O espalhamento acústico por uma superfície continuamente diferenciável mas com tangente fractal, o chamado caso tipo III, primeiramente introduzido por Jakeman em [27] e [26], tem sido tratado computacionalmente para perturbações ásperas de superfícies planas e ilimitadas. O presente trabalho analisa teoricamente o espalhamento acústico de uma perturbação aleatória áspera de tipo III de um círculo, utilizando o método de campo nulo e aproximações assintóticas. Os resultados principais são: uma expressão assintótica de baixa ordem para a onda espalhada e o padrão de campo distante. Pela falta de artigos e livros tratando este tópico, o presente trabalho pretende servir como base para futuros trabalhos. / The acoustic scattering by continuously differentiable surface but with fractal tangent, the so-called type III case, first introduced by Jakeman in [27] and [26], has been treated computationally for rough perturbations of plane unbounded regions. The present work analises theorically the acoustic scattering of a random rough perturbation of type III of a circle, using the null field method and asymptotic techniques. The principal results are: an asymptotic expression of low order for the scattered wave and the far field pattern. Due to the lack of papers and books dealing with this topic the present work pretends to serve as a basis for future works.

Abstract The adaptive Helmholtz resonator for decreasing harmonic pulsating pressure in a low-pressure hydraulic system is presented in this study. Adaptivity is executed by both open loop and closed loop controls so that continuous -20dB attenuation of the peak-to-peak value of the amplitude of pressure is reached. The study begins by a theory review including the theory of effective bulk modulus, sound velocity measurements, adjustable dynamic vibration absorbers and control methods of dynamic vibration absorbers. The main target of the paper, the Helmholtz resonator, is presented in its own chapter, albeit it is noted to be one application of the dynamic vibration absorber. The review is completed by the analytical model of the hydraulic pipe with a T-filter or Helmholtz resonator. After the theory review, the test equipment and its characteristics are presented. The main parts of the test equipment were a main pipe and an adjustable Helmholtz resonator, which were both developed for this study. Certain properties of the hydraulic oils used were determined experimentally to increase understanding of the system. The experimental section includes sound velocity measurements, sonic bulk modulus definitions, measurements of the resonant frequencies of the adaptive Helmholtz resonator in the test equipment, and tests of the open loop and closed loop control of the resonator. Control is verified to maintain -20dB attenuating of pressure pulsations in the system. The presented Helmholtz resonator and controls are available for installation into a hydraulic system to damp out harmonic vibrations at low frequency. For example, the roll in the size press of a paper machine might become excited to vibrate at its resonance frequency after the paper wad has washed through the nip. In that case, tuned Helmholtz resonators in the hydraulic cylinders of the size press would damp out the pulsating pressures, and if the resonators are adaptive, as presented in this study, they can operate in a wider frequency range.

Orientador: João Bosco Ribeiro do Val / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica / Made available in DSpace on 2018-07-19T23:13:25Z (GMT). No. of bitstreams: 1 AndradeFilho_MarinhoGomesde_D.pdf: 3458768 bytes, checksum: 63b6d55d2e095590016b5052abebb37c (MD5) Previous issue date: 1995 / Resumo: Nesta Tese é proposta uma abordagem numérica para a classe de problemas de Dirichlet envolvendo a equação de Helmholtz. Esta abordagem mostra-se como uma generalização do método a diferenças finitas para esta classe de problemas. Os fundamentos teóricos do método que estamos propondo baseiam-se no Princípio do Máximo e no Teorema do Valor Médio. A implementação do algoritmo toma como base o Método Alternante de Schwarz o qual associado a um operador contrativo assegura a convergência do procedimento. O método proposto dá origem a um sistema de equações lineares com a mesma estrutura dos sistemas encontrados nos métodos a diferenças finitas, porém com a vantagem de se ter uma avaliação do limitante superior do erro de aproximação, em função do passo de discretização h, inferior ao obtido por diferenças finitas tanto para a rede quadrada quanto para a rede triangular. Além disso, o sistema de equações obtido tem a dominância da diagonal principal superior à do sistema obtido por diferenças finitas levando a uma melhoria da taxa de convergência quando métodos iterativos de solução são adotados. O método aqui apresentado resulta em uma expressão para o erro do tipo O( h") onde h é o passo de discretização e n = 4 quando estamos considerando a rede triangular, e n = 2 para a rede quadrada / Doutorado / Doutor em Engenharia Elétrica

