Dissertations / Theses on the topic 'Acoustic noise'
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Epifanio, Chad Lawrence. "Acoustic daylight : passive acoustic imaging using ambient noise /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9823704.
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Zheng, Haosheng, and Kaichun Zhang. "Noise Analysis of Computer Chassis and Secondary Sound Source Noise Reduction." Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-18547.
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This article focuses on computer noise analysis and noise reduction processing. With the popularity of computers, people are increasingly demanding the comfort of using computers. Solving the noise problem of the computer case can make the working environment more comfortable. People working in a noisy environment for a long time can cause anxiety and the quality of work is not high. The main purpose of this paper is to analyse the characteristics of computer noise and to reduce the noise of the chassis through the secondary sound source. Through the comparison of the experimental and simulation results, the noise reduction effect of the secondary sound source on the computer case is obtained. This paper can provide a scientific reference for the manufacture of computer chassis and improvement of noise.
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Copley-Woods, Djuna S. (Djuna Sunlight) 1977. "Aircraft interior acoustic noise control." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9330.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.Includes bibliographical references (p. 45).
An experimental study was perfonned to determine which materials are best suited for internal aircraft noise reduction. An impedance tube with dimensions of a scaled aircraft was constructed and evaluated, and eleven materials were tested and compared based on their noise reduction properties, weight, and thickness. Polyvinylidene Fluoride was tested for use in active noise control for a large space.
by Djuna S. Copley-Woods.
S.B.
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Creasy, Miles Austin. "Adaptive Collocated Feedback for Noise Absorption in Acoustic Enclosures." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/45209.
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This thesis focuses on adaptive feedback control for low frequency acoustic energy absorption in acoustic enclosures. The specific application chosen for this work is the reduction of high interior sound pressure levels (SPL) experienced during launch within launch vehicle payload fairings. Two acoustic enclosures are used in the research: the first being a symmetric cylindrical duct and the other being a full scale model of a payload fairing. The symmetric cylindrical duct is used to validate the ability of the adaptive controller to compensate for large changes in the interior acoustical properties. The payload fairing is used to validate that feedback control, for a large geometry, does absorb acoustic energy.
The feedback controller studied in this work is positive position feedback (PPF) used in conjunction with high and low pass Butterworth filters. An algorithm is formed from control experiments for setting the filter parameters of the PPF and Butterworth filters from non-adaptive control simulations and tests of the duct and payload fairing. This non-adaptive control shows internal SPL reductions of 2.2 dB in the cylindrical duct for the frequency range from 100 to 500 Hz and internal SPL reductions of 4.2 dB in the full scale fairing model for the frequency range from 50 to 250 Hz.
The experimentally formed control algorithm is then used as the basis for an adaptive controller that uses the collocated feedback signal to actively tune the control parameters. The cylindrical duct enclosure with a movable end cap is used to test the adaptation properties of the controller. The movable end cap allows the frequencies of the acoustic modes to vary by more than 20 percent. Experiments show that a 10 percent change in the frequencies of the acoustic modes cause the closed-loop system to go unstable with a non-adaptive controller. The closed-loop system with the adaptive controller maintains stability and reduces the SPL throughout the 20 percent change of the acoustic modes' frequencies with a 2.3 dB SPL reduction before change and a 1.7 dB SPL reduction after the 20 percent change.Master of Science
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Sun, Guohua. "Active Control of Impact Acoustic Noise." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1413542213.
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Griffin, Steven F. "Acoustic replication in smart structure using active structural/acoustic control." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/13085.
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Fuller, Ryan Michael. "Adaptive Noise Reduction Techniques for Airborne Acoustic Sensors." Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1355361066.
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Kumar, Ashok. "Active structural-acoustic control of interior noise in vibro-acoustic cavities." Thesis, IIT Delhi, 2016. http://localhost:8080/iit/handle/2074/7036.
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Davies, Jonathan James. "Underwater acoustic communications." Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289679.
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Shou, Xingxian. "The Suppression of Selected Acoustic Noise Frequencies in MRI." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1281404517.
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Papinniemi, Antti Aerospace Civil & Mechanical Engineering Australian Defence Force Academy UNSW. "Vibro-acoustic studies of brake squeal noise." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Aerospace, Civil and Mechanical Engineering, 2008. http://handle.unsw.edu.au/1959.4/38696.
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Squeal noise has been an on-going concern with automotive brake systems since their inception. Even after many decades of research no single theory exists that adequately describes the phenomenon, and no general methods for eliminating squeal noise exist. Broadly speaking, three primary methods of analysis have been applied to understanding and eliminating brake squeal: analytical, experimental and numerical. Analytical models provide some insight into the mechanisms involved when a brake squeals, but have limitations in applicability to specific brake systems. Experimental methods provide the backbone of brake squeal investigations, especially in an industrial environment. However, the core focus of this thesis is to use a large scale finite element analysis (FEA) model to investigate brake squeal. Initially the FEA model was developed and the dynamic characteristics were validated against experimental modal analysis results. A complex eigenvalue analysis was performed to identify potential squeal modes which appear as unstable system vibration modes. Further techniques are described that allow the deeper probing of unstable brake system modes. Feed-in energy, which is the conversion of friction work into vibrational energy during the onset of squeal, is used to determine the relative contribution of each brake pad to the overall system vibration. The distribution of the feed-in energy across the face of a brake pad is also calculated. Component strain energy distributions are determined for a brake system as a guide to identifying which components might best be modified in addressing an unstable system mode. Finally modal participation is assessed by calculating the Modal Assurance Criterion (MAC) between component free modes and the component in the assembly during squeal. This allows participating modes to be visualised and aids in the development of countermeasures. The majority of the work in this thesis was performed using the commercial FEA code MSC.Nastran with user defined friction interfaces. An alternative approach using a contact element formulation available in Abaqus was also implemented and compared to the MSC.Nastran results. This analysis showed that considerable differences were noted in the results even though the overall predicted stability correlated relatively well to observed squeal. Abaqus was also used in a case study into the design of a brake rotor in a noisy brake system. The results of this study provided good correlation to observed squeal and facilitated effective rotor countermeasures to be developed. Some success was achieved in the main aims of predicting brake squeal and developing countermeasures. However, while the tools presented do allow a deeper probing of system behaviour during squeal, their use requires good correlation to observed squeal on brake system to be established. As such, their use as up-front design tools is still limited. This shortcoming stems from the complexity of brake squeal itself and the limitations in modelling the true nature of the non-linearities within a brake system.
