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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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Wilson, Rhonda Joy. "Noise source cancellation in audio recordings." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417685.
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Huat, Peck Chye. "Location of wideband impulsive noise source." Thesis, University of Bath, 2002. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393796.
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Sasidharan, Nair Unnikrishnan. "Jet noise source localization and identification." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1482412964456451.
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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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Williams, Richard G. D. "Noise source identification on large generator units." Thesis, Heriot-Watt University, 1992. http://hdl.handle.net/10399/1423.
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Balaban, Murat. "Noise Source Identification And Adoption Of Proper Noise Control Strategies On Wheeled Tractors." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12611838/index.pdf.
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This thesis is aimed at identifying the noise sources of a wheeled tractor to reduce the noise levels below the legislative limits by controlling noise sources through proper methodologies.
The study focuses firstly on identifying the noise sources of a wheeled tractor by using proper noise source identification techniques. These techniques can be summarized as sound intensity measurements, sound power level determination studies and spectral analysis of the noise data acquired in the
tests. Simple sound intensity mapping techniques are used and the intensity contour maps are generated to identify the noise sources.
Most important and effective noise sources are identified and the critical noise sources are focused to apply appropriate noise control strategies not only at the prototype production stages but also at the early design stages.
Consequently, upon consideration of both structure-borne and flow-induced noise, the pass-by noise level and the operator&rsquo<br>s ear noise levels of the tractor are reduced by nearly 3 dB (A) through application of proper noise
control strategies.
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Braun, Michael E. "Sound source contributions for the prediction of vehicle pass-by noise." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/16322.
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Current European legislation aims to limit vehicle noise emissions since many people are exposed to road traffic noise in urban areas. Vehicle pass-by noise is measured according to the international standard ISO 362 in Europe. More recent investigations of urban traffic have led to the proposal of a revised ISO 362 which includes a constant-speed test in addition to the traditional accelerated test in order to determine the pass-by noise value. In order to meet the legal pass-by noise requirements, vehicle manufacturers and suppliers must analyse and quantify vehicle noise source characteristics during the development phase of the vehicle. In addition, predictive tools need to be available for the estimation of the final pass-by noise value. This thesis aims to contribute to the understanding of vehicle pass-by noise and of the characteristics of the vehicle noise sources contributing to pass-by noise. This is supported through an extensive literature review in which current pass-by noise prediction methods are reviewed as well. Furthermore, three vehicle noise sources are replicated experimentally under laboratory conditions. This involves an orifice noise source, represented by a specially designed loudspeaker on a moving trolley, shell noise, represented by a metal cylinder structure, and tyre cavity and sidewall noise, represented by an annular membrane mounted on a tyre-like structure. The experimentally determined directivity characteristics of the acoustically excited noise sources are utilised in the pass-by noise prediction method. The predictive results are validated against experimental measurements of the three vehicle-like noise sources made within an anechoic chamber.
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Clum, Craig M. "Highway traffic noise barrier overlap gap model." Ohio : Ohio University, 1997. http://www.ohiolink.edu/etd/view.cgi?ohiou1177442958.
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Yardibi, Tarik. "Source localization and power estimation in aeroacoustic noise measurements." [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0024868.
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Takano, Yasushi. "Noise source localization and acoustical propagation analysis of fluid induced noise at low Mach numbers." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136364.
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Wills, Garvin David. "Shallow water propagation from an embedded source." Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242242.
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Ozdur, Ibrahim Tuna. "Low noise, narrow optical linewidth semiconductor-based optical comb source and low noise RF signal generation." Doctoral diss., University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5009.
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Recently optical frequency combs and low noise RF tones are drawing increased attention due to applications in spectroscopy, metrology, arbitrary waveform generation, optical signal processing etc. This thesis focuses on the generation of low noise RF tones and stabilized optical frequency combs. The optical frequency combs are generated by a semiconductor based external cavity mode-locked laser with a high finesse intracavity etalon. In order to get the lowest noise and broadest bandwidth from the mode-locked laser, it is critical to know the free spectral range (FSR) of the etalon precisely. First the etalon FSR is measured by using the modified Pound-Drever-Hall (PDH) based method and obtained a resolution of 1 part in 106, which is 2 order of magnitude better than the standard PDH based method. After optimizing the cavity length, RF driving frequency and PDH cavity locking point, the mode-locked laser had an integrated timing jitter of 3 fs (1 Hz- 100 MHz) which is, to the best of our knowledge, the lowest jitter ever reported from a semiconductor based multigigahertz comb source. The mode-locked laser produces ~ 100 comb lines with 10 GHz spacing, a linewidth of ~500 Hz and 75 dB optical signal-to-noise ratio. The same system can also be driven as a regeneratively mode-locked laser with greatly improved noise performance. Another way of generating a low noise RF tone is using an opto-electronic oscillator which uses an optical cavity as a high Q element. Due to the harmonic nature of OEOs, a mode selection element is necessary. Standard OEOs use an RF filter having drawbacks such as broad pass band, high loss, and high thermal noise. In our work, a novel optoelectronic scheme which uses an optical filter (Fabry-Perot etalon) as the mode filter instead of an RF filter is demonstrated. This method has the advantage of having ultra-narrow filtering bandwidths ( ~ 10 kHz for a 10 GHz FSR and 10[super6] finesse) and an extremely low noise RF signal. Experimental demonstration of the proposed method resulted in a 5-10 dB decrease of the OEO noise compared to the conventional OEO setup. Also, by modifying the etalon-based OEO, and using single side band modulation, an optically tunable optoelectronic oscillator is achieved with 10-20 dB lower noise than dual side band modulation. Noise properties of the OEO as a function of optical frequency detuning is also analyzed theoretically and the results are in agreement with experimental results.
The thesis concludes with comments on future work and directions.<br>ID: 029808830; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 98-106).<br>Ph.D.<br>Doctorate<br>Optics and Photonics
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Debost, Sophie. "Valve seating impact as a source of valve train noise." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11780.
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Turkdogru, Nurkan. "Validity of the point source assumption of a rotor for farfield acoustic measurements with and without shielding." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37226.
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Measuring the farfield noise levels of full-scale rotor systems is not trivial and can be costly. Researchers prefer to perform small-scale experiments in the laboratory so that they can extrapolate the model scaled results to the larger scale. Typically Inverse Square Law (ISL) is used to extrapolate the sound pressure levels (SPL), obtained from model-scale experiments at relatively small distances to predict noise at much larger distances for larger scale systems. The assumption underlying this extrapolation is that the source itself can be treated as a point sound source. At what distance from a rotor system it can be treated as a point source has never been established. Likewise, many theoretical models of shielding by hard surfaces assume the source to be a point monopole source. If one is interested in shielding the noise of a rotor system by interposing a hard surface between the rotor and the observer, can the rotor system really be considered to be a monopole? If rotating noise sources are under consideration what is the effect of configuration and design parameters? Exploring the validity of point source assumption alluded to above for a rotor for farfield acoustic measurements with and without shielding form the backbone of the present work.
