Experimental Investigation of Dynamic Nonlinearities in Rotating Machinery

Abstract

Abstract This paper presents laboratory experiments that confirm and further explore earlier computer simulations related to oil-whip and rub-impact. Both phenomena were explored using Spectrum Analysis, and Chaos tracking techniques (e.g. Poincare’ maps). The results show that oil-whip induces quasi-periodic rotor vibrations, while rub-impact generates complex dynamical behavior, such as chaotic vibrational motion. The nonlinear oil-whip hysteresis loop results presented confirm phenomena uncovered in previous computer simulations. A Sommerfeld number-consistent “instability threshold load” was experimentally observed, along with its corresponding hysteresis loop similar to the classic instability speed hysteresis loop, but probably the most important experimental discovery was a second Hopf bifurcation-Saddle node instability hysteresis loop (i.e., at higher speed than the classical hysteresis loop), separated by a region of stable-in-the-small operation. Another result of especially high practical importance, was the discovery that spectrum analysis of speed-up, or coast-down rotor-vibration data can be effectively used to locate the saddle node speed.