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Grad, Janet R. "H¦0¦0 control of acoustic noise." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0010/NQ30614.pdf.
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Brackley, Mark. "Acoustic noise from small electronically commutated motors." Thesis, University of Warwick, 2001. http://wrap.warwick.ac.uk/3065/.
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An analysis of acoustic noise in electronically controlled variable speed drives is presented. The causes of vibration and acoustic noise in switched reluctance motors are discussed and it is shown that brushless d.c. motors can produce resonant vibration and acoustic noise by similar mechanisms. The flux switching motor is introduced. This new class of reluctance motor is an advance on the established switched reluctance motor, retaining many of its benefits, but with a simpler and cheaper power electronic converter. The phase windings and method of flux control are different and tests are performed to quantify the effect on the acoustic noise produced. Measurements of acoustic noise are made on one flux switching motor and one 2-phase switched reluctance motor, made from the same laminations and mechanical components. It is shown that the flux switching motor produced 2dB less acoustic noise under the same conditions. Finite element analysis is used to calculate the radical force profiles of the two motors during normal rotation, and further analysis of this data provides evidence to support the experimental results. The experimental results go on to show how the acoustic noise from a second flux switching drive was found to be comparable to that of a split phase induction motor.
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Evernham, Jeffrey Thomas. "Acoustic noise suppression for helicopter communication systems." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/42553.
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Messing, David P. (David Patrick) 1979. "Noise suppression with non-air-acoustic sensors." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/87444.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (leaves [74]-[75]).
by David P. Messing.
S.M.
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Li, Qi. "Acoustic noise emitted from overhead line conductors." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/acoustic-noise-emitted-from-overhead-line-conductors(90a5c23c-a7fc-4230-bbab-16b8737b2af2).html.
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The developments of new types of conductors and increase of voltage level have driven the need to carry out research on evaluating overhead line acoustic noise. The surface potential gradient of a conductor is a critical design parameter for planning overhead lines, as it determines the level of corona loss (CL), radio interference (RI), and audible noise (AN). The majority of existing models for surface gradient calculation are based on analytical methods which restrict their application in simulating complex surface geometries. This thesis proposes a novel method which utilizes both analytical and numerical procedures to predict the surface gradient. Stranding shape, proximity of tower, protrusions and bundle arrangements are considered within this model. One of UK National Grid's transmission line configurations has been selected as an example to compare the results for different methods. The different stranding shapes are a key variable in determining dry surface fields. The dynamic behaviour of water droplets subject to AC electric fields is investigated by experiment and finite element modelling. The motion of a water droplet is considered on the surface of a metallic sphere. To understand the consequences of vibration, the FEA model is introduced to study the dynamics of a single droplet in terms of phase shift between vibration and exciting voltage. Moreover, the evolution of electric field within the whole cycle of vibration is investigated. The profile of the electric field and the characteristics of mechanical vibration are evaluated. Surprisingly the phase shift between these characteristics results in the maximum field occurring when the droplet is in a flattened profile rather than when it is ‘pointed’.Research work on audible noise emitted from overhead line conductors is reviewed, and a unique experimental set up employing a semi-anechoic chamber and corona cage is described. Acoustically, this facility isolates undesirable background noise and provides a free-field test space inside the anechoic chamber. Electrically, the corona cage simulates a 3 m section of 400 kV overhead line conductors by achieving the equivalent surface gradient. UV imaging, acoustic measurements and a partial discharge detection system are employed as instrumentation. The acoustic and electrical performance is demonstrated through a series of experiments. Results are discussed, and the mechanisms for acoustic noise are considered. A strategy for evaluating the noise emission level for overhead line conductors is developed. Comments are made on predicting acoustic noise from overhead lines. The technical achievements of this thesis are summarized in three aspects. First of all, an FEA model is developed to calculate the surface electric field for overhead line conductors and this has been demonstrated as an efficient tool for power utilities in computing surface electric field especially for dry condition. The second achievement is the droplet vibration study which describes the droplets' behaviour under rain conditions, such as the phase shift between the voltage and the vibration magnitude, the ejection phenomena and the electric field enhancement due to the shape change of droplets. The third contribution is the development of a standardized procedure in assessing noise emission level and the characteristics of noise emissions for various types of existing conductors in National Grid.
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Hebert, Robert Carleton University Dissertation Engineering Electrical. "Background acoustic noise suppression in mobile telephony." Ottawa, 1990.
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Edwards, Colin G. "Exposure to loud noise and risk of acoustic neuroma." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1187004419.
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Swanepoel, Rikus. "Vowel perception in severe noise." Diss., University of Pretoria, 2010. http://hdl.handle.net/2263/22971.
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A model that can accurately predict speech recognition for cochlear implant (CI) listeners is essential for the optimal fitting of cochlear implants. By implementing a CI acoustic model that mimics CI speech processing, the challenge of predicting speech perception in cochlear implants can be simplified. As a first step in predicting the recognition of speech processed through an acoustic model, vowel perception in severe speech-shaped noise was investigated in the current study. The aim was to determine the acoustic cues that listeners use to recognize vowels in severe noise and make suggestions regarding a vowel perception predictor. It is known that formants play an important role in quiet, while in severe noise the role of formants is still unknown. The relative importance of F1 and F2 is also of interest, since the masking of noise is not always evenly distributed over the vowel spectrum. The problem was addressed by synthesizing vowels consisting of either detailed spectral shape or formant information. F1 and F2 were also suppressed to examine the effect in severe noise. The synthetic stimuli were presented to listeners in quiet and signal-to-noise ratios of 0 dB, -5 dB and -10 dB. Results showed that in severe noise, vowels synthesized according to the whole-spectrum were recognized significantly better than vowels containing only formants. Multidimensional scaling and FITA analysis indicated that formants were still perceived and extracted by the human auditory system in severe noise, especially when the vowel spectrum consisted of the whole spectral shape. Although F1 and F2 vary in importance in listening conditions of quiet and less noisy conditions, the role of the two cues appears to be similar in severe noise. It was suggested that not only the availability formants, but also details of the vowel spectral shape can help to predict vowel recognition in severe noise to a certain degree.Dissertation (MEng)--University of Pretoria, 2013.