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Zavala, Paulo Alexandre Galarce. "Identificação de fontes aeroacústicas e fontes em movimento = Aeroacoustic source and moving source identification." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265357.
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Orientador: José Roberto de França Arruda<br>Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica<br>Made available in DSpace on 2018-08-20T09:40:59Z (GMT). No. of bitstreams: 1
Zavala_PauloAlexandreGalarce_D.pdf: 48986854 bytes, checksum: a4b9853c4e0f7957b591afad2a9d4974 (MD5)
Previous issue date: 2012<br>Resumo: Identificação de fontes acústicas é uma ferramenta de análise importante para as melhorias mecânicas necessárias para o atendimento de normas de ruído restritivas, em especial em duas áreas: engenharia de aeronaves e engenharia de veículos. Esses dois setores têm de cumprir com as normas de sobre-vôo de aeroportos e ruído de passagem, respectivamente. Este trabalho tem o objetivo de desenvolver um método de identificação para problemas de fontes aeroacústicas e fontes em movimento. O método baseado no beamforming inverso generalizado tem a vantagem de localizar fontes distribuídas e multipólos e é usado neste trabalho. A estratégia é a de se realizarem verificações em casos simples, com simulações e avaliações experimentais. No teste aeroacústico inicial, um cilindro sob fluxo subsônico, os eventos dominantes de ruído são analisados, e o centro do dipólo e sua orientação são identificados. No teste seguinte, duas-estruturas sob fluxo subsônico, o método híbrido e o mapeamento híbrido inverso generalizado, ambos propostos neste trabalho, permitem uma comparação direta dos níveis de mapeamento com os resultados de beamforming convencional, e uma atenuação das auto-potências da matriz de espectros cruzados é usada para melhorar a resolução. Na identificação de dipólos, uma grade 3D é usada, e a orientação do dipolo é identificada com um componente em direção à malha de microphones, o que é possível devido à utilização de um re-escalonamento da matriz de transferência. Avaliações de diretividade para as distribuições de dipólo são realizadas e comparadas com microfones de campo-distante. No terceiro caso aeroacústico, o aerofólio NACA-0012 sob fluxo subsônico, identificações de monopólos são comparados com resultados da literatura obtidos com o DAMAS2. Para os estudos de identificação de fonte em movimento, duas medições são realizadas: ruído de passagem de um veículo de passageiros, e ruído de passagem de caminhão. A de-Dopplerização baseada no centro da grade é adotada, e dois artifícios são desenvolvidos: uso de imagem de fonte na função de transferência; e compensação de foco para fonte de radiação não-esférica. A malha de microfones tem um arranjo especial para melhor resolução horizontal em frequências baixas. Mapeamentos com a contribuição no nível de ruído de passagem são utilizados nas verificações efetuadas de 50Hz a 7kHz, utilizando dois alto-falantes com radiação de ruído tonal e com ruído de banda larga. No final, o desempenho global do método beamforming inverso generalizado é discutido, apresentando suas vantagens, e.g. detecção de fonte multipólo, e suas desvantagens, e.g. sensibilidade a fontes estranhas<br>Abstract: Identification of acoustic sources is an important analysis tool for the mechanical design improvements required to compliance with restrictive noise regulations, specially on two areas: aircraft and vehicle engineering. These two industries have to comply with the airplane fly-over noise and vehicle pass-by noise limits, respectively. This thesis has the objective to develop an identification method for aeroacoustic and moving source problems. The method based on the generalized inverse beamforming has the advantage to locate distributed sources of multipole type of radiation and is used in this thesis. The strategy is to perform verifications on simple cases, with simulations and experimental assessments. On the aeroacoustic initial testing, with a cylinder under subsonic flow, peak noise events are analyzed, and the dipole center and orientation are identified. In the following test case, two-structures in subsonic flow, the Hybrid Method and the Hybrid Generalized Inverse Mapping, both proposed in this work, allow a direct comparison of mapping levels to the conventional beamforming results, and an attenuation of the auto-powers in the cross-spectral matrix is used to improve resolution. For dipole identification, a 3D grid is used, and its orientation is identified with a component towards array, which is possible due to the use of a transfer matrix re-scaling. Directivity assessments are performed for dipole distributions and compared to far-field microphones. In the third aeroacoustic case, NACA-0012 airfoil under subsonic flow, monopole identifications are compared to DAMAS2 results from the literature. On moving source identification, two measurements are performed: passenger vehicle pass-by noise; and truck pass-by noise test. The de-Dopplerization based on grid center is adopted, and two artifices are developed: image source in transfer function; and focus compensation for source non-spherical radiation. The microphone array has a special design for improved low frequency horizontal resolution. Pass-by noise level contribution mappings are used on verifications performed from 50Hz to 7kHz using two loudspeakers with tonal and broadband noise radiation. Finally, overall performance of the generalized inverse beamforming method is discussed, presenting its advantages, e.g. multipole source detection, and limitations, e.g. sensitivity to extraneous sources<br>Doutorado<br>Mecanica dos Sólidos e Projeto Mecanico<br>Doutor em Engenharia Mecânica
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Drouet, Julie. "Séparation des sources de bruit des moteurs Diesel : Application en hiérarchisation de source et qualité sonore." Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0053/document.
