Showing papers on "Critical speed published in 1977"

Permanent automatic rotor balancer for shafts operating above critical speed

Abstract: A pair of balancing weights are mounted on opposite sides of the center line of the rotor for movement about the axis of the rotor. The weights are automatically locked against movement about the axis of the rotor when the rotor is rotating below critical speed and automatically released for free movement about the axis of the rotor when the rotor is rotating above critical speed. The weights are exemplified as roller cages. The balancing weights are variously locked by mechanical clutches actuated at critical speed. The clutching for the weights is either individual or such that the weights are necessarily locked against movement and released simultaneously. Centrifugal force is used to control the clutches.

High-speed rotating crushing machinery

Abstract: Improved drive shafting elements suitable for use in high speed rotating crushing machinery are disclosed comprising a central cantilever shaft mounted within a surrounding sleeve to which the cantilever shaft 15 rigidly connected at one end and within which the cantilever shaft has substantial radial play at the other end to permit a rotating impeller or similar element mounted thereon to center itself automatically for rotation on its center of gravity at speeds above the first critical speed. Means are included for damping radial vibrations as the shafting rotates through the first critical speedand for damping whirl due to shaft instabilities and self-excited vibrations above the first critical speed. Improved impactor targets for use in centrifugal crushing machines and and improved centrifugal crushing method are also disclosed.

Motor speed control circuits

Abstract: A motor speed control circuit for use in a washing machine includes a timer which in normal operation accelerates the motor from a wash speed to a distribution speed before a fast acceleration to the spin dry speed. The control circuit includes speed measurement means for maintaining the motor at spin speed in the event of a power interruption during a spin cycle provided the drum speed remains above a given critical speed when the power returns. If not, a redistribution cycle takes place before the motor is accelerated to its spin speed.

Analytical and Experimental Investigation of the Stability of Intershaft Squeeze Film Dampers—Part 1: Demonstration of Instability

Abstract: Modern high-speed multishaft gas tubine engines incorporate viscous damped bearings to decrease overall system vibration and bearing loads. As viscous damper technology is applied to advanced engine design, more sophisticated analytical and experimental techniques are required to prove new concepts. This analysis will present the results of an investigation of the feasibility of damping engine vibration with a viscous damped intershaft bearing on a two-shaft gas turbine engine. Experimental results from a rotor dynamics simulation rig indicate an instability of the rotor system at speeds above a fundamental critical speed. An analytical model of the two-rotor system is presented and the results of both a classical stability analysis and a time transient response analysis verify the experimental data. The analytical model may be used to predict the stability of two-shaft engines which incorporate an intershaft damped bearing.

Effects of Radial Appendage Flexibility on Shaft Whirl Stability

Abstract: Introduction T move to lighter, more flexible gas turbine engine components has initiated several recent investigations into the effects of component flexibility on shaft whirl. Based on a study of a flexible shaft-disk model, Chivens and Nelson concluded that critical speeds are not affected significantly by disk flexibility. Some limitations concerning this conclusion have been discussed by Klompas. The object of this Note is to show that, provided that a sufficiently wide range of parameters is considered, the effects of an appendage's flexibility on critical speeds can become significant. Critical speed stability boundaries are shown to reduce to the expected limiting cases of a shaft containing rigid appendages as the appendage's stiffness increases, and to an elastic shaft with a concentrated mass at the point of appendage attachment when the appendage's stiffness decreases. Stability boundaries are obtained by a Liapunov analysis in which the system's dynamic potential serves as a Liapunov testing function.

Stability of numerical integration techniques for transient rotor dynamics

Abstract: A finite element model of a rotor bearing system was analyzed to determine the stability limits of the forward, backward, and centered Euler; Runge-Kutta; Milne; and Adams numerical integration techniques. The analysis concludes that the highest frequency mode determines the maximum time step for a stable solution. Thus, the number of mass elements should be minimized. Increasing the damping can sometimes cause numerical instability. For a uniform shaft, with 10 mass elements, operating at approximately the first critical speed, the maximum time step for the Runge-Kutta, Milne, and Adams methods is that which corresponds to approximately 1 degree of shaft movement. This is independent of rotor dimensions.

Acoustic fluctuations using the parabolic profile

Abstract: Calculations were performed using the normal‐mode solutions for the parabolic profile to determine the behavior of the acoustic field when either the axial or maximum profile sound speed was altered slightly from an unperturbed value. It was found that incrementing either the axial or maximum profile speed by small amounts produced a change in the focal length of the parabolic profile, which in turn caused a range‐dependent compression or expansion of the unperturbed acoustic field with no noticeable distortion for frequencies less than 400 Hz and range less than 550 km. Approximating the effect of the first‐mode semidiurnal internal tide by appropriate variations in axial velocity, this fact was used to show that for cw propagation between fixed source and fixed receiver, the fluctuation in acoustic amplitude produced by the internal tide can be obtained by sampling the amplitude function for the unperturbed profile a distance Δr either side of the range in question, where Δr is the distance the unperturbed acoustic field is shifted due to the change in axial speed produced by the internal tide. For a moving source, a range‐dependent critical source speed was determined such that for source speeds equal to or less than the critical speed, the effect of the internal tide predominates as a source of acoustic fluctuations, while for source speeds greater than this critical speed the effect of source motion is paramount.

Turbine control system

Abstract: PURPOSE:Vibration observing and protective system and turbine wall temperature observing system are set not only to control turbine revolving speed to reduce time for critical speed but also to obtain smooth increase of speed and load variation.