Showing papers on "Critical speed published in 1983"
TL;DR: Particle simulations of the modified two-stream instability demonstrate strong electron acceleration rather than bulk heating when the relative drift speed is below a critical speed as discussed by the authors, which accelerates the electrons much above the phase speed of the linearly unstable modes.
Abstract: Particle simulations of the modified two-stream instability demonstrate strong electron acceleration rather than bulk heating when the relative drift speed is below a critical speed Vc A very interesting nonlinear mode transition and autoresonance acceleration process is observed which accelerates the electrons much above the phase speed of the linearly unstable modes Simple criteria are presented that predict the value of Vc and the number density of the accelerated electrons
85 citations
TL;DR: In this paper, a single mass flexible rotor on damped flexible supports with active feedback control is considered and free vibrations and unbalance response of the rotor-control system are determined.
Abstract: This paper considers vibration control of a single mass flexible rotor on damped flexible supports with active feedback control. Both proportional and derivative feedback control are utilized. Free vibrations and unbalance response of the rotor-control system are determined. The effect of proportional control is to increase the critical speed of rotating machinery while the effect of derivative control is to reduce the amplitude of vibration. Generally larger ratios of support stiffness to shaft stiffness require larger values of control parameters to produce given amplitudes of vibration.
25 citations
TL;DR: In this article, the authors found that ground vibration from heavy freight trains on good quality welded track is found to have only a weak dependence on train speed above 30 km/h. At the site on which these tests were carried out, critical speed was found at which the vibration reached a peak.
23 citations
TL;DR: In this paper, a structural impedance approach is extended for the dynamic analysis of pipe structures conveying fluid flow and the critical speed associated with the dynamic stability is calculated and compared with available analytical and experimental results.
10 citations
TL;DR: In this article, the authors presented a theoretical model which allows one, with minimum computation, to design squeeze film damped rotors under conditions of high unbalance loading and derived closed form expressions for the maximum vibration amplitudes pertaining to optimally damped conditions.
Abstract: Assuming central preloading operation below the second bending critical speed and full film lubrication, this paper presents a theoretical model which allows one, with minimum computation, to design squeeze film damped rotors under conditions of high unbalance loading Closed form expressions are derived for the maximum vibration amplitudes pertaining to optimally damped conditions The resulting vibration amplitude and transmissibility data of design interest are presented for a wide range of practical operating conditions on a single chart It can be seen that for a given rotor, the lighter the bearing the more easily one can satisfy design constraints relating to allowable rotor vibration levels and lubricant supply pressure requirements The data presented are shown to be applicable to a wide variety of rotors, and a recommended procedure for optimal design is outlinedCopyright © 1982 by ASME
8 citations
TL;DR: In this article, a system for real-time control of the transverse vibration of a rotating circular plate, based on a thermal stressing technique and dynamic system identification, is presented.
7 citations
TL;DR: In this article, the synchronous response due to unbalance was studied both theoretically and experimentally for a three-mass rotor mounted in three-lobe and axial-groove bearings.
Abstract: The synchronous response due to unbalance was studied both theoretically and experimentally for a three-mass rotor mounted in three-lobe and axial-groove bearings. Offset factor, preload factor and load orientation were parametrically varied for the three-lobe bearings. Theoretical predictions indicate that low preload factors (with offset factors of 0.5) result in the smallest critical speed responses. Also, for a preload factor of 0.75, offset factors of approximately 0.65 minimize the critical speed response. Experimental data for peak responses agree within 42 percent (usually much less) of predictions. Reasons for the differences are attributed to the predicted bearing stiffness and damping coefficients. Presented at the 37th Annual Meeting in Cincinnati, Ohio, May 10–13, 1982
6 citations
01 Jun 1983
TL;DR: In this article, the critical speed and frequency of an interconnected pair of wheelsets based on an asymptotic expansion in a truck geometric parameter are derived, where no restriction is placed on the values of either the shear or bending stiffness.
Abstract: Analytic formulae for the critical speed and frequency of an interconnected pair of wheelsets based on an asymptotic expansion in a truck geometric parameter are derived. No restriction is placed on the values of either the shear or bending stiffness; consequently, the entire structure of the stability surface is obtained. The surface is a symmetric function of the two dimensionless stiffnesses and it depends predominantly on their series combination. Expressions are obtained for the local and global extrema and their locations. The frequency varies monotonically from the wheelset kinematic frequency to the rigid truck frequency as a function of stiffness. The results are compared with numerical solutions and found to be accurate in the region of physically obtainable values of the expansion parameter.
6 citations
TL;DR: In this article, the critical speeds of asymmetric rotors with inertia slots were calculated by using the transfer matrix method and the flexural rigidity of the element was determined by a three-dimensional finite element method.
6 citations
01 Mar 1983
TL;DR: In this article, a nonlinear autoresonance acceleration process is observed which accelerates the electrons much above the phase speed of the linearly unstable modes, and simple criteria are presented that predict the value of Vc and the number density of the accelerated electrons.
