INVESTIGATION OF DRAG & ADDED MASS PROPERTIES OF MID- WATER ARCH STRUCTURE FOR RISER DESIGN Presenter: Liangli(Michael) Li Industry Supervisor: Dan Brooker (Intecsea, Perth) Academic Supervisor: Stuart Higgins (Curtin)
INVESTIGATION OF DRAG & ADDED MASS
PROPERTIES OF MID-WATER ARCH STRUCTURE
FOR RISER DESIGN Presenter: L iangl i (Michael) L iIndustry Supervisor: Dan Brooker ( Intecsea, Perth)Academic Superv isor: Stuart Higgins (Curt in)
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1. Introduction
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2. Hydrodynamic Force Analysis Morison Equation
, Reference Area
Flow Velocity
Structure Volume
Fluid Density
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3. Analyzing Using Existing code MWA Design – buoyancy cylinder, gutters
Ca & Cd Analysis◦ Code method - DNV-RP-C205 ◦ Numerical approach–
◦ Panel Method, Ca◦ Computational Fluid Dynamics, Cd
Compare to Code Method
Verify the results
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4. Panel Method
Directions DNV-RP-205Circular Cylinder
DNV-RP-205Square Cylinder
Panel Method
Surge, ZZ 0.919 0.72 1.6Heave, YY 0.919 0.72 1.0Sway, XX 0.137 0.125 0.08
3D Model
ANSYS APDL
HydroD
Added Mass Matrix
Symmetry
Plane
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5. CFD Simulations
Velocity Reynolds Number, Re
Circular Cylinder
Square Cylinder
CFD
0.5 m/s 1.8381x106 0.523 1.61 1.2076
1 m/s 3.6762x106 0.523 1.61 1.1978
1.5 m/s 5.5143x106 0.523 1.61 1.1464
2 m/s 7.3524x106 0.523 1.61 1.1396
3D Model
ANSYS ICEM
Fluent
Forces over time
Flow
Flow
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6. Result Verification & Validation
Grid and Fluid Domain◦ Grid Quality: 99.87% OK◦ Wall interference◦ Meshing size,5.4 million cells
Turbulence Models
Compare to Published Cylinder Result
Compare to Published MWA Results
Flow
Symmetry Plane
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Turbulence ModelOptions Turbulence Model Options Applications Limitations
RANS
Spalart-Allmaras Model (1-eq)Developed for aerospace applications, suitable for external flow and flow with adverse pressure gradient
Work well only on simple geometry. Only work under low Reynolds number flow
k-ε Model (2-eqn)
Suitable for internal flow and heat transfer applications
Limited to high Re flow condition, and not work well if flow encounters bluff bodies
k-ω Model (2-eqn)
Also developed for aerospace applications, suitable for external flow and flow with adverse pressure gradient, in both low and high Re flow
Sensitive to free stream turbulence
Laminar-Turbulent Transition Models (3-4 eqn)
Provide prediction of laminar to turbulent transition of boundary layer
Rely on mesh refinement near wall and inlet initial condition.
RSM (5 or 7-eqn) Work with any complex flows, including strong swirl and rotation
Most costly to run
SRS
SAS (RANS-LES hybrid)
Provide more detailed vortex shedding simulation (using von-Karman length scale)
High dependence on grid size and time-steps
DES(RANS-LES hybrid)
Provide more detailed turbulence simulation (turbulence length scale)
High dependence on grid size and time-steps
LES(RANS-DNS hybrid)
Used for research purpose on sophisticated geometry or small geometry scale
Only work with very fine grid size and small time-steps
DNS Used for 2D problems Most costly to run.0 5 10 15 20 25 30 35 40 45 50
0.0
0.5
1.0
1.5
2.0
2.5
2m/s Case Drag Coefficient Time History
2m/s k-w-SST
2m/s DES-k-w-SST
Time (s)
Cd Transient response
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Turbulence Model
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Compare to Published Cylinder Result
Cases Reynolds Number
Cd after finite length reduction (as pre DNV Code)
Present simulation hexahedron, 3D k-ω-SST
3.6762x106 0.314
Present simulation tetrahedron, 3D k-ω-SST
3.6762x106 0.313
DNV-RP-C205 (Book: Fluid-Dynamic Drag, 1965)
>1.0x106 0.523
Ong et al. 2009, 2D k-ε 3.6x106 0.368
Catalano et al. 2003, 2D k-ε 4.0x106 0.370
Shih et al, 1993, Exp ~3.5x106 ~0.33
Schewe, 1983, Exp 4.0x106 ~0.41
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Comparing with MWA Results
Cd = ~0.85Re > 107
0 0.5 1 1.5 2 2.5 3 3.5 4 4.50
20
40
60
80
100
120
140
160Drag Force vs. Velocity^2
K-w-SSTLinear (K-w-SST)DES-k-w-SST
Velocity^2
Drag
(kN)
0 0.5 1 1.5 2 2.5 3 3.5 40
50
100
150
200
250
Drag Force vs V^2
Velocity^2
Drag
(kN)
Cd = ~1.17Re > 106 Cd = ~1.18
Re > 105
Cd = ~0.86Re > 105
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Closing RemarksAdded Mass Coefficient• Ca varies with MWA design• Code method has limitations• Circular cylinder better than square cylinder• Panel method gives better prediction of Ca
Drag Force Coefficient• Cd varies with MWA design• Code method gives a upper-lower bound• Cd independent to Re, matches well to Morison eqn• CFD gives better prediction of Cd
Possible Design Improvement
Future Work – other flow directions, roughness effect, model testing
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Cd comparison DNV code vs. Others
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0 10 20 30 40 50 60 70 80 90 1000.0
0.5
1.0
1.5
2.0
2.5
Drag Coefficient Over Time
0.5m/s k-w-SST
1.0m/s k-w-SST
1.5m/s k-w-SST
2.0m/s k-w-SST
Time (s)
Cd
MWA and Cylinder Plots
0 20 40 60 80 100 1200.0
0.1
0.2
0.3
0.4
0.5
0.6
Cd of Cylinder
Time (s)
Cd
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Quality Check by ICEM
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Allocating 12080x6232=75282560 pixel map.
57773920 pixels filled, area = 57.7731
Projected Area, Solidworks and Fluent