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Le spectrofiltre est un filtre de Wiener utilisé pour isoler le bruit de combustion du moteur Diesel. Ce filtre est déterminé pour chaque point de fonctionnement et nécessite un traitement important des données. Il est donc difficile de mener des études perceptives sur le bruit de combustion obtenu selon plusieurs réglages moteur. Afin de pallier à cet inconvénient, cette thèse a pour objectif de définir un filtre commun qui puisse synthétiser un bruit de combustion en tout point de fonctionnement. Pour cela, une étude perceptive a montré que la substitution du spectrofiltre conventionnel par un autre filtre de Wiener permet la synthèse d’un bruit de combustion. L’utilisation d’un spectrofiltre commun est donc possible. L’analyse modale expérimentale permet d’estimer le filtre de Wiener à partir de données caractéristiques de la structure du moteur. Après analyse sur un signal synthétique, la méthode ESPRIT apparait la plus appropriée, mais nécessite quelques optimisations pour être adaptée aux particularités des spectrofiltres. Les filtres de Wiener de plusieurs régimes sont estimés selon différentes conditions d’estimation, définies par le critère ESTER. Une évolution fictive de l’amortissement selon le régime moteur est observée, et rattachée au fenêtrage temporel effectué dans le calcul du spectrofiltre. Une expérience perceptive est ensuite menée pour identifier si le critère ESTER permet d’estimer des filtres assez précis pour synthétiser des bruits de combustion similaires aux bruits de combustion conventionnels. Les résultats amènent à concevoir le spectrofiltre obtenu au ralenti comme un bon filtre commun, tant d’un point de vue physique que perceptif<br>The spectrofilter is a Wiener filter used to extract combustion noise. This filter requires an important data processing and is determined in all operating conditions. Thus it is difficult to carry out perceptual studies on combustion noise from various motor adjustments. To overcome this drawback, this PhD dissertation aims to define a common filter which can synthesize a combustion noise in all operating conditions. For this, a perceptual study showed that the substitution of the conventional spectrofilter by another Wiener filter allows the synthesis of a combustion noise. The use of a common spectrofilter is thus possible. The experimental modal analysis allows to estimate the Wiener filter from characteristic data of the engine structure. After studying on a synthetic signal, the ESPRIT method seems to be the most appropriate, but requires some optimizations to be adapted to spectrofilter peculiarities. The Wiener filters of several running speeds are estimated in different estimating conditions, defined by the ESTER criterion. A fictitious damping evolution with the running speed is observed and linked to the temporal windowing applied on the spectrofilter computation. A perceptual experience is then carried out to identify if the ESTER criterion allows to estimate accurately filters to synthesize combustion noises similar to conventional combustion noises. The results lead to conceive the spectrofilter obtained in idling condition as a good common filter, as in a physical point of view that perception
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Preston, Giles Andrew. "Modelling sound source regions for the prediction of coaxial jet noise." Thesis, University of Southampton, 1995. https://eprints.soton.ac.uk/173779/.
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Badenhorst, Scott James. "Acceleration of the noise suppression component of the DUCHAMP source-finder." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/15507.
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The next-generation of radio interferometer arrays - the proposed Square Kilometre Array (SKA) and its precursor instruments, The Karoo Array Telescope (MeerKAT) and Australian Square Kilometre Path finder (ASKAP) - will produce radio observation survey data orders of magnitude larger than current sizes. The sheer size of the imaged data produced necessitates fully automated solutions to accurately locate and produce useful scientific data for radio sources which are (for the most part) partially hidden within inherently noisy radio observations (source extraction). Automated extraction solutions exist but are computationally expensive and do not yet scale to the performance required to process large data in practical time-frames. The DUCHAMP software package is one of the most accurate source extraction packages for general (source shape unknown) source finding. DUCHAMP's accuracy is primarily facilitated by the à trous wavelet reconstruction algorithm, a multi-scale smoothing algorithm which suppresses erratic observation noise. This algorithm is the most computationally expensive and memory intensive within DUCHAMP and consequently improvements to it greatly improve overall DUCHAMP performance. We present a high performance, multithreaded implementation of the à trous algorithm with a focus on 'desktop' computing hardware to enable standard researchers to do their own accelerated searches. Our solution consists of three main areas of improvement: single-core optimisation, multi-core parallelism and the efficient out-of-core computation of large data sets with memory management libraries. Efficient out-of-core computation (data partially stored on disk when primary memory resources are exceeded) of the à trous algorithm accounts for 'desktop' computing's limited fast memory resources by mitigating the performance bottleneck associated with frequent secondary storage access. Although this work focuses on 'desktop' hardware, the majority of the improvements developed are general enough to be used within other high performance computing models. Single-core optimisations improved algorithm accuracy by reducing rounding error and achieved a 4X serial performance increase which scales with the filter size used during reconstruction. Multithreading on a quad-core CPU further increased performance of the filtering operations within reconstruction to 22X (performance scaling approximately linear with increased CPU cores) and achieved 13X performance increase overall. All evaluated out-of-core memory management libraries performed poorly with parallelism. Single-threaded memory management partially mitigated the slow disk access bottleneck and achieved a 3.6X increase (uniform for all tested large data sets) for filtering operations and a 1.5X increase overall. Faster secondary storage solutions such as Solid State Drives or RAID arrays are required to process large survey data on 'desktop' hardware in practical time-frames.
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Aljets, Dirk. "Acoustic emission source location in composite aircraft structures using modal analysis." Thesis, University of South Wales, 2011. https://pure.southwales.ac.uk/en/studentthesis/acoustic-emission-source-location-in-composite-aircraft-structures-using-modal-analysis(6871e94b-6e94-4efd-b563-41b254ee27b4).html.
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The aim of this research work was to develop an Acoustic Emission (AE) source location method suitable for Structural Health Monitoring (SHM) of composite aircraft structures. Therefore useful key signal features and sensor configurations were identified and the proposed method was validated using both artificially generated AE as well as actual AE resulting from damage. Acoustic Emission is a phenomenon where waves are generated in stressed materials. These waves travel through the material and can be detected with suitable sensors on the surface of the structure. These stress waves are attributed to propagating damage inside the material and can be monitored while the structure is in service. This makes AE very suitable for SHM, in particular for aircraft structures. In recent years composite materials such as carbon fibre reinforced epoxy (CFRP) are increasingly being used for primary and secondary structures in aircraft. The anisotropic layup of CFRP can lead to different failure mechanisms such as delamination, matrix cracking or fibre breakage which affects the remaining life time of the structure to different extents. Accurate damage location is important for SHM systems to avoid further inspections and allows for a maintenance scheme which considers the severity of the damage, due to damage type, extent and location. This thesis presents a novel source location method which uses a small triangular AE sensor array. The method determines the origin of an AE wave by a combination of time of arrival and modal analysis. The small footprint of the array allows for a fast and easy installation in hard-to-reach areas. The possibility to locate damage outside and at a relatively far distance from the array could potentially reduce the overall number of sensors needed to monitor a structure. Important wave characteristics and wave propagation in particular in CFRP were investigated using AE simulated by an artificial source and actual damage in composite specimens.
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Latham, Michael. "Noise source location in the built environment, using a simple microphone array." Thesis, University of Plymouth, 1994. http://hdl.handle.net/10026.1/2876.
