Dissertations / Theses on the topic 'Acoustic absorber'
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Parkinson, Jerome P. "Acoustic absorber design." Thesis, University of Canterbury. Mechanical Engineering, 1999. http://hdl.handle.net/10092/6414.
Full textOnen, Onursal. "Development Of An Effective Single Layer Micro-perforated Sound Absorber." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/3/12610064/index.pdf.
Full textEstève, Simon J. "Control of sound transmission into payload fairings using distributed vibration absorbers and Helmholtz resonators." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/11183.
Full textPh. D.
Halama, Jakub. "Metodika pro bezkontaktní diagnostiku automobilových tlumičů." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-377521.
Full textIurasov, Volodymyr. "Contrôle passif en vibroacoustique avec absorbeur dynamique bistable." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0034.
Full textThe work presented in this thesis is dedicated to the study of a continuous bistable absorber based on the principle of Nonlinear Energy Sink (NES) and its use for the vibration mitigation of a many-degree-offreedom mechanical systems under acoustic excitation. The analytical model of the linear behavior of the absorber and its complete numerical model were presented, analyzed and validated by series of experiments. The complexity of the Targeted Energy Transfer (TET) between the absorber and the primary system did not allow a simple analytical description. We have chosen to concentrate this study on the experimental and numerical exploration of the absorber coupled to mechanical systems under harmonic and random excitations, as well as on the identification of the mechanisms of energy transfer. The coupled system have shown very rich dynamics as it possessed different regimes of TET, which were earlier described in literature for other types of NES. This project was funded by Saint-Gobain. The absorber was adapted for the application foreseen by the industrial supervisors of the PhD: the vibration control of partitioning double walls under acoustic excitation so that to improve the acoustic isolation provided by the system. The qualitative knowledge on the absorber dynamics obtained from the experimental and numerical results, as well as the analogy with the other types of NES, permitted the creation of an absorber which corresponds to the problematic. The ways for the further optimization and development of the absorber were identified and preliminary simulations were provided
Proctor, Martin J. "Ultrasound power measurement : a microprocessor based device utilising thermal expansion of a total absorber." Thesis, University of Aberdeen, 1987. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU009820.
Full textLeng, Julien. "Controlling flexural waves using subwavelength perfect absorbers : application to Acoustic Black Holes." Thesis, Le Mans, 2019. http://www.theses.fr/2019LEMA1027/document.
Full textThe vibration control adapted to light structures is a scientific and technological challenge due toincreasingly stringent economic and ecological standards. Meanwhile, recent studies in audible acoustics havefocused on broadband wave absorption at low frequencies by means of subwavelength perfect absorbers. Suchmetamaterials can totally absorb the energy of an incident wave. The generalisation of this method for applicationsin elastodynamics could be of great interest for the vibration control of light structures.This thesis aims at adapting the perfect absorption problem for flexural waves in 1D and 2D systems with localresonators using the critical coupling condition. A study of 1D systems with simple geometries is first proposed. Thisprovides methods to design simple resonators for an effective absorption of flexural waves. The 1D systems thenbecome more complex by studying the critical coupling of 1D Acoustic Black Holes (ABH). The ABH effect is theninterpreted using the concept of critical coupling, and key features for future optimisation procedures of ABHs arepresented. The critical coupling condition is then extended to 2D systems. The perfect absorption by the firstaxisymmetric mode of a circular resonator inserted in a thin plate is analysed. Multiple scattering by an array ofcircular resonators inserted in an infinite or semi-infinite 2D thin plate, called metaplate, is also considered to getclose to practical applications. Through this thesis, analytical models, numerical simulations and experiments areshown to validate the physical behaviour of the systems presented
Nash, Grant. "Utilizing Distributed Vibration Absorbers to Reduce Noise Transmission Through the Windshield of a Cessna 150." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/34508.
Full textReducing interior aircraft noise levels is a complicated joint effort, combining propeller radiation control; fuselage wall reduction methods; exhaust emission regulation, management of air turbulence; some propeller, wake-induced vibration control; and a little engine vibration restraint. For minimum propeller acoustic propagation, it is important to control propeller radiation by using techniques such as increasing the number of blades, altering blade airfoil (especially using a felix or grooved design); applying small angle of attack; utilizing swept blades; decreasing blade diameter; lowering tip speed; and reducing the load on a propeller (i.e. by controlling the blade thickness, tip volume, and blade shape). Controlling the vibration in the fuselage skin can also help to reduce interior noise. Some early attempts were made using ribs/stiffeners, tuned dampers, and a limp mass double wall. More recently, dynamic vibration absorbers have been utilized, quite successfully, to reduce fuselage skin vibration and thus, interior noise levels. Attempting to control the exhaust emission and induced vibration from air turbulence has contributed to lower airplane cabin noise levels as well. For large aircrafts, the strategic location of luggage compartments and bathrooms help in keeping the interior quiet. Most importantly for small single-engine aircraft, the windshield has been found to contribute heavily to aircraft interior noise levels.
