Topic
Critical speed
About: Critical speed is a research topic. Over the lifetime, 2764 publications have been published within this topic receiving 31365 citations.
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01 Jun 1966
TL;DR: In this paper, it is shown that contact between the shaft and annulus can radically alter the high-speed behavior of the shaft over a speed range possibly extending to several times the critical speed.
Abstract: Where it is intended to run the shaft at high speed—that is, above the first critical speed—contact between the shaft and annulus may take place in running up to speed just below the critical speed if the mass eccentricity is sufficient in relation to the damping. It is shown that such contact can radically alter the high-speed behaviour of the shaft over a speed range possibly extending to several times the critical speed. In this range, synchronous whirling can take place at a radius exceeding the annular clearance. The whirl radius in this condition may attain between ten and one hundred times the magnitude expected in normal high-speed running at the same speed. The dependence of magnitude and range of this type of whirling on annulus to shaft stiffness ratio, damping and surface friction is examined: the conditions for stability of equilibrium are theoretically examined. The essential features of the theory have been tested on a laboratory rig; some typical results are given. There is some evidence t...
11 citations
TL;DR: The results show that the modal frequency of the dual-rotor system increases when rub-impact occurs and has the feature of interval, which allows us to obtain the critical speeds of the rubbing system by traditional Campbell diagram.
11 citations
TL;DR: In this paper, a rotordynamic analysis of a large turbocompressor that models both the casing and supports along with the rotor-bearing system was performed, and the results of the fully coupled model validated the transfer function approach.
Abstract: A rotordynamic analysis of a large turbocompressor that models both the casing and supports along with the rotor-bearing system was performed. A 3D finite element model of the casing captures the intricate details of the casing and support structure. Two approaches are presented, including development of transfer functions of the casing and foundation, as well as a fully coupled rotor-casing-foundation model. The effect of bearing support compliance is captured, as well as the influence of casing modes on the rotor response. The first approach generates frequency response functions (FRFs) from the finite element case model at the bearing support locations. A high-order polynomial in numerator-denominator transfer function format is generated from a curve fit of the FRF. These transfer functions are then incorporated into the rotordynamics model. The second approach is a fully coupled rotor and casing model that is solved together. An unbalance response calculation is performed in both cases to predict the resulting rotor critical speeds and response of the casing modes. The effect of the compressor case and supports caused the second critical speed to drop to a value close to the operating speed and not compliant with the requirements of the American Petroleum Institute (API) specification 617 7th edition. A combination of rotor, journal bearing, casing, and support modifications resulted in a satisfactory and API compliant solution. The results of the fully coupled model validated the transfer function approach.
11 citations
TL;DR: In this paper, an approximate model is developed to predict the onset of instability when one elastic body slides in contact with another body, and the results show that, at a low number of waves, ring deflection predominate and greatly increase the speed at which instability begins.
11 citations
TL;DR: In this paper, the influence of the angular acceleration, the initial angular position of the unbalance ψn and the initial rotating speed ω on the maximum amplitude of a flexible rotating shaft with nonlinear spring characteristics during acceleration through a critical speed of a summed-and-differential harmonic oscillation was investigated.
Abstract: Nonstationary vibration of a flexible rotating shaft with nonlinear spring characteristics during acceleration through a critical speed of a summed-and-differential harmonic oscillation was investigated. In numerical simulations, we investigated the influence of the angular acceleration λ, the initial angular position of the unbalance ψn and the initial rotating speed ω on the maximum amplitude. We also performed experiments with various angular accelerations. The following results were obtained: (1) the maximum amplitude depends not only on λ but also on ψn and ω: (2) when the initial angular position ψn changes. the maximum amplitude varies between two values. The upper and lower bounds of the maximum amplitude do not change monotonously for the angular acceleration: (3) In order to always pass the critical speed with finite amplitude during acceleration. the value of λ must exceed a certain critical value.
11 citations