Two unique approaches for actively controlling the interior acoustic response of a cylindrical aircraft enclosure using active constrained layer damping and end actuation

Experimental results are reported involving the use of 12 active constrained layer damping (ACLD) patches instrumented on a fuselage section under radial point excitation. ACLD utilizes an active piezo film constraining layer over a viscoelastic layer to increase damping and apply restoring moments. Results reported to date showed that performance was achieved both in the reduction of the interior acoustic response and of the structural vibratory response. A more detailed analysis is reported here of the uncontrolled/controlled structural acoustics derived from high spatially sampled surface velocity and interior pressure measurements. A second control approach is reported where interior acoustic levels are reduced by control of the efficient end cap coupling to the interior by placing control actuators on each end. Analytic and numeric models are used to identify three dominate interior acoustic mechanisms: (1) a forced response on the interior by purely structural modes, (2) purely normal acoustic cavity modes, and (3) mixed structural/acoustic modes. Numeric control ‘‘experiments’’ are reported where both interior acoustic minimization and end-constraint control laws are employed. Good performance was found and discussion will involve the effectiveness of the control laws on each of these mechanisms. [Work supported in part by NASA, Langley.] a)Also SFA, Inc.