1 FPSO Roll Prediction and Mitigation Prof. Spyros A. Kinnas, Principal Investigator (Email:...
-
Upload
elijah-taylor -
Category
Documents
-
view
218 -
download
1
Transcript of 1 FPSO Roll Prediction and Mitigation Prof. Spyros A. Kinnas, Principal Investigator (Email:...
1
FPSO Roll Prediction andMitigation
Prof. Spyros A. Kinnas, Principal Investigator (Email: [email protected])Dr. Hanseong Lee, Post-doctoral FellowMr. Yi-Hsiang Yu, Doctoral Graduate StudentMr. Bharani Kacham, MS Graduate Student
The University of Texas at Austin Ocean Engineering Grouphttp://cavity.ce.utexas.edu
Supported by OTRC
May 1, 2003
2
Introduction
• Objectives - Develop accurate computationally efficient model t
o 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
GRID FOR OSCILLATING FLOW PAST A FLAT PLATE
Top
Bottom
Inflow Outflow
Plate
Direction of oscillating flow
Grid size: 201x101Domain size: -8 to 8 in x-direction and 0 to 8 in y-direction
0, 0, 0u p
vy y
0, 0, 0u p
vy y
cos( )
0, 0
mu U t
pv
x
cos( )
0, 0
mu U t
pv
x
0, 0, 0v p
ux x
Keulegan-Carpenter number: mU hKC
T
Um, T: Amplitude, and period of oscillating flow h: Height of the plate
5
Oscillating Flow Past a Flat PlateSarpkaya & O’Keefe’s Experiment (1995)
6
Oscillating Flow Past a Flat Plate
Inertia Coefficients (Cm) Drag Coefficients (Cd)
• Comparison of hydrodynamic coefficients predicted from Euler, Navier-Stokes solvers and Sarpkaya’s measurements
7
• Vorticity & Streamlines at t=0xT (KC=1)
Euler Solver Navier-Stokes Solver
• Vorticity & Streamlines at t=T/4 (KC=1)
8
• Vorticity & Streamlines at t=T/2 (KC=1)
Euler Solver Navier-Stokes Solver
• Vorticity & Streamlines at t=3T/4 (KC=1)
9
Movie (KC=1)
10
Movie(KC=10
)
11
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
• Hydrodynamic coefficients for various sizes of bilge keel for Roll motion
Damping Coefficients
FPSO Hull Motion (Preliminary Results)
b=B/2
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)
t = 0xT t = T/4
t = T/2 t = 3T/4
Froude Number: b
Fng
18
Oscillating flow around fixed FPSO Hull w/o free surface (FLUENT)
19
Oscillating flow around fixed FPSO Hull w/o free surface (FLUENT)
0
ReUh
U r
U: Max speed of bilge keel
A
• Effect of Reynolds Number
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 p
redicts 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.