Vibrations in systems with a periodic structure is the subject of many ongoing research activities. This work presents the analysis of such systems with the help of the theory of representation groups by finite element methods, dynamic Compliance and dynamic rigidness methods, specially adjusted for the analysis of engineering structures. The approach presented in this book permits a simplification and facilitates the understanding of mechanical vibrations in various structures. The book includes extended studies of even complicated machinery structures with an emphasis on flight vehicle engines.