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Research Papers

Simulations and Measurements of the Vibroacoustic Effects of Replacing Rolling Element Bearings With Journal Bearings in a Simple Gearbox

[+] Author and Article Information
Amanda D. Hanford

Applied Research Laboratory,
P.O. Box 30,
State College, PA 16804

Contributed by the Noise Control and Acoustics Division of ASME for publication in the Journal of Vibration and Acoustics. Manuscript received January 3, 2012; final manuscript received October 3, 2012; published online April 22, 2013. Assoc. Editor: Philippe Velex.

J. Vib. Acoust 135(3), 031012 (Apr 22, 2013) (18 pages) Paper No: VIB-12-1008; doi: 10.1115/1.4024087 History: Received January 03, 2012; Revised October 03, 2012

The effects of replacing rolling element bearings with journal bearings on the noise and vibration of a simple gearbox are computationally and experimentally evaluated. A modified component mode synthesis (CMS) approach is used, where the component modes of the shafting and gearbox housing are modeled using finite element analysis (FEA). Instead of using component modes with free boundary conditions, which is typical of CMS, the shafting and gearbox are coupled using nominal impedances computed for the different bearing types, improving convergence of the solution. Methods for computing the actual bearing impedances, including the high damping coefficients in journal bearings, are summarized. The sound radiated by the gearbox is computed using a boundary element (BE) model. The modeling results are validated against measurements made at the NASA Glenn Research Center. Both simulations and measurements reveal that the journal bearings, although highly damped, do not necessarily lead to strong reductions in gearbox vibration and noise.

Copyright © 2013 by ASME
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Figures

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Fig. 1

Schematic of the NASA GRC test gearbox: (left) top view with lid cut away, and (right) side view

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Fig. 2

Finite element model of the NASA GRC gearbox: (right) part of the top cover and front and side walls removed to reveal the inner shafting and gear blanks, and (bottom) enlarged view of the shafting and gear blanks

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Fig. 3

Approach for coupling shafting and housing models—nodes and constraints

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Fig. 4

Ball bearing schematic and force-displacement relationships

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Fig. 5

Radial load-deflection and stiffness-deflection curves for the NASA GRC gearbox ball and roller bearings

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Fig. 6

Journal bearing stiffness coefficients around the bearing circumference at 79.1 N m (700 in.-lb) torque and 3000 rpm

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Fig. 7

Journal bearing damping coefficients around the bearing circumference at 79.1 N m (700 in.-lb) torque and 3000 rpm

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Fig. 8

Comparison between the (top) journal bearing radial stiffnesses, and (bottom) rotational stiffness magnitudes to those of the ball and roller bearings at the input side of the gearbox at 79.1 N m (700 in.-lb) torque

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Fig. 9

Journal bearing radial damping at 79.1 N m (700 in.-lb) torque and variable rpm

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Fig. 10

Measured and simulated top panel modes attached to the housing

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Fig. 11

Simulated and measured drive point mobility of the top panel at two drive points on the top plate

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Fig. 12

Measured gearbox mode loss factors, along with averaged curve fits for the top plate, shaft, top housing, and miscellaneous modes (no curve fit)

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Fig. 13

Simulated (right) and measured (left) transfer accelerances between the gear tooth loads (in line of action) and bearing accelerometers with the top panel removed: (top) vertical, and (bottom) horizontal (without accelerometer 3, which malfunctioned)

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Fig. 15

Measured averaged vertical accelerations (upper left), horizontal accelerations (upper right), and pressures (bottom) at 1 × GMF for several operational speeds (rpm), 79.1 N m (700 in.-lb) torque

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Fig. 16

Measured averaged vertical accelerations (upper left), horizontal accelerations (upper right), and pressures (bottom) at 2 × GMF for several operational speeds (rpm), 79.1 N m (700 in.-lb) torque

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Fig. 14

Radiated sound power and high frequency limit (piston) radiated sound power for the gearbox with rolling element bearings and drive in the LOA of the meshing gears

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Fig. 20

Standard single land journal bearing

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Fig. 21

Fluid film pressure distribution for the journal bearing

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Fig. 17

Vertical vibration at the rolling element bearing on the gearbox input side at 1 × GMF (upper left). Measurements at the NASA GRC, (upper right) simulations, (lower left) differences between gearbox vibrations with rolling element and journal bearings, 79.1 N m (700 in.-lb) torque.

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Fig. 18

Differences between the vibrations and noise from the gearbox with rolling element and journal bearings for measured and simulated averaged vertical accelerations (upper left), horizontal accelerations (upper right), and pressures (bottom) at 1 × GMF for several operational speeds (rpm), 79.1 Nm (700 in-lb) torque

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Fig. 19

Differences between vibrations and noise from gearbox with rolling element and journal bearings for measured and simulated averaged vertical accelerations (upper left), horizontal accelerations (upper right), and pressures (bottom) at 2 × GMF for several operational speeds (rpm), 79.1 N m (700 in.-lb) torque

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Fig. 22

Effect of rotation about x (vertical) on the film pressure: (left) no rotation, and (right) with rotation—notice the slight asymmetry in the pressure field

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Fig. 23

Static gear transmission error for two torque conditions. The function is periodic around the shaft between 0 deg and 360 deg.

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Fig. 24

Harmonics of the gear transmission error at two torque conditions

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