Dissertations / Theses: 'Mitigation acoustic noise reduction'

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Cameron, Derrick E. (Derrick Eugene). "Origin and reduction of acoustic noise in variable-reluctance motors." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/57729.

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1990. Includes bibliographical references (leaves 116-118). by Derrick E. Cameron. M.S.

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Slagle, Adam Christopher. "Low Frequency Noise Reduction Using Novel Poro-Elastic Acoustic Metamaterials." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/64200.

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Low frequency noise is a common problem in aircraft and launch vehicles. New technologies must be investigated to reduce this noise while contributing minimal weight to the structure. This thesis investigates passive and active control methods to improve low frequency sound absorption and transmission loss using acoustic metamaterials. The acoustic metamaterials investigated consist of poro-elastic acoustic heterogeneous (HG) metamaterials and microperforated (MPP) acoustic metamaterials. HG metamaterials consist of poro-elastic material with a periodic arrangement of embedded masses acting as an array of mass-spring- damper systems. MPP acoustic metamaterials consist of periodic layers of micro-porous panels embedded in poro-elastic material. This thesis examines analytically, experimentally, and numerically the behavior of acoustic metamaterials compared to a baseline poro-elastic sample. The development of numerical techniques using finite element analysis will aid in understanding the physics behind their functionality and will influence their design. Design studies are performed to understand the effects of varying the density, size, shape, and placement of the embedded masses as well as the location and distribution of microperforated panels in poro- elastic material. An active HG metamaterial is investigated, consisting of an array of active masses embedded within poro-elastic material. Successful tonal and broadband noise control is achieved using a feedforward, filtered-x LMS control algorithm to minimize the downstream sound pressure level. Low-frequency absorption and transmission loss is successfully increased in the critical frequency range below 500 Hz. Acoustic metamaterials are compact compared to conventional materials and find applications in controlling low-frequency sound radiation in aircraft and launch vehicles. Master of Science

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Blaschke, Peter Gerhard. "Vibro-acoustic design tool for noise optimization of rotating machines." Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/7355.

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GAGLIARDI, PAOLO. "A study of airport noise impact and strategies for its mitigation and exposure reduction." Doctoral thesis, Università di Siena, 2017. http://hdl.handle.net/11365/1013780.

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Aviation noise pollution in urban areas can be considered as a major problem and source of conflict between airport infrastructure and residents. Its effects could significantly limit the growth of aviation as well as affect public health, mainly when airports are located near residential areas. Noise control measures both at the source and at the receivers are often expensive and limited. Nevertheless, they represent the most viable solutions for contrasting this phenomenon due to the difficulty of finding suitable measures to reduce aircraft noise along its propagation path. This work is focused on the development, the assessment, and the management of mitigation actions regarding the noise action plan of Pisa’s “Galileo Galilei” International Airport. This airport has recently presented its noise action plan in order to give itself the possibility of expansion without incurring in air traffic limitations. The action plan includes both the construction of a runway link to increase the take-off run length and the introduction of a noise-abatement departure procedure. The effectiveness of these actions against noise pollution has been evaluated by means of noise numerical modelling. In particular, the noise impact produced by the airport and the related exposed population have been estimated by using the Integrated Noise Model (INM). New strategies to ensure an effective noise reduction as a response to the growing aircraft traffic have been proposed. Noise maps calculated for present and future scenarios, including those following the application of noise reduction measures, are shown. For many situations, people’s exposure and the percentages of highly annoyed and highly sleep-disturbed people have been determined also including military aircraft noise. Moreover, a novel methodology for managing airport noise in the closest urban areas based on the Automatic Dependent Surveillance-Broadcast (ADS-B) technology is presented. ADS-B helps to track the 3D-flight paths with high data resolution and then to verify both the effectiveness of the action plan and the compliance with its provisions. A penetration gate has been strategically set considering the departures towards the city. The vertical distribution of the traffic crossing the gate and the correlation between take-off conditions and noise-related events have been investigated in order to establish rules for penalties due to the lack of compliance with the action plan requirements. The relationships between the operational characteristics of flight departures and aircraft noise by means of a statistical approach have been identified. Principal Component Analysis and Multiple Linear Regression were performed in order to extrapolate a simplified predictive model at a specific point on the ground. The findings may be useful to point out the operational characteristics causing the noisiest aircraft flyovers. Consequently, scheduled flight departures could be re-organized by introducing departure-direction and departureprocedure restrictions in order to minimize noise impact on the urban areas. The results confirm that ADS-B system may be considered a smart tool providing cost-effective solutions for the airport noise management in urban areas and its sustainable development, particularly when the radar tracks are not available.

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Ray, William H. (William Hamilton). "The reduction of acoustic noise emissions from a hard disk drive." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/34324.

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Chiang, Wayne Hui-Chung. "Adaptive filters for acoustic echo cancellation and noise reduction in a car." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ62201.pdf.

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Kodrasi, Ina [Verfasser]. "Dereverberation and Noise Reduction Techniques based on Acoustic Multi-Channel Equalization / Ina Kodrasi." München : Verlag Dr. Hut, 2016. http://d-nb.info/1113336366/34.

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Grage, Danielle L. "Study of jet exhaust noise sources and their mitigation through lobed mixers and chevrons." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1307323368.

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Taracila, Victor. "HIGH-FIELD MRI ISSUES: FINITE WAVELENGTH EFFECTS, TRANSVERSE COIL DESIGN AND ACOUSTIC NOISE REDUCTION." online version, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1151698057.

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As'ad, Hala. "Acoustic Beamformers and Their Applications in Hearing Aids." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/41540.

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This work introduces new binaural beamforming algorithms for hearing aids, with a robustness to errors in the estimate of the target speaker direction of arrival (DOA) and a good trade-off between noise reduction and preservation of the noise/interferers spatial impression. Three robust designs are proposed, and their robustness is confirmed by simulation results. These robust designs are a combination of binaural and monaural beamformers using two different microphone configurations: one for low frequency components and one for high frequency components. The robust designs are also found to be robust to mismatch between the anechoic propagation models used for the beamformers designs and the reverberant propagation models used to generate the signals at the microphones in the simulations. To preserve the binaural cues of the noise/interferers in the binaural beamformer outputs, a method based on a mixing/selection of different available binaural signals is proposed, using a classification from the phase and magnitude of a complex coherence function. This method is added as a post processor to the beamforming designs robust to target DOA mismatch. Simulation results show that the resulting mixed binaural output signals have a good binaural cues preservation level that outperform the benchmark design, with significant noise reduction and low target distortion. Since knowledge of source DOAs is important for beamforming noise reduction, a beamformer-based broadband multi-source DOA detection system is also developed in the thesis, using information from different frequencies or sub‐bands to obtain global estimates of sources DOAs. Simulation results shows that using one beamformer on each side is capable of detecting the DOAs of active sources under several acoustic scenarios, including scenarios with one, two, or three sources, and with or without the presence of some level of diffuse noise.

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Zarpoush, Rahil, and Rahil Zarpoush. "Mitigating Noise Levels Within the Main Campus of University of Arizona by Integrating Biodegradable Polylactic Acid as an Acoustic Panel to Buildings." Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/625326.

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People's experience of space is quite different because we experience our environment with all senses available to us. Environmental pollutions can affect everybody's experiences of space. Noise is one of the environmental pollutions that long-term exposure to high noise levels can cause sleep disruption, reduction of performance, permanent hearing loss, and the inability to enjoy the space. This research presents an assessment of noise levels on the main campus of the University of Arizona, based on noise measurements and noise maps, and defines problems associated with the high noise levels in specific areas. Then, strategically develops an acoustic panel, by using an environmentally friendly material which is called Polylactic Acid. PLA is a kind of biopolymers and it is biodegradable material made from renewable raw materials like corn starch. In addition, the University of Arizona's campus is surrounded by four streets with intense vehicle traffic, which contribute to causing the noise level to exceed the legal limits established for some of the educational areas. There are many methods for mitigating noise in urban areas, including the formation of the city, the geometry of buildings, vegetation, and sidewalk design, building façade design and using acoustic materials. All these responses for noise mitigation should be considered as environmentally friendly design concepts. The manufacturing of many materials can cause severe environmental pollutions, but by using Polylactic acid material we will save our planet.

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Douville, Hugo. "An approach using active structural acoustic control for the reduction of structure-borne road noise." Mémoire, Université de Sherbrooke, 2004. http://savoirs.usherbrooke.ca/handle/11143/1223.

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The reduction of the structure-borne road noise inside the cabin of an automobile is investigated using an Active Structural Acoustic Control (ASAC) approach. First, a laboratory test bench consisting of a wheel/suspension/lower suspension A-arm assembly has been developed in order to identify the vibro-acoustic transmission paths (up to 250 Hz) for realistic road noise excitation of the wheel. Frequency Response Function (FRF) measurements between the excitation/control electrodynamic shakers and each suspension/chassis linkages are used to characterize the different transmission paths that transmit energy through the chassis of the car. Secondly, a FE/BE model (Finite/Boundary Elements) was developed to simulate the acoustic field of an automobile cabin interior. This model is used to predict the acoustic field inside the cabin as a response to the measured forces applied on the suspension/chassis linkages. Finally, an implemented optimal active control algorithm using a feedforward structure to perform the simulation of an optimal active structural acoustic control (ASAC) by using experimental and numerical FRFs is presented. The control approach relies on the use of an electrodynamic actuator to modify the vibration behavior of the suspension and the automotive chassis such that its noise radiation efficiency is decreased. To predict the noise level reduction inside the passenger compartment, the measured FRFs of a control actuator, connected to the lower suspension A-arm, have been implemented by using the optimal active control algorithm in MATLAB ª . Its contribution to noise reduction has been evaluated in term of acoustic radiation efficiency, as measured by the sound pressure level (SPL) located at the driver's head.