Electrical, Electronic and Computer Engineering
unrestricted
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Smith, D. J. "Digital recording and analysis of noise with particular reference to jet noise." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376269.
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Lani, Shane W. "Passive acoustic imaging and monitoring using ambient noise." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/50136.
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An approximate of the Green's function can be obtained by taking the cross-correlation of ambient noise that has been simultaneously recorded on separate sensors. This method is applied for two experiments, which illustrate the advantages and challenges of this technique. The first experiment is in the ultrasonic regime [5-30] MHz and uses capacitive micromachined ultrasonic transducer arrays to image the near field and compares the passive imaging to the conventional pulse-echo imaging. Both the array and target are immersed in a fluid with the sensors recording the fluid's random thermal-mechanical motion as the ambient noise. The second experiment is a passive ocean monitoring experiment, which uses spatiotemporal filtering to rapidly extract coherent arrivals between two vertical line arrays. In this case the ambient noise in the frequency band [250 1500] Hz is dominated by non-stationary shipping noise. For imaging purposes, the cross-correlation needs to extract the Green's function so that the imaging can be done correctly. While for monitoring purposes, the important feature is the change in arrivals, which corresponds to the environment changing. Results of both experiments are presented along with the advantages of this passive method over the more accepted active methods.
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Krezel, Zbigniew Adam, and n/a. "Recycled aggregate concrete acoustic barrier." Swinburne University of Technology, 2006. http://adt.lib.swin.edu.au./public/adt-VSWT20060821.154340.
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This document reports on a research project aimed at developing a concrete acoustic barrier
made from Recycled Aggregate (RA) Concrete. The research project was undertaken in
response to the needs expressed by the Victorian concrete recycling industry. The industry,
the scientific community conducting research into relevant disciplines, and the community
at large, represented by Victorian government agencies, are of the opinion that there is a
need to devise a higher value utilisation application for selected concrete recycling
products.
This document outlines the rationale and objectives of the research project which involves
the examination of Recycled Concrete (RC) Aggregate, the design and examination of RA
Concrete, and finally the development of an acoustic barrier made from RA Concrete.
The literature review presented in this report examines aspects of concrete recycling and
concrete technology pertaining to traditional and alternative constituent materials for
concrete production. Firstly, the importance and influence of fine and coarse aggregate on
basic properties of concrete is introduced. Secondly, an account on the use of alternative
materials in concrete technology, especially of coarse recycled aggregates and
supplementary cementitious materials (SCM) is described. Thirdly, some of the physical
and mechanical properties and how the use of RC Aggregate and SCM changes these
properties are discussed. Fourthly, a number of commonly used techniques and neutron
scattering techniques to investigate aggregate and concrete properties are introduced and
discussed. Fifthly, the porosity of aggregate and concrete including durability are
specifically discussed and testing methods are reasoned. The literature review also
discusses the use of no-fines concrete; its physical, mechanical and acoustic properties.
Finally it presents an account of the use of concrete in transportation traffic noise
attenuation devices.
This document continues with an outline of a methodology that was adopted in this
research project. It outlines experimental work aimed at examining the properties of RC Aggregate which amongst other properties includes porosity, particle size distribution,
water absorption, shape and density. It continues examining RA Concrete properties and
includes, among other properties, compressive strength, porosity and durability as well as
sound absorption of acoustic barrier. The methodology introduces standard and purposely
modified test procedures used in the examination of aggregates, concrete and acoustic
barrier. An account of various research techniques is presented, spanning from simple
visual observations to more sophisticated neutron scattering techniques. The summary of
test procedures follows a description of test specimen composition and their sizes, and a
suite of tested specimens. It also introduces statistical methods used to analyse test results.
After a detailed description of the aggregate, concrete and RA Concrete acoustic barrier,
the document outlines a summary of data generated through the experimental program of
this research project. The data on fine aggregate, on selected 14/10mm coarse RC
Aggregate, on concrete made from natural and recycled aggregate and on acoustic barrier
are presented and discussed. Test results of various physical, mechanical and acoustic
properties of aggregate, concrete and barrier are reported, analysed and discussed. The data
from observations, visual assessment and scientific experimentation of specific properties
are then crossed analysed in a search for relationships between properties of fine and coarse
aggregates and properties of concrete made from such aggregates. A cross analysis of data
on ?less-fines? RA Concrete and on the acoustic performance of barrier is examined, and
the relationship between the volume of interconnected voids in a porous part of ?less-fines?
concrete, and the sound absorption of acoustic barrier is discussed and reported.
The document then presents a synthesis of the literature review results, project aims
adopted within the experimental program and test results in the three main areas of this
research project. These areas include recycled concrete aggregate, recycled aggregate
concrete and acoustic barrier made from RA Concrete.
Finally, conclusions reached through the course of this investigation are summarised and
recommendations are proposed in relation to the RA Concrete acoustic barrier. The main
conclusion is that selected RC Aggregate can be used in the production of concrete of a compressive strength of 25MPa, if the moisture content and water absorption in the
aggregate are closely monitored, and the foreign material content is kept below 1.5%. The
author concludes that acoustic barrier made from selected RC Aggregate has unique sound
absorption characteristics that can easily be tunable by a selection of appropriate aggregate
and by specific concrete mix designs. Recommendations for further research are also
proposed.
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Krezel, Zbigniew Adam. "Recycled aggregate concrete acoustic barrier." Australasian Digital Theses Program, 2006. http://adt.lib.swin.edu.au/public/adt-VSWT20060821.154340.
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Thesis (PhD) - Swinburne University of Technology, 2006.Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Civil Engineering, Swinburne University of Technology - 2006. Typescript. Includes bibliographical references.
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Blondel, Laurent Armand. "Compressed air acoustic sources for active noise control." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246196.
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Di, Stefano Danilo. "Investigating noise radiation from jets by acoustic analogy." Thesis, University of Leicester, 2018. http://hdl.handle.net/2381/42862.
