scholarly journals Actively Controlled Bearing Dampers for Aircraft Engine Applications

1999 ◽  
Author(s):  
John M. Vance ◽  
Daniel Ying ◽  
Jorgen L. Nikolajsen
Keyword(s):  
Critical Speed ◽  
Aircraft Engine ◽  
Viscous Damping ◽  
Aircraft Engines ◽  
Equivalent Viscous Damping ◽  
Critical Speeds ◽  
Speed Range ◽  
Coulomb Type ◽  
Er Damper ◽  
San Andres

This paper describes some of the requirements for bearing dampers to be used in an aircraft engine and briefly discusses the pros and cons of various types of dampers that were considered as candidates for active control in aircraft engines. A disk type of electrorheological (ER) damper was chosen for further study and testing. The paper explains how and why the choice was made. For evaluating potential applications to aircraft engines, an experimental development engine (XTE-45) was used as an example for this study. Like most real aircraft engines, the XTE-45 ran through more than one critical speed in its operating speed range. There are some speeds where damping is desirable and other speeds where it is not. Thus, the concept of a damper with controllable forces appears attractive. The desired equivalent viscous damping at the critical speeds along with the available size envelope were two of the major criteria used for comparing the dampers. Most previous investigators have considered the ER damper to produce a purely Coulomb type of damping force and this was the assumption used by the present authors in this study. It is shown in a companion paper (Vance and San Andres, 1999), however, that a purely Coulomb type of friction cannot restrain the peak vibration amplitudes at rotordynamic critical speeds and that the equivalent viscous damping for rotordynamics is different from the value derived by previous investigators for planar vibration. Control laws for Coulomb damping are derived in Vance and San Andres, (1999) to achieve minimum rotor vibration amplitudes in a test rig while avoiding large bearing forces over a speed range that includes a critical speed. The type of control scheme required and its effectiveness was another criterion used for comparing the dampers in this paper.

Actively Controlled Bearing Dampers for Aircraft Engine Applications

2000 ◽  
Vol 122 (3) ◽  
pp. 466-472 ◽  
Author(s):  
John M. Vance ◽  
Daniel Ying ◽  
Jorgen L. Nikolajsen
Keyword(s):  
Aircraft Engine ◽  
Companion Paper ◽  
Viscous Damping ◽  
Aircraft Engines ◽  
Damping Force ◽  
Equivalent Viscous Damping ◽  
Experimental Development ◽  
Critical Speeds ◽  
Coulomb Type ◽  
Er Damper

This paper describes some of the requirements for bearing dampers to be used in an aircraft engine and briefly discusses the pros and cons of various types of dampers that were considered as candidates for active control in aircraft engines. A disk type of electrorheological (ER) damper was chosen for further study and testing. The paper explains how and why the choice was made. For evaluating potential applications to aircraft engines, an experimental development engine (XTE-45) was used as an example for this study. Like most real aircraft engines, the XTE-45 ran through more than one critical speed in its operating speed range. There are some speeds where damping is desirable and other speeds where it is not. Thus, the concept of a damper with controllable forces appears attractive. The desired equivalent viscous damping at the critical speeds along with the available size envelope were two of the major criteria used for comparing the dampers. Most previous investigators have considered the ER damper to produce a purely Coulomb type of damping force and this was the assumption used by the present authors in this study. It is shown in a companion paper, however, that a purely Coulomb type of friction cannot restrain the peak vibration amplitudes at rotordynamic critical speeds and that the equivalent viscous damping for rotordynamics is different from the value derived by previous investigators for planar vibration. The type of control scheme required and its effectiveness was another criterion used for comparing the dampers in this paper. [S0742-4795(00)00803-6]

NONDIMENSIONAL ANALYSIS OF ANNULAR DUCT FLOW IN MAGNETORHEOLOGICAL/ELECTRORHEOLOGICAL DAMPERS

2005 ◽  
Vol 19 (07n09) ◽  
pp. 1577-1583 ◽  
Author(s):  
JIN-HYEONG YOO ◽  
NORMAN M. WERELEY
Keyword(s):  
Quadratic Equation ◽  
Damping Coefficient ◽  
Viscous Damping ◽  
Uniform Field ◽  
Duct Flow ◽  
Equivalent Viscous Damping ◽  
Performance Metric ◽  
Annular Duct ◽  
Er Damper ◽  
Analytical Expressions

Approximate analytical expressions describing MR/ER damper performance for an axisymmetric annular duct under the assumption of uniform field are presented. The key performance metric is the damping coefficient, which is the ratio of the equivalent viscous damping constant, Ceq, to the Newtonian viscous damping constant, C. To develop these approximations, a quadratic equation was used to approximate the center of the plug location in the annular duct. This equation simplified the calculation of the annular duct solution without resorting to numerical methods to solve the boundary value problem. Approximations for the damping coefficient are developed on this basis.

