NASTRAN modeling and analysis of rigid and flexible walled acoustic cavities

The acoustic slot elements, CSLOTi, are applied to analyze two-dimensional enclosures with fixed or moving boundaries. The capability utilized to compute (a) the acoustic natural modes and frequencies of a rigid walled enclosure and (b) the sound pressure at any point inside an enclosure when the surrounding walls are forced to vibrate. Applications to an automobile passenger compartment illustrate the technique. The axisymmetric fluid elements, CFLUIDi, are used in conjunction with a suitable choice of symmetry planes and a model of the surrounding structure to approximate a two-dimensional enclosure with flexible walls. The enclosure walls are modeled using finite elements or structural modes. Illustrative examples include a comparison of rectangular cavity modes with those calculated using the acoustic slot element and the free vibration modes of two enclosures coupled through a flexible rectangular panel

La théorie variation des rayons complexes pour le calcul des vibrations moyennes fréquences

A new approach named the "Variational Theory of Complex Rays" is introduced for computing the vibrations of elastic structures weakly damped in the medium frequency range. Emphasis has been placed here on the most fundamental aspects. The effective quantities (elastic energy, vibration intensity ...) are evaluated after computing a small system of equations which does not derive from a finite element dicretization of the structure. Numerical examples related to plates show the interest and the possibilities ofthe VTRC

The prediction of low- and mid-frequency internal road vehicle noise: a literature survey

Over the past 40 years the low- and mid-frequency internal noise of road vehiles has been of increasing interest to both manufacturers and customers, and there have been many papers written on the subject. It is particularly important that manufacturers are able to predict the noise at an early stage of a new design so that expensive mistakes can be avoided. This paper reviews the relevant literature published over this 40 year period and concludes that the finite element method (FEM), and/or the boundary element method (BEM) are currently the most accurate ways of predicting this noise. However, although the emphasis of this review is on the low- and mid-frequency structure-borne aspect of the noise, other prediction methods (which are normally considered to be only applicable at high frequencies) are also considered. In particular, the statistical energy analysis (SEA) is shown to be an increasingly useful tool for predicting structure-borne noise, as is the newly developed FEM/SEA hybrid method. Other essentially high-frequency techniques are also considered in this review because recent research indicates that it might be possible to apply these methods over a broader frequency range than was initially envisaged