Modelling and testing of trim panels for rotorcraft interior noise prediction

Interior noise comfort is becoming more and more of crucial importance in the automotive, railway, aircraft and rotorcrat industry. One the most difficult challenges, due to the vicinity of multiple noise sources contributing through multiple transfer paths, is that of improving the passengers comfort in rotorcrafts. Trim panels are the very last attenuation stage for vibrations and noise before reaching the cabin and are therefore critical components to be carefully designed, together with the vibration isolators connecting them to the fuselage, for reaching the target interior noise comfort level. In the present dissertation mathematical models for predicting the vibro-acoustic performance of trim panel-isolators system are presented, accounting for both airborne and structure-borne paths. The trim panel modelling is approached through a Discrete Laminate Model (DLM) accounting for panel asymmetric motion solely and an arbitrary stacking sequence. With reference to the airborne transfer path, models for predicting the Transmission Loss under diffuse acoustic field excitation, integrated with the DLM, are presented and experimentally validated on typical aeronautical sandwich panels. With reference to structure-borne path an extensive characterization of different vibration isolators is performed and their vibration isolation performance when coupled to a beam receiving structure assessed, both numerically and experimentally. Assuming a vibration source on the fuselage side, the space-averaged mean quadratic velocity of trim panels is investigated through a dedicated hybrid deterministic/SEA model of the trim panel coupled to vibration isolators. The model developed accounts for the isolator dynamics, trim panel uncertainties associated to uncertain boundary conditions or manufacturing process imperfections, as well as for the actual panel stacking sequence. Capabilities of the hybrid model in predicting the plate vibrational level for variations of the vibration isolator and trim panel properties is finally assessed.