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The aerodynamic noise radiating from an unsteady flow can be extracted by acoustic analogy from time-resolved Computational Fluid Dynamic (CFD) simulations. For this purpose, two Ffowcs Williams and Hawkings (FW-H) solvers are developed, based on an advanced time formulation (AFW-H) and on a convective formulation (CFW-H). The methods are coded in Python and embedded in Antares, a CFD post-processor of wide access and usability for the scientific community, developed by Cerfacs, France. The new FW-H solvers are tested on a hierarchy of noise sources of increasing complexity. The radiating field from elementary acoustic sources is considered first, progressing then to single-stream and dual-stream jets. The tests on monopoles, dipoles, and quadrupoles show good predictions of pressure fluctuation time-history and directivity against reference analytical results. CFD results obtained at Cerfacs by Large Eddy Simulation and at the University of Leicester by Detached Eddy Simulation provide the input to the acoustic analogy to estimate the noise radiation from jets. The jet noise predictions are compared against acoustic results obtained numerically by the elsA software (ONERA, France) and against sound measurements taken at the Von Karman Institute for Fluid Dynamics, Belgium. The tool is then used to assess dual-stream under-expanded jet noise in a configuration by Airbus SAS, at flow conditions that differ from the ones explored in previous aeroacoustic literature. Flight effects on jet noise are tested by applying the CFW-H tool to a single-stream under-expanded jet in-flight. The acoustic predictions for both static and in-flight jets are found in good agreement with reference predictions and with measurements, building confidence in using the new FW-H solvers to extract the aerodynamic noise generated by unsteady shock-containing jets.
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Long, Stephen Andrew. "Acoustic noise and vibration of switched reluctance machines." Thesis, University of Sheffield, 2002. http://etheses.whiterose.ac.uk/14498/.
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This thesis describes a systematic investigation into the sources of acoustic noise and vibration in switched reluctance machines, and encompasses the vibrational behaviour of the stator, the influence of control parameters, and an evaluation of the effectiveness of active vibration cancellation. The influence of leading design parameters, such as the width and number of poles and the yoke thickness, and geometric asymmetries, such as lamination notches in the stator core, and the effect of the stator windings, the frame, the end-caps and the mounting assembly, on the natural frequencies and modes of vibration are investigated, Chapter 3. Both two-dimensional and three-dimensional finite element analyses are employed, the predicted results being validated by measurements on various experimental models, which consequently highlights the limitation of the finite element technique for highly complex structures with discontinuities in their fabrication. The influence of the mass and stiffness of the laminated stator core and the stator windings on the natural frequencies and vibration modes is investigated, and effective material properties are deduced for the analyses. It is found that the number of poles and lamination notches on the stator influence the number of vibrational modes which occur in the audible frequency range due to the introduction of dual natural frequencies, viz. symmetrical and anti-symmetrical modes, which are shown to separate further in value as the asymmetries become more profound. As the diameter of the stator yoke is reduced the natural frequencies increase, whereas increasing the thickness of the yoke and the adding of a frame and end-caps significantly increase the natural frequencies. The effect of the stator poles is to significantly reduce the stator natural frequencies, which are irrespective to a variation to the width of the poles, a variation in their mass being annulled by the resulting change in stiffness. Similarly, it is shown that the winding mass and stiffness offset each other so that their influence is also relatively small, whereas, although quantification of the damping is not within the aims of this thesis, it is apparent that the windings introduce a high level of damping which consequently limits the magnitude of the vibrations and hence acoustic noise. Finally, the laminated nature of the core is quantified and is shown to affect the effective material properties compared to an equivalent solid core, and to increase the effective damping. Previous investigations have studied the influence of the drive control parameters, but generally limit the analysis to either the frequency or time domain or to measurements of the sound pressure level, and are generally carried out in isolation. Therefore. the influence of alternative operating modes and their associated control parameters on the acoustic noise and vibration of an SR machine is thoroughly investigated. the results being analysed in both the frequency and time domains, and compared with measurements of the sound pressure level, Chapter 4. The noise and vibration which results when the SR machine is operated under both voltage and current control. with both hard and soft chopping techniques, and various switching angles, and for various sampling and switching frequencies, is measured. The influence of speed and load is also investigated, and the vibration and noise are also investigated under single pulse mode operation. It is found that hard chopping results in a noisier operation than with soft chopping due to increased current ripple, especially under current control. The noise and vibration is clearly shown to differ under current control compared to voltage control and single pulse mode, due to the random switching of the phase voltages resulting in wideband harmonic spectra, thereby increasing the levels of all the mechanical resonances. Further, it is found that the noise and vibration increase with both speed and load. In general, the increases in noise and vibration are attributed to an increase in the rate of decay of current at phase turn-off, regardless of the control parameter under investigation. Finally, the effectiveness of active vibration cancellation for nOIse reduction is investigated under typical operating modes in Chapter 5, which, for the first time, is analysed in both the frequency and time domains, and validated by measurements of the sound pressure level. It is found that active vibration cancellation is less effective for machine stators which have more than one dominant vibration mode within the audible frequency range, since the technique is only capable of applying active cancellation for a single vibration mode, thus any further resonances remain unaffected. Further, during chopping control, especially current control which results in random switching, it has been shown, for the first time, that the effective time-delay varies to that applied, thus rendering the technique less effective. This is found to be attributed to the asynchronism of the final chopping edge and point of phase turn-off, therefore preventing the vibrations from being excited in anti-phase, as explained in section 5.6.
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Pawełczyk, Marek. "Feedback control of acoustic noise at desired locations." Praca habilitacyjna, Wydawnictwo Politechniki Śląskiej, 2005. https://delibra.bg.polsl.pl/dlibra/docmetadata?showContent=true&id=10178.
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García, Chocano Víctor Manuel. "New devices for noise control and acoustic cloaking." Doctoral thesis, Editorial Universitat Politècnica de València, 2015. http://hdl.handle.net/10251/53026.
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[EN] The aim of this work is to design new acoustic devices based on arrangements of scattering units. First, the use of sonic crystals as noise barriers for traffic noise control is comprehensively analyzed. Due to the limitations of the conventional structures based on rigid scatterers, the inclusion of absorbing elements is proposed. Two different types of absorbers are here considered: porous materials and microperforated plates. In the first case, the attenuation characteristics of barriers made with cylinders containing rubber crumb is analyzed. The second proposal is based on the construction of cylindrical microperforated shells. Analytical approaches modelling the behavior of the barriers have been developed in both cases. These models show a satisfactory agreement with the corresponding experimental realizations. Finally, it is performed an optimization process in order to obtain efficient sound barriers intended to attenuate traffic noise.
