Critical speed

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

Non-linear dynamical analysis for an axially moving beam with finite deformation

Abstract: Non-linear dynamical analysis of a simply supported translating beam considering the interactions between beam translation and flexible deformation is presented. The extended Hamilton's principle is employed to derive the equations of the longitudinal and transverse vibration of the beam under finite deformation theory which are non-linearly coupled. Runge–Kutta method is utilized to solve the non-linear governing equations. The numerical results describe the coupling responses between the beam extension and flexible deformation where the higher the axial velocity is, the stronger the interactions will be. Furthermore, numerical analysis also demonstrates that the resulting responses are distinctly different under small deformation theory and finite deformation theory, and there exists a critical speed under small deformation theory. When the speed exceeds the critical speed, the system becomes unstable because of the divergence or flutter instability. However, under finite deformation theory the system is always stable. Further analysis reveals that, for appropriately considering the influence of axial movement on the beam deformation, a geometrically non-linear beam theory should be utilized even if the deflection is very small. Coupling responses between the transverse and longitudinal vibrations are also numerically explored.

Dynamic analysis of an axially translating plate with time-variant length

Abstract: The linear dynamic analysis of a translating cantilever plate model characterized by time-variant length and axial velocity is investigated. A length-dependent governing partial differential equation (PDE) of motion is formulated by the extended Hamilton’s principle based on Kirchhoff–Love plate theory. The tension in the system arising from the longitudinal accelerations and in-plane stresses are incorporated. Further, the extended Galerkin method along with the Newmark direct time integration scheme is employed to simulate the response of the system. Stability and vibration characteristics are studied according to the quadratic eigenvalue problem from the governing PDE, which demonstrates that the coupling effects between the axial translation motion and the flexural deformation stabilizes the system during the extension and destabilizes it in the retraction. The computation results show that the translating velocity and the aspect ratio affect the natural frequencies and stability for the out-of-plane vibration of the moving plate. A domain for the traveling velocity associated with the stable system is given, and the critical failure velocity is also predicted based on numerical simulations.

Design optimization of rotor-bearing system considering critical speed using Taguchi method:

Abstract: The purpose of this study is to utilize Taguchi method, which can prove to be a handy and effective tool for determining minimum vibration response of rotor-bearing system set to avoid running at critical speed. In the study, three test cases considering different coupling type (elastic, jaw, and solid) and disc location (disc location A, B, and C) were conducted to observe behavioral changes of the shaft system considering vibration signatures. Each test case was conducted for three different shaft running speeds of 12, 18, and 24 Hz. To find the minimum peak amplitude values by experimenting different combinations of the rotor-bearing system set needs a lot of experiments for reaching solution. Moreover, the solution proves costly because of the time consumed in doing many experiments. This fact depicts the importance of an efficient optimization method to be used. Taguchi method can determine the design parameters, which have the greatest influence on the solution through a very limited number of exper...

Dynamic Response Analysis of a Simply Supported Double-Beam System under Successive Moving Loads

Abstract: The dynamic response of a simply supported double-beam system under moving loads was studied. First, in order to reduce the difficulty of solving the equation, a finite sin-Fourier transform was used to transform the infinite-degree-of-freedom double-beam system into a superimposed two-degrees-of-freedom system. Second, Duhamel’s integral was used to obtain the analytical expression of Fourier amplitude spectrum function considering the initial conditions. Finally, based on finite sin-Fourier inverse transform, the analytical expression of dynamic response of a simply supported double-beam system under moving loads was deduced. The dynamic response under successive moving loads was calculated by the analytical method and the general FEM software ANSYS. The analysis results show that the analytical method calculation results are consistent with ANSYS’ calculation, thus validating the analytical calculation method. The simply supported double-beam system had multiple critical speeds, and the flexural rigidity significantly affected both peak vertical displacement and critical speed.

Analysis of Critical-Speed Increase of Induction Machines via Winding Reconfiguration With Solid-State Switches

Abstract: Commonly used speed-control concepts permit speed ranges up to two-three times the base speed via voltage to frequency (V/f), that is, field-weakening control. This paper teaches the extension of the speed-control range up to nine times the base speed through online reconfiguration of the motor windings via electronic switches. The switchover of the windings, either from a winding with p1 poles to p2 poles, or from series to parallel connection of the number of turns per phase-so-called (V/Nldrf) control-lasts less than a 60-Hz cycle. Such fast switchover causes small transients only, and therefore, this concept is applicable to most variable-speed drives.