Zero (Or Low) Torsional Stiffness Couplings

1969 ◽  
Vol 11 (1) ◽  
pp. 76-87 ◽  
Author(s):  
C. W. Chapman
Keyword(s):  
The Other ◽  
Torsional Stiffness ◽  
Operating Speed ◽  
Critical Speeds ◽  
Operating Range ◽  
Rotating Systems ◽  
Speed Range ◽  
Coupling Stiffness

In many rotating systems shaft couplings of low torsional stiffness may bring dangerous one node critical speeds below the operating speed range. However, even soft couplings on multi-mass systems may allow higher node criticals to remain in the operating range. If two sections of a system be coupled by a coupling of zero stiffness torsional impulses cannot be transmitted from one section to the other, thus eliminating criticals. Coupling stiffness must be related to the torque transmitted, and experiments indicate that a stiffness/torque ratio below about 4 is almost as effective as zero stiffness.

Lateral Rotordynamic Analysis of a Large Alternator/Flywheel/Motor Train

2010 ◽  
Author(s):  
Jawad Chaudhry ◽  
Tim Dimond ◽  
Amir Younan ◽  
Paul Allaire
Keyword(s):  
Critical Speed ◽  
Operating Speed ◽  
Response Level ◽  
Critical Speeds ◽  
The Third ◽  
Unbalance Response ◽  
Speed Range ◽  
Stress Levels ◽  
Full Speed ◽  
Working Day

A large alternator/flywheel/motor train is employed as part of the power system for the ALCATOR C-MOD experiment at the MIT Plasma Fusion Center. The alternator is used to provide peak pulse power of 100 MW to the magnets employed in the fusion experiment. The flywheel diameter is 3.3m and the alternator is 1.8 m in diameter. After being driven up to full speed over a long period of time by a 1491 kW motor, the alternator is rapidly decelerated from approximately 1800 rpm to 1500 rpm during a 2 second interval. This sequence is repeated about six times per working day on average. A full lateral rotordynamic analysis of the including the rotors, fluid film bearings and unbalanced motor magnetic force was carried to assess the effects of rotor modifications in the alternator shaft bore. This paper provides a more detailed analysis of a complicated rotor train than is often performed for most rotors. Critical speeds, stability and unbalance response were evaluated to determine if lateral critical speeds might exist in the operating speed range in the existing or modified rotor train and if unbalance levels were within acceptable ranges. Critical speeds and rotor damping values determined for the rotor system with the existing and modified rotor. The first critical speed at 1069 rpm is an alternator mode below the operating speed range. The second critical speed is also an alternator mode but, at 1528 rpm, is in the rundown operating speed range. The third critical speed is a flywheel mode at 1538 rpm, also in the rundown operating speed range but well damped. The predicted highest rotor amplitude unbalance response level is at 1633 rpm, again in the operating speed range. Direct comparisons were made with measured bearing temperature values, with good agreement between calculations and measurements. Stress levels in the rotor were evaluated and found to be well below yield stress levels for the material for both original and modified rotors. Comparisons we carried out between standard vibration specifications and measured vibration levels which indicated that the third critical speed amplification factors were much higher than API standards indicate they should have been. Corrective actions to reduce unbalance were taken for the modified rotor.

Hybrid Active Vibration Control of Rotorbearing Systems Using Piezoelectric Actuators

1993 ◽  
Vol 115 (1) ◽  
pp. 111-119 ◽  
Author(s):  
A. B. Palazzolo ◽  
S. Jagannathan ◽  
A. F. Kascak ◽  
G. T. Montague ◽  
L. J. Kiraly
Keyword(s):  
Vibration Control ◽  
Search Algorithm ◽  
Active Vibration Control ◽  
Piezoelectric Actuators ◽  
Operating Speed ◽  
Speed Range ◽  
Active Vibration ◽  
Linear Fit ◽  
Hybrid Interface ◽  
Grid Search Algorithm

The vibrations of a flexible rotor are controlled using piezoelectric actuators. The controller includes active analog components and a hybrid interface with a digital computer. The computer utilizes a grid search algorithm to select feedback gains that minimize a vibration norm at a specific operating speed. These gains are then downloaded as active stiffnesses and dampings with a linear fit throughout the operating speed range to obtain a very effective vibration control.

Using Dynamic Analysis for Compact Gear Design

1998 ◽  
Author(s):  
Ping-Hsun Lin ◽  
Hsiang Hsi Lin ◽  
Fred B. Oswald ◽  
Dennis P. Townsend
Keyword(s):  
Dynamic Response ◽  
Bending Strength ◽  
Three Dimensional ◽  
Spur Gear ◽  
Dynamic Factor ◽  
Operating Speed ◽  
Gear Design ◽  
Dynamic Factors ◽  
Speed Range ◽  
Response Change

Abstract This paper presents procedures for designing compact spur gear sets with the objective of minimizing the gear size. The allowable tooth stress and dynamic response are incorporated in the process to obtain a feasible design region. Various dynamic rating factors were investigated and evaluated. The constraints of contact stress limits and involute interference combined with the tooth bending strength provide the main criteria for this investigation. A three-dimensional design space involving the gear size, diametral pitch, and operating speed was developed to illustrate the optimal design of spur gear pairs. The study performed here indicates that as gears operate over a range of speeds, variations in the dynamic response change the required gear size in a trend that parallels the dynamic factor. The dynamic factors are strongly affected by the system natural frequencies. The peak values of the dynamic factor within the operating speed range significantly influence the optimal gear designs. The refined dynamic factor introduced in this study yields more compact designs than AGMA dynamic factors.

