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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, an innovative estimated equation for pressure distribution in a magnetorheological squeeze film damper (MR-SFD) is presented, and the hydrodynamic forces of the damper are easily calculated as an algebraic equation.
Abstract: By using magnetorheological (MR) fluid as the lubricating oil in a traditional squeeze film damper (SFD), one can build a variable-damping SFD, thereby controlling the vibration of a rotor by controlling the magnetic field. This study aims to control the vibration of a flexible rotor system using a magnetorheological squeeze film damper (MR-SFD). In order to evaluate the performance of the damper, the Bingham plastic model is used for the MR fluid and the hydrodynamic equation of MR-SFD is presented. Usually, the numerical methods are necessary for solving this equation. These methods are too costly and time consuming, especially in the simulation of complex rotors and the implementation of model-based controllers. To fix this issue, an innovative estimated equation for pressure distribution in MR-SFD is presented in this paper. By integration of this explicit expression, the hydrodynamic forces of MR-SFD are easily calculated as an algebraic equation. It is shown that the pressure and forces, which are calculated from the introduced expression, are consistent with the corresponding results of the original equations. Furthermore, considering the structural and parametric uncertainties of the system, proportional-integral-furthermore controller (PID) and sliding mode controllers are chosen for reducing the vibration level of the flexible rotor system, which is modeled by the finite element method. The time and frequency responses of a flexible rotor in the presence of these controllers show a good performance in reducing vibration of the shaft's midpoint, although near the rotor's critical speed the results of the sliding mode controller (SMC) are better than the corresponding results of the PID controller. The last part of this article is devoted to an analysis of the system's uncertainties. The results of the open loop system indicate that changes in the stiffness coefficient of the elastic foundation and the temperature of the MR fluid (two uncertainties of the system) strongly affects the outputs while using the controllers well increases the robustness of the system. The obtained results indicate that both the PID and sliding mode controllers have good performance against the uncertainty of the stiffness coefficient, but for changes in the MR fluid's temperature, the SMC presents better outputs compared to the PID controller, especially for high rotational speeds.

14 citations

Journal ArticleDOI
TL;DR: In this paper, a new technique for rotor whirl damping in rotating machinery, based on the elastic suspension of the journal boxes and the use of dry friction surfaces normal to the shaft axis between their supports and the frame, is analyzed theoretically for several cases of rotor systems characterized by mass and constraint asymmetry.

14 citations

Journal ArticleDOI
TL;DR: In this paper, a self-optimizing support system for a rotating shaft is proposed to provide the self-tuning for the support stiffness such that the vibration of the rotating shaft usually occurs at the near antiresonance with changes of a rotating speed.
Abstract: This paper proposes a new design concept of a self-optimizing support system for a rotating shaft. The purpose of this support system is to provide the self-tuning for the support stiffness such that the vibration of a rotating shaft usually occurs at the near antiresonance with changes of a rotating speed. The optimal tuning values of support stiffness are obtained by the on-line estimations of rotating angular velocities of a rotating shaft. The effect of the self-optimizing support system is proved by the tests of nonstationary responses for a fundamental rotor-shaft system.

14 citations

Journal ArticleDOI
TL;DR: In this article, the authors extended the two-dimensional model to an annular three-dimensional disk model in order to consider more realistic brake and clutch geometries and to provide more accurate critical speed.
Abstract: The frictional heat generated during braking causes thermoelastic distortion that modifies the contact pressure distribution. If the sliding speed is sufficiently high, this can lead to frictionally-excited thermoelastic instability (TEI), characterised by major non-uniformities in pressure and temperature. In automotive applications, a particular area of concern is the relation between thermoelastically induced hot spots in the brake disks and noise and vibration in the brake system. Numerical implementation of Burton's perturbation analysis for thermoelastic instability in a two-dimensional model provides an extremely efficient method for determining the critical speed in simple sliding systems. In this paper, the two-dimensional model has been extended to an annular three-dimensional disk model in order to consider more realistic brake and clutch geometries and to provide more accurate critical speed. The results show that the eigenmodes exhibit focal hot spots along the circumference on each side of the disk and the thin disk is more stable than the thick disk when both disk thicknesses are below the optimal thickness.

14 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20241
202343
2022120
202182
202092
2019102