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Descripción
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| The scope of this thesis is to present the study of the aerovibroacoustic problem of a structure submitted to an acoustic test in a reverberant chamber. The developped work is focused on the two areas that comprise the problem: the structural response and the behaviour of the non-ideal fluid. As a start point, a brief introduction of the state of the art and the theory contents of the proposed problems is presented. The main objetive is to define the areas that need to be explored. In order to deep in the knowledge of the structural response two analitical methodologies are developped, one for the low frequency range and another for the middle frequency range. The first one consists on an evolution of a methodology for the low frequency range based on the coupling of FEM/BEM. The updated technique allows to obtain preciselly the load distribution within the structure as a secondary variable of the vibroacoustic problem. The second methodology faces up with the middle frequency range where components with different modal density are mixed. As a result of the study an hybrid model is obtained based on the combination of FEM/BEM tipe elements and SEA energetic elements. As an application exercise for both, the vibroacoustic analysis of a light-mass, flexible structure is completed. For instance, it corresponds to a deployable reflector of 2.4m diameter of 15.1kg, that presents a strong coupling with the fluid. The acoustic test data of this specimen is used for the validation of the presented methodologies. As stated, the methodology developped for the structural simulation in the low frequency range is an evolution of a previous technique. The procedure to obtain the strenght capability of the structure was based on equivalent quasi-static case of the acoustic load. The current method achieves to define the load distribution within the structure as a dynamic variable, taking into account the modal response. As a result, the evolution improves tha data quality and precision, moreover the knowledge of the structural behaviour is increased. As part of the method presented, the calibration exercise is developped covering all the i parameters nvolved in the analysis: ? Computation step and range of study ? Coupled flexible surfaces ? Structural damping ? Input load definition Tesis Doctoral: ABSTRACT__________________________________________________________ Finally, it has been achieved a methodology capable to simulate in a conservative way the vibroacoustic response of a reflector within a tolerance of ±3dB, for both RMS value and frequency response data. In comparison with the previous methology obtained through a static case, the improvements are remarkables. Due to the newness of the middle frequency range problem, the study presented corresponds to a preliminary phase where the initial hypothesis have been solved. A great work has been completed to define the hybrid model that best represents the vibroacoustic behaviour in this range. Very promising resutls have been obtained coming from the test data correlation of the acceleration response. Taking as an start point the modal response of the structure, two hybrid models have been developped. The one that best represent the vibroacoustic behaviour of the reflectors has been selected. It is described as follows: ? Dish modelled with Finite Elements ? Back structure composed by SEA elements, each section as a subsystem. ? Connection between the dish and back structure represented as dual punctual energy transmition paths. ? Acoustic load applied through Boundary element representation in the dish. From a quantitative perspective of the results achieved with the proposed methodology, it can be concluded, from the aplication exercise, that the methodlogy is capable to simulate within a tolerance of ±3dB the frequency response of the accelerometers in terms of PSD and in terms of RMS values, except puntual locations. | |
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Internacional
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ISBN
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Tipo de Tesis
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Doctoral |
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Calificación
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Sobresaliente cum laude |
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Fecha
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01/03/2011 |