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Analysis of Various Parameters Associated with Oil
Lubricated Journal Bearings
By: Paul Wolfinger
Background
• In marine bearing lubrication, the rotating shaft inside the bearing is in the presence of oil, which generates a wedge between the two due to the dynamics of the fluid. The fluid generally adheres to each body and must shear in order to accommodate the relative motion.
• Fluid film thickness between the bearing surface and rotor provides lubrication, of which one can determine a velocity and temperature profile.
Project Purpose
• This project evaluates full journal bearings, which completely surround the shaft journal to show relationships between diameter and RPM.
• Four full journal bearing types are evaluated in COMSOL at four different conditions to trade-off bearing stability and capability to handle load:– Plain journal– Elliptical journal– Pressure dam journal– Offset/lobe journal
Validation of COMSOL
• Reynolds equation with Sommerfeld solultion used to validate COMSOL
• Petroff’s Equation to compare cases
222
2
012
cos2sin6
c
Rp
c
lNRPower rev
500,7
233
Validation of COMSOL
Bearing Types
• Plain
• Elliptical
• Pressure Dam
• Offset/lobe
Conditions for Evaluation of Each Bearing in COMSOL
Case A B C D
Bearing Radius (m) 0.25 0.25 0.50 0.50
Rotor Radius (m) 0.24 0.24 0.48 0.48
Rotational Speed (rad/sec)
104.7 104.7 104.7 209.4
Offset in X-dir (m) 0 0.003 0.003 0.003
Offset in Y-dir (m) 0 0.003 0.003 0.003
Eccentricity (m)0 0.00424 0.00424 0.00424
Radial Clearance (m) 0.01 0.01 0.02 0.02
Eccentricity Ratio 0.000 0.424 0.212 0.212
Plain Journal Bearing ResultsCase A B C D
Bearing Radius (m) 0.25 0.25 0.50 0.50
Rotor Radius (m) 0.24 0.24 0.48 0.48
Rotational Speed (rad/sec)
104.7 104.7 104.7 209.4
Max Pressure (kPa) 4.36 104.98 190.74 701.24
Min Pressure (kPa)-5.49 -130.96 -209.30 -795.62
Max Temperature (K) 305.64 306.69 305.29 305.51
Elliptical Bearing ResultsCase A B C D
Bearing Radius (m) 0.25 0.25 0.50 0.50
Rotor Radius (m) 0.24 0.24 0.48 0.48
Rotational Speed (rad/sec)
104.7 104.7 104.7 209.4
Max Pressure (kPa) 36.73 106.13 245.79 1217
Min Pressure (kPa)-56.8 -154.5 -376 -1651
Max Temperature (K) 305.59 305.73 305.24 305.3
Pressure Dam Bearing ResultsCase A B C D
Bearing Radius (m) 0.25 0.25 0.50 0.50
Rotor Radius (m) 0.24 0.24 0.48 0.48
Rotational Speed (rad/sec)
104.7 104.7 104.7 209.4
Max Pressure (kPa) 48.8 108 249 763
Min Pressure (kPa)-22.4 -114 -224 -788
Max Temperature (K) 305.57 306.98 305.29 305.66
Offset/Lobe Bearing ResultsCase A B C D
Bearing Radius (m) 0.25 0.25 0.50 0.50
Rotor Radius (m) 0.24 0.24 0.48 0.48
Rotational Speed (rad/sec)
104.7 104.7 104.7 209.4
Max Pressure (kPa) 40.8 66.2 160 576
Min Pressure (kPa)-30.9 -90 -198 -728
Max Temperature (K) 305.73 306.10 305.33 305.59
Summary of Case A and B
BearingPlain Elliptical
Pressure Dam
Offset/Lobe
Max Pressure (kPa) 4.36 36.73 48.76 40.82
Min Pressure (kPa) -5.49 -56.77 -22.39 -30.94
Max Temperature (K) 305.64 305.59 305.57 305.73
BearingPlain Elliptical
Pressure Dam
Offset/Lobe
Max Pressure (kPa) 104.98 106.13 107.92 66.24
Min Pressure (kPa) -130.96 -154.52 -114.06 -89.62
Max Temperature (K) 306.69 305.73 306.98 306.10
Case A
Case B
Summary of Case C and D
BearingPlain Elliptical
Pressure Dam
Offset/Lobe
Max Pressure (kPa) 190.74 245.79 249.13 159.57
Min Pressure (kPa) -209.30 -376.15 -224.20 -197.65
Max Temperature (K) 305.29 305.24 305.29 305.33
Case C
BearingPlain Elliptical
Pressure Dam
Offset/Lobe
Max Pressure (kPa) 701.24 1,217.2 763.42 575.86
Min Pressure (kPa) -795.62 -1,651.7 -788.30 -727.71
Max Temperature (K) 305.51 305.30 305.66 305.59
Case D
