CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / FAPEG - Fundação de Amparo à Pesquisa do Estado de Goiás / FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais / Compressores herméticos alternativos são objetos de estudos de vários pesquisadores na busca do entendimento e redução do ruído. A análise de componentes independentes apresenta-se como uma atrativa ferramenta na identificação das fontes, com pouca ou nenhuma informação sobre as fontes e como são misturadas. Inicia-se o estudo e compreensão da ferramenta, e utilizam-se sinais conhecidos para reconhecer o processo e suas características. Dentre as técnicas analisadas observa-se que sinais de característica impulsiva são melhores recuperados com técnicas no domínio do tempo, enquanto sinais com característica harmônica apresentam melhor identificação no domínio da frequência, ainda alguns algoritmos destacam-se frente a outros e a adição da fonte de ruído melhora o índice de performance. Ao aplicar a técnica nos compressores verifica-se limitação às baixas frequências, região onde a diferença de fase entre os sinais é mínima e há correlação na sincronização dos sinais. Constatam-se duas componentes identificadas: desbalanceamento na frequência de 60 Hz e pulsação do gás nas regiões próximas a 500 Hz, para as três pressões de alimentação analisadas, vazio, 20 e 60 psi, relata-se que a pulsação do gás é melhor identifica para a pressão mais alta, enquanto na menor pressão há dificuldades em relacionar as componentes recuperadas com a fonte. Por fim, aliado ao método de elementos finitos estimam-se as contribuições das fontes recuperadas no nível de potência sonora do compressor. / Reciprocating hermetic compressors have been studied in several research programs aiming to noise reduction and understanding. The analysis of independent components is an important tool to allow identification of noise sources even without better information about their origin or how they had been mixed. The first stage of the present study is the tool understanding using known signal in order to figure out how the process is performed and its characteristics. Among the analyzed techniques, it was possible to observe that impulsive signals had been better recovered by time-domain techniques, while the harmonic signals had been better recovered by frequency-domain techniques. In addition, some algorithm stood out than other ones and extra noise source have improved performance results. When applying those mentioned techniques on the compressors, a limitation has been noticed in lower frequencies, because there is no phase difference between the analyzed signals and there is some correlation in signals syncing. Two components can be clearly identified, which are unbalanced forces at 60 Hz and gas pulsation for frequencies close to 500 Hz. The system has been tested on three different pressure levels: without any charge, 20 psi, and 60 psi. It has been found out that the gas pulsation can be better identified for the highest pressure level , while there is less correlation between the component and the signal for the lowest pressure level. Finally, the power pressure level contributions of recovered sources are estimated by a finite element method. / Tese (Doutorado)

Noise emission is a major drawback of the positive displacement machine. The noise source can be divided into structure borne noise source (SBNS) and fluid borne noise source (FBNS). Passive techniques such as valve plate optimization have been used for noise reduction of axial piston machines. However, passive techniques are only effective for limited operating conditions or at least need compromises in design. In this paper, active vibration control of swash plate is investigated for vibration and noise reduction over a wide range of operating conditions as an additional method to passive noise reduction techniques. A 75cc pump has been modified for implementation of active vibration control using the swash plate. One tri-axial acceleration sensor and one angle sensor are installed on the swash plate and a high speed servovalve is used for the swash plate actuation. The multi-frequency two-weight least mean square (LMS) filter synthesizes the servovalve input signal to generate a destructive interference force which minimizes the swash plate vibration. An experimental test setup has been realized using Labview field-programmable gate array (FPGA) via cRIO. Simulation and experimental studies are conducted to investigate the possibility of active vibration control.

Dissertation thesis falls within area of indoor climate and deals with investigation of acoustic microclimate in sanitary rooms of residential buildings during a mechanical ventilation. Sources of a noise in these areas are small fans. The thesis contains the evaluation of the existing situation concerning the referred issue, physical laws of acoustics and theoretical basics of acoustics of air conditioning. The part of the thesis is experimental measurement which aims to evaluate the situation in real applications and the possibility of influencing the acoustic microclimate by affixing of small fans on the building structure. The work contains a model for the verification of certain anticipated dependencies and theoretical investigation of the distribution of sound pressure levels in the sanitary room, depending on the location of the noise source. The last part of the work offers possible measures to improve the acoustic microclimate and elimination of the noise in sanitary rooms and in protected areas of residential buildings.

No description available.

