Evaluation of hydrodynamic coefficients on riser floaters using CFD

Transcription

1 Evaluation of hydrodynamic coefficients on riser floaters using CFD Erico Santos, Pedro Mendes, Bruno Luna PETROBRAS (CENPES/PDEP/TDUT) Ricardo Damian ESSS

2 AGENDA MOTIVATION PROCEADURE OVERVIEW RISER GLOBAL ANALYSIS CFX SIMULATION PARAMETER ESTIMATION PROCEDURE PRELIMINARY CONCLUSIONS CFD RESULTS HYDRODYNAMIC PARAMETERS RESULTS CONCLUSIONS & NEXT STEPS

3 MOTIVATION CFD Drag coeficient Added mass

4 PROCEADURE OVERVIEW Characterization Object Amplitude Period Current Estimation Morison Model Drag (Re, Direction) Added Mass (Re, Direction) CFD Domain Mesh Parametric Setup Export Forces Global Analysis

5 RISER GLOBAL ANALYSIS Waves Current Offset Soil Floatings Riser Properties Fluid Internal external

6 FLUID FORCES Morison s Equation Inertia: linear function of structural acceleration Added mass: proportional to the fluid acceleration Drag: proportional to the relative velocity between fluid and structure

7 FLUID FORCES Added Mass Drag Coefficient DNV-RP-H103

8 Amplitude MOTION CHARACTERIZATION 0,4 0,3 0,2 0,1 0 XL YL ZL -0,1-0,2-0,3-0, tempo [s] Z X

9 CFD DOMAIN Riser Sector: Diameter m Cylindrical Floaters: Diameter 1.6 m Length 1.8 m Spacing 4.2 m Corner Rounding 0.1 m Cylindrical Domain: Diameter 20 m Length 22.2 m

10 CFD MESH ANSYS Meshing (Workbench) Global Sizing: Min Size 0.05 m Max Size 2.0 m Growth Ration 1.1 Curvature Sensitive Riser & Floaters: Max Size 0.1 m 10 Prismatic Layers Growth Ration 1.25 Transition Ratio 0.6 Turbulence: SST Model Y + 100

11 CFD SETUP BOUNDARY CONDITIONS Transient Setup Moving Domain Rigid Mesh Motion Farfield: CFX Opening Moving Boundary Velocity Current Conditions Turbulence 5% Intensity Length Scale => L Floater Stationary Setup Farfield: CFX Opening Velocity Current Conditions Turbulence Riser & Floaters: Wall 5% Intensity Length Scale => L Floater Riser & Floaters: Moving Wall

12 CFD SETUP RISER/FLOATER MOTION Typical Motion Behavior Period Ocean Wave Motion 12.5 s chosen Amplitude Floater Diameter / m chosen Harmonic Motion chosen

13 CFD SETUP PARAMETERIZATION Current Parameters Direction (Horizontal Angle) Reynolds Number Characteristic Length Floater Diameter U, V, W, ρ & µ Motion Parameters Amplitude Orientation (i, j, k) Period Monitor Points Total Force (pressure + shear) Central Floater X, Y, Z directions Rigid Mesh Motion

14 CFD SETUP SOLVER SETTINGS

15 PARAMETER ESTIMATION PROCEDURE CFD Model Monitor Points Forces along time Minimum Square Method Optimization Algorithm Minimize Sum of the Quadratic Error Position Velocity Acceleration Morison Equation

16 PRELIMINARY CONCLUSIONS For the tested motion, added mass is the dominant force The amplitude and period produces small velocities The estimation of drag and added mass coefficients in the same time isn't precise for the drag The added mass coefficient doesn't depend on the current (speed or direction) Drag coefficient can be easily obtained with stationary runs New strategy established: Stationary CFD for all current direction Drag coefficient estimation Single Transient CFD w/ motion & no current Added Mass coefficient estimation

17 CFD RESULTS Vortex core isosurface colored with velocity N 90 NNE 67.5 NE 45 N 22.5 E 0

18 HYDRODYNAMIC PARAMETERS RESULTS Transverse Longitudinal

19 CONCLUSIONS & NEXT STEPS A systematic CFD procedure for hydrodynamic coefficient estimation of moving submerged bodies was established Stationary runs are used for drag estimation according to the current direction A single transient run with body motion is used for added mass estimation Only the drag coefficient depends on current direction The CFD setup parameterization saves user s time Next steps: To automate the parameter estimation step To perform similar analysis to complex bodies (manifold, anchor, subsea separator, etc)