Vibration control of stiffened cylindrical shells using active constrained layer damping

Active structural acoustic control of a full scale aircraft fuselage section (Cessna Citation II) is demonstrated using Active Constrained Layer Damping (ACLD), where both interior acoustic levels and surface vibrations are substantially reduced. The fuselage, on a basic level, is a thin walled cylindrical shell with flat endcaps stiffened by both ribs and stringers. On a more detailed level, there are manufacturing tolerances, some variability from one aircraft to the next and discontinuous features which make analysis, modeling and control inherently complex.; The response of the uncontrolled fuselage is first evaluated to identify dominate modes and relevant disturbances for ACLD control studies as well as to gain a knowledge of the physics which regulate the structural acoustics. High spatially-sampled broadband (10–1000 Hz) measurements are performed under several excitations: (1) a radial point force applied on the stiffener skeletal structure, (2) a radial point force applied between the stiffeners in the thin-walled panel area and (3) an external acoustic source. Case 1 reveals rich structural acoustics with broad wavenumbers and local resonances. This case is further investigated using SARA (Structural Acoustics Code) which utilizes acoustic and structural elements to obtain both surface vibrations and interior noise. The predicted results are compared with experimental measurement. These studies indicate that case 1 is relevant for ACLD control, with two global modes and a local mode targeted for control.; Twelve ACLD patches are strategically placed to correspond to the spatial distribution of the modes targeted for control. Each ACLD patch is constructed of a passive viscoelastic layer and an active NiCu metallized piezo film acting as a constraining layer. Control laws are implemented using both Least Mean Squared (LMS) and conventional Proportional-Rate minimization schemes. Controlled and uncontrolled experiments are conducted by measuring the surface velocity (480 spatial points) and the interior pressure (1536 spatial points) as performance metrics. Generally, both surface and interior attenuation is found to be on the order of 4 to 6 dB.