Currently, the use of active control methods (especially the active structural acoustic control methods) and the utilization of dynamic vibration absorbers (a form of passive noise control) are the most popular techniques to reduce interior aircraft noise levels. In small general aviation aircraft, the blade passage frequency (bpf) and the first few harmonics have been found to be the largest contributor to noise transmitting into the fuselage. This project analyzes a two degree-of-freedom (DOF) dynamic vibration absorber in hopes of reducing windshield vibration of a Cessna 150 fuselage at the fundamental blade passage frequency of approximately 87 Hz and thus, reducing noise transmitting into the interior of the aircraft.
This research project is unique in several ways. First, numerous passive noise control techniques have been utilized to control vibration and acoustics on an aircraft, but none have used the two degree of freedom Distributed Vibration Absorbers (DVA) employed in this project, as a noise reduction method on the windshield of an aircraft. Secondly, little research has been done on analyzing noise transmission into small, single engine general aviation aircraft, which is conducted in the work here. Third, little work has been done on analyzing and reducing noise propagation through the windshield of a small engine aircraft, which is also analyzed in this project. Finally, the modal analysis conducted on the windshield of the small engine plane is one of the few modal decompositions that has been conducted on a small general aircraft windshield.
Master of Science
Bryk, Pierre-Yvon. "Pompage énergétique en acoustique par absorbeur dynamique non-linéaire hybride passif-actif." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0114.
Full textThis thesis is devoted to the study of a hybrid passive-active nonlinear dynamic absorber for the reduction of noise in low frequencies. The passive part of the ADNLH is a membrane in latex with a nonlinear deformation and its front face coupled to the acoustic field to be reduced. This membrane is acting as a nonlinear oscillator and is part of the family of absorbers known as Nonlinear Sink Energy (NES). The rear face is enclosed and a active device is included inside this enclosure. This device is designed in order to modify the linear stiffness and the damping of the membrane. Previous work has been done only on the passive part (the membrane) and has validated the principle of energy pumping for Acoustics. However the membrane has some limitations (like the threshold of energy pumping) that restrain the practical applications. The goal of the ADNLH is to improve the performance of the energy pumping by modifying the linear properties of the membrane with the help of the active device. In a first time an experimental and theoretical study of the ADNLH is done. Then the ADNLH is coupled to a tube of air thanks to an academic assembly under a sinusoidal excitation or broadband. It allows to cut the top off the first acoustic resonance of the tube with better performances than the membrane alone. At last the ADNLH is set inside a weakly damped room. The ADNLH allows to attenuate the first resonance of the room in the case of a sinusoidal excitation. One also shows that the control of the damping of the membrane is the key parameter for the performance of the ADNLH
Hua, Xin. "ADVANCED STUDIES ON TRANSFER IMPEDANCE WITH APPLICATION TO AFTER-TREATMENT DEVICES AND MICRO-PERFORATED PANEL ABSORBERS." UKnowledge, 2013. http://uknowledge.uky.edu/me_etds/30.
Full textBellet, Romain. "Vers une nouvelle technique de contrôle passif du bruit : absorbeur dynamique non linéaire et pompage énergétique." Phd thesis, Université de Provence - Aix-Marseille I, 2010. http://tel.archives-ouvertes.fr/tel-00544719.
Full textHaufe, Daniel. "Untersuchung optischer Verfahren zur gleichzeitigen Messung von Strömungs- und Schallfeldern an aeroakustischen Schalldämpfern." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-197742.
Full textCebrecos, Ruiz Alejandro. "Transmission, reflection and absorption in Sonic and Phononic Crystals." Doctoral thesis, Universitat Politècnica de València, 2015. http://hdl.handle.net/10251/56463.
