Frédéric Ablitzer

Wall Pressure Identification by Using the Force Analysis Technique in Automotive, Naval and Aeronautic Applications

The aim of this research activity is to identify wall pressures which excite the structure, for automotive, aeronautic and naval domains, by using an inverse vibration method, such as FAT (Force Analysis Technique) and/or CFAT (Corrected Force Analysis Technique). The method is based on the local dynamic equilibrium equation of the structure, in which the partial derivatives are approximated by a finite difference scheme. Two schemes are proposed: the first (FAT method) consists in filtering the calculated force distribution by using an adequate spacing, but the associated wavenumber filtering presents a singularity at the flexural wavenumber of the structure, introducing an error around its value. The second uses a corrected finite difference scheme which acts as a complete low-pass wavenumber filter (CFAT method). In order to highlight the relevance of using both methods, results from simulations in the three industrial domains, automotive, aeronautic and naval are then presented where the comparison of FAT and CFAT results gives an interesting indicator to analyze the nature of the excitation. Moreover, for the naval application, a strategy for the identification of the strong fluid-structure coupling due to the pressure radiated by the structure is proposed. It is based on the identification of an effective wavenumber by using CFAT on a preliminary experiment where the structure immersed in the fluid is excited by a shaker. Finally, an experimental validation of the FAT/CFAT identification is shown for the car application. First, it is shown how both techniques identify very well the wall pressure on glass windows when the excitation is acoustic only (reverberant room). Second, the FAT/CFAT methods are applied to a car placed in a wind tunnel, where the analysis of results allows one to extract the whole acoustic component in a frequency range below the critical frequency of glass windows.