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This paper has presented a technique for the determination of an optimal configuration of fuselage mounted piezoelectric actuators for active structural acoustic control of interior noise in aircraft. The technique has demonstrated much potential in preliminary experiments where actuators were configured to couple into the first principal component of the acoustically coupled fuselage vibration. In this test, average reductions of 6 dB at the error microphones and 4 dB at five auxiliary microphones were observed for a pure tone disturbance at the left forward engine pylon of a business jet. This disturbance was used to simulate an oscillating force due to engine unbalance.

This work primarily consists of two main parts. First a series of acoustic system identification experiments of the interior space of a business aircraft were performed. The system was subjected to both a structural based excitation (at the left forward engine mount), and an acoustic based excitation (speaker mounted in cockpit). Sound pressure was measured at over 3000 points in the cabin over a frequency range of 0-400 Hz. Data was reduced to produce 3-D acoustic plots at single frequency bins and 2-D dispersion diagrams (wavenumber vs. frequency). Secondly, preliminary experiments on controlling interior noise using small patch type piezoceramic actuators bonded to the fuselage were investigated. The results demonstrate that the piezoceramic patch actuators have enough control authority for this application.

An active control system has been applied to an operational turbofan engine to reduce tonal inlet noise produced by the fan. Flow disturbing rods placed upstream of the fan assembly excite to dominance selective acoustic modes. An array of loudspeakers mounted on the inlet of the engine create the active, or secondary sound field that destructively interferes with the fan noise. The control system, an adaptive feedforward approach utilizing a Filtered-X Least Mean Square (LMS) algorithm, obtains error information via large area transducer microphones placed in the acoustic far-field. Born a single-input, single-output (SISO) and three channel, multi-input, multi-output (MIMO) controller versions were developed. Experiments have demonstrated tonal noise reduction of up to 16 dB over large sectors in the forward direction of the turbofan inlet.