Full text[ES] Los cristales fonónicos son materiales artificiales formados por una disposición periódica de inclusiones en un medio, pudiendo ambos ser de carácter sólido o fluido. Controlando la geometría y el contraste de impedancias entre los materiales constituyentes se pueden controlar las propiedades dispersivas de las ondas. Cuando una onda propagante se encuentra un medio con diferentes propiedades físicas puede ser transmitida y reflejada, en medios sin pérdidas, pero también absorbida, si la disipación es tenida en cuenta. La presente tesis está dedicada al estudio de diferentes efectos presentes en cristales sónicos y fonónicos relacionados con la transmisión, reflexión y absorción de ondas, así como el desarrollo de una técnica para la caracterización de sus propiedades dispersivas, descritas por la estructura de bandas. En primer lugar, se estudia el control de la propagación de ondas en transmisión en sistemas conservativos. Específicamente, nuestro interés se centra en mostrar cómo los cristales sónicos son capaces de modificar la dispersión espacial de las ondas propagantes, dando lugar al control del ensanchamiento de haces de sonido. Haciendo uso de las curvas de dispersión espacial extraídas del análisis de la estructura de bandas, se predice primero la difracción nula y negativa de ondas a frecuencias cercanas al borde de la banda, resultando en la colimación y focalización de haces acústicos en el interior y detrás de un cristal sónico 3D, y posteriormente se demuestra mediante medidas experimentales. La eficiencia de focalización de un cristal sónico 3D está limitada debido a las múltiples reflexiones existentes en el interior del cristal. Para superar esta limitación se consideran estructuras axisimétricas trabajando en el régimen de longitud de onda larga, como lentes de gradiente de índice. En este régimen, las reflexiones internas se reducen fuertemente y, en configuración axisimétrica, la adaptación de simetría con fuentes acústicas radiando haces de sonido incrementa la eficiencia drásticamente. Además, la teoría de homogenización puede ser empleada para modelar la estructura como un medio efectivo con propiedades físicas efectivas, permitiendo el estudio del frente de ondas en términos refractivos. Se mostrará el modelado, diseño y caracterización de un dispositivo de focalización eficiente basado en los conceptos anteriores. Considérese ahora una estructura periódica en la que uno de los parámetros de la red, sea el paso de red o el factor de llenado, cambia gradualmente a lo largo de la dirección de propagación. Los cristales chirp representan este concepto y son empleados aquí para demostrar un mecanismo novedoso de incremento de la intensidad de la onda sonora basado en un fenómeno conocido como reflexión "suave". Este incremento está relacionado con una ralentización progresiva de la onda conforme se propaga a través del material, asociado con la velocidad de grupo de la relación de dispersión local en los planos del cristal. Un modelo basado en la teoría de modos acoplados es propuesto para predecir e interpretar este efecto. Se observan dos fenómenos diferentes al considerar pérdidas en estructuras periódicas. Por un lado, si se considera la propagación de ondas sonoras en un array periódico de capas absorbentes, cuyo frente de ondas es paralelo a los planos del cristal, se produce una reducción anómala en la absorción combinada con un incremento simultáneo de la reflexión y transmisión a las frecuencias de Bragg, de forma contraria a la habitual reducción de la transmisión, característica de sistemas periódicos conservativos a estas frecuencias. En el caso de la misma estructura laminada en la que se cubre uno de sus lados mediante un reflector rígido, la incidencia de ondas sonoras desde un medio homogéneo, cuyo frente de ondas es perpendicular a los planos del cristal, produce un gran incremento de la fuerza de
[CAT] Els cristalls fonònics són materials artificials formats per una disposició d'inclusions en un medi, ambdós poden ser sòlids o fluids. Controlant la geometría i el contrast d'impedàncies dels seus materials constituents, és poden controlar les propietats dispersives de les ondes, permetent una gran varietatde fenòmens fonamentals interessants en el context de la propagació d'ones. Quan una ona propagant troba un medi amb pèrdues amb propietats físiques diferents es pot transmetre i reflectir, però també absorbida si la dissipació es té en compte. Aquests fenòmens fonamentals s'han explicat clàssicament en el context de medis homogenis, però també ha sigut un tema de creixent interés en el context d'estructures periòdiques en els últims anys. Aquesta tesi doctoral tracta de l'estudi de diferents efectes en cristalls