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The work presented in this thesis can be divided into two main subjects. First, lightweight designs for acoustic devices such as Helmholtz resonators and loudspeakers used for noise control in rocket payload compartments are developed. Second, active control using a hybrid control system (with structural and acoustic actuators) was tested experimentally. Due to the weight limitations for this application, Helmholtz resonators and loudspeakers are re-designed in order to reduce the device weight as much as possible while maintaining performance. For Helmholtz resonators, this is done by modeling the resonator for different structural shapes, wall materials and wall thicknesses using a finite element analysis software. The final design is then compared to the rigid resonators and is shown to perform effectively. These designs are then successfully applied to the full-scale fairing at Boeing facilities. In order to design a lightweight loudspeaker, a comparative approach was used. A standard 12' loudspeaker is taken as the reference loudspeaker and weight reduction solutions are applied to it while maintaining performance. The loudspeaker is characterized using mechanical, electrical and acoustical theories, and an optimization process is applied in order to minimize a defined cost function, which was taken as the total sound pressure output over a targeted frequency range per mass of the actuator. The results are used to build a lightweight loudspeaker together with a lightweight box, and the new designs are tested for comparison with the reference loudspeaker and shown to increase performance by 1.7 dB over 60-200 Hz band while reducing the mass by 78%. The second part of this thesis investigates the performance of a hybrid active control treatment featuring distributed vibration absorbers (DAVAs) and loudspeakers applied on a scale payload fairing. Several aspects such as causality, reference signals, and maximum controllable levels of this feedforward control scheme are the subjects of analyses. The results show that this active control approach can achieve significant amount of interior noise attenuation, and the total actuator weight required to control an external level of 138 dB can be reduced to 9.2kg using lightweight loudspeakers. However, it is shown that the attenuation levels can still be improved further by actuator positioning that gives more effective coupling of the actuators with the structural and acoustic modes and by using multiple references for the control system. / Master of Science

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A new method called the Direct Method is developed to solve for the propagating modes in waveguides via the finite-element method. The variational form of the Direct method is derived to ensure that an extremum is reached. The Direct method uses Maxwell's equations directly, both zero and first-order, scalar and vector bases that are used in the finite-element formulation. The direct solution method solves for both the magnetic and electric fields simultaneously. Comparisons are made with the traditionally used vector-Helmholtz equation set. The advantages and disadvantages of the newly developed method is described as well as several results displayed using the WR-90 waveguide and a circular waveguide as test waveguides. Results include a partially filled dielectric loaded rectangular waveguide. The effects of including the divergence of the fields in the functional as penalty terms on the quality of results obtained by the Direct method and the vector-Helmholtz method is explored. The quality of results is gauged on the accuracy of the computed modes as well as the elimination or a significant reduction in the number of 'spurious modes' that are often encountered in solutions to waveguide problems. It is shown that computational time for the solution and computer storage requirements exceed the typically used Helmholtz equation method but the results obtained can be more accurate. Future work may include developing a sparse eigenvalue solution method that could reduce the solution time and storage requirements significantly. The Direct method of solution in dynamics resulted after an initial search in magnetostatics for methods to solve for the magnetic field without using the magnetic-vector potential using finite-element methods. A variational derivation that includes the boundary conditions is developed for the magnetic-vector potential method. Several techniques that were used to attempt accurate solutions for the magnetostatic fields with multiple materials and without the use of the magnetic-vector potential are described. It was found that some of the newly developed general techniques for magnetostatics are only accurate when homogeneous media are present. A method using two curl equations is developed which is a Direct method in magnetostatics and reveals the interaction between the bases used. The transition from magnetostatics to dynamics is made and similar Direct methods are applied to the waveguide problem using different bases. / Ph. D.