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An inadequate level of noise attenuation provided by a building element is frequently the result of a lack of completeness in the construction. This often invisible fault acts as a noise source in a room, so in order to undertake remedial work the source position must be found. Recently, near field noise intensity measurement has been the popular method for noise source location in buildings. This method of using intensity studies requires a grid of readings to be taken. An alternative method, the one used in this work, employs a different strategy. Here, the source location is identified by direction scanning of time delays at a number of microphones arranged in a regular three-dimensional array. A novel arrangement of seven microphones, in the shape of a wheel-brace, is used to measure the differences in time taken for the sound waves to travel from a source to the various microphones. The magnitudes of these time differences are combined and converted into the coordinates of the source, relative to an origin which is placed at the centre of the wheel-brace array. The mathematics for this conversion is derived and the errors in the experimental arrangement discussed. The use of this airay for the identification of faults in built structures is explored. A significant contribution is made to the knowledge of noise source location in buildings, since the microphone array is used to demonstrate the location of a noise source irrespective of the direction of the incoming noise. The use of computerised data collection is described for a budget system, where time was cheap, but equipment expensive. The accuracy of the technique would be improved considerably if state-of-the-art electronics were used to measure the lime differences. The feasibility, advantages and potential performance of a modem system, that could be assembled today, is described and discussed.
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Davies, John. "Studies of a novel low noise plasma source for atomic emission spectrometry." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/38279.
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Zhang, Dongbing. "Switching mode power supply noise source impedance measurement and EMI filter characterization." Thesis, Virginia Polytechnic Institute and State University, 1996. http://hdl.handle.net/10919/51922.
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The effectiveness of an EMI filter is closely related to the impedance of the noise source. Due to the time-varying nature of the noise source impedance of an offline power supply, the measurement of it cannot be done using conventional impedance measuring methods. Two new methods, the insertion loss method and the signal injection method, are proposed to perform such a measurement. The insertion loss method utilizes the EMI emission as a signal source and derives the source impedance by measuring the emission attenuation caused by an inserted impedance. The signal injection method injects a signal to the power supply and measures the response. The insertion loss method is verified experimentally both for common mode and differential mode, The signal injection method for common mode source impedance measurement is experimentally verified. That for differential mode source impedance measurement requires a faster equipment and is not fully verified.
An EMI filter is usually characterized in the manufacturer’s catalog by its attenuation in a standard system (50Ω source impedance and 50Ω load impedance). The effectiveness of the filter in a practical system may significantly deviate from the manufacturer’s data. To provide the users with practically useful information, a scheme to characterize the EMI filter, the impedance matrix approach is proposed. This approach takes parasitic effect into consideration and the parameters can be measured relatively easily. The approach is verified experimentally by applying a commercial EMI filter to a power supply and comparing the predicted attenuation with the measured one.<br>Master of Science
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Lindberg, Anders Sven Axel. "Airborne noise characterisation of a complex machine using a dummy source approach." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0082/document.
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La caractérisation des sources sonores dues aux vibrations est un défi dans le domaine du bruit et des vibrations. Dans cette thèse, une approche expérimentale pour caractériser la propagation du son d’une machine complexe a été étudiée. Pour caractériser de manière appropriée la source sonore placée dans un environnement quelconque, il a été indispensable de prendre en compte les phénomènes de rayonnement et de diffraction. Cela permet de prédire une pression acoustique. Une technique particulière, appelée source mannequin, a été développée pour répondre à cette problématique. Le mannequin est une enceinte fermée de taille similaire mais qui a une forme simplifiée par rapport à la machine complexe, et sert de modèle de diffraction sonore. Le mannequin est équipé d’une série de haut-parleurs alignés dans le prolongement de la surface de l’enceinte. La superposition du champ acoustique créé par chaque haut-parleur modélise le rayonnement acoustique de la machine complexe. Cette thèse introduit donc le concept de source mannequin et traite de trois problèmes émanant de la mise en pratique de celui-ci : (1) l’estimation du transfert d’impédance dans l’espace (fonction de Green), (2) les spécifications de l’enceinte et de la série de haut-parleurs, et (3) l’estimation des sources équivalentes en termes de débit volumique. L’approche est étudiée au travers de cas d’études expérimentaux et numériques<br>The characterisation of vibrating sound sources is a challenge in noise and vibration engineering. In this thesis, an experimental approach to the characterisation of air-borne sound from a complex machine is investigated. A proper characterisation has to account for both radiation and diffraction phenomena in order to describe the sound source when inserted into an arbitrary space which enables prediction of sound pressure. A particular technique — a dummy source — has been conceived to deal with this problem. The dummy is a closed cabinet of similar size but much simpler shape than the complex machine, and it serves as a model of sound diffraction. The dummy is equipped with a flush-mounted array of loudspeaker drivers. The superposition of sound fields created by the individual drivers models sound radiation of the complex machine. This thesis introduces the concept of a dummy source and discusses three problems that need to be addressed for its practical application: (1) estimation of the transfer impedance of the space (the Green’s function), (2) the specification of the cabinet and the driver array, and (3) the estimation of the equivalent source strengths in terms of volume velocity. The approach is investigated via experimental and numerical case studies
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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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Sadeghisorkhani, Hamzeh. "Analyses and Application of Ambient Seismic Noise in Sweden : Source, Interferometry, Tomography." Doctoral thesis, Uppsala universitet, Geofysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-320169.
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Ambient seismic noise from generation to its application for determination of sub-surface velocity structures is analyzed using continuous data recordings from the Swedish National Seismic Network (SNSN). The fundamental aim of the thesis is to investigate the applicability of precise velocity measurements from ambient noise data. In the ambient noise method, a form of interferometry, the seismic signal is constructed from long-term cross correlation of a random noise field. Anisotropy of the source distribution causes apparent time shifts (velocity bias) in the interferometric signals. The velocity bias can be important for the study area (Sweden) which has relatively small velocity variations. This work explores the entire data path, from investigating the noise-source distribution to a tomographic study of southern Sweden. A new method to invert for the azimuthal source distribution from cross-correlation envelopes is introduced. The method provides quantitative estimates of the azimuthal source distribution which can be used for detailed studies of source generation processes. An advantage of the method is that it uses few stations to constrain azimuthal source distributions. The results show that the source distribution is inhomogeneous, with sources concentrated along the western coast of Norway. This leads to an anisotropic noise field, especially for the secondary microseisms. The primary microseismic energy comes mainly from the northeast. The deduced azimuthal source distributions are used to study the level of expected bias invelocity estimates within the SNSN. The results indicate that the phase-velocity bias is less than 1% for most station pairs but can be larger for small values of the ratio of inter-station distance over wavelength. In addition, the nature of velocity bias due to a heterogeneous source field is investigated in terms of high and finite-frequency regimes. Graphical software for phase-velocity dispersion measurements based on new algorithms is presented and validated with synthetic data and by comparisons to other methods. The software is used for phase-velocity measurements, and deduced azimuthal source distributions are used for velocity-bias correction. Derived phase-velocity dispersion curves are used to construct two-dimensional velocity maps of southern Sweden at different periods based on travel-time tomography. The effect of the bias correction is investigated, and velocity maps are interpreted in comparison to previous geological and geophysical information.