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Dangla, Vincent. "Robust design of acoustic treatment for nacelle noise reduction using computational aeroacoustics and uncertainty quantification." Thesis, Paris Est, 2020. http://www.theses.fr/2020PESC2024.

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Dans les moteurs d'avions modernes, le bruit de fan est une des principales sources de bruit du fait d'une augmentation constante du taux de dilution des moteurs visant à réduire leur consommation. Le bruit de fan étant caractérisé par des composantes tonales et multimodales, des traitements acoustiques appelés liners sont utilisés pour leur efficacité à réduire des composantes de bruit, par des effets de dissipation acoustique réglables en modifiant la géométrie du liner. Des modèles de prédictions numériques sont alors utilisés pour leur réglage. Le design du liner étant gelé dans des phases préliminaires du développement d'un avion, il existe une variabilité non négligeable sur son environnement de fonctionnement. Cette variabilité impacte directement le design du liner en induisant une large disparité des données utilisées pour son design. De plus, à mesure que la maturité de l'avion augmente, chaque mise-à-jour de ces données impose une réoptimisation du liner. Cette étape de réoptimisation induit alors d'importants coûts de calcul qui pourraient être évités en prenant en compte cette variabilité durant les phases préliminaires de design. Il s'agit de la principale problématique de ce travail. À mesure que cette variabilité externe impacte l'environnement d'opérabilité du liner, le modèle numérique de performance du liner devient alors incertain. Afin de quantifier et prendre en compte cette nature incertaine, une conception robuste du liner est alors entreprise, par quantifiant l'incertitude globale qui réside dans le modèle numérique de performance acoustique du liner. Le modèle aéroacoustique numérique utilisé est un code industriel, ACTRAN/TM, et nécessite d'être intensivement étudié afin d'en déduire les principaux composants les plus sensibles vis-à-vis de l'incertitude globale. Un modèle stochastique des incertitudes est alors introduit et greffé sur le modèle aéroacoustique. Il permet de simuler l'incertitude globale mentionnée précédemment, en prenant en compte l'incertitude qui réside dans le modèle numérique (erreurs de modèles et erreurs des paramètres du modèle), en utilisant les approches probabilistes paramétriques et non-paramétriques. Ensuite, la propagation des incertitudes dans le système est analysée en utilisant un solveur stochastique tel que la méthode de Monte Carlo. La réponse acoustique du système est alors aléatoire et la quantification des incertitudes consiste en une estimation de données statistiques telles que les intervalles de confiances associés à un certain niveau de confiance sur les quantités d'intérêts. À partir de cette information statistique, la robustesse d'un design spécifique de liner vis-à-vis d'une variabilité simulée sur son modèle de performance peut être définie, en plus de l'information classique de performance acoustique. Cette information permet alors de connaître la propension d'un design à maintenir sa performance nominale lorsque son environnement change dans un intervalle de variation préalablement défini par le niveau d'incertitudes imposé au modèle stochastique. Alors, le meilleur design peut être choisi en faisant un compromis entre performance et robustesse In modern turbofan engines, fan noise is one of the main noise sources due to the constant increasing of engines bypass ratio for fuel burn reduction purposes. As fan noise is characterized by broadband and tonal components, acoustic liners are introduced for their effectiveness in mitigating both components through dissipation effects that are tunable by modifying the liner geometry. Simulations issued from prediction numerical tools are thus extensively used for their tuning, since experiments cannot be considered for obvious costs reasons. As the design of liner systems is frozen in early stages of an aircraft development, it exists a non-negligible variability on its operating environment. This variability directly impacts the design of liners by inducing large discrepencies on the quantities used for its numerical design. Moreover, each time these quantities are updated due to the increased maturity of the aircraft program, lined surfaces are to be reoptimized. The updating phase thus represents important costs in terms of computational time, which could be avoided by accounting for such a variability in preliminary phases of the liner design. This is the main problematic of the present work. As this external variability directly impacts the liner environment, the computational modeling of the liner acoustic performance is uncertain. In order to quantify and account for such an uncertain nature, a robust design of the liner is carried out, by quantifying the overall uncertainty that lies within the liner design computational process. The state-of-the-art computational aeroacoustic model of nacelle liners performance is an industrial numerical code, Actran/TM, which therefore has to be extensively studied so as to exhibit the principle components that are subject to the overall uncertainty. A stochastic modeling of uncertainties is then introduced and grafted on the computational model. It allows for simulating the previously mentioned external variability, by accounting for the uncertainty that lies within the model (modeling errors and model parameters errors), through parametric and nonparametric probabilistic approaches of uncertainties. Then, the propagation of uncertainties in the system is analyzed using the computational model and the Monte Carlo stochastic solver. The acoustic response is then random and the quantification of uncertainties consists in estimating statistics, such as confidence regions associated with a certain confidence level of quantities of interest. From these statistical information, the robustness of a given liner design towards a simulated variability on its performance model can be defined, in addition to the state-of-the-art liner acoustic performance. This information then allows for knowing the propensity of a given liner design to maintain its nominal performance when its environment is changing in a predefined range of variation accounted for by the level of uncertainty imposed on the stochastic model. Then, making a compromise between performance and robustness, the best liner design can be chosen

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Tekgun, Didem. "Acoustic Noise and Vibration Reduction on Switched Reluctance Machines through Hole Placement in Stator/Rotor Laminations." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1491678743829375.

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Liang, Xiaobin. "Multi-physics modeling of a switched reluctance motor for the reduction of vibration and acoustic noise." Paris 6, 2013. http://www.theses.fr/2013PA066369.

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This thesis focuses on the construction of the multi-physical numerical models of switched reluctance motor (SRM) in order to predict the vibration and the noise caused by radial magnetic force. This modeling can be applied to reduce the vibration and the noise of SRM. The electromagnetic-vibration-acoustic performances of some SRM are analyzed through numerical modeling and experimental tests. This manuscript is divided in four chapters, and the main points of each chapter are as follows: The first part introduces the vibration and noise sources in SRM, the noise reduced methods, as well as the numerical models used in our study. The numerical models include electromagnetic model, mechanical model, and vibro-acoustic model. The principles and equations, used in multi-physic finite element modeling, are presented in details. The important physical parameters are introduced to describe the performance of SRM. In the second part, we introduce the numerical results of two SRMs: 6-slot/4-pole, and 12-slot/8-pole SRMs. The motors’ performances in different fields (electromagnetic, mechanical and vibro-acoustic) are presented in detail. The third part introduces the mutually coupled SRM (MCSRM). The multi-physic performances of this motor are obtained by our numerical models. It is found that the MCSRM can increase the output torque of motor, and moreover the vibration and noise can be reduced significantly. The comparative study between the classical SRM and mutually coupled SRM is presented. The 12-slot/8-pole SRM is used in experiments to verify the numerical results. At last, a fault model of 12-slot/8-pole SRM is proposed. This model is based on the combination of analytical and numerical simulation, and the short-circuit problem has been investigated. A fault detection method by measuring phase current, suitable for both classical SRM and MCSRM, is developed. A fault detection method by measuring the vibration is proposed for MCSRM Cette thèse porte sur la construction des modèles numériques multi-physiques de la machine à réluctance variable (MRV), afin de prédire les vibrations et le bruit causé par la force magnétique radial. Cette modélisation nous permet de réduire la vibration et le bruit de la MRV. Les performances multi-physiques (électromagnétiques-vibration-acoustiques) de certaines MRVs sont analysées par la modélisation numérique ainsi que par des tests expérimentaux. Ce manuscrit est divisé en quatre chapitres, et les points principaux de chaque chapitre se présentent comme suit : La première partie introduit les vibrations et les sources de bruit dans la MRV, les méthodes de réduction de bruits, ainsi que les modèles numériques utilisés dans notre étude. Les modèles numériques comprennent le modèle électromagnétique, le modèle mécanique et le modèle vibro-acoustique. Les principes et les équations, qui sont utilisées dans la modélisation, sont présentés en détail. Les paramètres physiques importants sont introduits pour décrire les performances multi-physiques de la MRV. Dans la deuxième partie, nous présentons les résultats numériques de deux MRVs : une MRV de 6-slot/4-pole et une MRV de 12-slot/8-pole. Les performances des moteurs dans différents domaines physiques (électromagnétiques, mécaniques et vibro-acoustique) sont présentées en détail. La troisième partie présente un moteur à réluctance variable non-conventionnelle (MRVNC). Les performances multi-physiques de ce moteur sont obtenues par nos modèles numériques. Il est constaté que la MRVNC peut augmenter le couple de sortie du moteur, et de plus, la vibration et le bruit de MRVNC peut être réduit de façon significative. L'étude comparative entre la MRV et la MRVNC est présenté. La MRV 12-slot/8-pole est utilisée dans des mesures expérimentales pour vérifier les résultats numériques. Enfin, un modèle de défaut de la MRV 12-slot/8-pole est proposé. Ce modèle est basé sur la combinaison de la simulation analytique et la simulation numérique. Le problème du court-circuit a été étudié. Une méthode de diagnostic par la mesure du courant, adaptée à la MRV et à la MRVNC, est développée. Une méthode de diagnostic par la mesure de la vibration est proposée pour la MRVNC

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Andersson, David. "Acoustic properties of a 5G Telecom Equipment Shroud Design for Noise suppression." Thesis, KTH, Marcus Wallenberg Laboratoriet MWL, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-302267.

