Conditions for backward whirling motion of a flexible rotor supported on hydrodynamic journal bearings
TL;DR: In this paper, the necessary conditions for backward motion of a Jeffcott rotor supported by identical hydrodynamic journal bearings are investigated, and it is shown that backward motion occurs if and only if the load parameter is greater than a limiting value corresponding to the flexibility parameter.
About: This article is published in Journal of Sound and Vibration.The article was published on 1986-11-22. It has received 6 citations till now. The article focuses on the topics: Rotor (electric) & Fluid bearing.
Citations
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01 Jan 2015
TL;DR: In this article, it is shown that the backward whirl can be observed when the rotor is coasting down to rest from above the critical speed corresponding to the backward Whirl.
Abstract: The determination of whirling frequencies of high speed turbines is always challenging in rotor dynamics. The natural frequencies of a Jeffcott rotor are split in the presence of gyroscopic effect. It is quite well known that the lower branch corresponds to the backward whirl and the upper branch corresponds to forward whirl. The forward whirl mode of the rotor has been observed experimentally, however, the backward whirl has not been observed. In this study it is shown that the backward whirl can be observed when the rotor is coasting down to rest from above the critical speed corresponding to the backward whirl. In order to illustrate the forward and the backward critical speeds of a simple Jeffcott rotor, the natural frequencies are obtained analytically for the second natural frequency of the system because of the large gyroscopic effect present in that mode. An experimental set up was used to verify the presence of backward whirl while the rotor is coasting down to rest. The rotor is also simulated using finite element method by ANSYS, and Campbell diagram is plotted. The analytical, experimental and ANSYS simulations confirm the existence of the backward whirl when the rotor is coasting down.
10 citations
TL;DR: In this article, the influence of the above combination on the stability of rotor bearing systems is investigated using a Jeffcot rotor with significant material damping and supported by fluid film bearings in the rotor dynamic model.
Abstract: Fluid film characteristics and shaft material damping form an interesting combination in rotor dynamic applications. Under certain conditions, a rotor which is unstable due to the damping, can be stabilized with the proper choice of fluid film bearings as supports. On the other hand, increasing the material damping in the rotor shaft can attenuate stress fluctuations in the rotors supported by fluid film bearings. The influence of the above combination on the stability of rotor bearing systems is investigated using a Jeffcot rotor with significant material damping and supported by fluid film bearings in the rotor dynamic model. The results indicate that under certain conditions, the interaction of the above two factors can be gainfully utilized in the design of rotor bearing systems. 8 refs.
4 citations
TL;DR: In this article, the precise condition for complete stress reversal and its relationship with the relative backward whirling of the disk with respect to the journal were investigated. But the relationship between complete stress reversals and backward motion is ambiguous.
Abstract: Under certain conditions a Jeffcot rotor supported on fluid film bearings can experience undesirable stress reversals at double the operating speed in synchronous whirl. When the damping in the hearings is not considered, the condition for complete stress reversal coincides with that for backward whirling of the disk. However, when the damping also is considered, the absolute whirl directions of the journal and the disk can be different under certain conditions. Hence, the rotor shaft may not experience backward whirl throughout its length. Under these circumstances, the relationship between complete stress reversal and backward whirling motion is ambiguous. The present investigation specifies the precise condition for complete stress reversal and identifies it with the relative backward whirling of the disk with respect to the journal. Presented at the 45th Annual Meeting In Denver, Colorado
3 citations
TL;DR: In this article, the influence of material damping on the stress fluctuations of the rotor shaft was investigated and the possibility of attenuating this stress fluctuation through control of shaft materials damping was explored.
Abstract: The unbalance whirling motion of a rotor supported on fluid film bearings, under certain circumstances, can induce severe stress fluctuations in the rotor shaft. This stress fluctuation can be attributed to the backward component of the elliptic whirling motion of the rotor. The present investigation studies the influence of shaft material damping on the stress fluctuations and explores the possibility of attenuating this stress fluctuation through control of shaft material damping. The result indicates that an optimum amount of material damping in the rotor shaft can improve the performance of flexible rotors supported on fluid film bearings. Presented at the 47th Annual Meeting in Philadelphia, Pennsylvania May 4–7, 1992
References
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TL;DR: In this article, the dynamic unbalance response of a single mass Jeffcott rotor in hydrodynamic bearings is analyzed and cross-coupled spring coefficients are considered in the analysis and damping has been neglected.
21 citations
TL;DR: In this article, a correction in the Reynolds boundary conditions is proposed and a new solution for the pressure distribution is obtained, which shows a sudden change in the pressure gradient at the position of maximum film thickness, which is possible only if the lubricant is added precisely at this position.
7 citations
TL;DR: In this paper, the authors provide information on the design of journal bearings for use in high speed rotating machinery to minimize the energy dissipation due to the out-of-balance of the flexible rotor.
4 citations
TL;DR: In this paper, the stiffness and damping characteristics of a finite hydrodynamic journal bearing using the new boundary conditions are compared with the wellknown characteristics incorporating the Reynolds boundary conditions.
3 citations