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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TL;DR: Linear parameter varying (LPV) control is a model-based control technique that takes into account time-varying parameters of the plant in the case of rotating systems supported by lubricated bearings, the dynamic characteristics of the bearings change in time as a function of the rotating speed.
14 citations
TL;DR: In this article, an axial collar (120) was used for intermittent support of a rotatable shaft (22) to prevent excessive vibration and consequent damage to the shaft, associated end couplings and housing.
Abstract: An apparatus (120) for intermittent support of a rotatable shaft (22) comprises an axial collar (120) substantially coaxial with the shaft (22) and fixed thereabout for rubbing contact with the shaft (22) only after the shaft deflects a predetermined amount from its rotational axis (140) to alter the bending mode of the shaft (22) thereby increasing the first order critical speed of the shaft (22) to a level above the maximum speed at which the shaft (22) may be driven to prevent excessive vibration and consequent damage to the shaft (22), associated end couplings (35,56) and housing (78,84,92).
14 citations
TL;DR: In this paper, the authors proposed a vibration suppression method utilizing the discontinuous spring characteristics together with an automatic ball balancer to overcome these defects and to suppress vibration, and the validity of the proposed method is confirmed theoretically, numerically, and experimentally.
Abstract: Automatic ball balancer is a balancing device where two balls inside a hollow rotor move to optimal rest positions automatically to eliminate unbalance. As a result, vibrations are suppressed to the zero amplitude in the rotational speed range higher than the major critical speed. However, it has the following defects. The amplitude of vibration increases in the rotational speed range lower than the major critical speed. In addition, almost periodic motions with large amplitude occur in the vicinity of the major critical speed due to the rolling of balls inside the rotor. Because of these defects, an automatic ball balancer has not been used widely. This paper proposes the vibration suppression method utilizing the discontinuous spring characteristics together with an automatic ball balancer to overcome these defects and to suppress vibration. The validity of the proposed method is confirmed theoretically, numerically, and experimentally. The results show that amplitude of vibration can be suppressed to a small amplitude in the vicinity of the major critical speed and the zero amplitude in the range higher than the major critical speed.
14 citations
TL;DR: In this paper, the authors examined the correctness of this equivalence and showed that the automatic records of the shaft vibrations at about a critical speed showed a large amplitude at the expected point, but the period of the vibration was twice that anticipated.
Abstract: It is well known that, in the case of reciprocating engines, there are certain critical speeds of running at which the torsional vibrations in the shaft become large in amplitude and introduce an element of danger into the system. Fairly simple methods have been devised for the practical calculation, from the constants of the machinery, of the location of these critical speeds. In these methods, the reciprocating parts of the engine are replaced by an “equivalent mass” which is assumed to contribute to the elastic vibrations of the shaft in exactly the same way as do the actual, rather complicated, system of crank, connecting-rod, piston and piston-rod. It is the main purpose of this paper to examine the correctness of this equivalence. In two particular cases examined by the author, the automatic records of the shaft vibrations at about a critical speed showed a large amplitude at the expected point, but the period of the vibration was twice that anticipated. This anomaly is examined on p.116 and the conditions of its existence exhibited.
14 citations
01 Jun 2010
TL;DR: In this paper, a rotating Timoshenko shaft with a rigid unsymmetrical disc was modelled as a parametrically excited system using the finite-element method, and dynamic stability of the system was checked, steady-state response, undamped resonance condition, and disc centre orbit were solved analytically and discussed numerically.
Abstract: Under a periodic axial force, a rotating Timoshenko shaft with a rigid unsymmetrical disc was modelled as a parametrically excited system using the finite-element method. Using a harmonic balance method, dynamic stability of the system was checked, steady-state response, undamped resonance condition, and disc centre orbit were solved analytically and discussed numerically. Furthermore, the time history response was calculated to verify the efficiency of the solutions. The discussion shows that the fluctuating part of the axial force results in system dynamic instability, and the parameter regions of dynamic instability are enlarged with increasing amplitude of the fluctuation; the disc centre orbit of the system steady-state response is limited to an annular region, and the orbit width is increased by the axial force fluctuating amplitude; besides the neighbourhood of the system critical speed, the shaftdisc system can undergo some additional resonances due to the fluctuating axial force.
14 citations