Thesis (M.S.)--Brigham Young University. Dept. of Physics and Astronomy, 2006. / Includes bibliographical references (p. 93-95).

No

With the need for stealth in defense applications steadily increasing, noise reduction continues to play an important role in the world of aeronautics. With the ever increasing number of small UAV flight vehicle designs and their stringent weight requirements, acoustic solutions become progressively more complex. This thesis investigates the use of refractory foam, a new class of porous material, for designing effective silencers for small IC engines. The solution must be lightweight, compact, conformable, and capable of handling the rigors of flight. Throughout the course of this research, many silencer designs were fabricated to take advantage of refractory foam technology. These silencer designs were then tested against existing designs using both anechoic and outdoor testing techniques. These results proved refractory foam to be a superior broadband noise absorber that can survive harsh flight environment. Silencer designs using this material showed overall improvements in the areas of noise reduction, weight, size, and backpressure, compared to commercial designs. The final silencer design boasted an Aweighted overall sound pressure level that was 12.1 dBA lower than the reference case. This result was accomplished using nearly half the volume required by other designs to attain similar results. / Master of Science

Yes / This 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.

Abstract Noise has become an increasing public health problem and has become serious environment pollution in our daily life. This indicates that it is in time to control and reduce noise from traffic and installations in homes and houses. Today a plethora of products are available for business, but none for the private market. The project describes a start up of development of a sound absorbing wall panel for the private market. It will examine whether it is possible to make a wall panel that can lower the sound pressure level with 3 dB, or reach 0.3 s in reverberation time, in a normally furnished bedroom and still follow the demands of price and environmental awareness. To start the project a limitation was made to use the textiles available per meter within the range of IKEA. The test were made according to applicable standards and calculation of reverberation time and sound pressure level using Sabine’s formula and a formula for sound pressure equals sound effect. During the project, tests were made whether it was possible to achieve a sound classification C on a A-E grade scale according to ISO 11654, where A is the best, with only textiles or if a classic sound absorbing mineral wool had to be used. To reach a sound classification C, a weighted sound absorption coefficient (αw) of 0.6 as a minimum must be reached. The project resulted in that it is technical possible to achieve a sound classification C with only textiles even though for this project another combination was chosen for proceeding with the calculations, because of account to price and environmental awareness. The calculations showed that it is possible to lower the reverberation time to 0.3 s in a normally furnished bedroom with 7 wall panels, and to achieve a lowering of the sound pressure level with 3dB with 7 wall panels. This project showed promising results and leave openings for further research with only textiles and further calculations where more factors are taken under consideration to get more precise and reliable results. / Program: Textilingenjörsutbildningen

In this study, the basic absorption and scattering characteristics of acoustic scatterers, specifically Schroeder Diffusers, are investigated. Schroeder Diffusers are one of the most widely used acoustic scatterers in which the scattering phenomenon is predictable due to the geometry of the diffuser, based on a particular mathematical sequence. It is shown that it is possible to increase the amount of absorption by modifying the diffuser structure by means of adding perforated panels into the wells or narrowing diffuser wells. In room acoustics applications, diffusers are conventionally mounted to a wall or ceiling assumed to be rigid enough such that sound wave cannot penetrate through. This thesis proposes a new modification on these diffusers where the diffuser is not backed by a rigid surface / it is hung over a space instead. To construct such a configuration, diffuser wells are terminated with micro-perforated panels (MPP). Inclusion of MPP introduces additional losses / hence, higher absorption can be achieved. However, the most significant absorption in this configuration is achieved below the first resonance frequency of the panel-air space system due to the existence of non-rigid backing. This thesis aims to model the absorption and scattering mechanisms enabled with the non-rigid backing by improving a previously introduced mathematical model.