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.

A New Foil Gas Bearing With Compression Springs as Compliant Structure for Microturbomachinery Applications

2006 ◽  
Author(s):  
Ju-Ho Song ◽  
Daejong Kim
Keyword(s):  
Critical Speed ◽  
Hydrodynamic Instability ◽  
Load Capacity ◽  
Viscous Damping ◽  
Equivalent Viscous Damping ◽  
Foil Bearings ◽  
Compliant Structure ◽  
Air Supply ◽  
Compression Springs ◽  
Gas Bearing

A new foil gas bearing is introduced in this paper. This foil gas bearing uses series of compression springs as a compliant structure instead of expensive corrugated bump foils. The new foil gas bearing is very simple in structure and easy to manufacture. A theoretical model to estimate stiffness and damping of the spring bump was developed. Measured stiffnesses of individual spring bump agree well with predictions. Load capacity was measured up to 62.5 N at 20,000rpm with both cooled and uncooled bearings. Initial selection of spring geometry rendered rather soft supports compared to other bump foil bearings, and allowed only limited load during the test. Developed cooling method using direct air supply holes machined on the bearing sleeve was very effective to cool the test bearing because the spring bumps are not connected along the circumferential direction, and allow very effective circumferential distribution of cooling air. A series of orbit simulation was performed to estimate critical speed and onset speed of instability. Bump dynamics was directly coupled with the orbit simulation. Critical speed was estimated at around 7500 rpm due to relatively soft support structure. Hydrodynamic instability with WFR 0.5 could be predicted at around 15,000 rpm. The rotor instability is predicted even under the equivalent viscous damping extracted from bump dynamics, implying the viscous damping alone within the bump cannot suppress hydrodynamic instability of foil bearings.

Critical Speed Damper

1963 ◽  
Vol 30 (3) ◽  
pp. 463-464
Author(s):  
Samuel Levy
Keyword(s):  
Critical Speed ◽  
Journal Bearing ◽  
Rotating Shaft ◽  
Critical Speeds ◽  
Speed Range ◽  
Spherical Bearing

It is shown that a damper applied to the spherical bearing at the ends of a rotating shaft to damp pitch and yaw motions of the journal bearing can markedly reduce the deflection caused by unbalance near critical speeds. Equations are given for optimizing the damping and for computing the damping moment which must be carried by the journal bearing. It is shown that with optimum damping of a centrally loaded uniform shaft, the load carried by the journal bearing in the critical-speed range is no more than 67 percent greater than it would have been for a rigid shaft. The corresponding moment carried by the journal bearing is less than the amount which would develop at the mid-length of the shaft in the absence of elastic deflections.

Critical Speeds Analysis for Dual Rotor Turbofan Engine Using Finite Element Method

2019 ◽  
Author(s):  
Kai Sun ◽  
Zhao Wan ◽  
Huiying Song ◽  
Shaohui Wang
Keyword(s):  
Finite Element ◽  
Rotational Speed ◽  
Critical Speed ◽  
Fixed Number ◽  
Rotor System ◽  
Speed Ratio ◽  
Aircraft Engines ◽  
Campbell Diagram ◽  
Critical Speeds ◽  
Rotor Model

Abstract Intershaft bearing is widely adopted in dual rotor turbofan aircraft engines. Since this kind of dual rotor system has two different rotor speeds and the intershaft bearing leads to the coupling between HP rotor and LP rotor, the calculation of the critical speeds is much more complicated than that of the rotor systems without intershaft bearing. Compared to a single rotor system, the dual rotor system has more critical speeds which can be classified as critical speeds excited by HP rotor and that by LP rotor. In the paper, a finite element rotor model of a high-bypass turbofan jet engine with intershaft bearing is established for the study of critical speeds analysis. The general axisymmetric element is used to model the shafts and disks, and the blades are simplified to mass points. The main bearings including the intershaft bearing are set up with spring element. Assuming that the rotational speed ratio of the two rotors for the dual rotor system is a fixed number, the critical speeds are calculated using three methods based on the finite element rotor model. For the first method, the system critical speeds are obtained directly by Campbell diagram based on QR damped solution method. Then the synchronous unbalance response analyses are carried out and the rotor critical speeds are derived from the amplitude-frequency curves. For the last method, multiple group Campbell diagram analyses are conducted. With one rotor speed fixed at constant rpm N, we can change the speed of the other rotor to obtain one group of critical speeds. By varying speed N of the two rotors, a critical speeds data set can be obtained and plotted as a dual rotor critical speed map. The critical speeds can be easily extracted from the critical speed map according to the rotational speed curve of the engine. The study shows that the dual rotor system critical speeds calculated from above three methods are identical. For the first two methods, the rotational speed ratio of two rotors must be a known and fixed number, which is impossible in reality. The third proposal has no rotation speed relation restriction for rotors, and therefore is recommended for analyzing the critical speeds of aircraft engines with intershaft bearing.

