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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Experimental analysis of noise reduction properties of sound absorbing foam

Wertel, Scotty John. January 2001 (has links) (PDF)
Thesis--PlanB (M.S.)--University of Wisconsin--Stout, 2001. / Includes bibliographical references.

Broadband noise control through a ducted opening

Cheung, Shuk-ching., 張淑晶. January 2012 (has links)
Fresh air ventilation openings or windows are essential to most buildings but the openings allow considerable portions of noise to be transmitted from the outdoor into the indoor environment. This project studies relevant theoretical models through accurate numerical solutions, and seeks better designs to gain extra noise attenuation through the openings. The spectral method of Chebyshev collocation and the corresponding technique of out-going wave boundary conditions, for both ducted and flanged opening, are developed as numerical tools and validated by analytical examples. After establishing the numerical tools, two prototype problems are studied. The first is one in which there is no special sound attenuation device. The configuration includes aperture of negligible thickness, aperture of finite thickness and aperture of semi-infinite length. The characteristics of the noise transmission through aperture of finite thickness are investigated with examples of sonic boom and traffic noise. The second prototype problem is the sound attenuation performance of side-branch design of the ducted opening. Side-branch configurations including porous material, single micro-perforated panel, double-layer micro-perforated panels, parallel micro-perforated panels and parallel micro-perforated panels with connected cavity are investigated. They are tested individually with parameters optimized for each of two examples of noise sources. The sound attenuation performances compared using appropriate subjective ratings of the noise sources. It is found that the parallel micro-perforated panels give the best performance for the sonic boom and the double-layer micro-perforated panels serve as the best substitute for the porous material with traffic noise source. Results from experiment are also presented to validate some numerical results. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Compact environmental noise absorber

Peng, Dandan, 彭丹丹 January 2014 (has links)
With the development of the industry and the society, noise pollution becomes increasingly severe, especially in large cities. Generally, there are three major noise sources, namely industrial noise, traffic noise and community noise. In response, several measurements have been developed to achieve effective noise control. Examples of noise control methods are reduction of noise at source and abatement of noise during the transmission. Since noise sources are more difficult to control, and sometimes already fixed, noise control during sound transmission is more broadly applied. Traditional passive noise control techniques include Helmholtz resonators and noise absorption materials like felt, glass mineral. The sound absorption materials (SAM) are found to be efficient in attenuating noise in high frequency domain, but their performance at low frequencies is quite poor. On the other hand, the Helmholtz resonator works perfect at any target frequency but suffers from its narrow absorption bandwidth, so that it’s only effective within a limited frequency band. As an innovative solution to passive noise control problem, micro-perforated panel absorber (MPPA) has attracted great interest in recent years. It turns out to be a competitive alternative to sound absorption materials and Helmholtz resonator. The parallel and series arrangement of MPPAs backed with cavities of different depths allows them to obtain decent noise absorption performance over a relatively broad frequency range. However, the performance of MPPA is restricted by its volume, as large volume is demanded for decent low-frequency absorption, which is also the case for noise absorption materials. In this thesis, a potential way to improve the low-frequency performance of the MPPA without occupying extra volume is proposed and implemented to tests. The focus is the adjustment of speed of sound and it is beneficial in different applications such as the following. In low frequency noise control, the size of the absorber in at least one dimension is often related to the wavelength and it is often too long. With a reduced speed of sound one can reduce this size while keeping the overall volume constant. Along this line of thinking, the effect of cavity configuration on its acoustic properties is investigated by two steps. Firstly, the property of a waveguide consisting of several identical elements is studied. The number of element is chosen to magnify the effect of the configuration. It turns out the irregularity of the duct shape can slow down the speed of sound of the plane wave by increasing the acoustic mass. Secondly, the absorption performance of an MPPA backed with an irregular cavity is evaluated. The shape of the cavity is the same as the element in the first step. In advance, the parallel arrangement of two MPPAs backed with irregular cavities is investigated, in order to look into the effect of cavity shape on inter-resonator interaction. The final results indicate that cavity design is an effective method to enhance the noise absorption performance of the MPPA arrays in the low-frequency domain. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

Novel methods of transduction for active control of harmonic sound radiated by vibrating surfaces

Burgemeister, Kym A. January 1996 (has links)
Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1996? / Bibliography: leaves 201-221. Also available in print form.

The influence of cutting parameters on noise reduction in the sawing of aluminum extrusions

Desanghere, Geert. January 1980 (has links)
Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 82-83).

Analysis of noise in coincident current memory

Nickel, Donald F. January 1964 (has links)
Thesis (M.S.)--University of Wisconsin--Madison, 1964. / eContent provider-neutral record in process. Description based on print version record. Bibliography: 1 l. at end.

Acoustic replication in smart structure using active structural/acoustic control

Griffin, Steven F. 12 1900 (has links)
Dissertation made openly available per email from author, 7/22/2016.

Active control of periodic machinery vibrations

Jenkins, Michael David January 1989 (has links)
No description available.

Optimal spatially fixed and moving virtual sensing algorithms for local active noise control.

Petersen, Cornelis D. January 2007 (has links)
Local active noise control systems aim to create zones of quiet at specific locations within a sound field. The created zones of quiet generally tend to be small, especially for higher frequencies, and are usually centred at the error sensors. For an observer to experience significant reductions in the noise, the error sensors therefore have to be placed relatively close to an observer’s ears, which is not always feasible or convenient. Virtual sensing methods have been proposed to overcome these problems that have limited the scope of successful local active noise control applications. These methods require non-intrusive sensors that are placed remotely from the desired locations of maximum attenuation. These non-intrusive sensors are used to provide an estimate of the sound pressures at these locations, which can then be minimised by a local active noise control system. This effectively moves the zones of quiet away from the physical locations of the transducers to the desired locations of maximum attenuation, such as a person’s ears. A number of virtual sensing algorithms have been proposed previously. The difference between these algorithms is the structure that is assumed to compute an estimate of the virtual error signals. The question now arises as to whether there is an optimal structure that can be used to solve the virtual sensing problem, which amounts to a linear estimation problem. It is well-known that the Kalman filter provides an optimal structure for solving such problems. An optimal solution to the virtual sensing problem is therefore derived in this thesis using Kalman filtering theory. The proposed algorithm is implemented on an acoustic duct arrangement to demonstrate its effectiveness. The presented experimental results indicate that the zone of quiet was effectively moved away from the physical sensor towards the desired location of maximum attenuation. The previously proposed virtual sensing algorithms have been developed with the aim to create zones of quiet at virtual locations that are assumed spatially fixed within the sound field. Because an observer is very likely to move their head, the desiredlocations of the zones of quiet are generally moving through the sound field rather than being spatially fixed. For effective control, a local active noise control system incorporating a virtual sensing method thus has to be able to create moving zones of quiet that track the observer’s ears. A moving virtual sensing method is therefore developed in this thesis that can be used to estimate the error signals at virtual locations that are moving through the sound field. It is shown that an optimal solution to the moving virtual sensing problem can be derived using Kalman filtering theory. A practical implementation of the developed algorithm is combined with an adaptive feedforward control algorithm and implemented on an acoustic duct arrangement. The presented experimental results illustrate that a narrowband moving zone of quiet that tracks the desired location of maximum attenuation has successfully been created. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1291123 / Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2007.

Axial-flow fan noise : with particular reference to the noise caused by vortex formation at the trailing edge and upper surface of blades

Gower, Stephen Newman. January 1966 (has links) (PDF)
No description available.

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