical specifications and are about to be implemented. There are two common methods to improve the impact sound of the floor. One is to install raised floor, the other is to lay surface decoration material on the floor. It is intended to use the small test specimen to conduct experiment and study floor impact sound insulation performance for different test group, with different acoustic flooring materials and resilient materials to form varies combinations. We use the CNS 15160-7 S3407-7 as the experimental specification of the spindle. Different from other domestic research for the small test specimens, the study use small test specimens with an area of 1.44m^2 and refer ASTM E1007-04 for the location of the impact source. We confirmed that the experimental results are equal. It simplify the experimental procedure again and enhance the efficiency of the study. A series of studies have been made on the improvement of the impact of the floor and the selection of the composition of acoustic flooring materials. The results of the experimental group are summarized according to the standards set forth in the building technical rules. This research can be used as a practical reference for the development of the floor impact sound insulation performance.
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Hsu, Yung-Chang, and 許永昌. "The Acoustic Field Research and Application of Porous Sound Absorbing Materials on Decreasing Automobile Noise." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/72562269015649965545.
Full textAbstract:
碩士國立交通大學
精密與自動化工程學程碩士班
92
N.V.H. shows the evaluated index of vehicle dynamics The improvement and design of N.V.H. is a theme, which the manufactures in Taiwan focus on. Especially the engine noise, drivers are always bothered by it. However, the characters of engine were set up already at design stage. Since there are many parts will be interfered, it’s hard to alter and needs high cost for the manufacturers who are licensees of the relationship of technical cooperation. For this reason, the following work of sound insulation and absorption becomes an important and necessary subject. This is the first time to apply the porous absorbing material to insulate the engine noise. We find the most economical and effective way to solve the engine noise is assembly the insulation that is made up of porous sound absorbing material, rubber and PU to the Dash Board. The aim of this research is base on acoustics theory and finds the new application of the porous sound absorbing material through the measurement and the analysis of its characters. In measurement aspect, the data will be gained through Two-microphone and Two-cavity method. In this study, we figure out the characters of porous sound absorbing material; meanwhile, it provides a way to solve the disturbing noise which automobile industry is always eager to overcome.
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Horoshenkov, Kirill V., David C. Hughes, and A. Cwizen. "The sound speed and attenuation in loose and consolidated granular formulations of high alumina cements." 2003. http://hdl.handle.net/10454/3691.
Full textAbstract:
NoClinkers of high alumina cements are separated into three granular formulations with particle sizes in the range 0.6-0.71 mm, 0.71-1.18 mm and greater than 1.18 mm. These are used to manufacture consolidated samples of porous concrete in an autoclave. The acoustic and microscopic properties of loose and consolidated porous samples of concrete are investigated using both experimental methods and mathematical modelling. Values of porosity, flow resistivity, tortuosity and parameters of the pore size distribution are determined and used to predict closely the sound speed, acoustic attenuation and normal incidence absorption coefficient of these materials. It is shown that high alumina cements do not require additional binders for consolidation and that the structural bonds in these cements are developed quickly between individual clinkers in the presence of water. The hydration product build-up during the consolidation process is insignificant which ensures good acoustic performance of the consolidated samples resulting from a sufficient proportion of the open pores. The value of porosity in the consolidated samples was found to be around 40%, which is close to that measured in some commercial acoustic absorbers. This work provides a foundation for the development of acoustically efficient and structurally robust materials, which can be integrated in environmentally sustainable concrete and masonry structures.
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Chen, Cheng Mine, and 陳承明. "The Study of the Acoustic Energy Loss in a Rectangular Duct Lined with Sound Absorption Materials." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/60450614197075364966.
Full textAbstract:
碩士國立臺灣大學
造船工程學系
86
In this paper, the acoustic energy loss in a rectangular duct lined with sound absorption material is studied. First of all, a simplified model is derived by way of using a semi-infinite duct to simulate a generally used duct. When making both of the modal attenuation and calculation of total energy loss in the simulated semi-infinite duct in progress, might we be able to estimate the energy loss of sound propagation in an actual rectangular ventilating and air-conditioning ducts. Similarly, using computer Therefore, the following two parts of study are included in this paper: (1) the study on the acoustic characteristics of absorption material involved, its acoustic performance when lined in duct, the modal attenuation and total transmission loss in a rectangular lining duct. The result of the above study demonstrates that the acoustic energy loss as described is got greater when increasing the diameter and the thickness of lining fiberglass but reducing its bulk density and the width of lined duct. (2) The The result of this study clearly shows the fact that the calculated transmission loss of a semi-infinite lining duct is almost coincident with the measured insertion loss for the actual lined duct in experiment. The maximum discrepancy of the measured transmission loss at the outlet of a duct of two-wall lining from that of its simulated lined duct of semi-infinite length is not greater than 3 dB, and otherwise the same thing can provide further reference to both of the academic study and professional application.
