Numerical estimation of the absorption coefficient of flexible micro-perforated plates in an impedance tube

In this study, we numerically model a vibro-acoustic system consisting of a flexible micro-perforated plate (f-MPP) and an acoustic medium. Combined with a back-cavity, micro-perforated plates are considered as a promising noise control technology due to their tunable, wide-band sound absorption characteristics and robust performance. An MPP consists of a plate with uniformly distributed perforations whose diameters are in the order of a millimeter. These perforations are small enough to dissipate the acoustic perturbations due to the viscous effects caused by the presence of the Stokes layers. When the plate is rigid, the sound dissipation mechanism for a specific frequency bandwidth is determined by the perforation diameter, plate thickness, plate porosity and the back cavity depth. Yet, when the plate is flexible, additional absorption peaks, which cannot be determined by the parameters mentioned before, are observed in the measurements. This phenomenon is due to the vibro-acoustic coupling of the flexible plate and the acoustic medium. To model the vibro-acoustic system numerically, we couple two 3D cylindrical acoustic mediums, i.e. incident and back cavity regions, with a flexible plate consisting of shell elements. The perforations are separately located on the plate as independent transfer admittance elements with impedance values obtained from existing models. The system is disturbed with a plane wave excitation and the assessment of the model is done by comparing the calculated absorption coefficient with the experiment results from the literature. In the future, we plan to investigate the effect of perforation positions with the help of the model built in this study.status: publishe