Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 117-119). Also available via the Internet.

The study involves the development of a finite element model of a hermetic reciprocating compressor for noise prediction applications. Inherent difficulties in developing the finite element model of a complicated structure are discussed and appropriate modeling strategies are evolved. The development of the complete compressor finite element model is carried out in two stages - modeling of the compressor housing and the assembly of components into the compressor assembly. The compressor housing is isolated for detailed modeling. Geometry complexity, secondary masses, spring mounts, lap-joint and manufacturing variations pose challenges in developing a reliable model. Frequent comparisons are made with experimental mobility scans to obtain insights into the actual behavior of the modeled structure. When possible, weaknesses are located in the finite element model and corrected. After sufficient revisions, 23 natural frequencies (excluding the rigid body modes) are found for the compressor housing in the low frequency range (below 2000 Hz) of analysis. Forced response calculations are also used to correlate the analytical model and test data, with a maximum of 5% disagreement for the 14 natural frequencies that could be correlated. Compressor assembly modeling involves detailed solid modeling of internal components for inertia properties, developing reduced-degrees-of-freedom models of mounting springs and modeling of the shockloop. The dynamic behavior of the crankcase is investigated separate from the compressor assembly model. Finally, the components are assembled and the compressor assembly is solved for its natural frequencies by the component mode synthesis method. Eighty seven natural frequencies below 2000 Hz (excluding the rigid body modes) are found for the compressor assembly model. This model can be used to predict velocity responses on the surface of the housing, with the internally generated forces as excitations. Velocity response data are directly used in sound prediction. / Master of Science

Through the use of multiple-input/single-output (MISO) modeling, the propagation paths of sound within a reciprocating refrigeration compressor have been investigated and ranked. By investigating the nature of sound propagation within reciprocating compressors, it is hoped that compressor manufacturers can effectively formulate strategies for compressor sound reduction. From experimental data of compressor far-field sound output, suspension spring forces, and internal pressure fluctuations, a MISO model has been developed. From this model, the importance of the suspension system to the compressor far-field sound spectrum has been identified. In the frequency range above 800 Hz, forces passing through the suspension system appear to be the dominant contributor to shell excitation and sound radiation. Based upon this finding, it is recommended that modified suspension systems be considered as an avenue for compressor sound reduction efforts in the future. / Master of Science

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