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As technology moves forward it has a tendency to consume more and more power that needs to be cooled by bigger and louder fans, this is especially true for the new generation of 5G radio equipment. This Master thesis is a collaboration with Ericsson and attempts to construct a shroud for containing a number of 5G radio units whilst attenuating the fan noise of the units as effectively as possible. In this project are air ducts used and at the ends silencers are created utilizing the Cremer impedance; the optimal wall impedance for damping an acoustic mode of a propagating wave. To predict the result, a simplified model in an acoustic FEM program was also explored and compared to the sound level of the constructed shroud. The finished shroud successfully reduces the noise of the radio units by 13 dB(A) while causing an increase in temperature of between 2.8°C to 5.9°C. This result was deemed to be a success and the Cremer impedance approach of reducing noise is therefore advised for future development. Allt eftersom tekniken går framåt tenderar den att också förbruka mer och mer energi som i sin tur måste kylas av kraftigare och mer högljudda fläktar, detta fenomen är särskilt påtagligt när det kommer till den senaste generationens radioutrustning för 5G. Detta examensarbete är ett samarbete mellan KTH och Ericsson med avsikt att skapa en kåpa som är designad för att innesluta ett bestämt antal 5G radiomoduler. Denna kåpa ska i så stor utsträckning som möjligt dämpa det fläktinducerade bullret. I det här projektet nyttjas kanaler med ljuddämpare vid ändarna som dämpar ljudet med hjälp av Cremerimpedans, dvs: den väggimpedans som optimalt dämpar en akustisk mod. För att kunna förutspå resultatet skapades en förenklad akustisk modell i ett FEM program. Resultatet från denna modell jämförs sedan med ljudeffektnivån från slutmätningen av den färdiga kåpan. Resultatet från slutmätningen visar att kåpan lyckas sänka radioenheternas totala ljudeffektnivå med 13 dB(A) samtidigt som en temperaturökning på mellan 2.8°C och 5.9°C erhålls. Det här resultatet bedöms vara en framgång, vilket leder till slutsatsen att ljuddämpning med användning av Cremerimpedans rekommenderas för vidare arbete.

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Roth, Brian D. "Acoustic source and data acquisition system for a helicopter rotor blade-vortex interaction (BVI) noise reduction experiment." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA326229.

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Thesis (M.S. in Engineering Acoustics) Naval Postgraduate School, December 1996. "December 1996." Thesis advisor(s): Robert M. Keolian, Steven R. Baker. Includes bibliographical references (p. 59). Also available online.

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Ross, Bradley W. "Attenuation of Low Frequency Structurally Radiated Noise With an Array of Weak Radiating Cells." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36555.

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The concept of a weak sound radiating cell is proposed to reduce the low frequency radiated noise from structures. The cell consists of two coupled surfaces such that, when placed on a vibrating structure, the responses of the two surfaces are nearly out-of-phase and of equal strength over a wide frequency range. This structure response leads the cell to behave as an acoustic dipole and thus as a poor sound radiating source. The control of low frequency structurally radiated noise is then achieved by covering the structure with an array of these weak radiating cells, i.e. surface treatment. Thus, the surface treatment essentially transforms the response of the structure to that of a distributed array of dipoles yielding a low sound radiating structure. Theoretical models are developed to predict the performance of the cell. Experimental verification is performed for a single cell applied to a piston-like structure to demonstrate the concept on a simple radiating structure. The results demonstrated an overall sound power level reduction of 5.2 dB between 400-1600 Hz with maximum reductions over 30 dB at discrete frequencies. Finally, an array of weak radiating cells is experimentally applied to a more complex structure, a rectangular plate. The results of the plate experiments reveal an overall sound power level reduction of 10.2 dB between 100-1600 Hz with maximum reductions of 25 dB at discrete frequencies. These results demonstrate the potential of the weak radiating cell concept to reduce low frequency structurally radiated noise. Master of Science

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Wang, Bin. "Reduction of acoustic fields of horn-like structures by optimization of network resonators." Thesis, Paris Est, 2015. http://www.theses.fr/2015PESC1155/document.

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Le bruit généré dans la zone de contact entre un pneumatique et une route peut être amplifié par des dièdres constitués des surfaces du pneumatique et la route. Cette étude est consacrée à l'optimisation et à la conception de bandes de roulement et de textures de la route pour réduire l'amplification de l'effet dièdre sur la base de l'annulation de sons. Les bandes de roulement et les textures de la route peuvent être considérées comme deux réseaux dans la zone de contact. Les surfaces du pneumatique et de la route peuvent être considérées comme des baffles. Un modèle de réseau à baffle est constitué pour le système pneumatique / chaussée, et des procédés de couplage multi-domaines sont développés pour le calcul des champs acoustiques autour des réseaux à baffles. Avec ce modèle, la réduction des amplifications de l'effet dièdre par les réseaux peut être estimée. Étant donné que les réductions sont autour des fréquences de résonance de l'air à l'intérieur des réseaux, des méthodes numériques simples pour estimer les fréquences de résonance sont développées. Afin de concevoir des réseaux pour obtenir les fréquences de résonance recherchées, une méthode d'optimisation sur la base des algorithmes génétiques est proposée. Les méthodes d'estimation des fréquences de résonance sont validées avec des mesures. Les méthodes d'optimisation et le modèle des réseaux bafflés sont également vérifiées par les expériences. Une structure avec un cylindre en bois et une feuille de contreplaqué est construite pour les validations. Un vrai pneumatique sur une feuille de contreplaqué est également mesuré et calculé avec les méthodes proposées. Les bandes de roulement sont optimisées avec les méthodes proposées. Plusieurs réductions des amplifications de l'effet dièdre peuvent être vues et sont estimées avec les méthodes de couplage multi-domaines. La dimension des motifs de texture de la route est également étudiée afin de trouver les réductions maximales des amplifications The noise generated in the contact zone between a tire and a road can be amplified by horns constituted of the surfaces of the tire and the road. This study is devoted to the optimization and the design of tire treads and road textures for reducing the amplification of horn effect based on the sound cancellation. The tire treads and the road textures can be considered as two dimensional networks in the contact zone. The surfaces of the tire and the road can be seen as flanges. A model of flanged networks is established for the tire/road system, and multi-domain coupling methods are developed for the calculation of the acoustic fields around the flanged networks. With this model the reductions of the amplifications of horn effect by the networks can be estimated. Since the reductions are around the resonant frequencies of air inside the networks, simple numerical methods for estimating the resonant frequencies are developed. In order to design the networks to get wanted resonant frequencies, an optimization method based on genetic algorithms is proposed. The methods for estimating the resonant frequencies are validated with measurements. The optimization methods and the model of the flanged networks are also proved to be effective by the experiments. The wooden networks between a wooden cylinder and a sheet of plywood are built for the validation. A real tire on a sheet of plywood is also measured and calculated with the proposed methods. Last the tire treads are optimized with the optimization methods. Multiple reductions of the amplifications of horn effect can be seen and are estimated with the multi-domain coupling methods. The road brick dimension is also investigated in order to find the maximum reductions of the amplifications

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Chong, Foong Yen. "The acoustic and perceptual effects of single-microphone noise reduction in hearing aids on Mandarin fricatives and affricates." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/59046.

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Single-microphone noise reduction (SMNR) is implemented in hearing aids to suppress background noise. The noise-like feature in fricatives and affricates is susceptible to SMNR processing when background noise is present. Most SMNR studies have examined English speech materials but very few have examined Mandarin fricatives and affricates. In the present research, three studies were conducted to examine the acoustic and perceptual effects of SMNR on Mandarin fricatives and affricates. Study 1 aimed to test the validity of the inversion technique as a tool for separating speech and noise signals recorded from hearing aids in sound field. Study 1 showed that the inversion technique is a feasible and reliable tool for separating speech and noise post hearing-aid processing. However, fidelity of the retrieved speech signals showed variability between hearing aids. The acoustic effects of SMNR on Mandarin and English fricatives and affricates were examined in Study 2. Speech-plus-noise signals were presented to and recorded from one of two hearing aids mounted on a manikin, under SMNR-on and SMNR-off conditions. Speech signals were retrieved for subsequent acoustic analysis. The results showed that SMNR processing did not produce substantial acoustical changes in the temporal and spectral domain as measured in the Hearing Aid Speech Quality Index. Spectrographic analysis showed a reduction in frication-noise and release-burst intensity, and changes in the spectral mean. In Study 3, the Mandarin retroflex fricative and affricates, processed with and without SMNR, were used to examine the effects of SMNR on novel speech sound identification in noise by naïve listeners. Native English talkers might rely on bottom up processing to categorize the Mandarin retroflex sounds because these sounds were not in the English phonemic inventory. All listeners underwent five sessions of identification training and testing. The results showed that SMNR did not degrade the identification of novel speech sound in naïve listeners. Significant contributions of the present research are (i) the acoustic effects of SMNR on Mandarin and English fricatives and affricates were systematically documented and (ii) provided further evidence on SMNR having no effect on speech perception in noise. Medicine, Faculty of Audiology and Speech Sciences, School of Graduate

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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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Manegar, Farhan [Verfasser]. "Aero-acoustic noise reduction measures for wind turbine blade sections - a comparative numerical and experimental study / Farhan Manegar." Düren : Shaker, 2021. http://d-nb.info/1229779590/34.

