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, the dynamic response of a cracked rotor near its critical speed has been computed via a numerical method to investigate the influence of nonlinear breathing of the crack and that of the imbalance orientation angle β on the stability, critical speed and peak response of the rotor.
64 citations
12 Jun 2001
TL;DR: In this article, the authors proposed a medium voltage adjustable speed drive that consists of a twelve-pulse diode rectifier and a three-level neutral point clamped inverter using high voltage IGBTs.
Abstract: This paper presents a solution to allow simple and risk-free retrofit of existing fixed speed induction motors with medium voltage adjustable speed drives to achieve attractive energy savings. The presented medium voltage adjustable speed drive consists of a twelve-pulse diode rectifier and a three-level neutral point clamped inverter using high-voltage IGBTs. Innovative features of the drive include series-connection of high-voltage IGBTs. The motor control is based on field-oriented vector control and an optimized PWM modulator, so that switching losses and current harmonics are minimized. An EMC-sinusoidal output filter is available to retrofit existing fixed speed motors with adjustable speed drive converter without incurring overvoltage stress on the winding insulation system, changes on the motors, the mechanical couplings, or the motor feeder cables, excitation of motor critical speed, or reduction in shaft power. Experimental and field results are also presented to confirm the proposed topology and related energy savings.
64 citations
TL;DR: In this article, a new elastic nonlocal stress model and analytical solutions for torsional dynamic behaviors of circular nanorods/nanotubes were developed for free torsion vibration.
64 citations
TL;DR: In this paper, an analytical investigation is made of a heretofore unimportant flutter phenomenon that may occur in a propeller-nacellewing combination, a flutter condition which involves propeller and nacelle precession, and which has been of major concern recently.
Abstract: An analytical investigation is made of a heretofore unimportant flutter phenomenon that may occur in a propeller-nacellewing combination—a flutter condition which involves propeller and nacelle precession, and which has been of major concern recently. One of the objects of the investigation is to isolate and show the influence of those parameters which appear to be most strongly linked with this whirl-type instability. Considered, for example, are various combinations of pitch and yaw stiffnesses of the nacelle, structural damping, and propeller speed. To understand the behavior of the system better, the motion due to various initial disturbances is also studied for both subcritical and supercritical conditions. The results presented are derived by digital and analog means, the analog setup being used primarily for the motion studies. Part of the study is devoted to a further examination of the propeller aerodynamics. Finally, a comparison is made of analytically determined critical conditions with results obtained in some wind-tunnel tests.
63 citations
TL;DR: In this paper, a study was made of the friction of nylon fiber (monofilament fishing line) rubbing against spinning aluminum and nylon capstans (cylinders), in the presence of various lubricants.
63 citations