El Hafidi A., Lay B., Plessy A.

The control of the vibratory and sound level inside the planes is a significant commercial argument, which has direct consequences on comfort, health and safety of the users. Systems SPADD® based on the damping brought by viscoelastic materials which work in shearing are passive systems used to reduce the vibratory levels. The objective of this presentation is to show, using numerical and experimental studies that this damping applied to the structure has an influence on the sound transmission (outside/inside), which makes it possible to increase the “noise reduction NR”. The experimental study is carried out on a model made up of a cylindrical shell coupled to a cavity and excited by a white noise. The cylindrical shell is equipped with a damping device implying viscoelastic materials which work in shearing. The noise reduction is obtained on the frequency band [ 300 - 12kH ]. Parallel to this experimental study a numerical study was carried out to : - predict the vibroacoustic behaviour of the stiffened cylindrical shell coupled with the cavity - validate the vibration attenuation brought by the SPADD®-skin technology in terms of acoustic performances. The high modal density and the big vibroacoustic size of the model are two problems for numerical modelling. A numerical study on the coupling of the acoustic and structural modes is necessary for modal truncations. These studies show that numerical and experimental results are similar.