Identification expérimentale de sources vibratoires par résolution du problème inverse modélisé par un opérateur éléments finis local

Abstract : The object of this thesis is the extension to complex structures of the RIFF method (Résolution Inverse Fenêtrée Filtrée). Considering a subpart of a structure, the main idea is to build a local Finite Element model using free boundary conditions. First, the general method was developed on beams. Vibration measurements are injected in the Finite Element model of the analysed part of the beam. Rotations are estimated using extra-displacement measurements and elementary shape functions. The method is highly sensitive towards errors present in measurements, so a regularisation had to be used. This one consists in a double inversion of the operator where a Tikhonov regularisation is applied when performing the second inversion. The regularisation parameter is tuned by the L-curve principle. Because of the smoothing effect of the Tikhonov procedure, moments cannot be reconstructed anymore at this stage, but they do still appear as sets of opposite forces. This setback led us to solve the problem by restricting it to forces only equations. At last, the study of the truncature of the domain was conducted in the aim to suppress coupling forces appearing at the limits of the studied area. Then, the case of plates was considered in order to increase progressively the models’ complexities. The Finite Element approach permitted us to implement dynamical condensation as well as Craig-Bampton reduction techniques. This allowed us to reduce the total number of degrees of freedom to be taken into account both from a numerical and an experimental standpoint. For example, dynamical condensation allows to eliminate rotations in the model. Besides, regularisation induces a lack of spatial resolution because of its smoothing effect. A spatial deconvolution technique was therefore developed; it is based on the Richardson-Lucy algorithm which is applied at a post-processing stage. At last, it was successfully proposed to extend the method to the application of detecting defaults present in the structure. The method was also validated on an industrial test bench in order to identify the forces applied by an oil pump taken from a truck’s engine. This phD thesis relied on numerical developments and the method was validated experimentally both in laboratory and industrial context. Main results provide a predictive tool to evaluate injected forces by vibration sources linked to a structure. It necessitates to inject vibratory displacements measurements into a Finite Element model.
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  • HAL Id : tel-00715820, version 2

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Cédric Renzi. Identification expérimentale de sources vibratoires par résolution du problème inverse modélisé par un opérateur éléments finis local. Autre. INSA de Lyon, 2011. Français. 〈NNT : 2011ISAL0146〉. 〈tel-00715820v2〉

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