Topic
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, a method suggested in the past to suppress the vibrations of flexible rotor systems passing through critical speeds is reconsidered, where an appropriate switching of the system stiffness (by using shape memory alloys, for instance) is utilized.
Abstract: A method suggested in the past to suppress the vibrations of flexible rotor systems passing through critical speeds is reconsidered. An appropriate switching of the system stiffness (by using shape memory alloys, for instance) is utilized. To model the nonstationary system behavior more realistically, the rotor is driven by a limited power supply. A special feature is the inclusion of unequal bending stiffnesses of the shaft. The stationary and transient behavior of the motor and system characteristic and the deformation amplitudes and phase angles, are examined. Attention is focussed on the strategy for switching the stiffness to yield small resonance deflections.
25 citations
TL;DR: In this article, the effects of bearing and shaft asymmetries on the stability of the rotor were investigated for design and diagnostic purposes, and the amplitude and phase modulation functions that quantify the effect of slowly varying the rotational speed on the motion characteristics were derived.
25 citations
TL;DR: In this article, the authors theoretically investigate the forced wetting transition for axisymmetric menisci on fibers of varying radii, and find that the maximum speed occurs at vanishing apparent contact angle.
Abstract: A solid object can be coated by a nonwetting liquid since a receding contact line cannot exceed a critical speed. We theoretically investigate this forced wetting transition for axisymmetric menisci on fibers of varying radii. First, we use a matched asymptotic expansion and derive the maximum speed of dewetting. For all radii, we find the maximum speed occurs at vanishing apparent contact angle. To further investigate the transition, we numerically determine the bifurcation diagram for steady menisci. It is found that the meniscus profiles on thick fibers are smooth, even when there is a film deposited between the bath and the contact line, while profiles on thin fibers exhibit strong oscillations. We discuss how this could lead to different experimental scenarios of film deposition
25 citations
TL;DR: In this paper, the long-term response of a slab track substructure to moving train loads as well as its relation with critical speed is evaluated using lower-bound dynamic shakedown analysis.
25 citations
TL;DR: Both the critical speed for ultrasmooth rotation and the ultimate speed decrease with increasing radius of the inner tube with constant intertube distance, as well as the centrifugal force and thermal motion of atoms will stimulate flexile deformation of CNTs, namely waving tube axis and distorting cross-section, which will lead to an increase in rotational friction.
Abstract: The behavior of nanobearings constructed from double-walled carbon nanotubes (DWCNTs) is investigated with molecular dynamics simulations. The results show that the (5, 5)/(10, 10) DWCNTs can work as stable and reliable nanobearings to a speed as high as ~2.65 r ps−1 with an inner tube as rotator. When the speed is lower than ~0.75 r ps−1, the nanobearings remain in an ultrasmooth state, beyond which the intertube friction increases and fluctuates sharply. The rotational friction is sensitive to many factors such as rotation speed, radial size, and flexibility of CNTs. Increase in rotation speed and the radial sizes of CNTs leads to increase of centrifugal force and decrease of intertube distance, thus, increases the intertube friction. As a result, both the critical speed for ultrasmooth rotation and the ultimate speed decrease with increasing radius of the inner tube with constant intertube distance. The centrifugal force and thermal motion of atoms will stimulate flexile deformation of CNTs, namely waving tube axis and distorting cross-section, which will lead to an increase in rotational friction. When the outer tube serves as the rotator, the DWCNT nanobearing becomes more easily damaged.
24 citations