This study aims to present a sustainable alternative to noise attenuation in external or internal environments through the application of vegetated arrangements as sound absorbers. This proposal arises from the need to adapt the conventional sound absorption systems, and from the concern for environmental preservation. There was also concern about the decorative applicability of these systems, so its appearance should be aesthetically interesting. To compose the proposal, plant arrangements, containing the Buriti palm (Trithrinax brasiliensis Mart.), arranged in ornamental flowerpots build in MDF (Medium Density Fiberboard plank) and decorated with another plant, known as Barba-de-pau (Tillandsia usneoides) were analyzed. Measurements were performed to identify the sound absorption coefficient (α) of these arrangements, through experiments in reverberation chamber of the Acoustic Engineering Laboratory in the Federal University of Santa Maria, according to ISO 354/2003 standard using the interrupted noise method. From these tests, it was determined the reverberation time (RT) and subsequently the sound absorption coefficient α. The composition containing the two plants and the ornamental flowerpots presented the average sound absorption coefficient between 0,11 and 0,27 from 100 Hz to 5000 Hz range. Thus, it is recommended to use this alternative for noise attenuation in a given room, or using their application in series, containing combined vegetated arrangements. / Este estudo busca apresentar uma alternativa sustentável para atenuação de ruído em ambientes externos ou internos, através da aplicação de arranjos vegetados como absorvedores sonoros. Esta proposta surge da necessidade de adaptação dos sistemas convencionais de absorção sonora, bem como a partir da preocupação com a preservação ambiental. Há também a preocupação com a aplicabilidade decorativa destes sistemas, portanto, sua aparência deve ser esteticamente interessante. Para compor a proposta, houve a análise de arranjos de plantas contendo a palmeira Buriti (Trithrinax brasiliensis Mart.), montadas em cachepôs confeccionados em MDF (Painéis de fibra de média densidade) e decorados com outra planta, conhecida como Barba-de-pau (Tillandsia usneoides). Foram realizadas medições para identificar o coeficiente de absorção sonora α destes arranjos, através de ensaios desenvolvidos em câmara reverberante do Laboratório de Engenharia Acústica da Universidade Federal de Santa Maria, segundo a norma ISO 354/2003, empregando a metodologia de ruído interrompido. A composição contendo as duas plantas e o cachepôs em MDF apresentou o coeficiente de absorção sonora médio que variou entre 0,11 e 0,27 no intervalo de 100Hz até 5000Hz. Assim, recomenda-se a utilização desta alternativa para atenuação de ruído em um dado recinto, ou ainda utilizando sua aplicação em série, contendo vários arranjos vegetados combinados.

Elastomeric wastes plague our time, polluting our environment and requiring urgent upcycling solutions. This research contributes to this agenda using an important source of waste, car tyre shred fibre residue (TSFR). It is demonstrated how using binders, non-foaming (SBR) and foaming (PU), we can transform these TSFR into structured porous acoustic-thermal insulation materials, suitable as underlay, cavity wall and pipe insulation. These structures were fabricated in purpose designed moulds and characterised for their porosity, tortuosity, flow resistivity and density. Their acoustic absorption performance was measured using industrial standards and the measurement underpinned with the Johnson-Champoux-Allard (JCA) model. With the under-layer materials, thermal insulation was also measured. The results were as follows: (i) 40%/60% SBR/TSFR was an optimal composition for the underlay with the addition of 15% w/w bumper crumb of size > 1mm enhancing both impact sound and thermal insulation, (ii) PU was found to produce well performing wall cavity insulation, particularly when vacuum pressure was applied, allowing micro and macro pores to be formed; (iii) PU applied with controlled amount of water to control foaming CO2 formation produced super-performing (compared with Armacell System B) stratified pipe cladding insulation, optimal at porosity stratification of 90%, 83%, and 70%; (iv) Very good agreement was observed with predictions using JCA model, allowing further research to be carried out with these now well characterised sound insulations. In addition to the developing materials, a novel technique for measuring sound absorption of pipe cladding was developed that could replace the expensive standard using a reverberation chamber.