Thermally Induced Synchronous Instability of a Radial Inflow Overhung Turbine: Part I

1997 ◽  
Author(s):  
H. B. Faulkner ◽  
W. F. Strong ◽  
R. G. Kirk
Keyword(s):  
Thermal Expansion ◽  
Operating Speed ◽  
Lateral Motion ◽  
Turbine Wheel ◽  
Thermally Induced ◽  
Lateral Dynamics ◽  
Morton Effect ◽  
Speed Range ◽  
Differential Thermal Expansion ◽  
Rotor Dynamic

Abstract This paper is in two parts, and concerns the lateral dynamics of a large turbocharger rotor with overhung wheels. Initial rotor dynamic analysis indicated no excessive motion in the operating speed range. However, testing showed excessive motion, which was initially traced to the radial-inflow turbine wheel becoming loose on the shaft, due to transient differential thermal expansion in the wheel on startup. The attachment of the wheel was modified to eliminate this problem. The discussion up to this point is in Part I of the paper, and the remainder is in Part II. The wheel attachment modification extended the range of satisfactory operation upward considerably, but excessive lateral motion was again encountered near the upper end of the operating speed range. This behavior was traced to thermal bowing of the shaft at the turbine end, known as the Morton Effect. The turbine end bearing was modified to eliminate this problem, and satisfactory operation was then achieved throughout the operating speed range.

Genetic Optimization of Geometrical Parameters of High Speed Rotor

2015 ◽  
Author(s):  
Behnam Ghalamchi ◽  
Adam Kłodowski ◽  
Jussi T. Sopanen ◽  
Aki M. Mikkola
Keyword(s):  
High Speed ◽  
Turbine Rotor ◽  
Optimization Techniques ◽  
Design Parameters ◽  
Geometrical Parameters ◽  
Campbell Diagram ◽  
Critical Speeds ◽  
Operation Speed ◽  
Wide Range ◽  
Speed Range

The main scope of this paper is optimization of high speed rotor systems by using Evolutionary Algorithm. The target of the optimization is finding geometrical parameters of the shaft, in such a way that the critical speeds are not occurring in the operation speed range. Rotating machines have a wide range of applications in industrial machinery and applying numerical optimization techniques helps engineers to improve the performance of rotor bearing systems. A schematic of a turbine rotor system is studied. The rotor is modeled using finite element method and Timoshenko beam elements having four degrees of freedom (DOF) per node — two translational and two rotational. Critical speeds are identified using Campbell diagram. The outcome of the simulation is looking to find the widest safe margin for operation speed range without any critical speed in Campbell diagram within the operation range. Design parameters for optimization are overhang shafts lengths and diameters. Several simulation runs with different variables shows a significant effect of these parameters in dynamic behavior of the system. Comparison of the results with the basic design of turbine rotor reveals that all constraints are satisfied.

Efficiency Improvement of an Automatic Ball Balancer

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Yukio Ishida ◽  
Tomonori Matsuura ◽  
Xiao Long Zhang
Keyword(s):  
Critical Speed ◽  
Vibration Suppression ◽  
The Self ◽  
The Other ◽  
Efficiency Improvement ◽  
Cylindrical Chamber ◽  
Rotor Systems ◽  
Speed Range ◽  
Excited Oscillation ◽  
Inside Wall

An automatic ball balancer is a unique vibration suppression device for rotor systems. Theoretically, two balls in a cylindrical chamber of the rotor are located at the optimal positions on the opposite side to the unbalance and cancel the unbalance automatically in the super-critical speed range. However, this device is not used widely due to two malfunctions. One is the influence of friction. Due to the inevitable friction between the balls and the inside wall of the channel, the balls stop near the optimal positions and do not balance the rotor perfectly. The other is the self-excited oscillation which occurs near and above the major critical speed. The objectives of the present paper are to clarify the fundamental characteristics of a ball balancer and to introduce some simple methods to eliminate these malfunctions.

Experimental Evaluation of Multiplane-Multispeed Rotor Balancing Through Multiple Critical Speeds

1976 ◽  
Vol 98 (3) ◽  
pp. 988-998 ◽  
Author(s):  
J. M. Tessarzik ◽  
R. H. Badgley ◽  
D. P. Fleming
Keyword(s):  
Experimental Tests ◽  
Influence Coefficient ◽  
Critical Speeds ◽  
Vibration Data ◽  
Vibration Sensors ◽  
Flexible Rotors ◽  
Speed Range ◽  
Full Speed ◽  
Influence Coefficient Method ◽  
Rotor Balancing

Experimental tests have been conducted to further demonstrate the ability of the Influence Coefficient Method to achieve precise balance of flexible rotors of virtually any design for operation through virtually any speed range. Four distinct practical aspects of flexible-rotor balancing were investigated in the present work: (1) Balancing for operation through multiple bending critical speeds; (2) balancing of rotors mounted in both rigid and flexible bearing supports, the latter having significantly different stiffnesses in the horizontal and vertical directions so as to cause severe ellipticity in the vibration orbits; (3) balancing of rotors with various amounts of measured vibration response information (e.g., numbers of vibration data sets, and numbers and types of vibration sensors), and with different number of correction planes; (4) balancing of rotors with different (though arbitrary) initial unbalance configurations. Tests were made on a laboratory quality machine having a 122-cm (48-in.) long rotor weighing 50 kg (110 lb) and covering a speed range up to 18,000 rpm. The balancing method was found in every instance to be effective, practical, and economical, permitting safe rotor operation over the full speed range covering four rotor bending critical speeds.

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