ABSTRACT
Although physics teaches us that matter is ultimately discrete at the microscopic level, at a more macroscopic level the physical properties of realworld systems can be treated as if they were continuously distributed in space. In vibration problems, in particular, one generally deals with systems – aircraft structures, buildings, pipelines, car bodies, cables or subsystems thereof, just to name a few – whose parameters of mass, stiffness and damping are not only assumed to be continuously distributed in more or less extended regions of space, but may also vary from point to point. At this macroscopic level of description, therefore, one deliberately ignores the discrete molecular and atomic structure of matter, introduces the ideal concept of continuous medium – a solid continuous medium in most cases of interest for our purposes – and considers these distributed-parameter systems as systems with infinitely many degrees of freedom.
