1. FPSO Roll Prediction and Mitigation
May 1, 2003
The University of Texas at Austin
Ocean Engineering Group
Prof. Spyros A. Kinnas, Principal Investigator (
Dr. Hanseong Lee, Post-doctoral Fellow
Mr. Yi-Hsiang Yu, Doctoral Graduate Student
Mr. Bharani Kacham, MS Graduate Student
Supported by OTRC

2. Introduction Objectives
- Develop accurate computationally efficient model to predict the hydrodynamic coefficients of FPSO hulls in roll motions.
- Investigate effectiveness of bilge keels (size, shape, location across and extent along the hull) on roll mitigation.

3. Related Publications
Kakar, K., “Computational Modeling of FPSO Hull Roll Motions and Two-Component Marine Propulsion Systems”, MS Thesis, Department of Civil Engineering, The University of Texas at Austin, August 2002
Kinnas, S.A., Yu, Y-H, Kacham, B. and Lee, H.S., “A model of the flow around bilge keels of FPSO hull sections subject to roll motions”, Proceedings of the 12th Offshore Symposium, Texas section of the SNAME, February, 2003, Houston, Texas
Kinnas, S.A., Yu, Y-H, Lee, H.S., and Kakar, K., “Modeling of Oscillating Flow Past a Vertical Plate”, ISOPE, May, 2003, Honolulu, Hawaii

4. Oscillating Flow Past a Flat Plate

5. Oscillating Flow Past a Flat Plate
Sarpkaya & O’Keefe’s Experiment (1995)

6. Oscillating Flow Past a Flat Plate
Comparison of hydrodynamic coefficients predicted from Euler, Navier-Stokes solvers and Sarpkaya’s measurements
Inertia Coefficients (Cm)
Drag Coefficients (Cd)

7. Vorticity & Streamlines at t=0xT (KC=1)
Vorticity & Streamlines at t=T/4 (KC=1)
Euler Solver
Navier-Stokes Solver

8. Vorticity & Streamlines at t=T/2 (KC=1)
Euler Solver
Navier-Stokes Solver

9. Movie
(KC=1)

10. Movie
(KC=10)

11. Fluid domain and Boundary Conditions (Euler Solver)
FPSO Hull Motion
Fluid domain and Boundary Conditions (Euler Solver)

12. FPSO Hull Motion
Grid and Geometry Details

13. FPSO Hull Motion
Hydrodynamic coefficients for Heave motion

14. FPSO Hull Motion (Preliminary Results)
Hydrodynamic coefficients for various sizes of bilge keel for Roll motion
b=B/2
Damping Coefficients

15. FPSO Hull Motion (Preliminary Results)
Comparison of hydrodynamic coefficients for roll motion with [Vugts, J., 1968] : No bilge keel
Note: These results are the same as those from potential flow,
due to the absence of bilge keel.

16. FPSO Hull Motion (Preliminary Results)
Comparison of hydrodynamic coefficients for roll motion with [Yeung et al, 2000] : 4% bilge keel

17. Vorticity contour and Streamlines for roll motion (6% bilge keel, roll angle=0.05(rad), and Fn = 0.8)
Froude Number:
t = T/4
t = 0xT
t = T/2
t = 3T/4

18. Oscillating flow around fixed FPSO Hull w/o free surface (FLUENT)

19. Oscillating flow around fixed FPSO Hull w/o free surface (FLUENT)
Effect of Reynolds Number A
U: Max speed of
bilge keel

20. Oscillating flow around fixed FPSO Hull w/o free surface (FLUENT)
Vorticity patterns at different instants of time
t = 0
t = T/4
t = 2T/4
t = 3T/4

21. Oscillating flow around fixed FPSO Hull w/o free surface (FLUENT)

22. Conclusions
Developed CFD model to solve the Euler equations around a flat plate and an FPSO hull subject to roll motions
Validated the present method:
- Flat plate subject to an oscillating flow: Euler solver predicts comparable flow patterns and forces with Navier-Stokes solver.
- Hull in Roll motion: The effect of Reynolds number on the separated flow around a bilge keel was investigated by using the commercial code, FLUENT, and was found not to be significant.

23. Future Work
Apply the current Navier-Stokes method on 2-D hull motions with and without bilge keels. Continue validation with other methods, and existing experiments.
Apply the modified hydrodynamic coefficients on an FPSO hull, using strip theory, and correct predictions from potential flow solvers. Validate with experiments
at OTRC’s Wave Basin.
Develop fully 3-D method for FPSO hulls, to assess the above model and include effects of “lift” on the bilge keel.