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Na, Seong-Won. "On a class of two-dimensional inverse problems: wavefield-based shape detection and localization and material profile reconstruction." Thesis, 2006. http://hdl.handle.net/2152/2583.
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Abreu, Marcos Paulo Gomes de. "A influência das características do material de enchimento da caixa-de-ar no desempenho acústico de painéis perfurados." Master's thesis, 2017. http://hdl.handle.net/10316/82914.
Full textAbstract:
Dissertação de Mestrado Integrado em Engenharia Civil apresentada à Faculdade de Ciências e TecnologiaO recurso a painéis perfurados em madeira como solução de revestimento constitui uma estratégia frequente quando se procuram soluções de condicionamento acústico de salas com forte impacto visual. Estas soluções apresentam características que determinam o seu desempenho acústico, em termos de absorção sonora, tais como a sua perfuração ou as condições de montagem, ou ainda as dimensões e o material que preenche (total ou parcialmente) a caixa-de-ar formada entre o painel e parede de suporte.No âmbito desta dissertação, caracterizou-se um conjunto de materiais fono-absorventes utilizados no tardoz de painéis perfurados em madeira e analisou-se a sua influência nos níveis de absorção sonora conferidos por estas soluções acústicas. Levou-se a cabo a realização de uma campanha experimental em amostras de dimensões reduzidas, recorrendo a um tubo de impedância. A fim de se estudar o material fono-absorvente, procedeu-se a implementação de duas metodologias para estimação da resistividade ao fluxo desses materiais: uma experimental, desenvolvida por Dragonetti et al (2011); outra analítica, que consiste na implementação do método inverso baseado no modelo teórico de Delany e Bazley modificado por Miki (1990).Adicionalmente, efetuou-se uma comparação de resultados experimentais com resultados de um modelo analítico, de modo a tentar aferir a sensibilidade do modelo em relação aos parâmetros que usualmente caracterizam os materiais absorventes.O comportamento relativo de sistemas de absorção sonora adotados em condicionamento acústico foi coerente, quer por via experimental, quer por via teórica, concluindo-se acerca da influência das diversas variáveis presentes e ainda acerca da fiabilidade das metodologias propostas. É notório que, recorrendo-se a métodos relativamente económicos e expeditos, de simples conceção e aplicação, se consegue obter resultados satisfatórios.
The use of wood perforated panels as lining solution is a frequent strategy when one is looking for an acoustic treatment of closed spaces with strong visual impact. These solutions reveal characteristics that determine their acoustic performance in terms of sound absorption, such as their perforation or mounting condition, or even their dimensions and filling material that may occupy totally or partially the existing air cavity between the panel and the rigid backing.In this work, it was characterized a group of absorbent materials used on the backing of wood perforated panels and analyzed its influence on sound absorption levels. It was carried on the execution of an experimental campaign in small sized samples, using an impedance tube. To study the absorbent material, were implemented two methodologies to estimate the airflow resistivity of these materials: an experimental one, developed by Dragonetti et al (2011), and a theoretical one, which consists in the implementation of an inverse method based on Delany and Bazley model modified by Miki (1990).Additionally, it was made a comparison between experimental and theoretical results, so one can assess the model’s sensibility to parameters that usually characterize absorbent materials.The relative behavior of sound absorption systems adopted in conditioning acoustic treatment was coherent, either experimentally or theoretically, concluding about the influence of various parameters considered in this work and about the reliability of proposed methodologies. It’s notorious that, using economic methodologies of simple design and application, one can obtain satisfactory results.
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Windisch, Thomas. "Laser-akustische Messtechnik in der Materialcharakterisierung: Numerische Schallfeldberechnung und praxisgerechte Auslegung für die kontaktlose Volumenprüfung." Doctoral thesis, 2015. https://tud.qucosa.de/id/qucosa%3A29775.
Full textAbstract:
Testing equipment based on the propagation of elastic waves are commonly used for measuring specific material properties. As a prerequisite for accurate measurements a reliable acoustic coupling of probe and specimen is highly important. Therefore, high-resolution testing equipment is using fluids as couplant. In certain conditions, only non-contacting methods can be considered. This is the case for example, if particular high or low temperatures are present, if topographic features impede the use of ultrasonic probes, diffusion or solubility processes exist, measurements at vacuum are addressed and if high purity requirements need to be fulfilled. Hence, subject of this work is a method which offers to handle these constraints.
With the emergence of modern laser systems the scientific basics for a non-contacting, laser-acoustic excitation of ultrasound were discovered. The tremendous development of commercially available laser systems during the last decade was taken as reason to investigate, to which extent former scientifically designed laboratory setups can now be merged into one single application oriented measuring system. All considerations are based on the thermoelastic excitation of ultrasound in combination with a likewise laser-based detection. By this, a self-contained measuring chain is built which combines the attributes non-destructive, non-contacting and application oriented within one ultrasonic measurement system for the first time.