Abstract: : Particle simulations of the modified two-stream instability demonstrate strong electron acceleration rather than bulk heating when the relative drift speed vd is below a critical speed Vc A very interesting nonlinear autoresonance acceleration process is observed which accelerates the electrons much above the phase speed of the linearly unstable modes Simple criteria are presented that predict the value of Vc and the number density of the accelerated electrons (Author)
5 citations
Patent•
14 Nov 1983
TL;DR: In this paper, an electric device for eliminating the jerking of vehicles, particularly automotive vehicles with internal combustion engines and with a control member which influences the intake thereof, and particularly idle-speed intake measures are taken in order for the jerk speed of rotation to run through automatically, that is it cannot be continuously set by the driver by any position of the gas pedal.
Abstract: An electric device for eliminating the jerking of vehicles, particularly automotive vehicles with internal combustion engines and with a control member which influences the intake thereof, and particularly idle-speed intake measures are taken in order for the jerk speed of rotation to run through automatically, that is it cannot be continuously set by the driver by any position of the gas pedal. For this purpose there are provided means for detecting the actual speed of rotation, means for comparing the actual speed of rotation with the set jerk speed of rotation as well as limiting means for producing a signal within a predetermined rotary speed range, which signal controls the control member, within which rotary range is the jerk speed of rotation. These means are developed such that the control member causes an intake which increases with the actual speed of rotation, within the critical speed of rotation range.
Patent•
10 Sep 1983
TL;DR: In this article, the rotational speed of a rotary shaft is controlled by changing the rigidity of a casing support stand in response to the speed of the rotary machine without passing a critical range.
Abstract: PURPOSE:To remove the vibration of a shaft when its speed passes a critical range by changing rigidity of a casing support stand in response to the rotational speed of a rotary machine so as to enable said speed to rise up to the rated one without passing the critical speed of said machine. CONSTITUTION:A casing 4 equipped with a rotary shaft 1, bearing 2a, bearing stand 2, rib 3 and the like is supported on the base 6 through a support stand 5. A slit 12 provided inside the casing support stand 5 communicates with a rotational speed responsive hydraulic device 14 provided outside through a hole 13. Accordingly, said hydraulic device 14 operates instantaneously in response to the rotational speed of the rotary shaft 1 and adds oil pressure to the slit so that it obtains the function as a damper. Further, spring rigidity and coefficient of damping of the casing support stand 5 are adjusted due to change in the pressure supplied to the slit 12.
Journal Article•
TL;DR: In this paper, the authors deal theoretically and experimentally with a nonlinear forced oscillation at a major critical speed in a rotating shaft which is initially bent, and show that the resonance curves at the critical speed are more complicated in shape than those in a straight shaft system and their shapes vary with the angular position of the rotor.
Abstract: This paper deals theoretically and experimentally with a nonlinear forced oscillation at a major critical speed in a rotating shaft which is initially bent. When an unsymmetrical shaft carrying a disc or a round shaft (a shaft with circular cross section) carrying an unsymmetrical rotor has an initial bend, and when it is supported by singlerow deep groove ball bearings having angular clearances, its nonlinear spring characteristic fluctuates with rotation of the shaft due to the initial bend. In such a rotating shaft system, there appears a nonlinear restoring force rotating with the shaft. The resonance curves at the major critical speed in this system are more complicated in shape than those in a straight shaft system and their shapes vary with the angular position of the rotor unbalance.
Patent•
09 Sep 1983
TL;DR: In this article, an automatic speed controller is used to increase the torque of a wound-rotor induction motor in the vicinity of critical speed, to prevent continuation for a prolonged time of dangerous vibration.
Abstract: PURPOSE:To pass speed in the vicinity of critical speed rapidly, and to prevent continuation for a prolonged time of dangerous vibration by increasing the torque of a motor in the vicinity of critical speed. CONSTITUTION:When a speed setting command is given by a speed pattern setter 11, an automatic speed controller 10 controls the position of a liquid resistor 5 in response to deviation between the speed command and speed detecting value from a speed detector 9, and controls the torque of a wound-rotor induction motor 4. A synchronous motor 1 is supplied with an output from a generator 3 for starting directly coupled with the wound-rotor induction motor 4. The speed detector 9 connects a metallic resistor 18 in parallel with the liquid resistor 5 and increases the torque of the wound-rotor induction motor 4 for a period when the number of revolution of the wound-rotor induction motor 4 is kept within speed before and behind critical speed n0, speed n1-speed n2. Accordingly, continuation for a prolonged time of dangerous vibration can be prevented.
TL;DR: In this article, the characteristics of flexible rotor systems with arbitrarily distributed mass passing through many critical speeds sequencially using numerical solutions obtained from the transition matrix method were clarified. But the authors did not consider the effect of the starting point of accelerations on the maximum amplitudes.
Abstract: This paper clarifies the characteristics of responses of flexible rotor systems with arbitrarily distributed mass passing through many critical speeds sequencially using numerical solutions obtained from the transition matrix method. The solutions superposed of each mode using these approximate equations coincided with numerical solutions very finely. Therefore, the total behaviors of the vibration of the shaft or the maximum amplitudes not only in passing through a single critical speed but also in passing through many critical speeds can be estimated by these approximate equations. It is made clear that the maximum amplitudes in transition through each critical speed are not influenced by the starting point of accelerations and they are close to those in the accelerated cases from the state of non-rotation.