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Fulford, Ross Anthony. "Structure-borne sound power and source characterisation in multi-point-connected systems." Thesis, University of Liverpool, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284262.
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Yoon, Seongho. "Reconstruction of acoustic source strength distributions and their interactions by inverse techniques." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264390.
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Uosukainen, Seppo. "JMC method applied to active control of sound : theoretical extensions and new source configurations /." Espoo [Finland] : Technical Research Centre of Finland, 1999. http://www.vtt.fi/inf/pdf/publications/1999/P386.pdf.
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Hursky, Paul. "Using ambient noise and sources of opportunity to estimate environment parameters and improve matched field source detection and localization /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2001. http://wwwlib.umi.com/cr/ucsd/fullcit?p3000404.
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Stout, Trevor Alden. "Vector Intensity and Holography-Based Acoustic Source Characterization of a Military Jet Aircraft." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/8120.
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The scientific community has employed multiple methods to analyze and describe the jet noise emanating from the turbulent exhaust flow from modern military aircraft engines, with the goal that better characterization of the sound radiation will improve noise reduction efforts. This thesis utilizes three different approaches to characterize the noise source region from a static F-22A Raptor. First, the energy flow field along planes near the aircraft and along an arc is measured using a multidimensional vector intensity probe. The resulting vector intensity maps give a clear indication of the directionality of the noise as a function of frequency at different engine conditions. A straightforward ray-tracing method show the utility of vector intensity measurements in source characterization by estimating the region from which the loudest portions of sound are emanating. Second, intensity reconstructions from near-field acoustical holography (NAH) provide an estimate of the three-dimensional radiated energy flow field. The sound field is shown to be dominated by mutually incoherent radiation lobes, which can be partially isolated by a partial decomposition method. Lastly, a wavepacket source model is optimized in light of amplitude-based NAH reconstructions near the jet axis. The wavepacket model successfully fits the NAH-reconstructed partial fields, especially at frequencies above 50 Hz, indicating that the source may be modeled by multiple wave packets at each frequency.
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Khatami, Iman. "Free-field inlet / outlet noise identification on aircraft engines using microphones array." Thèse, Université de Sherbrooke, 2014. http://hdl.handle.net/11143/7581.
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Abstract : This thesis considers the discrimination of inlet / exhaust noise of aero-engines in free-field static tests using far-field microphone arrays. Various techniques are compared for this problem, including classical beamforming (CB), regularized inverse method (Tikhonov regularization), LI - generalized inverse beamforming (LI-GIB), clean-PSF, clean-SC and two novel methods which are called hybrid method and clean-hybrid. The classical beamforming method is disadvantaged due to its need for a high number of measurement microphones in accordance with the requirements. Similarly, the inverse method is disadvantaged due to their need of having a priori source information. The classical Tikhonov regularization provides improvements in solution stability, however continues to be disadvantaged due to its requirement of imposing a stronger penalty for undetected source positions. Coherent and incoherent sources are resolved by LI-generalized inverse beamforming (L1-GIB). This algorithm can distinguish the multipole sources as well as the monopoles sources. However, source identification by LI-generalized inverse beamforming takes much time and requires a PC with high memory. The hybrid method is a new regularization method which involves the use of an a priori beamforming measurement to define a data-dependent discrete smoothing norm for the regularization of the inverse problem. Compared to the classical beamforming and the inverse modeling, the hybrid (beamforming regularization) approach provides improved source strength maps without substantial added complexity. Although the hybrid method rather solves the disadvantage of the former methods, the application of this method for identification of weaker sources in the presence of the strong sources isn't satisfactory. This can be explained by the large penalization being applied to the weaker source in the hybrid method, which results in underestimation of source strength for this source. To overcome this defect, the clean-SC method and the proposed clean-hybrid method, which is a combination of the hybrid method and the clean-SC, are applied. These methods remove the effect of the strong sources in source power maps to identify the weaker sources. The proposed methods which represent the main contribution of this thesis show promising results and opens new research avenues. Theoretical study of all approaches is performed for various sources and configurations of array. In order to validate the theoretical study, several laboratory experiments are conducted at Universito de Sherbrooke. The proposed methods have further been applied to the measured noise data from a Pratt & Whitney Canada turbo-fan engine and have been observed to provide better spatial resolution and solution robustness with a limited number of measurement microphones compared to the existing methods.<br>Résumé : La présente thèse étudie la discrimination du bruit d'entrée / de sortie des moteurs d'avion dans des tests statiques en champ libre en utilisant des antennes de microphones en champ lointain. Diverses techniques sont comparées pour ce problème, dont la formation de voie classique (CB), la méthode inverse régularisée (régularisation de Tikhonov), la formation de voies généralisée inverse (L1-GIB), Clean-PSF, Clean-SC et deux méthodes proposées qui s'appellent la méthode hybride et la méthode Clean-hybride. La méthode la formation de voie classique est désavantagée en raison de son besoin de nombreux microphones de mesure. De même, la méthode inverse est désavantagée en raison du besoin d'information a priori sur les sources. La régularisation Tikhonov classique fournit des améliorations dans. la stabilité de la solution; cependant elle reste désavantageuse en raison de son exigence d'imposer une pénalité plus forte pour des positions de source non détectées. Des sources cohérentes et incohérentes peuvent être résolues par la formation de voies généralisée inverse (L1-GIB). Cet algorithme peut identifier les sources multi- polaires aussi bien que les sources monopolaires. Cependant, l'identification de source par la formation de voies généralisée inverse prend beaucoup de temps et exige un ordinateur avec une capacité de mémoire élevée. La méthode hybride est une nouvelle méthode de régularisation qui implique l'utilisation d'un traitement par formation de voie a priori pour définir une norme discrète et dépendante des données pour la régularisation du problème inverse. En comparaison avec la formation de voie classique et la méthode inverse, l'approche hybride (régularisation par formation de voie) fournit des cartographies améliorées d'amplitudes de sources sans aucune complexité supplémentaire substantielle. Bien que la méthode hybride lève les limitations des méthodes classiques, l'application de cette méthode pour l'identification de sources de faible puissance en présence de sources de forte puissance n'est pas satisfaisante. On peut expliquer ceci par la plus grande pénalisation appliquée à la source plus faible dans la méthode hybride, qui aboutit à la sous-estimation de l'amplitude de cette source. Pour surmonter ce défaut, la méthode Clean-SC et la méthode Clean-hybrides proposée qui est une combinaison de la méthode hybride et de Clean-SC sont appliquées. Ces méthodes éliminent l'effet des sources fortes dans les cartographies de puissance de sources pour identifier les sources plus faibles. Les méthodes proposées qui représentent la contribution principale de cette thèse conduisent à des résultats fiables et ouvrent des nouvelles voies de recherche. L'étude théorique de toutes les approches est menée pour divers types de sources et de configurations microphoniques. Pour valider l'étude théorique, plusieurs expériences en laboratoire sont réalisées à Université de Sherbrooke. Les méthodes proposées ont été appliquées aux données de bruit mesurées d'une turbo-soufflante Pratt & Whitney Canada pour fournir une meilleure résolution spatiale des sources acoustique et une solution robuste avec un nombre limité des microphones de mesure comparé aux méthodes existantes.