Another application considered in this work is the construction of cloaks to render objects acoustically invisible. In particular, cloaks made with rigid inclusions are designed to operate with airborne sound. The first proposal consists of a cloak that utilizes the temperature of the background to control the properties of the effective medium. In addition, two and three-dimensional cloaks have been developed through the scattering cancellation technique. These devices have been designed by means of an optimization procedure and their performance has been experimentally demonstrated.[ES] El objetivo de este trabajo es el diseño de nuevos dispositivos acústicos basados en disposiciones de centros de dispersión. En primer lugar, el uso de cristales sónicos como barreras acústicas para el control de ruido de tráfico es analizado en detalle. Debido a las limitaciones que presentan las estructuras convencionales basadas en centros de dispersión rígidos, se propone la inclusión de elementos absorbentes en los mismos. Se han considerado dos tipos distintos de absorbente: materiales porosos y placas microperforadas. En el primer caso se analizan las propiedades atenuadoras de barreras formadas por cilindros que contienen granza de caucho. La segunda solución se basa en la construcción de coronas microperforadas. En ambos casos se han desarrollado modelos analíticos que permiten determinar el comportamiento de las barreras. Dichos modelos muestran un acuerdo satisfactorio con las correspondientes realizaciones experimentales. Finalmente se ha realizado un proceso de optimización con objeto de obtener barreras eficientes para la atenuación de ruido de tráfico. Otra aplicación considerada en este trabajo es el desarrollo de dispositivos de invisibilidad acústica. Concretamente se pretenden diseñar mantos constituidos con elementos rígidos para ondas acústicas en aire. La primera propuesta consiste en un manto que utiliza la temperatura del medio externo para controlar sus propiedades efectivas. Además se han desarrollado mantos en dos y tres dimensiones a través de la técnica de cancelación de la dispersión. Los diseños han sido realizados por medio de un proceso de optimización y su funcionamiento ha sido demostrado experimentalmente.
[CAT] L'objectiu d'aquest treball és el disseny de nous dispositius acústics basats en disposicions de centres de dispersió. En primer lloc, l'ús de vidres sònics com barreres acústiques per al control de soroll de trànsit és analitzat en detall. A causa de les limitacions que presenten les estructures convencionals basades en centres de dispersió rígids, es proposa la inclusió d'elements absorbents en els mateixos. S'han considerat dos tipus diferents de absorbent: materials porosos i plaques microperforades. En el primer cas s'analitzen les propietats atenuadores de barreres formades per cilindres que contenen gransa de cautxú. La segona solució es basa en la construcció de corones microperforades. En tots dos casos s'han desenvolupat models analítics que permeten determinar el comportament de les barreres. Aquests models mostren un acord satisfactori amb les corresponents realitzacions experimentals. Finalment s'ha realitzat un procés d'optimització per tal d'obtenir barreres eficients per l'atenuació de soroll de trànsit. Una altra aplicació considerada en aquest treball és el desenvolupament de dispositius d'invisibilitat acústica. Concretament es pretenen dissenyar mantells constituïts amb elements rígids per ones acústiques en aire. La primera proposta consisteix en un mantell que utilitza la temperatura del medi extern per controlar les seves propietats efectives. A més s'han desenvolupat mantells en dues i tres dimensions a través de la tècnica de cancel·lació de la dispersió. Els dissenys han estat realitzats per mitjà d'un procés d'optimització i el seu funcionament ha estat demostrat experimentalment.
García Chocano, VM. (2015). New devices for noise control and acoustic cloaking [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/53026
TESIS
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Green, Kimball W. "Piezoceramic Actuated Transducers for Interior Acoustic Noise Control." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/34541.
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Weight is a critical parameter in the design of any system launched into space. Current launch costs are on the order of 10,000 dollars per pound of payload capacity. Reducing weight and thus increasing payload capacity is always in the forefront of the design process. One method of increasing the payload capacity of launch vehicles is to reduce the acoustic environment in the interior of the fairing. A major problem is that passive methods currently used for noise suppression do not exhibit significant energy dissipation at low frequencies. This motivates the use of active noise control. Using active noise control for frequencies below 200 to 300 Hz in addition to the passive control means has potential to provide broadband noise suppression and thus a smoother, cheaper ride for any payload. The problem with this technique is that active noise control commonly uses electromagnetic speakers as the control element. The weight of the speaker adds more cost to the application due to the approximate cost per pound to send a launch vehicle and payload to space. At 10,000 dollars per pound of payload capacity, the added cost spent on protecting the payload can potentially reduce the amount of payload capacity a customer receives due to monies spent on non-payload mass. Therefore, necessity dictates a light weight noise control solution.
This work investigates the feasibility of a transducer with less mass than that of a conventional loudspeaker which dissipates energy at the acoustic resonances of an enclosed cavity. The test setup involves using the transducer to lower the sound pressure levels of acoustic resonances which are excited by an external source, thus simulating the launch phase of a launch vehicle. The transducer is used as an actuator to add damping through feedback control.
The transducer is comprised of three thin flexures that are actuated by piezoceramic material attached to both sides. The flexures actuate a speaker cone that is attached to the end of the flexures. The transducer can act as a sensor or an actuator due to the nature of the piezoceramics. The sound absorbing transducer is modeled to couple to the first acoustic resonance of a six foot cylindrical cavity. The cavity acts as a simplified model of a launch vehicle payload fairing. Equations of motion are derived to model actuator motion and the acoustic impedance of the cavity. A state-space model of the system was derived for two cases: a collocated sensor/actuator pair exciting the tube and an external source exciting the tube with the transducer acting as an absorber. The transducer is designed to affect the first mode, however damping is noticed in the next acoustic resonance.
Analysis of the theoretical model indicated up to 70 percent reduction of the open-loop RMS values or a reduction of 10 dB. Experimental results with the optimized transducer produced a 35 percent reduction of the open-loop RMS value or 3.73 dB. The first acoustic resonance coupled well with the first structural mode of the transducer providing optimal noise suppression for the first mode. Damping was also noted in the second acoustic mode. Neglecting the inertia of the tip mass introduced errors in the predictions of the transducer resonances at higher frequencies. This problem limited the ability to control the higher modes of the cavity.Master of Science
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Puri, Amrita. "Active control of noise in vibro-acoustic cavities." Thesis, IIT Delhi, 2019. http://eprint.iitd.ac.in:80//handle/2074/8063.
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Heckl, Maria Anna. "Heat sources in acoustic resonators." Thesis, University of Cambridge, 1985. https://www.repository.cam.ac.uk/handle/1810/250863.
