Critical speed

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

Nonlinear Analysis of Rotor Dynamics by Using the Method of Multiple Scales

Abstract: The method of multiple scales is modified to nonlinear analysis in rotor systems. Amplitude equations for forward and backward whirling modes are directly derived and the method makes it easier to understand resonance mechanism. As an example, we analyze near the major critical speed the nonlinear dynamics of a horizontally supported Jeffcott rotor and show that nonlinear and gravity effects cause the backward whirling mode in addition to the forward one. Some experiments are performed and the validity of the theoretical results is confirmed.

Design and test of a soft suspension system for cantilevered momentum wheel assembly

Abstract: This article concentrates on design and test of a soft suspension system for cantilevered momentum wheel assembly. First, a soft suspension system consisting of four folded beams was designed via the finite element method. Next, a mathematical model was employed to investigate the performance of the soft suspension cantilevered momentum wheel assembly. Finally, the natural frequencies of the cantilevered momentum wheel assembly were verified by ‘hammering test’ and the microvibrations produced were measured by a force-acceleration measurement system consisting of a Kistler table and several accelerometers. The results show that the natural frequencies and critical speed obtained by the experiment coincided well with the mathematical model; the soft suspension system can effectively isolate the disturbances produced by the rotor when the cantilevered momentum wheel assembly operates above the critical speed; and the maximum rotational speed increases from 4900 to 6400 r/min when the vertical beam of the so...

Rotordynamic Analysis of a 5-Kilonewton Thrust Gas Turbine by Considering Bearing Dynamics

Abstract: In this work, a full rotordynamic analysis is performed for a 5-kN thrust gas turbine while taking into account bearing stiffness and damping dynamics. The shaft of the studied single spool gas turbine is supported by a deep groove ball bearing and a squeeze film damper. The dynamic stiffness and damping coefficients of these two bearings are used in a finite element model belonging to a C-class formulation for the study of whirl speeds and unbalance responses. The first six modal orbits of the shaft are plotted at the most important frequencies, and a transient analysis is performed to simulate the transition of the system through resonance. As a result, the dynamic behavior of the studied rotor-bearing system is predicted, and vibration problems are avoided. A good agreement among the results could be verified in all numerical analyses.

Generation of Three-Dimensional Fully Nonlinear Water Waves by a Submerged Moving Object

Abstract: This paper describes a numerical investigation on the generation of three-dimensional (3D) fully nonlinear water waves by a submerged object moving at speeds varied from subcritical to supercritical conditions in an unbounded fluid domain. Considering a semispheroid as the moving object, simulations of the time evolutions of 3D free-surface elevation and flow field are performed. The present 3D model results are found to agree reasonably well with other published vertical two-dimensional (2D) and quasi-3D numerical solutions using Boussinesq-type models. Different from the 2D cases with near critical moving speeds, the 3D long-term wave pattern suggests that in addition to the circularly expanded upstream advancing solitonlike waves, a sequence of divergent and transverse waves are also developed behind the moving object. The velocity distributions and associated fluid-particle trajectories at the free-surface and middle layers are presented to show the 3D feature of the motion. The results under various vertical positions (referred as gap) of a moving object are also compared. It is found the gap has shown a substantial influence on the generated waves, especially in the wake region, when an object moves at a near critical or subcritical speed. However, the results under the case with a high supercritical moving speed indicate the gap has a negligible effect on the generated upstream and downstream waves.

Rotor Dynamic Analysis of Ultra-high Speed Switched Reluctance Machines over 1 Million rpm

Abstract: Ultra-high speed machines have drawn more and more interest for researchers in recent times. Switched reluctance machines (SRMs) are of particular interest due to their simple rotor geometry. For ultra-high speed machines, rotor dynamics are a major component and must be considered in the design stage. In this paper, a rotor dynamic study of an ultra-high speed SRM with a rated speed of 1 million rpm is presented. First, different rotors built with isotropic and orthotropic materials are studied, using both analytical and numerical methods. Then, the impact of using a laminated stack versus a solid stack is studied. Finally, three different geometries of single, tandem, and bilateral rotor shafts are proposed, analyzed and compared based on their cost, torque density, manufacturing complexity, and rotor dynamic stability.