A Practical Review of Rotating Machinery Critical （旋转机械的实际评估关键）.pdf

A Practical Review of Rotating Machinery Critical Speeds and Modes Erik Swanson, Xdot-Consulting, Chapel Hill, North Carolina Chris D. Powell, Structural Technology Corporation, Zoar, Ohio Sorin Weissman, Alfa Wasserman, Inc., West Caldwell, New Jersey The goal of this article is to present a practical understand- vibrational frequency (heavier objects result in lower fre- ing of terminology and behavior based in visualizing how a quency, stiffer springs yield higher frequency). After some shaft vibrates, and examining issues that affect vibration. It work, we reach the conclusion that the free vibration frequency is hoped that this presentation will help the nonspecialist bet- is controlled by the square root of the ratio of stiffness to mass. ter understand what is going on in the machinery, and that the Stiffness specialist may gain a different view and/or some new ex- Natural Frequency = Mass (1) amples. Experimentally, we could (in principle) build a single degree For the engineer unfamiliar with some of the unique char- of freedom system consisting of a rigid block sitting on a spring. acteristics of rotating machinery vibration, the terminology and Were we to push the block down and release it, we would find behavior of a machine can appear to be overwhelming. Like that the displacement versus time is a sinusoidal function at a most specialty areas, there are a number of excellent texts, but single frequency, which is equal to the natural frequency as pre- it can be difficult to quickly pull out the practical insight dicted by Equation 1 and shown in Figure 2. needed. At the other end of t