Orientador: Jose Roberto de França Arruda / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-05T19:37:58Z (GMT). No. of bitstreams: 1 Nunes_Osmar_M.pdf: 3751336 bytes, checksum: 2fc3b9c3cc2af03451617cae482065d1 (MD5) Previous issue date: 2005 / Resumo: As características acústicas de compressores herméticos têm se tomado cada vez mais críticas no projeto destes equipamentos e as predições destas características ao longo do projeto, obrigatórias para a adequação deste produto às condições de consumo. Este trabalho apresenta um método de avaliação vibro-acústica de compressores herméticos através de modelos de elementos finitos. Para estas avaliações, forças harmônicas com amplitudes unitárias são aplicadas em pontos específicos da carcaça e os seus campos de pressão sonora resultantes são calculados sob condições anecóicas, sendo que, estas condições foram modeladas através de elementos infinitos acústicos. Através deste método, é possível obter numericamente a potência acústica irradiada por diferentes versões de projeto, compará-las, escolher a versão mais adequada e, se for o caso, obter informações para direcionar modificações em uma versão para a sua adequação aos níveis de potência sonora exigidos. O trabalho mostra as verificações executadas durante o processo de desenvolvimento desta metodologia como análise modal, análises de convergência e comparações de resultados numéricos com analíticos através de modelos de fontes omnidirecionais. Para a verificação de seu funcionamento, são apresentadas as análises vibro-acústicas numéricas de duas versões de compressor. Além disto, dois protótipos com características semelhantes aos modelos analisados foram testados em câmara reverberante para a obtenção de suas potências sonoras e a comparação com os resultados numéricos. Os resultados obtidos desta comparação mostraram boas correlações entre numérico e experimental e fornecem subsídios para avaliar o desempenho entre as diferentes versões de projeto / Abstract: The importance of the acoustic characteristics in design of hermetic compressors has increased along the years. As a consequence, to predict these characteristics in the design phase is mandatory for this product to meet the consumption requirements. This work presents a method for evaluating the vibration and acoustic characteristics of hermetic compressors through finite element models. To perform these evaluations, harmonic forces with unitary amplitudes are applied in specific locations of the compressor housing and their resulting acoustic pressure fields are ca1culated under anechoic conditions obtained through the acoustic infinite elements. By using this method, it is possible to numerically obtain the acoustic power level irradiated by different versions of design in order to compare them and to choose the most adequate version. With the use of this method it is also possible to obtain information to guide modifications in the design and suit it to desired acoustic power levels. This work presents the verifications performed during the development process of this methodology such as modal analysis, convergence analysis and comparisons between analytical and numerical results by using omnidirectional sources. To validate this methodology, the acoustic numerical analysis of two versions of compressor' s housing was presented. Furthermore, two prototypes similar to the models characteristics were submitted to tests in reverberant chamber for obtaining their acoustic power levels and compared with the numerical results. The obtained results of this comparison presented a satisfactory correlation between numerical and experimental results and provided relevant information to evaluate different design versions / Mestrado / Mecanica Computacional / Mestre em Engenharia Mecânica

Outdoor heating, ventilating, and air-conditioning (HVAC) units emit a significant amount of noise, which may lead to poor sound quality and a perceived low product quality. It is the job of the noise control engineer to reduce the undesired noise and improve the sound quality of the outdoor HVAC unit to decrease consumer annoyance. There is great interest in developing a detailed and accurate acoustic model of the outdoor HVAC unit so that the sound of the outdoor HVAC unit can be listened to before the unit is constructed. Having an acoustic model which can synthesize sounds allows the noise control engineer to evaluate and improve the sound quality of the outdoor HVAC unit during the design process, without the need for extensive prototyping. Acoustical holography methods will be used to identify and localize noise due to the fan, and other significant noise sources, to visualize the sound field. In the current study, an acoustic model is described which can be used to model the noise due to structural radiation and vortex shedding of the outdoor HVAC unit’s rotating fan blades, one of the top contributors to the unit’s overall noise level. This moving source model simulates the Doppler effect which occurs when the blade moves towards and away from a receiver. The results from this moving source model is shown for different source signals, including sinusoidal, bandpass random, repeating random, and sinusoidal with time-varying frequency source signals. The parameters of this moving source model will be optimized to reproduce the experimental results, including the power spectral densities, tonal power component, and auralizations.