La caractérisation expérimentale de sources acoustiques est l'une des étapes essentielles pour la réduction des nuisances sonores produites par les machines industrielles. L'objectif de la thèse est de mettre au point une procédure complète visant à localiser et à quantifier des sources acoustiques stationnaires ou non sur un maillage surfacique par la rétro-propagation d'un champ de pression mesuré par un réseau de microphones. Ce problème inverse est délicat à résoudre puisqu'il est généralement mal-conditionné et sujet à de nombreuses sources d'erreurs. Dans ce contexte, il est capital de s'appuyer sur une description réaliste du modèle de propagation acoustique direct. Dans le domaine fréquentiel, la méthode des sources équivalentes a été adaptée au problème de l'imagerie acoustique dans le but d'estimer les fonctions de transfert entre les sources et l'antenne, en prenant en compte le phénomène de diffraction des ondes autour de l'objet d'intérêt. Dans le domaine temporel, la propagation est modélisée comme un produit de convolution entre la source et une réponse impulsionnelle décrite dans le domaine temps-nombre d'onde. Le caractère sous-déterminé du problème acoustique inverse implique d'utiliser toutes les connaissances a priori disponibles sur le champ sources. Il a donc semblé pertinent d'employer une approche bayésienne pour résoudre ce problème. Des informations a priori disponibles sur les sources acoustiques ont été mises en équation et il a été montré que la prise en compte de leur parcimonie spatiale ou de leur rayonnement omnidirectionnel pouvait améliorer significativement les résultats. Dans les hypothèses formulées, la solution du problème inverse s'écrit sous la forme régularisée de Tikhonov. Le paramètre de régularisation a été estimé par une approche bayésienne empirique. Sa supériorité par rapport aux méthodes communément utilisées dans la littérature a été démontrée au travers d'études numériques et expérimentales. En présence de fortes variabilités du rapport signal à bruit au cours du temps, il a été montré qu'il est nécessaire de mettre à jour sa valeur afin d'obtenir une solution satisfaisante. Finalement, l'introduction d'une variable manquante au problème reflétant la méconnaissance partielle du modèle de propagation a permis, sous certaines conditions, d'améliorer l'estimation de l'amplitude complexe des sources en présence d'erreurs de modèle. Les développements proposés ont permis de caractériser, in situ, la puissance acoustique rayonnée par composant d'un groupe motopropulseur automobile par la méthode de la focalisation bayésienne dans le cadre du projet Ecobex. Le champ acoustique cyclo-stationnaire généré par un ventilateur automobile a finalement été analysé par la méthode d'holographie acoustique de champ proche temps réel. / Experimental characterization of acoustic sources is one of the essential steps for reducing noise produced by industrial machinery. The aim of the thesis is to develop a complete procedure to localize and quantify both stationary and non-stationary sound sources radiating on a surface mesh by the back-propagation of a pressure field measured by a microphone array. The inverse problem is difficult to solve because it is generally ill-conditioned and subject to many sources of error. In this context, it is crucial to rely on a realistic description of the direct sound propagation model. In the frequency domain, the equivalent source method has been adapted to the acoustic imaging problem in order to estimate the transfer functions between the source and the antenna, taking into account the wave scattering. In the time domain, the propagation is modeled as a convolution product between the source and an impulse response described in the time-wavenumber domain. It seemed appropriate to use a Bayesian approach to use all the available knowledge about sources to solve this problem. A priori information available about the acoustic sources have been equated and it has been shown that taking into account their spatial sparsity or their omnidirectional radiation could significantly improve the results. In the assumptions made, the inverse problem solution is written in the regularized Tikhonov form. The regularization parameter has been estimated by an empirical Bayesian approach. Its superiority over methods commonly used in the literature has been demonstrated through numerical and experimental studies. In the presence of high variability of the signal to noise ratio over time, it has been shown that it is necessary to update its value to obtain a satisfactory solution. Finally, the introduction of a missing variable to the problem reflecting the partial ignorance of the propagation model could improve, under certain conditions, the estimation of the complex amplitude of the sources in the presence of model errors. The proposed developments have been applied to the estimation of the sound power emitted by an automotive power train using the Bayesian focusing method in the framework of the Ecobex project. The cyclo-stationary acoustic field generated by a fan motor was finally analyzed by the real-time near-field acoustic holography method.

The aim of the master’s thesis is the design of a new music club building in Valtice. The first part of the thesis is the architectural and structural design. The building of irregular rectangular shape with one underground floor and two above-ground floors is divided into two main operational units – a dance hall and a rock club. The chosen structural system is reinforced concrete columns with locally supported floors. The walls are made of sand-lime blocks. The main insulation material is hemp. The building is covered by a flat roof with extensive greenery. The second part deals with the building services. Ventilation, heating and cooling are provided by HVAC units. The heat source is condensing gas boilers, the cooling source is an outdoor VRV cooling unit. The third part of the master‘s thesis is the acoustic assessment of the building. As a noise source, it mainly addresses the acoustic impact on the surrounding buildings in the vicinity. Furthermore, it optimizes the reverberation time in the rock club. The project was produced in accordance with the legal regulations and technical standards and created in AutoCAD software.