Stiffened panels are used generally for body structures of automobiles, air-crafts, submarines, etc., for the purpose of increasing the structural stiffness. The increase is due to the addition of stiffeners or artificial modification of structure itself (swaging). The internal constraints imposed by stiffeners or swages distort the mode shapes of panels and, consequently, affect the sound radiation efficiency. For the analysis of natural vibrations of swaged panels, the transfer matrix method is utilized in this study. Experimental results show that the first four or five modes can be predicted with a good degree of accuracy. As a measure of the increased stiffness, natural frequencies are compared with those of flat panels having the same dimensions, as well as the changes of natural mode shapes. For the analysis of the sound radiation characteristics, the least square-error method is utilized and the results agree well with those of BEM in the subsonic range. Numerical results show that natural frequencies can increase by 6 times due to swaging and reveal that further stiffening is possible by the proper interplay between the structural parameters. It is observed that the radiation efficiencies can be increased slightly for frequencies below the critical frequency and the corresponding increase varies with the mode shape and structural parameters.