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Phillips, Timothy Jason Nirmal. "Sound Transmission Loss of Sandwich Panels." Thesis, University of Canterbury. Department of Mechanical Engineering, 2012. http://hdl.handle.net/10092/9210.

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The sound transmission loss characteristics of plywood based sandwich panels were investigated. Measurements were made of the sound transmission loss of a range of materials and used as a baseline for comparison while a sound transmission loss optimisation method was developed. A unique test rig was built and calibrated to determine selected mechanical properties of materials of interest. The results of sound transmission loss and material properties measurements were used to select an appropriate prediction model, which was then used in conjunction with a mathematical optimisation model to determine combinations of materials and panel parameters which result in improved sound transmission loss. An effort was made to reproduce these predictions in experimental testing by constructing several prototype panels.

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Taseska, Maja [Verfasser], and Emanuel [Gutachter] Habets. "Informed spatial filters for speech enhancement: Noise and Interference Reduction, Blind Source Separation, and Acoustic Source Tracking / Maja Taseska ; Gutachter: Emanuel Habets." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2018. http://d-nb.info/1152079034/34.

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31

Zhang, Nan. "SCALE MODELS OF ACOUSTIC SCATTERING PROBLEMS INCLUDING BARRIERS AND SOUND ABSORPTION." UKnowledge, 2018. https://uknowledge.uky.edu/me_etds/119.

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Scale modeling has been commonly used for architectural acoustics but use in other noise control areas is nominal. Acoustic scale modeling theory is first reviewed and then feasibility for small-scale applications, such as is common in the electronics industry, is investigated. Three application cases are used to examine the viability. In the first example, a scale model is used to determine the insertion loss of a rectangular barrier. In the second example, the transmission loss through parallel tubes drilled through a cylinder is measured and results are compared to a 2.85 times scale model with good agreement. The third example is a rectangular cuboid with a smaller cylindrical well bored into it. A point source is placed above the cuboid. The transfer function was measured between positions on the top of the cylinder and inside of the cylindrical well. Treatments were then applied sequentially including a cylindrical barrier around the well, a membrane cover over the opening, and a layer of sound absorption over the well. Results are compared between the full scale and a 5.7 times scale model and correlation between the two is satisfactory.

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32

DI, BLASIO SONJA. "Occupant behaviour as a resource for acoustic comfort. Validation and evaluation of a device for the reduction of noise generated by occupants in classrooms and offices." Doctoral thesis, Politecnico di Torino, 2020. http://hdl.handle.net/11583/2861840.

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33

Meyer, Virgile. "Réduction des amplitudes d’une onde acoustique convectée par un flux dans un guide aux parois vibrantes." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066670.

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Une onde acoustique plane propagée dans un guide couplée à des parois vibrantes, siège d'ondes transversale ou de flexion, donne un ensemble d'ondes dans le fluide et dans la structure. Les ondes dans le fluide sont évanescentes, propagatives, ou encore propagatives avec un amortissement. Il n'est pas besoin que l'ensemble soit dissipatif pour en arriver là car les résultats proviennent d'interférences destructives on constructives. Un amortissement dans la structure donne un système cette fois-ci dissipatif et ajoute ses effets à la dissipation mais pas de façon classique puisqu'il s'agit ici d'ondes couplées acoustique/structure. En présence d'un flux stationnaire et uniforme la capacité d'une paroi vibrante à produire de l'atténuation acoustique se réduit. Les opérateurs en jeu, les méthodes pour les résoudre dont celle des éléments finis donnent accès à des prédictions. Elles sont confrontées à des résultats expérimentaux. Sans écoulement, les prédictions font sens. En revanche, avec écoulement, il n'en est pas de même et le mémoire tentera d'analyser les raisons. En conclusion technologique, une atténuation d'une quinzaine de décibels en moyenne sur une gamme de fréquences de quelques centaines de Hz centrées dans les médiums (500Hz) est envisageable avec une paroi mince qui n'encombre pas le guide A plane acoustic wave propagated in a duct some walls of which are vibrating due to transversal or flexural waves gives rise to a set of various waves within the fluid and the structure. Within the fluid, the waves are evanescent, propagatives or propagatives with decreasing amplitudes. There is no need for the global operator to be dissipative for such a result since it is arising from destructive or constructive interferences. When the structural damping exists, as in the real life, it adds its effect to the coupling but not in a classical way as coupled acoustic/structure waves are at play rather than pure acoustic or structural waves. Now in presence of a convection of the fluid that bears the acoustic wave (a stationary and uniform flow), the attenuation is reduced sligtly at the very low Mach numbers, and significantly at higher Mach numbers. As far as technological conclusions are sought, an averaged acoustic attenuation of around fifteen dB in a frequency range of some hundreds Hz centered at 500Hz can be obtained with this system very light and needing almost no room

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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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35

Meyer, Virgile. "Réduction des amplitudes d’une onde acoustique convectée par un flux dans un guide aux parois vibrantes." Electronic Thesis or Diss., Paris 6, 2016. http://www.theses.fr/2016PA066670.

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Une onde acoustique plane propagée dans un guide couplée à des parois vibrantes, siège d'ondes transversale ou de flexion, donne un ensemble d'ondes dans le fluide et dans la structure. Les ondes dans le fluide sont évanescentes, propagatives, ou encore propagatives avec un amortissement. Il n'est pas besoin que l'ensemble soit dissipatif pour en arriver là car les résultats proviennent d'interférences destructives on constructives. Un amortissement dans la structure donne un système cette fois-ci dissipatif et ajoute ses effets à la dissipation mais pas de façon classique puisqu'il s'agit ici d'ondes couplées acoustique/structure. En présence d'un flux stationnaire et uniforme la capacité d'une paroi vibrante à produire de l'atténuation acoustique se réduit. Les opérateurs en jeu, les méthodes pour les résoudre dont celle des éléments finis donnent accès à des prédictions. Elles sont confrontées à des résultats expérimentaux. Sans écoulement, les prédictions font sens. En revanche, avec écoulement, il n'en est pas de même et le mémoire tentera d'analyser les raisons. En conclusion technologique, une atténuation d'une quinzaine de décibels en moyenne sur une gamme de fréquences de quelques centaines de Hz centrées dans les médiums (500Hz) est envisageable avec une paroi mince qui n'encombre pas le guide A plane acoustic wave propagated in a duct some walls of which are vibrating due to transversal or flexural waves gives rise to a set of various waves within the fluid and the structure. Within the fluid, the waves are evanescent, propagatives or propagatives with decreasing amplitudes. There is no need for the global operator to be dissipative for such a result since it is arising from destructive or constructive interferences. When the structural damping exists, as in the real life, it adds its effect to the coupling but not in a classical way as coupled acoustic/structure waves are at play rather than pure acoustic or structural waves. Now in presence of a convection of the fluid that bears the acoustic wave (a stationary and uniform flow), the attenuation is reduced sligtly at the very low Mach numbers, and significantly at higher Mach numbers. As far as technological conclusions are sought, an averaged acoustic attenuation of around fifteen dB in a frequency range of some hundreds Hz centered at 500Hz can be obtained with this system very light and needing almost no room

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36

Edwards, Matthew. "Prediction and control of rolling noise in buildings." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI097.

