Smart panels for active noise control in aircraft cabin

Active noise control is a key technology to enhance aircraft cabin comfort. This reflects the view of a vast amount of research aimed at reducing cabin noise levels by tackling structural vibration of the fuselage sidewalls. Aircraft interior trim panels and windows are characterized by poor sound transmission loss behaviour at low frequencies as a result of the mass-air-mass resonance phenomena. For next-generation transport aircraft, their impact on the cabin vibroacoustic environment is expected to become increasingly important with the upcoming use of larger passive windows providing a weak link in protecting aircraft interior from outside noise. This thesis presents a novel active structural acoustic control (ASAC) concept to reduce sound transmission through aircraft-type windows at low frequencies. The structural control inputs are achieved by piezoelectric actuators applied to the structure while the radiating pressure field is minimized. The control concept is developed by means of numerical and experimental investigations. A theoretical analysis of the fluid-structure interaction of vibrating structures is presented. A simulation procedure for the numerical evaluation of the sound transmission loss behaviour of plate-like multi wall structures is developed. The method is based on a hybrid FEM/Rayleigh methodology and utilises numerically calculated sound transmission loss of flat multi panel partitions and box like cavities with idealized boundary conditions. Several examples are presented to demonstrate the accuracy of the proposed technique. A suitable control algorithm based on an adaptive feed-forward Multi-Input Multi- Output control strategy is developed and implemented on a real-time Digital Signal Processing control board. The control strategy is based on the minimization of the sum of square outputs of a number of field microphones. Active noise control experiments are conducted for tonal and narrowband excitations by mounting the structure on a reference test suite. The sound power transmitted through the structure is determined by intensity measurements in anechoic chamber. Focus is finally given to the potential impact of active noise and vibration reduction on passengers from the point of view of comfort perception.