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Cockcroft, Paul William. "Acoustic impedance measurement for underground surfaces." Thesis, University of Nottingham, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328412.
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Nicholson, Guy Charles. "The active control of acoustic impedance." Thesis, University of Salford, 1994. http://usir.salford.ac.uk/14778/.
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The application of an active control force on a thin-walled acoustic boundary can modify the motional dynamics, and so influence the impedance presented to incident waves. This impedance determines transmission of acoustic energy, reflection of acoustic waves from the boundary and absorption of incident energy. This thesis studies control systems that generate control forces for the active control of surface acoustic impedance. The proposed systems rely on measurement of the acoustic pressure and surface velocity of the boundary. The systems can use adaptive digital signal processing, which offers significant advantages over non-adaptive techniques. The active control of the specific acoustic impedance of a loudspeaker that terminates a waveguide for axially propagating plane waves provides a motivating problem. Theoretical analysis establishes the control of specific acoustic impedance of a simple compliantly-suspended piston by a control force. Operational constraints of a physical piston define theoretical operating limits for controlled specific acoustic impedances. The control systems use either feedback or feed-forward techniques for which theoretical treatment reveals restrictions on the range of controlled specific acoustic impedance. A novel result is that conventional implementations of the control systems can be unstable for certain desired impedances unless feedback cancellation is used. Digital feedback techniques are less effective for broader frequency bandwidth where feed-forward techniques may work. Theoretical analysis produces solutions that confirm the feasibility of these control techniques for the active control of specific acoustic impedance. Potential errors in the implementation of the systems have predictable effects on the controlled specific acoustic impedance. Experimental results support the theoretical work presented in this thesis, demonstrating active control of specific acoustic impedance for normally incident acoustic plane waves. An adaptive digital feed-forward control system creates desired specific acoustic impedances for band-limited noise and transient signals.
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Uzoegbo, Herbert Chidozie. "Propagation of acoustic waves in concrete." Thesis, King's College London (University of London), 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321500.
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Harvey, Alan Paul. "Nonlinear surface acoustic waves and applications." Thesis, University of Southampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.255827.
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Hiller, Steven Mark. "Automatic acoustic analysis of waveform perturbations." Thesis, University of Edinburgh, 1985. http://hdl.handle.net/1842/18962.
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Filyayev, Anton A. "Noise Source Evaluation of Misalignment and Elastomeric Couplings using Nearfield Acoustic Holography." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1535373234815763.
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Woolfe, Katherine F. "Passive acoustic monitoring of the deep ocean using ambient noise." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53910.
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In the ocean, changes in the speed of sound can be related to changes in water temperature. By leveraging this relationship, acoustic methods – namely acoustic tomography- have been used to monitor temperature changes in the deep ocean for the purposes of providing inputs to climate change models. Traditionally, these acoustic methods involve loud, active sound sources which can be logistically challenging to operate and have been criticized for potentially disturbing marine animals. Therefore, this work demonstrates a passive acoustic method - previously only used in shallow water for short monitoring durations- that uses only recordings of low-frequency (1-40 Hz) ambient noise to continuously monitor variations in deep ocean temperature with an unprecedented degree of precision and temporal resolution. Numerical simulations were conducted to show the portions of the ocean that are monitored with this passive method. This work also provides recommendations (regarding sensor placement around the world) for future development of a global passive acoustic sensor network that makes use of distant noise sources (sea-ice or seismic sources) to extract meaningful information (whether temperature, currents, etc.) about the ocean. Finally, an optimization method is proposed to overcome one of the fundamental limitations of previous applications of this passive monitoring method: tracking oceanic fluctuations that occur over short time scales. Hence, the results of this study may assist in the development of more reliable climate models that include an enhanced understanding of the ocean’s role as a global heat sink. Finally, an optimization method was proposed to enhance the emergence rate of coherent arrivals from ambient noise correlations, thus allowing this passive monitoring method to track acoustic medium fluctuations on a shorter time scale. This optimization could also be used in other applications of noise-based passive monitoring in a rapidly fluctuating medium (seismic, structural health monitoring, biomedical, etc.).
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Robert, Rene Jean. "Measuring noise level reduction using an artificial noise source." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54480.
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Buildings located near airports may be subjected to significant noise levels due to aircraft flyovers. Aircraft noise is particularly annoying when compared to other traffic noises due to its intermittent nature. While noise control is typically performed at the source, sound insulation programs are in place to improve the acoustic performance of a residence affected by the flyovers. Noise Level Reduction (NLR) is a common metric used in the United States to determine whether a residence qualifies for such programs. Sound insulation programs are available to houses that have an indoor Day Night Average Sound Level (DNL) greater than 45 dBA. NLR is a single-number metric used to quantify the ability for a building or building element to reduce the transmission of external sound pressure levels generated by aircraft. In addition to determining whether a residence qualifies, NLR can be used to quantify the effectiveness of the modifications performed as a result of the sound insulation program. NLR measurements with a loudspeaker offer an alternative method to those performed with aircraft flyovers, offering flexibility to the consultants that perform these measurements in the field. The purpose of this research was to better understand and improve the loudspeaker test for measuring NLR, providing a resource to the aircraft noise industry. Testing was completed on a "test house" that was constructed on campus with construction methods typical of a mixed-humid climate. The angular dependency, repeatability, and reproducibility of NLR, among other factors, were evaluated with field measurements. Significant NLR variations were observed with changes in lateral and vertical angles of incidence.
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Cloutier, Martin André. "Optimal digital detection of acoustic signals in colored noise /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA305824.
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Thesis (M.S. in Electrical Engineering and M.S. in Engineering Acoustic) Naval Postgraduate School, December 1995.Thesis advisor(s): Hippenstiel, Ralph : Cristi, Roberto. "December 1995." DTIC Descriptor(s): Acoustic Detection, Acoustic Signals, Underwater Acoustics, Computer Programs, Surface Waves, Eigenvectors, White Noise, Theses, Turbulence, Power Spectra, Bubbles, Transducers, Spectral Energy Distribution, Acoustic Filters, Acoustic Absorption, Target Detection, Viscosity, Ambient Noise, Sea Water, Hydrodynamics, Sound Pressure, Machinery Noise. DTIC Indicator(s): Colored Noise, Matlab Computer Program. Author(s) subject terms: Detection, Ambient noise, Matrix decomposition, Colored noise. Includes bibliographical references. Also available online.
