Self-Induced Vibrations

A “self-induced” vibration is defined as a phenomenon in which the alternating forces furnishing the energy to the vibration are controlled by the motion, in contradistinction to a “forced” vibration, where the force depends on time only. The following are examples of self-induced vibrations: (1) All bowed string or blown musical instruments, (2) the vacuum-tube oscillator, (3) fluttering of valves in air or water lines, (4) nosing of locomotives and street cars, (5) airplane-wing flutter, (6) certain cases of hunting of generators, and (7) certain cases of vibration of transmission lines due to wind. In physics and electrical engineering self-induced vibrations are common and often very useful, whereas most mechanical or machinery vibrations do not fall in this classification, since unbalance forces and other alternating forces unaffected by the motion are very common. Kimball and Newkirk were the first to call attention to and to explain self-induced vibration phenomena capable of causing serious mechanical difficulties. This paper discusses methods of studying self-induced vibrations and describes several representative cases that have been studied by the author and his colleagues in the last few years.