[pt] O objetivo principal deste trabalho é o desenvolvimento de modelos computacionais para analisar a resposta eletromagnética de ferramentas de perfilagem LWD/MWD em formações geofísicas arbitrárias. Essa modelagem envolve a determinação precisa de campos eletromagnéticos em regiões tridimensionais (3D) complexas e, conseqüentemente, a solução de sistemas lineares não-hermitianos de larga escala. A modelagem numérica é realizada através da aplicação do método dos volumes finitos (FVM) no domínio da freqüência. Desenvolvem-se dois modelos computacionais, o primeiro válido em regiões isotrópicas e o segundo considerando a presença de anisotropias no meio. As equações de Maxwell são resolvidas através de duas formulações distintas: formulação por campos e formulação por potenciais vetor e escalar. A discretização por volumes finitos utiliza um esquema de grades entrelaçadas em coordenadas cilíndricas para evitar erros de aproximação de escada da geometria da ferramenta. Os modelos desenvolvidos incorporam quatro técnicas numéricas para aumentar a eficiência computacional e a precisão do método. As formulações por campos e por potenciais vetor e escalar são comparadas em termos da taxa de convergência e do tempo de processamento em cenários tridimensionais. Os modelos foram validados e testados em cenários tridimensionais complexos, tais como: (i) poços horizontais ou direcionais; (ii) formações não homogêneas com invasões de fluído de perfuração; (iii) formações anisotrópicas e (iv) poços excêntricos. Motivado pela flexibilidade dos modelos e pelos resultados numéricos obtidos em diferentes cenários tridimensionais, estende-se a metodologia para analisar a resposta de ferramentas LWD que empregam antenas inclinadas em relação ao eixo da ferramenta. Tais ferramentas podem prover dados com sensibilidade azimutal, assim como estimativas da anisotropia da formação, auxiliando o geodirecionamento de poços direcionais e horizontais. / [en] The main objective of this work is to develop computational models to analyze electromagnetic logging-while-drilling tool response in arbitrary geophysical formations. This modeling requires the determination of electromagnetic fields in three- dimensional (3-D) complex regions and consequently, the solution of large scale non-hermitian systems. The numerical modeling is done by using Finite Volume Methods (FVM) in the frequency domain. Both isotropic and anisotropic models are developed. Maxwell's equations are solved by using both the field formulation and the coupled vector-scalar potentials formulation. The proposed FVM technique utilizes an edge-based staggered-grid scheme in cylindrical coordinates to avoid staircasing errors on the tool geometry. Four numerical techniques are incorporated in the models in order to increase the computational efficiency and the accuracy of the method. The field formulation and the coupled vector-scalar potentials formulation are compared in terms of their accuracy, convergence rate, and CPU time for three-dimensional environments. The models were validated and tested in 3-D complex environments, such as:(i) horizontal and directional boreholes; (ii) multilayered geophysical formations including mud-filtrate invasions; (iii) anisotropic formations and (iv)eccentric boreholes. The methodology is extended to analyze LWD tools that are constructed with the transmitters and/or receivers tilted with respect to the axis of the drill collar. Such tools can provide improved anisotropy measurements and azimuthal sensitivity to benefit geosteering.

