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: In this article, the authors gave a model of twenty-seven degrees of freedom for a six-axle locomotive and set up the numerical bifurcation method as the method of nonlinear lateral stability analysis of a locomotive, and derived criteria of stabillity analysis.
Abstract: SUMMARY This paper gives a model of twenty-seven degrees of freedom for a six-axle locomotive with three-axle bogies, sets up the numerical bifurcation method as the method of nonlinear lateral stability analysis of a locomotive, and derives criteria of stabillity analysis. This paper makes a point that the subcritical Hopf bifurcation speed Vn and the derailing speed Vd must be obtained in order to describe a complete picture of the lateral stability of a locomotive. However, the critical speed Ve is not the most important index of locomotive stability. At the end of this paper, the diesel locomotive DF9 has been analyzed for nonlinear lateral stability. To solve the locomotive equations of motion about nonlinear lateral stability, the paper gives preference to Newmark's predictor-corrector integration scheme as an integration algorithm, and sets up the numerical integration programs using FORTRAN language. At the same time, the aftertreatment programs have been set up. Nonlinear geometry, changing conta...
9 citations
TL;DR: In this paper, nonlinear equations describing in-plane deformation of a rotating elastic rod, taking into account shear effect, were derived and the critical rotation speed was determined from the linearized equation.
Abstract: The nonlinear equations describing in-plane deformation of a rotating elastic rod, taking into account shear effect, are derived. It is shown that the critical rotation speed is determined from the linearized equation. The nonlinear equilibrium equations are solved numerically and the effect of shear on maximal deflection is studied.
9 citations
TL;DR: In this article, a wet critical speed combined analysis and test approach is described to properly account for the Lomakin effect, which occurs when the sealing annulus shifts off-center and can increase the first bending natural frequency of the pump rotor assembly by up to 200 percent.
Abstract: The accurate prediction of the rotordynamic characteristics of centrifugal pumps is complicated by the presence of strong restoring and cross-coupling forces within annular sealing cavities such as wearing rings and thrust balancing devices. This so-called Lomakin Effect occurs when the sealing annulus shifts off-center, and can increase the first bending natural frequency of the pump rotor assembly by up to 200 percent. In addition, the lower natural frequencies may become critically damped, or in the other extreme unstable, relative to what would be expected if the rotor were run in air rather than in the pumped fluid. To properly account for this Lomakin Effect, a wet critical speed combined analysis and test approach is described. Examples are given to illustrate its effectiveness in product development and field trouble-shooting. Presented at the 35th STLE/ASME Tribology Conference In Fort Lauderdale, Florida October 16–19, 1989
9 citations
TL;DR: In this article , a validated pantograph-catenary model is built to reproduce the phenomenon and a simple indicator that describes the overall contribution of all modes subjected to a moving pantograph at a given speed is proposed to facilitate the determination of the local optimal speed.
Abstract: The pantograph-catenary system is used in modern electrified railways to power electric trains. Common sense is that the increase of train speed leads to a deterioration of the interaction performance. But recent studies indicate that a higher speed may result in a better performance in some local speed regions. This paper is the first attempt to provide a theoretical explanation for this phenomenon. A validated pantograph-catenary model is built to reproduce this phenomenon. Referring the definition of critical speed in moving load problems, the catenary's critical speed is defined. The wavelength components can be extracted through the Fourier transformation to the contact wire's vertical mode shape. The speed that satisfies the resonance condition can be regarded as the potential critical speed. The corresponding contact wire amplitude is further evaluated to determine the critical speeds at a given mode. The analysis indicates that a good interaction performance happens when the speed falls in the transition procedure between the critical two speeds. Based on this idea, a simple indicator that describes the overall contribution of all modes subjected to a moving pantograph at a given speed is proposed to facilitate the determination of the local optimal speed. The variation of the proposed indicator with respect to the speed shows good consistency with the trend of the simulation results. The main finding in this paper can be used in the design phase to determine the optimal speed of the pantograph-catenary system in a local speed range.
9 citations
Patent•
03 Apr 1997
TL;DR: A composite electric motor shaft including axially distributed metallic and nonmetallic sections joined together exhibit increased mechanical damping, increased rotor critical speed, improved corrosion resistance and improved motor performance as discussed by the authors.
Abstract: A composite electric motor shaft including axially distributed metallic and nonmetallic sections joined together exhibit increased mechanical damping, increased rotor critical speed, improved corrosion resistance and improved motor performance.
9 citations