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Krueger, David William. "Array-Based Characterization of Military Jet Aircraft Noise." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3676.
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Since the 1950s the jet aeroacoustics community has been involved in predicting and measuring the noise distribution in jets. In this work, cylindrical and planar Fourier near-field acoustical holography are used to investigate radiation from a full-scale, installed jet engine. Practical problems involving measurement aperture and the highly directional nature of the source are addressed. Insights from numerical simulations reveal usable reconstruction regions. A comparison of cylindrical and planar NAH for the respective measurement apertures shows cylindrical NAH outperforms planar NAH on reconstructions both towards and away from the source.
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ビン, ヘラ ラディン ヒルミ, and Hilmi Bin Hela Ladin. "Research of noise and vibration analysis for structures involving transfer path and sound source." Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12981849/?lang=0, 2016. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12981849/?lang=0.
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本論文は，従来よりも信頼性や効率が良く実用的に構造物の振動・騒音を低減することを目指して，実験および解析技術に対する新たなアプローチを確立することを目的としている．そのために，統計的エネルギー解析法と伝達経路解析法を統合することで，両者の入力を相互利用可能な手法を提案し，構造物の振動・騒音の低減を支援するための，実験および解析手法を構築した．<br>In this thesis, we have established new theoretical approaches as well as some basic practical applications in the development of noise and vibration analysis for structures involving transfer path and sound source from airborne noise and structure-borne noise. These new approaches were extracted from the existing experimental and analysis technique of noise and vibration for structures, which will improve their efficiency and reliability for noise and vibration reduction on industrial machineries as well as other machines.<br>博士(工学)<br>Doctor of Philosophy in Engineering<br>同志社大学<br>Doshisha University
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Wass, Peter James. "The charged particle space environment as a noise source for LISA and LISA pathfinder." Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439783.
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Dungan, Mary Elizabeth. "Development of a compact sound source for the active control of turbofan inlet noise /." This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-03302010-020615/.
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Duke, Connor R. "Optimization of control source and error sensor locations in free field active noise control /." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd2087.pdf.
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Schölling, Björn. "Binaural signal processing for source localization and noise reduction with applications to mobile robotics." Münster Verl.-Haus Monsenstein und Vannerdat, 2009. http://d-nb.info/994281242/04.
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Duke, Connor Raymond. "Optimization of Control Source and Error Sensor Locations in Free Field Active Noise Control." BYU ScholarsArchive, 2007. https://scholarsarchive.byu.edu/etd/1169.
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Previous work has shown that active noise control (ANC) can be applied to axial cooling fans. Optimization of the control source and error sensor placement is desired to maximize the attenuation using ANC. A genetic algorithm was developed to find the optimal placement of control sources for a given primary source. The optimal configuration of control sources around a single primary source was shown to be a linear arrangement of the sources. This holds true for both two-dimensional as well as three-dimensional configurations. The higher-order radiation of the linear arrangement has also been verified experimentally, but the improvement in the experimental apparatus was not as dramatic as the theoretical model. Multiple flow visualization techniques have been used to find optimal near field error sensor locations. When there is little obstruction to the flow field of the fan, minimal airflow is found along the near field null that is created by minimizing the sound power of the system. Surface mounting of the error sensors can lead to a small increase in the signal-to-noise ratio of the error sensors if vortices exist in the near field of the fan due to obstructions in the main flow. It has also been shown that the introduction of the ANC system does not affect the flow field of the fan.
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Dungan, Mary E. "Development of a compact sound source for the active control of turbofan inlet noise." Thesis, Virginia Tech, 1992. http://hdl.handle.net/10919/41872.
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The concept of a compact sound source driven by piezoactuators is experimentally investigated, and analytical design tools are developed. The sound source, consisting of a thin, cylindrically curved aluminum panel and a pair of collocated, surface-bonded piezoceramic actuators, was developed with the objective of employing it as a secondary sound source in the active control of turbofan bladeinteraction inlet noise.
The sound source was fitted in an experimental duct representative of an aircraft engine inlet, and the interior and exterior sound pressure levels generated by the source were measured. The effects of excitation voltage, excitation frequency, duct length, and downstream termination of the duct were investigated. It was found that the source is capable of generating relatively high acoustic levels at its fundamental frequency (over 130 dB at maximum voltage input).
Techniques for analytically predicting the acoustic levels are investigated. A commercial code for numerical modelling of structural - acoustic radiation was utilized. Results show generally good agreement with experimental measurements for the case of the short duct. It is believed that the model accuracy can be further improved through additional refinements in the modelling techniques.<br>Master of Science
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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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Basu, Somayan. "Acoustic Source Characterization of a Road." Thesis, KTH, Skolan för teknikvetenskap (SCI), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-290036.
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A road can be considered as a noise source based on its traffic density. Intuition says, a road, with closely spaced vehicles, can be classified as a line source and for sparsely spaced vehicles, a collection of point sources. This study deals with the classification of a stretch of highway into either a line source or a collection of point sources based on the sound pressure measured by 7 microphones placed at certain distances from the highway and on the law of attenuation applicable. The results indicate a strong dependence of source classification with the traffic density.<br>En väg kan betraktas som en bullerkälla baserat på dess trafikintensitet. Intuitivt bör en väg med hög trafikintensitet klassificeras som en linjekälla och för få fordon en samling punktkällor. Denna studie handlar om klassificeringen av en motorvägssträcka till antingen en linjekälla eller en samling punktkällor baserat på ljudtrycket uppmätt med sju mikrofoner placerade på varierande avstånd från motorvägen. Resultaten visar att källklassificeringen är beroende av trafiktätheten och av avståndet till vägen.
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Hajipour, Sardouie Sepideh. "Signal subspace identification for epileptic source localization from electroencephalographic data." Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S185/document.