Thermal calculations lead to more precise equations which predict a laser-induced, local temperature rise of about 100 K. The examination of sound field simulations, as a prerequisite for the design of ultrasonic systems, identified an additional complex of problems. Although existing calculation approaches presuppose laser intensity profiles what can be described in analytical terms, real-world laser sources exhibit a complex shaped spatial distribution of laser energy. Based on a preceding CEFIT simulation, the developed CPSS method enables the calculation of the time resolved, 3D wave propagation of arbitrary shaped sources. A comparison to measured data successfully validated the results of simulation.
By presenting selected scenario of measurements, the practical suitability of this non-contacting method is demonstrated. Using a transmission setup enables the characterization of open-pore ceramic coatings as well as the deduction of longitudinal and transversal speeds of sound. Equally, the imaging and estimation of the depth position of artificial defects with 0.7 mm in diameter is shown. Measurements based on a reflection setup provided evidence of a resolution limit of at least FBH = 1 mm in 4.5 mm depth. Additional examples demonstrate the ability to detect close-surface defects, the analysis of the challenging lamb waves zero-group-velocity S1 mode as well as the utilization of buried laser-acoustic sources.Prüfsysteme, welche die Ausbreitungseigenschaften elastischer Wellen zur Ableitung spezifischer Messgrößen nutzen, sind etablierte Messverfahren. Voraussetzung für zuverlässige Ergebnisse ist stets die sichere akustische Kopplung zwischen Sensor und Material. Daher arbeiten hochauflösende Prüfsysteme mit Fluiden als Koppelmedium. Unter bestimmten Bedingungen scheiden kontaktierende Ultraschallsysteme allerdings ersatzlos aus. Dies ist beispielsweise der Fall, wenn die Probe eine besonders niedrige oder hohe Temperatur besitzt, topografische Eigenschaften ein sicheres Ankoppeln der Kontaktprüfköpfe erschweren, Diffusionsvorgänge oder Löslichkeiten zu beachten sind, in Vakuum zu arbeiten ist oder erhöhte Reinheitsanforderungen vorliegen. Gegenstand der vorliegenden Arbeit ist eine Technik welche hilft, diese Einschränkungen zu umgehen. Mit dem Aufkommen der ersten Laserquellen entstanden die wissenschaftlichen Grundlagen zur kontaktlosen Anregung und Detektion von Ultraschall. Die rasante Entwicklung kommerziell verfügbarer Lasersysteme der vergangenen Dekade wurde zum Anlass genommen zu untersuchen, in wie weit sich die einst wissenschaftlich orientierte Laboraufbauten zu einem anwendungsnahen Messsystem zusammenführen lassen. Basis der Arbeiten ist die thermoelastische Anregung von Ultraschall in Kombination mit einer ebenfalls kontaktlosen Detektion. Damit entsteht eine geschlossene Messkette welche erstmals die Eigenschaften zerstörungsfrei, kontaktlos und anwendungsorientiert in einem Ultraschallmesssystem vereint. Ausgangspunkt stellt die thermische Simulation der Anregung dar. Mit Hilfe präzisierter Gleichungen wird eine lokale Erwärmung von lediglich 100 K vorausgesagt. Für die zur Auslegung eines akustischen Messsystems notwendige Schallfeldsimulation wurde eine weitere Problematik identifiziert. Während bekannte Rechenansätze stets analytisch beschreibbare Strahlprofile des Lasers voraussetzen, zeigen reale Laserquellen kompliziert gestaltete räumliche Intensitätsverteilungen. Auf Basis einer vorangestellten CEFIT-Simulation ist mit der entwickelten CPSS-Methode eine zeitdiskrete Berechnung der 3D-Wellenausbreitung beliebiger Quellgeometrien möglich. Vergleiche mit realen Messdaten bestätigen die Simulationsrechnungen. Anhand ausgewählter Messszenarien wird die Praxistauglichkeit der kontaktlosen Arbeitsweise demonstriert. Neben der Charakterisierung einer offenporigen keramischen Beschichtung erlauben Transmissionsmessungen die Berechnung der longitudinalen und transversalen Schallgeschwindigkeiten. Ebenso ist die Abbildung wie auch die Beurteilung der Tiefenlage von Referenzfehlern mit lediglich 0,7 mm Durchmesser möglich. In Reflexionsmessungen wurde eine Auflösungsgrenze von mindestens KSR = 1 mm in 4,5 mm Tiefe nachgewiesen. Weitere Beispiele zeigen die Sensitivität hinsichtlich oberflächennaher Fehler, die Auswertung der anspruchsvollen „Zero Group Velocity“ S1-Mode der Lambwelle wie auch die Nutzung eingebetteter Quellen.