Development of new technique for damping identification and sound transmission analysis of various structures

A new experimental method to identify damping characteristics of dynamic systems and unique analytical techniques to study sound transmission characteristics of various structures were developed in this dissertation work.; The damping identification method developed in this work identifies damping characteristics of a dynamic system in matrix forms from measured frequency response functions. A theoretical example was used to validate the method and study the noise effect on the identification results. A unique set of experimental measurements was devised to verify the practicality of the method in real engineering applications. Some potential applications and possible improvements of the method were discussed.; While sound transmission characteristics of structures are important basic information in noise control, the related analysis usually becomes a very difficult task because of the complicated interactions between the structures and acoustic media. Solution techniques were developed to study sound transmission characteristics of various cylindrical structures with a single wall, double walls, and double walls lined with porous material for the first time in this study. Generally the system was idealized as an infinitely long circular cylinder subjected to a plane incident wave. The solution technique was extended to solve the sound transmission problems of periodically stiffened panels and cylinders. For all cases, exact solutions were obtained by using the full shell vibration equations coupled with the acoustic wave equations using the mode superposition method.; An approximate analysis technique was proposed to calculate sound transmission through cylindrical walls lined with porous material. Because the porous material has both solid and fluid phases, which makes the related analysis very complicated. The unique approximate method was developed as a two-step analysis allowing relatively easy calculation of the sound transmission in such structures.; An analysis method for stiffened plates and stiffened circular cylindrical shells was also developed for the first time in this work. The space harmonic expansion method was used to solve for the periodically stiffened structures.; In all cases of the sound transmission studies, analytical solutions were compared to corresponding measured results except for the periodically stiffened structures. The effects of important design parameters are studied to obtain useful design guidelines.