THE STRUCTURAL ACOUSTICS AND ACTIVE CONTROL OF INTERIOR NOISE IN A RIBBED CYLINDRICAL-SHELL

Numerical studies are carried out regarding the structural acoustics o f a ribbed aluminum cylindrical shell structure intended to represent the essential structural features of a small aircraft fuselage. Calcul ations are made to determine both the wall normal displacements and th e interior acoustic pressures for the case in which the shell wall is forced dynamically at a point. The structural responses are further de composed into their frequency-wave-number components. Through a series of comparisons between those responses for an infinite shell, the rib bed vacuum-filled shell, and the ribbed air-filled shell, the relevant structural acoustic mechanisms are interpreted. The frequencies at wh ich interior acoustic ''resonances'' are observed are connected to spe cific mechanisms, including cavity responses driven by structural mode s, cavity modes forcing the structure, and mixed structure/air-cavity modes. Numerically based active control experiments are carried out us ing end actuation, and the relative performance of this control ''syst em'' is compared when operating on the various mode types.