Thesis (D.Tech.: Electronic Engineering)-Dept. of Electronic Engineering, Durban University of Technology, 2007 vii, 150 leaves / Detecting and minimising distortion in audio signals is an important aspect of sound engineering. Distortion of a signal passing through an audio system may be caused by a number of factors and it is necessary to detect these effects for optimal sound. The problem is of interest to users and operators of high quality audio equipment and transmission facilities. The objective of this thesis was the development of techniques for the blind identification of distortion in a high quality audio signal using digital signal processing techniques. The techniques developed are based on digital signal processing techniques and statistical analysis of a recorded audio signal, which is treated as a random, non-stationary signal.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2005. / Vehicle Noise, Vibration and Harshness (NVH) is now a more important component of the vehicle design process than ever. Road noise is one of the key criteria used by potential buyers (albeit subconsciously) to choose what they perceive as the best vehicle. Road rumble is a key concern for vehicle manufacturers. Light Utility Vehicles (LUVs) are especially sensitive to a low frequency booming noise due to the fundamental acoustic mode that exists in the vehicle cabin. An investigation into this booming noise in an LUV is documented. The noise is identified and quantified after which the source of the noise in the vehicle cabin is identified using NVH techniques such as Acoustic Modal Analysis (AMA), Experimental Modal Analysis (EMA) and Transfer Path Analysis (TPA). The cabin’s fundamental acoustic mode lay at 100 Hz. Finally the source of the vibrations in the vehicle leading to the booming noise in the cabin is identified, along with its transfer path to the cabin. Solutions for the specific vehicle’s booming noise are proposed, two of which are tested with some success. Solutions to the problems associated with the fundamental acoustic mode of LUVs are also proposed and discussed.

published_or_final_version / Urban Planning / Master / Master of Science in Urban Planning

published_or_final_version / abstract / Transport Policy and Planning / Master / Master of Arts in Transport Policy and Planning

<div>Bladeless fans are well known for their unique shape and efficient performance, which have a great impact on the fan industry. At present, there are few studies on the bladeless fan and the research on the improvement of fan design is a lack. Therefore, the study on the performance of the bladeless fan with different design is the main purpose of this thesis. </div><div>In the present study, a bladeless fan prototype is created and studied by numerical simulations. When characterizing the aerodynamic and aeroacoustic performances of the bladeless fan, the entire fan prototype, including wind channel, base, rotor and stator, is adopted; when investigating the influence of the wind channel's geometric parameters, only wind channel is considered in simulations. The influence of the slit width, the height of the cross-section, the slit location and the profile of the cross-section are studied. </div><div><br></div><div>It is found that the flow outside the bladeless fan consists of the air blown out from the wind channel and entrained from the back and side of the fan. The air entrained from the side is the main source of flow rate increase. As for the aeroacoustic performance, the rotor and stator inside the base are the predominated source of the noise generated by the bladeless fan. </div><div>The performances of the bladeless fan are very sensitive to the geometric details of the wind channel. The generated noise always increases as the wind strength improves. The slit width of the wind channel has the greatest impact. With the slit moves away from the leading edge, the wind produced by the bladeless fan becomes more powerful and the noise becomes louder. The cross-sectional height of 4cm has the best aerodynamic performance but the generated noise is a little larger than other designs. The profile of the cross-section shows insignificant influence on the performances. </div>