More than one billion vehicle tires reach the end of their useful service life annually. Less than a quarter of rubber waste is reused or recycled in some way. Interest has grown in working to discover means by which to incorporate rubber tire waste into construction materials. This study sought to delve into the use of micronized rubber powder (MRP) as an acoustic agent within particleboard and concrete. In addition, work was conducted to characterize the effect that MRP has on the strength and flexural properties of concrete. Furthermore, research sought to provide insight into how pine biomass, a forest products industry waste, would interact with MRP in concrete as it relates to strength and acoustic properties. As expected, particleboard that contained MRP resulted in lower strength but higher flexibility. Acoustic testing revealed that there was minimal sound absorption improvement at some frequencies and less absorption at low and high frequencies. Sound transmission loss was slightly improved by the addition of MRP to the particleboard. Adding pine biomass and MRP to concrete yielded much lower compressive strength as compared to plain concrete. Visual inspection of the sound absorption coefficient curves over the full range of test frequencies identified limited, if any, advantage for the addition of MRP or biomass. Some ranges of frequencies offered minimal improvement. There appeared to be no appreciable sound absorption advantage to adding MRP, pine biomass, or the combination of the two into concrete mix proportions. Modulus of rigidity was decreased as compared to plain concrete when MRP, pine biomass, or a combination of both were incorporated into the concrete mixture as volume replacement for aggregate. Visual observation revealed that flexural failure for the MRP or pine beams were less sudden and less catastrophic than the plain concrete samples. Modulus of elasticity was decreased as compared to plain concrete when MRP, pine biomass, or a combination of both were incorporated into the concrete mixture as volume replacement for aggregate. The more flexible and ductile concrete produced with MRP and biomass provides a combination of properties that serve to lessen the propagation of cracks throughout the specimen.

Pour des raisons liées au confort, les constructions modernes exigent des matériaux isolants acoustiques et thermiques, offrant de bonnes performances mécaniques. Dans ce cadre, la valorisation des fibres végétales issues de l’industrie agro-alimentaire, présente des avantages économiques et environnementaux. C’est ainsi que, la présente étude a pour objectif le développement d’un agro-composite multifonctionnel à base de fibres de canne à sucre, alliant de bonnes propriétés acoustiques et mécaniques.Les renforts étudiés présentent des distributions morphologiques (longueur et diamètre) pouvant être approchées par une loi log-normale. De plus, leur comportement hygroscopique révèle une forte capacité de reprise en eau (23%) en fonction de l’humidité relative et de la température, même si la masse volumique reste constante, malgré l’hétérogénéité des fibres.Les composites thermo-comprimés avec une matrice époxy, ont été caractérisés à l’aide d’un plan d’expériences ayant pour paramètres le diamètre des fibres (entre 0,5 et 4 mm) et leur taux massique (entre 40 et 70%). L’analyse de la microstructure révèle une isotropie dans le plan de fabrication et une anisotropie transverse. L’étude des propriétés acoustiques a montré que l’absorption sonore augmente avec le diamètre des fibres, tout en diminuant avec leur proportion massique, sur une gamme de fréquences comprises entre 500 et 1000 Hz. La caractérisation mécanique par des essais de flexion, a montré un comportement fragile, avec des écarts de raideur et d’effort maximal de l’ordre de 30%. En flexion, les matériaux dont le diamètre et le taux massique de fibres sont élevés ont les propriétés mécaniques optimales. De plus, l’analyse par stéréo-corrélation d’images a révélé un gradient de déformations non linéaire dans l’épaisseur de l’éprouvette, dû à l’hétérogénéité du matériau. Cette analyse a permis de montrer qu’une localisation des déformations normales conduit à la rupture de l’éprouvette. Par ailleurs, les essais de compression ont souligné l’anisotropie des matériaux et ont montré que les propriétés optimales sont obtenues pour des matériaux dont le taux massique de fibres se situe autour de 55% avec les fibres les plus fines. Enfin, un outil a été mis en place afin de trouver un compromis entre les propriétés mécaniques et acoustiques. / For reasons of comfort, modern constructions require acoustic and thermal insulating materials, offering good mechanical performances. In this context, the valorization of plant fibres from the agro-food industry presents economic and environmental benefits. Thus, the aim of the present study is to develop a multifunctional sugarcane fibres reinforced epoxy porous composite combining good acoustic and mechanical properties.The study of the bagasse fibres geometry has shown that fibres’ length and diameter distribution can be fitted by lognormal laws. Composites manufactured by thermocompression process with an epoxy matrix were characterized using an experimental design whose parameters were the diameter of the fibres (between 0.5 and 4 mm) and their mass ratio (between 40 and 70%). The study of acoustic properties showed that the sound absorption increases with the diameter of the fibres, while decreasing with their mass proportion, over a frequency range between 500 and 1000 Hz. Mechanical characterisation by bending tests, has showed a fragile behavior, with deviations of stiffness and maximum stress around 36%. The stereo-correlation image analysis confirmed the heterogeneity of the strain fields throughout the thickness, in relation to the fracture observation.