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Lorsque l'on enregistre l'activité cérébrale en électroencéphalographie (EEG) de surface, le signal d'intérêt est fréquemment bruité par des activités différentes provenant de différentes sources de bruit telles que l'activité musculaire. Le débruitage de l'EEG est donc une étape de pré-traitement important dans certaines applications, telles que la localisation de source. Dans cette thèse, nous proposons six méthodes permettant la suppression du bruit de signaux EEG dans le cas particulier des activités enregistrées chez les patients épileptiques soit en période intercritique (pointes) soit en période critique (décharges). Les deux premières méthodes, qui sont fondées sur la décomposition généralisée en valeurs propres (GEVD) et sur le débruitage par séparation de sources (DSS), sont utilisées pour débruiter des signaux EEG épileptiques intercritiques. Pour extraire l'information a priori requise par GEVD et DSS, nous proposons une série d'étapes de prétraitement, comprenant la détection de pointes, l'extraction du support des pointes et le regroupement des pointes impliquées dans chaque source d'intérêt. Deux autres méthodes, appelées Temps Fréquence (TF) -GEVD et TF-DSS, sont également proposées afin de débruiter les signaux EEG critiques. Dans ce cas on extrait la signature temps-fréquence de la décharge critique par la méthode d'analyse de corrélation canonique. Nous proposons également une méthode d'Analyse en Composantes Indépendantes (ICA), appelé JDICA, basée sur une stratégie d'optimisation de type Jacobi. De plus, nous proposons un nouvel algorithme direct de décomposition canonique polyadique (CP), appelé SSD-CP, pour calculer la décomposition CP de tableaux à valeurs complexes. L'algorithme proposé est basé sur la décomposition de Schur simultanée (SSD) de matrices particulières dérivées du tableau à traiter. Nous proposons également un nouvel algorithme pour calculer la SSD de plusieurs matrices à valeurs complexes. Les deux derniers algorithmes sont utilisés pour débruiter des données intercritiques et critiques. Nous évaluons la performance des méthodes proposées pour débruiter les signaux EEG (simulés ou réels) présentant des activités intercritiques et critiques épileptiques bruitées par des artéfacts musculaires. Dans le cas des données simulées, l'efficacité de chacune de ces méthodes est évaluée d'une part en calculant l'erreur quadratique moyenne normalisée entre les signaux originaux et débruités, et d'autre part en comparant les résultats de localisation de sources, obtenus à partir des signaux non bruités, bruités, et débruités. Pour les données intercritiques et critiques, nous présentons également quelques exemples sur données réelles enregistrées chez des patients souffrant d'épilepsie partielle<br>In the process of recording electrical activity of the brain, the signal of interest is usually contaminated with different activities arising from various sources of noise and artifact such as muscle activity. This renders denoising as an important preprocessing stage in some ElectroEncephaloGraphy (EEG) applications such as source localization. In this thesis, we propose six methods for noise cancelation of epileptic signals. The first two methods, which are based on Generalized EigenValue Decomposition (GEVD) and Denoising Source Separation (DSS) frameworks, are used to denoise interictal data. To extract a priori information required by GEVD and DSS, we propose a series of preprocessing stages including spike peak detection, extraction of exact time support of spikes and clustering of spikes involved in each source of interest. Two other methods, called Time Frequency (TF)-GEVD and TF-DSS, are also proposed in order to denoise ictal EEG signals for which the time-frequency signature is extracted using the Canonical Correlation Analysis method. We also propose a deflationary Independent Component Analysis (ICA) method, called JDICA, that is based on Jacobi-like iterations. Moreover, we propose a new direct algorithm, called SSD-CP, to compute the Canonical Polyadic (CP) decomposition of complex-valued multi-way arrays. The proposed algorithm is based on the Simultaneous Schur Decomposition (SSD) of particular matrices derived from the array to process. We also propose a new Jacobi-like algorithm to calculate the SSD of several complex-valued matrices. The last two algorithms are used to denoise both interictal and ictal data. We evaluate the performance of the proposed methods to denoise both simulated and real epileptic EEG data with interictal or ictal activity contaminated with muscular activity. In the case of simulated data, the effectiveness of the proposed algorithms is evaluated in terms of Relative Root Mean Square Error between the original noise-free signals and the denoised ones, number of required ops and the location of the original and denoised epileptic sources. For both interictal and ictal data, we present some examples on real data recorded in patients with a drug-resistant partial epilepsy
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Fridlund, Julia. "Processing of Noisy Controlled Source Audio Magnetotelluric (CSAMT) Data." Thesis, Uppsala universitet, Geofysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-396255.
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Controlled Source Audio Magnetotellurics (CSAMT) is a geophysical method for characterizing the resistivity of the subsurface with the help of electromagnetic waves. The method is used for various purposes, such as geothermal- and hydrocarbon exploration, mineral prospecting and for investigation of groundwater resources. Electromagnetic fields are created by running an alternating current in a grounded electric dipole and by varying the frequency, different depths can be targeted. Orthogonal components of the electromagnetic fields are measured at receiver stations a few kilometers away from the source. From these field components, so called magnetotellurics transfer functions are estimated, which can be used to invert for the resistivity of the subsurface. The data used in this project is from a survey conducted in 2014 and 2016 in Kiruna by Uppsala University and the mining company LKAB. Measurements were made at 31 stations along two orthogonal profiles. The data have been processed earlier, but due to noise, especially in the lower frequencies, a significant part of the data set could not be inverted. The aim of this project was to improve the results by analyzing the data and testing different methods to remove noise. First, robust regression was used to account for possible non-Gaussian noise in the estimation of the magnetotelluric transfer functions. Except for one station on profile 1, the robust method did not improve the results, which suggests that the noise is mostly Gaussian. Then modified versions of least squares, each affected by a different bias, were used to estimate the transfer functions. Where there is more noise, the estimates should differ more due to their different biases. The estimates differed most for low frequencies and especially on the part of profile 2 that was measured in 2014. It was investigated whether the railway network could explain part of the low frequency noise. Measures were taken to reduce spectral leakage from the railway signal at 16 ⅔ Hz to the closest transmitter frequencies 14 Hz and 20 Hz, but no clear improvement was seen and more detailed studies need to be conducted to determine this matter. Finally, a method based on comparing the ratio of short-term and long-term averages was tested to remove transients in the measured time series of the electromagnetic field components. This proved difficult to implement due to the variability of the time series’ behavior between different stations, frequencies and field components. However, the method showed some potential for stations 9 and 10 on profile 1, and could probably be developed further to remove transients more efficiently and thus improve the data.