The vibro-acoustic response and analysis of a full-scale aircraft fuselage section for interior noise reduction

The surface and interior response of a Cessna Citation fuselage section under three different forcing functions (10-1000 Hz) is evaluated through spatially dense scanning measurements. Spatial Fourier analysis reveals that a point force applied to the stiffener grid provides a rich wavenumber response over a broad frequency range. The surface motion data show global structural modes (less than or similar to 150 Hz), superposition of global and local intrapanel responses (similar to 150-450 Hz), and intrapanel motion alone (greater than or similar to 450 Hz). Some evidence of Bloch wave motion is observed, revealing classical stop/pass bands associated with stiffener periodicity. The interior response (less than or similar to 150 Hz) is dominated by global structural modes that force the interior cavity. Local intrapanel responses (greater than or similar to 150 Hz) of the fuselage provide a broadband volume velocity source that strongly excites a high density of interior modes. Mode coupling between the structural response and the interior modes appears to be negligible due to a lack of frequency proximity and mismatches in the spatial distribution. A high degree-of-freedom finite element model of the fuselage section was developed as a predictive tool. The calculated response is in good agreement with the experimental result, yielding a general model development methodology for accurate prediction of structures with moderate to high complexity. (c) 2005 Acoustical Society of America.