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Les nouveaux bâtiments dans les zones urbaines sont divisés en zones commerciales et en zones habitables. Les magasins commerciaux se trouvent généralement au rez-de-chaussée, les résidences privées aux étages supérieurs. Cette utilisation a révélé des perturbations critiques dues au bruit généré par les chariots de livraison lorsque les bâtiments sont principalement occupés (par exemple tôt le matin). Ces chariots génèrent des vibrations à basse fréquence (moins de 100 Hz) qui se propagent facilement dans la structure du bâtiment et aux étages supérieurs, perturbant les habitants qui s'y trouvent. Si des travaux ont été réalisés pour étudier le bruit d'impact, peu de recherches ont été menées dans le domaine du bruit de roulement dans les bâtiments. Cette thèse présente un modèle original du bruit de roulement dans les bâtiments, prenant en compte les facteurs d'influence tels que la rugosité de la roue et du sol, les propriétés matérielles de la roue et du sol, la vitesse du chariot, et la charge sur le chariot. Les irrégularités discrètes, telles que les méplats des roues et les joints de sol, sont également prises en compte. Le modèle est capable de saisir les phénomènes physiques présents dans le contact de roulement à l'intérieur, ainsi que d'estimer l'avantage relatif du niveau sonore de l'ajout d'un revêtement de sol à un système de plancher donné. Le modèle peut être utilisé comme un outil pour étudier comment différents systèmes de revêtement de sol (y compris les systèmes multicouches) réagissent à l'excitation par roulement, dans le but de développer des solutions de construction à plusieurs étages qui sont mieux équipées pour combattre ce type de source de bruit New buildings in urban areas are divided into commercial and residential areas. Commercial stores are generally located on the ground floor, private residences on the upper floors. This use has revealed critical disturbances due to noise generated by delivery carts when buildings are mainly occupied (e.g. early morning). These carts generate low frequency vibrations (less than 100 Hz) which easily propagate through the building structure and to the upper floors, disturbing the residents therein. While work has been done to study impact noise, little research has been done in the area of rolling noise in buildings. This thesis presents an original model for rolling noise in buildings: taking into account the influencing factors such as the roughness of the wheel and floor, the material properties of the wheel and floor, the speed of the trolley, and the load on the trolley. Discrete irregularities, such as wheel flats and floor joints, are also taken into account. The model is capable of capturing the physical phenomena present in the rolling contact indoors, as well as estimating the relative noise benefit of adding a floor covering to a given floor system. The model can be used as a tool to study how different flooring systems (including multi-layer systems) respond to rolling excitation, with the aim of developing multi-story building solutions that are better equipped to combat this type of noise source

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37

Jelínek, Ondřej. "Akustické mikroklima nevýrobních objektů." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-225943.

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This master´s thesis focuses on effect of acoustic microclimate in non-production buildings to human. Within elaboration this topic was made measurment acoustic power level and created protocols by valid technical standards and law. I dedicate to damping noise and aerodynamic noise in airconditioning in part topic analysis. The part aplication on real object deal with assessment current status and draft measure for improve acoustic ratio in laboratories in center of research located in Brno. That includes describe of air-cndition unit and development two variants and their rating.

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38

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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Anderson, Shaun David. "Space-time-frequency processing from the analysis of bistatic scattering for simple underwater targets." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45771.

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The development of low-frequency SONAR systems, using a network of autonomous systems in unmanned vehicles, provides a practical means for bistatic measurements (i.e. when the source and receiver are widely separated, thus allowing multiple viewpoints of a target). Furthermore, time-frequency analysis, in particular Wigner-Ville analysis, takes advantage of the evolution of the time dependent echo spectrum to differentiate a man-made target (e.g. an elastic spherical shell, or cylinder) from a natural one of the similar shape (e.g. a rock). Indeed, key energetic features of man-made objects can aid in identification and classification in the presence of clutter and noise. For example, in a fluid-loaded thin spherical shell, an energetic feature is the mid-frequency enhancement echoes (MFE) that result from antisymmetric Lamb waves propagating around the circumference of the shell, which have been shown to be an acoustic feature useful in this pursuit. This research investigates the enhancement and benefits of bistatic measurements using the Wigner-Ville analysis along with acoustic imaging methods. Additionally, the advantage of joint space-time-frequency coherent processing is investigated for optimal array processing to enhance the detection of non-stationary signals across an array. The proposed methodology is tested using both numerical simulations and experimental data for spherical shells and solid cylinders. This research was conducted as part of the Shallow Water Autonomous Mine Sensing Initiative (SWAMSI) sponsored by ONR.

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Peiró, Torres María del Pilar. "Research of the acoustic phenomenon produced by isolated scatterers and its applicability as a noise reducing device in transport infrastructures. Search for an optimised and sustainable design." Doctoral thesis, Universitat Politècnica de València, 2021. http://hdl.handle.net/10251/164903.

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[ES] El control de ruido ambiental es una preocupación de primera magnitud para las sociedades avanzadas, debido a los problemas derivados que ocasionan en la salud de los ciudadanos. Una de las soluciones más extendidas para el control del ruido en su fase de transmisión en la utilización de pantallas acústicas. La aparición de nuevos materiales formados por redes de dispersores acústicos aislados, denominados cristales de sonido, está revolucionando el campo del apantallamiento acústico, posibilitando el avance tecnológico de esta área. Así, en los últimos años, las pantallas acústicas basadas en cristales de sonido se han posicionado como una alternativa viable a las pantallas acústicas tradicionales, puesto que ofrecen múltiples ventajas frente a las soluciones actuales. En el presente trabajo se muestra primeramente una recopilación de los avances realizados en el campo del apantallamiento acústico mediante esta tipología de pantallas. No obstante, aún existen líneas de investigación abiertas en esta área, que es necesario abordar para conseguir el objetivo de aplicar esta tecnología como atenuadores de sonido en las infraestructuras de transporte. Durante el periodo de formación de la doctoranda, se ha trabajado en algunas de las líneas de investigación activas en este campo del apantallamiento acústico. Una de estas investigaciones condujo al descubrimiento de interferencias entre los efectos de la resonancia y la dispersión múltiple de los cristales de sonido cuando estos efectos se producen en rangos de frecuencia cercanos. También hemos diseñado un nuevo dispositivo de reducción de ruido basado en cristales de sonido, utilizando herramientas de optimización multiobjetivo, que permitan apantallar y reflejar de forma difusa el ruido. El empleo de esta nueva herramienta de diseño identificó la necesidad de realizar un estudio comparativo de los métodos de simulación más utilizados para estimar el rendimiento de los dispositivos basados en cristales de sonido. Por último, hemos realizado un estudio psicoacústico para determinar la percepción de la reducción de molestia que proporcionan las pantallas acústicas basadas en cristales sonido y las barreras tradicionales, determinando si los parámetros objetivos que evalúan su rendimiento coinciden con la respuesta subjetiva de los usuarios. [CA] El control de soroll ambiental és una preocupació de primera magnitud per a les societats avançades, a causa dels problemes derivats que ocasionen en la salut dels ciutadans. Una de les solucions més esteses per al control del soroll en la seua fase de transmissió en la utilització de pantalles acústiques. L'aparició de nous materials formats per xarxes de dispersors acústics aïllats, denominats cristals de so, està revolucionant el camp de l'apantallament acústic, possibilitant l'avanç tecnològic d'esta àrea. Així, en els últims anys, les pantalles acústiques basades en cristals de so s'han posicionat com una alternativa viable a les pantalles acústiques tradicionals, ja que oferixen múltiples avantatges enfront de les solucions actuals. En el present treball es mostra primerament una recopilació dels avanços realitzats en el camp de l'apantallament acústic per mitjà d'esta tipologia de pantalles. No obstant això, encara hi ha línies d'investigació obertes en esta àrea, que és necessari abordar per a aconseguir l'objectiu d'aplicar esta tecnologia com a atenuadors de so en les infraestructures de transport. Durant el període de formació de la doctoranda, s'ha treballat en algunes de les línies d'investigació actives en este camp de l'apantallament acústic. Una d'estes investigacions va conduir al descobriment d'interferències entre els efectes de la ressonància i la dispersió múltiple dels cristals de so quan estos efectes es produïxen en rangs de freqüència pròxims. També hem dissenyat un nou dispositiu de reducció de soroll basat en cristals de so, utilitzant ferramentes d'optimització multiobjectiu, que permeten apantallar i reflectir de forma difusa el soroll. L'ús d'esta nova ferramenta de disseny va identificar la necessitat de realitzar un estudi comparatiu dels mètodes de simulació més utilitzats per a estimar el rendiment dels dispositius basats en cristals de so. Finalment, hem realitzat un estudi psicoacústic per a determinar la percepció de la reducció de molèstia que proporcionen les pantalles acústiques basades en cristals so i les barreres tradicionals, determinant si els paràmetres objectius que avaluen el seu rendiment coincidixen amb la resposta subjectiva dels usuaris. [EN] Control of environmental noise is a major concern for advanced societies because of the resulting problems for citizens' health. One of the most widespread solutions for controlling noise in its transmission phase is the use of acoustic screens. The emergence of new materials made up of arrays of isolated acoustic scatterers, called sonic crystals, is revolutionizing the field of acoustic screening. In recent years, acoustic screens based on sonic crystals have positioned themselves as a viable alternative to traditional acoustic screens, as they offer multiple advantages over current traditional solutions. This Doctoral dissertation compiles the advances in the field of acoustic screening using this type of sonic crystals. However, there is still active research in this area which needs to be addressed and studied in order to apply this technology as noise reduction devices in transport infrastructures. Therefore, during the PhD student's training period, we have researched the acoustic phenomena produced by isolated scatterers in order to better understand the physical phenomena behind the lasts designs of this type of screen. One of these researches led to the discovery of interferences between the effects of resonance and multiple scattering of sonic crystals when occurring in nearby frequency ranges. Also we have designed a new noise reduction device based on sonic crystals, using multi-objective optimization tools, which would block and diffuse the noise. This new designing tool identified the need for a comparative study of the most commonly used simulation methods to estimate the performance of devices based on sonic crystals. Finally, we have carried out a psychoacoustic study that determined the perception of the annoyance reduction provided by acoustic screens based on sonic crystals and traditional barriers, determining whether the objective parameters that evaluate their performance match to the subjective response of the users. Agradezco al Ministerio de Ciencia e Innovación por la ayuda concedida dentro del programa Doctores Industriales. Asimismo, a mi tutor en empresa Dr. Juan José Martín Pino, por posibilitar la realización de esta investigación dentro de la empresa BECSA. Al Departamento de Física Aplicada de la Universitat Politècnica de València, a la Comisión Académica del Programa de Doctorado de Matemáticas y al Centro de Tecnologías Físicas: Acústica, Materiales y Astrofísica. Peiró Torres, MDP. (2021). Research of the acoustic phenomenon produced by isolated scatterers and its applicability as a noise reducing device in transport infrastructures. Search for an optimised and sustainable design [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/164903 TESIS

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Mbailassem, Fulbert. "Contrôle du bruit par effets de localisation par géométries irrégulières." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI095/document.