fonònics i sònics lligats a la transmissió, reflexió i absorció d'ones, així com del desenvolupament d'una tècnica de caracterització de les propietats dispersives, descrites mitjançant la estructura de bandes. En primer lloc, s'estudia el control de la propagació ondulatori en transmissió en sistemes conservatius. Més específicament, el nostre interés és mostrar com els cristalls sonors poden modificar la dispersió espacial d'ones propagants donant lloc al control de l'amplària per difracció dels feixos sonors. Mitjançant les corbes dispersió espacial obtingudes de l'anàlisi de l'estructura de bandes, es prediu, en primer lloc, la difracció d'ones zero i negativa a freqüències próximes al final de banda. El resultat és la collimació i focalització de feixos sonors dins i darrere de cristalls de so. Després es mostra amb mesures experimentals. L'eficiència de focalització d'un cristall de so 3D està limitada per la gran dispersió d'ones dins del cristall, que és característic del règim difractiu. Per a superar aquesta limitació, estructures axisimètriques que treballen en el règim de llargues longituds d'ona, i es comporten com a lents de gradient d'índex. En aquest règim, la dispersió es redueix enormement i, en una configuració axisimètrica, a causa de l'acoblament de la simetría amb les fonts acústiques que radien feixos sonors, l'eficiència de radiació s'incrementa significativament. D'altra banda, la teoria d'homogeneïtzació es pot utilitzar per a modelar, dissenyar i caracteritzar un dispositiu eficient de focalització basat en aquests conceptes. Considerem ara una estructura periòdica en la qual un dels seus paràmetres de xarxa, com ara la constant de xarxa o el factor d'ompliment canvia gradualment al llarg de la direcció de propagació. Els cristalls chirped representen aquest concepte i s'utilitzen ací per a demostrar un mecanisme nou d'intensificació d'ones sonores basat en el fenòmen conegut com a reflexió "suau". La intensificació està relacionada amb la alentiment progressiva de l'ona conforme propaga al llarg del material, que està associada amb la velocitat de grup de la relació de dispersió local en els diferents plànols del cristall. Es proposa un model basat en la teoria de modes acoblats per a predir i interpretar este efecte. Dos fenòmens diferents cal destacar quan es tracta d'estructures periòdiques amb dissipació. Per un costat, al considerar la propagació d'ones sonores en el plànol en un array periòdic de capes absorbents, s'observa una disminució anòmala de l'absorció i es combina amb un augment simultani de reflexió i transmissió en les freqüències de Bragg que contrasta amb la usual disminució de transmissió, característica dels sistemes conservatius a eixes freqüències. Per a un medi similar de capes, amb un reflector rígid darrere, les ones fora del pla incidint l'estructura des de un medi homogeni, augmentaran considerablement la interacció. En altres paraules, el retràs temporal de les ones sonores dins del sistema periòdic augmentarà significativament produint un augmen
Cebrecos Ruiz, A. (2015). Transmission, reflection and absorption in Sonic and Phononic Crystals [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/56463
TESIS
Premiado
Thieury, Margaux. "Développement de métamatériaux super-absorbants pour l’acoustique sous-marine." Thesis, Université Paris sciences et lettres, 2020. http://www.theses.fr/2020UPSLS004.
Full textThe constant evolution of sonar performance requires new designs of absorbent coatings for underwater acoustics. Such coatings are used to improve stealth of submarines but can also improve the efficiency of on-board detection systems. Bubble meta-screens (reminiscent of the so-called Alberich coatings) are a possible solution to tackle this issue. A bubble meta-screen consists of a periodic distribution of sub-wavelength air cavities trapped in a visco-elastic matrix. The cavities acoustically behave as bubbles and exhibit a low frequency resonance, known as the Minnaert resonance. Under certain conditions, the meta-screen can achieve a total absorption when placed in front of a perfect reflector. This doctoral work allowed us to build a phenomenological model, validated by numerical simulations and experiments, which can predict the reflection and transmission coefficients of the meta screen as a function of its geometric and rheological characteristics. Our model takes into account the influence of the temperature and static pressure on the performance of a meta-screen, as well as the role played by the shape of the cavities
Segura, Alcaraz María del Pilar. "Empleo de textiles en aplicaciones de absorción sonora." Doctoral thesis, Universitat Politècnica de València, 2021. http://hdl.handle.net/10251/159786.