A poluição sonora urbana, em especial a gerada por motocicletas com escapamentos modificados, afeta indistintamente a saúde de toda população de diversas maneiras e tende a aumentar, ao contrário da emissão de gases, que vem se reduzindo ao longo dos anos. Com o objetivo de conter o ruído gerado pelo tráfego urbano, vários países desenvolvem procedimentos, leis e ações mitigatórias como barreiras acústicas e asfaltos fonoabsorventes, porém há grande quantidade de motocicletas, veículo tipicamente de alto potencial de incômodo e ruidoso, que circulam com sistemas de escapamento adulterados e emitem ainda mais excesso de ruído. A inspeção veicular é ferramenta importante no controle de emissões de gases poluentes de veículos em uso, mas falha em restringir aqueles que ultrapassam os limites legais de ruído e, somado a isto, há o agravante de o condutor submeter-se a poluição sonora que ele mesmo produz. A fiscalização de rua surge como alternativa de controle ambiental, mas algumas vezes é contestada por ser subjetiva ou por faltar uma metodologia simples, confiável e eficaz. Buscou-se então compreender a relação entre o aumento do nível sonoro da motocicleta com escapamento modificado ao circular no trânsito e a emissão sonora medida na condição de inspeção, o chamado ruído parado, para trazer subsídios à formação de métodos mais eficazes de fiscalização e controle. Para isto foram avaliadas motocicletas quanto à emissão de ruído em circulação e ruído parado e os resultados obtidos apontam que os escapamentos modificados possuem nível sonoro muito mais elevado que os originais, com forte correspondência entre os dois métodos de medição. Esta poluição sonora atinge de modo particularmente intenso os profissionais, motoboys, que modificam suas motocicletas, pois eles se submetem a todos os fatores que favorecem a perda auditiva por excesso de ruído. Outras questões surgiram em paralelo ao tema principal e foram brevemente avaliadas para se compor o quadro geral, como o nível sonoro de escapamentos não originais avaliados segundo os procedimentos de homologação, a contribuição que a motocicleta traz ao ruído urbano e que resultados estes trazem quanto ao torque e potência da motocicleta. Estes estudos indicaram que a motocicleta modificada contribui fortemente para a poluição sonora urbana, afetando principalmente o condutor e sem trazer ganhos efetivos em termos de potência e dirigibilidade. / The urban noise pollution, in particular the one produced for motorcycles with tampered exhaust systems, affects indistinctly the health of all people in many ways and tends to grow up, in opposite to gaseous emissions, that is getting down through years. With the goal of mitigate noise generated from urban traffic, many countries develop procedures, laws and actions as acoustic barrier and phono absorbent asphalt, but there are still a great amount of motorcycles, typically a high annoying and noisy vehicle, running with tampered mufflers and producing excessive noise. In use vehicle inspection is an important tool on gaseous emissions control but fails to restrain excessive noise, a problem that get worse up due the rider is subjects him/herself to the own sound pollution. Roadside control comes as an alternative but sometimes is rejected as subjective or due a lack of a simple, easy, trustable method. This research looks for the relationship between increased sound level of modified motorcycles in traffic and noise emission in inspection mode, also known as stationary noise, to bring subsidies to develop more efficient control methods. For this, it were evaluated motorcycles for traffic and stationary noise emission and the results point that modified exhaust systems have a very higher sound level than original mufflers, with strong relationship between these two measurement methods. This sound pollution affects in a very special mode the professionals, called in Brazil motoboys, which modify their motorcycles, because they subjected themselves to all factors for noise-induced hearing loss. Other questions come in parallel to the main focus and were briefly studied in order to compound the whole picture as sound level of replacement mufflers according homologation procedures, the motorcycle contribution to the urban sound pollution and the results for power and torque. These studies point to that modified motorcycles strongly contribute to urban noise, affecting especially the driver and with no effective gain in engine power and motorcycle handling.