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Cette thèse s'inscrit dans le cadre de la recherche des moyens de réduction du bruit. Le but est d’analyser et de créer par une méthode passive, le confinement d’énergie acoustique dans les irrégularités géométriques via le phénomène de localisation pour ensuite la dissiper. En prélude à l'atténuation du bruit par les géométries irrégulières, les mécanismes de la dissipation acoustique sont rappelés et illustrés par quelques exemples de réseaux de résonateurs quart-d'onde. Le phénomène de localisation est ensuite étudié par une analyse modale. Le caractère localisé d'un mode est quantifié par son volume d'existence relatif (VER) qui donne, en fraction du volume total du domaine, le volume effectif concerné par l'énergie du mode. Il ressort de cette étude que seules les cavités irrégulières ayant des irrégularités en forme de sous-cavités couplées à une cavité principale sont « localisantes ». La fréquence d'un mode localisé est liée aux dimensions de la zone irrégulière de localisation. Le lien entre les irrégularités géométriques et la dissipation acoustique est ensuite analysé au moyen des indicateurs tels que le facteur de qualité, le coefficient d'absorption ou le taux d'amortissement de l'énergie. Cette étude montre que les cavités irrégulières amortissement mieux une onde acoustique comparativement aux cavités à géométrie régulière. Toutefois, la dissipation de l'énergie acoustique des cavités irrégulières n'est pas uniquement liée à la localisation. Elle dépend également d'autres paramètres (porosité, résistivité, etc.). Lorsque les irrégularités des parois rigides ne permettent pas de réaliser une dissipation suffisante, elles peuvent être réalisées dans les matériaux poroélastiques à performance acoustique moyenne pour augmenter leur capacité dissipative. Enfin, des études expérimentales menées ont permis de valider l'existence du phénomène de localisation et de confirmer la tendance plus dissipative des géométries irrégulières par rapport aux géométries régulières. De même, des mesures du coefficient d'absorption d'un échantillon de forme préfractale d'un béton de chanvre (matériau ayant une performance acoustique moyenne) montrent une augmentation de la dissipation de plus de 40% induite par la forme irrégulière. La contribution majeure de cette thèse est d’avoir répondu à un défi technologique important consistant à effectuer une mise en évidence expérimentale du phénomène de localisation jusque-là difficile à réaliser avec des microphones. Pour y parvenir, un outil optique peu conventionnel dans la métrologie acoustique est adopté; il s'agit de la réfracto-vibrométrie qui consiste à utiliser, sous certaines conditions, le vibromètre laser pour mesurer un champ acoustique (pression acoustique). Bien que contraignante, cette technique présente l'avantage d'être non intrusive et donc moins encombrante même pour de petites cavités comparativement aux microphones In this thesis, the acoustical behavior of irregular cavities leading to localization phenomenon is investigated for noise reduction applications. The aim of this work is to study and create by means of passive method, an accumulation of acoustical energy and dissipate it. Before addressing geometrical irregularities effects on the sound field, viscothermal dissipation mechanisms of sound are recalled and illustrated through few networks of quarter-wave resonators. In a second part, a study of the localization phenomenon is carried out by a modal analysis approach. The localization is quantified by the relative existence volume (VER), an indicator which gives a measure of the volume of the region in which a mode is localized as a fraction of the total cavity volume. The localization analysis is conducted using both regular and irregular cavities. It has been shown that only cavities with irregular geometry, such that sub-cavities are formed, can localize some acoustical modes. Moreover, the frequency of a localized mode is related to the dimensions of the localization region. Following the investigation of the localization phenomenon, the relation between cavities geometry and sound energy dissipation has been studied by the estimation of damping indicators, such as the quality factor, the sound absorption coefficient or the energy damping rate. According to this study, irregular cavities have higher capability to damp sound waves compared to regular cavities. However, for the case of irregular cavities only, the induced dissipation is not proportional to the localization. Nevertheless, when irregularities of rigid walls are not able to achieve sufficient dissipation, this can be obtained with slightly absorptive porous materials of irregular geometry. In fact, the dissipative properties of some porous materials can be optimized by giving them irregular interface. Finally, an experimental set-up has been designed to validate the localization phenomenon and to confirm the damping tendency of irregular geometries in comparison to regular ones. Moreover, measurements of the sound absorption coefficient of a hemp concrete reveal that the sample of irregular geometry achieves sound dissipation more than 40% higher than the one achieved by a regular plane sample. Finally, this thesis has addressed a technological challenge consisting of experimentally validating the localization phenomenon which is so far very difficult to obtain by the use of conventional pressure microphones. In the framework of this thesis, an optical non-conventional sound pressure measurement technique has been used. The used technique is the laser refracto-vibrometry which consists of using a laser vibrometer in some specific conditions to measure the acoustical field (sound pressure). This technique is difficult to conduct but it has the advantage of being contactless, thus less cumbersome for even very small cavities as compared to pressure microphones

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Cardenas, Cabada Edouard. "L'imagerie acoustique au service de la surveillance et de la détection des défauts mécaniques." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI124/document.

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L’analyse vibratoire constitue une part très importante des moyens de mesures pour la surveillance et la détection des défauts mécaniques des machines tournantes. Le positionnement des accéléromètres est stratégique et contribue fortement à la réussite du diagnostic ; la proximité du capteur de l’élément défaillant est une condition très utile, mais pas toujours réalisable. La corrélation entre le bruit émis par une machine et son état est assez étroite et montre l’apport des mesures acoustiques pour l’optimisation du diagnostic. L’imagerie acoustique, très appliquée pour détecter des sources dans le domaine du transport, avec ses multiples méthodes (holographie, beamforming, etc…) peut être un moyen pour remonter aux défauts mécaniques. Dans cet objectif, plusieurs stratégies basées sur l’algorithme de beamforming sont développées. Premièrement, des indicateurs communément utilisés pour le diagnostic des machines sont visualisés en fonction de l’espace. Le kurtosis permet de localiser les sources impulsives qui peuvent être reliées à un défaut. De nouveaux indicateurs basés sur le spectre d’enveloppe des signaux focalisés sont également mis en place pour détecter les défauts de roulement de bague interne et externe. D’autre part, la moyenne synchrone angulaire est utilisée pour extraire le champ acoustique synchrone avec la rotation d'un composant de la machine. Les sources reliées à un défaut sont affectées au champ résiduel et peuvent être identifiées dans les cartographies. Enfin, une nouvelle méthode d'imagerie acoustique qui exploite les fonctions de transfert vibroacoustiques entre des accéléromètres positionnés sur la machine et une antenne acoustique est développée. Elle permet d'obtenir des cartographies de la pression rayonnée sur une surface de la machine uniquement à partir d'accéléromètres. Son applicabilité à la détection de défaut est également démontrée sur un banc à engrenages Vibration analysis is mainly used in condition monitoring and fault detection of rotating machine domain. The success of the diagnosis is strongly related to the position of the accelerometers. However, the machine geometry sometimes prevents the sensors to be placed close enough to the faulted part causing the diagnostic failure. The sound emitted by a mechanism and its condition are related. Using microphones to optimize condition monitoring is then justified. Acoustic imaging techniques (acoustic holography, beamforming, etc…) are mainly used as a source localization and quantification tool but they can be turned into a powerful diagnosis tool. Several strategies based on the beamforming algorithm are developed in this work. Firstly, diagnosis features commonly used in condition monitoring of rotating machinery are mapped as a function of space. Kurtosis allows localizing impulsive sources which eventually can be related to a mechanism failure. New features based on the squared envelope spectrum of the focused signals are also introduced. They aim toward the detection of inner and outer race fault in roller element bearings. On the other hand, angular synchronous average is used to extract the acoustic field synchronous with one component rotation. The sources related to a fault are localized in the residual field mappings. Finally, a new imaging technique based on the vibroacoustic transfer functions between a few accelerometers placed on the machine and the microphone array is developed. It allows obtaining the mappings of the radiated pressure on the machine surface only thanks to the accelerometers. It is tested as a fault detection tool on a test bench

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Navarro, Cárdenas Harold Alexis, and Quiroz Jhon Charly Rayme. "Elaboración del concreto poroso con fibra de polipropileno como alternativa para reducir la contaminación sonora causada por la interacción del neumático y la calzada aplicado en la avenida San Luis, distrito de San Borja." Bachelor's thesis, Universidad Peruana de Ciencias Aplicadas (UPC), 2021. http://hdl.handle.net/10757/656331.