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Yan, Zheng. "Background noise cancellation for acoustic detection of manatee vocalizations." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0015634.
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Cloutier, Martin Andre. "Optimal digital detection of acoustic signals in colored noise." Thesis, Monterey, California. Naval Postgraduate School, 1995. http://hdl.handle.net/10945/31291.
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This thesis addresses optimal methods for the detection of acoustic signals corrupted by colored noise. In achieving this we provide a study of the characteristics of ambient noise in the ocean and the digital techniques which can be used in the process of detecting known acoustic signals which are corrupted by that noise. Various techniques are studied, in particular the use of matrix decomposition techniques applied to the correlation matrix or to a data matrix, and the matched filter for colored noise. Other methods such as the inverse filter, the differential operator, and the adaptive prediction-error filter will also be looked at for their whitening properties. The theoretical foundations of those techniques are presented as well as the application of each method to the problem. Simulations are conducted for each technique in order to provide quantified performance measurements supporting the use of each method.
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Alvarez-Tinoco, Antonio Mario. "Adaptive algorithms for the active attenuation of acoustic noise." Thesis, Heriot-Watt University, 1985. http://hdl.handle.net/10399/1607.
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Cheng, Yi. "Acoustic noise and vibration of brushless motors for fans." Thesis, University of Leicester, 2005. http://hdl.handle.net/2381/34751.
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An investigation on vibration and acoustic noise on brushless motors for fan or blower applications is presented, particularly concentrating on the vibration due to electromagnetic origin within the brushless electronically commutated motors. The flux switching motor is introduced as a relatively new class of reluctance machine, which retains the benefits of switched reluctance machines, but with simpler and cheaper power electronic converters. The novel work of this thesis is the introduction of two 8/4 flux switching motors with permanent magnets of internal rotor and external rotor configuration respectively, which are presented as alternatives for the brushless DC motor, and called the permanent magnet flux switching motor. The two new permanent magnet flux switching motors were able to show potential in reducing power consumption, reducing vibration and noise, and reducing the cost of the power electronic drive when compared with an existing commercial 3-phase brushless DC and induction motor. Investigation on the vibration and noise of the flux switching motor was also done by performing experiments, mechanical finite element analysis and algebraic frequency equation analysis. Algebraic frequency equations were implemented into the electromagnetic design environment, stressing the need and potential in having algebraic frequency equations to predict the mechanical resonant frequency of any shape of the electrical machine stator lamination in the electromagnetic design environment.
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Ma, Zhaokai. "Numerical investigation of slat noise attenuation using acoustic liners." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/66083/.
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Abstract Noise generated by high-lift devices such as slats on a wing is a major contributor to the overall airframe noise during the landing approach of a commercial aircraft. In this work the concept of attenuating slat noise using absorptive acoustic lin- ers in the slat/main element gap is explored using a time domain computational aeroacoustic (CAA) technique. The aims of the development and application of the computational method are to reveal the mechanism of the slat noise generation and demonstrate the feasibility of controlling the slat noise using acoustic liners. A model scale three-element high-lift airfoil comprising a main element, a leading edge slat and trailing edge °ap geometry is employed in the investigation. Numerical simulations are performed to investigate the generation and far ¯eld propagation of the slat noise. A numerical approach is developed that combines near ¯eld °ow computation with an integral radiation model to predict the far ¯eld acoustic signal. A time domain impedance boundary condition (TDIBC) is implemented to simulate the e®ect of the liner material directly. Both the high frequency tonal noise and low frequency broadband noise generated from the slat are investigated. For the high frequency tonal noise, an unsteady Reynolds-averaged Navier-Stokes (URANS) simulation using high-order spatial and temporal schemes for the wing without acoustic liners shows the presence of vortex shedding and associated high frequency acoustic sources behind the slat trailing edge. To evaluate the mitigating performance of liners on the generated noise and ¯nd an optimized liner impedance value, an exercise is conducted on a range of liner impedance values by solving the linearized Euler equations (LEE) for a modeled acoustic source located at the trailing edge of the slat to ¯nd a optimized one. Using the optimized impedance value, URANS computations for the wing with liner treatment are conducted. The results show that acoustic liners on the slat cove and on the main element can provide useful attenuation of the high frequency slat trailing edge noise. For the low frequency broadband noise, the noise sources are calculated by both the pseudo-laminar zonal method and the stochastic noise generation and radiation i (SNGR) approach. The pseudo-laminar zonal calculation is basically an URANS calculation with the two-equation shear stress transport (SST) · ¡ ! model to model the e®ect of turbulence and a region in the slat cove is set as laminar zone. In the SNGR approach broadband sources of noise are modeled using stochastic noise generation method from a numerical solution of the steady Reynolds-averaged Navier-Stokes (RANS) equations using the · ¡ ! closure and then the acoustic ¯eld is calculated by solving the acoustic perturbation equations (APE) using high- order spatial and temporal schemes. By comparing the results of pseudo-laminar method and that of SNGR approach, the SNGR method has been shown to be a potentially useful method to model the generation of broadband slat noise and to investigate the attenuation of slat gap acoustic liners, for which the interest is in changes of noise level rather than the absolute value. The broadband noise attenuation e®ect of the acoustic liner treatment is studied by applying a broadband TDIBC to the acoustic ¯eld obtained by the SNGR method. The far-¯eld directivity is obtained through an integral surface solution of Ffowcs Williams and Hawkings (FW-H) equation. Predictions for a non-optimized acoustic liner show a moderate amount of attenuation. To accurately simulate the broadband noise generation and radiation, a LES using a high-order spatial scheme and implicit temporal integration is conducted for the high-lift con¯guration with slat deployed and the calculated results show the characteristic of the unsteady °ow and the mechanisms of the broadband noise generation. The recorded noise sources are then used to drive the APE to simulate the noise propagation and the attenuation by acoustic liners. The source driven APE results agree well with that of LES in term of far ¯eld directivity and sound pressure level. Similar to the SNGR simulation, a moderate amount of attenuation is achieved by the acoustic liner treatment.
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Gonçalves, Da Silva Pinto Wagner José. "Modelling airframe noise : from aerodynamic topology to acoustic efficiency." Thesis, Poitiers, 2019. http://www.theses.fr/2019POIT2289.