<br>Magnetotellurik med kontrollerad källa (förkortat CSAMT på engelska) är en metod där elektromagnetiska fält används för att undersöka markens resistivitet. Resisitivitet är ett mått på hur bra eller dåligt marken leder elektriska strömmar. Metoden används till exempel för att mäta djupet till berggrunden, som oftast har högre resistivitet (sämre ledningsförmåga) än marken ovanför. Man kan också hitta metaller, så som guld och koppar, vilka har väldigt låg resistivitet (bra ledningsförmåga). Elektromagnetiska vågor skapas genom att man låter en växelström gå igenom en lång ledning. Vågorna färdas först genom luften och sen ner i marken. Hur djupt ner de når beror på växelströmmens frekvens; med låga frekvenser når vågorna djupare ner i marken än med höga. Under markytan inducerar de elektromagnetiska vågorna elektriska strömmar, så kallade telluriska strömmar (dvs. jordströmmar). Strömmarna blir svagare ju längre de färdas och hur snabbt de avtar i styrka beror på jordens resistivitet. Strömmarna skapar också nya elektriska och magnetiska fält som färdas tillbaka mot ytan. Vid markytan mäter man fältens styrka för olika frekveser, vilket då ger information om resistiviteten på olika djup. Från mätningarna tar man ofta fram så kallade magnetotelluriska överföringsfunktioner. Dessa överföringsfunktioner gör det lättare att tolka datan och ta reda på resistiviteten hos marken. I detta projekt har CSAMT-data använts från en undersökning i Kiruna som genomfördes av Uppsala Universitet och gruvföretaget LKAB. Datan har bearbetats tidigare, men på grund av mycket brus i mätningarna blev inte resultatet så bra som väntat. Brus kan komma från allt som genererar elektromagnetiska fält, till exempel elledningar, tågledningar eller naturliga variationer i jordens egna magnetfält. Målet med projektet var att förbättra resultatet genom att analysera datan och testa olika metoder för att ta bort brus. Den vanligaste metoden för att beräkna överföringsfunktionerna antar att det magnetiska fältet är fritt från brus. Detta är inte nödvändigtvis sant och kan leda till bias, alltså ett snedvridet resultat. Andra sätt att beräkna överföringsfunktionerna på ger olika bias. Det här kan man utnyttja för att se hur mycket brus som finns i datan. Om det inte finns något brus alls så blir alla överföringsfunktioner lika, medan om det finns mycket brus så skiljer de sig mer åt. På detta sätt upptäcktes att det var mer brus för frekvenserna 14 och 20 Hz (där 1 Hz är 1 svängning per sekund). En förklaring till det kan vara att tågledningar, som genererar elektromagnetiska fält med 16.67 Hz, ligger nära i frekvens och stör dessa signaler. För att minska brusets påverkan testades så kallad robust processering. Det innebär att man lägger mindre vikt vid de mätningar som tycks vara mycket annorlunda (alltså innehåller mer brus) från andra mätningar. Tyvärr så hjälpte inte denna strategi nämnvärt för att förbättra resultatet. Till sist tog vi fram en metod för att ta bort transienter, vilket är kortvarigt brus med hög intensitet. Transienter kan till exempel komma från åskblixtar, som ju är kortvariga elektriska urladdningar. Det visade sig dock att detta inte var helt enkelt, då det var svårt att se vad som var brus och vad som bara var naturliga variationer hos de elektromagnetiska fälten. Men i några fall kunde bruset urskiljas och därför verkar det troligt att fortsatt arbete med denna metod skulle kunna ge ännu bättre resultat.
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Fernandes, Roland Anthony Savio. "The effects of cultural noise on controlled source electromagnetic resonses of subsurface fractures in resistive terrain." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2751.
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Erkoca, Arif Emre. "The Red Noise Power Density Estimation Techniques And Application To The Source Sax J2103.5+4545." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605069/index.pdf.
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In this thesis,red noise analysis techniques are presented. The necessity of the use of the window functions and the Deeter polynomial method in order to determine red noise is discussed. The method was applied to the source SAX J2103.5+4545 which showed a white torque noise with a relatively low noise strength due to its being a transient system.
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Cardon, Christopher Don. "1/f AM and PM noise in a common source heterojunction field effect transistor amplifier." Laramie, Wyo. : University of Wyoming, 2007. http://proquest.umi.com/pqdweb?did=1317343431&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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FRENZ, ERIC R. "NOISE SOURCE REDUCTION OF A HYDRAULIC ROAD SIMULATOR FOR USE AS A BSR EVAULATION PLATFORM." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1123792819.
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Valguarnera, Enrico. "Estrazione del Pattern Noise da video per un processo di identificazione di una fotocamera sorgente." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/17817/.
Full textAbstract:
Oggigiorno, devices digitali quali telefoni cellulari, smartphone, tablet e palmari sono diventati di uso comune e ancor di più costituiscono oggetti di utilizzo personale, rivelandosi ormai indispensabili. Tali devices posseggono un elevato numero di sensori, come la fotocamera, tramite i quali riusciamo ad ottenere numerose e rilevanti informazioni. Ogni giorno viene prodotta una quantità spropositata di dati digitali e proprio per questo motivo l’abuso dell’utilizzo di tali dati potrebbe comportare
danni irreparabili. Registrazioni illegali di proiezioni di film nei cinema hanno causato ingenti danni. Inoltre è possibile manipolare i contenuti digitali tramite tools che permettono di modificarne i metadati come ad esempio quelli presenti nell’header di un file video, quali brand e modello del dispositivo samrtphone, data, ora, etc. Modificando tali informazioni è facile compromettere contenuti digitali che potrebbero essere oggetto di prova di un processo giuridico. Dunque acquista maggiore importanza il ruolo dell’informatica forense alla quale spetta il compito di assicurare l’integrità dell’analisi di contenuti digitali. Si può quindi pensare di ottenere a partire da un’immagine o da un video, effettuando studi mirati, l’unicità di tale dato e sapere da quale sorgente è stato catturato. Quest’area di ricerca è conosciuta come source camera identification. L’elaborato si prefigge di analizzare un dataset di video, messo a disposizione dal dipartimento di Informatica dell’Università di Bologna, al fine di effettuare un procedimento di estrazione del rumore caratteristico tramite una tecnica di eliminazione del rumore, in modo da costruire un insieme di firme identificative.
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Nance, Donald Kirby. "Separating contributions of small-scale turbulence, large-scale turbulence, and core noise from far-field exhaust noise measurements." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19768.
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Thesis (Ph.D)--Aerospace Engineering, Georgia Institute of Technology, 2008.<br>Committee Chair: Ahuja, Krishan K.; Committee Member: Cunefare, Kenneth; Committee Member: Lieuwen, Tim C.; Committee Member: Mendoza, Jeff; Committee Member: Sankar, Lakshmi.