1. Analysis of Various Parameters Associated with Oil Lubricated Journal Bearings
By: Paul Wolfinger

2. 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.

3. 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

4. Validation of COMSOL
Reynolds equation with Sommerfeld solultion used to validate COMSOL
Petroff’s Equation to compare cases

5. Validation of COMSOL

6. Bearing Types
Plain
Elliptical
Pressure Dam
Offset/lobe

7. Conditions for Evaluation of Each Bearing in COMSOL
Case A B C D
Bearing Radius (m)
0.25
0.50
Rotor Radius (m)
0.24
0.48
Rotational Speed (rad/sec)
104.7
209.4
Offset in X-dir (m)
0.003
Offset in Y-dir (m)
Eccentricity (m)
Radial Clearance (m)
0.01
0.02
Eccentricity Ratio
0.000
0.424
0.212

8. Plain Journal Bearing Results
Case A B C D
Bearing Radius (m)
0.25
0.50
Rotor Radius (m)
0.24
0.48
Rotational Speed (rad/sec)
104.7
209.4
Max Pressure (kPa)
4.36
104.98
190.74
701.24
Min Pressure (kPa)
-5.49
Max Temperature (K)
305.64
306.69
305.29
305.51

9. Elliptical Bearing Results
Case A B C D
Bearing Radius (m)
0.25
0.50
Rotor Radius (m)
0.24
0.48
Rotational Speed (rad/sec)
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

10. Pressure Dam Bearing Results
Case A B C D
Bearing Radius (m)
0.25
0.50
Rotor Radius (m)
0.24
0.48
Rotational Speed (rad/sec)
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

11. Offset/Lobe Bearing Results
Case A B C D
Bearing Radius (m)
0.25
0.50
Rotor Radius (m)
0.24
0.48
Rotational Speed (rad/sec)
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

12. Summary of Case A and B Case A Case B Bearing Plain 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
Case B
Bearing
Plain
Elliptical
Pressure Dam
Offset/Lobe
Max Pressure (kPa)
104.98
106.13
107.92
66.24
Min Pressure (kPa)
-89.62
Max Temperature (K)
306.69
305.73
306.98
306.10

13. Summary of Case C and D Case C Case D Bearing Plain Elliptical
Pressure Dam
Offset/Lobe
Max Pressure (kPa)
190.74
245.79
249.13
159.57
Min Pressure (kPa)
Max Temperature (K)
305.29
305.24
305.33
Case D
Bearing
Plain
Elliptical
Pressure Dam
Offset/Lobe
Max Pressure (kPa)
701.24
1,217.2
763.42
575.86
Min Pressure (kPa)
-1,651.7
Max Temperature (K)
305.51
305.30
305.66
305.59