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Este documento describe la elaboración de un concreto poroso con fibra de polipropileno (CPF). Se propone este material como una alternativa para reducir la contaminación sonora causada por la interacción entre el neumático y calzada. La propuesta consta de dos etapas de estudio: Elaboración de un concreto poroso y evaluación acústica mediante un modelo matemático microestructural. En la primera etapa, se evaluó dieciséis diseños, los cuales de cada mezcla se realizaron doce muestras para posteriormente ser sometidas al ensayo de resistencia a la compresión. Así se obtuvieron un total de 192 probetas que fueron evaluadas a los 7, 14 y 28 días de tiempo de curado. Los diseños están compuestos con agregados recomendados por el ACI 522R, agregados de HUSO 8 y agregados de HUSO 67, de los cuales se pretende seleccionar un concreto poroso que pueda cumplir las especificaciones mínimas de un pavimento manteniendo un porcentaje de vacíos óptimo para su posterior evaluación acústica. De los diseños obtenidos se estudió la influencia de la porosidad y porcentaje de vacíos en las propiedades mecánicas del concreto. De esta manera, se encontró una dosificación de CPF adecuado para la propuesta con una relación agua cemento de 0.36, fibra tipo I, 0% de aditivo y piedra de HUSO 8, con el cual se obtuvo una resistencia a la compresión de 296.37 kg/cm2, con el cual se cumplía los requisitos mínimos de resistencia del concreto para su aplicación a un pavimento. En la segunda etapa, se pretende obtener resultados del coeficiente de absorción acústica mediante una simulación numérica basados en la teoría microestructural de Neithalath. Este modelo fue aplicado a los diseños de CPF obtenidos en la primera parte, teniendo en cuenta el tamaño, forma de los agregados y la relación de vacíos. El desarrollo de este modelo matemático y su correlación con las mediciones físicas permiten la predicción del coeficiente máximo absorción acústica de un CPF basado en las características geométricas de la estructura de poros. Los diseños óptimos sometidos a la simulación numérica obtuvieron un coeficiente de absorción acústica de 0.79 y 0.63 para agregados de HUSO 8 y HUSO 67 respectivamente. De esta manera, con la investigación y experimentación se llegó a la conclusión que el CPF permite reducir el ruido generado por la interacción del neumático y la calzada, con lo cual se verificó un nuevo beneficio del concreto poroso en la ingeniería de pavimentos. This document describes the fabrication of a polypropylene fiber (CPF) porous concrete. This material is proposed as an alternative to reduce noise pollution caused by the interaction between the tire and road. The proposal consists of two stages of study: Preparation of a porous concrete and acoustic evaluation using a microstructural mathematical model. In the first stage, sixteen designs were evaluated, of which twelve samples were made from each mixture and subsequently subjected to the compression resistance test. Thus, a total of 192 specimens were obtained, which were evaluated at 7, 14 and 28 days of curing time. The designs are composed of aggregates recommended by ACI 522R, aggregates of HUSO 8 and aggregates of HUSO 67, of which it is intended to select a porous concrete that can meet the minimum specifications of a pavement while maintaining an optimal percentage of voids for its subsequent evaluation. acoustics. The influence of porosity and void percentage on the mechanical properties of concrete was studied from the designs obtained. In this way, a suitable CPF dosage was found for the proposal with a water-cement ratio of 0.36, type I fiber, 0% additive and HUSO 8 stone, with which a compressive strength of 296.37 kg / cm2, with which the minimum strength requirements of concrete for its application to a pavement were met. In the second stage, it is intended to obtain results of the acoustic absorption coefficient by means of a numerical simulation based on the microstructural theory of Neithalath. This model was applied to the CPF designs obtained in the first part, taking into account the size, shape of the aggregates and the ratio of voids. The development of this mathematical model and its correlation with physical measurements allow the prediction of the maximum acoustic absorption coefficient of a CPF based on the geometric characteristics of the pore structure. The optimal designs submitted to the numerical simulation obtained a sound absorption coefficient of 0.79 and 0.63 for aggregates of HUSO 8 and HUSO 67 respectively. In this way, with the investigation and experimentation, it was concluded that the CPF allows to reduce the noise generated by the interaction of the tire and the road, which verified a new benefit of porous concrete in pavement engineering. Tesis

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Carbajal, Guillaume. "Apprentissage profond bout-en-bout pour le rehaussement de la parole." Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0017.

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Cette thèse s'insère dans le développement des systèmes de télécommunication mains-libres, en particulier avec des enceintes intelligentes en environnement domestique. L'utilisateur interagit avec un correspondant distant en étant généralement situé à quelques mètres de ce type de système. Les microphones sont susceptibles de capter des sons de l'environnement qui se mêlent à la voix de l'utilisateur, comme le bruit ambiant, l'écho acoustique et la réverbération. Ces types de distorsions peuvent gêner fortement l'écoute et la compréhension de la conversation par le correspondant distant, et il est donc nécessaire de les réduire. Des méthodes de filtrage existent pour réduire individuellement chacun de ces types de distorsion sonore, et leur réduction simultanée implique de combiner ces méthodes. Toutefois, celles-ci interagissent entre elles, et leurs interactions peuvent dégrader de la voix de l'utilisateur. Il est donc nécessaire d'optimiser conjointement ces méthodes. En premier lieu, nous présentons une approche de réduction de l'écho acoustique combinant un filtre d'annulation d'écho avec un post-filtre de suppression d'écho résiduel conçu de manière à s'adapter à différents modes de fonctionnement du filtre d'annulation. Pour cela, nous proposons d'estimer les coefficients du post-filtre en utilisant les spectres à court terme de plusieurs signaux observés, dont le signal estimé par le filtre d'annulation, en entrée d'un réseau de neurones. Nous montrons que cette approche améliore la performance et la robustesse du post-filtre en matière de réduction d'écho, tout en limitant la dégradation de la parole de l'utilisateur, sur plusieurs scénarios dans des conditions réelles. En second lieu, nous décrivons une approche conjointe de réduction multicanale de l'écho, de la réverbération et du bruit. Nous proposons de modéliser simultanément la parole cible et les signaux résiduels après annulation d'écho et déréverbération dans un cadre probabiliste et de représenter conjointement leurs spectres à court terme à l'aide d'un réseau de neurones récurrent. Nous intégrons cette modélisation dans un algorithme de montée par blocs de coordonnées pour mettre à jour les filtres d'annulation d'écho et de déréverbération, ainsi que le post-filtre de suppression des signaux résiduels. Nous évaluons notre approche sur des enregistrements réels dans différentes conditions. Nous montrons qu'elle améliore la qualité de la parole ainsi que la réduction de l'écho, de la réverbération et du bruit, par rapport à une approche optimisant séparément les méthodes de filtrage et une autre approche de réduction conjointe. En dernier lieu, nous formulons une version en ligne de notre approche adaptée aux situations où les conditions acoustiques varient dans le temps. Nous évaluons la qualité perceptuelle sur des exemples réels où l'utilisateur se déplace durant la conversation This PhD falls within the development of hands-free telecommunication systems, more specifically smart speakers in domestic environments. The user interacts with another speaker at a far-end point and can be typically a few meters away from this kind of system. The microphones are likely to capture sounds of the environment which are added to the user's voice, such background noise, acoustic echo and reverberation. These types of distortion degrade speech quality, intelligibility and listening comfort for the far-end speaker, and must be reduced. Filtering methods can reduce individually each of these types of distortion. Reducing all of them implies combining the corresponding filtering methods. As these methods interact with each other which can deteriorate the user's speech, they must be jointly optimized. First of all, we introduce an acoustic echo reduction approach which combines an echo cancellation filter with a residual echo postfilter designed to adapt to the echo cancellation filter. To do so, we propose to estimate the postfilter coefficients using the short term spectra of multiple known signals, including the output of the echo cancellation filter, as inputs to a neural network. We show that this approach improves the performance and the robustness of the postfilter in terms of echo reduction, while limiting speech degradation, on several scenarios in real conditions. Secondly, we describe a joint approach for multichannel reduction of echo, reverberation and noise. We propose to simultaneously model the target speech and undesired residual signals after echo cancellation and dereveberation in a probabilistic framework, and to jointly represent their short-term spectra by means of a recurrent neural network. We develop a block-coordinate ascent algorithm to update the echo cancellation and dereverberation filters, as well as the postfilter that reduces the undesired residual signals. We evaluate our approach on real recordings in different conditions. We show that it improves speech quality and reduction of echo, reverberation and noise compared to a cascade of individual filtering methods and another joint reduction approach. Finally, we present an online version of our approach which is suitable for time-varying acoustic conditions. We evaluate the perceptual quality achieved on real examples where the user moves during the conversation

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Ezzine, Mouhamed Mounibe. "Etude de dispositifs passifs et actifs de réduction du bruit d’interaction soufflante–redresseur." Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2024. http://www.theses.fr/2024ECDL0022.