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L’influence de la forme de cylindres longs sur leur rayonnement acoustique en écoulement est étudiée. Des simulations bidimensionnelles (2D) sont réalisées à bas nombre de Reynolds (Re=20-200), à l’aide du code de calcul direct (DNS) incompressible incompact3D au moyen d’une méthode de frontière immergée (IBM). Une formule dérivée de l’équation de Curle pour un cylindre compact permet la quantification de l’émission acoustique en 2D. En soufflerie anéchoïque, la signature acoustique d’une trentaine de géométries est mesurée, Re=4,000-53,000 ; l’anémométrie par fil chaud est utilisée pour la description des propriétés axiales de l’écoulement. L’avant corps et l’allongement (AR) sont les plus importantes propriétés géométriques tant pour l’écoulement que pour le rayonnement acoustique en 2D. Les géométries allongées sont généralement les plus silencieuses car les tourbillons sont moins intenses et repoussés vers l’aval et l’apparition de l’instationnarité est retardée. De leur côté, les résultats expérimentaux montrent que les géométries allongées sont les plus bruyantes, ce qui est à l’opposé des conclusions précédentes. Ceci est justifié par une augmentation significative de la cohérence de l’écoulement en envergure pour les AR les plus longs, presque complètement en phase, donc plus efficace acoustiquement. Globalement, cela implique que les géométries dont l’écoulement 2D est faiblement perturbé, marqué par un déclenchement plus tardif de l’instationnarité (Reynolds critique plus élevé), sont aussi plus organisées en 3D aux Re des mesures. La relation sous-jacente entre les transitions successives vers la turbulence nécessite une étude approfondieThe influence of the shape on the sound emission of cylindrical bluff-bodies is studied. Simulations are performed in two-dimensions (2D) at low-Reynolds number (Re=20-200), with the incompressible direct Navier-Stokes (DNS) solver incompact3D, using the Immersed Boundary Method (IBM) formalism; the acoustic emission is evaluated by a single formula derived from Curle’s equation for compact cylinders. In anechoic wind tunnel, the acoustic signature is measured for about 30 geometries, Re=4,000-53,000; hot-wire measurements of the spanwise flow characteristics are performed for a subset of the tested cylinders. The influence of both the shape of the upstream portion of the geometry and the breadth-to-height ratio (AR) are proved to be major features in terms of both the flow and its acoustic emission in 2D. By reducing the strength of the vortices and pushing them downstream and affecting the mechanics of the von Kármán instability (delaying the transition to unsteadiness), stretched shapes (with higher AR) are generally quieter. From the experiments, it is found that the geometries of biggest AR are the loudest, contraposing the results obtained in 2D. The disparity is justified by a significant increase of the spanwise coherence associated with the larger AR’s, practically fully-phased, thus more acoustically efficient. Globally, it is implied that geometries which have weakly perturbed flow in 2D, marked by a later transition to unsteadiness (larger critical Reynolds number), are also more organized in 3D, high-Reynolds number regimes. The underlying relationship between low and high-Reynolds number transitions must be further investigated
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Edwards, Colin. "Exposure to loud noise and risk of acoustic neuroma." The Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=osu1187004419.
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Reed, Veronica Arlene. "Natural and Experimental Noise Affects Acoustic Communication in Songbirds." DigitalCommons@CalPoly, 2021. https://digitalcommons.calpoly.edu/theses/2279.
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Background noise is ubiquitous and can impair acoustic communication and influence signaling behavior in animals. Despite evidence demonstrating myriad effects of anthropogenic noise on animal communication, precisely how natural background noise influences communication and behavior remains unclear. Yet, natural sources of background noise, such as rushing rivers or crashing ocean surf, share similar power spectra to sources of anthropogenic noise and can occur at high amplitudes, potentially masking acoustic signals.
To investigate the effects of water-generated noise on songbird behavior, we experimentally broadcast landscape-level playbacks of ocean surf and river noise in coastal California, USA, and riparian habitat in Idaho, USA, respectively. In Chapter 1, we conducted a conspecific playback experiment examining how territorial defense behaviors of lazuli buntings (Passerina amoena) and spotted towhees (Pipilo maculatus) vary in response to broadcast water noise. We also incorporated cicada noise from a serendipitous Okanagana spp. emergence as a biotic source influencing lazuli bunting behavior. Both species produce songs that share substantial spectral overlap with low-frequency, water-generated noise, and lazuli bunting song shares an additional high-frequency overlap with cicada calls. Thus, there is potential for background acoustic conditions to mask conspecific signals. We found that detection and discrimination of conspecific playback occurred more slowly for both species as sound level increased. Lazuli buntings also exhibited divergent flight behaviors in response to high- and low-frequency acoustic sources, both dependent and independent of sound level.
In Chapter 2, we investigated how amplitude and frequency of water-generated noise influences spectral and temporal song characteristics in six songbird species. We recorded individuals defending territories across 37 sites, with each site representing one of four acoustic environments: naturally quiet ‘controls’, naturally noisy ‘positive controls’ adjacent to the ocean or a whitewater river, ‘phantom’ playback sites with continuous broadcast of low-frequency water noise, and ‘shifted’ playback sites with continuous broadcast of high-frequency water noise. We predicted that all individuals exposed to ‘positive control’, ‘phantom’, or ‘shifted’ noise would adjust song structure, but the magnitude of signal modification would be larger in noisier locations and the type of modification would depend on the spectral profile of the acoustic environment. No two species altered songs in precisely the same way. However, song structure of all six species varied with amplitude and/or frequency of background noise.
Together our results demonstrate that natural noise can impair agonistic behaviors and influence vocal structure. These findings suggest that the natural acoustic environment shapes acoustic communication, highlighting natural soundscapes as an under-appreciated axis of the environment.
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AlMuhanna, Khalid A. "Acoustic modeshape inversion using deep water ambient noise measurements." Fairfax, VA : George Mason University, 2008. http://hdl.handle.net/1920/3214.
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Thesis (M.S.)--George Mason University, 2008.Vita: p. 69. Thesis director: Kathleen E. Wage. Submitted in partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering. Title from PDF t.p. (viewed Aug. 27, 2008). Includes bibliographical references (p. 67-68). Also issued in print.
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Rankle, Hugo Elias Camargo. "Acoustic prediction and noise control of a refrigeration compressor." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-09052009-040840/.
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