Presentation on theme: "FPSO Roll Prediction and Mitigation"— Presentation transcript:
1FPSO Roll Prediction and Mitigation May 1, 2003The University of Texas at AustinOcean Engineering GroupProf. Spyros A. Kinnas, Principal Investigator(Dr. Hanseong Lee, Post-doctoral FellowMr. Yi-Hsiang Yu, Doctoral Graduate StudentMr. Bharani Kacham, MS Graduate StudentSupported by OTRC
2Introduction 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.
3Related PublicationsKakar, 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 2002Kinnas, 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, TexasKinnas, S.A., Yu, Y-H, Lee, H.S., and Kakar, K., “Modeling of Oscillating Flow Past a Vertical Plate”, ISOPE, May, 2003, Honolulu, Hawaii
13FPSO Hull MotionHydrodynamic coefficients for Heave motion
14FPSO Hull Motion (Preliminary Results) Hydrodynamic coefficients for various sizes of bilge keel for Roll motionb=B/2Damping Coefficients
15FPSO Hull Motion (Preliminary Results) Comparison of hydrodynamic coefficients for roll motion with [Vugts, J., 1968] : No bilge keelNote: These results are the same as those from potential flow,due to the absence of bilge keel.
16FPSO Hull Motion (Preliminary Results) Comparison of hydrodynamic coefficients for roll motion with [Yeung et al, 2000] : 4% bilge keel
17Vorticity contour and Streamlines for roll motion (6% bilge keel, roll angle=0.05(rad), and Fn = 0.8)Froude Number:t = T/4t = 0xTt = T/2t = 3T/4
18Oscillating flow around fixed FPSO Hull w/o free surface (FLUENT)
19Oscillating flow around fixed FPSO Hull w/o free surface (FLUENT) Effect of Reynolds NumberAU: Max speed ofbilge keel
20Oscillating flow around fixed FPSO Hull w/o free surface (FLUENT) Vorticity patterns at different instants of timet = 0t = T/4t = 2T/4t = 3T/4
21Oscillating flow around fixed FPSO Hull w/o free surface (FLUENT)
22ConclusionsDeveloped CFD model to solve the Euler equations around a flat plate and an FPSO hull subject to roll motionsValidated 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.
23Future WorkApply 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 experimentsat 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.