Full text[CAT] Aquesta memòria de tesi presenta una contribució a l'estudi dels materials tèxtils en el camp de l'absorció sonora. En concret, s'hi ha treballat amb l'associació d'una capa absorbent fibrosa constituïda per un no teixit de polièster i una capa resistiva a base de teixit de calada de composició polièster. L'objectiu d'aquest treball consisteix a avaluar les variacions que provoquen els canvis en diferents paràmetres de construcció de la capa resistiva, sobre el comportament del conjunt davant el so. Per a abordar el problema s'empren diferents teixits de calada, com ara teles simples, múltiples, encoixinats i ris, amb diferents paràmetres de construcció. Es mesura el coeficient d'absorció en aplicarles a diferents grossàries de no teixit de polièster, emprant el tub d'ones estacionàries. S'observen diferències en els coeficients d'absorció de so obtinguts, les quals s'expliquen atenent la grossària del no teixit, però també a les característiques constructives dels teixits emprats. Finalment, s'empra el disseny d'experiments per a obtenir la combinació òptima de paràmetres que proporciona el major coeficient d'absorció de so per a un tipus de teixit donat en totes les freqüències estudiades. Es conclou que la modificació en l'absorció de so d'un no teixit en aplicar una capa resistiva de teixit de calada és prou significativa per a ser tinguda en compte a l'hora de dissenyar productes tèxtils per a condicionament acústic i que el disseny d'experiments constitueix una eina de gran utilitat a aquest efecte.
[EN] This thesis report presents a contribution to the study of textile materials in the field of sound absorption. Specifically, we have worked with the association of a fibrous absorbent layer consisting of a polyester nonwoven and a resistive layer based on openwork fabric. The objective of this work is to evaluate the variations that cause the changes in different construction parameters of the resistive layer, on the behaviour of the whole before the sound. To address the problem, different openwork fabrics are used, such as single, multiple, quilted and curl fabrics, with different construction parameters. The absorption coefficient is measured when applied to different thicknesses of polyester nonwoven, using the standing wave tube. Differences are observed in the sound absorption coefficients obtained, which are explained according to the thickness of the nonwoven, but also to the constructive characteristics of the fabrics used. Finally, the design of experiments is used to obtain the optimal combination of parameters that provides the highest sound absorption coefficient for a given type of tissue at all frequencies studied. It is concluded that the modification in the sound absorption of a nonwoven when applying a resistive layer of openwork fabric is significant enough to be taken into account when designing textual products for acoustic conditioning and that the design of experiments constitutes a very useful tool for this purpose.
Al departamento de Ingeniería Textil y Papelera y a la unidad docente de Alcoy del departamento de Mecánica de los Medios Continuos y Teoría de Estructuras, por facilitarme los medios necesarios para realizar todas las actividades que han sido necesarias. A Jaime Ramis Soriano, por recibirme en el laboratorio de Grupo de Acústica Aplicada del IUFACyT de la Universidad de Alicante.
Segura Alcaraz, MDP. (2020). Empleo de textiles en aplicaciones de absorción sonora [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/159786
TESIS
Ouedraogo, Boureima. "Modélisation du rayonnement acoustique dans les guides traités par des matériaux absorbants à réaction localisée ou non localisée en présence d'écoulement par la méthode des éléments finis." Phd thesis, Université de Bourgogne, 2011. http://tel.archives-ouvertes.fr/tel-00674031.
Full textAyub, Md. "Experimental and numerical investigation of a carbon nanotube acoustic absorber." Thesis, 2016. http://hdl.handle.net/2440/112038.
Full textThesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2016.
FRASER, ROBERT. "REDUCING THE EFFECTS OF MRI ACOUSTIC NOISE USING MICRO-PERFORATED PANELS." Thesis, 2012. http://hdl.handle.net/1974/7520.
Full textThesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2012-09-25 16:54:41.118
Chang, Hsiu-Yuan, and 張修源. "Study in situ measurement of N-type Sound Absorber acoustic characteristic Using oblique incidence technique." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/z3aes2.
Full text國立臺灣海洋大學
系統工程暨造船學系
105
The purpose of this thesis is to determine the acoustic characteristic of the N-type absorber in situ, by applying the EU standards EN 1793-5 and using oblique incidence to realize its possibility and the properties of aforementioned absorber. In this paper, different in situ methods have been compared, and the EU standards EN 1793-5 was selected. The experiments have been conducted with both new and old version of EN 1793-5 standards, and found the new version of EN 1793-5 standard was more suitable for oblique incidence technique in situ owing to its different measuring process and different formula for computing reflection index. As the absorbers are non-flat, which makes it difficult to measure their acoustic characteristic, but the results have indicated its possibility by applying the EU standards EN 1793-5 and using oblique incidence technique in situ. Also the reversed N-shaped absorber’s properties surpass the W-shaped absorber owing to the form of absorber.
