Stiffener shape design to minimize interior noise

Results of a research program to develop computational methods to minimize noise transmission into aircraft fuselage interiors are discussed. A design tool to perform a constrained optimization of the acoustic environment wit hin a vibrating structure is developed utilizing finite element methods and boundary element methods (FEM/BEM), and its application to aircraft cabin noise problems is studied. The results of ri study to optimize the cross se ction shapes of frames and stringers of an idealized aircraftlike stiffened cylinder are reviewed. The structure is optimized for minimum noise at spe cified points in the interior, as a result of a single frequency (tonal) ex terior acoustic disturbance. For the cylinder and excitation frequency stud ied, it has been found that spatially varying the stiffener sizes over the cylinder is more important than optimizing the shape of the cross sections. Because FEM/BEM methods are only reliable for lower frequencies, the probl ems studied are applicable to low-frequency tonal noise such as seen in tur boprop aircraft.