Critical speed

About: Critical speed is a research topic. Over the lifetime, 2764 publications have been published within this topic receiving 31365 citations.

A Two-Dimensional Numerical Model to Analyze the Critical Velocity of High Speed Infrastructure

Abstract: This paper illustrates the phenomenon of the critical speed in the range 100- 300 km/h. A real explanation and a precise calculation of the critical speed seems to rest an unresolved problem in many cases. Some authors, analogous to "Mach effect", have attributed this phenomenon to the reaching the Rayleigh wave speed of substructure by trains. But this explanation can't be thorough in many cases because the Rayleigh wave speed is very high and the phenomenon happens even for lower speeds. This work shows an evident relationship between the receptance of the train/track coupling system and the so called sleeper-passing frequency. It is shown that the amplification of vibrations happens when the train speed causes the equivalence between the sleeper-passing frequency and the receptance of the train/track coupling system. This explanation seems to be definitively complete even if only a numeric validation is presented in the paper.

Effects of rotary inertia on sub- and super-critical free vibration of an axially moving beam

Abstract: The most important issue in the vibration study of an engineering system is dynamics modeling. Axially moving continua is often discussed without the inertia produced by the rotation of the continua section. The main goal of this paper is to discover the effects of rotary inertia on the free vibration characteristics of an axially moving beam in the sub-critical and super-critical regime. Specifically, an integro-partial-differential nonlinear equation is modeled for the transverse vibration of the moving beam based on the generalized Hamilton principle. Then the effects of rotary inertia on the natural frequencies, the critical speed, post-buckling vibration frequencies are presented. Two kinds of boundary conditions are also compared. In super-critical speed range, the straight configuration of the axially moving beam loses its stability. The buckling configurations are derived from the corresponding nonlinear static equilibrium equation. Then the natural frequencies of the post-buckling vibration of the super-critical moving beam are calculated by using local linearization theory. By comparing the critical speed and the vibration frequencies in the sub-critical and super-critical regime, the effects of the inertia moment due to beam section rotation are investigated. Several interesting phenomena are disclosed. For examples, without rotary inertia, the study overestimates the stability of the axially moving beam. Moreover, the relative differences between the super-critical fundamental frequencies of the two theories may increase with an increasing beam length.

Dynamic behaviour of an axially moving thin orthotropic plate

Abstract: A new approach to analysis of the dynamic behaviour of axially moving orthotropic plates is presented. The nonlinear orthotropic plate theory is modified to include the inertial forces resulting from the moving web. The results of numerical investigations show the solution to a linear problem. The effects of the orthotropy factor, axial transport velocity and rolls support system on transverse and torsional natural frequencies and stability of the plate motion are presented. The lowest natural frequencies decrease with the increasing axial velocity at undercritical transport speeds. The plate may experience divergent or flutter instability at supercritical transport speeds. A second stable region above the critical speed may exist as well.

The research on mechanical properties of direct drive high-speed permanent-magnet machine for compression

Abstract: The high speed permanent-magnet (HSPM) machine is appropriate for high speed operation due to its simple structure and high power density. In order to avoid stress damage to rotor caused by the centrifugal force and thermal stress, the strength analysis is very important. The rotor should have enough stability to avoid spaning the critical speed of bending mode. In addition, the structural vibration associated characteristics between the parts and the whole machine needs to be studied. This paper introduces a kind of hybrid rotor with carbon/glass fibre sleeve and compressor impeller. The three ply composite rotor is deduced by the 3D finite element method (FEM) model. Design guidelines of the high speed interference fit rotor that offers theory base for optimal design was generalized. Finite element (FE) analysis is used to study structural vibration associated characteristics for a HSPM machine with 315 kW, 18000 rpm.

Nonlinear response analysis of aero-engine rotor bearing rub-impact system caused by horizontal yawing maneuver load

Abstract: Based on the simplified aero-engine rotor system, a new nonlinear response prediction model of rotor bearing rub-impact system is established. Different from the traditional rotor system rub-impact model, based on the detailed characteristics of the blade–disc system, this paper considers the influence of the number of blades and the dynamic to static clearance on the rub-impact force. In addition, the influence of additional load on the established rotor-bearing system due to the change in the flight motion state of the horizontal yawing maneuver is also considered The Newmark- β numerical method is used to solve the system, and the effects of maneuver load and rub-impact stiffness on the nonlinear dynamics of the system are studied The results show that the system produces a kind of sub harmonic resonance rub-impact phenomenon, that is, the system will produce 1/2 sub harmonic resonance under the action of maneuver load near the double critical speed, which will increase the vibration response amplitude of the system. With the increase of maneuver load, the system always has complex nonlinear phenomenon; with the increase of rub-impact stiffness, the system produces a large number of frequency division and frequency multiplication components, which can be used as the characteristic frequency of rub-impact faults.