A disc with mass m is mounted on a shaft with stiffness k and internal viscous damping c i. When this phenomenon is studied, a system like that in the figure below is often used. However, in the first half of the twentieth century many engineers learned the hard way that increasing the damping in rotating structures may lead to catastrophic failures. Damping almost always works for a non-rotating system. The video below shows a Jeffcott rotor starting from a rotational speed of zero and accelerating through the critical speed:ĭamping in a mechanical system is a technique for lowering vibration. Here one of these phenomena, internal damping, will be explored using Wolfram SystemModeler. ![]() Traditionally, research on gas and steam turbines, jet engines, and pumps have contributed to our understanding of the field. Such a rotor is now called the de Laval rotor or Jeffcott rotor and is the standard rotor model used in most basic equations describing various phenomena.Īlmost all machines have something that rotates or vibrates, so rotor dynamics is a large field of mechanical engineering. Thirty years later in 1929, the American Henry Jeffcott wrote the equation for a similar system, a simple shaft supported at its ends. The trick was to accelerate fast through the critical speed. In 1889, the famous Swedish engineer Gustaf de Laval pursued the opposite strategy: he ran a machine faster than the critical speed, finding that at speeds above the critical threshold, vibration decreased. Until the end of the nineteenth century the primary way of improving performance, increasing the maximum speed at which a machine rotates without an unacceptable level of vibration, was to increase the lowest critical speed: rotors became stiffer and stiffer. ![]() The critical speed of a rotating machine occurs when the rotational speed matches one of these natural frequencies, often the lowest. Machine vibration caused by imbalance is one of the main characteristics of machinery in rotation.Īll structures have natural frequencies. Classical dynamics had a new branch: rotor dynamics. In 1869, Rankine extended Euler and Bernoulli’s century-old theory of lateral vibrations of bars to an understanding of rotating machinery that is out of balance. Explore the contents of this article with a free Wolfram SystemModeler trial.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |