Experimental and Computational Modal Analysis of a Half Scale Business Jet Fuselage Tail Section

Structure borne noise caused by the engine is a significant source of discomfort for business aircraft passengers. Aircraft with fuselage mounted engines have increased structure borne noise levels in the cabin due to the shortened vibration transmission path between the engines and the cabin. The research objective of the work reported in this paper was to characterize the in-situ structural dynamics of an aircraft cabin rear bulkhead experimentally and use these results to validate a finite element (FE) model of the same structure. Experimental modal analysis (EMA) identified dynamic properties of the fuselage (natural frequencies, mode shapes) which could guide structural dynamic modifications, which should yield reduced noise, increasing passenger comfort. The EMA used an electromechanical shaker to excite a half-scale physical model of a generic fuselage tail section at the engine support yokes with the response measured at the cabin rear bulkhead. The FE and experimental models exhibited five correlated mode pairs across the 50 Hz to 400 Hz frequency range. Furthermore, FE model updating was conducted whereby the material properties were altered slightly to account for pre-stress caused by skin bending during physical model construction. This reduced average eigenvalue discrepancies when compared to the experimental model to 8%.