Lee, Fan-Ching, and 李芳慶. "On the acoustic absorption of multi-layer absorbers." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/87828828905110686928.
Full text國立清華大學
動力機械工程學系
89
Owing to the rapid industrial development and the rising of environmental consciousness in Taiwan, the researches on noise control become more important. Perforated plates and porous materials (such as glass fiber materials and foams) are usually applied as the acoustic absorbing materials for noise control. However, since single kind of acoustic absorbing material has better acoustic absorption only at certain frequency bands, the multi-layer absorbers composed of perforated plates, porous materials and airspaces are usually applied to absorb broadband noise. The acoustic absorption of these multi-layer absorbers is very dependent on the shape and arrangement of their components. The main objective of this work is thus to respectively discuss the influence of the shape and arrangement of those components on the acoustic absorption of the multi-layer absorbers thoroughly. In this work, the multi-layer transmission analysis, which can be used to successfully analyze the acoustic absorption of the multi-layer absorbers composed of arbitrary number of compartments, is first derived. Each compartment is composed of one layer of perforated plates and multi-layer porous materials and/or airspaces. Such a multi-layer transmission analysis can also compensate the drawback of the equivalent electrical circuit approach in analyzing multi-layer absorbers, which cannot deal with multi-layer porous materials and airspaces between two adjacent perforated plates. Due to the geometric constraint of components, the application of analytical approach is limited. Hence, a rigorous finite element analysis model which can accurately tackle the acoustic effects of perforated plates, porous materials and airspaces with arbitrary shapes is also developed in this work. Four types of basic inner structure compartments adopted in the multi-layer absorbers are selected to study the influence of the inner structures on the acoustic absorption of the multi-layer absorbers. These compartments are composed of porous materials inlaid with perforated plates of various shapes, say, triangle, semicircle, convex rectangle and plate shapes. As is different from the conventional finite element analysis for acoustics, the perforated plates are simulated by appropriate equivalent boundary conditions, depending on their thickness, hole radius, hole pitch and porosity and the air contained in the holes. A large number of total degrees of freedoms generated from meshing the air in the holes of perforated plates are thus avoided. Based on the results obtained, the multi-layer absorber composed of a novel inner structure and proper perforated plates and porous materials is designed and manufactured successfully. Both the finite element and experimental results show that its acoustic absorption is distinctly higher than the conventional acoustic absorbers. Finally, some acoustic applications are also discussed in this work, such as the insertion loss of multi-layer acoustic bafflers. It is found that the insertion loss of the acoustic baffler composed of perforated plates, porous materials and airspaces is higher than the acoustic baffler composed of concrete. In addition, the sound pressure distribution of this system also reveals that the sound diffraction has significant influence on the sound attenuation caused by the acoustic bafflers.
Wang, Jung Kuo, and 王俊國. "Vibro-acoustic Response Reduction of a Fluid-Loaded Beam Uing Unequally-spaced Absorbers." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/02000460713729581354.
Full textKhan, 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 textThis 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.
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 text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.
Li, Wei-Peng, and 黎瑋鵬. "Research of Acoustical Properties for the Suspended Sound Absorber Panel and the Seat Variation Used in Sound Field." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/c6tx9t.
Full text國立臺灣海洋大學
系統工程暨造船學系
102
In nowadays, a variety of different types of room space are more and more with our quality of life enhance, however, there are different room space requiring at different acoustic design. The initial research of this paper is used a room space that before and after acoustic improvement to measure it’s acoustical properties : Reverberation Time (RT), Clarity index (C50&;C80), Articulation Loss of Consonants(Alcons), Rapid Speech Transmission Index(RaSTI). The improvement using absorber material include the suspended sound absorber panel and others, then compare the simulated result using acoustical simulation software EASE with the measured result. In the second part, we used the Kath&;Kuhl method to measure the seat absorption coefficient with different cushion and the other absorber material, and find the suspended sound absorber panel which has the best absorption coefficient used in the room space. Finally, we took the different seat absorption coefficient used in the room space to simulate the acoustical properties, and discuss the accurate of the simulation. The results can be provided to the relate field.
Haufe, Daniel. "Untersuchung optischer Verfahren zur gleichzeitigen Messung von Strömungs- und Schallfeldern an aeroakustischen Schalldämpfern." Doctoral thesis, 2015. https://tud.qucosa.de/id/qucosa%3A29252.
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