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Deux approches de diminution du bruit d'origine aéroacoustique associé à l'OGV des moteurs d'avion ont été examinées dans cette thèse. La première repose sur des solutions passives, utilisant des matériaux comme de la mousse poreuse et du tissu métallique (wire mesh) pour atténuer le bruit. L'efficacité de ces matériaux a été testée dans diverses configurations, montrant une capacité de réduction du bruit jusqu'à 6 dB sous certaines conditions, bien que cette efficacité puisse être affectée par des facteurs comme la vitesse de l'écoulement. La seconde partie de l'étude s'est intéressée aux techniques actives, notamment à l'utilisation de cellules piézoélectriques pour le contrôle du bruit. Ces technologies ont montré une réduction notable du bruit, atteignant jusqu'à 15 dB dans certains cas, bien qu'une amplification du bruit ait été notée dans d'autres situations, soulignant l'importance de la précision du design dans l'application de ces technologies. Enfin, l'optimisation numérique de l'impédance acoustique sur les profils aérodynamiques a été explorée, avec pour objectif de réduire davantage le bruit généré par les écoulements turbulents. Cette démarche a permis d'identifier des valeurs d'impédance optimales, conduisant à des réductions significatives de bruit pour certaines fréquences. Les résultats suggèrent qu'un choix précis de l'impédance acoustique sur les surfaces des profils peut être une méthode efficace pour minimiser le bruit d'origine aéroacoustique, bien que la géométrie du profil puisse influencer les résultats. Dans l'ensemble, ces études mettent en évidence le potentiel de différentes stratégies pour la réduction du bruit aéroacoustique, tout en soulignant la nécessité d'une application soigneuse et adaptée aux conditions spécifiques pour maximiser leur efficacité Two approaches to reduce aeroacoustic noise associated with the OGV of aircraft engines have been examined in this thesis. The first relies on passive solutions, using materials such as porous foam and wire mesh to attenuate noise. The effectiveness of these materials has been tested in various configurations, demonstrating a noise reduction capacity of up to 6 dB under certain conditions, although this efficiency may be affected by factors such as flow velocity. The second part of the study focused on active techniques, particularly the use of piezoelectric cells for noise control. These technologies have shown a notable reduction in noise, reaching up to 15 dB in some cases, although noise amplification has been noted in other situations, emphasizing the importance of precise design in the application of these technologies. Finally, numerical optimization of acoustic impedance on aerodynamic profiles was explored, aiming to further reduce noise generated by turbulent flows. This approach identified optimal impedance values, leading to significant noise reductions for certain frequencies. The results suggest that precise selection of acoustic impedance on profile surfaces can be an effective method for minimizing aeroacoustic noise, although profile geometry may influence the results. Overall, these studies highlight the potential of different strategies for aeroacoustic noise reduction, while emphasizing the need for careful application tailored to specific conditions to maximize their effectiveness

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Li, Gemin. "REDUCING ACOUSTIC NOISE IN MRI SCANNERS." Thesis, 2010. http://hdl.handle.net/1974/6200.

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A study of methods for reducing the acoustic noise in magnetic resonance imaging (MRI) scanners is presented in this thesis. The structural-acoustic coupling mechanism of MRI scanners was investigated using a method of structural-acoustic modal analysis. Mathematical expressions of generalized radiation impedances of gradient coil ducts with perforated panel inserts were developed and the effects of the perforated panel inserts on the acoustic noise in the duct were discussed. The possibility of using micro-perforated panel (MPP) absorbers in MRI scanners to reduce the acoustic noise was then investigated through analytical and computational modeling. A comprehensive experimental study was conducted after the analytical and computational investigation. Finally, design methods and procedures were developed specifically for the MPP absorbers in MRI scanners. Design considerations and recommendations were given as well. Several major conclusions can be made from this research. Firstly, the method of structural-acoustic modal analysis is effective for finding the structural-acoustic coupling modes which should be avoided in the design of MRI scanners. Secondly, a perforated panel insert produces significant effects on the radiation impedance of gradient coil ducts and MRI scanner bores. This attribute partly contributes to its capability of reducing the acoustic noise in a duct. Thirdly, the effectiveness of MPP absorbers in MRI scanners can be accurately predicted using a combination of theoretical analysis and computational modeling. Moreover, it has been proved that well designed MPP absorbers are effective in reducing the acoustic noise in MRI scanners. Lastly, the presented design methods and recommendations for the MPP absorbers can be relatively easily used by MRI designers or engineers to tackle the acoustic noise problem in MRI scanners. Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2010-07-13 11:46:03.585

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Lee, Chih-Wei, and 李志偉. "An Implementation of Improving Noise Reduction and Acoustic Echo Cancellation." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/19194971990895536292.

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碩士 淡江大學 資訊工程學系碩士班 93 In general, adaptive signal processing applied in echo cancellations all need a desired signal value, This desired signal is used along with the source signal as references to continuously calculate and tune up the needed signal. However, under a communications environment the effort of obtaining the signal by computing the result of the desired and source signal in order to eliminate ambient noise and echo would increase the system''s complexity. This thesis proposes a method to reduce noise and eliminate echo without introducing excessive complications to the infrastructure of the system. Our method involves using a particular process to find echo route relations with the signals produced by the noise reduction system, and using this data as the desired signal value combined with the source signal as inputs of the echo cancellation step. The experiment''s environmental setup involves using a single microphone as the sound input recording the sounds in a driving automobile as samples instead of capturing data from a simulated environment. We apply our improved method to the samples and perform the steps of reducing noise and eliminating echo. The result will show our method is capable of eliminating noise and echo produced in a car''s interior and at the same time avoiding complexities added to our system''s infrastructure.

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Jackson, JM. "Pro-active acoustic noise reduction for magnetic resonance imaging scanners." Thesis, 2012. https://eprints.utas.edu.au/15922/2/whole-jackson-2012.pdf.

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Large acoustic noise generated by magnetic resonance imaging (MRI) scanners pose significant problems for a patient undergoing a scan, in addition to attending medical staff. A heightened sense of anxiety, difficulty communicating with medical staff, and mild irritation through to acute discomfort are all results of the large noise amplitude produced during the scanning process. Gradient coils are a component of MRI hardware that have been found to be the major contributor of acoustic noise and are thus the subject of this thesis. A gradient coil is required to produce a homogeneous linear field to excite nuclei in a predictable manner so that clear images can be obtained. A feature of gradient coils is that they must be switched on and off repeatedly during the imaging process. This switching generates large Lorentz forces on the chamber, which causes the chamber to deform and promotes a pressure wave inside the chamber that can be heard as acoustic noise. The problem becomes one of designing current winding patterns on the gradient coil that produce a specified linear field and have a reduced simulated acoustic noise output. This problem is studied in detail and is accomplished using a Tikhonov regularisation process. This thesis looks directly at theoretical methods to actively reduce simulated acoustic noise during the MRI scanning process. Pro-active noise reduction, in this work, is achieved by reducing the deflection of the gradient coil, which leads to the design of quiet gradient coils. Beginning with a relatively simple one dimensional radial coil deformation model and requiring a high level of linearity of the gradient field, designs for the current windings on the gradient coils are produced. In this first model a comparatively small reduction of 0.6 dB was attained; however, previous work was extended to account for realistic switching sequences. Next, a more sophisticated three dimensional deflection model was considered, which produced a similar small level of noise reduction, but nonetheless substantial insight into the physical process behind the generation of noise was obtained. Finally, a robust technique for designing very quiet gradient coils, reducing the noise by 49 dB, was achieved by abandoning the requirement that the gradient

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Chu, Nan-chun, and 朱楠群. "Noise Reduction and Acoustic Echo Cancellation for Voice over IP." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/12931824749359755860.

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碩士 國立臺灣科技大學 資訊工程系 97 In this paper, we study the production of acoustic echo cancellation and noise reduction software, and then into WinRTP Internet phone software, to improve the quality of internet phone calls. In the area of noise reduction, first to improve the degree of entropy detection method for voice activity detection, then noise spectrum is estimated. We combine non-linear spectrum subtraction with improved spectrum subtraction, two-stage action of the spectrum subtraction, to reduce the noise. In the echo cancellation, we use normalized least mean square adaptive algorithm to filter out echo signals, and by analysis of the delay to reduce computation load and convergence speed. Based on the experimental measurement to the hearing and subjective assessment of test scores, we show that the noise subtraction and echo cancellation device significantly attenuate the noise and echo signal, and therefore enhance the quality of voice.

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Wu, Tsung-Chen, and 吳宗振. "Deep Learning Based Noise Reduction for Acoustic Hearing Preserved Cochlear Implant." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/92rwg6.

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碩士 國立交通大學 電信工程研究所 106 Vocoder simulations are generally adopted to simulate the electrical hearing induced by the cochlear implant (CI). Our research group is developing a new four-electrode CI microsystem that induces high-frequency electrical hearing while preserving low-frequency acoustic hearing. To assess the functionality of this CI, a previously developed hearing-impaired (HI) hearing model is combined with a 4-channel vocoder in this thesis to respectively mimic the perceived acoustic hearing and electrical hearing. Psychoacoustic experiments are conducted on Mandarin speech recognition for determining spectral coverages of electrodes for this CI. Simulation results show that initial consonants of Mandarin are more difﬁcult to recognize than ﬁnal vowels of Mandarin via acoustic hearing of HI patients. After electrical hearing being induced through logarithmic-frequency distributed electrodes, speech intelligibility of HI patients is boosted for all Mandarin phonemes, especially for initial consonants. Similar results are consistently observed in clean and noisy test conditions. Next, we combine a deep neural network based noise reduction algorithm with the proposed CI system in the hope to improve the Mandarin speech intelligibility for seen and unseen noise types. Ultimately, we use objective evaluation and subjective evaluation scores to verify this model, hence, to provide the proof of concept of this combinational system.

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Dissertations / Theses on the topic 'Mitigation acoustic noise reduction'

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