Formation of Standing Waves in Radial Tires

1984 ◽  
Vol 12 (1) ◽  
pp. 44-63 ◽  
Author(s):  
Y. D. Kwon ◽  
D. C. Prevorsek
Keyword(s):  
High Speed ◽  
Critical Speed ◽  
Unit Length ◽  
Standing Waves ◽  
Rolling Resistance ◽  
Damping Coefficient ◽  
Circular Membrane ◽  
Critical Speeds ◽  
Steel Cord ◽  
The Individual

Abstract Radial tires for automobiles were subjected to high speed rolling under load on a testing wheel to determine the critical speeds at which standing waves started to form. Tires of different makes had significantly different critical speeds. The damping coefficient and mass per unit length of the tire wall were measured and a correlation between these properties and the observed critical speed of standing wave formation was sought through use of a circular membrane model. As expected from the model, desirably high critical speed calls for a high damping coefficient and a low mass per unit length of the tire wall. The damping coefficient is particularly important. Surprisingly, those tire walls that were reinforced with steel cord had higher damping coefficients than did those reinforced with polymeric cord. Although the individual steel filaments are elastic, the interfilament friction is higher in the steel cords than in the polymeric cords. A steel-reinforced tire wall also has a higher density per unit length. The damping coefficient is directly related to the mechanical loss in cyclic deformation and, hence, to the rolling resistance of a tire. The study shows that, in principle, it is more difficult to design a tire that is both fuel-efficient and free from standing waves when steel cord is used than when polymeric cords are used.

Taylor-vortex instability and annulus-length effects

1976 ◽  
Vol 75 (1) ◽  
pp. 1-15 ◽  
Author(s):  
J. A. Cole
Keyword(s):  
Critical Speed ◽  
Taylor Vortex ◽  
Vortex Instability ◽  
Critical Speeds ◽  
Taylor Vortices ◽  
Torque Measurements ◽  
Concentric Cylinders ◽  
Theoretical Predictions ◽  
Range Of Values ◽  
Visual Observations

Critical speeds for the onset of Taylor vortices and for the later development of wavy vortices have been determined from torque measurements and visual observations on concentric cylinders of radius ratios R1/R2 = 0·894–0·954 for a range of values of the clearance c and length L: c/R1 = 0·0478–0·119 and L/c = 1–107. Effectively zero variation of the Taylor critical speed with annulus length was observed. The speed at the onset of wavy vortices was found to increase considerably as the annulus length was reduced and theoretical predictions are realistic only for L/c values exceeding say 40. The results were similar for all four clearance ratios examined. Preliminary measurements on eccentrically positioned cylinders with c/R1 = 0·119 showed corresponding effects.

Three-dimensional predator–prey interactions: a computer simulation of bird flocks and aircraft

1986 ◽  
Vol 64 (11) ◽  
pp. 2624-2633 ◽  
Author(s):  
Peter F. Major ◽  
Lawrence M. Dill ◽  
David M. Eaves
Keyword(s):  
Computer Simulation ◽  
Prey Species ◽  
Three Dimensional ◽  
Aircraft Engine ◽  
Aquatic Environments ◽  
Aircraft Engines ◽  
Predator Prey ◽  
Simulation Techniques ◽  
Computer Simulation Techniques ◽  
Individual Prey

Three-dimensional interactions between grouped aerial predators (frontal discs of aircraft engines), either linearly arrayed or clustered, and flocks of small birds were studied using interactive computer simulation techniques. Each predator modelled was orders of magnitude larger than an individual prey, but the prey flock was larger than each predator. Expected numbers of individual prey captured from flocks were determined for various predator speeds and trajectories, flock–predator initial distances and angles, and flock sizes, shapes, densities, trajectories, and speeds. Generally, larger predators and clustered predators caught more prey. The simulation techniques employed in this study may also prove useful in studies of predator–prey interactions between schools or swarms of small aquatic prey species and their much larger vertebrate predators, such as mysticete cetaceans.The study also provides a method to study problems associated with turbine aircraft engine damage caused by the ingestion of small flocking birds, as well as net sampling of organisms in open aquatic environments.

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