Entre 1855 e 1862 o físico e fisiologista Hermann von Helmholtz dedicou-se primariamente a questões relativas à física e fisiologia acústicas, e à aplicação dos resultados obtidos à epistemologia da música e à estética musical. Ainda que tais investigações tenham sido desenvolvidas por período restrito, seus principais frutos cuja apresentação mais completa se encontra na obra de 1863 Die Lehre von den Tonempfindungen als physiologische Grundlage für die Theorie der Musik (que traduziríamos por A doutrina das sensações tonais como uma base fisiológica para a teoria da música) tiveram impacto imediato e duradouro sobre a musicologia ocidental. Em um primeiro momento, o presente trabalho objetiva analisar os antecedentes filosófico-científicos que orientaram tal empreitada, bem como a metodologia empregada na mesma; isso a fim de podermos, em um segundo momento, abordar criticamente a forma como Helmholtz aplica seus resultados ao âmbito da estética musical. Afinal, ao fixar deterministicamente causas físicas e fisiológicas para noções eurocêntricas de musicalidade, não estaria Helmholtz operando certa naturalização dos sistemas de organização tonal imperantes em sua conjuntura histórico-cultural em detrimento de sistemas oriundos de outros períodos e culturas, amiúde dotados de critérios distintos de ordenação sonora? O trabalho proposto ganha em complexidade na medida em que a musicologia de Helmholtz, particularmente em sua dimensão epistemológica, não se mostra inteiramente insensível a riscos dessa espécie. Assim, figura entre nossos objetivos avaliarmos em que medida tal musicologia, de grande rigor científico, é capaz de coexistir com sistemas musicais que escapem às diretrizes estéticas que busca naturalizar. Seríamos mesmo racionalmente compelidos a adotar, como parece tacitamente sugerir a obra de Helmholtz, uma espécie de hierarquia valorativa no que toca aos sistemas musicais de diferentes períodos e culturas? Dentre tais sistemas, seriam alguns verdadeiramente mais aptos que os demais em plasmar uma suposta musicalidade universal? Acreditamos que, por meio de investigação renovada do nó epistêmico presente na percepção musical na qual se veem entretecidas considerações de natureza física, fisiológica, psicológica e filosófica , algumas distinções possam ser esboçadas entre fatores determinantes necessários (físicos e fisiológicos e, portanto, transculturais) e contingentes (biográfico-culturais) da mesma, e o problema devidamente atacado. / In the second half of the nineteenth century, German physicist and physiologist Hermann von Helmholtz devoted himself to the investigation of questions pertaining to physical and physiological acoustics, and to the application of the results of said research to the epistemology of music and musical aesthetics. While such endeavors represent a relatively brief part of his career, the chief innovations they brought forth the most thorough presentation of which may be found in On the Sensations of Tone as a Physiological Basis for the Theory of Music (originally published in 1863) have had a lasting impact on the whole of Western musicology. An analysis of the philosophical and scientific foundations and methodological principles his investigations rested upon occupies the opening chapters of the present work. Subsequent chapters present, in addition, a critical assessment of the scientists problematic attempt to extend the reach of his results to the sphere of musical aesthetics. The following two questions are central to our efforts: by establishing material and physiological traits as an ultimate, deterministic ground for the criteria for sound classification and ordering prevalent in nineteenth-century European art music, was Helmholtz not arguing for the naturalization of the musical systems prevalent in his own historical and cultural juncture? And, should this indeed be the case, would such a naturalization not be accomplished to the detriment of musical systems employed in other cultures and/or historical periods, often based on distinct modes of classification and ordering? Ultimately, then, the central aim of the present work is to evaluate and discuss to what an extent the rigorous scientific component of a musicology such as Helmholtzs is able to coexist with musical systems that obey aesthetic principles other than the ones said musicology espouses. Are we indeed rationally compelled to adopt a value-based hierarchy in regards to the systems of different cultures and/or historical periods, as the scientists work appears to suggest? Are certain musical systems indeed more apt than others to actualize human musicality? We believe an investigation of the epistemic knot which characterizes musical perception a phenomenon in which physical, physiological, psychological and philosophical strands are intricately intertwined may allow us to advance a few preliminary distinctions between its necessary (physical and physiological, which is to say transcultural) and its contingent (cultural and biographical) determinants, and thus properly attack the problem.

No description available.