In this paper a FEM-BEM numerical methodology to simulate soundproofing effects generated by an engine\ud
beauty cover was developed. Indeed, the engine beauty cover is not only an aesthetic element but also accomplishes the\ud
specific function of soundproofing and thus it is important to calculate the noise attenuation it can provide. The\ud
methodology was implemented by using the commercial software Virtual Lab, produced by LMS: the indirect BEM\ud
(IBEM), with a variational solution algorithm, was adopted to assess the acoustic scenario whereas the dynamic structural\ud
analysis was performed by the Finite Element Method (FEM). A correlation with experimental data obtained in the Fiat\ud
Research Centre in Pomigliano d’Arco (Naples) was carried out to verify the efficacy of such a method. The procedure\ud
can be applied to any structural element of the same typology (not only of automotive type), with the aim to numerically\ud
determine its effectiveness in noise attenuation. The numerical and experimental Insertion Loss showed a satisfactory\ud
degree of correlation in all the range of frequencies of relevant importance in the automotive field
Abstract:In this work, a vibro-acoustic numerical and experimental analysis was carried out for the chain cover of a low powered four-cylinder four-stroke diesel engine, belonging to the FPT (FCA Power Train) family called SDE (Small Diesel Engine). By applying a methodology used in the acoustic optimization of new FPT engine components, firstly a finite element model (FEM) of the engine was defined, then a vibration analysis was performed for the whole engine (modal analysis), and finally a forced response analysis was developed for the only chain cover (separated from the overall engine). The boundary conditions applied to the chain cover were the accelerations experimentally measured by accelerometers located at the points of connection among chain cover, head cover, and crankcase. Subsequently, a boundary element (BE) model of the only chain cover was realized to determine the chain cover noise emission, starting from the previously calculated structural vibrations. The numerical vibro-acoustic outcomes were compared with those experimentally observed, obtaining a good correlation. All the information thus obtained allowed the identification of those critical areas, in terms of noise generation, in which to undertake necessary improvements.
In this work, the vibration behavior of a 4-cylinder, 4-stroke, petrol engine was simulated by leveraging on the Finite Element Method (FEM). A reduced modelling strategy based on the component mode synthesis (CMS) was adopted to reduce the size of the full FEM model of the engine. Frequency response function (FRF) analyses were used to identify the resonant frequencies and corresponding modes of the different FEM models, and the obtained results were compared with experimental data to get the model validation. Subsequently, modal-based frequency forced response analyses were performed to consider the loads acting during the real operating conditions of the engine. Finally, the impact on vibrations at the mounts, produced by an additional bracket connecting the engine block and gearbox, was also investigated. Both the full and reduced FEM model demonstrated and reproduced with high accuracy the vibration response at the engine mounts, providing a satisfactory agreement with the vibrations measured experimentally. The reduced modelling strategy required significantly shorter runtimes, which decreased from 24 h for the full FEM model to nearly 2 h for the reduced model.
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