Critical speed

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

Design of a Squeeze-Film Damper for a Multi-Mass Flexible Rotor

Abstract: A single mass flexible rotor analysis was used to optimize the stiffness and damping of a flexible support for a symmetric five-mass rotor. The flexible support attenuates the rotor motions and forces transmitted to the support bearings when the rotor operates through and above its first bending critical speed. An oil squeeze-film damper was designed based on short bearing lubrication theory. The damper design was verified by an unbalance response computer program. Rotor amplitudes were reduced by a factor of 16 and loads reduced by a factor of 36 compared with the same rotor on rigid bearing supports.

Rotordynamic Bearing Dampers for Cryogenic Rocket Engine Turbopumps

Abstract: It is a common practice for cryogenic turbomachines to utilize stiffly mounted bearings due to the incapability of providing significant damping with conventional methods and designs. With no damping available, the historical motive behind this design practice was to elevate all critical speeds above the maximum running speed. The desire for higher energy density has raised the running speeds of rocket engine turbopumps very near, or even above, the first three critical speeds. A companion paper gives experimental evidence that accurate prediction of these critical speeds with the turbopump rotor on ball bearings with stiff supports is not practically possible. The feasibility of applying a metal mesh damper with soft supports in a cryogenic engine is investigated. To date the focus has been on cryogenic experimental tests, rotordynamic simulations, and possible bearing support design schemes to justify the incorporation of a metal mesh bearing support in a liquid rocket engine fuel turbopump. Success of the design is dependent on the amount of damping that the damper retains at cryogenic temperatures and its ultimate effect on fuel turbopump rotordynamics, especially subsynchronous instability.

Evaluation of PCC Pile Method in Mitigating Embankment Vibrations from a High-Speed Train

Abstract: Dynamic response of a railway embankment to a high-speed train is simulated for two cases: the soft ground is improved by cast–in situ concrete pipe (PCC) piles, and the soft ground is not improved The obtained results are compared to evaluate the effectiveness of ground improvement in mitigating embankment vibration from a high-speed train The study shows that ground improvement significantly reduces embankment vibration at all considered train speeds (36–360 km/h) The possibility of vibrational resonance when the train speed approaches the critical speed governed by the soft soil is completely excluded However, vibrational resonance still happens when the train speed approaches the critical speed governed by the embankment material, and this suggests the following implication Even when the soft ground of a railway embankment system has already been improved, vibrational resonance can still happen at high train speeds Furthermore, for a given site, each ground improvement scheme results in

Soft EHL Simulations of U-Cup and Step Hydraulic Rod Seals

Abstract: A numerical soft elastohydrodynamic lubrication model of a reciprocating hydraulic seal has been used to simulate the performance of a U-cup seal and a step seal in a conventional actuator. The model consists of coupled steady state fluid mechanics, deformation mechanics, contact mechanics, and thermal analyses, with an iterative computational procedure. The results indicate that for a given seal roughness and stroke length there is a critical rod speed above which the seal will not leak. The critical speed is dependent on both seal roughness and sealed pressure.

Condition Monitoring of Rotor Using Active Magnetic Actuator

Abstract: It has been widely recognized that the changes in the dynamic response of a rotor could be utilized for general fault detection and monitoring. Current methods rely on the monitoring of synchronous response of the machine during its transient or normal operation. Very little progress has been made in developing robust techniques to detect subtle changes in machine condition caused by rotor cracks. It has been demonstrated that the crack-induced changes in the rotor dynamic behavior produce unique vibration signatures. When the harmonic excitation force is applied to the cracked rotor system, nonlinear resonances occur due to the nonlinear parametric excitation characteristics of the crack. These resonances are the result of the coexistence of a parametric excitation term and different frequencies present in the system, namely critical speed, the synchronous frequency, and excitation frequency from the externally applied perturbation signals. This paper presents the application of this approach on an experimental test rig. The simulation and experimental study for the given rig configuration, along with the application of active magnetic bearings as a force actuator, are presented.