Critical speed

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

Actively Controlled Bearing Dampers for Aircraft Engine Applications

Abstract: This paper describes some of the requirements for bearing dampers to be used in an aircraft engine and briefly discusses the pros and cons of various types of dampers that were considered as candidates for active control in aircraft engines. A disk type of electrorheological (ER) damper was chosen for further study and testing. The paper explains how and why the choice was made. For evaluating potential applications to aircraft engines, an experimental development engine (XTE-45) was used as an example for this study.Like most real aircraft engines, the XTE-45 ran through more than one critical speed in its operating speed range. There are some speeds where damping is desirable and other speeds where it is not. Thus, the concept of a damper with controllable forces appears attractive. The desired equivalent viscous damping at the critical speeds along with the available size envelope were two of the major criteria used for comparing the dampers.Most previous investigators have considered the ER damper to produce a purely Coulomb type of damping force and this was the assumption used by the present authors in this study. It is shown in a companion paper (Vance and San Andres, 1999), however, that a purely Coulomb type of friction cannot restrain the peak vibration amplitudes at rotordynamic critical speeds and that the equivalent viscous damping for rotordynamics is different from the value derived by previous investigators for planar vibration. Control laws for Coulomb damping are derived in Vance and San Andres, (1999) to achieve minimum rotor vibration amplitudes in a test rig while avoiding large bearing forces over a speed range that includes a critical speed. The type of control scheme required and its effectiveness was another criterion used for comparing the dampers in this paper.Copyright © 1999 by ASME

Investigation of structural parameters of high speed grinder spindle system on dynamic performance

Abstract: This study was focused on the theoretical modelling and numerical simulation about the dynamic characteristics of coupled double-rotor spindle system of high speed grinder. The influences of the grinder spindle’s major structural parameters on its critical speed and vibration mode were investigated. The results showed that the critical speeds of coupled double-rotor system were arranged in a similar increasing order as to those of each single rotor. It was thus indicated that the critical speeds of each order for coupled double-rotor system corresponded to those of single rotor. Furthermore, the effect of preload of bearing, overhang length, span of bearing, rotor structure and mass of spindle system on critical speeds of various orders for the coupled spindle system was analysed. Under the impact of unbalance, vibration response of the spindle’s front end as well as the front and back bearings was examined. Finally, the changing effect of preload of bearing, overhang length and bearing span on dynamic and static rigidities of spindle ends was investigated.

Calculated estimation of railway wheels equivalent conicity influence on critical speed of railway passenger car

Abstract: The article presents the results of determining the equivalent conicity characterizing the geometric interaction of wheels and rails on 1520 mm track gauge. The cases of interactions of rails and wheelsets, wheels of which have different profiles, are considered. The computer model of the motion speeds of the passenger car is developed. According to the results of computer simulation, critical speeds for the bogie moving through the tracks of intended gauge are received. Based on the results of the simulation anslysis, the significant dependence of the value of the equivalent conicity on the critical speed is confirmed. The necessity of considering the limit values of equivalent conicity in tests of high speed rolling stock is emphasized. This work is supported by: KEGA

Effects of Nonlinearity of Magnetic Force on Passing Through a Critical Speed of a Rotor With a Superconducting Bearing

Abstract: High-Tc superconducting magnetic levitation systems have a feature of noncontact stable levitation. Recently, flywheel energy storage systems using superconducting magnetic bearings have reached its validation phase. Also, varied combinations of magnetic bearings have been used in this system. However, increase in amplitude has become a problem because of its low damping. Also, nonlinear phenomena can occur in such low-damping systems using electromagnetic force. This study investigates vibration reduction of a rotor system with an electromagnet. The nonlinearity of the magnetic force is taken into consideration in the case. First of all, we developed an essential model of a rotor supported by a superconductor, a permanent magnet and an electromagnet. Equations were derived by taking into account the nonlinearity of the electromagnetic force. These equations were then calculated by using the Runge-Kutta method. Numerical results show vibration reduction of the rotor by changing the electromagnetic force at appropriate rotating speed. Good agreements were obtained between experimental results and numerical results. In summary, changing of not only linear stiffness but also nonlinear stiffness affects vibration reduction of a rotor supported by a superconducting bulk, a permanent magnet, and an electromagnet.