O ruído excessivo é considerado problema de saúde pública devido ao seu impacto a saúde humana. Nas edificações residenciais, os ruídos emitidos por instalações hidrossanitárias são maioria nas reclamações dos usuários. Neste contexto, destaca-se a necessidade do controle acústico em edificações residenciais, em específico deste estudo, para o controle do ruído hidrossanitário em instalações prediais. A norma NBR 15575: 2013 estabelece parâmetros para que os ruídos gerados por instalações hidrossanitárias não produzam níveis de pressão sonora elevados no interior dos dormitórios. Os níveis elevados provocam uma percepção auditiva desagradável e podem gerar constrangimentos entre vizinhos, devido à falta de privacidade. O objetivo deste artigo é avaliar e comparar os resultados de possíveis soluções acústicas para mitigar os níveis de pressão sonora gerados pelas instalações hidrossanitárias prediais, devido o acionamento de descargas de vasos sanitários e abertura de torneiras. Foram realizadas medições de níveis de pressão sonora conforme a norma ISO 16032: 2004 adaptada para laboratório em câmara de ensaios acústicos hidrossanitários do Instituto de Pesquisas Tecnológicas (IPT) para nove amostras de envelopamento acústico. Os resultados técnicos encontrados através das grandezas LZeq,nT, LAeq,nT e LASmax,nT foram analisados e comparados para cada amostra medida no tubo envelopado e no tubo aparente. Para as amostras analisadas, a maioria das amostras apresenta ? L >= 20 dB no acionamento da descarga do vaso sanitário e ? L >= 10 dB para o ruído oriundo da abertura da torneira. Através da estimativa custo-benefício, verificou-se que a amostra C possui a melhor relação entre as amostras estimadas. / Excessive noise is considered a public health problem due to its impact on human health. In residential buildings, the noises emitted by hydrosanitary are the source of most complaints from users. In this context, we highlight the need for acoustic control in residential buildings, in the specific case of this work, for the control of hydrosanitary systems noise in building. The standard NBR 15575: 2013 establishes parameters for the noises generated by hydrosanitary systems do not produce highs sound pressure levels inside the bedroom. When these levels are high, they cause a nasty hearing perception and can generate constraints between neighbors, due to the lack of privacy. The goal of this dissertation is to evaluate and analyze the results of possible acoustic solutions to mitigate the sound pressure levels generated by hydrosanitary systems, due to the triggering of discharge activation of toilets and tap opening. For this, measurements of sound pressure levels as ISO 16032: 2004 adapted to laboratory in acoustic testing environment hydrosanitary Instituto de Pesquisas Tecnológicas (IPT) to nine samples. Evaluated and compared the technical results found through the variable, LZeq,nT, LAeq,nT e LASmax,nT, for each sample as the tube enveloped and apparent tube. The results for the samples analysed are satisfactory, since most samples reduce more than 20 dB for noise generated due to the discharge activation and 10 dB for noise from the tap opening. Through the cost-benefit analysis, it was found that the sample C has the best relation between estimated samples.

The goal of a speech enhancement algorithm is to remove noise and recover the original signal with as little distortion and residual noise as possible. Most successful real-time algorithms thereof have done in the frequency domain where the frequency amplitude of clean speech is estimated per short-time frame of the noisy signal. The state of-the-art short-time spectral amplitude estimator algorithms estimate the clean spectral amplitude in terms of the power spectral density (PSD) function of the noisy signal. The PSD has to be computed from a large ensemble of signal realizations. However, in practice, it may only be estimated from a finite-length sample of a single realization of the signal. Estimation errors introduced by these limitations deviate the solution from the optimal. Various spectral estimation techniques, many with added spectral smoothing, have been investigated for decades to reduce the estimation errors. These algorithms do not address significantly issue on quality of speech as perceived by a human. This dissertation presents analysis and techniques that offer spectral refinements toward speech enhancement. We present an analytical framework of the effect of spectral estimate variance on the performance of speech enhancement. We use the variance quality factor (VQF) as a quantitative measure of estimated spectra. We show that reducing the spectral estimator VQF reduces significantly the VQF of the enhanced speech. The Autoregressive Multitaper (ARMT) spectral estimate is proposed as a low VQF spectral estimator for use in speech enhancement algorithms. An innovative method of incorporating a speech production model using multiband excitation is also presented as a technique to emphasize the harmonic components of the glottal speech input. / The preconditioning of the noisy estimates by exploiting other avenues of information, such as pitch estimation and the speech production model, effectively increases the localized narrow-band signal-to noise ratio (SNR) of the noisy signal, which is subsequently denoised by the amplitude gain. Combined with voicing structure enhancement, the ARMT spectral estimate delivers enhanced speech with sound clarity desirable to human listeners. The resulting improvements in enhanced speech are observed to be significant with both Objective and Subjective measurement. / by Werayuth Charoenruengkit. / Vita. / Thesis (Ph.D.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.